From NASA: “NASA’s NICER Catches Record-setting X-ray Burst”

NASA image
From NASA

Nov. 7, 2019

Francis Reddy
francis.j.reddy@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.

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Illustration depicting a Type I X-ray burst. The explosion first blows off the hydrogen layer, which expands and ultimately dissipates. Then rising radiation builds to the point where it blows off the helium layer, which overtakes the expanding hydrogen. Some of the X-rays emitted in the blast scatter off of the accretion disk. The fireball then quickly cools, and the helium settles back onto the surface. Credit: NASA’s Goddard Space Flight Center/Chris Smith (USRA)

NASA/NICER on the ISS

NASA’s Neutron star Interior Composition Explorer (NICER) telescope on the International Space Station detected a sudden spike of X-rays at about 10:04 p.m. EDT on Aug. 20. The burst was caused by a massive thermonuclear flash on the surface of a pulsar, the crushed remains of a star that long ago exploded as a supernova.

The X-ray burst, the brightest seen by NICER so far, came from an object named SAX J1808.4-3658, or J1808 for short. The observations reveal many phenomena that have never been seen together in a single burst. In addition, the subsiding fireball briefly brightened again for reasons astronomers cannot yet explain.

“This burst was outstanding,” said lead researcher Peter Bult, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland, College Park. “We see a two-step change in brightness, which we think is caused by the ejection of separate layers from the pulsar surface, and other features that will help us decode the physics of these powerful events.”

The explosion, which astronomers classify as a Type I X-ray burst, released as much energy in 20 seconds as the Sun does in nearly 10 days. The detail NICER captured on this record-setting eruption will help astronomers fine-tune their understanding of the physical processes driving the thermonuclear flare-ups of it and other bursting pulsars.


A thermonuclear blast on a pulsar called J1808 resulted in the brightest burst of X-rays seen to date by NASA’s Neutron star Interior Composition Explorer (NICER) telescope. The explosion occurred on Aug. 20, 2019, and released as much energy in 20 seconds as our Sun does in almost 10 days. Watch to see how scientists think this incredible explosion occurred. Credits: NASA’s Goddard Space Flight Center

A pulsar is a kind of neutron star, the compact core left behind when a massive star runs out of fuel, collapses under its own weight, and explodes. Pulsars can spin rapidly and host X-ray-emitting hot spots at their magnetic poles. As the object spins, it sweeps the hot spots across our line of sight, producing regular pulses of high-energy radiation.

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

J1808 is located about 11,000 light-years away in the constellation Sagittarius. It spins at a dizzying 401 rotations each second, and is one member of a binary system. Its companion is a brown dwarf, an object larger than a giant planet yet too small to be a star. A steady stream of hydrogen gas flows from the companion toward the neutron star, and it accumulates in a vast storage structure called an accretion disk.

Gas in accretion disks doesn’t move inward easily. But every few years, the disks around pulsars like J1808 become so dense that a large amount of the gas becomes ionized, or stripped of its electrons. This makes it more difficult for light to move through the disk. The trapped energy starts a runaway process of heating and ionization that traps yet more energy. The gas becomes more resistant to flow and starts spiraling inward, ultimately falling onto the pulsar.

Hydrogen raining onto the surface forms a hot, ever-deepening global “sea.” At the base of this layer, temperatures and pressures increase until hydrogen nuclei fuse to form helium nuclei, which produces energy — a process at work in the core of our Sun.

“The helium settles out and builds up a layer of its own,” said Goddard’s Zaven Arzoumanian, the deputy principal investigator for NICER and a co-author of the paper. “Once the helium layer is a few meters deep, the conditions allow helium nuclei to fuse into carbon. Then the helium erupts explosively and unleashes a thermonuclear fireball across the entire pulsar surface.”

Astronomers employ a concept called the Eddington limit — named for English astrophysicist Sir Arthur Eddington — to describe the maximum radiation intensity a star can have before that radiation causes the star to expand. This point depends strongly on the composition of the material lying above the emission source.

“Our study exploits this longstanding concept in a new way,” said co-author Deepto Chakrabarty, a professor of physics at the Massachusetts Institute of Technology in Cambridge. “We are apparently seeing the Eddington limit for two different compositions in the same X-ray burst. This is a very powerful and direct way of following the nuclear burning reactions that underlie the event.”

As the burst started, NICER data show that its X-ray brightness leveled off for almost a second before increasing again at a slower pace. The researchers interpret this “stall” as the moment when the energy of the blast built up enough to blow the pulsar’s hydrogen layer into space.

The fireball continued to build for another two seconds and then reached its peak, blowing off the more massive helium layer. The helium expanded faster, overtook the hydrogen layer before it could dissipate, and then slowed, stopped and settled back down onto the pulsar’s surface. Following this phase, the pulsar briefly brightened again by roughly 20 percent for reasons the team does not yet understand.

During J1808’s recent round of activity, NICER detected another, much fainter X-ray burst that displayed none of the key features observed in the Aug. 20 event.

In addition to detecting the expansion of different layers, NICER observations of the blast reveal X-rays reflecting off of the accretion disk and record the flickering of “burst oscillations” — X-ray signals that rise and fall at the pulsar’s spin frequency but that occur at different surface locations than the hot spots responsible for its normal X-ray pulses.

