//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29819 SUBJECT: GRB 210413B: Swift/BAT detection and probable localization of a short burst DATE: 21/04/16 00:04:06 GMT FROM: Aaron Tohuvavohu at U Toronto Swift/BAT did not successfully trigger on GRB 210413B (T0: 2021-04-13 23:46:52.45 UTC, Fermi/GBM TRIGGER 640050417). The GUANO system is currently offline, thus no extended GUANO data is available for this time, and so the sensitive GUANO MLL analysis (DeLaunay et al. 2021, in prep) can not be run. Swift/BAT triggered in real-time onboard in the rates domain (trigger #1043009), but no strong source was found to be associated in the onboard imaging. This 'failed trigger' resulted in 10s of BAT TTE data being saved and sent to the ground. The duration of the burst, as seen by BAT, is T90 = 1.088 s +/- 0.09 s. In ground analysis of the available TTE data, we find a source using typical imaging analysis, that is the likely location of the GRB, with SNR 6 in the image domain. The BAT position is RA, Dec = 182.558 +55.965, which is: RA (J2000) 12h 10m 13.920s Dec (J2000) +55d 57' 54.00" with an estimated uncertainty of 3 arcminutes. This location is consistent with the Fermi/GBM localization distributed in the Final Position notice. XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29821 SUBJECT: GRB 210413B: Swift ToO observations DATE: 21/04/16 04:32:21 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Swift/BAT GRB 210413B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021428 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Swift/BAT event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29825 SUBJECT: GRB 210413B: LOAO optical upper limit DATE: 21/04/17 06:45:28 GMT FROM: Gregory SungHak Paek at SNU Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Chung-Uk Lee (KASI), Seung-Lee Kim (KASI), Hyun-Il Sung (KASI) on behalf of a larger collaboration We searched for the optical counterpart of GRB 210413B (A. Tohuvavohu et al. GCN #29819, and P. A. Evans et al., GCN #29821) with the 1-m class telescope in Lemonsan Optical Astronomy Observatory (LOAO), one of facilities of the GW EM-Counterpart Korean Observatory (GECKO). We observed the center of Swift/BAT localization (RA, Dec = 182.558 +55.965), but could not find any transient within the field of view of LOAO (28.1'x28.1'). We calibrated flux with the PS1 catalog and used an AB magnitude system. ------ Filter Date-obs[UT] Exp.time[s] Depth(5sigma) B 2021-04-16T03:17:51.667 180*3 20.780 V 2021-04-16T03:27:54.933 180*3 20.347 R 2021-04-16T03:37:58.867 180*3 19.594 I 2021-04-16T03:47:55.800 180*3 19.293 We thank the LOAO opertator for performing the observation. Gravitational-wave EM Counterpart Korean Observatory (GECKO) is a network of 10+ 0.5m to 1m class telescopes over the world. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29827 SUBJECT: GRB 210413B: Swift-XRT observations DATE: 21/04/17 20:07:06 GMT FROM: Antonino D'Ai at IASF-PA J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), B. Sbarufatti (PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Swift/BAT-detected burst GRB 210413B (Swift/BAT did not successfully trigger on GRB 210413B et al. GCN Circ. 29819), collecting 4.9 ks of Photon Counting (PC) mode data between T0+185.0 ks and T0+206.7 ks. One uncatalogued X-ray source has been detected consistent with being within 394 arcsec of the Swift/BAT position, it is below the RASS limit and shows no definitive signs of fading. Therefore, at the present time we cannot confirm this as the afterglow. Details of this source are given below: Source 1: RA (J2000.0): 182.5333 = 12:10:7.98 Dec (J2000.0): +56.0497 = +56:02:59.0 Error: 5.7 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (4.5 +/- 1.2)e-3 ct s^-1 Distance: 309 arcsec from Swift/BAT position. Flux: (1.42 +/- 0.39)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Three uncatalogued sources were also detected too far from the GRB position to be likely afterglow candidates. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/ToO_GRBs/00021428. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29860 SUBJECT: GRB 210413B: MITSuME Okayama optical upper limits DATE: 21/04/21 09:41:19 GMT FROM: Naohiro Ito at Tokyo Tech N. Ito, K. L. Murata, R. Hosokawa, M. Niwano, H. Takamatsu, Y. Yatsu, and N.Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 210413B (Fermi/GBM TRIGGER 640050417, P. A. Evans et al. GCN Circular #29821, Gregory S.H. Paek et al. GCN Circular #29825, J.A. Kennea et al. GCN Circular #29827) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Okayama Astronomical Observatory, Okayama, Japan. The observation with a series of 60 sec exposures started at 2021-04-17 13:31:10 UT (85.8 hours after the Fermi/GBM trigger 640050417). We stacked the images with good conditions. We did not find any transients within the BAT error region (A. Tohuvavohu et al. GCN Circular #29819) in all three bands. We obtained the 5-sigma limits of the stacked images as follows. T0+[hour] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 86.8 15:06 2340 g'>17.4, Rc>17.6, Ic>17.3 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used the PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29912 SUBJECT: GRB 210413B: Swift/UVOT Observations DATE: 21/04/30 00:54:43 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Swift/UVOT team: Swift/UVOT performed follow-up observations of the Swift/BAT-detected burst GRB 210413B (Tohuvavohu et al., GCN Circ. 29819) 185 ks after the BAT trigger. We detect a faint source close to the XRT source reported by Kennea et al. (GCN Circ. 29827). The preliminary UVOT position is: RA (J2000) = 12:10:07.75 = 182.53230 (deg.) Dec (J2000) = +56:02:58.9 = 56.04970 (deg.) with an estimated uncertainty of 0.4 arc sec. (radius, 90% confidence). The preliminary detection using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) is wh=19.68+-0.03 mag (Vega) or wh=20.48+-0.03 mag (AB). We note, however, that the DECaLs survey shows faint source at this position at a g magnitude of 21.09 mag (AB). It is thus not clear if this detection represents a brightening of that source, which could indicate a host galaxy. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30066 SUBJECT: GRB210413B: further Swift-XRT observations DATE: 21/05/21 14:38:33 GMT FROM: Antonino D'Ai at IASF-PA A. D’Ai (INAF-IASFPA), A. Tohuvavohu (U Toronto) and M. H. Siegel (PSU) report on behalf of the Swift team: Swift-XRT has performed further follow-up observations of the ground-detected burst GRB 200413B (Tohuvavohu et al. GCN Cir. 29819), collecting a total of 9.2 ks of Photon Counting (PC) mode data between T0+2.1 days and T0+37 days. The uncatalogued candidate X-ray source (Source 1) reported in Kennea et al. (GCN Circ. 29827) which had also a possible UV counterpart (Siegel, GCN Circ. 29912) is still detected in XRT at a count rate consistent with the first observations. We thus rule out a possible association with the burst. The results of the XRT-team automatic analysis are at https://www.swift.ac.uk/ToO_GRBs/00021428/ This circular is an official product of the Swift-XRT team.