Recent Evolution of PSN J14021678+5426205 in M101 Using LBT

ATel #7069; J. Gerke, S. M. Adams, C. S. Kochanek, K. Z. Stanek (Ohio State)
on 14 Feb 2015; 20:19 UT
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

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PSN J14021678+5426205 in M101 (see also Atel #7063) has been observed using UBVR filters for seven years (22 epochs) as part of the Large Binocular Telescope (LBT) search for failed supernovae (Gerke et al. 2014). Prior to mid-2012 the star was variable with mean magnitudes of U=21.33+/-0.19, B=21.30+/-0.19, V=20.97+/-0.17, and R=20.69+/-0.17 Afterwards, it steadily brightened, reaching U=20.43+/-0.02, B=20.02+/-0.04, V=19.78+/-0.03, and R=19.59+/-0.03 in mid-2014. When next observed on 2015-01-19, it had dramatically brightened in V (18.80+/-0.02) and R (18.23+/-0.02), changed little at B (20.20+/-0.02) and faded at U (21.04+/-0.02). The UBVR spectral energy distributions are well modeled (using Kurucz model atmospheres with no extinction) as:

 
Date           log(L/Lsun)  T (K) 
2008-03-10        5.30      7200 
2012-06-12        5.32      7500 
2014-06/07        5.66      7900 
2015-01-19        6.24      4400 

Thus, the current brightening is in part a true increase in luminosity, but the drop in effective temperature is significantly enhancing the flux observed in standard transient search bands (V/R).