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Classification of AT2020ddv as a tidal disruption event

ATel #13655; S. Gezari (UMd), S. van Velzen (UMd and NYU), D. Goldstein (Caltech), S. B. Cenko (GSFC), S. Frederick (UMd), C. Ward (UMd), E. Hammerstein (UMd), T. Hung (UCSC), M. Graham (Caltech), S. R. Kulkarni (Caltech)
on 22 Apr 2020; 19:20 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Suvi Gezari (suvi@astro.umd.edu)

Subjects: Optical, Ultra-Violet, X-ray, Tidal Disruption Event

We report follow-up observations of the nuclear transient, AT2020ddv, in the center of galaxy SDSS J095833.41+465440.4, discovered by ATLAS on UT 2020 Feb 23 as ATLAS20gee. The first detection of AT2020ddv by the ZTF MSIP Survey was made on UT 2020 Jan 25 as ZTF20aamqmfk. The latest ZTF detection was on UT 2020 April 15 with g=20.00 +\- 0.19 mag, 39 days after the peak on UT 2020 Mar 07 with g=19.25 +/- 0.21 mag. Due to the persistent blue color (g-r ~ -0.3 mag) of this nuclear transient and its relatively slow rise to peak, we flagged the transient as a photometric tidal disruption event (TDE) candidate for further follow-up observations.

We triggered a Spectral Energy Distribution Machine (SEDM) (range 350-950nm, spectral resolution R~100) mounted on the Palomar 60-in (P60) telescope (Blagorodnova et al. 2018, PASP, 130, 5003) spectrum on 2020 Feb 26 which detected a blue continuum, and a follow-up spectrum from the Palomar 200-in (P200) DBSP spectrograph (R~1000) on 2020 Feb 27, which measured the host galaxy redshift to be z=0.152 from Ca II H,K stellar absorption features.

Here we also report Neil Gehrels Swift telescope observations on 2020 April 22 (PI: Gezari) that demonstrate that the nuclear transient is UV bright (uvw2=18.72 +/- 0.11 mag), and is detected in the soft X-rays (< 1.5 keV) with 0.005 +/- 0.001 cts/sec, corresponding to an X-ray flux of 1e-13 erg/cm^2/s, or an X-ray luminosity of ~6e42 ergs/s for a luminosity distance of 723 Mpc.

We classify this source as a tidal disruption event (TDE) based on the location in the center of the host galaxy, its persistent blue optical colors and spectrum, the extremely blue UV-optical color of the transient (uvw2 - g ~ -1.3 mag) over a month after peak, the detection in the soft X-rays, and the lack of spectroscopic features associated with a supernova or AGN. We have triggered XMM, and more Swift monitoring observations. Higher spectral resolution optical spectra and multi-band imaging are encouraged.

ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATel #11266), and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW,USA; DESY, Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. Alert distribution service provided by DIRAC@UW. Alert filtering is being undertaken by the GROWTH marshal system, supported by NSF PIRE grant 1545949.