Swift observations of the super-soft emission during the 2024 eruption of Nova LMC 1968
ATel #16772; K. L. Page (U. Leicester), N. P.M. Kuin (UCL/MSSL) and M. J. Darnley (LJMU)
on 14 Aug 2024; 16:05 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)
Subjects: Ultra-Violet, X-ray, Nova
As noted in ATel #16752, the Neil Gehrels Swift Observatory observed the Large
Magellanic Cloud Recurrent Nova LMC 1968 (LMC V1341) within a few
hours of its most recent eruption on 2024 August 1. Monthly monitoring observations of the nova by Swift have been performed since the end of the 2020 eruption, and we were lucky that the August observation occurred on the day the latest eruption began!
Following that
discovery, daily observations have been (and are continuing to be)
taken since August 6, with the XRT data collected on August 8 (7.8
days post-eruption; 1.2 ks of exposure time) revealing an obvious soft X-ray
component, at a 0.3-10 keV count rate of 0.052 ± 0.007 count
s-1. The vast majority of the detected counts are below 1
keV. Approximating the spectrum with an absorbed BB, we measure kT =
71 +28/-50 eV and NH < 7 x 1021
cm-2. A longer observation the following day (August 9; 2.3
ks), at a count rate of 0.096 ± 0.007 count s-1, provided
better constrained spectral parameters, with kT = 66 ± 12 eV and
NH = (1.5 +1.3/-0.8) x 1021 cm-2;
this absorbing column is consistent with the value found by Kuin et
al. (2020, MNRAS, 491, 655), after an initial clearing of the ejecta
following the 2016 eruption of this nova.
Multi-band photometry is being collected by UVOT. Following the
initial magnitudes reported in ATel #16752, the source faded by three
magnitudes by the following observation on August 6 (uvm2 = 13.05 ±
0.03 and uvw1 = 13.14 ± 0.03), allowing for standard photometry to
be used. After further fading, the UV and optical magnitudes have
plateaued since August 8, as is often seen during the supersoft X-ray
phase of recurrent novae (e.g. Hachisu et al. 2008, ASP
Conf. Ser. 261, 629; Schaefer 2010, ApJS, 187, 275), around uvm2 =
15.11 ± 0.04 and uvw1 = 15.23 ± 0.03.
Swift observations are ongoing, and we thank the Swift PI, Brad
Cenko, and his deputies for approving the monitoring, as well as the
Swift planning and operations teams for their continuing support.
