Classification of ZTF18actaqdw as a tidal disruption flare
ATel #12543; S. Frederick (UMd), S. Gezari (UMd), S. B. Cenko (GSFC), S. van Velzen (UMd and NYU), T. Hung (UCSC), L. Yan (Caltech), S. R. Kulkarni (Caltech)
on 1 Mar 2019; 22:54 UT
Credential Certification: Suvi Gezari (suvi@astro.umd.edu)
Subjects: Optical, Ultra-Violet, X-ray, Tidal Disruption Event
We report the discovery of ZTF18actaqdw in ZTF imaging data at a position of:
RA=04:09:37.65 Dec=+73:53:41.7 (J2000)
The transient was found near the center of the galaxy PSO J062.4068+73.8948.
The first detection was obtained on 2018-Nov-28, while the source was on the rise. The source is slowly fading with a constant blue color (g-r=-0.1 mag) from its peak at r=19.5 mag 2 months ago, and has now faded to r=20.1 mag. Follow-up spectroscopy with DBSP on the Palomar P200 telescope obtained 2019-Jan-07 showed a blue continuum with broad Halpha line emission and tentative detection of broad He II 4686 line emission. We obtained a spectrum with the Discovery Channel Telescope (DCT) DeVeny spectrograph on 2019-03-01 that confirms the detection of broad Halpha and He II 4686. We determine a redshift of z~0.138 from narrow stellar absorption features from the host galaxy.
Observations with the Neil Gehrels Swift telescope, obtained on 2019-Feb-27, show the transient is detected in the UV 2 months after peak. We measure UVM2=20.23 +/- 0.16 (AB), implying a UV-optical color: UVM2-r ~ +0.1 mag. The source is not detected in XRT (3-sigma upper limit on the X-ray count rate is 9.3e-3 counts/s).
The TDE classification is based on the location in the center of the host galaxy (offset 0.09 +/- 0.23 arcsec with respect to the coordinates of the host), a blue and constant optical color post peak, the detection of broad emission lines in the optical spectrum, and the UV detection with Swift/UVOT.
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. These results made use of the Discovery Channel Telescope at Lowell Observatory. Lowell is a private, non-profit institution dedicated to astrophysical research and public appreciation of astronomy and operates the DCT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University and Yale University. The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale.
