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  • richardmitnick 12:17 pm on February 11, 2021 Permalink | Reply
    Tags: "A brief history: what we know so far about fast radio bursts across the universe", Arecibo Radio Observatory, , , ​Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, , Caltech STARE2 Radio telescope at Owens Valley Radio Observatory, , Fast radio bursts are one of the great mysteries of the universe., , , , The first FRB was discovered in 2007 by a team led by British-American astronomer Duncan Lorimer using Murriyang-the traditional Indigenous name for the iconic Parkes Radio Telescope., The Lorimer burst had travelled through far too much gas to have originated in our galaxy., The NASA Neil Gehrels Swift Observatory captured X-rays from a very magnetic and erratic neutron star in our own Milky Way., We need to detect an FRB with a radio interferometer-an array of antennas spread out over at least a few kilometres.   

    From The Conversation (AU): “A brief history: what we know so far about fast radio bursts across the universe” 

    From The Conversation (AU)

    February 10, 2021
    Ryan Shannon
    Associate Professor, Swinburne University of Technology (AU)

    Keith Bannister
    Astronomer, CSIRO (AU)

    1
    CSIRO/Parkes Observatory [ Murriyang, the traditional Indigenous name] , located 20 kilometres north of the town of Parkes, New South Wales, Australia, 414.80m above sea level.

    Fast radio bursts are one of the great mysteries of the universe. Since their discovery, we have learned a great deal about these intense millisecond-duration pulses.

    But we still have much to learn, such as what causes them.

    We know the intense bursts originate in galaxies billions of light years away. We have also used these bursts (called FRBs) to find missing matter that couldn’t be found otherwise.

    With teams of astronomers around the world racing to understand their enigma, how did we get to where we are now?

    The first burst

    The first FRB was discovered in 2007 by a team led by British-American astronomer Duncan Lorimer using Murriyang, the traditional Indigenous name for the iconic Parkes radio telescope.

    The team found an incredibly bright pulse — so bright that many astronomers did not believe it to be real. But there was yet more intrigue.

    Radio pulses provide a tremendous gift to astronomers. By measuring when a burst arrives at the telescope at different frequencies, astronomers can tell the total amount of gas that it passed through on its journey to Earth.

    2
    A typical Fast Radio Burst. The burst arrives first at high frequencies and is delayed by as much as several seconds at the lower frequencies. This tell-tale curve is what astronomers are looking for. Credit:Ryan Shannon and Vikram Ravi.

    The Lorimer burst had travelled through far too much gas to have originated in our galaxy, the Milky Way. The team concluded it came from a galaxy billions of light years away.

    To be visible from so far away, whatever produced it must have released an enormous amount of energy. In just a millisecond it released as much energy as our Sun would in 80 years.

    Lorimer’s team could only guess which galaxy their FRB had come from. Murriyang can’t pinpoint FRB locations very accurately. It would take several years for another team to make the breakthrough.

    Locating FRBs

    To pinpoint a burst location, we need to detect an FRB with a radio interferometer — an array of antennas spread out over at least a few kilometres.

    When signals from the telescopes are combined, they produce an image of an FRB with enough detail not only to see in which galaxy the burst originated, but in some cases to tell where within the galaxy it was produced.

    The first FRB localised was from a source that emitted many bursts. The first burst was discovered in 2012 with the giant Arecibo telescope in Puerto Rico.


    NAIC Arecibo Observatory operated by University of Central Florida, Yang Enterprises and UMET, Altitude 497 m (1,631 ft), which has now collapsed.

    Subsequent bursts were detected by the Very Large Array, in New Mexico, and found to be coming from a tiny galaxy about 3 billion light years away.

    NRAO Karl G Jansky Very Large Array, located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes.

    In 2018, using the Australian Square Kilometre Array Pathfinder Telescope (ASKAP) in Western Australia, our team identified the second FRB host galaxy.

    Australian Square Kilometre Array Pathfinder (ASKAP) is a radio telescope array located at Murchison Radio-astronomy Observatory (MRO) in the Australian Mid West on the traditional lands of the Wajarri peoples. ASKAP consists of 36 identical parabolic antennas, each 12 metres in diameter, working together as a single instrument with a total collecting area of approximately 4,000 square metres.

    In stark contrast to the previous galaxy, this galaxy was very ordinary. But our published discovery was this month awarded the 2020 AAAS Newcomb Cleveland Prize by the American Association for the Advancement of Science.

    Teams including ours have now localised roughly a dozen more bursts from a wide range of galaxies, large and small, young and old. The fact FRBs can come from such a wide range of galaxies remains a puzzle.

    A burst from close to home

    On April 28, 2020, a flurry of X-rays suddenly bashed into the Swift telescope orbiting Earth.

    NASA Neil Gehrels Swift Observatory.

