High Energy X-ray Modulation Discovered in Black Hole with AstroSat

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In a recent study, AstroSat has enabled the discovery of the ‘aperiodic modulation’ of high-energy X-ray photons during an 'unusual' outburst phase of the black hole binary source Swift J1727.8-1613. This significant discovery, carried out utilizing the unique capabilities of AstroSat, is reported by a team of astrophysicists led by U R Rao Satellite Centre (URSC)/ISRO in collaboration with the Indian Institute of Technology Guwahati (IITG), University of Mumbai, and Tata Institute of Fundamental Research (TIFR) in the international journal Monthly Notices of the Royal Astronomical Society (MNRAS).

In an astrophysical black hole X-ray binary (BH-XRB) system, both the black hole and its companion are locked in a gravitational embrace. A black hole pulls matter from its tidally deformed companion, leading to the formation of a luminous accretion disk. As matter accretes through the disk, it becomes extremely hot, reaching temperatures in the millions of degrees and emitting high-energy X-rays. These electromagnetic radiations act as cosmic messengers, indirectly detecting the black holes shrouded in darkness. In a way, BH-XRBs serve as cosmic laboratories, offering insights into the intricate processes governing accretion dynamics around compact objects and providing invaluable opportunities to study fundamental physical mechanisms in extreme environments.

Swift J1727.8-1613 is a black hole X-ray transient (BH-XRT) recently discovered by Swift/BAT on August 24, 2023. Immediate monitoring by MAXI/GSC identified the source as one of the brightest, with an X-ray peak value of approximately 7 Crab (Crab is a standard candle and 1 Crab = 3.8 photons per sq.cm. per s). AstroSat first observed this source on September 2, 2023 (MJD 60189), followed by subsequent observations spanning from September 8, 2023 (MJD 60195) to September 14, 2023 (MJD 60201), with a total exposure time of approximately 207 ks.

ISRO

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