From SLAC: “Fermi Researchers Explore New Ways of Searching for Dark Matter”

SLAC Lab

August 12, 2016

Three Studies Expand the Hunt for Unexplained Cosmic Gamma-ray Signals

Researchers working with more than six years of data from NASA’s Fermi Gamma-ray Space Telescope have used novel approaches to search for cosmic signals that could reveal what mysterious dark matter is made of.

NASA/Fermi Telescope

The scientists looked for hypothetical axion particles, studied the gamma-ray emissions from a large satellite galaxy of our Milky Way and analyzed the faint glow of gamma rays that covers the entire sky.

Although none of these studies identified signals clearly attributable to dark matter, the results help scientists determine what dark matter cannot be by ruling out numerous theoretical dark matter models.

“The new approaches have set tight limits on the properties of dark matter, complementing and extending previous results,” says Seth Digel, who leads the Fermi team at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

The nature of invisible dark matter remains one of the biggest mysteries of modern science. Because dark matter makes up 85 percent of all matter in the universe, it affects how galaxies rotate and how light passes through massive galaxy clusters. But what exactly is dark matter, and what are its constituents?

Astrophysicists do not know the answers, but they believe that dark matter might be composed of hypothetical particles. Gamma rays as detected by the Fermi telescope can potentially help reveal their existence. Previously, Fermi has searched for telltale gamma-ray signals associated with dark matter in the center of our galaxy and in small dwarf galaxies orbiting our own. The new studies take this search to the next level.

Gamma Rays Turning into Axions and Vice Versa

The first study investigated the possibility that dark matter consists of hypothetical particles called axions or other contenders with similar properties. An intriguing aspect of axion-like particles is their ability to convert into gamma rays and back again when they interact with strong magnetic fields. These conversions would leave behind characteristic traces, like gaps or steps, in the spectrum of a bright gamma-ray source.

A team led by Manuel Meyer at Stockholm University searched for these effects in the gamma rays from the central galaxy of the Perseus galaxy cluster, whose high-energy emissions are thought to be associated with a supermassive black hole at its center. Like all galaxy clusters, the Perseus cluster is filled with hot gas threaded with magnetic fields, potentially enabling the switch from gamma rays to axion-like particles and vice versa.

Top: Gamma rays (magenta) coming from a bright source such as the central galaxy (at left) of the Perseus galaxy cluster have a particular type of spectrum that is detected by the Fermi telescope (at right). Bottom: Gamma rays could potentially convert into hypothetical axion-like particles (green) and back again in the presence of the cluster’s magnetic field (gray lines). This would lead to steps and gaps in the spectrum (lower curve at right). (SLAC National Accelerator Laboratory). (T. Wistisen/Aarhus University)

Meyer’s team collected observations from Fermi’s Large Area Telescope (LAT) but didn’t find any axion-related distortions in the gamma-ray signal.

NASA/Fermi LAT

The findings, published April 20 in Physical Review Letters, exclude a small range of axion-like particles that could have comprised about 4 percent of dark matter.

“While we don’t yet know what dark matter is, our results show we can probe axion-like models and provide the strongest constraints to date for certain masses,” Meyer says. “Remarkably, we reached a sensitivity we thought would only be possible in a dedicated laboratory experiment, which is quite a testament to Fermi.”

WIMPs Decaying or Annihilating Each Other in Space

Other dark matter candidates are so-called weakly interacting massive particles (WIMPs). In some theoretical models, colliding WIMPs either annihilate each other or decay in space; both scenarios should result in gamma rays that could be detected by the LAT.

In the second study, scientists sought these signals from the Small Magellanic Cloud (SMC), the second-largest of the satellite galaxies orbiting our Milky Way. The SMC’s conventional sources of gamma rays, such as pulsars and processes related to the formation of massive stars, are well established, and its dark matter content is known from the galaxy’s well-measured rotation.

“These properties make the SMC a great object for searches for any unexplained gamma-ray excess, which could potentially be a WIMP signature,” says KIPAC researcher Eric Charles, co-author of a paper published on March 22 in Physical Review D.

The Small Magellanic Cloud (SMC, at center) is the second-largest satellite galaxy orbiting our Milky Way. The image superimposes a photograph of the SMC with one-half of a model of its dark matter. Lighter colors indicate greater density and show a strong concentration of dark matter toward the SMC’s center. Ninety-five percent of the dark matter is contained within a circle tracing the outer edge of the model shown here. (R. Caputo; A. Mellinger/Central Michigan University)

The researchers modeled the dark matter content of the satellite galaxy, showing it possesses enough dark matter to theoretically produce detectable signals for two WIMP types.

However, “no signal from dark matter annihilation was found to be statistically significant,” says lead author Regina Caputo from the University of California, Santa Cruz. “The LAT definitely sees gamma rays from the SMC, but we can explain them all through conventional sources.”

An Extragalactic Glow of Gamma Rays

In the third study, a research team led by Clemson University’s Marco Ajello and KIPAC’s Mattia Di Mauro took the search in a different direction. Instead of looking at specific astronomical targets, the team analyzed the background glow of gamma rays seen all over the sky.

The nature of this light, called the extragalactic gamma-ray background (EGB), has been debated since it was first measured by NASA’s Small Astronomy Satellite 2 in the early 1970s.

This view of the gamma-ray sky is constructed from one year of Fermi Large Area Telescope (LAT) observations. The blue color includes the extragalactic gamma-ray background. The map shows the rate at which the LAT detects gamma rays with energies above 300 million electron volts — about 120 million times the energy of visible light — from different sky directions. Brighter colors represent higher rates. Credit: NASA/DOE/Fermi LAT Collaboration

Fermi has shown that much of this light arises from gamma-ray sources that cannot be identified as individual sources, particularly galaxies called blazars that are powered by material falling toward gigantic black holes.

Some models predict that EGB gamma rays could also arise from distant interactions of dark matter particles, such as the annihilation or decay of WIMPs.

“We performed a statistical analysis of the EGB, in which we looked at very dim objects and asked whether we can account for all detected gamma-ray photons with known astrophysical sources,” says Di Mauro.

This animation switches between two images of the gamma-ray sky: one using the first three months of data from Fermi’s Large Area Telescope (LAT), the other showing an exposure over seven years. The background glow of gamma rays seen all over the sky (blue contours) is mostly caused by blazars, galaxies that are powered by material falling toward gigantic black holes. With increasing exposure, Fermi reveals more and more of them. (NASA/SLAC National Accelerator Laboratory/Fermi-LAT collaboration)

The detailed analysis, published April 14 in Physical Review Letters, shows that the researchers can in fact explain nearly all of this emission.

