X-ray high-resolution Chandra spectrum and optical observations of nova Monocerotis 2012

ATel #4569; J.-U. Ness (ESA/ESAC), S. N. Shore (Pisa, INFN), J. J. Drake (CfA), J. P. Osborne, K. L. Page, and A. Beardmore (Leicester), G. Schwarz (AAS), S. Starrfield (ASU)
on 13 Nov 2012; 09:59 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Jan-Uwe Ness (Jan-Uwe.Ness@asu.edu)

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Nova Mon 2012 was discovered in the optical on August 9 (CBET#3202) and is likely associated with the gamma-ray transient Fermi J0639+0548 discovered about two months earlier (ATel#4224, ATel#4310). Follow up observations were performed in radio (ATel#4352, ATel#4376, ATel#4408), infrared (Atel#4542), optical (ATel#4320), UV and X-ray (with Swift Atel#4321), and the progenitor was found in archival IR observations from 2004 November (ATel #4365). Here, we report results from a 24500-second Chandra high-resolution X-ray grating spectrum, taken 2012, September 12.37, 34 days after optical discovery and 82 days after the Fermi-LAT detection.

The count rate was 0.16 and 0.08 counts per second (cps) in the Medium- and High-Energy Gratings, respectively, and 0.2 cps in the zero-th order.

The X-ray light curve is variable, although not apparently periodic, with a range of 20% of the median count rate and peak count rates of 60% above the median.

The spectrum consists of bremsstrahlung continuum plus emission lines of S, Si, Mg, and Ne. The strongest lines originate from H-like MgXII and SiXIV, while the He-like lines of MgXI and SiXIII are much weaker. Their profiles are structured with their peaks slightly blue shifted by ~700 km/s. A solar-abundance APEC model under-predicts these emission lines, implying non-solar composition. The continuum is consistent with an electron temperature of close to 10^8K (T_e=8.6keV) at N_H=8.7E21 cm^-2.

The amount of photoelectric absorption has decreased since August 10, when a value of 2.2E22 cm^-2 was found from an analysis of Swift data (ATel#4321). However, this value is still a factor of 10 above the interstellar extinction estimated from the LAB survey of Galactic HI reported in Kalberla et al (2005, A&A, 440, 775). Kalberla et al. used the HI profile and obtained a value of ~ 2E21 cm^-2. Optical NOT spectra taken 2012, September 6 and October 8, covering 3800-7300A (see ATel#4310), show profiles with a double-peaked structure for all species with FWZI ~ 4000 km/s and with an asymmetry that depends on the ionization.

We thank the Chandra director for funding the observation out of the Director's Discretionary Time budget.