India’s first multi-wavelength space-based observatory, AstroSat, has detected intense sub-second X-ray bursts emanating from a neutron star with an ultrahigh magnetic field, known as a magnetar. This discovery holds the potential to unravel the perplexing astrophysical conditions surrounding magnetars.
Magnetars are neutron stars distinguished by an ultrahigh magnetic field, exceeding that of Earth by over one quadrillion times. The emission of high-energy electromagnetic radiation in these celestial objects results from the decay of their magnetic fields. Additionally, magnetars exhibit notable temporal variability, including slow rotations, rapid spin-downs, and brief but intense bursts, extending to months-long outbursts.
One such magnetar, designated SGR J1830-0645, was identified in October 2020 by NASA’s Swift spacecraft. This relatively young and isolated neutron star, approximately 24,000 years old, prompted scientists from the Raman Research Institute (RRI) and the University of Delhi to conduct in-depth studies using AstroSat’s instruments—the Large Area X-Ray Proportional Counter (LAXPC) and Soft X-Ray Telescope (SXT).
“One of the key findings was the detection of 67 short sub-second X-ray bursts, with an average duration of 33 milliseconds. Of these bursts, the brightest one lasted for about 90 milliseconds”, said Dr. Rahul Sharma, a post-doctoral fellow at RRI and the lead author of the published study in the Monthly Notices of the Royal Astronomical Society.
The research concluded that SGR J1830–0645 is a distinctive magnetar that exhibits an emission line in its spectra. However, the study acknowledges that the origin of this emission line—whether from iron fluorescence, proton cyclotron line features, or instrumental effects—remains a topic for consideration.
“The energy-dependence in SGR J1830-0645 was different from what was observed in several other magnetars. Here, there were two thermal blackbody emission components originating from surface of neutron star (radius of 0.65 and 2.45 km). This research, thus, contributes to our understanding of magnetars and their extreme astrophysical conditions,” said Dr. Sharma.
“We noticed that the pulsed component of the overall X-ray emission showed significant variation with energy. It increased for energies up to about 5 kiloelectron Volt (keV) and showed a steep drop thereafter. This trend is different from that observed in several other magnetars,” said co-author Prof. Chetana Jain from Hansraj College, University of Delhi.
The research team’s future plans involve expanding their investigation to understand the origin of these highly energetic emissions.
