Radiation emitted from the vicinity of an extragalactic black hole located in the Large Magellanic Cloud, a small companion galaxy to the Milky Way have been detected for the first time through technique called X-ray polarimetry, paving the way for understanding the underlying physical processes around black hole sources.

LMC X-3 is a binary system that consists of a black hole and a "normal" star that is much hotter, bigger, and more massive than the Sun. The thermally dominated persistent extra-galactic black hole source was discovered by an orbiting X-ray telescope in 1971. In the four decades since, several teams of astronomers have studied the system with optical telescopes on the ground and ultraviolet and X-ray telescopes in orbit. The Imaging X-ray Polarimetry Explorer (IXPE), the first mission of NASA to study the polarization of X-rays from celestial objects offers a unique observational technique launched in 2021 opens up a new window for understanding the emission processes and geometry of the accreting objects in a more sophisticated way by investigating the X-ray polarimetric properties. 

Scientists from Indian Institute of Technology Guwahati (IITG) and U. R. Rao Satellite Centre (URSC), ISRO have investigated the X-ray polarization properties of LMC X-3, considered a LMC X-3 ideal cosmic laboratory to study the X-ray polarization signatures, using IXPE. The most intriguing results they have found are the detection of significant polarized emissions resulting possibly due to the combined effects of the direct and/or reflected emissions from a partially ionized disc atmosphere.

The team led by Prof. Santabrata Das (IIT Guwahati) and Dr. Anuj Nandi (URSC) including research scholars Mr. Seshadri Majumder (IIT Guwahati) and Mr. Ankur Kushwaha (URSC) also measured the source spin by analysing observations from Neutron Star Interior Composition Explorer (NICER) Mission and Nuclear Spectroscopic Telescope Array (NuSTAR) Mission, and found that the black hole is weakly rotating in nature.

This study published in Monthly Notices of the Royal Astronomical Society: Letters was supported by Science and Engineering Research Board (SERB), an attached institution of the Department of Science and Technology. 

Publication link: https://doi.org/10.1093/mnrasl/slad148

For more details, contact Santabrata Das (sbdas[at]iitg[dot]ac[dot]in)

Figure 1: Confidence contours of energy dependent polarization parameters (PA and PD) of LMC X-3. Shaded region and regions bounded with dashed and dotted curves represent 64.2%, 95.4% and 99.6% detection confidence of PA and PD.