[vsnet-grb-info 14778] Fermi418277210: iPTF optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16092
SUBJECT: Fermi418277210: iPTF optical observations
DATE:    14/04/10 02:32:55 GMT
FROM:    Leo Singer at CIT/PTF  <lsinger at caltech.edu>

L. P. Singer (Caltech), S. B. Cenko (NASA/GSFC), M. M. Kasliwal
(Carnegie Observatories/Princeton), Adam Waszczak (Caltech),
Sagi Ben-Ami (Weizmann), Joel Johansson (Stockholm University), and
Avishay Gal-Yam (Weizmann) report on behalf of the intermediate
Palomar Transient Factory (iPTF) collaboration:

We have searched for optical counterparts of Fermi GBM trigger
Fermi418277210 (2014-04-04 04:06:47.51) using the Palomar 48-inch
Oschin telescope (P48). Based on the last automated Fermi ground
software localization sent at 04:07:29, we began observing 10 fields
covering 73 deg2, 12 minutes after the trigger. Since the final Fermi
localization sent at 05:16:07 differed by 3 deg (well within the
1-sigma statistical-only uncertainty), we observed five more fields
for a total area of 109 deg2. We estimate a 68% chance that one of
these 15 fields contains the location of the source.

Sifting through candidate variable sources using image subtraction
and standard iPTF vetting procedures including photometry with the
robotic Palomar 60" telescope (P60), we detected several optical
transients, none of which showed evidence of significant fading.

For the following sources, we obtained spectra with the Double
Spectrograph (DBSP) on the Palomar 200" Hale telescope (P200):

14ain, detected at r = 18.67 +/- 0.03 mag and possibly rising,
coincident with galaxy SDSS J111725.00+293457.4, identified as SN Ia,
at z = 0.08, also reported by MASTER (Rufanov et al. 2014, ATel 6055),
at the coordinates:
 RA(J2000)  =  11h 17m 25.04s (169.354352 deg)
 Dec(J2000) = +29d 34' 58.3"  (+29.582861 deg)

14ait, detected at r = 20.5 +/- 0.1 mag, on the outskirts of the
galaxy SDSS J113303.95+330719.3, with the nebular spectrum of an old
SN Ib/c at z = 0.039, at the coordinates:
 RA(J2000)  =  11h 33m 04.04s (173.266841 deg)
 Dec(J2000) = +33d 07' 23.9"  (+33.123292 deg)

14aiz, detected at r = 19.28 +/- 0.04 mag, coincident with the
z=0.09701 galaxy SDSS J111407.50+390243.0, with an inconclusive
spectrum showing only host light, at the coordinates:
 RA(J2000)  =  11h 14m 07.28s (168.530319 deg)
 Dec(J2000) = +39d 02' 43.2"  (+39.045337 deg)

The following transient candidates were placed on the P200 queue,
but not observed due to other higher-priority targets:

14aim, detected at r = 19.68 +/- 0.06 mag and coincident with the
galaxy SDSS J114155.45+351813.9, at the coordinates:
 RA(J2000)  =  11h 41m 55.57s (175.481562 deg)
 Dec(J2000) = +35d 18' 14.9"  (+35.304133 deg)

14aip, detected at r = 19.40 +/- 0.05 mag and rising, clearly offset
from the galaxy SDSS J111215.58+313056.2, at the coordinates:
 RA(J2000)  =  11h 12m 16.02s (168.066732 deg)
 Dec(J2000) = +31d 30' 57.9"  (+31.516089 deg)

14aiq, detected at r = 20.62 +/- 0.17 mag, coincident at the galaxy
SDSS J111506.79+292025.1, at the coordinates:
 RA(J2000)  =  11h 15m 06.89s (168.778719 deg)
 Dec(J2000) = +29d 20' 24.0"  (+29.340007 deg)

14ais, detected at r = 20.33 +/- 0.08 mag, with no clearly associated
host in SDSS, at the coordinates:
 RA(J2000)  =  11h 51m 08.46s (177.785253 deg)
 Dec(J2000) = +31d 17' 03.2"  (+31.284218 deg)

14aiu, detected at r = 20.20 +/- 0.14 mag and apparently hostless, at
the coordinates:
 RA(J2000)  =  11h 15m 09.30s (168.788748 deg)
 Dec(J2000) = +34d 26' 35.8"  (+34.443280 deg)

14aiy, detected at r = 20.30 +/- 0.09 mag, coincident with the galaxy
SDSS J114936.42+374417.3, at the coordinates:
 RA(J2000)  =  11h 49m 36.47s (177.401968 deg)
 Dec(J2000) = +37d 44' 18.2"  (+37.738379 deg)

Due to the relative promptness of our first 10 observations, we were
concerned that a bright (r <~ 14 mag) afterglow would have saturated
on the P48 CCD and have been missed by our automated image
subtraction pipeline. We therefore also visually inspected the 110
single-chip images from the first epoch of observations. We found no
saturated objects that were absent from both the SDSS and the
USNO-B1.0 catalogs. We also performed a semi-automated search over
all of the P48 source extractions that contained saturated pixels.
There were 6579 saturated objects, of which all were either present
in the USNO-B1.0 catalog or clearly visible in archival SDSS images.

The diagram
http://www.its.caltech.edu/~lsinger/iptf/Fermi418277210.pdf shows the
fifteen P48 fields (dark gray: the 10 prompt fields, light gray: the
remaining 5) in relation to the Fermi GBM 1- and 2-sigma
statistical+systematic contours.