Early X-ray detection of Nova Ophiuchi 2009 / V2672 Oph

ATel #2173; G. J. Schwarz (AAS), J. P. Osborne, K. Page, A. Beardmore (U. Leicester), F. Walter (Stony Brook University), J.-U. Ness (ESAC/ESA), Koji Mukai (NASA/GSFC), M. F. Bode, , M. J. Darnley (Liverpool John Moores University), E. Kuulkers (ISOC, ESAC/ESA; on behalf of the INTEGRAL GB monitoring team), R. D. Saxton (ESAC/ESA), S. Starrfield (Arizona State U.), J. Drake (Harvard-Smithsonian CfA), D. Takei (Rikkyo University), S. Balman (METU), T. O'Brien (U. Manchester), R. M. Wagner (LBT/OSU), M. Orio (U. Wisconson, Madison)
on 25 Aug 2009; 07:26 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)

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The extremely fast nova V2672 Oph (IAUC 9064 ) was detected by Swift with both the XRT and UVOT instruments just 1.43d after discovery on UT 2009 Aug 17.948. During the 0.8 ks observation we detected 7 photons at V2672 Oph's position for a rate of 0.017+/-0.005 ct/s after bad column and PSF loss corrections. The source was faint as seen through the uvw2 filter (1928A) at ~18.1 mag. Swift has continued to monitor V2672 Oph since Aug 18.257. The X-ray light curve from all the data is relatively constant at ~0.036 ct/s. The combined XRT spectrum is very absorbed, peaking near 2 keV. The spectrum can be modeled with an absorbed, optically thin component (Mekal kT = 5.1 +8.0/-2.0 keV and NH = (6.8+3.3/-2.4)E21 cm^-2). The observed (unabsorbed) 0.3-10 keV flux for this model is 2.0E-12 (3.0E-12) erg cm^-2 s^-1. The uvw2 filter light curve continued to decline rapidly from 19.0 on Aug 19.600 to ~20.8 mag 3 days later. The faint uvw2 magnitudes relative to optical photometry obtained at the same time confirm that the extinction toward V2672 Oph is quite large.

Optical spectra were obtained with the RC spectrograph on the SMARTS 1.5m telescope on UT Aug 20 & 21. The Halpha line resembles that of the recurrent nova YY Dor; the profile is tri-peaked with the central spike centered -160 km/s and the outer peaks at +/-3200 km/s. The FWZI of the profile is 11,000 km/s (see also IAUC 9064 ). HeI (5876, 6678A) is also seen weakly in emission. HeII (4686A) is the strongest line in the region between 4050 and 4750A.

There is a 2MASS source visible at V2672 Oph's position in all three IR bands but it is blended with a nearby source of similar brightness and color. Upper limits on the progenitor can be obtained from crowded field photometry of the blended sources. The limits are J >= 13.5, H >= 13.5+/-0.2 and K_S >= 13.1+/-0.2.

There are 10 excess photons above a background of 44 photons within ~20'' of V2672 Oph's position in the RASS catalog (11.76 ks). However, the count concentration is not consistent with a point source in the image. In addition, the small number of photons makes a true detection highly model dependent. An upper limit on the unabsorbed flux from a Mekal (kT = 1.17 keV, NH = 9.4E21 cm^-2) model in the 0.3-10 keV range is 1.4E-14 erg cm^-2 s^-1. In a pointed ROSAT/PSPC image obtained in Mar. 1992 V2672 Oph was not detected. An ASCA/GIS image taken on 1995 Mar 15 showed no source at V2672 Oph's position with a 90% confidence upper limit of 3.5E-3 ct/s or an observed 2-10 keV flux of 2E-13 erg cm^-2 s^-1 using the same absorbed Mekal model described above. V2672 Oph was also not detected in the XMM slew survey in a pass on 2006 Feb 27, with a 2-sigma 0.2-10 keV flux upper limit of 2.1E-12 erg cm^-2 s^-1. The archival evidence implies that there was no significant X-ray emission associated with V2672 Oph prior to the current outburst.

No source was detected with INTEGRAL/IBIS during the Galactic bulge monitoring observations taken on 2009 Aug 20 and 23/24, with typical 3-sigma upper limits of ~ 5mCrab (20-40 keV), which corresponds to ~3.5E-11 erg cm^-2 s^-1.

The rapid decline in the optical/UV light curves, the extremely broad emission lines, and the early X-ray detection imply that V2672 Oph is either a recurrent nova or a very fast classical nova. The early hard X-ray emission is likely due to shocks between the fast ejecta and a pre-existing circumstellar medium (as in the recurrent nova RS Oph) or intra-ejecta shocks (as in the very fast classical nova V838 Her). Additional observations with Swift and SMARTS are planned and we urge others to monitor this interesting object.

We thank the Swift PI and operations team for their support.