[vsnet-grb-info 21483] GRB 181222B: Swift follow-up observations of MASTER optical transient J204928.79+245744.0

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23582
SUBJECT: GRB 181222B: Swift follow-up observations of MASTER optical transient J204928.79+245744.0
DATE:    18/12/28 17:36:50 GMT
FROM:    Antonino D'Ai at IASF-PA  <antonino.dai at ifc.inaf.it>

A. Tohuvavohu (PSU), A. D'Ai (INAF-IASFPA), M. Siegel (PSU), J.A.
Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester),
A. Melandri (INAF-OAB), and P.A. Evans (U. Leicester) report on behalf
of the Swift-XRT and Swift-UVOT teams:

Swift has performed follow-up observations of the MASTER optical
transient J204928.79+245744.0  (V. Lipunov et al. GCN Circ. 23588),
within the IPN localization region of Fermi/GBM and Konus detected GRB
181222B (P. Veres GCN Circ. 23551, D. Svinkin et al. GCN Circ. 23556).

Swift/XRT collected 3.9 ks of Photon Counting (PC) mode data between
T0+414.9 ks and T0+427.0 ks. No X-ray source was detected at the MASTER
position with an upper limit of 2.4 e-3 ct s^-1.

Two uncatalogued X-ray sources have been detected in the field during
this observation.  Both sources are below the RASS limit and show no
definitive signs of fading. Given the large localization region of this
burst and the amount of time elapsed between the GRB and these
observations, we believe it unlikely that these X-ray sources are
related to the GRB.
Details of the sources are given below:

Source 1:
 RA (J2000.0): 312.2708 = 20:49:52.88
 Dec (J2000.0): +25.0419= +25:02:30.9
 Error: 2.5 arcsec (radius, 90% conf.)
 Count-rate (9.9 [+2.0, -1.9])e-3 ct s^-1
 Distance: 7.2 arcminutes from MASTER position.
 Flux: (2.3 [+0.5, -0.4])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 2:
  RA (J2000.0):  312.3700  =  20:49:28.81
  Dec (J2000.0): +24.9769  =  +24:58:37.0
  Error: 7.7 arcsec (radius, 90% conf.)
  Count-rate: (3.03 [+1.21, -0.97])e-3 ct s^-1	 
  Distance: 53 arcsec from MASTER position.
  Flux: (1.22 [+0.49, -0.39])e-13 erg cm^-2 s^-1 (observed, 0.3-10
keV).

Swift/UVOT began observing the field in the White filter 414 ks after
the GRB trigger. We do not find any optical source at the MASTER
position, with an upper limit of 21.48 +/- 0.22 magnitude (AB) in a 
3094 second exposure.  This magnitude is not corrected for the Galactic
extinction due to the reddening of E(B-V) = 0.24 in the direction of
the burst (Schlegel et al. 1998).

The results of the XRT-team automatic analysis of the XRT observations,

including a position-specific upper limit calculator, are available at
http://www.swift.ac.uk/ToO_GRBs/00020850/.

This circular is an official product of the Swift team.