Swift observations of the 2018 nova eruption from V392 Persei
ATel #11905; M. J. Darnley (LJMU), K. L. Page (U. Leicester), A. P. Beardmore (U. Leicester), M. Henze (SDSU), S. Starrfield (ASU)
on 2 Aug 2018; 19:21 UT
Credential Certification: Matt Darnley (M.J.Darnley@ljmu.ac.uk)
Subjects: Optical, Ultra-Violet, X-ray, Cataclysmic Variable, Nova, Transient
The known dwarf nova V392 Per underwent its first detected classical nova eruption on or shortly before 2018 April 29 (CBAT). Subsequently, the eruption has been followed extensively in the optical from the ground (see ATel #11588, #11590, #11594, #11601, #11605, #11617, #11647, #11846 and #11872, ARAS, and Darnley & Starrfield 2018 for further details).
Here we report on the initial few observations by the Neil Gehrels Swift Observatory following the exit of V392 Per from the Swift Sun-constraint on 2018 July 20.
The Swift UVOT photometry obtained on July 20, July 26, and during two visits on July 27 provide the following measurements:
Date Filter Mag Day since t0 MJD
20 July v 14.04 81.6752 58319.1492
b 14.73 81.6873 58319.1613
u 14.21 81.6841 58319.1581
w1 14.99 81.6811 58319.1551
m2 16.81 81.6782 58319.1521
w2 15.92 81.6722 58319.1462
26 July w2 16.07 88.3132 58325.7872
w1 15.10 88.3303 58325.8043
27 July w1 15.23 88.6965 58326.1705
m2 16.96 88.6931 58326.1671
w2 16.30 88.6895 58326.1635
m2 17.03 89.4442 58326.9182
w1 15.33 89.4598 58326.9338
The large flux deficit through the Swift UVOT uvm2 filter suggests a high extinction toward the system.
During the 1.6 ks observation on Jul 20y, the Swift XRT recorded a count rate of 0.060 ± 0.006 count/sec. The X-ray spectrum could be fitted with a single temperature optically thin component, with very little column (NH): kT = 2.8 +3.1/-0.8 keV and NH < 7×1020 cm-2. However, adding a soft component does improve the fit at the ~99% confidence level, which gives: APEC kT = 0.53 +0.23/-0.14 keV, atmosphere kT > 42 eV and a much higher NH of (3.0 ± 0.5)×1022 cm-2. Alternatively, a similar fit could be obtained with 2 APEC components.
Eleven ksec of Swift XRT data were obtained across 2018 July 26 and 27. With the additional statistics from this longer exposure time, the spectrum is better fitted with three temperature components: either three APECs or two APECs and a soft model atmosphere component. Given that we might expect super-soft source emission to be modelled with an atmosphere component, we present this fit here:
APEC kT1 = 0.29 +0.10/-0.07 keV; APEC kT2 > 13 keV; atmosphere kT < 57 eV; NH = (1.9 ± 0.3)×1022 cm-2.
Swift will continue to observe the eruption with an approximately weekly cadence.
We thank the Swift PI, Brad Cenko, for approving the observations, and the Swift planning and operations teams for their ongoing support.
