Photometric evolution of seven recent novae and the double-component characterizing the light curve of those emitting in gamma rays

Abstract

The B V I lightcurves of seven recent novae have been extensively mapped with daily robotic observations from Atacama (Chile). They are V1534 Sco, V1535 Sco, V2949 Oph, V3661 Oph, MASTER OT J010603. 18-744715.8, TCP J1734475-240942 and ASASSN-16ma. Five belong to the Bulge, one to SMC and another is a Galactic disk object. The two program novae detected in γ-rays by Fermi-LAT (TCP J1734475-240942 and ASASSN-16ma) are Bulge objects with unevolved companions. They distinguish themselves in showing a double-component optical lightcurve. The first component to develop is the fireball from freely-expanding, ballistic-launched ejecta with the time of passage through maximum which is strongly dependent on wavelength (∼1 day delay between B and I bands). The second component, emerging simultaneously with the nova detection in γ-rays and for this reason termed gamma, evolves at a slower pace, its optical brightness being proportional to the γ-ray flux, and its passage through maximum not dependent on wavelength. The fact that γ-rays are detected from novae at the distance of the Bulge and at peak flux levels differing by 4× seems to contradict some common belief like: only normal novae close to the Sun are detected by Fermi-LAT, most normal novae emit γ-rays, and they emit γ-rays in similar amounts. The advantages offered by high-quality photometric observations collected with only one telescope (as opposed to data provided by a number of different instruments) are discussed in connection to the actual local realization of the standard filter bandpasses and the spectrum of novae dominated by emission lines. It is shown how, for the program novae, such high-quality and single-telescope optical photometry is able to disentangle effects like: the wavelength dependence of a fireball expansion, the recombination in the flashed wind of a giant companion, the subtle presence of hiccups and plateaus, tracing the super-soft X-ray phase, and determining the time of its switch-off. The non-detection by 2MASS of the progenitor excludes a giant or a sub-giant being present in four of the program novae (V2949 Oph, V3661 Oph, TCP J18102829-2729590, and ASASSN-16ma). For the remaining three objects, by modelling the optical-IR spectral energy in quiescence it is shown that V1534 Sco contains an M3III giant, V1535 Sco a K-type giant, and MASTER OT J010603.18-744715.8 a sub-giant.

The Peculiar Multiwavelength Evolution Of V1535 Sco

“…This distance agrees well with estimates in Munari et al (2017) based on both MMRD and the Buscombe & de Vaucouleurs (1955) method of estimating the absolute magnitude 15 days after optical maximum.…”

“…Covey et al (2007) gives the absolute J magnitude for a K3 III star as -1.13, which is remarkably close for such a simple model. Munari et al (2017) also conclude that the companion in V1535 Sco is consistent with a K3-4 III giant. Srivastava et al (2015) presented measurements of the ejecta velocity for V1535 Sco based on the Paβ emission line at 1.2818 µm starting 7 days after the detection and ending 40 days after the detection.…”

“…Srivastava et al (2015) apply the maximum magnitude rate of decline (MMRD) relations from della Valle & Livio (1995) and Downes & Duerbeck (2000) to get distance estimates of 13.7 ± 0.4 and 14.7 ± 3.8 kpc, respectively. However, Munari et al (2017) reported a distance to V1535 Sco of approximately 9.7 kpc, despite using the same MMRD method as Srivastava et al (2015). This indicates the MMRD distance may be highly dependent on the data used, as Munari et al (2017) performed all their observations on a single telescope and Srivastava et al (2015) obtained their data from multiple telescopes via the American Association of Variable Star Observers (AAVSO).…”

“…However, Munari et al (2017) reported a distance to V1535 Sco of approximately 9.7 kpc, despite using the same MMRD method as Srivastava et al (2015). This indicates the MMRD distance may be highly dependent on the data used, as Munari et al (2017) performed all their observations on a single telescope and Srivastava et al (2015) obtained their data from multiple telescopes via the American Association of Variable Star Observers (AAVSO). Furthermore, substantial uncertainty has been shed on the MMRD method in general by the work of Kasliwal et al (2011) andCao et al (2012).…”

“…This gives a distance modulus of m − M = 15.212 ± 1.253, or a distance between 6.2 and 19.6 kpc. If we instead use E(B − V ) = 0.96, as reported in Munari et al (2017), our distance range is 5.8 to 14.0 kpc.…”