We report the results of a multi-year spectroscopic and photometric survey of novae in M31 that resulted in a total of 53 spectra of 48 individual nova candidates. Two of these, M31N 1995-11e and M31N 2007-11g, were revealed to be long-period Mira variables, not novae. These data double the number of spectra extant for novae in M31 through the end of 2009 and bring to 91 the number of M31 novae with known spectroscopic classifications. We find that 75 novae (82%) are confirmed or likely members of the Fe II spectroscopic class, with the remaining 16 novae (18%) belonging to the He/N (and related) classes. These numbers are consistent with those found for Galactic novae. We find no compelling evidence that spectroscopic class depends sensitively on spatial position or population within M31 (i.e., bulge vs. disk), although the distribution for He/N systems appears slightly more extended than that for the Fe II class. We confirm the existence of a correlation between speed class and ejection velocity (based on line width), as in the case of Galactic novae. Follow-up photometry allowed us to determine light-curve parameters for a total of 47 of the 91 novae with known spectroscopic class. We confirm that more luminous novae generally fade the fastest, and that He/N novae are typically faster and brighter than their Fe II counterparts. In addition, we find a weak dependence of nova speed class on position in M31, with the spatial distribution of the fastest novae being slightly more extended than that of slower novae.

RS Ophiuchi began its latest outburst on 2006 February 12. Previous outbursts have indicated that high-velocity ejecta interact with a preexisting red giant wind, setting up shock systems analogous to those seen in supernova remnants. However, in the previous outburst in 1985, X-ray observations did not commence until 55 days after the initial explosion. Here we report on Swift observations covering the first month of the 2006 outburst with the Burst Alert Telescope (BAT) and X-Ray Telescope (XRT) instruments. RS Oph was clearly detected in the BAT 14Y25 keV band from t ¼ 0 to t $ 6 days. XRT observations from 0.3 to 10 keV started 3.17 days after outburst. The rapidly evolving XRT spectra clearly show the presence of both line and continuum emission, which can be fitted by thermal emission from hot gas whose characteristic temperature, overlying absorbing column (N H ) W , and resulting unabsorbed total flux decline monotonically after the first few days. Derived shock velocities are in good agreement with those found from observations at other wavelengths. Similarly, (N H ) W is in accord with that expected from the red giant wind ahead of the forward shock. We confirm the basic models of the 1985 outburst and conclude that standard phase I remnant evolution terminated by t $ 6 days and the remnant then rapidly evolved to display behavior characteristic of phase III. Around t ¼ 26 days, however, a new, luminous, and highly variable soft X-ray source began to appear, whose origin will be explored in a subsequent paper.

A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground-and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.

Of the approximately 400 known Galactic classical novae, only ten of them, the recurrent novae, have been seen to erupt more than once. At least eight of these recurrents are known to harbor evolved secondary stars, rather than the main sequence secondaries typical in classical novae. In this paper, we propose a new nova classification system, based solely on the evolutionary state of the secondary, and not (like the current schemes) based on the properties of the outbursts. Using archival optical and near-infrared photometric observations of a sample of thirty eight quiescent Galactic novae we show that the evolutionary state of the secondary star in a quiescent system can predicted and several objects are identified for follow-up observations; CI Aql, V2487 Oph, DI Lac and EU Sct.

