TITLE:   GCN CIRCULAR
NUMBER:  24212
SUBJECT: LIGO/Virgo S190425z: Swope follow-up observations
DATE:    19/04/26 06:25:48 GMT
FROM:    Ryan Foley at UC Santa Cruz  <foley@ucsc.edu>

C. D. Kilpatrick, D. A. Coulter, C. Rojas-Bravo, J. S. Brown, G. Dimitriadis,
R. J. Foley, T. Hung, D. O. Jones, M. R. Siebert, K. Siellez (UCSC),
A. L. Piro (Carnegie), A. Rest (STScI), M. Drout (University of Toronto)

report on behalf of the One Meter, Two Hemisphere (1M2H) collaboration:

Using the 1-m Swope telescope at Las Campanas Observatory, we obtained
images of ZTF19aarzaod and ZTF19aarykkb (Kasliwal et al., GCN 24191) in the
localization region of LIGO/Virgo S190425z (LIGO-Virgo Collaboration,
GCN 24168). We processed the data using photpipe (Rest et al., 2005)
calibrating to the Pan-STARRS system (Chambers et al., 2016).  We performed
PSF photometry on the images and did not perform any template subtraction.

Target       | UTC                 | Filter | Mag (Err)
ZTF19aarykkb | 2019-04-26 04:23:04 | r      | 18.4 (0.1)
ZTF19aarykkb | 2019-04-26 04:28:49 | i      | 18.2 (0.1)
ZTF19aarykkb | 2019-04-26 04:34:45 | g      | 19.2 (0.1)
ZTF19aarzaod | 2019-04-26 04:45:24 | r      | 20.1 (0.1)
ZTF19aarzaod | 2019-04-26 04:56:44 | i      | 19.5 (0.1)

Note: Given the level of background emission and lack of template subtractions,
we caution a systematic uncertainty of 0.1 mag.

We note that all fluxes are similar to previous reports (Hiramatsu et al.,
GCN 24194).  In particular, we note that ZTF19aarykkb has a similar r-band
magnitude at 2019-04-25 17:53:45 UT (Tan et al., GCN 24193) and g-band
magnitude at 2019-04-25 19:21:09 UT (Hiramatsu et al., GCN 24194).  We do not
see evidence for significant fading as reported by Bhalerao et al. (Bhalerao
et al., GCN 24201).

The reported photometry is consistent with SNe II at z ~ 0.025, as suggested
by their spectra (Pavana et al., GCN 24200; Perley et al., GCN 24204; Buckley
et al., GCN 24205; Izzo et al., GCN 24208; Wiersema et al., GCN 24209; Nicholl
et al., GCN 24211).