A paper describing the findings has been published by The Astrophysical Journal Letters.

NICER is an Astrophysics Mission of Opportunity within NASA’s Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined, and efficient management approaches within the heliophysics and astrophysics science areas. NASA’s Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

See the full article here .

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The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA] Greenhouse Gases Observing Satellite.

#nasas-nicer-catches-record-setting-x-ray-burst, #astronomy, #astrophysics, #basic-research, #cosmology, #nasa-nicer-on-the-iss, #pulsars, #sax-j1808-4-3658

From CSIROscope: “A chance encounter with a pulsar”

CSIRO bloc

From CSIROscope

22 October 2019
Louise Jeckells

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The ASKAP radio telescope in all it’s glory.

When you think you’ve seen it all, look again – there might be a pulsar staring back at you.

Our scientists accidentally stumbled upon a pulsar, which is not an easy, or simple, task.

Ok, hold on – what is a pulsar?

When a giant star explodes, the core it leaves behind is a neutron star
Neutron stars are roughly 10 km in radius and about 1.4 times heavier than the Sun
A teaspoon of neutron star material would weigh about 10 million tons
A highly-magnetized rotating neutron star that emits a beam of electromagnetic radiation (think of a lighthouse) is a pulsar.

Astrophysicist Jocelyn Bell Burnell discovered the first pulsar in 1967.

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Today, astronomers have discovered most of the brighter and slower pulsars using large telescopes like our Parkes Radio Telescope (aka The Dish).

CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia

Emil Lenc is a research scientist with our Astronomy and Space Science team. He’s not a pulsar astronomer. Emil works on the Australian Square Kilometre Array Pathfinder (ASKAP) in remote Western Australia. His job is to put the telescope through its paces. To experiment with innovative ways to process telescope data.

SKA Square Kilometer Array

But Emil, alongside a group of other scientists, discovered one of these highly-magnetized rotating neutron stars. It’s called PSR J1431-6328. Very creative.

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The densely packed matter of a pulsar spins at incredible speeds, and emit radio waves that can be observed from Earth. Credit: Swinburne Astronomy Productions/CAASTRO.

The accidental discovery

In May, PhD student Andrew Zic planned to observe the red dwarf star Proxima Centauri – the closest star to the Sun. He wanted to better understand the flaring process and the implications for life on exoplanets around that star. But his four-day observation helped discovered something new.

During the Proxima Centauri observation, Emil wanted to test a new feature on ASKAP. The feature gave ASKAP the ability to see in circular polarisation. This is where the wave component of light from a source rotates in a circular motion. This form of light is not common in astronomical sources but can be seen in flaring stars and some pulsars.

“Our eyes can’t distinguish between circularly polarised light and unpolarised light. But ASKAP has the equivalent of polaroid sunglasses that can help highlight such sources against the glare of thousands of unpolarised sources,” Emil said.

“It worked a treat. Proxima Centauri stood out like a sore thumb. But I noticed another weaker source at the edge of the image. I had one of those ‘hmm, that’s weird’ moments.”

Emil let the Variable and Slow Transients (VAST) team that he collaborates with know of the potential discovery. They gathered clues from any previous observations to track down the culprit. Was it a flare star, a new pulsar, or perhaps something else?

“My colleague Shi Dai used the Parkes Radio Telescope to confirm that our mystery source had periodic pulses and was indeed a newly discovered pulsar.”

A rare sighting

Not only was this the first pulsar discovered with ASKAP but also the first pulsar revealed by its circular polarisation. As it turns out, it’s also in the top 90 fastest spinning pulsars (out of about 2700 known pulsars). And it’s spinning at a rate of around 360 times a second!

“When you’re looking at the sky for the first time through a new instrument, you’re bound to find something fascinating. In this case, there was nothing else in the field. It’s very rare you have something that sticks out so much.”

“There are hints the pulsar we discovered is part of a binary system,” Emil explained.

A binary system is simply one in which two objects orbit around a common centre of mass. That is, they are gravitationally bound to each other. Binary systems with pulsars are of immense importance to astronomers as they allow them to test our understanding of gravity.

“Being part of this system would affect the timing of the pulsar ever so slightly depending on whether it is heading towards us or away from us during its orbit around a companion.”

The team has been given extra time with the Parkes Radio Telescope to get a better estimate of the timing. And to see if they can find evidence of its companion.

If you’d like to read more, these findings have been published in The Astrophysical Journal.

See the full article here .


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SKA/ASKAP radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid West region of Western Australia

So what can we expect these new radio projects to discover? We have no idea, but history tells us that they are almost certain to deliver some major surprises.

Making these new discoveries may not be so simple. Gone are the days when astronomers could just notice something odd as they browse their tables and graphs.

Nowadays, astronomers are more likely to be distilling their answers from carefully-posed queries to databases containing petabytes of data. Human brains are just not up to the job of making unexpected discoveries in these circumstances, and instead we will need to develop “learning machines” to help us discover the unexpected.

With the right tools and careful insight, who knows what we might find.

