Optical Confirmation of the 7.1 hour UV/X-ray Period in Nova Mon 2012

ATel #4737; R. M. Wagner (LBT Observatory and Ohio State University), C. E. Woodward (University of Minnesota), and S. Starrfield (Arizona State University)
on 15 Jan 2013; 12:31 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

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Recently, Osborne, Beardmore, and Page (ATEL #4727) reported the detection of a 7.1 hour UV/X-ray periodicity in data obtained at daily intervals with the Swift UVOT and XRT instruments of the neon nova and gamma-ray transient Nova Mon 2012 (ATEL #4727, #4709, #4633, #4614, #4590, #4572, #4569, #4542, #4408, #4376, #4365, #4352, #4321, #4320, and #4310). Analysis of the UVOT data revealed a strong period at 0.2957 +/- 0.0007 days that was present in the uvw1, uvm2, and uvw2 bands with an amplitude of about +/- 0.05 magnitudes. In addition, time series analysis of the Swift XRT data also shows the same period at P = 0.2955 +/- 0.0015 days. Both modulations are roughly sine-like in shape with similar phasing between the UV and X-ray spectral regions.

We obtained differential time series optical photometry in the I-band (725-1025 nm FWHM) of Nova Mon 2012 between 2013 January 8-13 UT with the 1.3 m McGraw-Hill telescope of the MDM Observatory on Kitt Peak using the MDM4K CCD imager windowed to a field of view of 5.4 x 5.4 arcmin to obtain higher time resolution. 2401 individual measurements were obtained of Nova Mon 2012 at a time resolution of 30 seconds with respect to two anonymous comparison stars in the field of comparable brightness to the nova. Nightly light curves exhibit short-time scale fluctuations in brightness reminiscent of flickering superposed on broader modulations that have a full amplitude of about 0.1 magnitudes. A monotonic decline in the overall night-to-night brightness of the nova is also evident over the time interval of these observations.

Temporal analysis of these data using the PDM method after the subtraction of a linear detrend reveals the presence of a strong and significant optical period in the I-band with a period of P = 0.2956 +/- 0.0010 days and with a full amplitude of 0.13 magnitudes. The light curve is nearly sinusoidal but the minimum is more sharply peaked with a full duration between ingress and egress of about 0.18 days. The epoch of minimum brightness is t0 = JD 2,456,305.6901. Our discovery of the optical period confirms the detection of the 7.1 hour period identified by Osborne, Beardmore, and Page (ATEL #4727) and excludes the two shorter alias periods.

The detection of the same 7.1 hour period in the optical, UV, and X-ray bands strongly suggests that it is the orbital period of Nova Mon 2012. This period is similar to the orbital period of the fast ONeMg nova V838 Her 1991 for example (7.14 hours; Leibowitz et al. 1992, ApJ, 385, L49; Ingram et al. 1992, PASP, 104, 402). Additional observations and analyses are underway.