GCN Circular 17733
Subject
GRB 150423A: Keck optical afterglow confirmation
Event
Date
2015-04-23T14:34:27Z (11 years ago)
From
Daniel Perley at Caltech <dperley@astro.caltech.edu>
D. A. Perley (Caltech) reports:
I acquired observations of the optical afterglow candidate of GRB
150423A (Pagani et al., GCN 17726; Varela et al., GCN 17732) using the
Low Resolution Imaging Spectrometer (LRIS) on the Keck I 10m telescope.
Two epochs of V- and i-band imaging were acquired, the first beginning
at UT 07:13 (approximately 0.75 hours after the trigger, as soon as the
target cleared the telescope Nasmyth limit), the second beginning at UT
13:12 (approximately 6.75 hours after the trigger).
The sources mentioned by Varela et al. are well-detected in both epochs.
Source 2 remains constant between the frames, while Source 1 declines
by approximately 0.9 magnitude in both V- and i-band, confirming that it
is the optical afterglow.
Shortly after the second imaging epoch, I also acquired 1600 seconds of
low-resolution spectroscopy with the slit oriented to cover both S1 and
S2. A faint trace is detected for both sources. Source 2 shows a clear
emission line in the blue arm and at least one marginal emission line in
the red arm, indicating a low to moderate redshift. Source 1 (the
afterglow) shows no clear features in emission or absorption, but the
signal is very weak. Further analysis will reported at a later time
pending wavelength calibration of the spectra.