CSIRO campus

CSIRO, the Commonwealth Scientific and Industrial Research Organisation, is Australia’s national science agency and one of the largest and most diverse research agencies in the world.

#a-chance-encounter-with-a-pulsar, #astronomy, #astrophysics, #basic-research, #cosmology, #csiroscope, #dame-susan-jocelyn-bell-burnell-discovered-pulsars, #pulsars

From AAS NOVA: “Should We Blame Pulsars for Too Much Antimatter?”

AASNOVA

From AAS NOVA

9 October 2019
Susanna Kohler

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Artist’s illustration of Geminga, a nearby pulsar that has been proposed to be the source of excess positrons measured at Earth. [Nahks Tr’Ehnl]

The Earth is constantly being bombarded by cosmic rays — high energy protons and atomic nuclei that speed through space at nearly the speed of light. Where do these energetic particles come from? A new study examines whether pulsars are the source of one particular cosmic-ray conundrum.

Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

An Excess of Positrons

In 2008, our efforts to understand the origin of cosmic rays hit a snag: data from a detector called PAMELA showed that more high-energy positrons were reaching Earth in cosmic rays than theory predicted.

INFN PAMELA spacecraft


INFN PAMELA Schematic

Positrons — the antimatter counterpart to electrons — are thought to be primarily produced by high-energy protons scattering off of particles within our galaxy. These interactions should produce decreasing numbers of positrons at higher energies — yet the data from PAMELA and other experiments show that positron numbers instead go up with increasing energy.

Something must be producing these extra high-energy positrons — but what?

Clues from Gamma-rays

One of the leading theories is that the excess positrons are produced by nearby pulsars — rapidly rotating, magnetized neutron stars. We know that pulsars gradually spin slower and slower over time, losing power as they spew a stream of high-energy electrons and positrons into the surrounding interstellar medium. If the pulsar is close enough to us, positrons produced in and around pulsars might make it to Earth before losing energy to interactions as they travel.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

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Observations from the High-Altitude Water Čerenkov (HAWC) Gamma-Ray Observatory show TeV nebulae around pulsars Geminga and PSR B0656+14. But do these sources also have extended GeV nebulae that would provide more direct constraints on positron density? [John Pretz]

HAWC High Altitude Čerenkov Experiment, located on the flanks of the Sierra Negra volcano in the Mexican state of Puebla at an altitude of 4100 meters(13,500ft), at WikiMiniAtlas 18°59′41″N 97°18′30.6″W. searches for cosmic rays

Could nearby pulsars produce enough positrons — and could they diffuse out from the pulsars efficiently enough — to account for the high-energy excess we observe here at Earth? A team of scientists now addresses these questions in a new publication led by Shao-Qiang Xi (Nanjing University and Chinese Academy of Sciences).

To test whether pulsars are responsible for the positrons we see, Xi and collaborators argue that we should look for GeV emission around candidate sources. As the pulsar-produced positrons diffuse outward, they should scatter off of infrared and optical background photons in the surrounding region. This would create a nebula of high-energy emission around the pulsars that glows at 10–500 GeV — detectable by observatories like the Fermi Gamma-ray Space Telescope.

NASA/Fermi LAT


NASA/Fermi Gamma Ray Space Telescope

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Fermi LAT gamma-ray count map (top) and residuals after the background is subtracted (bottom) for the region containing Geminga and PSR B0656+14. [Adapted from Xi et al. 2019]

Two Pulsars Get an Alibi

Xi and collaborators carefully analyze 10 years of Fermi LAT observations for two nearby pulsars that have been identified as likely candidates for the positron excess: Geminga and PSR B0656+14, located roughly 800 and 900 light-years away from us.

The result? They find no evidence of extended GeV emission around these sources. The authors’ upper limits on emission from Geminga and PSR B0656+14 give these objects an alibi, suggesting that pulsars can likely account for only a small fraction of the positron excess we observe.

So where does this leave us? If pulsars are cleared, we will need to look to other candidate sources of high-energy positrons: either other nearby cosmic accelerators like supernova remnants, or more exotic explanations, like the annihilation or decay of high-energy dark matter.

Citation

“GeV Observations of the Extended Pulsar Wind Nebulae Constrain the Pulsar Interpretations of the Cosmic-Ray Positron Excess,” Shao-Qiang Xi et al 2019 ApJ 878 104.
https://iopscience.iop.org/article/10.3847/1538-4357/ab20c9

See the full article here .


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1

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

#aas-nova, #antimatter, #astronomy, #astrophysics, #basic-research, #cosmic-rays, #cosmology, #positrons, #pulsars

From Max Planck Institute for Gravitational Physics: “Pulsating gamma rays from neutron star rotating 707 times a second”

From Max Planck Institute for Gravitational Physics

September 19, 2019

Media contact

Dr. Benjamin Knispel
Press Officer AEI Hannover
Phone:+49 511 762-19104
Fax:+49 511 762-17182
benjamin.knispel@aei.mpg.de

Science contacts
Lars Nieder
Phone:+49 511 762-17491
Fax:+49 511 762-2784
lars.nieder@aei.mpg.de

Prof. Dr. Bruce Allen
Director
Phone:+49 511 762-17148
Fax:+49 511 762-17182
bruce.allen@aei.mpg.de

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A black widow pulsar and its small stellar companion, viewed within their orbital plane. Powerful radiation and the pulsar’s “wind” – an outflow of high-energy particles — strongly heat the facing side of the star to temperatures twice as hot as the sun’s surface. The pulsar is gradually evaporating its partner, which fills the system with ionized gas and prevents astronomers from detecting the pulsar’s radio beam most of the time. NASA’s Goddard Space Flight Center/Cruz deWilde

Second fastest spinning radio pulsar known is a gamma-ray pulsar, too. Multi-messenger observations look closely at the system and raise new questions.

