Photometry of Gaia17btl/AT2017fmd

ATel #10578; R. Konyves-Toth, J. Vinko (Konkoly Obs)
on 17 Jul 2017; 19:14 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)

Subjects: Optical, Supernovae, Transient

We report photometric observations of AT2017fmd / Gaia17btl (R.A.= 09:24:09.36, Dec= +79:24:19.91), a transient discovered by Gaia at 17.19 magnitude on 2017-07-15. Our data were taken with the 60/90 cm Schmidt telescope through Bessell B,V,R,I filters at Konkoly Observatory, Piszkesteto, Hungary on 2017 July 16.03 and 17.03 UT.

The transient is clearly present on all frames close to the presumed host galaxy 2MASX J09240789+7924200. Photometry on the transient and several other local comparison stars was made via PSF-fitting in IRAF/daophot. The magnitudes of the local comparison stars were determined from their PS1-photometry after transforming the PS1 gri magnitudes to the Johnson-Cousins BVRI system.

The following Vega-magnitudes have been measured for Gaia17btl/AT2017fmd:

 
   Date       JD        B      eB    V      eV     R      eR     I    eI 
2017-07-16 2457950.53 17.098 0.022 16.908 0.041 16.699 0.035 16.759 0.076 
2017-07-17 2457951.53 17.076 0.017 16.889 0.032 16.750 0.037 16.798 0.067 

Since the redshift of the host galaxy is unknown, we assumed that the transient is in between z=0 and z=0.1. After correcting for Milky Way extinction, we fitted blackbodies to the Spectral Energy Distribution (SED) of the transient. The fitting resulted in temperatures between 10,000 and 11,000 K depending on the assumed redshift. This result is consistent with the transient being a pre-maximum supernova in its early photospheric phase.

We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team (http://gsaweb.ast.cam.ac.uk/alerts).