We present observations and analysis of 18 stripped-envelope supernovae observed during 2013 -2018. This sample consists of 5 H/He-rich SNe, 6 H-poor/He-rich SNe, 3 narrow lined SNe Ic and 4 broad lined SNe Ic. The peak luminosity and characteristic time-scales of the bolometric light curves are calculated, and the light curves modelled to derive 56 Ni and ejecta masses (M Ni and M ej ). Additionally, the temperature evolution and spectral line velocity-curves of each SN are examined. Analysis of the [O i] line in the nebular phase of eight SNe suggests their progenitors had initial masses < 20 M . The bolometric light curve properties are examined in combination with those of other SE events from the literature. The resulting dataset gives the M ej distribution for 80 SE-SNe, the largest such sample in the literature to date, and shows that SNe Ib have the lowest median M ej , followed by narrow lined SNe Ic, H/He-rich SNe, broad lined SNe Ic, and finally gamma-ray burst SNe. SNe Ic-6/7 show the largest spread of M ej ranging from ∼ 1.2 − 11 M , considerably greater than any other subtype. For all SE-SNe = 2.8 ± 1.5 M which further strengthens the evidence that SE-SNe arise from low mass progenitors which are typically < 5 M at the time of explosion, again suggesting M ZAMS < 25 M . The low and lack of clear bimodality in the distribution implies < 30 M progenitors and that envelope stripping via binary interaction is the dominant evolutionary pathway of these SNe.

We present light curves of three classical novae (KT Eridani, V598 Puppis, V1280 Scorpii) and one recurrent nova (RS Ophiuchi) derived from data obtained by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. SMEI provides near complete sky-map coverage with precision visible-light photometry at 102-minute cadence. The light curves derived from these sky maps offer unprecedented temporal resolution around, and especially before, maximum light, a phase of the nova eruption normally not covered by ground-based observations. They allow us to explore fundamental parameters of individual objects including the epoch of the initial explosion, the reality and duration of any pre-maximum halt (found in all three fast novae in our sample), the presence of secondary maxima, speed of decline of the initial light curve, plus precise timing of the onset of dust formation (in V1280 Sco) leading to estimation of the bolometric luminosity, white dwarf mass and object distance. For KT Eri, Liverpool Telescope SkyCamT data confirm important features of the SMEI light curve and overall our results add weight to the proposed similarities of this object to recurrent rather than to classical novae. In RS Oph, comparison with hard X-ray data from the 2006 outburst implies that the onset of the outburst coincides with extensive high velocity mass-loss. It is also noted that two of the four novae we have detected (V598 Pup and KT Eri) were only discovered by ground-based observers weeks or months after maximum light, yet these novae reached peak magnitudes of 3.46 and 5.42 respectively. This emphasizes the fact that many bright novae per year are still overlooked, particularly those of the very fast speed class. Coupled with its ability to observe novae in detail even when relatively close to the Sun in the sky, we estimate that as many as 5 novae per year may be detectable by SMEI.PACS numbers: 90

Results. Photometry of the 2013 eruption, combined with three previous eruptions, enabled construction of a template lightcurve of a very fast nova (t 2 (V) 4 days). The archival data allowed recovery of the progenitor system in optical and near-UV data, indicating a red-giant secondary with bright accretion disk, or alternatively a system with a sub-giant secondary but dominated by a disk. Conclusions. The eruptions of M 31N 2008-12a, and a number of historic X-ray detections, indicate a unique system with a recurrence timescale of ∼1 yr. This implies the presence of a very high-mass white dwarf and a high accretion rate. The recovered progenitor system is consistent with such an elevated rate of accretion. We encourage additional observations, especially towards the end of 2014.

We present observations of M31LRN 2015 (MASTER OT J004207.99+405501.1), discovered in M31 in 2015 January, and identified as a rare and enigmatic luminous red nova (LRN). Spectroscopic and photometric observations obtained by the Liverpool Telescope showed the LRN becoming extremely red as it faded from its = − ± M 9.4 0.2 V peak. Early spectra showed strong Hα emission that weakened over time as a number of absorption features appeared, including Na I D and Ba II. At later times strong TiO absorption bands were also seen. A search of archival Hubble Space Telescope data revealed a luminous red source to be the likely progenitor system, with pre-outburst Hα emission also detected in ground-based data. The outburst of M31LRN 2015 shows many similarities, both spectroscopically and photometrically, with that of V838 Mon, the best studied LRN. We finally discuss the possible progenitor scenarios.