    The satellite telescope dutifully noted the rays had come from a very magnetic and erratic neutron star in our own Milky Way. This star has form: it goes into fits every few years.

    Two telescopes, CHIME in Canada and the STARE2 array in the United States, detected a very bright radio burst within milliseconds of the X-rays and in the direction of that star.

    CHIME Canadian Hydrogen Intensity Mapping Experiment -A partnership between the University of British Columbia (CA), the University of Toronto (CA), McGill University (CA), Yale and the National Research Council in British Columbia (CA), at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, (CA) Altitude 545 m (1,788 ft).

    Caltech STARE2 Radio telescope at Owens Valley Radio Observatory, located near Big Pine, California (US) in Owens Valley. It lies east of the Sierra Nevada, approximately 350 kilometers (220 mi) north of Los Angeles and 20 kilometers (12 mi) southeast of Bishop. It was established in 1956, and is owned and operated by the California Institute of Technology (Caltech), Altitude 1,222 m (4,009 ft).

    Caltech Owens Valley Radio Observatory, Owens Valley, California, Altitude 1,222 m (4,009 ft).

    This demonstrated such neutron stars could be a source of the FRBs we see in galaxies far away.

    The simultaneous release of X-rays and radio waves gave astrophysicists important clues to how nature can produce such bright bursts. But we still don’t know for certain if this is the cause of FRBs.

    So what’s next?

    While 2020 was the year of the local FRB, we expect 2021 will be the year of the the far-flung FRB, even further than already observed.

    The CHIME telescope has collected by far the largest sample of bursts and is compiling a meticulous catalogue that should be available to other astronomers soon.

    A team at Caltech is building an array specifically dedicated to finding FRBs.

    Caltech Deep Synoptic Array being built at Owens Valley Radio Observatory Owens Valley, California, Altitude 1,222 m (4,009 ft)

    There’s plenty of action in Australia too. We are developing a new burst-detection supercomputer for ASKAP that will find FRBs at a faster rate and find more distant sources.

    It will effectively turn ASKAP into a high-speed, high-definition video camera, and make a movie of the universe at 40 trillion pixels per second.

    By finding more bursts, and more distant bursts, we will be able to better study and understand what causes these mysteriously intense bursts of energy.


    Fast Radio Burst Research Earns AAAS Newcomb Cleveland Prize

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Conversation (AU) launched as a pilot project in October 2014. It is an independent source of news and views from the academic and research community, delivered direct to the public.
    Our team of professional editors work with university and research institute experts to unlock their knowledge for use by the wider public.
    Access to independent, high quality, authenticated, explanatory journalism underpins a functioning democracy. Our aim is to promote better understanding of current affairs and complex issues. And hopefully allow for a better quality of public discourse and conversation.

     
  • richardmitnick 9:32 am on April 15, 2020 Permalink | Reply
    Tags: , , , ​Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, , , ,   

    From astrobites: “How It’s Made, Fast Radio Burst Edition” 

    Astrobites bloc

    From astrobites

    1
    Artist’s conception of the localization of a fast radio burst to its host galaxy. [Danielle Futselaar]

    Title: Spectropolarimetric analysis of FRB 181112 at microsecond resolution: Implications for Fast Radio Burst emission mechanism
    Authors: Hyerin Cho et al.
    First Author’s Institution: Gwangju Institute of Science and Technology, Korea
    Status: Published in ApJL

    Fast radio bursts (FRBs) are probably the fastest growing and most interesting field in radio astronomy right now. These extragalactic, incredibly energetic bursts last just a few milliseconds and come in two flavors, singular and repeating. Recently the number of known FRBs has exploded, as the ​Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope has discovered about 20 repeating FRBs (and also redetected the famous FRB 121102) and over 700 single bursts (hinted at here).

    CHIME Canadian Hydrogen Intensity Mapping Experiment -A partnership between the University of British Columbia, the University of Toronto, McGill University, Yale and the National Research Council in British Columbia, at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, CA Altitude 545 m (1,788 ft)

    However, despite the huge growth in the known FRB population, we still don’t know what the source(s) of these bursts is (are). Today’s paper looks at possible explanations for the properties of one FRB in particular to try to figure out what its source might be.

    Your Friendly Neighborhood FRB

    A number of previous astrobites have discussed the basics of FRBs (here, here, and here for example) but the FRB that the authors of this paper focus on is FRB 181112. FRB 181112 was found with the Australian Square Kilometer Array Pathfinder (ASKAP) and localized to a host galaxy about 2.7 Gpc away from us even though it has not been observed to repeat.

    Australian Square Kilometre Array Pathfinder (ASKAP) is a radio telescope array located at Murchison Radio-astronomy Observatory (MRO) in the Australian Mid West. ASKAP consists of 36 identical parabolic antennas, each 12 metres in diameter, working together as a single instrument with a total collecting area of approximately 4,000 square metres.

