A Double-peaked Changing-look AGN with a Large Amplitude Flare in the UV/optical and X-rays
ATel #13460; S. Frederick (UMd), M. J. Graham (Caltech), S. Gezari (UMd), S. van Velzen (NYU & UMd), C. Ward (UMd)
on 8 Feb 2020; 02:16 UT
Credential Certification: Sara Frederick (sfreder2@umd.edu)
Subjects: Optical, Ultra-Violet, X-ray, Request for Observations, AGN, Transient
The Zwicky Transient Facility (ZTF) survey has discovered a changing-look AGN (AT2019aabw/ZTF19aagwzod, RA=04:28:38.79 Dec=-00:00:39.7 (J2000), z=0.0713) undergoing a smooth, large amplitude flare of ~1.5 mag.
This source was first detected as a nuclear transient (within <0.5" of its host galaxy) using difference imaging photometry on 2019 Jan 31 (TNS Report No. 61285), after which it displayed stochastic variability typical of an AGN (at the <0.5 mag level). On 2019 Dec 16, ZTF caught the smooth, rapid, large-amplitude rise of the nuclear transient from g=19.6 mag to g=17.9 mag in 34 days. This optical flaring is extreme compared to the low level variability previously observed in this AGN.
We classify the source as a changing-look AGN from our 2020 Jan 23 spectrum taken with the LRIS spectrograph on the Keck I telescope, based on its broad H-alpha and H-beta emission lines with both blue and red peaks with velocities of +/- 2000 km/s. A 6dF Galaxy Survey spectrum of this source (target ID g0428388-000040) showed it was a Type 1.9 AGN (i.e. with a broad component visible in H-alpha but not in H-beta) in 2005. However, it is now a double peaked emitter with a strong blue continuum.
We obtained a Target of Opportunity observation with the Neil Gehrels Swift telescope on 2020 Feb 06 showing that it is UV- and X-ray bright, with UVM2=17.86 +/- 0.08 mag (compared to the archival GALEX NUV=20.0 mag) and a 2-10 keV flux of (2.9 +/- 0.4)e-12 erg/s/cm^2 (compared to an archival ROSAT 2-sigma upper limit of <1.6e-13 erg/s/cm^2), indicating this emission is associated with the transient. The X-ray spectrum is consistent with an AGN, with power law spectral index of 1.8 +/- 0.1. We are continuing Swift monitoring of this source with a 3 day cadence. All magnitudes are given in the AB system.
We encourage spectroscopic monitoring observations of this source, to see how it evolves in response to the large amplitude flare in the X-ray and UV/optical continuum.
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 database searches are done by AMPEL (Nordin et al. 2019). Alert filtering and follow-up co-ordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019), supported by NSF PIRE grant 1545949.