On April 28, a super-magnetized stellar remnant referred to as a magnetar blasted out a simultaneous mixture of X-ray & radio signals never observed before. The flare-up included the first Fast Radio Rurst (FRB) ever seen from within our Milky Way galaxy and shows that magnetars can produce these mysterious & powerful radio blasts earlier only seen in other galaxies.
“Before this event, a good sort of scenarios could explain the origin of FRBs” said Chris Bochenek, a doctoral student in astrophysics at Caltech who led one study of the radio event. “While there should be exciting twists in the story of FRBs in the future. For me, right now, I think it’s fair to mention that the most FRBs come from magnetars until proven otherwise.”Neuron
A magnetar is a sort of isolated neuron star, the crushed city-size remains of a star repeatedly more massive than our Sun. What makes a magnetar so-special is its intense magnetic field. The magnetic field are often 10 trillion times stronger than a refrigerator magnet’s & up to thousand times stronger than a typical neutron star. This represents a huge storehouse of energy that astronomers suspect powers magnetar outbursts.
The X-ray portion of the synchronous bursts was detected by several satellites including NASA’s Wind mission.
The radio component was discovered by Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope located at Dominion Radio Astrophysical Observatory in British Columbia and led by McGill University in Montreal, the University of British Columbia & University of Toronto.
A NASA funded project named Survey for Transient Astronomical radio wave 2 (STARE2) also detected the radio burst seen by CHIME. Consisting of a trio of detectors in California & Utah and operated by Caltech and in Southern California, STARE 2 is led by Bochenek, Shri Kulkarni at Caltech & Konstantin Belov at JPL. They determined the burst’s energy was like FRBs.
By the time these bursts occurred, astronomers had monitoring their source for more than half a day.
Late on April 27, NASA’s Neil Gehrels Swift Observatory spotted a new round-of-activity from a magnetar called SGR 1935+2154 (SGR 1935 for short) located in the constellation Vulpecula. It had been the object’s most prolific flare-up yet, a storm of rapid-fire X-ray bursts, each lasting less than a second. The storm which raged for hours was picked up at various times by Swift, NASA’s Fermi Gamma Ray Space Telescope & NASA’s star Interior Composition Explorer (NICER), an X-ray telescope mounted on the International space Station (ISS).
About 13 hours after the storm subsided, the magnetar was out of view for Swift, Fermi & NICER, one special X-ray burst erupted. The blast was seen by the European Space Agency’s INTEGRAL mission, China National Space Administration’s Huiyan X-ray satellite & Russian Konus instrument on Wind. Because the half-second-long X-ray burst flared, CHIME & STARE2 detected the radio burst, which lasted only a thousandth of a second.
“The radio burst was far brighter than anything we had seen before, so we immediately knew it had been an exciting event” said Paul Scholz, a researcher at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics and also a member of the CHIME/FRB Collaboration. “We’ve studied magnetars in our galaxy for many years, while FRBs are an extragalactic phenomenon whose origins are still a mystery. This event shows-that the 2 phenomena are likely connected.”
Papers from both the CHIME/FRB Collaboration & the STARE2 team were published on November 4 in the journal ‘Nature’.
SGR 1935’s distance remains poorly established with estimates starting from 14,000-41,000 light years. Assuming it lies at the nearer end of this range, the X-ray portion of the simultaneous bursts carried the great amount energy as our Sun produces over a month. Intriguingly however, it had been not as powerful as a few of the flares in the magnetar’s storm eruption.
“The bursts seen by NICER & Fermi during the storm are clearly different in their spectral characteristics from the one associated to the radio blast” said George Younes, a researcher at Washington University in Washington & the lead author of two papers analyzing the burst storm that are now undergoing peer review. “We attribute this difference to the location of the X-ray flare on the star’s surface with the FRB-associated burst likely occurring at or on the brink of the magnetic pole. This might be key to understanding the origin of the exceptional radio signal.”
SGR 1935’s radio burst was thousands of times brighter than any radio emissions from magnetars in our galaxy. If this event had occurred in another galaxy, it might be indistinguishable from a number of the weaker FRBs observed.
In addition, the radio pulse arrived during an X-ray burst, something that has never-before been seen in association with FRBs. Taken together, the observations strongly suggest that SGR 1935 produced the Milky Way’s equivalent of an FRB, which mean that magnetars in other galaxies likely produce at least few of these signals.
For ironclad proof of the magnetar connection, researchers ideally would really like to seek out an FRB outside of our galaxy that coincides with an X-ray burst from a same source. This combination may only be possible for nearby galaxies, which is why CHIME, STARE2 & NASA’s high-energy satellites will keep watching the skies.