Spectroscopic classification of AT 2020oio and SN 2020qef with MMT and Binospec

ATel #13970; G. Terreran, P. Blanchard, L. DeMarchi, D. Brethauer, R. Margutti, A. A. Miller (Northwestern University), M. Berton (FINCA/MRO), D. Matthews, A. Baldeschi, A. Hajela, M. C. Stroh, K. D. Alexander (Northwestern University)
on 26 Aug 2020; 18:20 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Giacomo Terreran (giacomo.terreran@northwestern.edu)

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We report the spectroscopic classification of 2 active transients, discovered by the Zwicky Transient Facility (Kulkarni 2018; ATel #11266) and by ATLAS (Tonry et al. 2016; ATel #8680).

The observations were performed with Binospec, mounted on the 6.5m MMT telescope (range 385-920 nm; resolution 0.4 nm).

 
 
Survey Name   |  IAU Name   |   Discovery MJD  | Discovery mag |    z    |   Type  |  Phase  | Notes 
ZTF20abgxlut  | AT 2020oio  |    59038.25      |     19.4      |  0.257  |  NLS1?  |    -    | (1)   
ATLAS20ulh    | SN 2020qef  |    59053.51      |     19.8      |  0.183  | SLSN-Ib | at peak | (2)   
 

(1) AT 2020oio was first detected by the ZTF public stream on 2020-06-22 (MJD 59022) with a small offset of 0.04” from the galaxy WISEA J171103.66+064410.7. The spectrum shows narrow Balmer emission lines (FWHM ~1200 km/s), He I, He II and [O III]. The reported redshift was measured from these features. Applying the distance inferred from this redshift, we obtain a current absolute magnitude of M_g ~ -21.5 mag. The spectrum resembles a SLSN-II in some ways, but the presence of [O III] and He II, together with the small offset from the nucleus, instead suggest an AGN classification. In addition, the host galaxy has a history of optical variability in the PS1 DR2 catalog (though the amplitude of variability is lower than the current transient/outburst) and has been previously classified as a likely QSO (p > 95%) by Bailer-Jones et al. (2019; MNRAS, 490, 5615). For these reasons, we tend to favour an association of AT 2020oio with nuclear activity. This is further supported by the colors reported in the WISE catalog (W1-W2= 0.859 mag; W2-W3 = 2.755 mag). The [O III] to Hb ratio (< 3), and the width of the emission lines (< 2000 km/s) are consistent with a narrow-line Seyfert 1 (NLS1) classification. However, a broad component (~5000 km/s) seems to be present in the hydrogen lines, in contrast with this latter interpretation. Further follow-up in the upcoming weeks is highly encouraged.

(2) The discovery of SN 2020qef was first reported by ATLAS on 2020-07-23 (MJD 59053), however the object has been detected by the ZTF public stream (internal name ZTF20ablkuio) since at least 2020-07-13 (MJD 59043). The object has been rising for over a month, and is now peaking at an absolute magnitude of -20.16 mag (given the inferred redshift), in the luminosity range of superluminous supernovae (SLSNe). The redshift is measured from the narrow features from the host. The spectrum shows similarities with the SLSN-I 2010md, which Yan et al. (2020; arXiv:2006.13758) classified as a SLSN-Ib, due the presence of broad He I absorption. Similar features are also present in SN 2020qef. From the minimum of the absorption feature of He I 5876 we infer a velocity of ~9500 km/s of the bulk material.