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GCN Circular 34119

Subject
GRB 230625B: AstroSat CZTI detection
Date
2023-06-29T09:19:30Z (a year ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
P K. Navaneeth (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a GRB 230625B which was also detected by CALET (Trig. 1371713313) and Swift/BAT-GUANO (Ronchini et al., GCN Circ. 34084Not found
 
 
).

The source was clearly detected in the 20-200 keV energy range. The light curve peaks at 2023-06-25 07:28:57.50 UTC. The measured peak count rate associated with the burst is 279 (+55, -14) counts/s above the background in the combined data of all quadrants, with a total of 9279 (+893, -648) counts. The local mean background count rate was 504 (+3, -5) counts/s. Using cumulative rates, we measure a T90 of 65 (+3, -4) s.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2023-06-25 07:28:57.50 UTC. The measured peak count rate associated with the burst is 266 (+80, -19) counts/s above the background in the combined data of all quadrants, with a total of 7354 (+1143, -1181) counts. The local mean background count rate was 1607 (+5, -6) counts/s. We measure a T90 of 70 (+3, -15) s from the cumulative Veto light curve.

We further report the detection of 2 more bright bursts, with multiple peaks, about 50 s after the first burst reported above had ended. Preliminary analysis shows that these subsequent emission bursts had similar signatures to GRB 230625B and lasted for about 200 s, after which AstroSat entered the South Atlantic Anomaly (SAA) region. We caution that since AstroSat was close to SAA, these bursts may not be related to GRB 230625B.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb