Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce pi(0) decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.

The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption 10 times, including yearly eruptions from 2008 to 2014. With a measured recurrence period of =  P 351 13 rec days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground-and space-based follow-up programs. In this paper we present the 2015 detection, visible to near-infrared photometry and visible spectroscopy, and ultraviolet and X-ray observations from the Swiftobservatory. The LCOGT 2 m (Hawaii) discovered the 2015 eruption, estimated to have commenced at August 28.28±0.12 UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities ∼13,000 km s −1 ,

Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed in eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white dwarf and a high accretion rate,

The Andromeda Galaxy recurrent nova M31N 2008-12a has been caught in eruption nine times. Six observed eruptions in the seven years from 2008 to 2014 suggested a duty cycle of ∼1 yr, which makes this the most rapidly recurring system known and the leading single-degenerate Type Ia Supernova progenitor candidate; but no 2010 eruption has been found so far. Here we present evidence supporting the recovery of the 2010 eruption, based on archival images taken at and around the time of eruption. We detect the 2010 eruption in a pair of images at 2010 Nov. 20.52 UT, with a magnitude of m R = 17.84 ± 0.19. The sequence of seven eruptions shows significant indications of a duty cycle slightly shorter than one year, which makes successive eruptions occur progressively earlier in the year. We compared three archival X-ray detections with the well-observed multi-wavelength light curve of the 2014 eruption to accurately constrain the time of their optical peaks. The results imply that M31N 2008-12a might actually have a recurrence period of ∼6 months (175 ± 11 days), making it even more exceptional. If this is the case, then we predict that two eruptions per year will be observable soon. Furthermore, we predict that the next eruption will occur in late Sep. 2015. We encourage additional observations.

We report photometric and spectroscopic observations of the nearby Type Ia Supernova (SN Ia) 2012ht from −15.8 days to +49.1 days after B-band maximum. The decline rate of the light curve is ∆m 15 (B)= 1.39 ± 0.05 mag, which is intermediate between normal and subluminous SNe Ia, and similar to that of the 'transitional' Type Ia SN 2004eo. The spectral line profiles also closely resemble those of SN 2004eo. We were able to observe SN 2012ht at very early phase, when it was still rising and was about three magnitudes fainter than at the peak. The rise time to the B-band maximum is estimated to be 17.6 ± 0.5 days and the time of the explosion is MJD 56277.98 ± 0.13. SN 2012ht is the first transitional SN Ia whose rise time is directly measured without using light curve templates, and the fifth SN Ia overall. This rise time is consistent with those of the other four SNe within the measurement error, even including the extremely early detection of SN 2013dy. The rising part of the light curve can be fitted by a quadratic function, and shows no sign of a shock-heating component due to the interaction of the ejecta with a companion star. The rise time is significantly longer than that inferred for subluminous SNe such as SN 1991bg, which suggests that a progenitor and/or explosion mechanism of transitional SNe Ia are more similar to normal SNe Ia rather than subluminous SNe Ia. Subject headings: supernovae: general -supernovae: individual (SN 2012ht) -supernovae: individual (SNe