The first X-ray detection of the dust-forming C-rich nova V1280 Sco
ATel #2063; J.-U. Ness (ESAC/ESA), G. Schwarz (West Chester), C. E. Woodward, L. A. Helton (U. Minnesota), M. Sitko (U. Cincinnati and Space Science Institute), R. W. Russell, D. K. Lynch, R. J. Rudy (The Aerospace Corp), S. Starrfield (Arizona State U.), J. P. Osborne, K. Page (U. Leicester), M. F. Bode (U. Liverpool)
on 28 May 2009; 20:10 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Jan-Uwe Ness (Jan-Uwe.Ness@asu.edu)
Subjects: Sub-Millimeter, Far-Infra-Red, Optical, X-ray, Cataclysmic Variable, Nova
We report the first detection in X-rays of the Classical Nova
V1280 Sco (IAUC # 8803 ). After V2362 Cyg, this is only the second
carbon-rich dust-forming nova detected in X-rays.
We have obtained X-ray, optical, and Infrared observations on a number
of dates. Optical spectra were obtained at the Steward Observatory Bok
2.29-m telescope on 2008-Jun-25.2 and 2009-May-7.4. Spitzer IR spectra
were obtained on 2007-Apr-17.6, 2007-May-2.8, and 2008-May-6.2.
IRTF/SpeX observations were made on 2009-May-20. Swift observed for
1010s, 1910s, and 4790s on 2007-Feb-21.5 (ATel #1011), 2007-Apr-9.9,
and on 2009-May-18.7, respectively.
The first two Swift observations only gave X-ray telescope
(XRT: 0.3-10 keV range) 95% upper
limits of 0.018 c/s and 0.0014 c/s respectively. However, the
latest observation yields a clear detection with a
count rate of 0.021+/-0.002 c/s.
With only 82 counts, the XRT spectrum is not sufficiently exposed
for detailed spectral modelling. However, comparing a black body
fit with an APEC (optically thin plasma) model suggests that the
emission originates from an optically thin, thermal plasma.
Although both models reproduce the data, the best-fit black body
temperature is 195+/-45 eV (NH < 3E21 cm^-2,
Lbol=2.8E32 erg/s assuming d=1.6 kpc; Chesneau et al.
2008, A&A 487, 223), which is too high for photospheric emission
from a white dwarf. The APEC fit yields values of kT of 227+98-53 eV
(for NH=(7.2+/-2.5) E21 cm^-2). The XRT spectrum does not
resemble that of a Super Soft Source (SSS), even this
late in the outburst, and so is probably not being produced by
nuclear burning on the white dwarf.
The first detection of formation of dust was reported 2007-Mar-5
(CBET #866), and recent Spitzer and IRTF/SpeX
observations indicate that significant amounts of dust are still
present (CBET #1809, IAUC # 9046 ). The detection of UIR features suggests
the ejection of a dense carbon-rich dust shell.
The reddening deduced from OI lines (IAUC # 9046 )
is lower than on 2007-May-31 (IAUC # 8845 ), but
still higher than the Schlegel et al. (1998, ApJ, 500, 525)
galactic extinction maps, yielding only E(B-V) = 0.36 at V1280 Sco's
position. We conclude that significant circumstellar extinction must
still be present. Here, we report the continued presence of
P-Cyg absorption on 2009-May-7.4 on the HeI 667.8-nm line and on the
Balmer lines with
a mean velocity of ~1000 km/s. The expansion velocity has thus
increased from only 500 km/s on 2007-Feb-5.9-8.7 (IAUC # 8803 and # 8807 ).
Since some of the emission in the Swift XRT spectrum occurs where
strong lines are expected (NVII, OVIII, FeXVII, and
MgXII), we interpret the X-ray emission as originating from
overlapping emission lines, unresolved by the XRT. Compared to other
novae, the detection of shock-related hard emission is quite late in
the outburst. The detection of P-Cygni profiles at such a late time,
on the other hand, may indicate that the conditions for shock-induced
X-ray emission are still present. We note that in the novae
V1974 Cyg (Krautter et al. 1996, ApJ, 456, 789) and V458 Vul
(Ness et al. 2008, AJ, 137, 4160), the earlier "hard" X-ray emission
phase was followed by bright SSS X-ray emission,
and we may yet detect SSS emission from the white dwarf.
More observations at all wavelengths are encouraged.
We thank the Swift PI, Neil Gehrels, the Swift science team and
the Swift mission operations team for their support of these observations.