[vsnet-grb-info 5340] GRB 071031: Swift/UVOT detection of afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7028
SUBJECT: GRB 071031: Swift/UVOT detection of afterglow
DATE:    07/10/31 18:10:56 GMT
FROM:    Alice Breeveld at MSSL-UCL  <aad at 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).