“There is very little room left for signals from exotic sources in the EGB, which in turn means that any contribution from these sources must be quite small,” Ajello says. “This information may help us place limits on how often WIMP particles collide or decay.”

NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. A number of researchers from SLAC are members of the international Fermi-LAT collaboration. SLAC assembled the LAT and hosts the operations center that processes LAT data.

See the full article here .

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Stem Education Coalition

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

From particlebites: “The Fermi LAT Data Depicting Dark Matter Detection”

particlebites

June 27, 2016
Chris Karwin

The center of the galaxy is brighter than astrophysicists expected. Could this be the result of the self-annihilation of dark matter? Chris Karwin, a graduate student from the University of California, Irvine presents the Fermi collaboration’s analysis.

Presenting: Fermi-LAT Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center
Authors: The Fermi-LAT Collaboration (ParticleBites blogger is a co-author)
Reference: 1511.02938, Astrophys.J. 819 (2016) no.1, 44

NASA/Fermi

Introduction

Like other telescopes, the Fermi Gamma-Ray Space Telescope is a satellite that scans the sky collecting light. Unlike many telescopes, it searches for very high energy light: gamma-rays. The satellite’s main component is the Large Area Telescope (LAT).

NASA/Fermi LAT

When this detector is hit with a high-energy gamma-ray, it measures the the energy and the direction in the sky from where it originated. The data provided by the LAT is an all-sky photon counts map:

All-sky counts map of gamma-rays. The color scale correspond to the number of detected photons. Image from NASA

In 2009, researchers noticed that there appeared to be an excess of gamma-rays coming from the galactic center. This excess is found by making a model of the known astrophysical gamma-ray sources and then comparing it to the data.

What makes the excess so interesting is that its features seem consistent with predictions from models of dark matter annihilation. Dark matter theory and simulations predict:

The distribution of dark matter in space. The gamma rays coming from dark matter annihilation should follow this distribution, or spatial morphology.
The particles to which dark matter directly annihilates. This gives a prediction for the expected energy spectrum of the gamma-rays.

Although a dark matter interpretation of the excess is a very exciting scenario that would tell us new things about particle physics, there are also other possible astrophysical explanations. For example, many physicists argue that the excess may be due to an unresolved population of milli-second pulsars. Another possible explanation is that it is simply due to the mis-modeling of the background. Regardless of the physical interpretation, the primary objective of the Fermi analysis is to characterize the excess.

The main systematic uncertainty of the experiment is our limited understanding of the backgrounds: the gamma rays produced by known astrophysical sources. In order to include this uncertainty in the analysis, four different background models are constructed. Although these models are methodically chosen so as to account for our lack of understanding, it should be noted that they do not necessarily span the entire range of possible error. For each of the background models, a gamma-ray excess is found. With the objective of characterizing the excess, additional components are then added to the model. Among the different components tested, it is found that the fit is most improved when dark matter is added. This is an indication that the signal may be coming from dark matter annihilation.
Analysis

This analysis is interested in the gamma rays coming from the galactic center. However, when looking towards the galactic center the telescope detects all of the gamma-rays coming from both the foreground and the background. The main challenge is to accurately model the gamma-rays coming from known astrophysical sources.

Schematic of the experiment. We are interested in gamma-rays coming from the galactic center, represented by the red circle. However, the LAT detects all of the gamma-rays coming from the foreground and background, represented by the blue region. The main challenge is to accurately model the gamma-rays coming from known astrophysical sources. Image adapted from Universe Today.

An overview of the analysis chain is as follows. The model of the observed region comes from performing a likelihood fit of the parameters for the known astrophysical sources. A likelihood fit is a statistical procedure that calculates the probability of observing the data given a set of parameters. In general there are two types of sources:

1. Point sources such as known pulsars
2. Diffuse sources due to the interaction of cosmic rays with the interstellar gas and radiation field

Parameters for these two types of sources are fit at the same time. One of the main uncertainties in the background is the cosmic ray source distribution. This is the number of cosmic ray sources as a function of distance from the center of the galaxy. It is believed that cosmic rays come from supernovae. However, the source distribution of supernova remnants is not well determined. Therefore, other tracers must be used. In this context a tracer refers to a measurement that can be made to infer the distribution of supernova remnants. This analysis uses both the distribution of OB stars and the distribution of pulsars as tracers. The former refers to OB associations, which are regions of O-type and B-type stars. These hot massive stars are progenitors of supernovae. In contrast to these progenitors, the distribution of pulsars is also used since pulsars are the end state of supernovae. These two extremes serve to encompass the uncertainty in the cosmic ray source distribution, although, as mentioned earlier, this uncertainty is by no means bracketing. Two of the four background model variants come from these distributions.

An overview of the analysis chain. In general there are two types of sources: point sources and diffuse source. The diffuse sources are due to the interaction of cosmic rays with interstellar gas and radiation fields. Spectral parameters for the diffuse sources are fit concurrently with the point sources using a likelihood fit. The question mark represents the possibility of an additional component possibly missing from the model, such as dark matter.

The information pertaining to the cosmic rays, gas, and radiation fields is input into a propagation code called GALPROP. This produces an all-sky gamma-ray intensity map for each of the physical processes that produce gamma-rays. These processes include the production of neutral pions due to the interaction of cosmic ray protons with the interstellar gas, which quickly decay into gamma-rays, cosmic ray electrons up-scattering low-energy photons of the radiation field via inverse Compton, and cosmic ray electrons interacting with the gas producing gamma-rays via Bremsstrahlung radiation.

Residual map for one of the background models. Image from 1511.02938

The maps of all the processes are then tuned to the data. In general, tuning is a procedure by which the background models are optimized for the particular data set being used. This is done using a likelihood analysis. There are two different tuning procedures used for this analysis. One tunes the normalization of the maps, and the other tunes both the normalization and the extra degrees of freedom related to the gas emission interior to the solar circle. These two tuning procedures, performed for the the two cosmic ray source models, make up the four different background models.

Point source models are then determined for each background model, and the spectral parameters for both diffuse sources and point sources are simultaneously fit using a likelihood analysis.

