TITLE: GCN CIRCULAR NUMBER: 42642 SUBJECT: GRB 251013C: Chandra X-ray observations and jet break detection DATE: 25/11/11 10:50:45 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie> A. Martin-Carrillo (UCD), B. P. Gompertz (Birmingham), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of a larger collaboration: We observed the afterglow of GRB 251013C (Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with the Chandra X-ray Observatory starting on 2025-11-09 at 03:09:42 UT (i.e., T0+27.396 d, observer frame), for a total of 40 ks exposure, in response to our DDT request (PI A. Martin-Carrillo, ObsID 31983). A faint X-ray source is detected at a location consistent with that of the afterglow (Palmerio et al., GCN 42223; Laskar et al., GCN 42243). Assuming a spectrum model consistent with the one measured by Swift/XRT (Evans et al., GCN 42232; https://www.swift.ac.uk/xrt_spectra/03000137/), we infer a flux in the 0.3-10 keV energy range of ~2.5e-15 erg s^-1 cm^-2. This late Chandra observation implies that the source has undergone significant steepening in its X-ray flux decay when compared with the earlier Swift/XRT and EP/FXT observations (Evans et al., GCN 42232; Wang et al., GCN 42247), suggesting a jet break sometime between 6 and 10 days since trigger in the observer frame. We thank the entire CXO team for the rapid evaluation and scheduling of our observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42642. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...