Nova SMC 2012 (OGLE-2012-NOVA-002) is an ONe nova, which is now a super-soft X-ray source

ATel #4853; K. L. Page (U. Leicester), F. M. Walter (Stony Brook University), G. J. Schwarz (AAS), J. P. Osborne (U. Leicester)
on 4 Mar 2013; 18:12 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)

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In 2012 October, Swift observed Nova SMC 2012 (OGLE-2012-NOVA-002), finding a very faint X-ray source and a uvw2 magnitude of 14.4 mag (ATel #4501). A second observation the following month confirmed the weak X-ray source, while the UV emission had faded slightly to 14.7 mag.

During a new observation on 2013 March 2, Swift detected a significantly brighter X-ray source, at a count rate of 0.097 +/- 0.006. The source is very soft, with all counts below 1 keV, and can be fitted with an atmosphere model with kT = 64 +/- 3 eV, absorbed by a column of (6.5 +6.1/-5.0) x 10²⁰ cm^-2. Fitting using Cash statistics, but using the chi^2 test parameter to provide a goodness-of-fit, gives χ²/dof = 35.6/32. The 0.3-10 keV observed (unabsorbed) flux is 3.3 +/- 0.5 (8.6 +10.0/-4.1) x 10^-12 erg cm^-2 s^-1. The UVOT magnitude has now faded to uvw2 = 16.12 +/- 0.03.

Nova SMC 2012 was been photometrically monitored (BVRIJHK) with SMARTS/ANDICAM from 2012 October 19 to 2013 February 15, with spectra being obtained by SMARTS/RC from 2012 October 16 to 2012 December 15. After this time, the source was too faint to obtain spectra with SMARTS. The optical magnitudes decline linearly, with a rate of 0.008 mag day^-1 in the V-band, and 0.015 mag day^-1 in R, which reflects the decrease in Hα emission.

The optical spectrum, that of an O-Ne nova, is nearly identical to that of Nova Mon 2012. The strongest lines are [Ne V] and [Ne III] ([Ne III] 3869 is stronger than [O III] 5007). Other lines seen include O I 7774, 8227, 8446, 9264, [O II] 7325, N II 5679, 5755, and He I 4471, 6678, 7025. He II 4686 is not seen between the stronger 4640 Bowen blend and [Ne IV] 4714. Over the span of the observations, relative to the continuum the forbidden lines strengthened while the Balmer lines faded. The Bowen blend did not vary.

Although neither the exact time of the start of the supersoft phase nor the time of the nova outburst is known (it occurred sometime between 2012 May 20 and June 5; ATel #4483, ATel #4485), this identification of the SSS comes some 9 months after the first detection of the nova (2012 June 5).

A daily monitoring campaign has been initiated with Swift and follow-up observations at all wavelengths are encouraged. We thank the Swift PI and mission operations team for their support.