GCN Circular 10750
Subject
GRB 100513A: Lick observations and R-band dropout
Date
2010-05-13T07:03:07Z (15 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley, C. R. Klein, and A. N. Morgan (UC Berkeley) report:
We began observing the location of the afterglow of GRB 100513A
(Baumgartner et al., GCN 10746) at 04:06 UT using the Nickel 40-inch
telescope at Lick Observatory. A total of fourteen 300-second images
were acquired in the R-band under clear sky conditions.
A co-add of the first 9 images (midpoint 04:35 UT) reveals a faint point
source at the position reported by Morgan et al (GCN 10747). The source
is near the detection limit of the co-add and is not detected in
individual images.
Photometry of the object relative to three nearby SDSS stars (converted
to Rc via the Lupton transformation equation) gives the following magnitude:
R = 21.39 +/- 0.25 (t_mid = 2.46 hours)
We note that this is significantly fainter than expected from the
preliminary JHK magnitudes of Morgan et al (GCN 10749). The IR spectral
index is relatively flat (beta~0.5), suggesting little host extinction.
Assuming no extinction in addition to the Galactic value, a direct
power-law extrapolation of the JHK data to R-band over-predicts the
observed flux by >2 magnitudes, strongly suggesting an R-band dropout
and likely redshift of 4.6 < z < 6.0. We note also that the X-ray
column is consistent with no absorption beyond Galactic (Baumgartner et
al.), consistent with a high-redshift origin.
We encourage I/z/Y-band follow-up to better constrain the redshift and
dust extinction. Spectroscopic observations are planned.