An international research team led by the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hannover has discovered that the radio pulsar J0952-0607 also emits pulsed gamma radiation. J0952-0607 spins 707 times in one second and is 2nd in the list of rapidly rotating neutron stars. By analyzing about 8.5 years worth of data from NASA’s Fermi Gamma-ray Space Telescope, LOFAR radio observations from the past two years, observations from two large optical telescopes, and gravitational-wave data from the LIGO detectors, the team used a multi-messenger approach to study the binary system of the pulsar and its lightweight companion in detail.

Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

TFC HiPERCAM mounted on the Gran Telescopio Canarias,

ESO/NTT at Cerro La Silla, Chile, at an altitude of 2400 metres

ESO La Silla NTT ULTRACAM is an ultra fast camera capable of capturing some of the most rapid astronomical events. It can take up to 500 pictures a second in three different colours simultaneously. It was designed and built by scientists from the Universities of Sheffield and Warwick (United Kingdom), in collaboration with the UK Astronomy Technology Centre in Edinburgh. ULTRACAM employs the latest in charged coupled device (CCD) detector technology in order to take, store and analyse data at the required sensitivities and speeds. CCD detectors can be found in digital cameras and camcorders, but the devices used in ULTRACAM are special because they are larger, faster and most importantly, much more sensitive to light than the detectors used in today’s consumer electronics products. Since it was built, it has operated at the William Herschel Telescope, the New Technology Telescope, and the Very Large Telescope. It is now permanently mounted on the Thai National Telescope.

NASA/Fermi LAT


NASA/Fermi Gamma Ray Space Telescope

ASTRON LOFAR European Map


ASTRON LOFAR Radio Antenna Bank, Netherlands

Their study published in The Astrophysical Journal shows that extreme pulsar systems are hiding in the Fermi catalogues and published in the Astrophysical Journal today shows that extreme pulsar systems are hiding in the Fermi catalogues and motivates further searches. Despite being very extensive, the analysis also raises new unanswered questions about this system.

MIT /Caltech Advanced aLigo

Pulsars are the compact remnants of stellar explosions which have strong magnetic fields and are rapidly rotating.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

They emit radiation like a cosmic lighthouse and can be observable as radio pulsars and/or gamma-ray pulsars depending on their orientation towards Earth.

The fastest pulsar outside globular clusters

PSR J0952-0607 (the name denotes the position in the sky) was first discovered in 2017 by radio observations of a source identified by the Fermi Gamma-ray Space Telescope as possibly being a pulsar. No pulsations of the gamma rays in data from the Large Area Telescope (LAT) onboard Fermi had been detected. Observations with the radio telescope array LOFAR identified a pulsating radio source and – together with optical telescope observations – allowed to measure some properties of the pulsar. It is orbiting the common center of mass in 6.2 hours with a companion star that only weighs a fiftieth of our Sun. The pulsar rotates 707 times in a single second and is therefore the fastest spinning in our Galaxy outside the dense stellar environments of globular clusters.

Searching for extremely faint signals

Using this prior information on the binary pulsar system, Lars Nieder, a PhD student at the AEI Hannover, set out to see if the pulsar also emitted pulsed gamma rays. “This search is extremely challenging because the Fermi gamma-ray telescope only registered the equivalent of about 200 gamma rays from the faint pulsar over the 8.5 years of observations. During this time the pulsar itself rotated 220 billion times. In other words, only once in every billion rotations was a gamma ray observed!” explains Nieder. “For each of these gamma rays, the search must identify exactly when during each of the 1.4 millisecond rotations it was emitted.”

This requires combing through the data with very fine resolution in order not to miss any possible signals. The computing power required is enormous. The very sensitive search for faint gamma-ray pulsations would have taken 24 years to complete on a single computer core. By using the Atlas computer cluster at the AEI Hannover it finished in just 2 days.

MPG Institute for Gravitational Physics Atlas Computing Cluster

A strange first detection

“Our search found a signal, but something was wrong! The signal was very faint and not quite where it was supposed to be. The reason: our detection of gamma rays from J0952-0607 had revealed a position error in the initial optical-telescope observations which we used to target our analysis. Our discovery of the gamma-ray pulsations revealed this error,” explains Nieder. “This mistake was corrected in the publication reporting the radio pulsar discovery. A new and extended gamma-ray search made a rather faint – but statistically significant – gamma-ray pulsar discovery at the corrected position.”

Having discovered and confirmed the existence of pulsed gamma radiation from the pulsar, the team went back to the Fermi data and used the full 8.5 years from August 2008 until January 2017 to determine physical parameters of the pulsar and its binary system. Since the gamma radiation from J0952-0607 was so faint, they had to enhance their analysis method developed previously to correctly include all unknowns.

