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GCN Circular 20393

Subject
LIGO/Virgo G268556: Palomar 200-inch detects ATLAS17aeu, possible afterglow of GRB070105A?
Date
2017-01-07T16:44:34Z (7 years ago)
From
Mansi M. Kasliwal at Caltech <mansi@astro.caltech.edu>
M. M. Kasliwal (Caltech), S. M. Adams (Caltech), H. Vedantham (Caltech), V.
Bhalerao (IUCAA), S. B. Cenko (NASA/GSFC), R. Quimby (SDSU)

report on behalf of the GROWTH (Global Relay of Observatories Watching
Transients Happen) and iPTF (intermediate Palomar Transient Factory)
collaborations

We observed the position of the fast-fading ATLAS17aeu (Tonry et al. LVC
GCN#20382) with the Large Format Camera on the Palomar 200-inch Hale
Telescope. At 2017-01-07 08:05:33 UTC, we found that ATLAS17aeu had faded
further to  i=21.9 +/- 0.3 mag (AB mags, calibration wrt SDSS).

If we fit a power law to the decay, the best-fit slope is 1.1 +/- 0.2  and
best-fit t_zero is 57758.322 +/- 0.043 (i.e. 21.5 hr after GW trigger, LVC
GCN#20364). We caution that we have not corrected for the filter
differences between ATLAS and LFC. Incidentally, this t_zero is consistent
with GRB070105A reported by POLAR (GCN#20387) and detected by ASTROSAT
(GCN#20389). The hypothesis that this is the afterglow of the GRB appears
consistent with the X-ray detection reported by Swift (Evans et al. LVC
GCN#20390).
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