Optical and mid-infrared photometry of the luminous red nova 2015 in M101

ATel #8891; T. Szalai (U Szeged, Hungary), J. Vinko (Konkoly Obs. / U Szeged), K. Sarneczky (Konkoly Obs.)
on 1 Apr 2016; 08:05 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)

Tweet

Inspired by ATel #7082, #8599 and #8848, we checked the Spitzer Heritage Archive (SHA) in order to find the remnant of the luminous red nova PSN J14021678+5426205 in M101 (ATel #7069, #7070, #7072, #7079, #7082, #7206) on archive mid-infrared images. Although the galaxy M101 has been observed several times since the appearance of the nova, the transient itself was captured only at two epochs, 2015 June 18.82 and July 17.79 UT, in Channel 1 (3.6 micron) of Spitzer/IRAC (PID 11063, PI M. Kasliwal). The remnant of the nova is bright on both images, it appears slightly brighter on the later frame. We determined the following mid-IR fluxes and Vega magnitudes of the source by applying simple aperture photometry on the Spitzer images:

 
Date         MJD       F_nu (uJy)    Mag 
2015-06-18   57191.8   443.1(32.6)   14.50(0.08) 
2015-07-17   57220.8   502.1(37.0)   14.37(0.08) 

The 3.6 micron image obtained in June can be seen here: http://titan.physx.u-szeged.hu/~szaszi/m101_rednova_150618_ch1.jpg We compared our mid-IR photometry with nearly contemporaneous BVRI measurements obtained with the 0.6/0.9m Schmidt-telescope at the Piszkesteto Mountain Station of Konkoly Observatory, Hungary. We applied PSF photometry using IRAF/daophot and obtained the following magnitudes for the transient:

 
Date         MJD       B            V           R            I 
2015-06-12   57185.9   21.81(0.35)  20.44(0.15) 19.51(0.07)  18.22(0.05) 
2015-07-20   57223.7   --           --          20.08(0.44)  18.83(0.48) 

We also calculated the combined SED of the nova from the observed optical and mid-IR fluxes. After fitting a simple blackbody (with T_eff = 3000 K) to the BVRI data, the transient shows significant excess flux at 3.6 micron on both epochs. This might suggest either local dust formation or the heating of some pre-existing dust in the environment of the nova. A plot of the SED calculated from the observations obtained in 2015 June can be accessed here: http://titan.physx.u-szeged.hu/~szaszi/M101_rednova2015_1506_sed.jpg As noted in ATel #8848, the object may still be visible in the mid-IR, thus, further observations in this wavelength range are encouraged.