GCN Circular 10645
Subject
GRB 100418A: Continuing Swift/UVOT Observations
Event
Date
2010-04-21T19:26:57Z (16 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@astro.psu.edu>
M. H. Siegel (PSU), F. E. Marshall (NASA/GSFC), S. T. Holland
(NASA/GSFC), M. M. Chester (PSU), M. de Pasquale (MSS-UCL) and
S. R. Oates (MSSL-UCL) report on behalf of the Swift/UVOT team.
Ongoing Swift/UVOT observations of the field of GRB 100418A
(Marshall et al., GCN Circ. 10612) have continued to monitor the
behavior of the optical transient. UVOT photometry taken about
50 ks after the burst shows an increase in brightness of about a
magnitude compared to the initial detection, confirming the late
increase in brightness reported by Bikamev et al. (GCN Circ. 10635).
The OT has since decayed from this peak with a decay rate of -1.0+-0.1
in the UVOT white filter. This decay is slightly shallower than the
decay observed by Malesani et al. (GCN Circ. 10631, 10643), Updike et
al. (GCN Circ. 10637) and Filgas et al. (GCN Circ 10644). Such a late
peak in brightness is very unusual and Swift will continue to monitor
the GRB.
Photometry from the summed exposures is reported below:
FILTER T_start(s) T_stop Exposure Mag
=========================================================
white fc 88 237 147 20.62+-0.29
white 88 1548 390 20.58+-0.20
white 6143 6343 196 20.32+-0.20
white 50996 52990 1959 19.38+-0.03
white 86204 92193 2308 19.77+-0.04
white 149282 156466 3812 20.54+-0.06
=========================================================
The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.07 (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383, 627).