    That’s over a hundred times farther away than the closest galaxy cluster, the Virgo Cluster!

    Virgo Supercluster NASA


    Virgo Supercluster, Wikipedia

    One quality of FRB 181112 that makes it particularly interesting to study is that the way ASKAP records data allows the authors to study the polarization of the radio emission. Polarization of light is a measure of how much the electromagnetic wave (here the radio emission) rotates due to any magnetic fields it propagates through. The two types of polarization are linear polarization (Q for vertical/horizontal, or V for ±45°), which occurs if the electromagnetic wave rotates in a plane, and circular (either left- or right-handed depending on the rotation direction) if the light rotates on a circular path. By looking at the polarization of FRB 181112, shown in Figure 1, the authors can determine the strength of the magnetic field it traveled through.

    2
    Figure 1: a) The full polarization profile of FRB 181112 showing four profile components. The black line, I, is the sum of all the polarizations of light, or the total intensity of the burst. The red line, Q, is the profile using only (linearly) horizontally or vertically polarized light; the green line, U, is using only the (linearly) ±45° polarized light; and the blue line, V, is the profile using only circularly polarized light. Negative values describe the direction of the polarization. b) The polarization position angle of the zoomed in profiles from panel (a) seen in panel (c). Variation here suggests the emission is coming from different places in the source. d) A three second time series of the data where the FRB is clearly visible at about 1.8 seconds. [Cho et al. 2020]

    In addition to polarization, the dispersion measure (DM), or difference in time of arrival of the FRB at the telescope between the highest and lowest radio emission frequencies due to its journey through the interstellar medium (ISM), can provide information about the properties of the environment(s) the burst travels through. Each of the four components of FRB 181112 (visible in panel (a) of Figure 1 in three different polarizations, Q, U, and V, as well as total intensity, I) are shown in the bottom row of Figure 2, and each component has a slightly different DM. By looking at how the DM changes, the authors can not only look at different emission processes that could lead these apparent changes, but can also measure how scattered the radio emission of FRB 181112 might be due to the ISM. The intensity of the emission as a function of time and radio frequency for each of the four polarization profiles (I , Q, U, and V) are shown in the top row of Figure 2. The four different components that make up FRB 181112 are shown in total intensity, I, in the bottom row of Figure 2.

    3
    Figure 2: Top row: Intensity of the radio emission of each of the four polarization profiles, I, Q, U, and V (described in Figure 1) as a function of time and radio frequency. Bottom row: Close up of the four different pulse components of the total intensity polarization profile, I, of FRB 181112 as a function of time and radio frequency. All components have been assumed to have a DM of 589.265 pc cm-3 , and a slight slope in the intensity as a function of time and frequency can be seen in pulse 4, indicating it may have a slightly different DM. [Cho et al. 2020]

    Properties of FRB 181112

    4
    Figure 3: Degree of polarization of FRB 181112. The black line (P/I) shows the total polarization, the red line (L/I) shows the linear polarization, and the blue line (V/I) shows the circular polarization. The red and black lines show a large amount of polarization constant in time, while the blue line shows the circular polarization changes over the pulse. [Cho et al. 2020]

    The authors first find that FRB 181112 is highly polarized (see Figures 1 and 3), and while the degree of both the total (P/I) and linear (L/I) polarization is constant across all four components of the pulse, the degree of circular (V/I) polarization varies, as shown in Figure 3. This indicates that the FRB must have either traveled through a relativistic plasma, a cold plasma in the ISM that is moving at relativistic speeds, or that the emission was already highly polarized at the time it was emitted, meaning the source of FRB 181112 would have to be highly magnetized. However if the source of the polarization is due to the plasma in the ISM, the expected polarization would be almost completely linear (Q or U), whereas we observe significant circular polarization (V).

    The authors next analyzed the four different components shown in the bottom row of Figure 2 for variations in DM and find there are some small, but significant differences between each component. These differences could be due to some unmodeled structure in the ISM, again possibly a relativistic plasma, but is unlikely since the burst lasts for only 2 milliseconds. The authors also suggest these differences in DM could be due to gravitational lensing, the radio light being bent around a massive object.

    Gravitational Lensing

    Gravitational Lensing NASA/ESA

    This would mean different components travel through different paths in the ISM, accounting for the different DMs and four different components. However, gravitational lensing cannot explain the high degree of polarization seen in FRB 181112.

    The Million Dollar Question

    So how was FRB 181112 made? What caused the polarization and differences in DM? Well, the authors can’t say anything for certain. They suggest that the most likely model is a relativistic plasma close to the source of the emission, which has polarization properties similar to known magnetars (highly magnetized neutron stars known to emit radio bursts), but none of their models can fully explain all of the different properties of FRB 181112. The source of FRB 181112 remains a mystery for now, but with the huge number of FRBs now being detected, the answer may lie just around the corner.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    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. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
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