AstroSat Observes Milli-Second X-ray Bursts from Unique Neutron Star, Unraveling Magnetic Field Mysteries


New Delhi, 25 DEC 2023: India’s premier multi-wavelength space-based observatory, AstroSat, has made a groundbreaking discovery, detecting brief sub-second X-ray bursts from a newly identified neutron star with an ultrahigh magnetic field (magnetar). This finding holds the key to unlocking the mysteries of extreme astrophysical conditions surrounding magnetars.

Magnetars, distinguished by ultrahigh magnetic fields trillions of times more potent than Earth’s, emit high-energy electromagnetic radiation as a result of magnetic field decay. Characterized by unique temporal variability, including slow rotation, rapid spin-down, and short bursts, magnetars present an intriguing area for astrophysical exploration.

The specific magnetar under study, named SGR J1830-0645, was initially discovered in October 2020 by NASA’s Swift spacecraft. Boasting an ultrahigh magnetic field, SGR J1830-0645 prompted scientists from the Raman Research Institute (RRI) and the University of Delhi to conduct comprehensive timing and spectral analyses using AstroSat’s instruments—the Large Area X-Ray Proportional Counter (LAXPC) and Soft X-Ray telescope (SXT).

Dr. Rahul Sharma, the lead author of the study, shared a key finding: “We detected 67 short sub-second X-ray bursts, with an average duration of 33 milliseconds. The brightest burst lasted about 90 milliseconds.” Published in the Monthly Notices of the Royal Astronomical Society, the study highlighted SGR J1830-0645’s uniqueness by showcasing emission lines in its spectra.

The presence of these emission lines, potentially linked to iron fluorescence, proton cyclotron line features, or instrumental effects, remains under scrutiny. Dr. Sharma emphasized that the energy-dependent characteristics observed in SGR J1830-0645 differ from other magnetars, featuring two thermal blackbody emission components originating from the neutron star’s surface.

Co-author Prof. Chetana Jain from Hansraj College, University of Delhi, noted, “The pulsed component of the overall X-ray emission exhibited significant energy variation, increasing up to 5 kiloelectron Volt (keV) and sharply dropping thereafter, a trend distinct from several other magnetars.”

The research team now plans to delve deeper into understanding the origin of these energetic emissions, determining whether they stem from astrophysical phenomena or have instrumental origins.

Publication Link: AstroSat observation of the magnetar SGR J1830−0645 during its first detected X-ray outburst

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