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GCN Circular 21488

Subject
LIGO/Virgo G297595: Pan-STARRS coverage and transients over the first 5hrs
Date
2017-08-15T16:11:56Z (8 years ago)
From
S. J. Smartt at Queens U Belfast <s.smartt@qub.ac.uk>
K. C. Chambers (IfA), K. W. Smith (QUB), M. E. Huber (IfA),
S. J. Smartt, D. R. Young (QUB), M. Coughlin (Harvard), T.-W. Chen
(MPE), L. Denneau, H. Flewelling, A. Heinze, E. Kankare (QUB),
T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA),
A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters,
R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB)

Following Katsavounidis et al. (GCN 21474Loading...
 
 ), we report Pan-STARRS
imaging observations of the skymap (bayestar.fits) of G297595, a GW
source with event time 2017/08/14 10:30:43.526780 == MJD
57979.43800378

We covered around 60 square degrees on the first night following the
release of the G297595 alert. We began taking data at 2017-08-14.564
UT (57979.564; 3hrs after the event detection, and 2.5hrs after the
alert).  We estimate that this first night of data coverage
corresponds to a probability of containing the source of around 60%,
(based on the bayestar.fits map; Singer et al. 2016, ApJL 829,
15). Our coverage map will be posted on GraceDB.  Note that we could
not go below dec=-48, and did not cover the most southern part of the
skymap.

Images were taken in the Pan-STARRS i-band filter in a series of
overlapping 45s exposures, with typically 4-6 images at each position.
Difference images were produced by subtracting the Pan-STARRS1 3Pi
reference image from these separate 45s exposures (Chambers et
al. arXiv:1612.05560Loading...
 
 , and available at http://panstarrs.stsci.edu).
At airmass of 2.8 to 2.3, we reach i ~ 21 in the individual exposures.

Using techniques discussed in Smartt et al. (2016, MNRAS, 462, 4094),
we have located and vetted transients with quality filters and a
machine learning algorithm on the difference images.

Obvious variable sources which are likely AGN/QSOs or variable stars
have, as far as possible, been removed from this transient list
through catalogue matching.

We found 6 objects that are likely astrophysical transients, but all 6
are close to or coincident with the cores of resolved galaxies.  The
difference images are good quality and these are likely real, but
may be AGN activity. Given the recent interest in nuclear transients
and their nature we report them here for follow-up.

The ���prob countour��� gives the bayestar.fits map probability which
contains the transient.

We found no SN-like, or GRB-afterglow like candidates which are
associated with a galaxy and offset from the core, and 
similarly no orphan hostless transients to a limit of i ~ 21. 
Some of the following transients could be nuclear supernovae but
have no measurable offsets. 


name    ra           dec           mjd      disc mag   prob contour Notes  
PS17edg 02:51:44.91 -39:39:29.0    57979.568  20.29 i    70           1
PS17edm 02:54:18.07 -41:31:25.8    57979.576  20.62 i    40           2
PS17edh 02:54:07.09 -41:37:31.8    57979.576  18.36 i    40           3
PS17edn 02:55:45.77 -40:40:17.4    57979.576  20.78 i    50           4
PS17edl 02:52:48.23 -41:25:51.3    57979.578  20.51 i    40           5
PS17edj 02:30:45.31 -45:07:02.1    57979.587  18.39 i    90           6


1. The transient is associated with APMUKS(BJ) B024948.84-395146.3; a
20.03 mag galaxy found in the NED catalogue. It's located 0.34" S,
0.30" W from the galaxy centre.

2. The transient is associated with LCRS B025225.0-414335; a 18.86 mag
galaxy found in the NED catalogue. It's located 0.3" from the galaxy
core.

3.  The transient is associated with LCRS B025214.1-414941; a 17.26
mag galaxy found in the NED catalogue. It's located 0.3" (0.7 Kpc)
from the galaxy core. A host z=0.146 implies a transient M = -20.85.

4. The transient is associated with 02554579-4040171 ; a J=16.85 mag
stellar source found in the 2MASS PSC catalogue. It's located 0.4"
from the source core. The object appears slightly extended in the PS1
images and is likely a galaxy.

5. The transient is associated with 02524824-4125517 ; a J=16.72 mag
stellar source found in the 2MASS PSC catalogue. It's located 0.4"
from the source core. The object appears slightly extended in the PS1
images and is likely a galaxy.

6. The transient is synonymous with LCRS B022852.4-452018; a 18.45 mag
galaxy found in the NED catalogue. It's located 0.2" (0.5 Kpc) from
the galaxy core. A host z=0.143 implies a transient M = -20.56.