Classification of AT2018hco (ATLAS18way/ZTF18abxftqm) as a tidal disruption flare
ATel #12263; S. van Velzen (UMd and NYU), S. Gezari (UMd), S. B. Cenko (GSFC), A. Ho, Y. Yao, S. R. Kulkarni, K. De, M. M. Kasliwal, C. Fremling, M. J. Graham, L. Yan (Caltech), J. C. A. Miller-Jones (Curtin), A. Horesh (Hebrew University)
on 4 Dec 2018; 13:05 UT
Credential Certification: Sjoert van Velzen (sjoert@astro.umd.edu)
Subjects: Radio, Infra-Red, Optical, Ultra-Violet, X-ray, AGN, Supernovae, Transient, Tidal Disruption Event
The source AT2018hco was discovered by ATLAS on 2018-Oct-04 and reported to TNS on 2018-Oct-05. The source was also detected on the rise in ZTF partnership data, with a first detection on 2018-Sep-18. The fading part of the light curve, which is part of public ZTF MSIP data and reported to TNS on 2018-Nov-04, shows a blue and constant color (g-r ~ -0.1).
We report the classification of AT2018hco based on Swift/UVOT and ground-based spectroscopic follow-up observations. Our SEDM (Blagorodnova, PASP, 130, 2018) spectrum, obtained 2018-Oct-26, showed a blue continuum with no significant emission lines. Follow-up spectroscopy with Keck/LRIS, obtained 2018-Dec-1, showed broad Halpha emission and broad He I (5876) emission. From Ca H, and K absorption we determine a redshift of z~0.09.
We requested Swift observations on 2018-Nov-15. These were obtained on 2018-Nov-29 and showed the transient is UV-bright. We measure UVW2=18.67 +/- 0.07 (AB), implying a blue UV-optical color: UVW2-g ~ 0. The source is not detected in XRT.
The TDE classification is based on the location in the center of the host galaxy (offset 0.1 +/- 0.1 arcsec), blue and constant color post peak, the detection of broad H and He in the optical spectrum, and finally the UV detection in Swift/UVOT. The source shows no prior variability in ZTF, PTF, or CRTS data. The W1-W2 color, based on unWISE forced photometry (Lang 2014 arXiv:1410.7397), is 0.07 +/- 0.09, indicating a quiescent host galaxy.
Follow-up with VLA, AMI, XMM, and Spitzer has been triggered. We encourage further follow-up of this source, in particular spectroscopic monitoring and multi-band imaging.
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.