GCN Circular 7028
Subject
GRB 071031: Swift/UVOT detection of afterglow
Event
Date
2007-10-31T18:10:56Z (18 years ago)
From
Alice Breeveld at MSSL-UCL <aad@mssl.ucl.ac.uk>
A. A. Breeveld (MSSL/UCL) and M. Stroh (PSU) report on behalf of the
Swift-UVOT team:
The Swift/UVOT observed the burst GRB 071031 (Stroh et al. GCN Circ.
7020) starting with the finding chart exposure in white, 114 seconds
after the BAT trigger. The afterglow is detected at the UVOT position
given in Stroh et al. (GCN Circ. 7020) in white, v and b until at least
7000s after the trigger. It is barely detected in u and not at all in
the UV filters; this is consistent with the redshift of z=2.692 found by
Ledoux et al. (GCN Circ. 7023). The brightness apparently increases for
the first few hundred seconds and then fades with an estimated temporal
slope in the v filter of alpha = 0.56.
The initial UVOT magnitudes and upper limits from single exposures or
co-added exposures are as follows:
Filter Tstart(s) Tstop(s) Exp(s) Mag
white 114 213 99.8 19.88 � 0.14
715 724 9.8 19.3 � 0.3
867 966 99.8 19.41 � 0.1
6778 6977 199.8 20.67 � 0.18
v 220 619 399.8 19.08 � 0.15
973 1219 246.2 18.5 � 0.13
11517 11816 299.8 19.93 � 0.32
b 700 709 9.8 >18.77 (3 sigma UL)
6573 6772 199.8 20.25 � 0.23
u 675 847 38.9 19.38 � 0.38
4933 6567 393.3 >20.82 (3 sigma UL)
uvw1 651 16990 1317.7 >21.41 (3 sigma UL)
uvm2 626 12782 1089.4 >21.23 (3 sigma UL)
uvw2 730 11206 1118.4 >21.46 (3 sigma UL)
The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E_{B-V} = 0.012 mag in the
direction of the burst (Schlegel et al. 1998).