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The pulse profile (distribution of gamma-ray photons during one rotation of the pulsar) of J0952-0607 is shown at the top. Below is the corresponding distribution of the individual photons over the ten years of observations. The greyscale shows the probability (photon weights) for individual photons to originate from the pulsar. From mid 2011 on, the photons line up along tracks corresponding to the pulse profile. This shows the detection of gamma-ray pulsations, which is not possible before mid 2011. L. Nieder/Max Planck Institute for Gravitational Physics.

Another surprise: no gamma-ray pulsations before July 2011

The derived solution contained another surprise, because it was impossible to detect gamma-ray pulsations from the pulsar in the data from before July 2011. The reason for why the pulsar only seems to show pulsations after that date is unknown. Variations in how much gamma rays it emitted might be one reason, but the pulsar is so faint that it was not possible to test this hypothesis with sufficient accuracy. Changes in the pulsar orbit seen in similar systems might also offer an explanation, but there was not even a hint in the data that this was happening.

Optical observations raise further questions

The team also used observations with the ESO’s New Technology Telescope at La Silla and the Gran Telescopio Canarias on La Palma to examine the pulsar’s companion star. It is most likely tidally locked to the pulsar like the Moon to the Earth so that one side always faces the pulsar and gets heated up by its radiation. While the companion orbits the binary system’s center of mass its hot “day” side and cooler “night” side are visible from the Earth and the observed brightness and color vary.

These observations create another riddle. While the radio observations point to a distance of roughly 4,400 light-years to the pulsar, the optical observations imply a distance about three times larger. If the system was relatively close to Earth, it would feature a never-seen-before extremely compact high density companion, while larger distances are compatible with the densities of known similar pulsar companions. An explanation for this discrepancy might be the existence of shock waves in the wind of particles from the pulsar, which could lead to a different heating of the companion. More gamma-ray observations with Fermi LAT observations should help answer this question.

Searching for continuous gravitational waves

Another group of researchers at the AEI Hannover searched for continuous gravitational wave emission from the pulsar using LIGO data from the first (O1) and second (O2) observation run. Pulsars can emit gravitational waves when they have tiny hills or bumps. The search did not detect any gravitational waves, meaning that the pulsar’s shape must be very close to a perfect sphere with the highest bumps less than a fraction of a millimeter.

Rapidly rotating neutron stars

Understanding rapidly spinning pulsars is important because they are probes of extreme physics. How fast neutron stars can spin before they break apart from centrifugal forces is unknown and depends on unknown nuclear physics. Millisecond pulsars like J0952-0607 are rotating so rapidly because they have been spun up by accreting matter from their companion. This process is thought to bury the pulsar’s magnetic field. With the long-term gamma-ray observations, the research team showed that J0952-0607 has one of the ten lowest magnetic fields ever measured for a pulsar, consistent with expectations from theory.

Einstein@Home searches for test cases of extreme physics

“We will keep studying this system with gamma-ray, radio, and optical observatories since there are still unanswered questions about it. This discovery also shows once more that extreme pulsar systems are hiding in the Fermi LAT catalogue,” says Prof. Bruce Allen, Nieder’s PhD supervisor and Director at the AEI Hannover. “We are also employing our citizen science distributed computing project Einstein@Home to look for binary gamma-ray pulsar systems in other Fermi LAT sources and are confident to make more exciting discoveries in the future.”

Einstein@home, a BOINC project

See the full article here.

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Please help promote STEM in your local schools.

Stem Education Coalition

The Max Planck Institute for Gravitational Physics (Albert Einstein Institute) is the largest research institute in the world specializing in general relativity and beyond. The institute is located in Potsdam-Golm and in Hannover where it is closely related to the Leibniz Universität Hannover.

#astronomy, #astrophysics, #basic-research, #boinc-berkeley-open-infrastructure-for-network-computing, #cosmology, #einsteinhome, #max-planck-institute-for-gravitational-physics, #multimessenger-astrophysics, #pulsars, #the-radio-pulsar-j0952-0607

From NANOGrav via COSMOS: “Now let’s find a pair of black holes”

From NANOGrav

via

Cosmos Magazine bloc

COSMOS Magazine

16 April 2019
Richard A Lovett

Last week, scientists studying black holes reported that they’d managed to turn the entire Earth into a giant virtual telescope that allowed them to make an image of a supermassive black hole 55 million light years away.

Now, another group of black hole researchers is reporting on a way to turn our entire galaxy into an even more gargantuan black hole detector – this time looking for pairs of such supermassive black holes, orbiting each other in distant galaxies.

The project, called NANOGrav, was described at a meeting of the American Physical Society in Denver, Colorado. It is attempting to spot supermassive black hole pairs via the effect of gravitational waves created by them on a class of astronomical objects known as millisecond pulsars.

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In this radio image, two supermassive black hole engines are seen as red dots, their large-scale jet structures clearly visible. NANOGRAV.

Gravitational waves are ripples in the fabric of space-time, created by movements of massive objects, including black holes. These waves cause space to expand, contract, or vibrate, thereby distorting the medium in which we all live.

