AstroSat observation of the magnetar SGR J1830-0645 during its first detected X-ray outburst

We present here timing and spectral analyses of SGR J1830-0645 based on an AstroSat observation carried out on 2020 October 16, about a week after the onset of its first detected X-ray outburst. Using data taken with the Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC), we have detected 0.9-10 keV coherent pulsations at a period of ~10.4 s. The pulse profiles were single-peaked, asymmetric, and consisted of minor peaks attributable to hotspots on the neutron star surface. The pulsed fraction evolved significantly with energy, increasing to energies around 5 keV with a steep drop thereafter. The 0.9-25 keV SXT-LAXPC energy spectrum is best described with two thermal components having temperatures ~0.46 and ~1.1 keV (emission radii of ~2.4 and ~0.65 km, respectively, assuming a distance of 4 kpc) along with a power-law component having a photon index of ~0.39. We report the detection of 67 X-ray bursts having an average duration of ~33 ms. The brightest burst lasted for about 90 ms and had a 3-25 keV fluence of ~5 × 10^-9 erg cm^-2.