Swift/UVOT constrains outburst of Nova M31 2015-02a to well before optical detection
ATel #7104; Corentin Delvaux, Jochen Greiner, Wolfgang Pietsch (all MPE Garching)
on 18 Feb 2015; 20:24 UT
Credential Certification: J. Greiner (firstname.lastname@example.org)
Subjects: Ultra-Violet, Nova
Based on monitoring observations of the central region of the Andromeda Galaxy M31
with the Ultraviolet/Optical Telescope (UVOT) on board the Swift
satellite from 2015-01-17 to 2015-02-18, we derived the UV light curve (UVW1
filter, 181-321 nm) for the recently discovered nova M31 2015-02a (ATel
The following table gives the observation ID, the exposure time, the date
and start time of the observations, UVW1 magnitudes (Vega system) and
2-sigma statistical uncertainties for M31 2015-02a.
ObsID Exp Date Time Magnitude
[ks] (MJD) (Vega)
00031283028 4.0 2015-01-17 57039.46 <21.01
00031283029 3.9 2015-01-25 57047.31 20.19±0.52
00031283030 4.1 2015-02-02 57055.24 18.90±0.16
00031283031 3.2 2015-02-10 57063.55 18.87±0.17
00031283032 3.7 2015-02-14 57067.48 19.88±0.40
00031283033 1.1 2015-02-18 57071.28 >19.50
The systematic uncertainty of these magnitudes is estimated to be 0.03 mag.
M31 2015-02a has been detected by Swift/UVOT already 20 days before the
first optical detection at Feb 13.75625 UT as reported in ATel #7065
. The upper
limit on 2015-01-17 constrains the outburst time to Jan 18-24. The nova
seems to have reached its maximum in the UVW1 filter around 2015-02-10 and
appears to have faded since then.
We encourage spectroscopic observations of M31 2015-02a.
We would like to thank the Swift Team for making these observations
possible, in particular N. Gehrels, the duty scientists, as well as the