[vsnet-grb-info 21083] GRB 180728A: classification of the associated SN 2018fip

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23181
SUBJECT: GRB 180728A: classification of the associated SN 2018fip
DATE:    18/08/27 23:18:21 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

J. Selsing (DAWN/NBI), L. Izzo (HETH/IAA-CSIC), A. Rossi (INAF/OAS), D. 
B. Malesani (DAWN/NBI and DARK/NBI), K. E. Heintz (Univ. Iceland and 
DAWN/NBI), P. Schady (Univ. Bath), R. L. C. Starling (Univ. Leicester), 
J. Sollerman (OKC Stockholm), G. Leloudas (DTU space), Z. Cano (BCA), J. 
P. U. Fynbo (DAWN/NBI), M. Della Valle (INAF-Naples), E. Pian 
(INAF/OAS), D. A. Kann (HETH/IAA-CSIC), D. A. Perley (LJMU), E. Palazzi 
(INAF/OAS), S. Klose (TLS Tautenburg), J. Hjorth (DARK/NBI), S. Covino 
(INAF-OAB), V. D'Elia (SSDC), N. R. Tanvir (Univ. Leicester), A. J. 
Levan (Univ. Warwick), D. Hartmann (Clemson U.), and C. Kouveliotou 
(GWU) report on behalf of a larger collaboration:

We observed again the SN associated with GRB 180728A (Starling et al., 
GCN 23046; Izzo et al., GCN 23142) with the ESO VLT UT2 equipped with 
X-shooter. Observations had a mean epoch of 2018 August 21.078 UT (23.3 
days after the GRB) and spanned the wavelength range 3200-20,900 AA.

The features previously observed in our spectroscopic sequence (Izzo et 
al., GCN 23142) have evolved and become more prominent. Using the 
Superfit tool (Howell et al. 2005, ApJ, 634, 1190; 
http://www.dahowell.com/superfit.html) we find a convincing match with 
the type-Ic SN 2002ap at a phase of 8 days after maximum. The timing is 
consistent with the epoch of our observation (21 days after the GRB 
after correcting for cosmic time dilation). We thus conclusively 
classify the SN as a broad-lined type-Ic SN. We note however that the 
velocity measured at this epoch (~10,000 km/s) is at the low end of what 
measured for GRB-associated SNe (e.g. Modjaz et al. 2016, 832, 108).

The SN associated to GRB 180728A has been dubbed SN 2018fip via the 
Transient Name Server: https://wis-tns.weizmann.ac.il/object/2018fip