TITLE:   GCN CIRCULAR
NUMBER:  25455
SUBJECT: LIGO/Virgo S190814bv: Further Pan-STARRS z-band observations and AT2019npv photometry
DATE:    19/08/23 13:03:24 GMT
FROM:    Stephen Smartt at Queen's U/Belfast  <s.smartt@qub.ac.uk>

S. Smartt, K. W. Smith, S. Srivastav (QUB), T.-W. Chen
(MPE), M. Huber (IfA), , 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 made further observations of the LALInference skymap of the NSBH
event S190814bv (The LIGO Scientific Collaboration and the Virgo
Collaboration, GCN 25324, 25333) with the Pan-STARRS1 telescope
(Chambers et al. 2016, Huber et al. GCN25356) on MJD 58716.5. 

As described in Srivastav et al. (GCN 25417), we focused on the inner
50% probability with deep stacks reaching a typical 5-sigma limiting
magnitude of z < 22.2. We found one more. previously unreported
transient at z = 21.41 +/- 0.15, with details available on the TNS
(AT2019ofb). 

Here we report the photometric evolution of the transient AT2019npv
(DG19wxnjc), discovered by DECam-GROWTH (Goldstein et al. GCN25393).
Jonker et al. (GCN 25454) measured the redshift of the nearby blue
galaxy (PSO J013.3850-23.8322 or GALEXASC J005332.30-234955.3) to be
z = 0.056, placing it within the distance range of S190814bv. 

The following table contains the z-band photometry reported to date
and new PS1 measurements. 

58710.58   ~20.8    PS1,marginal 2-3 sigma detection in z (mag uncertain)
58711.3       20.7    DECam (TNS Trans. Report 1507)
58713.34     20.6    DECam (GCN 25393)
58713.54     21.3    PS1
58716.54     21.5    PS1

The DECam photometry needs checked on 58713.34. The last two PS1
points have uncertainties of +/- 0.2 mag. The first has an error of
0.3 to 0.4 mag. Within the uncertainties, there could be a slow fade
of around 0.1 mag per day, but fast fading can be ruled out with a
clear detection on 58716.54. 

Spectra of this faint object is still difficult due to the moon
position. However it should still be pursued, as this appears to be one
of the only remaining viable counterpart candidates.

We note the existence of another possible host galaxy. The transient
would be about 40kpc from 2MASS J00533400-2350224, if both were at
about ~250 Mpc.

2MASS J00533400-2350224      13.391293   -23.839395   V = 18.6