AstroNote 2019-33

We draw attention to the unusual lightcurve of AT2019fdr from ATLAS survey data combined with the ZTF public alert stream (Lasair : https://lasair.roe.ac.uk/object/ZTF19aatubsj/, Smith et al.  RNAAS, 3,26 2019), and encourage rapid spectroscopic follow-up. 

AT2019fdr was discovered by ZTF on 2019-05-03 (TNS Astronomical Transient Report No. 34906) in the host galaxy  SDSS J170906.84+265120.5; (an r=19.26 mag galaxy with photoZ=0.231±0.042). It was also independently detected by Gaia and by ATLAS (7 and 21 days later respectively). 

We applied forced photometry (on the co-added 4 x 30sec exposures) and find a 40 day rise time and a bump in the rising lightcurve. The transient is coincidenct with the galaxy core and is now at o = 18.5 +/- 0.1 mag. The ZTF g-r colour indicates it is still relatively blue. 

The combination of the photometric redshift of the host, long rise time, persistent blue colour and bump suggests it could be an unusual very luminous transient and we encourage spectroscopic follow-up to determine the nature of this unusual object. The bump feature we see in ATLAS lies in a coverage gap of ZTF  https://lasair.roe.ac.uk/object/ZTF19aatubsj/ although the ZTF lightcurve is compatible with the feature.  

A plot of the forced ATLAS lightcurve is available below (with the flux in micro-Janskys) along with a finder from Pan-STARRS 3Pi Survey, data. 

Deatails of the ATLAS transient search are in Smith et al. 2019 (AstroNote 2019-17) and the ATLAS system is described in (Tonry et al. 2018, PASP, 13, 064505). This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area.  The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, and the Space Telescope Science Institute. 

Lasair is supported by the UKRI Science and Technology Facilities Council and is a collaboration between the University of Edinburgh (grant ST/N002512/1) and Queen’s University Belfast (grant ST/N002520/1) within the LSST:UKScience Consortium. ZTF is supported by National Science Foundation grant AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. This research has made use of ``Aladin sky atlas'' developed at CDS, Strasbourg Observatory, France 2000A\&AS..143...33B and 2014ASPC..485..277B.