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Spectroscopic Classifications of Optical Transients with Mayall/KOSMOS

ATel #10549; M. R. Siebert, Y.-C. Pan, C. D. Kilpatrick, R. J. Foley (UCSC)
on 1 Jul 2017; 11:52 UT
Credential Certification: Charles Kilpatrick (cdkilpat@ucsc.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 10554, 10556

We report the following classifications of optical transients from spectroscopic observations with KOSMOS on the KPNO Mayall 4-m telescope. Targets were supplied by the Asteroid Terrestrial-impact Last Alert System (ATLAS; ATel #8680), the Pan-STARRS Survey for Transients (PSST) and Gaia. Observations were made on 2017 June 30 UT. Classifications were performed with SNID (Blondin & Tonry, 2007, ApJ, 666, 1024).

 
Name       | IAU Name  | RA (J2000)  | Dec (J2000)  | z     | Type  | Phase| Notes
ATLAS17hkr | AT2017ewi | 15:59:23.11 | +53:16:35.31 | 0.043 | II | | Gaia17bpn | AT2017exh | 22:58:27.30 | -00:16:00.52 | 0.054 | Ia | +18d | ATLAS17hnm | AT2017eye | 14:37:45.11 | +21:20:29.02 | 0.031 | Ic | -2d | (1) Gaia17bpt | AT2017eym | 00:27:34.00 | -12:32:02.76 | 0.059 | Ia | +3d | (2) PS17dlw | AT2017eyz | 22:04:07.00 | +00:52:52.78 | 0.164 | Ia | -1d | PS17dlv | AT2017eza | 21:54:18.70 | -03:00:02.41 | 0.083 | II | | (3) ATLAS17hpt | AT2017faf | 17:34:39.98 | +26:18:22.00 | 0.029 | SLSN-I| | (4)

Notes: When the redshift is given to 2 decimal places, it is derived from the SN spectrum. Otherwise, the redshift is determined from the host galaxy.

(1) Good match to SN 2004aw at -2 days. The SN has strong C II absorption.
(2) We measure a Si II 6355 velocity of -10,300 km/s.
(3) We measure a H alpha velocity of -8,100 km/s.
(4) The spectrum is relatively featureless redward of rest-frame 4600 A, but has two strong, distinct features at ~4170 and ~4420 A. We identify these features as O II absorption present in pre-maximum SLSN-I spectra (e.g., Quimby et al., 2011, Nature, 474, 487). We find a reasonable match to SN 2005ap and especially SN 2010gx about a week before maximum. The continuum of AT2017faf is redder than SN 2005ap and 2010gx at that phase, consistent with an additional reddening of E(B-V) ~ 0.45 mag. From an acquisition image, we measure an r-band magnitude of 17.1 +/- 0.1 (indicating that it has risen since discovery), which corresponds to Mr ~ -18.7 mag if there is no host-galaxy extinction. If we correct for E(B-V) = 0.45 mag, AT2017faf would have Mr ~ -19.8 mag. We conclude that AT2017faf is a Type I SLSN. At z = 0.029, AT2017faf is the lowest-redshift SLSN-I yet discovered.