GCN Circular 2082
Subject
GRB030329, new UBVRcIc field photometry
Date
2003-04-03T16:39:38Z (22 years ago)
From
Arne A. Henden at USNO/USRA <aah@nofs.navy.mil>
A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:
We have acquired additional UBVRcIc all-sky photometry for
an 11x11 arcmin field centered at the coordinates
of the optical transient (Peterson and Price, GCN 1985)
for the HETE burst GRB030329 (GCN 1997) with the USNOFS
1.0-m telescope. Stars brighter than V=13.5 are saturated and
should be used with care. We have replaced the photometric data
with the same file name on our anonymous ftp site:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb030329.dat
The astrometry in this file is based on linear plate solutions
with respect to UCAC2. The external errors are less than 100mas.
The second night of photometry shows that the first night was
acceptable, and that the external error is now about 0.02mag.
For those of you not used to doing high-accuracy
photometry, here are some comments. Star "A" of Martini et al.
(GCN2012) has been used with either its USNO-A magnitude of
R=16.2, or the more correct Rc=16.06, in various GCNs. This
will lead to confusion when trying to fit light curves. However,
the larger problem is that this star is red (B-V=1.19,
V-I=1.41), while the afterglow itself is blue (B-V=0.35,
V-I=0.77). Using this star as a comparison and following
it over a large airmass will generally lead to fading/brightening
trends that correlate with airmass due to differential
color corrections unless proper transformations are made.
This will be even more apparent when comparing Johnson R,I
magnitudes with the Cousins Rc,Ic values reported here.
You should also be aware of the nice eclipsing binary discovered
by Fitzgerald and Orosz (GCN 2056), as this is the brightest
object near the afterglow and might be used when performing
early-time photometry or U-band photometry. Finally, as
several observers have mentioned, there are not many real stars
in this field; most of the objects are extended. You should
look at the good-seeing finding charts that have been posted
before selecting comparison stars, especially as the afterglow
fades. Many extended objects are near-enough to stellar that
they will appear in our field photometry file.
We intend to extend this file with more nights and to fainter
magnitudes as the afterglow fades. As always, you should check
the dates on the .dat file prior to final publication to get the
latest photometry.