The 2011 Eruption of the Recurrent Nova T Pyxidis: The Discovery, the Pre-Eruption Rise, the Pre-Eruption Orbital Period, and the Reason for the Long Delay

Abstract

We report the discovery by M. Linnolt on JD 2, 455,665.7931 (UT 2011 April 14.29) of the sixth eruption of the recurrent nova T Pyxidis. This discovery was made just as the initial fast rise was starting, so with fast notification and response by observers worldwide, the entire initial rise was covered (the first for any nova), and with high time resolution in three filters. The speed of the rise peaked at 9 mag day −1 , while the light curve is well fit over only the first two days by a model with a uniformly expanding sphere. We also report the discovery by R. Stubbings of a pre-eruption rise starting 18 days before the eruption, peaking 1.1 mag brighter than its long-time average, and then fading back toward quiescence 4 days before the eruption. This unique and mysterious behavior is only the fourth known (with V1500 Cyg, V533 Her, and T CrB) anticipatory rise closely spaced before a nova eruption. We present 19 timings of photometric minima from 1986 to 2011 February, where the orbital period is fast increasing with P /Ṗ = +313,000 yr. From 2008 to 2011, T Pyx had a small change in this rate of increase, so that the orbital period at the time of eruption was 0.07622950 ± 0.00000008 days. This strong and steady increase of the orbital period can only come from mass transfer, for which we calculate a rate of (1.7-3.5) × 10 −7 M yr −1 . We report 6116 magnitudes between 1890 and 2011, for an average B = 15.59 ± 0.01 from 1967 to 2011, which allows for an eruption in 2011 if the blue flux is nearly proportional to the accretion rate. The ultraviolet-optical-infrared spectral energy distribution is well fit by a power law with f ν ∝ ν 1.0 , although the narrow ultraviolet region has a tilt with a fit of f ν ∝ ν 1/3 . We prove that most of the T Pyx light is not coming from a disk, or any superposition of blackbodies, but rather is coming from some nonthermal source. We confirm the extinction measure from IUE with E(B − V ) = 0.25 ± 0.02 mag.

SALT observations of southern post-novae

“…The last outburst was excellently covered with systematic observations in the whole electromagnetic wavelength region from X-ray to radio. More details on the previous and the last outbursts of T Pyx can be found in Schaefer (2010a), Schaefer et al (2013), Shore et al (2011), Shore et al (2013), De Gennaro Aquino et al (2014, Surina et al (2014), and references therein. An extended shell, different from the other nova shells and composed of many small knots, was discovered by Duerbeck & Seitter (1979).…”

Pre-outburstChandraobservations of the recurrent nova T Pyxidis

“…Selvelli et al (2008) predict a disk luminosity of about 3 × 10 35 erg s −1 (from UV and optical bands) for T Pyx consistent with the accretion rate they calculate in the optical and UV regimes (1−4) × 10 −8 M yr −1 for a WD mass of (0.7−1.4) M . I note that larger accretion rates of (1−10) × 10 −7 M yr −1 have been suggested for T Pyx as well (Schaefer et al 2013;Godon et al 2014). In this accretion rate range, the nature of the boundary layer should be discussed in the framework of the calculations of the standard steady-state disk models expected for CVs (e.g., of Narayan & Popham 1993;Popham & Narayan 1995;Popham 1999).…”

“…A warped disk intercepts and reprocesses radiation from the inner regions, the effective temperature distribution could flatten from the canonical r −3/4 to r −1/2 , which would produce a long-wavelength SED of f ∝ ν 1 , much redder than the canonical ν 1/3 distribution. This may be what is observed by Schaefer et al (2013). Therefore, to understand T Pyx, the possibility of reprocessing of the X-ray photons from the inner disk (e.g., ADAF-like bounday layer) or an X-ray corona by an outer warped, flared, or ruffled disk needs similar to AGN-type disks, e.g., nonstandard disks needs to be explored.…”

“…Schaefer et al (2013) argues that the ultraviolet portion of the T Pyx SED is consistent with a f ∝ ν 1/3 power law, but the entire UBVRIJHK part of the SED has f ∝ ν 1 which shows that the UBVRIJHK emission is not from an accretion disk. Studies have shown that median optical to UV continuum slope in radio-quiet QSOs/AGNs is also f ∝ ν 1/3 power law (Francis et al 1991).…”

“…Therefore, T Pyx is believed to be a nonmagnetic CV accreting at high rates as expected from RN precursers with a distance estimate of 3.50 ± 0.35 kpc (Selvelli et al 2008). Recently, the ultravioletoptical-infrared SED is found to be fitted by a power law ( f ν ∝ ν 1 ) which suggests that most of the T Pyx light in quiescence may not originate from a standard accretion disk, or any superposition of blackbodies, but rather comes from some nonthermal source (Schaefer et al 2013).…”