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تسجيل مستخدم جديدThe Distance to Nova V959 Mon from VLA Imaging
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Determining reliable distances to classical novae is a challenging but crucial step in deriving their ejected masses and explosion energetics. Here we combine radio expansion measurements from the Karl G. Jansky Very Large Array with velocities derived from optical spectra to estimate an expansion parallax for nova V959 Mon, the first nova discovered through its gamma-ray emission. We spatially resolve the nova at frequencies of 4.5-36.5 GHz in nine different imaging epochs. The first five epochs cover the expansion of the ejecta from 2012 October to 2013 January, while the final four epochs span 2014 February to 2014 May. These observations correspond to days 126 through 199 and days 615 through 703 after the first detection of the nova. The images clearly show a non-spherical ejecta geometry. Utilizing ejecta velocities derived from 3D modelling of optical spectroscopy, the radio expansion implies a distance between 0.9 +/- 0.2 and 2.2 +/- 0.4 kpc, with a most probable distance of 1.4 +/- 0.4 kpc. This distance implies a gamma-ray luminosity much less than the prototype gamma-ray-detected nova, V407 Cyg, possibly due to the lack of a red giant companion in the V959 Mon system. V959 Mon also has a much lower gamma-ray luminosity than other classical novae detected in gamma-rays to date, indicating a range of at least a factor of 10 in the gamma-ray luminosities for these explosions.
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Two observations of V959 Mon, done using the Chandra X-ray gratings during the late outburst phases (2012 September and December), offer extraordinary insight into the physics and chemistry of this Galactic ONe nova. the X-ray flux was 1.7 x 10(-11)
erg/cm(2)/s and 8.6 x 10(-12) erg/cm(2)/s, respectively at the two epochs. The first result, coupled with electron density diagnostics and compared with published optical and ultraviolet observations, indicates that most likely in 2012 September the X-rays originate from a very small fraction of the ejecta, concentrated in very dense clumps. We obtained a fairly good fit to the September spectrum with a model of plasma in collisional ionization equilibrium (CIE) with two components; one at a temperature of 0.78 keV, blueshifted by 710-930 km/s, the other at a temperature of 4.5 keV, mostly contributing to the high-energy continuum. However, we cannot rule out a range of plasma temperatures between these two extremes. In December, the central white dwarf (WD) became visible in X-rays. We estimate an effective temperature of about 680,000 K, consistent with a WD mass ~1.1 M(sol). The WD flux is modulated with the orbital period, indicating high inclination, and two quasi-periodic modulations with hour timescales were also observed. No hot plasma component with temperature above 0.5 keV was observed in December, and the blue-shifted component cooled to kT~0.45 keV. Additionally, new emission lines due to a much cooler plasma appeared, which were not observed two months earlier. We estimate abundances and yields of elements in the nova wind that cannot be measured in the optical spectra and confirm the high Ne abundance previously derived for this nova. We also find high abundance of Al, 230 times the solar value, consistently with the prediction that ONe novae contribute to at least 1/3rd of the Galactic yield of Al(26).
V959 Mon is one of the gamma-ray detected novae. It was optically discovered about 50 days after the gamma-ray detection due to proximity to the Sun. The nova speed class is unknown because of lack of the earliest half of optical light curve and shor
t supersoft X-ray phase due to eclipse by the disk rim. Using the universal decline law and time-stretching method, we analyzed the data of V959 Mon and obtained nova parameters. We estimated the distance modulus in the V band to be (m-M)_V=13.15pm0.3 for the reddening of E(B-V)=0.38pm0.01 by directly comparing with the similar type of novae, LV Vul, V1668 Cyg, IV Cep, and V1065 Cen. The distance to V959 Mon is 2.5pm0.5 kpc. If we assume that the early phase light curve of V959 Mon is the same as that of time-stretched light curves of LV Vul, our model light curve fitting suggests that the white dwarf (WD) mass is 0.9-1.15 M_sun, being consistent with a neon nova identification. At the time of gamma-ray detection the photosphere of nova envelope extends to 5-8 R_sun (about two or three times the binary separation) and the wind mass-loss rate is (3-4)times 10^{-5} M_sun yr^{-1}. The period of hard X-ray emission is consistent with the time of appearance of the companion star from the nova envelope. The short supersoft X-ray turnoff time is consistent with the epoch when the WD photosphere shrank to behind the elevating disk rim, that occurs 500 days before nuclear burning turned off.
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spectra are consistent with a two-temperature plasma model with non-solar abundances. We interpret the X-rays as due to shock interaction between the slow equatorial torus and the fast polar outflow that were inferred from radio observations of V959 Mon. We further propose that the hotter component, responsible for most of the flux, is from the reverse shock driven into the fast outflow. We find a systematic drop in the column density of the absorber between Days 60 and 140, consistent with the expectations for such a picture. We present intriguing evidence for a delay of around 40 days in the expulsion of the ejecta from the central binary. Moreover, we infer a relatively small (a few times 10$^{-6}$ Msun) ejecta mass ahead of the shock, considerably lower than the mass of 10$^4$ K gas inferred from radio observations. Finally, we infer that the dominant X-ray shock was likely not radiative at the time of our observations, and that the shock power was considerably higher than the observed X-ray luminosity. It is unclear why high X-ray luminosity, closer to the inferred shock power, is never seen in novae at early times, when the shock is expected to have high enough density to be radiative.
Symbiotic stars often contain white dwarfs with quasi-steady shell burning on their surfaces. However, in most symbiotics, the origin of this burning is unclear. In symbiotic slow novae, however, it is linked to a past thermonuclear runaway. In June
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We present multi-frequency radio observations of the 2010 nova event in the symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array and spanning 1-45 GHz and 17-770 days following discovery. This nova---the first ever detected
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