GCN Circular 25675
Subject
LIGO/Virgo S190901ap: ZTF19abwvals is a type-Ia SN near maximum
Date
2019-09-06T12:41:49Z (6 years ago)
From
Daniele B Malesani at DTU Space <malesani@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.