TITLE:   GCN CIRCULAR
NUMBER:  20527
SUBJECT: LIGO/Virgo G270580: NOT observations of PS17yt
DATE:    17/01/25 19:35:48 GMT
FROM:    Daniele Malesani at DARK/NBI  <malesani@dark-cosmology.dk>

D. Malesani (DARK/NBI), G. Leloudas (WIS, DARK/NBI), E. Pian (SNS Pisa), 
L. A. Antonelli (INAF/OAR), S. Benetti (INAF/OAPd), M. Branchesi (Univ. 
Urbino), E. Brocato (INAF/OAR), S. Campana (INAF/OABr), E. Cappellaro 
(INAF/OAPd), S. Covino (INAF/OABr), P. D'Avanzo (INAF/OABr), V. D'Elia 
(INAF/OAR; ASI/ASDC), J. P. U. Fynbo (DARK/NBI), A. Grado (INAF/OAC), G. 
Greco (Univ. Urbino), J. Hjorth (DARK/NBI), A. Melandri (INAF/OABr), B. 
Milvang-Jensen (DARK/NBI), E. Palazzi (INAF/IASF Bo), D. A. Perley 
(DARK/NBI), S. Piranomonte (INAF/OAR), A. Stamerra (INAF/OATo), G. 
Stratta (Univ, Urbino), G. Tagliaferri (INAF/OABr), L. Tomasella 
(INAF/OAPd), and D. J. Watson (DARK/NBI), report:

We observed the transient PS17yt (Chambers et al., LVC Circ. 20512) 
within the error area of the LIGO event G270580, using the Nordic 
Optical Telescope (NOT) equipped with the AlFOSC instrument. Two spectra 
by 1200 s were acquired starting on 2017 Jan 25 at 01:05 UT (4.5 days 
after the GW event), covering the wavelength range 3500-9000 AA.

Using SNID (Blondin & Tonry 2007, ApJ, 666, 1024) we confirm that the 
object is a type-Ia SN approximately 1 week before maximum, consistent 
with the findings of Castro-Tirado et al. (LVC Circ. 20521) and 
Copperwheat et al. (LVC Circ. 20526). In agreement with Copperwheat et 
al. (LVC Circ. 20526), the matching SN template indicates a redshift z = 
0.068 +- 0.004, consistent with the SDSS spectroscopic redshift of a 
nearby galaxy (z = 0.0698) first noted by Chambers et al. (LVC Circ. 20512).

We acknowledge excellent support from the NOT observing staff, in 
particular Emanuel Gafton and Thomas Augusteijn.