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A powerful burst of X-rays erupts from a magnetar – a supermagnetized version of a stellar remnant known as a neutron star – in this illustration. A radio burst detected on April 28 occurred during an outbreak like this on a magnetar called SGR 1935. Credit: NASA Goddard Space Flight Center / Chris Smith (USRA)
NASA missions help locate source of single x-ray, radio burst
This is the first time that one of these mysterious repetitive radio bursts has been identified in our own galaxy, and the first identification of an object that caused one.
On April 28, a supermagnetized stellar remnant known as a magnetar detonated a simultaneous mixture of X-rays and radio signals never seen before. The outbreak included the first rapid radio burst (FRB) ever seen from inside our Milky Way galaxy and shows that magnetars can produce those mysterious and powerful radio explosions that were previously only seen in other galaxies.
“Before this event, a wide variety of scenarios could explain the origin of FRBs,” said Chris Bochenek, a doctoral student in astrophysics at Caltech who led a study on the radio event. “While there may still be some exciting twists and turns in FRB history going forward, for me at this point in time I think it’s fair to say that most FRBs have come from magnetars up to proof to the contrary.
A magnetar is a type of neutron star, the crushed city-sized remnants of a star far more massive than our Sun. What makes a magnetar so special is its strong magnetic field. The field can be 10 trillion times stronger than that of a fridge magnet and up to a thousand times stronger than that of a typical neutron star. This represents a huge store of energy that astronomers suspect from magnetar explosions.
The X-ray part of synchronous bursts has been detected by several satellites, including NASAMission Wind.
The radio component was discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope located at the Federal Radio Astrophysical Observatory in British Columbia and led by McGill University in Montreal, the University of British Columbia and the University of Toronto.
This aerial view shows the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope located at the Federal Radio Astrophysical Observatory in British Columbia. Credit: Richard Shaw / UBC / CHIME Collaboration
A NASA-funded project called Survey for Transient Astronomical Radio Emission 2 (STARE2) also detected the radio burst seen by CHIME. Comprised of a trio of detectors in California and Utah and operated by Caltech and NASA’s Jet Propulsion Laboratory in Southern California, STARE 2 is led by Bochenek, Shri Kulkarni at Caltech and Konstantin Belov at JPL. They determined that the energy of the burst was comparable to FRBs.
By the time these bursts occurred, astronomers had already been monitoring their source for over half a day.
Late on April 27, NASA’s Neil Gehrels Swift Observatory spotted a new cycle of activity of a magnetar called SGR 1935 + 2154 (SGR 1935 for short) located in the constellation Vulpecula. It was the object’s most prolific outbreak to date – a storm of rapid-fire x-ray bursts, each lasting less than a second. The storm, which raged for hours, was repeatedly picked up by Swift, NASA’s Fermi Gamma Space Telescope, and NASA’s Interior Composition Explorer (NICER) Neutron Star, an x-ray telescope mounted on the International Space Station.
One of the three radio detectors that make up the Survey for Transient Astronomical Radio Emission 2 (STARE2) network is shown here at the Goldstone Deep Space Communications Complex in the Mojave Desert, California. The other detectors are located in Big Pine, California, and Delta, Utah. Credit: NASA
About 13 hours after the storm ended, when the magnetar was out of sight for Swift, Fermi, and NICER, a special x-ray burst erupted. The explosion was seen by the European Space Agency’s INTEGRAL mission, the Chinese Space Administration’s Huiyan X-ray satellite and the Russian instrument Konus on Wind. When the half-second X-ray burst flared, CHIME and STARE2 detected the radio burst, which only lasted a thousandth of a second.
“The radio burst was far brighter than anything we had seen before, so we immediately knew it was an exciting event,” said Paul Scholz, a research fellow at the Dunlap Institute for Astronomy and Astrophysics at University of Toronto and member of the CHIME / FRB Collaboration. “We have studied magnetars in our galaxy for decades, while FRBs are an extragalactic phenomenon whose origins are a mystery. This event shows that the two phenomena are probably linked. “
Articles from the CHIME / FRB collaboration and the STARE2 team were published on November 4 in the journal Nature.
The distance of SGR 1935 remains unclear, with estimates ranging from 14,000 to 41,000 light years. Assuming it’s at the closest end of that range, the x-ray portion of simultaneous bursts was carrying as much energy as our Sun produced over a month. Oddly, however, it wasn’t as powerful as some of the flares in the Magnetar Storm’s eruption.
“The bursts observed by NICER and Fermi during the storm are clearly different in their spectral characteristics from that associated with the radio explosion,” said George Younes, a researcher at George Washington University in Washington and lead author of two papers analyzing the storm surge which are currently the subject of peer review. “We attribute this difference to the location of the X-ray flare on the star’s surface, with the burst associated with the FRB probably occurring at or near the magnetic pole. This can be essential to understand the origin of the exceptional radio signal. “
The SGR 1935 radio burst was thousands of times brighter than any radio emission from magnetars in our galaxy. Had this event occurred in another galaxy, it would have been indistinguishable from some of the weaker FRBs observed.
Additionally, the radio pulse came during an X-ray burst, which had never been seen in association with FRBs before. Taken together, the observations strongly suggest that SGR 1935 produced the Milky Way equivalent of an FRB, meaning that magnetars from other galaxies are likely producing at least some of these signals.
For flawless proof of the magnetar connection, researchers would ideally like to find an FRB outside of our galaxy that coincides with an X-ray burst from the same source. This combination is only possible for nearby galaxies, which is why the high-energy satellites of CHIME, STARE2 and NASA will continue to monitor the sky.
Read Astronomers Detect Short, Intense Radio Burst From Relatively Close In The Milky Way To learn more about this study.
References:
“A brilliant radio burst lasting a millisecond from a galactic magnetar” by the CHIME / FRB collaboration, November 4, 2020, Nature.
DOI: 10.1038 / s41586-020-2863-y
“A rapid radio burst associated with a galactic magnetar” by CD Bochenek, V. Ravi, KV Belov, G. Hallinan, J. Kocz, SR Kulkarni and DL McKenna, November 4, 2020, Nature.
DOI: 10.1038 / s41586-020-2872-x
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