GCN Circular 25417

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

We report further observations of the LALInference skymap of the NSBH
event S190814bv (The LIGO Scientific Collaboration and the Virgo
Collaboration, GCN 25324
Not found
 
 
, 25333
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) with the Pan-STARRS1 telescope
(Chambers et al. 2016 arXiv :161205560C, Huber et al. GCN25356
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).
Images were taken in the PS1 z-band between 2019-08-18 11:03:19 UT
 and 2019-08-18 14:54:11 UT (58713.46 - 58713.62). A sequence of
 53 x 240 sec dithered exposures was taken covering the central 
(approximately) 50% probability region. Given the moon position, and 
the time lapsed after s190814bv, and the low probability of a bright 
transient at this epoch, we made the choice to focus on the central part 
of the skymap, with extra depth and one filter. The 240s sec exposures 
were combined into a single epoch stack, covering the GPC1 camera chip gaps.

The images were processed with the IPP (Magnier et al. 2016,
arXiv:1612.05240
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) and difference images for the co-added stacks were
produced using the Pan-STARRS1 Science Consortium 3Pi data to detect
transient objects. The median 5-sigma depth of the stacked sky cells
was z < 21.6 (AB mag). We may be able to significantly improve on
depth by collecting a deep reference frame during the next lunation.

Standard filtering procedures, combined with a machine learning
algorithm (Wright et al. 2015, MNRAS, 449, 451) were applied 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).

Given the extra depth compared to our first epoch (z < 20.4) on
2019-08-15 12:40:37 UT (58710.5282 ; see Huber et al. GCN 25356
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), we
detected a significant number of fainter new transients, given in the
table below. Examining potential host galaxies, and the weak
constraints we have from earlier epoch data, we do not find a source
that appears consistent with being a candidate for the counterpart to
s190814bv. All candidates have been registered on the IAU TNS.

We recovered several of the DECam GROWTH and DESGW transients (e.g.
those reported in Goldstein et al. GCN 25393
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, Herner et al. GCN 25398
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and related GCNs). We find that the combination of photometric
evolution and redshift constraints (through possible hosts) leaves no
obvious counterpart candidate for the objects in common.

Name    | TNS Name  | RA (J2000)  | Dec (J2000) | Disc MJD |  z Mag err 
PS19epz | AT2019nuw
Not found
 
 
 | 00:50:26.34 | -25:52:57.8 | 58713.54 |  21.85 0.24
PS19eqa | AT2019nux
Not found
 
 
 | 00:50:21.01 | -23:42:46.7 | 58713.54 |  21.75 0.20
PS19eqc | AT2019nuz
Not found
 
 
 | 00:49:52.26 | -25:31:25.6 | 58713.54 |  21.89 0.22
PS19eqd | AT2019nva
Not found
 
 
 | 00:52:43.39 | -23:37:54.0 | 58713.54 |  21.49 0.18
PS19eqe | AT2019nvb
Not found
 
 
 | 00:46:51.16 | -25:25:39.3 | 58713.54 |  21.72 0.22
PS19eqf | AT2019nvc
Not found
 
 
 | 00:52:18.32 | -26:19:42.0 | 58713.54 |  21.31 0.18
PS19eqg | AT2019nvd
Not found
 
 
 | 00:55:42.30 | -24:41:50.2 | 58713.54 |  21.47 0.17
PS19eqh | AT2019nve
Not found
 
 
 | 00:56:05.51 | -24:38:26.3 | 58713.54 |  21.30 0.15
PS19eqo | AT2019nvr
Not found
 
 
 | 00:48:16.08 | -25:28:14.9 | 58713.54 |  20.89 0.13
PS19eqp | AT2019nvs
Not found
 
 
 | 00:52:37.75 | -26:11:41.4 | 58713.55 |  21.44 0.24