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Milli-second burst detected by AstroSat

Published: 28th Dec, 2023

Context

AstroSat, India's first multi-wavelength space-based observatory, has made a groundbreaking discovery, detecting bright sub-second X-ray bursts from a novel neutron star with an ultrahigh magnetic field, known asa Magnetar.

What are Magnetars?

Magnetars are neutron stars characterized by ultrahigh magnetic fields, surpassing Earth's magnetic field by over one quadrillion times. These extreme astrophysical objects emit high-energy electromagnetic radiation due to the decay of their magnetic fields.

About

Key Characteristics:

  • Strong temporal variability, including slow rotation and rapid spin-down.
  • Display of bright but short bursts, extending to months-long outbursts.

SGR J1830-0645 - A Unique Magnetar

Discovery and Background:

  • SGR J1830-0645 was discovered in October 2020 by NASA's Swift spacecraft.
  • Relatively young, around 24,000 years old.
  • Isolated neutron star.
  • Motivation for Study: Scientists from the Raman Research Institute (RRI) and the University of Delhi aimed to study and explore the characteristics of SGR J1830-0645 using AstroSat's instruments.

Scientific Analysis with AstroSat

Instruments Used: The study utilized two instruments onboardAstroSat: the Large Area X-Ray Proportional Counter (LAXPC) and the Soft X-Ray telescope (SXT).

Key Findings:

  • Detection of 67 short sub-second X-ray bursts.
  • Average duration of bursts: 33 milliseconds.
  • Brightest burst lasted approximately 90 milliseconds.
  • Published Study:
    • The research, published by the Royal Astronomical Society, highlights SGR J1830–0645 as a unique magnetar exhibiting emission lines in its spectra.

Unraveling the Mysteries

Emission Lines and Their Origins:

  • The study noted the presence of emission lines in the spectra of SGR J1830-0645.
  • Potential origins include fluorescence of iron, proton cyclotron line feature, or instrumental effects.

Energy-Dependence Findings:

  • Different energy-dependence observed compared to other magnetars.
  • Two thermal blackbody emission components with distinct radii (0.65 and 2.45 km) observed on the neutron star's surface.

Future Research Aims

Varied X-ray Emission Behavior:

  • The pulsed component of the overall X-ray emission showed significant variation with energy, increasing up to 5 kiloelectron Volt (keV) and exhibiting a steep drop thereafter.
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