Swift detection of the new WZ Sge-type dwarf nova TCP J06373299-0935420
ATel #12531; K. Sokolovsky, E. Aydi, L. Chomiuk, A. Kawash, J, Strader (Michigan State University), I. Mereminskiy (Space Research Institute, Moscow), K. Mukai (NASA/GSFC)
on 26 Feb 2019; 05:21 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
Subjects: Ultra-Violet, X-ray, Cataclysmic Variable, Transient, Variables
The 10.4 mag. optical transient TCP J06373299-0935420 was
discovered on 2019-02-21.4516 UT by S. Kaneko on images obtained
with a DSLR camera + 200-mm f/2.8 lens. The ASAS-SN survey (Shappee
et al. 2014 ApJ, 788, 48, Kochanek et al. PASP, 129, 4502) observed
the source at g=12.56 +-0.1 on 2019-02-21.1564 as the transient was
rising to its peak brightness.
Swift observed TCP J06373299-0935420 for 1.8ks on 2019-02-22.065.
The XRT detected a bright X-ray source with the net count rate
of 0.28 +/-0.01 cts/s at the position, consistent with the optical
astrometry 06:37:32.99 -09:35:42.1 J2000 reported by G. Masi at
the Transient Object Followup Reports page linked below.
The source is so bright in the ultraviolet that it saturates
the UVOT W1-band image precluding accurate photometry
and astrometry.
The X-ray spectrum can be approximated by a combination of two
thermal plasma emission components having kT = 3.2 +-0.5 keV and
0.19 +-0.02 keV, respectively, affected by the absorbing column
n_H1 = (1.6 +-0.7)x10^21 cm^-2. The total Galactic column in
the direction of the source is n_H1 = 2.96x10^21 cm^-2 (Kalberla et
al. 2005 A&A, 440, 775). Multi-temperature emission is often found
in X-ray observations of cataclysmic variables (Mukai et al. 2003,
ApJ, 586, L77; Pandel et al. 2005, ApJ, 626, 396). The observed
0.3-10 keV flux is (7.9 +-0.5)x10^-12 ergs/cm^2/s. This corresponds
to the unabsorbed luminosity of 2.0x10^32 ergs/s at the distance of
370 pc to the likely counterpart Gaia DR2 3002549823466339200
located 0.2" from the transient position.
The hard X-ray emission observed by Swift/XRT, together with
the optical spectrum dominated by blue continuum with absorption
lines (reported by R. Leadbeater in vsnet-alert 23014), superhumps
observed by A. Oksanen (vsnet-alert 23016) and G. Masi (vsnet-alert
23019, 23022), taken together with the absence of previous
outbursts in the ASAS-SN lightcurve are all consistent with
TCP J06373299-0935420 being an outburst of a previously unknown
WZ Sge-type dwarf nova.
We thank the Neil Gehrels Swift Observatory team and PI,
Brad Cenko, for rapid scheduling of this ToO observation.
CBAT Transient Object Followup Reports for TCP J06373299-0935420
