The hybrid, coronal lines nova V5588 Sgr (2011 N.2) and its six repeating secondary maxima

Abstract

The outburst of Nova Sgr 2011 N.2 (=V5588 Sgr) was followed with optical and near-IR photometric and spectroscopic observations for 3.5 years, beginning shortly before the maximum. V5588 Sgr is located close to Galactic center, suffering from E B−V =1.56 (±0.1) extinction. The primary maximum was reached at V =12.37 on UT 2011 April 2.5 (±0.2), and the underlying smooth decline was moderately fast with t V 2 =38 and t V 3 =77 days. On top of an otherwise normal decline, six self-similar, fast evolving and bright secondary maxima (SdM) appeared in succession. Only very few other novae have presented so clear secondary maxima. Both the primary maximum and all SdM occurred at later times with increasing wavelengths, by amounts in agreement with expectations from fireball expansions. The radiative energy released during SdM declined following an exponential pattern, while the breadth of individual SdM and the time interval between them widened. Emission lines remained sharp (FWHM∼1000 km/s) throughout the whole nova evolution, with the exception of a broad pedestal with a trapezoidal shape (∆vel=3600 km/sec at the top and 4500 km/sec at the bottom) which was only seen during the advanced decline from SdM maxima and was absent in between SdM. V5588 Sgr at maximum light displayed a typical FeII-class spectrum which did not evolve into a nebular stage. About 10 days into the decline from primary maximum, a typical high-ionization He/N-class spectrum appeared and remained visible simultaneously with the FeII-class spectrum, qualifying V5588 Sgr as a rare hybrid nova. While the FeII-class spectrum faded into oblivion, the He/N-class spectrum developed strong [FeX] coronal lines.

Ogle Atlas of Classical Novae. I. Galactic Bulge Objects

“…We measured a characteristic timescale of decay of 66 ± 9 days from the data presented by Munari et al (2015). A similar value (72 days) was found here for V5585 Sgr.…”

“…The energy emitted during rebrightenings, both in V5585 Sgr and V5588 Sgr, decays exponentially with time. We measured a characteristic timescale of decay of 66 ± 9 days from the data presented by Munari et al (2015). A similar value (72 days) was found here for V5585 Sgr. Time intervals between successive rebrightenings increased with time, from 18 to 42 days in V5588 Sgr (Munari et al 2015) and from 8 to 60 days in V4745 Sgr (Strope et al 2010).…”

“…V5588 Sgr (Munari et al 2015; see also Figure A1) and V4745 Sgr (Strope et al 2010). Munari et al (2015) noticed that although V4745 Sgr and V5588 Sgr have similar light-curve shapes, their spectroscopic evolution was different. V5588 Sgr was a hybrid nova, which means that spectral features typical for the "Fe II" and "He/N" class existed simultaneously, while V4745 Sgr did not develop He/N spectrum at all.…”

“…V5588 Sgr (Nova Sgr 2011b) This object was discovered by Koichi Nishiyama and Fujio Kabashima (2011) in images taken on 2011 March 27.832 UT. V5588 Sgr belongs to a rare class of hybrid novae -it showed spectral features typical of Fe II and He/N types simultaneously (Munari et al 2015).…”

High-energy Emission from Nonrelativistic Radiative Shocks: Application to Gamma-Ray Novae

“…The optical fluxes at the time of the X-and gammaray observations were approximately 10 −7 erg cm −2 s −1 (V339 Del) and 6 × 10 −7 erg cm −2 s −1 (V5668 Sgr); the corresponding gamma-ray to optical flux ratios were ∼ 3 × 10 −4 and ∼ 3 × 10 −5 , respectively (Skopal et al 2014, Metzger et al 2015, Munari et al 2015.…”