Further Spitzer Observations of the 2015 M31 Stellar Merger

ATel #7485; S. Adams (OSU), C. S. Kochanek (OSU), Subo Dong (KIAA-PKU), R. M Wagner (LBTO)
on 8 May 2015; 22:38 UT
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Credential Certification: Subo Dong (dongsubo@pku.edu.cn)

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We report further Spitzer observations of the 2015 M31 stellar merger ("Nova" M31N 2015-01a = MASTER J004207.99+405501.1, Shumkov et al. 2015) on April 18.65 and 23.69 when the source was not otherwise observable from Earth.

We find preliminary Vega aperture magnitudes of
-----Date------------[3.6]---------------[4.5]-----------log(L/Lsun)-----
April 06.87 12.79+/-0.07 12.80+/-0.09         5.45
April 13.12 12.82+/-0.07 12.91+/-0.09         5.43
April 18.65 12.89+/-0.07 13.01+/-0.10         5.39
April 23.69 12.99+/-0.08 13.15+/-0.10         5.34
The luminosities are estimated by fitting a fixed T=3500K Castelli & Kurucz (2004) stellar atmosphere model to the Spitzer data.

Figure 1 shows the recent evolution of the SED assuming an M31 distance of 0.8 Mpc (Stanek & Garnavich 1998) and (only) Galactic extinction of E(B-V)=0.05 mag, adding recent optical (Pessev et al. 2015, Williams et al. 2015) and near-IR (Srivastava et al. 2015) data.

We thank Director B.T. Soifer for approving this Spitzer Director's Discretionary time program and the Spitzer team for implementing these observations so rapidly.