Swift observation of the LMC nova candidate MASTER OT J051032.58-692130.4
ATel #9048; Kirill Sokolovsky (IAASARS NOA/SAI MSU/ASC Lebedev)
on 13 May 2016; 16:47 UT
Credential Certification: Kirill Sokolovsky (firstname.lastname@example.org)
Subjects: Optical, Ultra-Violet, X-ray, Nova, Star, Transient, Variables
The optical transient MASTER OT J051032.58-692130.4
was discovered by MASTER-SAAO on 2016-05-10.72797 (ATel #9039).
Pre-discovery images by OGLE-IV indicate that the outburst occurred
some time between 2016-04-21.00403 and 28.97626 (ATel #9040).
The object was observed by Swift for 2ks starting
on 2016-05-12.07560 UT.
The transient is clearly visible in Swift/UVOT images at
the position 05:10:32.58 -69:21:30.5 +/-0.1" J2000 measured with
respect to UCAC4 stars within the UVOT field of view. The object's
observed Vega magnitudes in three ultraviolet bands are white
JD(TT)2457520.59876 W1 11.52 +/-0.02
JD(TT)2457520.59166 M2 11.68 +/-0.02
JD(TT)2457520.58271 W2 11.76 +/-0.02
corresponding to a T~10^4 K black body after correcting for
the Galactic extinction.
No X-ray source is detected by Swift/XRT at the position of the
optical/ultraviolet transient above the background level of
2.6e-03 cts/s. Assuming kT=5 keV thermal bremsstrahlung
emission and absorption with HI column density of 2e21 cm^-2,
this corresponds to a 0.3-10 keV flux limit
of 1.2e-13 ergs/cm^2/s.
The intriguing feature of the transient is its suggested OGLE-IV
progenitor reportedly showing a 2.65 d eclipse-like
periodicity (ATel #9040). Such period is unusually long for
a classical nova system and makes one suspect a nova in a symbiotic
binary or even a V1309 Sco-like stellar merger event.
An object LMC_SC10_20872 offset by 0.4" from the reported OGLE-IV
position and 0.6" from the UVOT position is present in
OGLE-II photometric database, but a period search reveals
no obvious periodicity in its lightcurve. The relation
between the OGLE-II and OGLE-IV objects is unclear as this is
a crowded field. Apart from the suggested eclipsing binary
progenitor, observed properties of the transient so far are
consistent with a classical nova outburst.
We thank Neil Gehrels and the Swift team for rapid
approval and scheduling of this ToO observation.
Finding chart and additional plots