We describe observed properties of the Type Iax class of supernovae (SNe Iax), consisting of SNe observationally similar to its prototypical member, SN 2002cx. The class currently has 25 members, and we present optical photometry and/or optical spectroscopy for most of them. SNe Iax are spectroscopically similar to SNe Ia, but have lower maximum-light velocities (2000 |v| 8000 km s −1 ), typically lower peak magnitudes (−14.2 ≥ M V,peak −18.9 mag), and most have hot photospheres. Relative to SNe Ia, SNe Iax have low luminosities for their light-curve shape. There is a correlation between luminosity and light-curve shape, similar to that of SNe Ia, but offset from that of SNe Ia and with larger scatter. Despite a host-galaxy morphology distribution that is highly skewed to late-type galaxies without any SNe Iax discovered in elliptical galaxies, there are several indications that the progenitor stars are white dwarfs (WDs): evidence of C/O burning in their maximum-light spectra, low (typically ∼ 0.5 M ⊙ ) ejecta masses, strong Fe lines in their late-time spectra, a lack of X-ray detections, and deep limits on massive stars and star formation at the SN sites. However, two SNe Iax show strong He lines in their spectra. The progenitor system and explosion model that best fits all of the data is a binary system of a C/O WD that accretes matter from a He star and has a deflagration. At least some of the time, this explosion will not disrupt the WD. The small number of SNe in this class prohibit a detailed analysis of the homogeneity and heterogeneity of the entire class. We estimate that in a given volume there are 31 +17 −13 SNe Iax for every 100 SNe Ia, and for every 1 M ⊙ of iron generated by SNe Ia at z = 0, SNe Iax generate ∼0.036 M ⊙ . Being the largest class of peculiar SNe, thousands of SNe Iax will be discovered by LSST. Future detailed observations of SNe Iax should further our understanding of both their progenitor systems and explosions as well as those of SNe Ia.

We present an analysis of the diversity of V -band light-curves of hydrogen-rich type II supernovae. Analyzing a sample of 116 supernovae, several magnitude measurements are defined, together with decline rates at different epochs, and time durations of different phases. It is found that magnitudes measured at maximum light correlate more strongly with decline rates than those measured at other epochs: brighter supernovae at maximum generally have faster declining light-curves at all epochs. We find a relation between the decline rate during the 'plateau' phase and peak magnitudes, which has a dispersion of 0.56 magnitudes, offering the prospect of using type II supernovae as purely photometric distance indicators. Our analysis suggests that the type II population spans a continuum from low-luminosity events which have flat light-curves during the 'plateau' stage, through to the brightest events which decline much faster. A large range in optically thick phase durations is observed, implying a range in progenitor envelope masses at the epoch of explosion. During the radioactive tails, we find many supernovae with faster declining light-curves than expected from full trapping of radioactive emission, implying low mass ejecta. It is suggested that the main driver of light-curve diversity is the extent of hydrogen envelopes retained before explosion. Finally, a new classification scheme is introduced where hydrogen-rich events are typed as simply 'SN II' with an 's 2 ' value giving the decline rate during the 'plateau' phase, indicating its morphological type. Subject headings: (stars:) supernovae: general * Based on observations obtained with the du-Pont and Swope telescopes at LCO, and the Steward Observatory's CTIO60, SO90 and CTIO36 telescopes.

