[vsnet-grb-info 24740] LIGO/VIRGO S200115j: No obvious candidates from Pan-STARRS2 observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26839
SUBJECT: LIGO/VIRGO S200115j: No obvious candidates from Pan-STARRS2 observations
DATE:    20/01/21 15:55:18 GMT
FROM:    Shubham Srivastav at QUB  <S.Srivastav at qub.ac.uk>

S. Srivastav, S. J Smartt (QUB), M. Huber (IfA, Univ. of Hawaii), K. W. Smith (QUB), K. Chambers,
A. Schulz (IfA), D. R. Young, O. McBrien, J. Gillanders, D. O'Neil, P. Clark, S. Sim (QUB),
T. de Boer, J. Bulger, J. Fairlamb, M. Huber, C.-C. Lin, T. Lowe, E. Magnier, R. J. Wainscoat,
M. Willman (IfA, Univ.  of Hawaii), T.-W, Chen (Stockholm), A. Rest (STScI),
C. Stubbs (Harvard)

We report observations of the skymap of the mass gap event S200115j (LVC, GCN 26759).
We targeted one of the eastern lobes in the Lal Inference probability region (RA ~ 3 hr)
with the Pan-STARRS2 telescope. The images were obtained in the w-band
(Tonry et al. 2012, ApJ 750, 99). A sequence of quads (4 x 45 sec) was taken at
each pointing position during the nights of 2020-01-18 and 2020-01-19.

The images were processed with the IPP (Magnier et al. 2016,arXiv:1612.05240)
and difference images were produced using the Pan-STARRS1 Science Consortium 3Pi
images as reference frames. Transient candidates were run through our standard filtering
procedures, combined with a machine learning algorithm
(Wright et al. 2015, MNRAS, 449, 451) and all candidates were spatially
cross-matched with known minor planets, and major star, galaxy, AGN and multi-wavelength
catalogues (as described in Smartt et al. 2016, MNRAS, 462 4094).

We report the following transients within the 90% contour of the skymap.
All the candidates are offset from a clear galaxy. PS20ev and PS20fr have spectroscopic
host redshifts (from NED), while the rest have photometric redshifts from GLADE or SDSS.
The GW event was reported by LVC on MJD 58863.18.

Name     TNS Name    RA (J2000)     Dec (J2000)  Disc. MJD  Disc. Mag  redshift
PS20ev   AT2020ait    02:36:56.51    -02:12:03.5    58866.30     20.23     0.0701 (s)
PS20fs   AT2020ajy    02:53:21.00    +03:23:17.4    58866.32     21.46     0.301 (p)
PS20fo   AT2020ajw    02:25:53.75    -03:13:04.6    58866.30     19.90     0.138 (p)
PS20fr   AT2020ajx    02:25:23.51    -07:50:15.5    58866.30     20.42     0.0538 (s)
PS20fu   AT2020ajz    02:49:02.17    +04:59:11.6    58866.30     21.16       -
PS20fv   AT2020aka    02:37:24.50    -01:09:20.1    58867.26     19.91     0.142 (p)
PS20fw   AT2020akb    03:10:05.41    +05:59:16.4    58867.32     21.05     0.098 (p)
PS20fx   AT2020akc    02:52:35.05    +07:15:11.9    58866.30     20.89       -

Only PS20fs (AT2020ajy) shows a ~0.5 mag rise, the other transients show a flat
w-band light curve. There are no obvious candidates that show rapid fading.
The LVC distance of 332 +/- 78 Mpc corresponds to 0.06 < z < 0.09 (for Ho = 70).

We also recover the following transients discovered by the ATLAS and ZTF surveys
after the GW event. Our photometry does not indicate any unusual rise or fade.

Source    TNS Name    RA (J2000)     Dec (J2000)    MJD         PS2 Mag   redshift
ATLAS     AT2020afo    02:27:31.13    -01:06:41.6   58867.26    18.61     0.0857 (s)
ZTF       AT2020agw    02:34:02.13    -04:26:44.3   58866.30    20.62       -
ZTF       AT2020aeo    02:59:39.07    +06:41:11.2   58867.25    20.89       -