[vsnet-grb-info 23576] LIGO/Virgo S190901ap: ZTF19abwvals is a type-Ia SN near maximum

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25675
SUBJECT: LIGO/Virgo S190901ap: ZTF19abwvals is a type-Ia SN near maximum
DATE:    19/09/06 12:41:49 GMT
FROM:    Daniele B Malesani at DTU Space  <malesani at space.dtu.dk>

L. Izzo (DARK/NBI), G. Leloudas (DTU Space), S. H. Bruun (DARK/NBI), K. 
E. Heintz (Univ. Iceland), B. Milvang-Jensen (DAWN/NBI), J. Hjorth 
(DARK/NBI), J. P. U. Fynbo (DAWN/NBI), D. B. Malesani (DTU Space), S. 
Piranomonte (INAF/OARm), T. Pursimo (NOT), J. Martikainen (NOT and Univ. 
Helsinki), report on behalf of a larger collaboration:

We observed the transient ZTF19abwvals (Stein et al., GCN 25656) 
discovered by the Zwicky Transient Facility as a candidate counterpart 
of the LIGO/Virgo GW event S190901ap (LIGO Scientific Collaboration and 
Virgo Collaboration, GCNs 25606, 25614), using the Nordic Optical 
Telescope equipped with the ALFOSC spectrograph. A spectrum by 2x1200 s 
was acquired covering the wavelength range 3200-9600 AA, starting on 
2019 September 5.20 UT.

In the acquisition image (taken without filter) the transient is 
detected, approximately 0.9" to the NW of the galaxy nucleus and hence 
blended with it given the seeing of approximately 1". In the spectral 
extraction, a sizable contribution from the host galaxy is present.

Template-matching using SNID (Blondin & Tonry, 2007, ApJ, 666, 1024) and 
DASH (https://astrodash.readthedocs.io) shows that ZTF19abwvals is a 
normal type-Ia SN at a phase of 4-6 days after maximum, at a redshift z 
= 0.091 +- 0.004. The redshift is consistent with the SDSS photometric 
value z_ph = 0.13 +- 0.03 of the host galaxy. Considering the foreground 
Galactic extinction (A_r = 1.04 mag) and the measurement by Stein et al. 
(GCN 25656), the absolute magnitude of the transient at z = 0.091 is M_r 
~ -19.4, consistent with a type-Ia SN near peak.

The above classification excludes ZTF19abwvals as a counterpart of 
S190901ap.