TITLE:   GCN CIRCULAR
NUMBER:  25457
SUBJECT: LIGO/Virgo S190814bv: GROND follow-up observations of AT2019npv
DATE:    19/08/23 15:20:12 GMT
FROM:    Ting-Wan Chen at MPE  <jchen@mpe.mpg.de>

T.-W. Chen (MPE), T. Schweyer (MPE), A. Nicuesa Guelbenzu (TLS Tautenburg), P. Schady (Bath), A. Rau (MPE), J. Bolmer (MPE), S. Klose (TLS Tautenburg) report:

We observed the counterpart candidate AT2019npv (=DG19wxnjc; GCN #25393, Goldstein et al.; GCN #25398, Herner et al.) of S190814bv (GCN #25324) simultaneously in g'r'i'z'JHKs with GROND (Greiner et al. 2008, PASP 120, 405) mounted on the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). The redshift of the galaxy nearby to AT2019npv is consistent within the distance range of S190814bv (GCN #25454, Jonker et al.).

Observations were obtained between 19 and 23 August 2019, 4.4, 5.4 and 8.3 days after the S190814bv detection. The magnitudes are measured using aperture photometry with a aperture size of 1*FWHM of the average of the field stars (seeing 0".99, 0".84, and 0".79, resp.). We caution that the magnitudes contain underlying host-galaxy light. Given magnitudes are calibrated against Pan-STARRS field stars in the optical and against 2MASS field stars in the NIR. All magnitudes are given in the AB system. The magnitudes are not corrected for Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.02 mag in the direction of the counterpart (Schlafly & Finkbeiner 2011). In terms of no detection, we measured the host-galaxy backgrond light at the transient position. 

MJD             g'                      r'                       i'                       z'            
58714.328   21.55 (0.08)      21.06 (0.11)     21.26 (0.10)     20.67 (0.12)
                    J                        H                      Ks 
                    20.82 (0.18)       >21.0               >20.2
                    
MJD             g'                      r'                       i'                       z'                                            
58715.246   21.82 (0.05)      21.18 (0.11)     21.10 (0.07)     20.82 (0.13)
                    J                        H                      Ks 
                    20.77 (0.14)      20.90 (0.27)      >20.3
                    
MJD             g'                      r'                       i'                       z'                                            
58718.203   21.83 (0.04)     21.03 (0.14)      21.20 (0.05)     20.89 (0.13) 
                    J                        H                      Ks 
                    21.01 (0.17)      >21.2                >20.2

Over the timescale of our observations we do not detect any significant variation in the brightness of this object. We note that our z'-band magnitude is slightly brighter compared to PanSTARRS (GCN #25455, Smartt et al.), because we did not perform any host template subtraction.
                  
We acknowledge excellent help in obtaining these data from Angela Hempel and Regis Lachaume on La Silla.