GCN Circular 11844
Subject
GRB 110328A / Swift J164449.3+573451: No optical variability of the optical counterpart
Event
Date
2011-03-30T20:49:44Z (15 years ago)
From
Giorgos Leloudas at Dark Cosmology Centre <giorgos@dark-cosmology.dk>
G. Leloudas, D. Malesani (DARK/NBI), D. Xu (WIS), P. Jakobsson (U.
Iceland), J. Telting (NOT), report on behalf of a larger collaboration.
We observed again the field of the peculiar source GRB 110328A / Swift
J164449.3+573451 (Cummings et al., GCN 11823; Kennea et al., ATel
3242) with the NOT equipped with ALFOSC, using the same instrument
setup adopted in our first observation (Leloudas et al. GCN 11830).
Observations were carried in the R and z filters with exposures of
3x600 and 8x300 s, respectively. The observations were carried out
starting on 04:10 UT, roughly 26 hr after our first observations and
39 hr after the first Swift trigger.
The reported galaxy at z=0.35 (Cenko et al., GCN 11827; Levan et al.,
GCN 11833; Thoene et al., GCN 11834), which is consistent with the
position of the X-ray and radio emission (Osborne et al., GCN 11826;
Zauderer et al., GCN 11836), does not show measurable variability over
this time range.
Its R-flux has remained constant to within 0.02 +- 0.07 mag, relative
to several stars in the field. Image subtraction using ISIS (Alard
2000, A&AS 144, 363) also does not reveal any variable source on the
potential host galaxy or nearby. Similarly, no variability is observed
in the z-band up to 0.02 +- 0.15 mag. Given the strong variability of
the X-ray counterpart over the same time span, this suggests that the
optical emission is dominated by the host galaxy contribution.
Preliminary photometric calibration using the Landolt standard field
SA 107 yields R = 19.35 for the USNO star 1475-0312998, close to its
archival value (R=19.4) that was used in GCN 11830.