GCN Circular 20802
Subject
LIGO/Virgo G275697: Additional iPTF Optical Transient Candidates
Date
2017-03-03T04:29:33Z (8 years ago)
From
Mansi M. Kasliwal at Caltech <mansi@astro.caltech.edu>
S. M. Adams (Caltech), C. Cannella (Caltech), A. A. Miller
(Northwestern/Adler), S. Papadogiannakis (OKC), R. Lunnan (Caltech), N.
Blagorodnova (Caltech), L. P. Singer (NASA/GSFC), S. B. Cenko (NASA/GSFC),
R. Walters (Caltech), T. Barlow (Caltech), J. Rana (IUCAA), V. Bhalerao
(IIT-B), Y. Cao (UW), R. Laher (IPAC), F. Masci (IPAC) and M.M. Kasliwal
(Caltech)
report on behalf of the iPTF (intermediate Palomar Transient Factory) and
GROWTH (Global Relay of Observatories Watching Transients Happen)
collaborations:
We have continued tiled observations of LIGO/Virgo G275404 (LVC, GCN
20738) and LIGO/Virgo G275697 (LVC, GCN 20763) using the Palomar 48-inch
Oschin telescope (P48). Including our first night of observations on
2017-03-01 UTC (GCN 20791) and a second night on 2017-03-02, we have
observed a total of 240 fields spanning 1747 square degrees. We estimate a
20% chance that these fields contain the true location of G275404 and a
25% chance that they containing the true location of G275697.
During preliminary sifting through candidate variable sources using image
subtraction by our IPAC (Masci et al. 2016) and NERSC (Cao et al. 2016)
pipelines, a total of 115 candidates were saved in the fields imaged.
Applying standard iPTF vetting procedures and removing transients with a
history of previous variability, we flagged 16 optical transient candidates
in the 90% localization contour of G275697, listed below, for further
follow-up.
We encourage spectroscopic classification of these candidates. In
particular, we highlight 17bub and 17buo as fast-evolving by more than 0.3
mag in the same night.
We are grateful to the Palomar crew (John Henning, Jeff Zolkower, Carolyn
Heffner, Jamey Eriksen, Nick Ganciu) for their hard work in reviving a
faulty declination encoder essential to collecting this dataset during the
last two days of iPTF survey operations.
iPTF17bti 0.800077 67.402379 02:38 18.67
pstar=0.957; nuclear/stellar?
iPTF17btj 27.422253 68.506993 02:53 18.34
pstar=0.91; nuclear/stellar?
iPTF17bto 53.02396 70.025567 03:38 17.87
nuclear/stellar?
iPTF17btp 68.216762 72.512217 03:46 19.23
pstar=0.969; nuclear/stellar?
iPTF17bub 85.525185 70.159774 04:32 18.72
pstar=0.946; nuclear/stellar?; fading (0.84 mag intra-night)
iPTF17bue 54.623802 71.407755 03:38 18.04
off-center from host galaxy
iPTF17bun 57.584087 72.275187 03:35 18.63
pstar=0.909; nuclear/stellar?
iPTF17buo 49.553246 73.391128 03:35 18.39
pstar=0.166; nuclear/stellar?; fading (0.69 mag intra-night)
iPTF17buq 41.070946 69.589982 03:28 18.9
pstar=0.996; nuclear/stellar?
iPTF17bvd 83.199221 71.328788 04:32 20.1 hostless
in iPTF reference; possible marginal counterpart seen in PS1.
iPTF17bvw 85.92019 70.584375 04:32 19.74 hostless
in iPTF and PS1
iPTF17bvx 72.69051 69.373832 04:17 19.36
pstar=0.918; nuclear/stellar?
iPTF17bvz 66.258018 69.031885 04:17 19.81
pstar=0.889; nuclear/stellar?
iPTF17bwi 82.2476 71.146032 04:24 20.16
pstar=0.958; nuclear/stellar?
iPTF17bwj 141.533287 7.757573 07:09 19.39 0.441 specz;
nuclear; SDSS QSO
iPTF17bxa 76.262387 69.156295 04:26 19.66 nuclear;
pstar=0.01
Two known transients detected in early January also fall in the
localization region and were recovered with iPTF: PS17m (=iPTF17D) and
PS17n/Gaia17aan (=iPTF17G).
Positions are stated in the ICRS. Discovery times are noted in UTC hh:mm on
2017-03-02. Magnitudes are based on image subtraction and in the Mould R
filter, calibrated with respect to point sources in SDSS as described in
Ofek et al. 2012.
We caution that many candidates are outside the SDSS footprint and lack a
secure star/galaxy classification for the underlying source. We flag these
as "nuclear/stellar?". Where available, we provide machine-learning
probability scores on whether the underlying source is a galaxy/star (0/1)
(Miller et al. 2016).
We encourage spectroscopic classification of these candidates. In
particular, we highlight 17bub and 17buo as fast-evolving by more than 0.3
mag in the same night.
We are grateful to the Palomar crew (John Henning, Jeff Zolkower, Carolyn
Heffner, Jamey Eriksen, Nick Ganciu) for their hard work in reviving a
faulty declination encoder essential to collecting this dataset during the
last two days of iPTF survey operations.