Pulsars are the collapsed remnants of dead stars, which emit radio beams that sweep across the heavens like the blink-blink-blink of cosmic lighthouses.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

Millisecond pulsars blink so fast that they emit numerous pulses per second.

“They’re like really stable clocks, scattered all over the Milky Way,” says Joseph Simon, an astrophysicist at NASA’s Jet Propulsion Laboratory, in Pasadena, California.

“Pulsars are some of the most accurate clocks we have in the universe,” says Brad Tucker, an astrophysicist and cosmologist at Australian National University, who is not a member of the NANOGrav team. “Observations of them are even used to calibrate GPS satellites.”

Black holes have no direct effect on pulsars, but when galaxies merge, astrophysicists believe, the supermassive black holes at their centres go into orbit around each other for a long time before they too eventually merge.

As these pairs circle each other, they should emit gravitational waves that oscillate in tandem with their orbital cycle. The goal of NANOGrav is to detect these waves via their effect on the otherwise-precise timing of pulsar signals coming through them.

“As a gravitational wave passes by the Earth, it will stretch and squeeze space-time,” Simon says. “So, the pulse from that pulsar will have to travel a slightly longer distance or a slightly shorter distance. It will get here a bit sooner or slightly after what we expect.”

Not that it’s a huge effect. “The change we are searching for is less than a microsecond,” Simon says – a formidable challenge to detect, given that our planet also spins and orbits the Sun, both of which create far greater differences in the arrival time of any given pulsar signal at any given radio telescope than the tiny effect the NANOGrav project is looking for.

Nor is it a rapid effect. The “nano” in the project’s name doesn’t refer to nanoseconds. Rather, it refers to nanohertz: events that complete only 1 billionth of a cycle per second.

In other words, a full cycle takes about 30 years.

To detect this, the NANOGrav team has been monitoring 48 pulsars since late 2006. That means they’ve accumulated 12½ years of data, but that’s not yet a large enough fraction of a nanohertz cycle to be able to spot it.

It is, however, getting close.

“We are expecting that within the next three to four years, we will be able to detect this, depending on how strong it actually is,” Simon says.

The goal, he adds, is very different from that of the LIGO project (and its European counterpart, Virgo), which have successfully used multi-kilometer-long laser detectors to spot the much more rapid gravitational-wave oscillations created by the mergers of much smaller (stellar mass) black holes and neutron stars.

It’s also a world apart from a project at Louisiana State University, Baton Rouge, which has built a “table-top” version of LIGO that incorporates extremely tiny mirrors, about the diameter of a human hair, in an effort to ratchet up the sensitivity of the next round of advanced detectors used in LIGO and Virgo themselves.

But gravitational wave researchers of all types are impressed by NANOGrav’s vision.

“The work that NANOGrav does is fantastic,” says Thomas Corbitt, leader of the Louisiana State University team. “It’s amazing to see that the same physics governs these vastly different black holes.”

“This is yet another clever way to probe extreme environments in space,” adds Tucker. “These are the sorts of ideas that get me excited – using a precise observation for something completely different – much like how the Kepler Space Telescope, which was designed to find planets, has told us a lot about exploding stars and black holes.”

Learning more about supermassive black holes, he continues, is important in and of itself. “We think nearly every large galaxy has them,” he says. “[They] are the ultimate laboratory for testing extreme physics—not only of gravity but time itself.”

“The great thing,” adds David McClelland, director of Australian National University’s Centre for Gravitational Physics, is that LIGO and Virgo have already proved that gravitational waves exist, “and can be detected directly.” It’s only a matter of time, he says, until other projects, such as NANOGrav also detect them.

See the full article here .

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NANOGrav stands for North American Nanohertz Observatory for Gravitational Waves. As the name implies, NANOGrav members are drawn from across the United States and Canada and our goal is to study the Universe using gravitational waves. Gravitational waves are ripples in the fabric of space and time that cause objects to shrink and stretch by very, very small amounts. NANOGrav uses the Galaxy itself to detect gravitational waves with the help of objects called pulsars — exotic, dead stars that send out pulses of radio waves with extraordinary regularity. This is known as a Pulsar Timing Array, or PTA. NANOGrav scientists make use of some of the world’s best telescopes and most advanced technology, drawing on physics, computer science, signal processing, and electrical engineering. Our short term goal is to detect gravitational waves within the next decade, an event which may be the first direct detection ever. But detection is only the first step towards studying our Universe in a completely new and revolutionary way, and we are sure to make unexpected discoveries in the process.

NANOGrav cooperates with similar experiments in Australia (the Parkes Pulsar Timing Array) and Europe (the European Pulsar Timing Array). Together, we make up the International Pulsar Timing Array, or IPTA. By sharing our resources and knowledge, we hope to usher in the era of gravitational wave astronomy more quickly and with greater impact.

NANOGrav was founded in October 2007 and has since grown to over 60 members at over a dozen institutions. NANOGrav members have been awarded over $10M in competitive scientific grants and awards to perform NANOGrav-related research at their institutions.

