A Light Curve Analysis of Gamma-ray Nova V959 Mon -- Distance and White Dwarf Mass

TL;DR

This study analyzes the gamma-ray nova V959 Mon using light curve modeling to estimate its distance, white dwarf mass, and other physical parameters, providing insights into its eruption and evolution.

Contribution

It applies the universal decline law and time-stretching method to determine nova parameters, including distance and white dwarf mass, for V959 Mon, a gamma-ray detected nova.

Findings

Distance to V959 Mon is 2.5±0.5 kpc.

White dwarf mass is estimated at 0.9-1.15 M_sun.

Photosphere extended to 5-8 R_sun during gamma-ray detection.

Abstract

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 short 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=13.15\pm0.3 for the reddening of E(B-V)=0.38\pm0.01 by directly comparing with the similar type of novae, LV Vul, V1668 Cyg, IV Cep, and V1065 Cen. The distance to V959 Mon is 2.5\pm0.5 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.