TITLE: GCN CIRCULAR NUMBER: 44839 SUBJECT: GRB 260601B / EP260601a: AstroSat CZTI detection DATE: 26/06/05 11:44:11 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com> A. Arya (IITB), A. Goyal (IITB), Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (Caltech/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 long GRB 260601B, associated with EP260601a, which was also detected by Einstein Probe / WXT (Yang et. al., GCN Circ. 44766), GECAM-C (Yu et al., GCN Circ. 44767), NuSTAR (Waratkar et. al. , GCN Circ. 44771), CALET (Sugita et. al., GCN Circ. 44773), and Insight HXMT (Wang et. al., GCN Circ. 44785). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-01 19:12:50.54 UTC. AstroSat was departing the South Atlantic Anomaly (SAA) region and hence the background rates were higher. The measured peak count rate associated with the burst is 498 (+39, -46) counts/s above the background in the combined data of three quadrants (out of four), with a total of 12100 (+491, -799) counts. The local mean background count rate was 278 (+4, -4) counts/s. Using cumulative rates, we measure a T90 of 54 (+2, -2) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-01 19:12:50.66 UTC. The measured peak count rate associated with the burst is 1468 (+92, -129) counts/s above the background in the combined data of four quadrants, with a total of 29202 (+2008, -3307) counts. The local mean background count rate was 1805 (+20, -8) counts/s. We measure a T90 of 51 (+1, -2) s from the cumulative Veto light curve. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/ET20260601T191246/ET20260601T19... 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/44839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...