#astronomy, #astrophysics, #basic-research, #cosmology, #dame-susan-jocelyn-bell-burnell-1943, #nanograv-north-american-nanohertz-observatory-for-gravitational-waves, #pulsars

From National Radio Astronomy Observatory: “Astronomers Find “Cannonball Pulsar” Speeding Through Space”


From National Radio Astronomy Observatory

NRAO Banner

March 19, 2019

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu

Object got powerful “kick” from supernova explosion.

1
Credit: Composite by Jayanne English, University of Manitoba; F. Schinzel et al.; NRAO/AUI/NSF; DRAO/Canadian Galactic Plane Survey; and NASA/IRAS.

Astronomers using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) [below] have found a pulsar speeding away from its presumed birthplace at nearly 700 miles per second, with its trail pointing directly back at the center of a shell of debris from the supernova explosion that created it. The discovery is providing important insights into how pulsars — superdense neutron stars left over after a massive star explodes — can get a “kick” of speed from the explosion.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

“This pulsar has completely escaped the remnant of debris from the supernova explosion,” said Frank Schinzel, of the National Radio Astronomy Observatory (NRAO). “It’s very rare for a pulsar to get enough of a kick for us to see this,” he added.

The pulsar, dubbed PSR J0002+6216, about 6,500 light-years from Earth, was discovered in 2017 by a citizen-science project called Einstein@Home, running on BOINC software from UC Berkeley Space Science Center. That project uses computer time donated by volunteers to analyze data from NASA’s Fermi Gamma-ray Space Telescope. So far, using more than 10,000 years of computing time, the project has discovered a total of 23 pulsars.

einstein@home

NASA/Fermi Gamma Ray Space Telescope

Radio observations with the VLA clearly show the pulsar outside the supernova remnant, with a tail of shocked particles and magnetic energy some 13 light-years long behind it. The tail points back toward the center of the supernova remnant.

“Measuring the pulsar’s motion and tracing it backwards shows that it was born at the center of the remnant, where the supernova explosion occurred,” said Matthew Kerr, of the Naval Research Laboratory. The pulsar now is 53 light-years from the remnant’s center.

“The explosion debris in the supernova remnant originally expanded faster than the pulsar’s motion,” said Dale Frail, of NRAO. “However, the debris was slowed by its encounter with the tenuous material in interstellar space, so the pulsar was able to catch up and overtake it,” he added.

The astronomers said that the pulsar apparently caught up with the shell about 5,000 years after the explosion. The system now is seen about 10,000 years after the explosion.

The pulsar’s speed of nearly 700 miles per second is unusual, the scientists said, with the average pulsar speed only about 150 miles per second. “This pulsar is moving fast enough that it eventually will escape our Milky Way Galaxy,” Frail said.

Astronomers have long known that pulsars get a kick when born in supernova explosions, but still are unsure how that happens.

“Numerous mechanisms for producing the kick have been proposed. What we see in PSR J0002+6216 supports the idea that hydrodynamic instabilities in the supernova explosion are responsible for the high velocity of this pulsar,” Frail said.

“We have more work to do to fully understand what’s going on with this pulsar, and it’s providing an excellent opportunity to improve our knowledge of supernova explosions and pulsars,” Schinzel said.

Schinzel, Kerr, and Frail worked with Urvashi Rau and Sanjay Bhatnagar, both of NRAO. The scientists are reporting their results at the High Energy Astrophysics Division meeting of the American Astronomical Society in Monterey, California, and have submitted a paper to the Astrophysical Journal Letters.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Einstein@Home is a World Year of Physics 2005 and an International Year of Astronomy 2009 project. It is supported by the American Physical Society (APS), the US National Science Foundation (NSF), the Max Planck Society (MPG), and a number of international organizations.

See the full article here .


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NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

The NRAO operates a complementary, state-of-the-art suite of radio telescope facilities for use by the scientific community, regardless of institutional or national affiliation: the Very Large Array (VLA), and the Very Long Baseline Array (VLBA)*.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).

NRAO VLBA

NRAO VLBA

*The Very Long Baseline Array (VLBA) comprises ten radio telescopes spanning 5,351 miles. It’s the world’s largest, sharpest, dedicated telescope array. With an eye this sharp, you could be in Los Angeles and clearly read a street sign in New York City!

Astronomers use the continent-sized VLBA to zoom in on objects that shine brightly in radio waves, long-wavelength light that’s well below infrared on the spectrum. They observe blazars, quasars, black holes, and stars in every stage of the stellar life cycle. They plot pulsars, exoplanets, and masers, and track asteroids and planets.

And the future Expanded Very Large Array (EVLA).

#astronomers-find-cannonball-pulsar-speeding-through-space, #astronomy, #astrophysics, #basic-research, #cosmology, #dame-susan-jocelyn-bell-burnell, #einsteinhome, #psr-j00026216, #pulsars

From Caltech: “Magnetar Mysteries in our Galaxy and Beyond”

Caltech Logo

From Caltech

01/09/2019

Whitney Clavin
(626) 395-1856
wclavin@caltech.edu

1
Illustration of a magnetar—a rotating neutron star with incredibly powerful magnetic fields.
Credit: NASA/CXC/M.Weiss

2
The 70-meter radio dish (DSS-43) in Canberra, Australia, part of NASA’s Deep Space Network.
Credit: NASA/DSN

New research looks at possible links between magnetars and extragalactic radio bursts.

In a new Caltech-led study, researchers from campus and the Jet Propulsion Laboratory (JPL) have analyzed pulses of radio waves coming from a magnetar—a rotating, dense, dead star with a strong magnetic field—that is located near the supermassive black hole at the heart of the Milky Way galaxy. The new research provides clues that magnetars like this one, lying in close proximity to a black hole, could perhaps be linked to the source of “fast radio bursts,” or FRBs. FRBs are high-energy blasts that originate beyond our galaxy but whose exact nature is unknown.

“Our observations show that a radio magnetar can emit pulses with many of the same characteristics as those seen in some FRBs,” says Caltech graduate student Aaron Pearlman, who presented the results today at the 233rd meeting of the American Astronomical Society in Seattle. “Other astronomers have also proposed that magnetars near black holes could be behind FRBs, but more research is needed to confirm these suspicions.”

The research team was led by Walid Majid, a visiting associate at Caltech and principal research scientist at JPL, which is managed by Caltech for NASA, and Tom Prince, the Ira S. Bowen Professor of Physics at Caltech. The team looked at the magnetar named PSR J1745-2900, located in the Milky Way’s galactic center, using the largest of NASA’s Deep Space Network radio dishes in Australia. PSR J1745-2900 was initially spotted by NASA’s Swift X-ray telescope, and later determined to be a magnetar by NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), in 2013.

NASA Neil Gehrels Swift Observatory

NASA NuSTAR X-ray telescope

“PSR J1745-2900 is an amazing object. It’s a fascinating magnetar, but it also has been used as a probe of the conditions near the Milky Way’s supermassive black hole,” says Fiona Harrison, the Benjamin M. Rosen Professor of Physics at Caltech and the principal investigator of NuSTAR. “It’s interesting that there could be a connection between PSR J1745-2900 and the enigmatic FRBs.”

Magnetars are a rare subtype of a group of objects called pulsars; pulsars, in turn, belong to a class of rotating dead stars known as neutron stars. Magnetars are thought to be young pulsars that spin more slowly than ordinary pulsars and have much stronger magnetic fields, which suggests that perhaps all pulsars go through a magnetar-like phase in their lifetime.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

The magnetar PSR J1745-2900 is the closest-known pulsar to the supermassive black hole at the center of the galaxy, separated by a distance of only 0.3 light-years, and it is the only pulsar known to be gravitationally bound to the black hole and the environment around it.

In addition to discovering similarities between the galactic-center magnetar and FRBs, the researchers also gleaned new details about the magnetar’s radio pulses. Using one of the Deep Space Network’s largest radio antennas, the scientists were able to analyze individual pulses emitted by the star every time it rotated, a feat that is very rare in radio studies of pulsars. They found that some pulses were stretched, or broadened, by a larger amount than predicted when compared to previous measurements of the magnetar’s average pulse behavior. Moreover, this behavior varied from pulse to pulse.

“We are seeing these changes in the individual components of each pulse on a very fast time scale. This behavior is very unusual for a magnetar,” says Pearlman. The radio components, he notes, are separated by only 30 milliseconds on average.

One theory to explain the signal variability involves clumps of plasma moving at high speeds near the magnetar. Other scientists have proposed that such clumps might exist but, in the new study, the researchers propose that the movement of these clumps may be a possible cause of the observed signal variability. Another theory proposes that the variability is intrinsic to the magnetar itself.

“Understanding this signal variability will help in future studies of both magnetars and pulsars at the center of our galaxy,” says Pearlman.

In the future, Pearlman and his colleagues hope to use the Deep Space Network radio dish to solve another outstanding pulsar mystery: Why are there so few pulsars near the galactic center? Their goal is to find a non-magnetar pulsar near the galactic-center black hole.

“Finding a stable pulsar in a close, gravitationally bound orbit with the supermassive black hole at the galactic center could prove to be the Holy Grail for testing theories of gravity,” says Pearlman. “If we find one, we can do all sorts of new, unprecedented tests of Albert Einstein’s general theory of relativity.”

The new study, titled, “Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900,” appeared in the October 20, 2018, issue of The Astrophysical Journal and was funded by a Research and Technology Development grant through a contract with NASA; JPL and Caltech’s President’s and Director’s Fund; the Department of Defense; and the National Science Foundation. Other authors include Jonathon Kocz of Caltech and Shinji Horiuchi of the CSIRO (Commonwealth Scientific and Industrial Research Organization) Astronomy & Space Science, Canberra Deep Space Communication Complex.

See the full article here .


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Please help promote STEM in your local schools.


Stem Education Coalition

The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

Caltech campus


Caltech campus

#astronomy, #astrophysics, #basic-research, #caltech, #cosmology, #frbs-fast-radio-bursts-one-of-todays-big-mysteries-in-astronomy, #neutron-stars, #pulsars, #radio-magnetars, #the-team-looked-at-the-magnetar-named-psr-j1745-2900-located-in-the-milky-ways-galactic-center-using-the-largest-of-nasas-deep-space-network-radio-dishes-in-australia