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X-ray detection of Nova V2468 Cygni and multiwavelength monitoring

ATEL # 2157; G.J. Schwarz (AAS), J.P. Osborne, K.L. Page (U. Leicester), J.-U. Ness (ESAC/ESA), C.E. Woodward, L.A. Helton (U. Minnesota), S. Starrfield (Arizona State U.), M.F. Bode, M.J. Darnley (Liverpool JMU), S. Balman (METU), R.M. Wagner (LBT/OSU)
on 12 Aug 2009; 10:13 UT
Password Certification: Kim Page (kpa@star.le.ac.uk)

Subjects: Optical, Ultra-Violet, X-ray

V2468 Cyg was first observed and detected by Swift with both the XRT and UVOT instruments on June 9th, 2009. Subsequent observations were obtained during a high cadence campaign on June 14, 15, and 16th, 2009 and as part of a long term monitoring program on August 1st, 2009. Swift will continue to obtain observations roughly twice a month through October 2009. The average X-ray (0.3-10 keV) count rate on these five dates was 0.020 count s-1. The X-ray light curve was variable with a large amplitude of ~ 0.02 count s-1 on timescales of 500 seconds. The X-ray spectrum was similar in all observations with both soft and hard components. The combined spectrum (32.9 ks), assuming a NH ~ 4.6 x 1021 cm-2 (from E(B-V) = 0.77; IAUC 8936), is fit with a two component model consisting of a blackbody (kT = 85+10-9 eV) and an optically thin Mekal model (kT = 5.1+2.2-1.2 keV). The blackbody model is dominant below 1 keV. The hard component, 1-10 keV, was primarily responsible for the observed variations.

The Swift UVOT was set to the "filter of the day" and thus data were obtained in the uvw1 (2600 Angstroms), u (3465 Angstroms), uvw2 (1928 Angstroms), uvm2 (2246 Angstroms), and u filters, respectively, during the 5 Swift observations. All UVOT observations showed large amplitude variations of order 0.3 magnitudes. The mean uvw2, uvm2, uvw1, and u band magnitudes were 16.23 +/- 0.03, 17.07 +/- 0.06, 15.27 +/- 0.01, 14.57 +/- 0.01, respectively. The X-ray light curve is not correlated with the UVOT light curves.

Coincident with the Swift observations, we have monitored photometrically V2468 Cyg with the 2m robotic Liverpool Telescope (LT; La Palma, Canaries) and ROTSE IIId on Bakirlitepe (TUBITAK National Observatory, Turkey). The LT observed V2468 Cyg from June 12, 2009 to June 19, 2009 with the RATCam CCD camera through Sloan u', r', and i' filters and Bessell B and V filters. The mean magnitudes were 14.20 +/- 0.05, 13.76 +/- 0.01, 13.75 +/- 0.01, 14.70 +/- 0.03, and 13.78 +/- 0.01, respectively. The unfiltered ROTSE IIId data set began June 12th, 2009 through July 12, 2009 with a total of 171 five second pointed exposures. Similar to the UV photometry, the ground based data also shows large amplitude variations. Preliminary analysis of the higher cadence ROTSE IIId data set implies a 0.242 +/- 0.002 day (5.8 hours) period from the power spectrum. There is no strong signal in the UVOT time series at this period. We expect to refine this result with additional long term monitoring.

An optical spectrum of V2468 Cyg was obtained with the B&C spectrograph on the Steward Observatory 2.3m telescope on July 12, 2009. The spectrum is typical of a CO type nova in its nebular phase. Prominent lines include the Balmer lines, [Ne III] (3870 angstrom), [O III] (4363, 4959, 5007 angstrom), [N II] (5755 angstrom) and [Fe VII] (6087 angstrom). The average emission line FWHM was ~ 1500 km s-1. The Balmer decrement provides a reddening of E(B-V) = 0.8 which is consistent with the earlier reports.

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


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R. E. Rutledge , Editor
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