Swift observations of super-soft X-rays from the 2020 eruption of Nova LMC 1968

ATel #13731; K. L. Page (U. Leicester), N. P.M. Kuin (UCL/MSSL) and M. J. Darnley (LJMU)
on 13 May 2020; 15:57 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)

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The Neil Gehrels Swift Observatory began observing the 2020 eruption of the recurrent Nova LMC 1968 (LMC V1341) on May 12. This latest eruption comes only 4 years after the last one in 2016 (Kuin et al. 2020, MNRAS, 491, 655). While the previous five nova eruptions implied a recurrence time of around 6 years, these latest data suggest that instead the recurrence time may be ~4 years, with the 2016 eruption being late to occur (rather than the 2020 eruption early).

This latest Swift observation shows a soft X-ray source, at a mean XRT count rate of 0.23 +/- 0.01 count s^-1. There is some variability, with the count rates from the 2 snapshots separated by ~1.5 hours being 0.21 +/- 0.01 and 0.31 +/- 0.03 count s^-1 respectively. The spectrum is very soft, with all but one photon detected below 1 keV; it can be approximated by an absorbed blackbody, with kT = 62 +9/-8 eV and N_H = (1.9 +0.9/-0.8)x10²¹ cm^-2. This absorbing column is consistent with the value found by Kuin et al. (2020), after an initial clearing of the ejecta.

The UVOT collected data using the uvm2 filter, measuring magnitudes of 14.55 +/- 0.03 and 14.88 +/- 0.04 for the two snapshots.

Matching ASASSN data for the new eruption with SMARTS data from 2016 suggests the 2020 eruption began on May 02, around 21 UT (JD 2458972.4) with an uncertainty of +/- 0.4 days. In this case, the Swift observations occurred on days 9.68 and 9.73. Assuming no difference in the light-curve between eruptions, the X-ray and UV results also appear consistent with this estimate.

Daily observations with Swift are planned for the next 2 weeks, and, as always, we thank the Swift PI, Brad Cenko, for approving the monitoring, as well as the Swift planning and operations teams for their continuing support. We also thank Patrick Schmeer for highlighting the new eruption.

We strongly encourage ground-based follow-up, including spectroscopic observations, of this LMC nova, bearing in mind that many of the larger ground-based telescopes are currently closed because of the COVID-19 pandemic.