Burst activity of the magnetic SGR J1830–0645 observed by Astrosat

Using India’s Astrosat spacecraft, astronomers have observed the magnetar known as SGR J1830–0645 during its latest burst of activity. The results of the monitoring campaign were published on the preprint server on October 6 arXiv and accepted for publication Monthly Notices of the Royal Astronomical SocietyMore light on the properties and behavior of this material.

Magnetic fields are isolated neutron stars with very strong magnetic fields, about 1 quadrillion times stronger than our planet’s magnetic field. Observations show that the decay of magnetic fields in these materials enables the emission of high-energy electromagnetic radiation. In general, magnets are relatively young and their dynamic magnetosphere has strong temporal variability.

SGR J1830–0645 is a magnetar discovered on October 10, 2020 by NASA’s Swift spacecraft that exhibited a soft, short gamma-ray burst. It has an orbital period of approximately 10.41 seconds, a rotational age of 24,000 years, and a dipole magnetic field with a strength of approximately 550 trillion gauss.

A team of astronomers led by Rahul Sharma of the Raman Research Institute (RRI) in Bangalore, India, began observing SGR J1830–0645 shortly after its discovery. For this purpose, they used Astrosat’s Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC).

Sharma’s team conducted a time and spectral analysis of SGR J1830–0645. They found short sub-second X-ray bursts, 0.9–10 keV pulses, variation in the morphology of pulse profiles with energy with significant variations in pulse fraction, and a 6.4 keV emission line with an equivalent width of 0.24 keV. . Therefore, these findings make SGR J1830–0645 one of the few magnetars shown to have emission lines.

„The emission line may be a result of the luminescence of iron due to the presence of relatively cool material near the neutron star,” the scientists speculate.

In total, astronomers detected 67 bursts with an average duration of 33 milliseconds and the brightest one lasting about 90 milliseconds. Burst spectra show no evidence of a 6.4 keV emission line.

The researchers noted that the pulse region of SGR J1830-0645 shows a significant evolution with increasing energy, as it can be seen increasing in energy up to about 5 keV and then showing a steep drop. This trend is different from that observed in many other magnets.

The study also found that SGR J1830–0645 shows spectral properties typical of most magnetites in the soft X-ray band. The authors of the paper explained that the energy spectrum of SGR J1830-0645 consists of two dark matter (thermal) components and up-scattering soft thermal photons corresponding to a non-thermal power-law vibration.