Results and Conclusion

Best fit dark matter spectra for the four different background models. Image: 1511.02938

In the plot of the best fit dark matter spectra for the four background models, the hatching of each curve corresponds to the statistical uncertainty of the fit. The systematic uncertainty can be interpreted as the region enclosed by the four curves. Results from other analyses of the galactic center are overlaid on the plot. This result shows that the galactic center analysis performed by the Fermi collaboration allows a broad range of possible dark matter spectra.

The Fermi analysis has shown that within systematic uncertainties a gamma-ray excess coming from the galactic center is detected. In order to try to explain this excess additional components were added to the model. Among the additional components tested it was found that the fit is most improved with that addition of a dark matter component. However, this does not establish that a dark matter signal has been detected. There is still a good chance that the excess can be due to something else, such as an unresolved population of millisecond pulsars or mis-modeling of the background. Further work must be done to better understand the background and better characterize the excess. Nevertheless, it remains an exciting prospect that the gamma-ray excess could be a signal of dark matter.

See the full article here .

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Stem Education Coalition

What is ParticleBites?

ParticleBites is an online particle physics journal club written by graduate students and postdocs. Each post presents an interesting paper in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

The papers are accessible on the arXiv preprint server. Most of our posts are based on papers from hep-ph (high energy phenomenology) and hep-ex (high energy experiment).

Why read ParticleBites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. With each brief ParticleBite, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in particle physics.

Who writes ParticleBites?

ParticleBites is written and edited by graduate students and postdocs working in high energy physics. Feel free to contact us if you’re interested in applying to write for ParticleBites.

ParticleBites was founded in 2013 by Flip Tanedo following the Communicating Science (ComSciCon) 2013 workshop.

Flip Tanedo UCI Chancellor’s ADVANCE postdoctoral scholar in theoretical physics. As of July 2016, I will be an assistant professor of physics at the University of California, Riverside

It is now organized and directed by Flip and Julia Gonski, with ongoing guidance from Nathan Sanders.

From NASA Fermi: “NASA’s Fermi Telescope Helps Link Cosmic Neutrino to Blazar Blast”

Fermi

April 28, 2016
By Francis Reddy
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Nearly 10 billion years ago, the black hole at the center of a galaxy known as PKS B1424-418 produced a powerful outburst. Light from this blast began arriving at Earth in 2012. Now astronomers using data from NASA’s Fermi Gamma-ray Space Telescope and other space- and ground-based observatories have shown that a record-breaking neutrino seen around the same time likely was born in the same event.

Access mp4 video here.
NASA Goddard scientist Roopesh Ojha explains how Fermi and TANAMI uncovered the first plausible link between a blazar eruption and a neutrino from deep space. Credits: NASA’s Goddard Space Flight Center

“Neutrinos are the fastest, lightest, most unsociable and least understood fundamental particles, and we are just now capable of detecting high-energy ones arriving from beyond our galaxy,” said Roopesh Ojha, a Fermi team member at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a coauthor of the study. “Our work provides the first plausible association between a single extragalactic object and one of these cosmic neutrinos.”

Although neutrinos far outnumber all the atoms in the universe, they rarely interact with matter, which makes detecting them quite a challenge. But this same property lets neutrinos make a fast exit from places where light cannot easily escape — such as the core of a collapsing star — and zip across the universe almost completely unimpeded. Neutrinos can provide information about processes and environments that simply aren’t available through a study of light alone.

The IceCube Neutrino Observatory, built into a cubic kilometer of clear glacial ice at the South Pole, detects neutrinos when they interact with atoms in the ice.

U Wisconsin ICECUBE neutrino detector

This triggers a cascade of fast-moving charged particles that emit a faint glow, called Cerenkov light, as they travel, which is picked up by thousands of optical sensors strung throughout IceCube. Scientists determine the energy of an incoming neutrino by the amount of light its particle cascade emits.

To date, the IceCube science team has detected about a hundred very high-energy neutrinos and nicknamed some of the most extreme events after characters on the children’s TV series “Sesame Street.” On Dec. 4, 2012, IceCube detected an event known as Big Bird, a neutrino with an energy exceeding 2 quadrillion electron volts (PeV). To put that in perspective, it’s more than a million million times greater than the energy of a dental X-ray packed into a single particle thought to possess less than a millionth the mass of an electron. Big Bird was the highest-energy neutrino ever detected at the time and still ranks second.

Where did it come from? The best IceCube position only narrowed the source to a patch of the southern sky about 32 degrees across, equivalent to the apparent size of 64 full moons.

Enter Fermi. Starting in the summer of 2012, the satellite’s Large Area Telescope (LAT) witnessed a dramatic brightening of PKS B1424-418, an active galaxy classified as a gamma-ray blazar.

NASA/Fermi LAT

An active galaxy is an otherwise typical galaxy with a compact and unusually bright core. The excess luminosity of the central region is produced by matter falling toward a supermassive black hole weighing millions of times the mass of our sun. As it approaches the black hole, some of the material becomes channeled into particle jets moving outward in opposite directions at nearly the speed of light. In blazars, one of these jets happens to point almost directly toward Earth.

Left

Right

Fermi LAT images showing the gamma-ray sky around the blazar PKS B1424-418. Brighter colors indicate greater numbers of gamma rays. The dashed arc marks part of the source region established by IceCube for the Big Bird neutrino (50-percent confidence level). Left: An average of LAT data centered on July 8, 2011, and covering 300 days when the blazar was inactive. Right: An average of 300 active days centered on Feb. 27, 2013, when PKS B1424-418 was the brightest blazar in this part of the sky. Credits: NASA/DOE/LAT Collaboration

During the year-long outburst, PKS B1424-418 shone between 15 and 30 times brighter in gamma rays than its average before the eruption. The blazar is located within the Big Bird source region, but then so are many other active galaxies detected by Fermi.

The scientists searching for the neutrino source then turned to data from a long-term observing program named TANAMI. Since 2007, TANAMI has routinely monitored nearly 100 active galaxies in the southern sky, including many flaring sources detected by Fermi. The program includes regular radio observations using the Australian Long Baseline Array (LBA) and associated telescopes in Chile, South Africa, New Zealand and Antarctica. When networked together, they operate as a single radio telescope more than 6,000 miles across and provide a unique high-resolution look into the jets of active galaxies.

Australian Long Baseline Array map

ATNF TANAMI array Australia

Radio images from the TANAMI project reveal the 2012-2013 eruption of PKS B1424-418 at a wavelength of 8.4 GHz. The core of the blazar’s jet brightened by four times, producing the most dramatic blazar outburst TANAMI has observed to date. Credits: TANAMI

Three radio observations of PKS B1424-418 between 2011 and 2013 cover the period of the Fermi outburst. They reveal that the core of the galaxy’s jet had brightened by about four times. No other galaxy observed by TANAMI over the life of the program has exhibited such a dramatic change.

