NuSTAR upper limit on X-ray emission of nova V462 Lupi
ATel #17281; Kirill Sokolovsky (UIUC), Elias Aydi (TTU), Laura Chomiuk, Peter Craig, Isabella Molina (MSU), Jennifer Sokoloski (Columbia), Justin Linford (NRAO), Koji Mukai (NASA/GSFC)
on 9 Jul 2025; 19:30 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
Nova Lupi 2025, also known as V462 Lup (CBET #5570), AT 2025nlr and
ASASSN-25cm, was discovered by the ASAS-SN survey (Shappee et al.
2014, ApJ, 788, 48; Kochanek et al.2017, PASP, 129, 104502) on
2025-06-12.870 UTC and reported via the Transient Name Server
(Stanek et al. 2025, TNS Astronomical Transient Report No. 258408).
It was spectroscopically confirmed as a classical nova
(ATel #17228). Pre-discovery detections and improved astrometry
with GOTO-South telescope were reported in ATel #17237. An orbital
period of 1.797 hours was suggested on the basis of pre-eruption
TESS photometry (ATel #17240). The nova was detected at E>100 MeV
by Fermi-LAT (ATel #17249) and upper limits on its neutrino flux
were derived with IceCube (ATel #17266).
V462 Lupi was observed with NuSTAR from 2025-06-30.038 to
2025-07-01.017 for a total exposure of 45 ks. No X-ray source is
found at the nova position with a combined two-module count rate
upper limit of 0.0013 cts/s. Assuming kT= 4 keV thermal plasma
emission (as observed in V1674 Her; Sokolovsky et al. 2023, MNRAS,
521, 5453) and the total line of sight HI column density
of 7.1x10^20 cm^-2 (Kalberla et al. 2005 A&A, 440, 775;
https://www.astro.uni-bonn.de/hisurvey/AllSky_profiles/index.php )
this corresponds to a galactic-absorption-corrected 3.0-78 keV flux
limit of 5x10^-14 ergs/cm^2/s. Extrapolated down to the Swift/XRT
0.3-10.0 keV band, the NuSTAR upper limit translates
to 1x10^-13 ergs/cm^2/s, or XRT PC mode count rate of 0.002 cts/s.
Given the Fermi-LAT detection, we speculate that a shock is present
within the ejecta of V462 Lup, but its thermal emission is
invisible to NuSTAR due to extreme absorption intrinsic to
the ejecta.
