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GCN Circular 20401

Subject
LIGO/Virgo G268556: Continued iPTF Observations and Additional Optical Transient Candidates
Date
2017-01-09T00:58:15Z (7 years ago)
From
Leo Singer at NASA/GSFC <leo.p.singer@nasa.gov>
L. P. Singer (NASA/GSFC), T. Kupfer (Caltech), R. Roy (OKC),
M. M. Kasliwal (Caltech), S. B. Cenko (NASA/GSFC), and T. Barlow (Caltech)
report on behalf of the iPTF and GROWTH collaborations:

We continued our tiled observations of LIGO/Virgo G268556 (LVC, GCN 20364)
using the Palomar 48-inch Oschin telescope (P48) on the night of
2017-01-08 UTC. Including our original observations on 2017-01-07
(Kasliwal et al., GCN 20398), we have now imaged 151 fields spanning 1069
square degrees, with a 51% chance of containing the true location of the
source.

Applying standard iPTF vetting procedures to the images taken on
2017-01-08, we flagged the following additional optical transient
candidates that had no previous history of detection or variability in
iPTF. We have listed the transients in order of priority for follow-up:

---------------------------------------------------------
  name      RA        Dec      time  mag    z    notes
---------------------------------------------------------
              No host or quiescent source
---------------------------------------------------------
iPTF17fs 162.900034 +69.833971 10:46 18.94
---------------------------------------------------------
         Coincident galaxy with unknown redshift
---------------------------------------------------------
iPTF17ha 230.580928 +80.725830 13:14 19.29
iPTF17gf 272.970627 +68.486958 13:32 20.03
iPTF17ft 201.323053 +78.426314 11:09 19.95
iPTF17fu 192.417627 +80.149750 11:11 18.78
iPTF17fw 156.366148 +71.757620 10:46 18.24
iPTF17gr 193.895770 +79.226903 11:11 20.21
iPTF17gv 176.227516 +82.619152 11:04 19.77
iPTF17hc 165.400920 +68.097753 10:47 19.52
---------------------------------------------------------
 Known redshift inconsistent with LIGO distance estimate
---------------------------------------------------------
iPTF17fe 330.745910 -03.303166 02:33 17.80 0.044
iPTF17fg 339.797294 -17.341041 02:49 16.63 0.074
iPTF17gw 178.409537 +72.864968 10:58 19.41 0.176 photo-z
iPTF17gj 257.427906 +70.158947 13:29 19.74 0.258 photo-z
---------------------------------------------------------
  Unresolved host or quiescent source, possibly stellar
---------------------------------------------------------
iPTF17he 214.716535 +79.793033 13:07 19.88
iPTF17ge 159.042893 +69.146836 10:47 19.87
iPTF17hf 195.818782 +80.173138 11:11 19.52
iPTF17hh 194.925476 +75.016124 11:08 20.34
iPTF17gu 194.101611 +78.204729 11:09 19.47
iPTF17gt 191.763759 +76.839773 11:09 19.70
iPTF17gs 199.058226 +76.521298 11:09 20.07
iPTF17hi 180.885869 +72.050360 10:58 20.30
iPTF17gn 232.045095 +74.611299 13:15 19.99
iPTF17gm 235.823172 +74.750334 13:15 19.69
iPTF17hd 213.248302 +79.332924 13:07 19.44
iPTF17gc 240.341194 +78.345723 13:17 19.54
---------------------------------------------------------

The known blazar NVSS J120651+772222 was excluded from this list.

Positions are stated in the ICRS. Times are in UTC. Magnitudes are based
on image subtraction; they are in the Mould R filter. Spectroscopic
redshifts of coincident galaxies are obtained from NED and photometric
redshifts from SDSS DR12.

We encourage further follow-up of the candidates above, especially of
iPTF17fs, for which no host galaxy or quiescent source was visible in
archival iPTF images. Observations of this source have been requested from
the GROWTH network (http://growth.caltech.edu).
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