TITLE: GCN CIRCULAR NUMBER: 39994 SUBJECT: GRB 250322B possible detection by the AstroSat Satellite DATE: 25/04/01 05:55:08 GMT FROM: Tilak Katoch at TIFR tilak@tifr.res.in

Tilak Katoch, H. M. Antia and Parag Shah from TIFR, Mumbai, India report for the LAXPC onboard AstroSat.

AstroSat LAXPC data analysis revealed the presence of a strong long duration multiple peaks complex GRB 250322B. The GRB burst profile shows that it was triggered at T0 = 20h 08m 05s UT on 22 Mar 2025, when the satellite was in a normal operating mode and well before and after the SAA region.

This multiple peak complex burst profile has been recorded by both LAXPC instruments (LAXPC10 and LAXPC20) in their respective lightcurves. The burst profile observed in these lightcurves lasted for T90 ~ 97 sec. The strongest peak measured has a count rate 526 +/- 28 count/sec in LAXPC10 above the background and 1110 +/- 36 count/sec in LAXPC20 at T0+12 sec. A precursor peak is observed by both LAXPC10 and LAXPC20 at T0-50 sec.

LAXPC20 has a nominal energy range of 3-100 keV, but due to the lower gain in LAXPC10, the energy range is approximately 15-400 keV. The background subtracted lightcurves of the LAXPC instruments with 1 sec time bin is available at the website: https://www.tifr.res.in/~astrosat_laxpc/grb250322b.jpg

LAXPC was built by TIFR in collaboration with the Indian Space Research Organisation. The Indian Space Research Organisation funded, managed and facilitated the project.

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