“We combed through the field where Big Bird must have originated looking for astrophysical objects capable of producing high-energy particles and light,” said coauthor Felicia Krauss, a doctoral student at the University of Erlangen-Nuremberg in Germany. “There was a moment of wonder and awe when we realized that the most dramatic outburst we had ever seen in a blazar happened in just the right place at just the right time.”

In a paper* published Monday, April 18, in Nature Physics, the team suggests the PKS B1424-418 outburst and Big Bird are linked, calculating only a 5-percent probability the two events occurred by chance alone. Using data from Fermi, NASA’s Swift and WISE satellites, the LBA and other facilities, the researchers determined how the energy of the eruption was distributed across the electromagnetic spectrum and showed that it was sufficiently powerful to produce a neutrino at PeV energies.

NASA/SWIFT Telescope

NASA/Wise Telescope

“Taking into account all of the observations, the blazar seems to have had means, motive and opportunity to fire off the Big Bird neutrino, which makes it our prime suspect,” said lead author Matthias Kadler, a professor of astrophysics at the University of Wuerzburg in Germany.

Francis Halzen, the principal investigator of IceCube at the University of Wisconsin–Madison, and not involved in this study, thinks the result is an exciting hint of things to come. “IceCube is about to send out real-time alerts when it records a neutrino that can be localized to an area a little more than half a degree across, or slightly larger than the apparent size of a full moon,” he said. “We’re slowly opening a neutrino window onto the cosmos.”

For more information about NASA’s Fermi, visit:

http://www.nasa.gov/fermi

*Science paper:
Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

From Science Alert: “Astronomers might have finally detected where mysterious, extragalactic neutrinos are coming from”

Science Alert

29 APR 2016
FIONA MACDONALD

NASA/DOE/LAT Collaboration

Just over three years ago, physicists working in Antarctica announced they’d detected the first evidence of mysterious subatomic particles, known as neutrinos, coming from outside our galaxy. It was a huge moment for astrophysics, but since then, no one’s quite been able to figure out where those particles are coming from, and what’s sending them hurtling our way.

Until now, that is – a team of astronomers has just identified the possible source of one these extragalactic visitors, and it appears that it started its journey to us nearly 10 billion years ago, when a massive explosion erupted in a galaxy far, far away (seriously, George Lucas couldn’t make this stuff up).

Let’s step back for a second here though and explain why this is a big deal. Neutrinos are arguably the weirdest of the fundamental subatomic particles. They don’t have any mass, they’re incredibly fast, and they’re pretty much invisible, because they hardly ever interact with matter. Like tiny ghosts, billions of neutrinos per second are constantly flowing through us, and we never even know about it.

In order to detect them, researchers have step up extravagant labs, like the IceCube Neutrino Observatory at the South Pole, where they wait patiently to capture glimpses of neutrinos streaking through the planet, and measure how energetic they are, to try to work out where they came from.

U Wisconsin ICECUBE neutrino detector

Usually that source is radioactive decay here on Earth or inside the Sun, or maybe from the black hole at the centre of our galaxy. But in 2013, the IceCube researchers announced they’d detected a couple of neutrinos so unimaginably energetic, they knew they must have come from outside our galaxy.

These neutrinos were named ‘Bert’ and ‘Ernie’ (seriously) and they were the first evidence of extragalactic neutrinos. Their discovery was followed by the detection of a couple of dozen more, slightly less energetic, extragalactic neutrinos over the coming months.

Then at the end of 2012, they spotted ‘Big Bird’. At the time it was the most energetic neutrino ever detected, with energy exceeding 2 quadrillion electron volts – that’s more than a million million times greater than the energy of a dental X-ray. Not bad for a massless ghost particle.

Since then, teams across the world have been working to figure out where the hell this anomaly had come from. And now we might finally have a suspect.

“It’s like a crime scene investigation,” said lead researcher Matthias Kadler from the University of Würzburg in Germany, “The case involves an explosion, a suspect, and various pieces of circumstantial evidence.”

Using that circumstantial evidence, the best astronomers could do at the time was narrow the source down to a patch of the southern sky about 32 degrees across – roughly the size of 64 full moons.

That sounds pretty specific, but an area that size in the night sky covers a whole lot of galaxies, and researchers had the tough job of sifting through all that data to figure out what happened in one of those galaxies to send Big Bird to us.

They now think they have their answer – a huge explosion known as a blazar, which occurred in a galaxy called PKS B1424-418 around 10 billion years ago, but was only detected by our telescopes between 2011 and 2013 because of how far away it is.

Blazar. NASA Fermi Gamma ray Space Telescope. Credits M. Weiss/CfA

A blazar is one of the most energetic events in the known Universe, and it occurs when a galaxy’s material falls towards the supermassive black hole at its centre, and some of that material ends up being blasted in huge jets directly towards Earth.

Publishing* in Nature Physics, the team has now calculated that there’s only a 5 percent chance that Big Bird and the blazar at PKS B1424-418 coincidentally hit Earth at the same time, but weren’t linked.

“Taking into account all of the observations, the blazar seems to have had means, motive and opportunity to fire off the Big Bird neutrino, which makes it our prime suspect,” said Kadler.

The fact that these two individually fascinating events are associated is pretty exciting in itself.

“There was a moment of wonder and awe when we realised that the most dramatic outburst we had ever seen in a blazar happened in just the right place at just the right time,” said co-author Felicia Krauß, from the University of Erlangen-Nürnberg.

This hypothesis now needs to be independently verified before we can say for sure where Big Bird, and potentially other extragalactic neutrinos, come from. But it’s pretty exciting that we might finally, finally be getting close to understanding more about these enigmatic subatomic particles.

Francis Halzen, who’s the principal investigator of IceCube, and wasn’t involved in this study, thinks the research heralds in an exciting new time in neutrino research.

“IceCube is about to send out real-time alerts when it records a neutrino that can be localised to an area a little more than half a degree across, or slightly larger than the apparent size of a full moon,” he explains. “We’re slowly opening a neutrino window onto the cosmos.” Bring it on.

*Science paper:
Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

From Fermi: “NASA’s Fermi Telescope Poised to Pin Down Gravitational Wave Sources”

NASA Fermi

April 18, 2016
By Francis Reddy
NASA’s Goddard Space Flight Center, Greenbelt, Maryland

On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works.

Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

Caltech/MIT Advanced aLIGO Hanford Washington USA installation

Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA’s Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light.

Access mp4 video here .
This visualization shows gravitational waves emitted by two black holes (black spheres) of nearly equal mass as they spiral together and merge. Yellow structures near the black holes illustrate the strong curvature of space-time in the region. Orange ripples represent distortions of space-time caused by the rapidly orbiting masses. These distortions spread out and weaken, ultimately becoming gravitational waves (purple). The merger timescale depends on the masses of the black holes. For a system containing black holes with about 30 times the sun’s mass, similar to the one detected by LIGO in 2015, the orbital period at the start of the movie is just 65 milliseconds, with the black holes moving at about 15 percent the speed of light. Space-time distortions radiate away orbital energy and cause the binary to contract quickly. As the two black holes near each other, they merge into a single black hole that settles into its “ringdown” phase, where the final gravitational waves are emitted. For the 2015 LIGO detection, these events played out in little more than a quarter of a second. This simulation was performed on the Pleiades supercomputer at NASA’s Ames Research Center. Credits: NASA/J. Bernard Kelly (Goddard), Chris Henze (Ames) and Tim Sandstrom (CSC Government Solutions LLC)

“This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks we’ll need to see more bursts associated with gravitational waves from black hole mergers,” said Valerie Connaughton, a GBM team member at the Universities Space Research Association’s Science and Technology Institute in Huntsville, Alabama, and lead author of a paper* on the burst now under review by The Astrophysical Journal.

Detecting light from a gravitational wave source will enable a much deeper understanding of the event. Fermi’s GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV.

This image, taken in May 2008 as the Fermi Gamma-ray Space Telescope was being readied for launch, highlights the detectors of its Gamma-ray Burst Monitor (GBM). The GBM is an array of 14 crystal detectors. Credits: NASA/Jim Grossmann

With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together.

Black holes merging Swinburne Astronomy Productions

These same systems also are suspected to be prime producers of gravitational waves.

“With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB,” said Lindy Blackburn, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a member of the LIGO Scientific Collaboration. “There is an incredible synergy between the two observations, with gamma rays revealing details about the source’s energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event.” He will be discussing the burst and how Fermi and LIGO are working together in an invited talk at the American Physical Society meeting in Salt Lake City on Tuesday.

Currently, gravitational wave observatories possess relatively blurry vision. This will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States.

“That’s a pretty big haystack to search when your needle is a short GRB, which can be fast and faint, but that’s what our instrument is designed to do,” said co-author Eric Burns, a GBM team member and graduate student at the University of Alabama in Huntsville. “A GBM detection allows us to whittle down the LIGO area and substantially shrinks the haystack.”

Access mp4 video here .
Fermi’s GBM saw a fading X-ray flash at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of the LIGO source on the assumption that the burst is connected to it. In this case, the LIGO search area is reduced by two-thirds. Greater improvements are possible in future detections.
Credits: NASA’s Goddard Space Flight Center

Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, Earth blocked a large swath of the burst’s likely location as seen by Fermi at the time, allowing scientists to further narrow down the burst’s position.

The GBM team calculates less than a 0.2-percent chance random fluctuations would have occurred in such close proximity to the merger. Assuming the events are connected, the GBM localization and Fermi’s view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible.

The LIGO event was produced by the merger of two relatively large black holes, each about 30 times the mass of the sun. Binary systems with black holes this big were not expected to be common, and many questions remain about the nature and origin of the system.

Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.

Albert Einstein predicted the existence of gravitational waves in his general theory of relativity a century ago, and scientists have been attempting to detect them for 50 years. Einstein pictured these waves as ripples in the fabric of space-time produced by massive, accelerating bodies, such as black holes orbiting each other. Scientists are interested in observing and characterizing these waves to learn more about the sources producing them and about gravity itself.

NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

For more information about NASA’s Fermi Gamma-ray Space Telescope, please visit:

http://www.nasa.gov/fermi

*Science paper:
Fermi GBM Observations of LIGO Gravitational Wave event GW150914

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

From NASA Fermi: “NASA’s Fermi Telescope Poised to Pin Down Gravitational Wave Sources”

NASA Fermi

April 18, 2016
Francis Reddy
NASA’s Goddard Space Flight Center, Greenbelt, Maryland

On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana.

Black holes merging Swinburne Astronomy Productions

Cornell SXS team. Two merging black holes simulation

MIT/Caltech Advanced aLIGO Hanford Washington USA installation

This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works.

Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA’s Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light.

Access mp4 video here . This visualization shows gravitational waves emitted by two black holes (black spheres) of nearly equal mass as they spiral together and merge. Yellow structures near the black holes illustrate the strong curvature of space-time in the region. Orange ripples represent distortions of space-time caused by the rapidly orbiting masses. These distortions spread out and weaken, ultimately becoming gravitational waves (purple). The merger timescale depends on the masses of the black holes. For a system containing black holes with about 30 times the sun’s mass, similar to the one detected by LIGO in 2015, the orbital period at the start of the movie is just 65 milliseconds, with the black holes moving at about 15 percent the speed of light. Space-time distortions radiate away orbital energy and cause the binary to contract quickly. As the two black holes near each other, they merge into a single black hole that settles into its “ringdown” phase, where the final gravitational waves are emitted. For the 2015 LIGO detection, these events played out in little more than a quarter of a second. This simulation was performed on the Pleiades supercomputer at NASA’s Ames Research Center. Credits: NASA/J. Bernard Kelly (Goddard), Chris Henze (Ames) and Tim Sandstrom (CSC Government Solutions LLC)

“This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks we’ll need to see more bursts associated with gravitational waves from black hole mergers,” said Valerie Connaughton, a GBM team member at the National Space, Science and Technology Center in Huntsville, Alabama, and lead author of a paper on the burst now under review by The Astrophysical Journal.

Detecting light from a gravitational wave source will enable a much deeper understanding of the event. Fermi’s GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV.

NASA Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor (GBM)

With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. These same systems also are suspected to be prime producers of gravitational waves.

“With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB,” said Lindy Blackburn, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a member of the LIGO Scientific Collaboration. “There is an incredible synergy between the two observations, with gamma rays revealing details about the source’s energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event.” He will be discussing the burst and how Fermi and LIGO are working together in an invited talk at the American Physical Society meeting in Salt Lake City on Tuesday.

