NuSTAR detection of Nova Reticuli 2020 = MGAB-V207
ATel #13900; K. V. Sokolovsky, E. Aydi, L. Chomiuk, A. Kawash, J. Strader (MSU), K. Mukai (NASA/GSFC), K.-L. Li (NTHU), A. Babul, A. Derdzinski, B. D. Metzger, J. L. Sokoloski, E. Steinberg (Columbia), I. Vurm (Tartu), J. D. Linford, A. J. Mioduszewski (NRAO), M. P. Rupen (NRC), R. Lopes de Oliveira (U Sergipe/Obs. Nacional Brazil), K. L. Page, A. Beardmore (U Leicester), M. Orio (UoW, INAF)
on 28 Jul 2020; 04:59 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
The classical nova explosion in the previously known cataclysmic
variable MGAB-V207 was reported by R. H. McNaught on
2020-07-15.590 UT (CBET #4811). Pre-discovery all-sky camera images
by M. A. Phillips show the nova peaking on 2020-07-11.76 at 3.7mag
(CBET #4812). Considering the latest non-detection by
M. A. Phillips on 2020-07-07.79 (>5.5mag), we take
the pre-discovery detection by ASAS-SN (Shappee et al. 2014, ApJ,
788, 48; Kochanek et al. 2017, PASP, 129, 104502) on 2020-07-08.171
as the estimate of the eruption date. The nova was
spectroscopically confirmed (ATel #13867) and classified as a He/N
type (ATel #13874). GeV emission from the nova was detected
by Fermi/LAT (ATel #13868).
We observed MGAB-V207 with NuSTAR starting on 2020-07-17.98 (ten
days after eruption) for a total exposure of 67ks. The nova is
detected with SNR~11 at both focal plane modules. The 3.5-78 keV
count rate is gradually increasing from 0.01 to 0.02 cts/s over
the duration of the NuSTAR observation. The NuSTAR spectrum can be
fit by heavily absorbed optically thin thermal plasma emission
(APEC) with kT = 6.5 +/-1.5 keV. The unabsorbed 3.5-78 keV flux
is 1.1x10^-12 erg/cm^2/s. To obtain a good fit, we had to allow for
non-solar abundances of N, O and/or Fe for both absorber and
emitter. The choice of the abundances dramatically affects
the absorbing column (that is normalized to Hydrogen). The same
situation was described earlier for V906 Car
by Sokolovsky et al. (2020, arXiv:2007.07885).
MGAB-V207 was also observed with Swift for a total exposure
of 7.9ks between 2020-07-16 (8.5 days post-eruption) and
2020-07-21. Swift/XRT operating in the windowed timing mode (to
avoid optical loading) detected no X-ray source with the count rate
above 0.05 cts/s (0.3-10 keV). Swift/UVOT had to be blocked due to
the high optical brightness of the nova.
The X-ray emission observed with NuSTAR is likely produced by
plasma heated by shocks deep within the expanding nova shell, which
also absorbs soft X-rays. As the ejecta clears, the nova should
become detectable for Swift/XRT. We encourage further
multiwavelength observations of this nova.
We thank the teams of NuSTAR and Neil Gehrels Swift Observatory
for rapid scheduling these observations.
ASAS-SN optical lightcurve of MGAB-V207
