India’s maiden multi-wavelength space-based observatory, AstroSat, has ventured into uncharted celestial territories once again. In a groundbreaking discovery, AstroSat has detected vivid sub-second X-ray bursts emanating from a newfound and distinctive neutron star, a magnetar, possessing an ultrahigh magnetic field. This remarkable revelation promises to unravel the enigmatic and extreme astrophysical conditions that characterize magnetars.
Magnetars, a specific type of neutron stars, boast magnetic fields exponentially stronger than Earth’s—surpassing it by over a quadrillion times. The intriguing emission of high-energy electromagnetic radiation from these celestial entities stems from the gradual decay of their immensely potent magnetic fields. Known for their temporal dynamism, magnetars exhibit peculiar features including slow rotation, rapid spin-down, and sporadic, bright but fleeting bursts extending up to months-long outbursts.
Among these captivating magnetars stands SGR J1830-0645, discovered by NASA’s Swift spacecraft in October 2020. This relatively youthful and isolated neutron star, estimated to be around 24,000 years old, has captured the attention of astronomers.
Driven by a desire to delve deeper into the unique characteristics of SGR J1830-0645, scientists from the Raman Research Institute (RRI) and the University of Delhi embarked on an expedition utilizing AstroSat’s instrumentation—the Large Area X-Ray Proportional Counter (LAXPC) and Soft X-Ray telescope (SXT)—to conduct comprehensive timing and spectral analyses.
Dr. Rahul Sharma, the lead author of the study and a post-doctoral fellow at RRI, unveiled the study’s key discovery: “We detected 67 short-lived sub-second X-ray bursts, averaging a duration of 33 milliseconds. The most luminous burst persisted for about 90 milliseconds.”
Published in the Monthly Notices of the Royal Astronomical Society, the study shed light on SGR J1830–0645’s uniqueness by identifying emission lines in its spectra.
However, the study raises intriguing questions about these emission lines and their genesis—whether they stem from iron fluorescence, a proton cyclotron line feature, or an instrumental anomaly.
Dr. Sharma further elaborated, “The energy characteristics observed in SGR J1830-0645 diverge from those witnessed in several other magnetars. Notably, two thermal blackbody emission components originating from the neutron star’s surface (with radii of 0.65 and 2.45 km) were identified. This research thus contributes significantly to our comprehension of magnetars and their extraordinary astrophysical conditions.”
Co-author Prof. Chetana Jain from Hansraj College, University of Delhi, highlighted a striking observation: “The pulsed segment of the X-ray emission exhibited substantial energy-dependent variations. It peaked until about 5 kiloelectron Volts (keV) and sharply declined thereafter—a pattern distinct from other magnetars.”
With their sights set on unraveling the origins of these highly energetic emissions, the research team endeavors to discern whether they originate from astrophysical phenomena or are of instrumental origin, marking a critical stride in deciphering the mysteries of magnetars.