Swift observation of Nova Vulpeculae 2024 (V615 Vul) at optical peak
ATel #16751; Kirill Sokolovsky (UIUC), Elias Aydi, Laura Chomiuk, Peter Craig, Isabella Molina (MSU), Jennifer Sokoloski (Columbia), Justin Linford, Montana Williams (NRAO), Koji Mukai (NASA/GSFC), Stanislav Korotkiy (Astroverty, Ka-Dar), Nikolay Potapov
on 6 Aug 2024; 05:12 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
Subjects: Optical, Ultra-Violet, X-ray, Nova
Referred to by ATel #: 16788
The eruption of Nova Vulpeculae 2024 (V615 Vul,
PNV J19430751+2100204) was discovered on 2024-07-29.8317 UT by
the New Milky Way survey operating a wide-field camera
(135mm f/2.0 telephoto lens + unfiltered ST-8300M CCD) at
Nizhnii Arkhyz, Karachay-Cherkessia, Russia (Sokolovsky et al.
2014, ASPC, 490, 395). The transient was promptly spectroscopically
confirmed as as a classical nova (ATel #16743, #16746, CBET #5423).
Pre-eruption imaging by Tadashi Kojima showed the nova was fainter
than magnitude 14.0 on 2024-07-29.513. The nova peaked at V=9.6
around 2024-07-31.0 and declined by two magnitudes in ~4.5 days,
according to photometry reported to the AAVSO.
Swift observed Nova Vulpeculae 2024 for 1.8ks on 2024-07-30.87.
No X-ray source was detected by Swift/XRT at the nova position with
an upper limit of 0.004 cts/s. Assuming kT=2 keV thermal plasma
emission and the line-of-sight hydrogen column density
of 7.89x10^21 cm^-2 (Kalberla et al. 2005 A&A, 440, 775),
this corresponds to an unabsorbed 0.3-10.0 keV flux limit
of 3x10^-13 ergs/cm^2/s. The nova is clearly visible at
the Swift/UVOT images having ultraviolet UVW2 band magnitude
UVW2=15.07 +/-0.02 (Vega system).
The 0.3-10.0 keV X-ray non-detection near optical peak is
consistent with previous observations of classical (dwarf donor)
novae, where X-rays are absent between the initial fireball phase
(Konig et al. 2022, Nature, 605, 248) and the emergence of
shock-heated plasma emission days to weeks later (Gordon et al.
2021, ApJ, 910, 134). This behavior contrasts with novae embedded
in giant donor winds, which often show shock-powered X-rays
detectable by Swift/XRT near optical peak (e.g. Page et al. 2022,
MNRAS, 514, 1557).
Nova Vulpeculae 2024 erupted within TESS Sector 81 that is being
observed from July 15 through August 10. Once downlinked to
the ground, TESS full-frame images may provide an exceptionally
detailed optical lightcurve of the event. Previous TESS
observations of nova eruptions were reported by Luna et al.
(arXiv:2310.02220) and Sokolovsky et al. (arXiv:2311.04903).
Optical spectroscopy, multi-color photometry, and multi-wavelength
observations are encouraged to maximize this observing opportunity.
