In this illustration, a powerful X-ray beam breaks out from a magnetar – a super-magnetized version of a star remnant known as a neutron star. A radio burst detected on April 28th occurred during such a flare-up on a magnetar called SGR 1935. Photo credit: NASA Goddard Space Flight Center / Chris Smith (USRA)
NASA missions are helping to locate the source of a unique X-ray beam, radio burst
This is the first time any 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 super-magnetized star remnant known as a magnetar emitted a simultaneous mix of X-ray and radio signals that had never been observed before. The flare-up included the first high-speed radio burst (FRB) ever seen from inside Milky Way Galaxy and shows that magnetars can create these mysterious and powerful radio beams that were previously only seen in other galaxies.
“Prior to this event, a variety of scenarios could explain the origin of FRBs,” said Chris Bochenek, PhD student in astrophysics at Caltech, who led a study on the radio event. “While there may be exciting twists and turns in the history of FRBs in the future, I think most FRBs are currently from Magnetars until proven otherwise.”
A magnetar is a type of insulated Neutron star, the crushed, city-sized remains of a star many times more massive than our sun. What makes a magnetar so special is its intense magnetic field. The field can be 10 trillion times stronger than that of a refrigerator magnet and up to a thousand times stronger than that of a typical neutron star. This is a huge storage of energy that astronomers suspect is powering magnetic bursts.
The X-ray portion of the synchronous bursts was captured by several satellites, including NASAWind mission.
The radio component was discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope at the Dominion Radio Astrophysical Observatory in British Columbia, which is led by McGill University in Montreal, the University of British Columbia and the University of Toronto.
This aerial photo shows the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope at the Dominion Radio Astrophysical Observatory in British Columbia. Photo credit: Richard Shaw / UBC / CHIME Collaboration
A NASA-funded project called the Survey for Transient Astronomical Radio Emission 2 (STARE2) also detected the radio burst observed by CHIME. STARE 2 consists of three detectors in California and Utah and is operated by Caltech and NASA’s Jet Propulsion Laboratory in Southern California. The company is run by Bochenek, Shri Kulkarni from Caltech and Konstantin Belov from JPL. They found that the energy of the burst was comparable to FRBs.
By the time these outbursts occurred, astronomers had been monitoring their source for more than half a day.
On late April 27, NASA’s Neil Gehrels Swift Observatory discovered a new round of activity from a magnetar called SGR 1935 + 2154 (SGR 1935 for short) in the constellation Vulpecula. It was the object’s most productive flare-up to date – a storm of rapid-fire x-rays, each lasting less than a second. The storm, which raged for hours, was captured at various times by Swift, NASA’s Fermi gamma-ray space telescope, and NASA’s Neutron Star Interior Composition Explorer (NICER), an X-ray telescope mounted on the International Space Station.
One of three radio detectors that make up the STARE2 array (Survey for Transient Astronomical Radio Emission 2) is shown here in the Goldstone Deep Space Communications Complex in California’s Mojave Desert. The other detectors are in Big Pine, California and Delta, Utah. Photo credit: NASA
About 13 hours after the storm ended, when the magnet was out of sight for Swift, Fermi, and NICER, a special X-ray beam erupted. The explosion was seen by the European Space Agency’s INTEGRAL mission, the China National Space Administration’s Huiyan X-ray satellite, and the Russian Konus Instrument on Wind. When the half-second long X-ray beam broke out, CHIME and STARE2 discovered the radio burst that lasted only a thousandth of a second.
“The radio burst was much brighter than anything we had seen before, and we knew immediately it was an exciting event,” said Paul Scholz, researcher at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto and a member of CHIME / FRB cooperation. “We have studied magnetars in our galaxy for decades, while FRBs are an extragalactic phenomenon whose origin has been a mystery. This event shows that the two phenomena are likely related. ”
Contributions from both the CHIME / FRB collaboration and the STARE2 team were published in the journal on November 4th nature.
The distance from SGR 1935 is still poorly established, with estimates between 14,000 and 41,000 light years. Assuming it’s nearer the end of this range, the X-ray portion of the simultaneous bursts carries as much energy as our sun produces over a month. Interestingly, however, it wasn’t as powerful as some of the flares during the Magnetar storm eruption.
“The bursts that NICER and Fermi saw during the storm differ significantly in their spectral properties from those associated with the radio explosion,” said George Younes, researcher at George Washington University in Washington and lead author of two articles, who analyzed the outbreak, which is now being peer reviewed. “We attribute this difference to the position of the X-ray flare on the star’s surface, with the FRB-associated breakout likely occurring at or near the magnetic pole. This can be key to understanding the origin of the extraordinary radio signal. ”
The radio burst from SGR 1935 was a thousand times brighter than the radio emissions from magnetars in our galaxy. If this event had occurred in a different galaxy, it would have been indistinguishable from some of the weaker FRBs observed.
In addition, the radio pulse arrived during an X-ray, which has never been seen before in conjunction with FRBs. Taken together, the observations strongly suggest that SGR produced the equivalent of an FRB in the Milky Way in 1935, meaning that magnetars in other galaxies are likely to produce at least some of these signals.
For the iron proof of the magnetic connection, researchers would ideally want to find an FRB outside our galaxy that coincides with an X-ray from the same source. This combination may only be possible for nearby galaxies, which is why CHIME, STARE2, and NASA’s high-energy satellites continue to observe the sky.
For more information about this study, see Astronomers Detect Brief, Intense Radio Interference From Relatively Nearby Areas in the Milky Way.
References:
“A radiant millisecond radio burst from a galactic magnetar” by the CHIME / FRB collaboration, November 4, 2020, nature.
DOI: 10.1038 / s41586-020-2863-y
“A quick radio burst in connection 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
