TITLE: GCN CIRCULAR NUMBER: 31342 SUBJECT: GRB 211229A: Swift-XRT and UVOT observations DATE: 21/12/30 17:29:06 GMT FROM: Phil Evans at U of Leicester pae9@leicester.ac.uk
V. D'Elia (SSDC & INAF-OAR), S. R. Oates (U.Birmingham), A. D'Ai (INAF-IASFPA), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri (INAF-OAB) 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-GUANO-detected burst GRB 211229A (Tohuvavohu et al., GCN Circ. 31334), also detected by Fermi/GBM and GECAM (Fermi GBM team, GCN Circ. 31329, Zhao et al., GCN Circ. 31331), collecting 5.0 ks of Photon Counting (PC) mode data between T0+43.6 ks and T0+66.8 ks.
Four uncatalogued X-ray sources have been detected consistent with being within 394 arcsec of the Swift/BAT-GUANO position, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below:
Source 1: RA (J2000.0): 295.1317 = 19:40:31.60 Dec (J2000.0): +23.1983 = +23:11:53.8 Error: 6.3 arcsec (radius, 90% conf.) Count-rate: (3.5 [+1.3, -1.0])e-3 ct s^-1 Distance: 252 arcsec from Swift/BAT-GUANO position. Flux: (2.78 [+1.01, -0.83])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
Source 2: RA (J2000.0): 295.0615 = 19:40:14.76 Dec (J2000.0): +23.2617 = +23:15:42.0 Error: 9.7 arcsec (radius, 90% conf.) Count-rate: (1.60 [+0.88, -0.66])e-3 ct s^-1 Distance: 398 arcsec from Swift/BAT-GUANO position.
Source 5: RA (J2000.0): 295.0738 = 19:40:17.70 Dec (J2000.0): +23.1573 = +23:09:26.3 Error: 6.6 arcsec (radius, 90% conf.) Count-rate: (2.12 [+0.97, -0.76])e-3 ct s^-1 Distance: 20 arcsec from Swift/BAT-GUANO position. Flux: (1.59 [+0.72, -0.57])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
Source 6: RA (J2000.0): 295.1187 = 19:40:28.49 Dec (J2000.0): +23.1638 = +23:09:49.7 Error: 5.3 arcsec (radius, 90% conf.) Count-rate: (2.94 [+1.13, -0.91])e-3 ct s^-1 Distance: 151 arcsec from Swift/BAT-GUANO position.
An uncatalogued source was also detected, however this was too far from the GRB position to be the afterglow.
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/00021475.
No optical afterglow consistent with the GUANO position (Tohuvavohu et al., GCN Circ. 31334) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 43722 66830 4882 >21.0
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 5.811 in the direction of the burst (Schlegel et al. 1998).
This circular is an official product of the Swift-XRT and UVOT team.