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VLT/FORS2 spectroscopic classification of nuclear transient OGLE17hil as normal Supernova Type Ia

ATel #10860; N. Ihanec (University of Nova Gorica), M. Gromadzki, L. Wyrzykowski, P. Iwanek, A. Udalski (Warsaw University Astronomical Observatory)
on 17 Oct 2017; 13:06 UT
Credential Certification: Lukasz Wyrzykowski (wyrzykow@astrouw.edu.pl)

Subjects: Optical, Supernovae, Transient

We report on the spectroscopic classification of a nuclear transient discovered by the OGLE-IV Transient Search System on 2017-10-13 (http://ogle.astrouw.edu.pl/ogle4/transients/ Wyrzykowski et al. 2014, Acta Astronomica 64, 197). The spectrum was obtained on 2017-10-14, using the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) on the Very Large Telescope (VLT). The spectroscopic classification was done using SNID code (Blondin & Tonry 2007, ApJ, 666, 1024) and it was matched to SN Type Ia-norm at about 7 days past maximum. We estimated redshift z=0.0612 base on host lines: H-alpha, [N II] SII, [O II] and [O III] in emission and Hdelta, Na and CaII H&K in absorption. OGLE photometric measurements do not constrain the maximum date, however at the moment of detection the observed magnitude at this redshift corresponds to the absolute magnitude of approximately -18.7 mag which is consistent with SN Type Ia.

We note that the archival OGLE-IV photometry of this host galaxy reveals there was another (previously undetected) supernova near its nucleus in October 2011. Its light curve resembles that of SN Ia, with the secondary bump visible in the I-band.

Name | IAU name | RA (J2000) | Dec (J2000) | Disc. Date | Disc. Mag | Obs. Date | z | Host | Type | Notes
OGLE17hil | 2017hil | 05:57:30.04 | -62:28:44.60 | 2017-10-13 | 18.56 | 2017-10-13 | 0.0612 | OGLE-GAL-LMC605.05-897.374-1129.222 | SN Ia-norm | +7 days

The classification spectrum will be available on the IAU's Transient Name Server (TNS). The observations were carried under ToO programme 0100.B-0503(A), PI: M. Gromadzki. We thank ESO/VLT staff for their support.

Finding chart and light curve is available here