NuSTAR detection of shock-powered X-rays from Nova Sagittae 2026 = V488 Sge
ATel #18028; Kirill Sokolovsky, Katie Barnhart, Darien Perla, Pragati Acharya, John Worley, Anthony Pearce, Vallia Antoniou, Elias Aydi (TTU), Laura Chomiuk, Peter Craig, Isabella Molina (MSU), Jennifer Sokoloski (Columbia), Justin Linford (NRAO), Koji Mukai (NASA/GSFC)
on 2 Sep 2026; 19:29 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
Subjects: Optical, X-ray, Nova
Nova Sagittae 2026 (V488 Sge, PNV J19450648+1822422) was
discovered on its rise to optical peak by the NMW-TexasTech
survey at 2026-08-25.1278 UTC having an unfiltered magnitude 9.0
(CBET #5729, ATel #18008, #18009, #18012, #18014, #18021, #18022).
Observations reported to the AAVSO indicate that the nova peaked
around 2026-08-25.9 at visual magnitude 7.0 then declined to
magnitude 9.0 by 2026-08-30.0 (t_2= 4 days) with the observations
on 2026-09-02.2 putting it around magnitude 10 (t_3= 7 days).
NuSTAR observed V488 Sge between 2026-08-31.0 (5 days past
peak) and 2026-09-01.2 for an effective exposure of 50 ks.
The nova is clearly detected at a count rate of 0.15 counts/s
per Focal Plane Module. No orbit-to-orbit variability in the X-ray
flux is detected during the NuSTAR observation. The spectrum can be
well described (Chi-Squared 162.6 with 175 d.o.f.)
by single-temperature kT= 7.0 (-0.5, +0.6) keV plasma with
super-solar by a factor of 38 (-15, +23; by number) nitrogen and
oxygen abundances that is affected by a combination of Galactic
N_H_gal= 3.35x10^21 cm^-2 (fixed total line-of-sight value from
Kalberla et al. 2005 A&A, 440, 775) and intrinsic
N_H_int= 6 (-2, +3) x10^21 cm^-2 absorption. In our model,
the abundances of the intrinsic absorber are tied to those of
the X-ray emitting plasma, while the Galactic absorber abundances
are fixed to solar values (Asplund et al. 2009 ARAA, 47, 481).
The unabsorbed 3-78 keV flux is 6.2 (+/-0.5) x10^-12 ergs/cm^2/s.
An unresolved Fe K emission line complex is clearly detected in
the NuSTAR data; a solar abundance plasma model can approximate
the observed spectrum but leaves residuals around
this spectral feature.
Overall, the NuSTAR spectrum of V488 Sge is
characteristic of shock-heated plasma within the nova shell.
The NuSTAR spectrum of V488 Sge
