In a significant breakthrough, AstroSat, India’s first multi-wavelength space-based observatory, has detected bright sub-second X-ray bursts from a newly discovered neutron star, classified as a magnetar. This discovery opens a window into the extreme astrophysical conditions of these fascinating celestial objects.
Magnetars are neutron stars characterized by an ultrahigh magnetic field, surpassing the terrestrial magnetic field by over one quadrillion times. The emission of high-energy electromagnetic radiation from magnetars is powered by the decay of their intense magnetic fields. These enigmatic stars often exhibit strong temporal variability, including slow rotation, rapid spin-down, and short bursts lasting mere milliseconds, extending to months-long outbursts.
One particular magnetar, SGR J1830-0645, discovered by NASA’s Swift spacecraft in October 2020, intrigued scientists due to its relatively young age of approximately 24,000 years and its status as an isolated neutron star. Motivated by the desire to delve into the characteristics of this magnetar, scientists from the Raman Research Institute (RRI) and the University of Delhi conducted timing and spectral analyses using AstroSat’s instruments—the Large Area X-Ray Proportional Counter (LAXPC) and the Soft X-Ray telescope (SXT).
Dr. Rahul Sharma, the lead author of the study and a post-doctoral fellow at RRI, revealed one of the key findings: “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.”
Published in the Monthly Notices of the Royal Astronomical Society, the study concluded that SGR J1830–0645 is a unique magnetar exhibiting emission lines in its spectra. However, the origin of these emission lines—whether due to fluorescence of iron, proton cyclotron line feature, or an instrumental effect—remains a subject of consideration.
Dr. Sharma emphasized, “The energy-dependence in SGR J1830-0645 was different from what was observed in several other magnetars. This research contributes to our understanding of magnetars and their extreme astrophysical conditions.”
Co-author Prof. Chetana Jain from Hansraj College, University of Delhi, highlighted the significant variation in the pulsed component of the overall X-ray emission with energy. This variation, increasing up to about 5 kiloelectron Volts (keV) and sharply dropping thereafter, distinguishes SGR J1830-0645 from other magnetars.
The research team now aims to expand their study to unravel the origin of these highly energetic emissions, distinguishing between astrophysical and instrumental factors. AstroSat’s continued exploration promises to unveil more mysteries, providing insights into the complex nature of celestial bodies and their profound impact on our understanding of the universe.
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