[vsnet-grb-info 23808] LIGO/Virgo S190930t: Upper limits on the two of the ZTF/GROWTH candidates

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25907
SUBJECT: LIGO/Virgo S190930t: Upper limits on the two of the ZTF/GROWTH candidates
DATE:    19/10/01 19:16:47 GMT
FROM:    Tomoki Morokuma at U of Tokyo  <tmorokuma at ioa.s.u-tokyo.ac.jp>

Morokuma, T. (U. Tokyo); Utsumi, Y. (Stanford/SLAC) on behalf of J-GEM 
collaboration

We report optical follow-up imaging observations for the electromagnetic 
counterpart candidates of the gravitational wave event S190930t (The 
LIGO Scientific Collaboration and the Virgo Collaboration, GCN Circ. 
25876) reported by Stein et al. (GCN Circ. 25899).

We took 12 contiguous frames of 0.5-second exposures 19-22 hours from 
the possible neutron star and black hole merger for the regions around 
ZTF19acbpqlh (AT2019rpn) and ATLAS19wyn (AT2019rpj) with Tomo-e Gozen 
(Sako et al. 2018, SPIE, 10702, 107020J) on the 1.05-m Kiso Schmidt 
telescope. No filters are used and the data are calibrated relative to 
r-band data from Pan-STARRS DR2. We find no transients at the reported 
locations down to depths in the AB system shown below.

| MJD | AT | depth (5 sigmas) |
| 58757.40871 | ZTF19acbpqlh (AT2019rpn) | 18.69 |
| 58757.51431 | ZTF19acbpqlh (AT2019rpn) | 17.66 |
| 58757.43221 | ATLAS19wyn (AT2019rpj) | 18.53 |
| 58757.52506 | ATLAS19wyn (AT2019rpj) | 18.04 |

We note that the ZTF/GROWTH reported magnitudes are 1.0-2.4 magnitudes 
fainter than our detection limits above.