[vsnet-grb-info 24958] LIGO/Virgo S191213g: AT2019wxt Wendelstein optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27057
SUBJECT: LIGO/Virgo S191213g: AT2019wxt Wendelstein optical observations
DATE:    20/02/13 13:47:49 GMT
FROM:    Ulrich Hopp at U Observatory Munich  <hopp at mpe.mpg.de>

Ulrich Hopp, Matthias Kluge, Claus Goessl, Christoph Ries,
Michael Schmidt (University Observatory Munich, LMU, Munich Germany)

AT2019wxt = PS19hgw was reported as a potential optical counterpart
for the LIGO/Virgo S191213g target at RA = 01:55:41.94,
Dec = +31:25:04.4, McBrien et al. 2019 (GCN26485). Follow-up
photometry pointed towards a blue and fastly faiding object (Huber
et al. 2019, GCN 26577). Follow-up spectroscopy favored the
identification as a supernova similar to SN2011fu of type SN IIb
(Valeev et al. 2019, GCN 26591 and references therein).

We here present three channel optical and near-infrared photometry
in g', i' and J taken with the 3KK camera (Lang-Bardl et al., 2016,
SPIE 9908) mounted at the 2m telescope of the Wendelstein Observatory
(University of Munich). Five epochs were obtained from shortly after
detection until about 20 days after maximum. A further
image set was taken after the SN faded below our detection limit.
That image served for difference image photometry of the SN to
minimize the impact of the host galaxy light on the SN photometry.
The SN location is within the disk of the spiral host galaxy
KUG 0152+311. On our images, the SN appears to be in a inter-arm
area of the spiral galaxy.

Eigth comparison stars within the detector field served as magnitude
reference for our aperture photometry. Magnitudes were obtained through
the CDS Strassbourg portal from SDSS DR9 (g', i') and 2MASS (J)
catalogs. Errors in the below table include the statistical error
of the SN measurement and of the zero-point determination.

  Date        UT      g'   +/-  i'   +/-    J   +/-  exp.time
                                                     sec

2019 12 18         19.78 0.08 20.10 0.09 20.26 0.08 1560
2019 12 19         19.83 0.11 19.84 0.09 19.18 0.11 2340
2019 12 21         20.10 0.06 19.83 0.06 18.96 0.10 1560
2019 12 29         22.77 0.05 20.92 0.06 19.75 0.11 1560
2020 01 06         23.68 0.08 22.64 0.07 20.69 0.12 1560
2020 01 14        <24.0      <22.7      <21.0

Our data around the maximum agree with previously reported optical
photometry (e.g. CGN 26485, 26500, 26503, 26517, 26577). Only one
NIR observation was reported so far (D'Avanco et al. 2019 GCN 26499).

Our data show that the object was very blue in the maximum phase but
turned to a much redder color during the decline. The decline
was fast with a rate of delta mag/5d 1.12 in g', 0.80 in i', and 0.54
in J, respectively. Our decline rates confirm the early estimate of
Huber et al. in g' and i' obtained shortly after maximum. These rates
are much faster than the decline of SN2011fu (see Kumar et al.
2013 MNRAS 431, 308).


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*			         Dr. Ulrich Hopp                          *
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