Long duration gamma-ray bursts (GRBs) mark 1 the explosive death of some massive stars and are a rare sub-class of Type Ibc supernovae (SNe Ibc). They are distinguished by the production of an energetic and collimated relativistic outflow powered 2 by a central engine (an accreting black hole or neutron star).Observationally, this outflow is manifested 3 in the pulse of gamma-rays and a long-lived radio afterglow. To date, central engine-driven SNe have been discovered exclusively through their gamma-ray emission, yet it is expected 4 that a larger population goes undetected due to limited satellite sensitivity or beaming of the collimated emission away from our line-of-sight. In this framework, 2 Soderberg et al.the recovery of undetected GRBs may be possible through radio searches 5,6 for SNe Ibc with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary Type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. The lack of a coincident GRB makes SN 2009bb the first engine-driven SN discovered without a detected gamma-ray signal. A comparison with our extensive radio survey of SNe Ibc reveals that the fraction harboring central engines is low, ∼ 1%, measured independently from, but consistent with, the inferred 46 rate of nearby GRBs. Our study demonstrates that upcoming optical and radio surveys will soon rival gamma-ray satellites in pinpointing the nearest engine-driven SNe.A similar result for a different supernova is reported 8 independently. A Relativistic SN 3Unlike the optical emission from SNe which traces only the slowest explosion debris, radio observations uniquely probe 35 the fastest ejecta as the expanding blastwave (velocity, v) shocks and accelerates electrons in amplified magnetic fields. The resulting synchrotron emission is suppressed by self-absorption (SSA) producing a low frequency radio turnover that defines the spectral peak frequency, ν p . Combining our observations from the VLA and the Giant Meterwave Radio Telescope (GMRT), the radio spectra of SN 2009bbare well described by an SSA model across multiple epochs ( Figure 2). From our earliest spectrum on Apr 8 UT (∆t ≈ 20 days), we infer ν p ≈ 6 GHz and a spectral peak luminosity,Making the conservative assumption that the energy of the radio emitting material is partitioned equally into accelerating electrons and amplifying magnetic fields (equipartition), the properties of the SSA radio spectrum enable 13,35 a robust estimate of the blastwave radius, R ≈ 2.9 × 10 16 (L ν,p /10 28 erg ssynchrotron sources with a low spectral peak frequency thus require larger sizes (Figure 3).For SN 2009bb, we infer R ≈ 4.4 × 10 16 cm at ∆t ≈ 20 days and thus the mean expansion velocity is R/∆t = 0.85 ± 0.02c, where c is the speed of light. The transverse expansion speed, Γβc = R/∆t indicates that the blastwave is relativistic, Γ 1.3, at this time [bulk Lorentz factor Γ = (1 − β 2 ) −1/2 with β = v/c]. This is a lower limit on the initial velocity since th...

3It is now accepted that long duration γ-ray bursts (GRBs) are produced during the collapse of a massive star 1,2 . 11,12 . GRB 060505 was a faint burst with a duration of 4 s. GRB 060614 had a duration of 102 s and a pronounced hard to soft evolution. Both were rapidly localised by Swift's X-ray telescope (XRT). Subsequent follow-up of these bursts led to the discovery of their optical afterglows, locating them in galaxies at low redshift: GRB 060505 at z = 0.089 13 and GRB 060614 at z = 0.125 14,15 . The relative proximity of these bursts engendered an expectation that a bright SN would be discovered a few days after the bursts, as had been found just a few months before in 4 another low-redshift Swift burst, GRB 060218 (z = 0.033) 9 , and in all previous wellobserved nearby bursts 1,5-8 .We monitored the afterglows of GRB 060505 and 060614 using a range of telescopes (see supplementary material for details). These led to early detections of the afterglows. We continued the monitoring campaign and obtained stringent upper limits on any re-brightening at the position of the optical afterglows up to 12 and 5 weeks after the bursts, respectively. The light-curves obtained based on this monitoring are shown in Fig. 1. For GRB 060505 we detected the optical afterglow at a single epoch. All subsequent observations resulted in deep upper limits. For GRB 060614 we followed the decay of the optical afterglow in the R-band up to four nights after the burst. In later observations no source was detected to deep limits (see also 14,15 for independent studies of this event). As seen in Fig. 1, the upper limits are far below the level seen in previous SNe, in particular previous SNe associated with long-duration GRBs 5-9 . For both GRBs A concern in any attempt to uncover a SN associated with a GRB is the presence of a poorly quantified level of extinction along the line of sight. In these cases however,we are fortunate that the levels of Galactic extinction in both directions are very low,. In the case of GRB 060505, our spatially resolved spectroscopy of the host galaxy allows us to use the Balmer emission line ratios to limit the dust obscuration 5 at the location of the burst. The Balmer line ratio is consistent with no internal reddening. In the case of GRB 060614, the detection of the early afterglow in many bands, including the Swift UV bands UVW1 and UVW2 17 , rules out significant obscuration of the source in the host galaxy and we conclude that there is no significant dust obscuration in either case (see also 15 ).Both GRBs were located in star-forming galaxies. The host galaxy of GRB 060505 has an absolute magnitude of about M B = -19.6 and the spectrum displays the prominent emission lines typically seen in star-forming galaxies. The 2-dimensional spectrum shows that the host galaxy emission seen at the position of the afterglow is due to a compact H II region in a spiral arm of the host (see the supplementary material for details). We estimate a star-formation rate of 1 M  yr −1 and a specific rate of about 4T...