//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27799 SUBJECT: ZTF Discovery of ZTF20abbiixp: The Likely Optical Afterglow to GRB 200524A DATE: 20/05/24 18:47:58 GMT FROM: Anna Ho at Caltech Anna Y. Q. Ho, Yuhan Yao (Caltech), Daniel A. Perley (LJMU) report on behalf of the Zwicky Transient Facility collaboration: The Zwicky Transient Facility (ZTF, Bellm et al. 2019, Graham et al. 2019) discovered ZTF20abbiixp, a fast transient at 14h12m10.33s +60d54m19.0s (J2000) 213.043037 +60.905288 (J2000) as part of the ZTF Uniform Depth Survey (Goldstein et al. in prep). ZTF20abbiixp was first detected at r~17.4 mag on UT 2020-05-24T06:52:07 and faded by 0.3 mag over the next 30 minutes, with a total of four observations showing continuous fading. The last non-detection was 24 hours prior (2020-05-23T06:43:03) with a limiting magnitude of r>20.4 mag. There is no counterpart in ZTF reference images down to a limiting magnitude of r>22.90. We searched the GCN archive and determined that ZTF20abbiixp is in the error circle of GRB 200524A, which was detected by Fermi-GBM and Fermi-LAT (GCN 27797). The position of ZTF20abbiixp is 0.151 degrees offset from the LAT position, within the 0.2 degree error radius (90% containment). The time of GRB 200524A was 1.802 hours prior to the first detection of ZTF20abbiixp. We conclude that ZTF20abbiixp is very likely to be the GRB afterglow. Follow-up observations are highly encouraged. ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266), and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW,USA; DESY, Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. Alert distribution service provided by DIRAC@UW. Alert filtering is being undertaken by the GROWTH marshal system, supported by NSF PIRE grant 1545949. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27802 SUBJECT: GRB 200524A: CrAO observations of ZTF20abbiixp DATE: 20/05/24 20:53:20 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev (CrAO), A. Pozanenko (IKI), S. Belkin (IKI), E. Mazaeva (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We observed Fermi-LAT detected GRB 200524A (Dirirsa et al., GCN 27797) with ZTSh 2.6m telescope of CrAO starting on 2020-05-24 (UT) 19:35:16. We clearly detected the OT discovered by ZTF (Ho et al., GCN 27799); see also Kumar et al. (GCN 27800). The R magnitude of the OT is 20.1 +/- 0.2 at the time of the first exposure. Observations and data reduction is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27803 SUBJECT: GRB 200524A: 3.6m DOT observations of the afterglow candidate ZTF20abbiixp DATE: 20/05/24 21:50:57 GMT FROM: Kuntal Misra at ARIES,India Pankaj Sanwal, Kuntal Misra, Ankur Ghosh, Dimple, Amit Kumar, Amar Aryan, Rahul Gupta, S. B. Pandey, Brijesh Kumar, T. S. Kumar and Amitesh Omar (ARIES) report on behalf of the GRB collaboration: We observed the field of GRB 200524A (Fana Dirirsa et al., GCN 27797) with the 3.6m Devasthal Optical Telescope (DOT) located in Devasthal, India on 2020-05-24T19:18:00 (UT) using the recently commissioned ADFOSC instrument. We observed a sequence of 300 sec images in g, r and i bands. We clearly detect the optical transient discovered by ZTF (Ho et al., GCN 27799) and also reported by Kumar et al. (GCN 27800) and Rumyantsev et al. (GCN 27802). In the first r band image the afterglow has a r band magnitude of 21.1+/-0.03. Further processing of the data is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27806 SUBJECT: GRB 200524A: 1.3m DFOT Optical Observation of ZTF20abbiixp DATE: 20/05/24 22:32:48 GMT FROM: Amit Kumar at ARIES, India A. Kumar (ARIES), S. B. Pandey (ARIES), A. Ghosh (ARIES), Dimple (ARIES), K. Misra (ARIES), R. Gupta (ARIES), K. Chand (ARIES) and A. Aryan (ARIES) report: We observed the optical afterglow of GRB 200524A (F. F. Dirirsa et al., GCN 27797, Evans et al., GCN 27798) with the 1.3m Devasthal Fast Optical Telescope (DFOT) at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital (India), from 2020-05-24T19:50:12 UTC (corresponding to ~14.770 hours after the burst). We observed 5 frames each of 300 seconds in Bessell I filter. In the stacked image, we clearly detected the optical afterglow of GRB 200524A (detected by Ho et al., GCN 27799, see also Kumar et al., GCN 27800, Rumyantsev et al., GCN 27802 and Sanwal et al., GCN 27803). The observed magnitude is as follows: T_start-T0 (hours) Start Date (UTC) End Date (UTC) Filter Magnitudes (mag) --------------------------------------------------------------------------------------------------------------- 14.770 2020-05-24T19:50:12 2020-05-24T20:32:37 I 20.33 +- 0.07 Photometry is done based on the USNO-B1.0 catalog. The quoted magnitude is not corrected for Galactic extinction. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27808 SUBJECT: GRB 200524: Swift/UVOT observations missed the ZTF20abbiixp position DATE: 20/05/24 23:43:57 GMT FROM: Paul Kuin at MSSL Paul Kuin (MSSL/UCL) and Kim Page (Leicester University) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200524 36366 s after the LAT trigger (Evans et al., GCN Circ. 27798). The initial Swift UVOT follow up missed the likely afterglow of 200524A as reported by Ho et al, GCN Circ. 27799, and confirmed by Kumar et al. GCN Circ. 27800/27804/27806, Rumyantsev et al. GCN Circ. 27802, Sanwal et al. GCN Circ. 27803, Perley et al., GCN Circ. 27805 and de Ugarte Postigo et al, GCN.Circ. 27807. The UVOT field of view is smaller than the XRT field of view and XRT source 6 (Evans et al., GCN Circ. 27798), which is consistent with the PTF source, falls outside the field observed by Swift UVOT.