Astronomers using ISRO’s AstroSat space observatory have detected a very rare ultraluminous X-ray source in the Magellanic Bridge, a 43,000-light-year-long filament of gas, dust and stars that stretches from the Large Magellanic Cloud to the Small Magellanic Cloud, two dwarf satellites of our Milky Way Galaxy.
An artist’s impression of an ultraluminous X-ray pulsar. Image credit: NASA / JPL-Caltech.
Ultraluminous X-ray sources are observable as single points in the sky, but with brightnesses comparable to entire galaxies.
“The conventional theory is that in order to shine so brightly, these objects must be glowing accretion disks around black holes,” said lead author Dr. Amar Deo Chandra, an astronomer in the Center of Excellence in Space Sciences India at the Indian Institute of Science Education and Research Kolkata.
“However, recent discoveries of pulsations in these objects suggest that they may in fact have neutron stars at their heart.”
Known as RX J0209.6-7427, the pulsar was first discovered during a 6-month long outburst in 1993.
Dr. Chandra and colleagues observed the object using the Soft X-ray Telescope and the Large Area X-ray Proportional Counter on board the AstroSat satellite.
This image of RX J0209.6-7427 was captured by the Soft X-ray Telescope on board the AstroSat satellite. The circle with a 4 arcmin radius is centered on the source. Image credit: Chandra et al, doi: 10.1093/mnras/staa1041.
The researchers detected broad-band X-ray pulsations from RX J0209.6-7427 during the rare outburst in November 2019.
They found that the pulsar resides in the Magellanic Bridge in the vicinity of the Small Magellanic Cloud and has an orbital period of 9.28 seconds.
According to the team, RX J0209.6-7427 is the second-closest ultraluminous X-ray source known to date, after a 2018 discovery in our own Milky Way Galaxy, and is only the eighth such object ever discovered.
“This is only the eighth ULXP detected so far, and the first one near the Magellanic Clouds,” Dr. Chandra said.
“It raises the interesting possibility that a significant fraction of ultraluminous X-ray sources may really be neutron stars accreting at super Eddington rates, rather than black holes as previously thought.”
The team’s paper was published in the journal Monthly Notices of the Royal Astronomical Society.
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Amar Deo Chandra et al. 2020. Study of recent outburst in the Be/X-ray binary RX J0209.6−7427 with AstroSat: a new ultraluminous X-ray pulsar in the Magellanic Bridge? MNRAS 495 (3); doi: 10.1093/mnras/staa1041