Currently, gravitational wave observatories possess relatively blurry vision. This will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States.

“That’s a pretty big haystack to search when your needle is a short GRB, which can be fast and faint, but that’s what our instrument is designed to do,” said Eric Burns, a GBM team member at the University of Alabama in Huntsville. “A GBM detection allows us to whittle down the LIGO area and substantially shrinks the haystack.”

Access mp4 video here. Fermi’s GBM saw a fading X-ray flash at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of the LIGO source on the assumption that the burst is connected to it. In this case, the LIGO search area is reduced by two-thirds. Greater improvements are possible in future detections. Credits: NASA’s Goddard Space Flight Center

Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, Earth blocked a large swath of the burst’s likely location as seen by Fermi at the time, allowing scientists to further narrow down the burst’s position.

The GBM team calculates less than a 0.2-percent chance random fluctuations would have occurred in such close proximity to the merger. Assuming the events are connected, the GBM localization and Fermi’s view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible.

The LIGO event was produced by the merger of two relatively large black holes, each about 30 times the mass of the sun. Binary systems with black holes this big were not expected to be common, and many questions remain about the nature and origin of the system.

Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.

Albert Einstein predicted the existence of gravitational waves in his general theory of relativity a century ago, and scientists have been attempting to detect them for 50 years. Einstein pictured these waves as ripples in the fabric of space-time produced by massive, accelerating bodies, such as black holes orbiting each other. Scientists are interested in observing and characterizing these waves to learn more about the sources producing them and about gravity itself.

For more information about NASA’s Fermi Gamma-ray Space Telescope, please visit:

http://www.nasa.gov/fermi

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

From AAS NOVA: “Found: A Galaxy’s Missing Gamma Rays”

American Astronomical Society

Recent observations have detected high-energy gamma-ray emission for the first time from the massive, star-forming galaxy Arp 220 (shown here in optical wavelengths, as imaged by Hubble). [NASA/ESA/C. Wilson (McMaster University)]

NASA/ESA Hubble Telescope

Recent reanalysis of data from the Fermi Gamma-ray Space Telescope has resulted in the first detection of high-energy gamma rays emitted from a nearby galaxy.

NASA/Fermi Telescope

This discovery reveals more about how supernovae interact with their environments.

Colliding Supernova Remnant

Supernova remnant Crab nebula. NASA/ESA Hubble

After a stellar explosion, the supernova’s ejecta expand, eventually encountering the ambient interstellar medium. According to models, this generates a strong shock, and a fraction of the kinetic energy of the ejecta is transferred into cosmic rays — high-energy radiation composed primarily of protons and atomic nuclei. Much is still unknown about this process, however. One open question is: what fraction of the supernova’s explosion power goes into accelerating these cosmic rays?

In theory, one way to answer this is by looking for gamma rays.

Gamma rays from the Fermi Gamma-ray Space Telescope, could be produced by proposed dark matter interactions

In a starburst galaxy, the collision of the supernova-accelerated cosmic rays with the dense interstellar medium is predicted to produce high-energy gamma rays. That radiation should then escape the galaxy and be visible to us.

Pass 8 to the Rescue

Observational tests of this model, however, have been stumped by Arp 220. This nearby ultraluminous infrared galaxy is the product of a galaxy merger ~700 million years ago that fueled a frenzy of starbirth. Due to its dusty interior and extreme levels of star formation, Arp 220 has long been predicted to emit the gamma rays produced by supernova-accelerated cosmic rays. But though we’ve looked, gamma-ray emission has never been detected from this galaxy … until now.

In a recent study*, a team of scientists led by Fang-Kun Peng (Nanjing University) reprocessed 7.5 years of Fermi observations using the new Pass 8 analysis software. The resulting increase in resolution revealed the first detection of GeV emission from Arp 220!

Gamma-ray luminosity vs. total infrared luminosity for LAT-detected star-forming galaxies and Seyferts. Arp 220’s luminosities are consistent with the scaling relation. [Peng et al. 2016]

Acceleration Efficiency

Peng and collaborators argue that this emission is due solely to cosmic-ray interactions with interstellar gas. This picture is supported by the lack of variability in the emission, and the fact that Arp 220’s gamma-ray luminosity is consistent with the scaling relation between gamma-ray and infrared luminosity for star-forming galaxies. The authors also argue that, due to Arp 220’s high gas density, all cosmic rays will interact with the gas before escaping.

Under these two assumptions, Peng and collaborators use the gamma-ray luminosity and the known supernova rate in Arp 220 to estimate how efficiently cosmic rays are accelerated by supernova remnants in the galaxy. They determine that 4.2 ± 2.6% of the supernova remnant’s kinetic energy is used to accelerate cosmic rays above 1 GeV.

This is the first time such a rate has been measured directly from gamma-ray emission, but it’s consistent with estimates of 3-10% efficiency in the Milky Way. Future analysis of other ultraluminous infrared galaxies like Arp 220 with Fermi (and Pass 8!) will hopefully reveal more about these recent-merger, starburst environments.

Fang-Kun Peng et al 2016* ApJ 821 L20. doi:10.3847/2041-8205/821/2/L20

Science paper:
THE FIRST DETECTION OF GeV EMISSION FROM AN ULTRALUMINOUS INFRARED GALAXY: Arp 220 AS SEEN WITH THE FERMI LARGE AREA TELESCOPE

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

From AAS NOVA: “Upgrading Fermi Without Traveling to Space”

Amercan Astronomical Society

3 February 2016
Susanna Kohler

NASA Fermi

This image, constructed from 6+ years of observations by NASA’s Fermi Gamma-ray Space Telescope, is the first to show how the entire sky appears at energies between 50 GeV and 2 TeV. A recent improvement to Fermi-LAT’s data analysis software has significantly increased the instrument’s sensitivity, resulting in this spectacular high-energy sky map. [NASA/DOE/Fermi LAT Collaboration]

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has received an upgrade that increased its sensitivity by a whopping 40% — and nobody had to travel to space to make it happen!

Fermi LAT

The difference instead stems from remarkable improvement to the software used to analyze Fermi-LAT’s data, and it has resulted in a new high-energy map of our sky.

Pass 8

Fermi-LAT has been surveying the whole sky since August 2008. It detects gamma-ray photons by converting them into electron-positron pairs and tracking the paths of these charged particles. But differentiating this signal from the charged cosmic rays that also pass through the detector — with a flux that can be 10,000 times larger! — is a challenging process. Making this distinction and rebuilding the path of the original gamma ray relies on complex analysis software.

