TITLE: GCN CIRCULAR NUMBER: 37021 SUBJECT: EP240802a: Time coincidence with GRB 240802A and optical upper limits with Kinder observations DATE: 24/08/03 17:49:08 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com> A. Aryan, T.-W. Chen (both NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), W.-J. Hou, H.-Y. Hsiao, Y. J. Yang, Y.-C. Pan, C.-C. Ngeow, C.-S. Lin, C.-H. Lai, A. Sankar. K, M.-H. Lee, H.-C. Lin, J.-K. Guo (all NCU), S. J. Smartt (Oxford/QUB), H.-W. Lin (UMich), G. H. Sun, Z. N. Wang (both HNAS), J. Gillanders, H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP240802a (Wang et al., GCN 37019) using the One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C). The first LOT epoch of observations started at 15:46 UTC on 3rd of August 2024 (MJD = 60525.657), 1.22 days after the EP trigger. In particular, we highlight a time coincidence between EP240802a and GRB 240802A (Waratkar et al. GCN 37018). The EP transient was observed to start at 2024-08-02T10:27:22 (UTC) and lasted for more than 500 seconds. AstroSat CZTI detected a long burst GRB 240802A with a T90 of 39 (+3, -8) seconds, showing multiple emission peaks, with the strongest peak at 2024-08-02T10:34:04.5 (UTC). The durations of these two events overlap and could potentially be physically related. Waratkar et al. also mentioned that GRB 240802A was detected by INTEGRAL/SPI-ACS (Trigger 10829) and Konus/WIND (IPN notices). There is no positional information from INTEGRAL at the time of writing and we cannot confirm if they overlap spatially. However, given the time coincidence, we strongly encourage further follow-up investigations. We use the Kinder pipeline (Yang et al. A&A 646, A22) to stack six reduced frames, and to subtract the stacked image with the Pan-STARRS1 template image. However, we do not detect any optical counterpart in the errorbox of 10 arcseconds around the FXT reported position of the EP240802a in the subtracted frames. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follow: Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass LOT | r | 60525.657 | 1.22 days | 300 sec * 6 | > 21.32 | 1".6 | 1.26 The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.56 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/37021. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...