[vsnet-alert 11434] (fwd) ATEL: Early X-ray detection of Nova Ophiuchi 2009 / V2672 Oph

[Taichi Kato]

http://www.astronomerstelegram.org/?read=2173 

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; 7:26 UT 
Password Certification: Kim Page (kpa at star.le.ac.uk) 

Subjects: X-ray, Novae 

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.