“Pass 8” is a complete reprocessing of all data collected by Fermi-LAT. The software has gone through many revisions before now, but this is the first revision that has taken into account all of the experience that the Fermi team has gained operating the LAT in its orbital environment.

The improvements made in Pass 8 include better background rejection of misclassified charged particles, improvements to the point spread function and effective area of the detector, and an extension of the effective energy range from below 100 MeV to beyond a few hundred GeV. The changes made in Pass 8 have increased the sensitivity of Fermi-LAT by an astonishing 40%.

Map of the High-Energy Sky

The first result from the improvements of Pass 8 is 2FHL, the second catalog of high-energy Fermi sources, constructed from 80 months of data from Fermi-LAT. The 2FHL catalog contains 360 sources from across the sky in the 50 GeV–2TeV range. Here are just a few details:

47 of the sources are new — they have not previously been detected by Fermi or ground-based gamma-ray detectors.
86% of the sources can be associated with counterparts at other wavelengths. This includes
75% that are active galactic nuclei, and
11% that originate in our galaxy, the majority of which are associated with objects at the final stage of stellar evolution, such as pulsar wind nebulae. and supernova remnants.

Because the quality of Fermi-LAT’s observations is limited by the number of photons collected, longer observing time will only serve to improve the detections in this catalog. And since only 22% of the 2FHL sources have been observed by ground-based gamma-ray detectors (which have much more limited fields of view), this catalog provides an excellent list of candidates that these detectors can now follow up at very high energies.

Bonus

Want to learn more about Pass 8? Check out this video, created by the Fermi team. [NASA’s Goddard Space Flight Center]

download mp4 video here .

Citation

M. Ackermann et al 2016 ApJS 222 5. doi:10.3847/0067-0049/222/1/5

See the full article here .

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From NASA Fermi: “NASA’s Fermi Satellite Kicks Off a Blazar-detecting Bonanza”

Fermi

Dec. 15, 2015
Francis Reddy
NASA’s Goddard Space Flight Center, Greenbelt, Maryland

A long time ago in a galaxy half the universe away, a flood of high-energy gamma rays began its journey to Earth. When they arrived in April, NASA’s Fermi Gamma-ray Space Telescope caught the outburst, which helped two ground-based gamma-ray observatories detect some of the highest-energy light ever seen from a galaxy so distant. The observations provide a surprising look into the environment near a supermassive black hole at the galaxy’s center and offer a glimpse into the state of the cosmos 7 billion years ago.

download mp4 video here .
Explore how gamma-ray telescopes in space and on Earth captured an outburst of high-energy light from PKS 1441+25, a black-hole-powered galaxy more than halfway across the universe. Credits: NASA’s Goddard Space Flight Center

“When we looked at all the data from this event, from gamma rays to radio, we realized the measurements told us something we didn’t expect about how the black hole produced this energy,” said Jonathan Biteau at the Nuclear Physics Institute of Orsay, France. He led the study of results from the Very Energetic Radiation Imaging Telescope Array System (VERITAS), a gamma-ray telescope in Arizona.

VERITAS

Astronomers had assumed that light at different energies came from regions at different distances from the black hole. Gamma rays, the highest-energy form of light, were thought to be produced closest to the black hole.

“Instead, the multiwavelength picture suggests that light at all wavelengths came from a single region located far away from the power source,” Biteau explained. The observations place the area roughly five light-years from the black hole, which is greater than the distance between our sun and the nearest star.

The gamma rays came from a galaxy known as PKS 1441+25, a type of active galaxy called a blazar. Located toward the constellation Boötes, the galaxy is so far away its light takes 7.6 billion years to reach us. At its heart lies a monster black hole with a mass estimated at 70 million times the sun’s and a surrounding disk of hot gas and dust. If placed at the center of our solar system, the black hole’s event horizon — the point beyond which nothing can escape — would extend almost to the orbit of Mars.

As material in the disk falls toward the black hole, some of it forms dual particle jets that blast out of the disk in opposite directions at nearly the speed of light. Blazars are so bright in gamma rays because one jet points almost directly toward us, giving astronomers a view straight into the black hole’s dynamic and poorly understood realm.

Black-hole-powered galaxies called blazars are the most common sources detected by NASA’s Fermi Gamma-ray Space Telescope. As matter falls toward the supermassive black hole at the galaxy’s center, some of it is accelerated outward at nearly the speed of light along jets pointed in opposite directions. When one of the jets happens to be aimed in the direction of Earth, as illustrated here, the galaxy appears especially bright and is classified as a blazar.Credits: M. Weiss/CfA

In April, PKS 1441+25 underwent a major eruption. Luigi Pacciani at the Italian National Institute for Astrophysics in Rome was leading a project to catch blazar flares in their earliest stages in collaboration with the Major Atmospheric Gamma-ray Imaging Cerenkov experiment (MAGIC), located on La Palma in the Canary Islands.

MAGIC telescope

Using public Fermi data, Pacciani discovered the outburst and immediately alerted the astronomical community. Fermi’s Large Area Telescope revealed gamma rays up to 33 billion electron volts (GeV), reaching into the highest-energy part of the instrument’s detection range. For comparison, visible light has energies between about 2 and 3 electron volts.

NASA/Fermi LAT

“Detecting these very energetic gamma rays with Fermi, as well as seeing flaring at optical and X-ray energies with NASA’s Swift satellite, made it clear that PKS 1441+25 had become a good target for MAGIC,” Pacciani said.

NASA/Swift

Following up on the Fermi alert, the MAGIC team turned to the blazar and detected gamma rays with energies ranging from 40 to 250 GeV. “Because this galaxy is so far away, we didn’t have a strong expectation of detecting gamma rays with energies this high,” said Josefa Becerra Gonzalez, a researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who analyzed Fermi LAT data as part of the MAGIC study. “There are fewer and fewer gamma rays at progressively higher energies, and fewer still from very distant sources.”

The reason distance matters for gamma rays is that they convert into particles when they collide with lower-energy light. The visible and ultraviolet light from stars shining throughout the history of the universe forms a remnant glow called the extragalactic background light (EBL). For gamma rays, this is a cosmic gauntlet they must pass through to be detected at Earth. When a gamma ray encounters starlight, it transforms into an electron and a positron and is lost to astronomers. The farther away the blazar is, the less likely its highest-energy gamma rays will survive to be detected.

