[AAVSO-HEN] GRB 070520A: Swift UVOT Upper Limits

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
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TITLE:   GCN CIRCULAR
NUMBER:  6439
SUBJECT: GRB 070520A: Swift UVOT Upper Limits
DATE:    07/05/21 13:26:54 GMT
FROM:    Stefan Immler at NASA/GSFC  <immler at milkyway.gsfc.nasa.gov>

S. Immler (USRA/GSFC) and P. Romano (Univ. Bicocca & INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT observed the field of GRB 070525A starting 152 s after
the BAT trigger (Romano et al., GCN 6423).  We do not find any source
in any of the UVOT observations inside the XRT error circle. The 3-sigma
upper limits for detecting a source inside the XRT error circle in the
co-added frames are:

Filter            T_start(s)   T_stop(s)     Exp(s)     Mag (3-sigma UL)

White             168          4793          345        >20.2
V                 152          11162         1288       >19.6
B                 4389         6021          393        >20.0
U                 4184         16822         1142       >20.3
UVW1              3979         16047         1279       >20.1
UWM2              3774         11805         1021       >20.4
UVW2              4799         10249         1082       >20.5

The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E(B-V) = 0.02 mag towards
the direction of the burst (Schlegel et al. 1998).