Nova Scorpii 2024 (V1723 Sco) has entered the super-soft X-ray phase
ATel #16641; Gerardo Juan Manuel Luna (CONICET/UNAHUR), N. Paul Kuin (MSSL), Kirill Sokolovsky (UIUC)
on 6 Jun 2024; 11:36 UT
Credential Certification: Paul Kuin (npkuin@gmail.com)
Subjects: X-ray, Nova, Transient
V1723 Sco was detected in optical as an erupting nova on 2024-02-08.827 UT (CBET #5346) and soon after was detected as a gamma-ray source by Fermi-LAT (on 2024-02-09.50, ATel #16439). After initially being dark in X-rays (ATel #16444), V1723 Sco was detected as an X-ray source on 2024-02-22.268 by Swift/XRT (ATel #16484).
The X-rays produced by shock-heated plasma peaked around 2024-03-13 (33 days after eruption) and were unusually bright reaching
~0.3 Swift/XRT counts/s with virtually all counts being above 2 keV due to extreme intrinsic absorption within the nova ejecta (N_H ~ 1e23 cm^-2). The shock-powered X-ray emission was gradually declining and softening after the peak.
We report here the first detection of the super-soft X-ray emission from the burning of leftover material on the white dwarf surface. A dramatic increase in soft counts was observed by Swift/XRT on 2024-05-29.682 (111 days past eruption): 0.21 +/-0.02 cts/s
below 2 keV, 0.28 +/-0.02 cts/s 0.3-10 keV total. The Swift/XRT spectrum shows two components: the soft one that can be modeled with an absorbed (N_H < 0.8e22 cm^-2) black-body with a temperature of 0.05 +/-0.02 keV and unabsorbed luminosity of 8e34 ergs/s (at a fiducial distance of 4 kpc adopted in ATel #16492). The other hard spectral component, consists of a strongly absorbed (N_H = 2e22 cm^-2) optically thin thermal plasma with a temperature of ~1.4 keV and unabsorbed luminosity of 6e34 ergs/s. This can be compared to the peak shock-powered luminosity of ~1.3e35 ergs/s on day 33 (the temperature was not well constrained by Swift/XRT data at that epoch).
We thank the Neil Gehrels Swift Observatory team and the PI, Brad Cenko, for supporting the V1723 Sco monitoring.
