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Swift UVOT UVW2 filter light curves of optical novae in M31 with outbursts in July 2007

ATel #1157; W. Pietsch (Max Planck Institut f. extraterr. Physik Garching MPE, Germany), G. Sala (MPE), F. Haberl (MPE), J. Greiner (MPE)
on 26 Jul 2007; 19:25 UT
Credential Certification: Wolfgang Pietsch (wnp@mpe.mpg.de)

Subjects: Ultra-Violet, Nova

Analysing Swift UVOT observations of the central area of M31 we detected the four known optical novae with outbursts in July 2007 in the ultraviolet UVW2 filter (180+-20nm). Light curve information is given in the table below. All novae are detected in UV after the optical maximum. The UV emission in this phase is probably related to emission lines of excited species ionized by the central source. The UV emission detected in two cases previous to the optical maximum (M31N 2007-07c; ATEL #1149, M31N 2007-07d) may correspond to the initial fireball phase, before recombination of low ionized species increases the opacity and moves the emission to the optical band.

Name           optical            Swift date
detection UVW2 mag

M31N 2007-07d 2007-Jul-25.93 2007-Jul-24.19 2007-Jul-25.52 2007-Jul-25.59 2007-Jul-26.46
ATEL #1156 [19.75(5sigma) 18.57+/-0.16 18.43+/-0.13 18.66+/-0.11

M31N 2007-07c 2007-Jul-19.01 2007-Jul-12.90 2007-Jul-18.91 2007-Jul-24.19 2007-Jul-25.56 2007-Jul-26.46
ATEL #1146 [19.63(5sigma) 17.68+/-0.05 18.71+/-0.13 18.59+/-0.09 18.57+/-0.12

M31N 2007-07b 2007-Jul-08.05 2007-Jul-12.90 2007-Jul-18.91 2007-Jul-24.19 2007-Jul-25.56 2007-Jul-26.46
ATEL #1141 [20.14(5sigma) 18.64+/-0.07 18.83+/-0.16 18.93+/-0.14 19.16+/-0.23

M31N 2007-07a 2007-Jul-05.05 2007-Jun-02.47 2007-Jul-12.90 2007-Jul-18.91
ATEL #1131 [21.17(5sigma) 19.84+/-0.15 [20.35(5sigma)

We would like to thank the Swift Team for making these observations possible, in particular N. Gehrels, the duty scientists as well as the science planners.