More distant blazars show a loss of higher-energy gamma rays thanks to the extragalactic background light (EBL), a “cosmic fog” of visible and ultraviolet starlight that permeates the universe. From studies of nearby blazars, scientists know how many gamma rays should be emitted at different energies. If a gamma ray on its way to Earth collides with lower-energy light in the EBL, it converts into a pair of particles and is lost to astronomers. As shown by the graphs at left in this illustration, the more distant the blazar, the fewer high-energy gamma rays we can detect. During the April 2015 outburst of PKS 1441+25, MAGIC and VERITAS saw rare gamma rays exceeding 100 GeV that managed to survive a journey of 7.6 billion light-years. Credits: NASA’s Goddard Space Flight Center

Following the MAGIC discovery, VERITAS also detected gamma rays with energies approaching 200 GeV. Findings from both teams are detailed in papers published Dec. 15 in The Astrophysical Journal Letters.

PKS 1441+25 is one of only two such distant sources for which gamma rays with energies above 100 GeV have been observed. Its dramatic flare provides a powerful glimpse into the intensity of the EBL from near-infrared to near-ultraviolet wavelengths and suggests that galaxy surveys have identified most of the sources responsible for it.

NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

For more information about NASA’s Fermi, visit:

http://www.nasa.gov/fermi

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

From NASA Fermi: “NASA’s Fermi Space Telescope Sharpens its High-energy Vision”

Fermi

Jan. 7, 2016
Francis Reddy
NASA’s Goddard Space Flight Center, Greenbelt, Maryland

Major improvements to methods used to process observations from NASA’s Fermi Gamma-ray Space Telescope have yielded an expanded, higher-quality set of data that allows astronomers to produce the most detailed census of the sky yet made at extreme energies. A new sky map reveals hundreds of these sources, including 12 that produce gamma rays with energies exceeding a trillion times the energy of visible light. The survey also discovered four dozen new sources that remain undetected at any other wavelength.

This image, constructed from more than six years of observations by NASA’s Fermi Gamma-ray Space Telescope, is the first to show how the entire sky appears at energies between 50 billion (GeV) and 2 trillion electron volts (TeV). For comparison, the energy of visible light falls between about 2 and 3 electron volts. A diffuse glow fills the sky and is brightest in the middle of the map, along the central plane of our galaxy. The famous Fermi Bubbles, first detected in 2010, appear as red extensions north and south of the galactic center and are much more pronounced at these energies.

Gamma-Ray bubbles at the center of the Milky Way. Credit: NASA’s Goddard Space Flight Center

Discrete gamma-ray sources include pulsar wind nebulae and supernova remnants within our galaxy, as well as distant galaxies called blazars powered by supermassive black holes. Labels show the highest-energy sources, all located within our galaxy and emitting gamma rays exceeding 1 TeV.
Credits: NASA/DOE/Fermi LAT Collaboration

“What made this advance possible was a complete reanalysis, which we call Pass 8, of all data acquired by Fermi’s Large Area Telescope (LAT),” said Marco Ajello, a Fermi team member at Clemson University in South Carolina. “The end result is effectively a complete instrument upgrade without our ever having to leave the ground.”

By carefully reexamining every gamma-ray and particle detection by the LAT since Fermi’s 2008 launch, scientists improved their knowledge of the detector’s response to each event and to the background environment in which it was measured. This enabled the Fermi team to find many gamma rays that previously had been missed while simultaneously improving the LAT’s ability to determine the directions of incoming gamma rays. These improvements effectively sharpen the LAT’s view while also significantly widening its useful energy range.

download mp4 video here .
Watch Fermi scientists explain why they’re so excited about Pass 8, a complete reprocessing of all data collected by the mission’s Large Area Telescope. This analysis increased the LAT’s sensitivity, widened its energy range, and effectively sharpened its view through improved backtracking of incoming gamma rays. Credits: NASA’s Goddard Space Flight Center

Using 61,000 Pass 8 gamma rays collected over 80 months, Ajello and his colleagues constructed a map of the entire sky at energies ranging from 50 billion (GeV) to 2 trillion electron volts (TeV). For comparison, the energy of visible light ranges from about 2 to 3 electron volts.

download mp4 video here .
Tour the best view of the high-energy gamma-ray sky yet seen. This video highlights the plane of our galaxy and identifies objects producing gamma rays with energies greater than 1 TeV. Credits: NASA’s Goddard Space Flight Center

“Of the 360 sources we cataloged, about 75 percent are blazars, which are distant galaxies sporting jets powered by supermassive black holes,” said co-investigator Alberto Domínguez at the Complutense University in Madrid. “The highest-energy sources, all located in our galaxy, are mostly remnants of supernova explosions and pulsar wind nebulae, places where rapidly rotating neutron stars accelerate particles to near the speed of light.” One famous example, the Crab Nebula, tops the list of the highest-energy Fermi sources, producing a steady drizzle of gamma rays exceeding 1 TeV.

Astronomers think these very high-energy gamma rays are produced when lower-energy light collides with accelerated particles. This results in a small energy loss for the particle and a big gain for the light, transforming it into a gamma ray.

download mp4 video here.
Gamma-ray emission from the highest-energy sources detected by Fermi is likely produced by what scientists call the inverse Compton process. When an electron moving near the speed of light strikes a low-energy photon, the collision slightly slows the electron and boosts the light’s energy into the gamma-ray regime. Credits: NASA’s Goddard Space Flight Center

For the first time, Fermi data now extend to energies previously seen only by ground-based detectors. Because ground-based telescopes have much smaller fields of view than the LAT, which scans the whole sky every three hours, they have detected only about a quarter of the objects in the catalog. This study provides ground facilities with more than 280 new targets for follow-up observations.

“An exciting aspect of this catalog is that we find many new sources that emit gamma rays over a comparatively large patch of the sky,” explained Jamie Cohen, a University of Maryland graduate student working with the Fermi team at NASA’s Goddard Space Flight Center in Greenbelt. “Finding more of these objects enables us to probe their structures as well as better understand mechanisms that accelerate the subatomic particles that ultimately produce gamma-ray emission.” The new catalog identifies 25 of these extended objects, including three new pulsar wind nebulae and two new supernova remnants.

Ajello presented the findings Thursday at the 227th meeting of the American Astronomical Society in Kissimmee, Florida. A paper describing the catalog has been accepted for publication in The Astrophysical Journal Supplement.

NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

For more information about NASA’s Fermi, visit:

http://www.nasa.gov/fermi

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition