The recurrent nova T Pyx: fading in optical/UV, brightening in X-rays, H alpha development, and a request for photometry

ATel #3549; J. P. Osborne (U. Leicester), A. P. Beardmore (U. Leicester), K. L. Page (U. Leicester), P Kuin (MSSL), F. M. Walter (Stony Brook U.), B. E. Schaefer (Louisiana State U.), E. Kuulkers (ESA/ESAC), S. Shore (U. Pisa), M. F. Bode (LJMU), G. J. Schwarz (AAS), J. J. Drake (CfA), J.-U. Ness (ESA/ESAC), S. Balman (METU), S. Starrfield (Arizona State U.), M. J. Darnley (LJMU), S. P.S. Eyres (U. Central Lancashire), T. J. O'Brien (U. Manchester), M. Orio (INAF & U. Wisconsin), A. Oksanen (Caisey Harlingten Obs.), M. Streamer (Lexy's Palace Obs.)
on 12 Aug 2011; 08:06 UT
Credential Certification: Julian P Osborne (julo@star.le.ac.uk)

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The recurrent nova T Pyx was discovered in outburst on 14 April 2011 (CBET #2700), which we take as day 0. Swift observations have continued generally every three days since the first X-ray detection by Kuulkers et al. (ATEL #3285).

UVOT uvm2 filter observations (central wavelength 2246 A) show a slow ~1 magnitude rise from around day 20 to day 50, and then a steep decline by 3 magnitudes from about 70 to 115 days after the outburst. These results are estimated from annular photometry using an experimental conversion. The AAVSO V band light curve has an earlier peak, around day 24, and a lesser decline of 2.2 mag in the same interval. The recent optical magnitudes have declined from V=9.85 mag on day 105 (28 July) to V=10.36 on day 117 (9 August), with this decline coming substantially earlier than a similar drop in the 1967 eruption light curve around day 130. The later peak at shorter wavelengths is expected as the pseudo-photosphere in the thinning nova ejecta shrinks to smaller effective radius with increasing effective temperature.

In X-rays, after its initial detection at 11 c/ks, T Pyx has been very faint (below 1.0 c/ks) since around day 12, the Swift XRT 0.3-10 keV count rate being 0.33+/-0.11 c/ks between days 29 - 109. However, from 3 Aug 2011 (day 111) the X-ray source has brightened and continues to increase in flux: the XRT has detected T Pyx on 4 days to 9 Aug 2011 (day 117) at a mean level of 5.0 +/- 0.6 c/ks. The recently detected counts are insufficient to allow a useful spectral model fit, but are soft, as in the earlier detection. We speculate that the rising X-ray flux may signal the initial unveiling of the hot white dwarf.

Spectra obtained with the Chiron spectrograph (R=28,000) on the SMARTS 1.5m telescope at Cerro Tololo in Chile show the H alpha emission line has evolved from an initially narrow core atop a broad emission wing (days 3 to 13) into a broad flat-topped profile near maximum light. By day 63 the profile evolved into the broad shoulders (+/-1200 km/s) with a superposed double-lined core (+/- 400 km/s) similar to that seen in other recurrent novae. Extended wings show maximum velocities to +/- 3000 km/s.

During the solar conjunction in late August, T Pyx is 47 degrees from the Sun, and we urge optical observers to push deep into the twilight to provide magnitudes (preferably in the V-band) so as to fill the solar gap in the light curve during the fast drop predicted to occur in mid-August.

Swift observations will continue until the source enters the Sun constraint on 16 Aug, and will be requested again when the source re-emerges on 4 Sept.

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