This is the second paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). In this paper, a complete SN sample is constructed, and the observed (uncorrected for host-galaxy extinction) luminosity functions (LFs) of SNe are derived. These LFs solve two issues that have plagued previous rate calculations for nearby SNe: the luminosity distribution of SNe and the host-galaxy extinction. We select a volume-limited sample of 175 SNe, collect photometry for every object, and fit a family of light curves to constrain the peak magnitudes and light-curve shapes. The volume-limited LFs show that they are not well represented by a Gaussian distribution. There are notable differences in the LFs for galaxies of different Hubble types (especially for SNe Ia). We derive the observed fractions for the different subclasses in a complete SN sample, and find significant fractions of SNe II-L (10%), IIb (12%), and IIn (9%) in the SN II sample. Furthermore, we derive the LFs and the observed fractions of different SN subclasses in a magnitudelimited survey with different observation intervals, and find that the LFs are enhanced at the high-luminosity end and appear more “standard” with smaller scatter, and that the LFs and fractions of SNe do not change significantly when the observation interval is shorter than 10 d. We also discuss the LFs in different galaxy sizes and inclinations, and for different SN subclasses. Some notable results are that there is not a strong correlation between the SN LFs and the host-galaxy size, but there might be a preference for SNe IIn to occur in small, late-type spiral galaxies. The LFs in different inclination bins do not provide strong evidence for extreme extinction in highly inclined galaxies, though the sample is still small. The LFs of different SN subclasses show significant differences. We also find that SNe Ibc and IIb come from more luminous galaxies than SNe II-P, while SNe IIn come from less luminous galaxies, suggesting a possible metallicity effect. The limitations and applications of our LFs are also discussed.

Nearby Supernova Rates from the Lick Observatory Supernova Search. II. The Observed Luminosity Functions and Fractions of Supernovae in a Complete Sample

With its rapid-response capability and multiwavelength complement of instruments, the Swift satellite has transformed our physical understanding of γ-ray bursts (GRBs). Providing high-quality observations of hundreds of bursts, and facilitating a wide range of follow-up observations within seconds of each event, Swift has revealed an unforeseen richness in observed burst properties, shed light on the nature of short-duration bursts, and helped realize the promise of GRBs as probes of the processes and environments of star formation out to the earliest cosmic epochs. These advances have opened new perspectives on the nature and properties of burst central engines, interactions with the burst environment from microparsec to gigaparsec scales, and the possibilities for nonphotonic signatures. Our understanding of these extreme cosmic sources has thus advanced substantially; yet, more than 40 years after their discovery, GRBs continue to present major challenges on both observational and theoretical fronts.

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Gamma-Ray Bursts in the Swift Era

We present ground-based optical and Hubble Space Telescopeoptical and near-IR observations of the shorthard GRB 130603B at z = 0.356, which demonstrate the presence of excess near-IR emission matching the expected brightness and color of an r-process powered trans ient (a “kilonova”). The early afterglow fades rapidly with � . -2.6 at t � 8 - 32 hr post-burst and has a spectral index of � � -1.5 (F� / t � � � ), leading to an expected near-IR brightness at the time of the first HST observation of mF160W(t = 9.4 d) & 29.3 AB mag. Instead, the detected source has mF160W = 25.8± 0.2 AB mag, corresponding to a rest-frame absolute magnitude of MJ � -15.2 mag. The upper limit in the HST optical observations is mF606W & 27.7 AB mag (3�), indicating an unusually red color of V - H & 1.9 mag. Comparing the observed near-IR luminosity to theoretical models of kilonovae produced by ejecta from the merger of an NS-NS or NS-BH binary, we infer an ejecta mass of Mej � 0.03 - 0.08 M⊙ for vej � 0.1 - 0.3c. The inferred mass matches the expectations from numerical merger simulations. The presence of a kilonova provides the strongest evidence to date that short GRBs are produced by compact object mergers, and provides initial insight on t he ejected mass and the primary role that compact object merger may play in the r-process. Equally important, it demonstrates that gravitational wave sources detected by Advanced LIGO/Virgo will be accompanied by optical/near-IR counterparts with unusually red colors, detectable by existing and upcoming large wide-fiel d facilities (e.g., Pan-STARRS, DECam, Subaru, LSST).

https://iopscience.iop.org/article/10.1088/2041-8205/774/2/L23/pdf

An r-process Kilonova Associated with the Short-hard GRB 130603B

The Zwicky Transient Facility (ZTF), a public-private enterprise, is a new time domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg$^2$ field of view and 8 second readout time. It is well positioned in the development of time domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities which provided funding ("partnership") are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r $\sim$ 20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei and tidal disruption events, stellar variability, and Solar System objects.

The Zwicky Transient Facility: Science Objectives

The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two ‘relativistic’ candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report a luminous ultraviolet–optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.

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An ultraviolet-optical flare from the tidal disruption of a helium-rich stellar core

Massive stars end their short lives in spectacular explosions—supernovae—that synthesize new elements and drive galaxy evolution. Historically, supernovae were discovered mainly through their 'delayed' optical light (some days after the burst of neutrinos that marks the actual event), preventing observations in the first moments following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of the explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the 'break-out' of the supernova shock wave from the progenitor star, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We predict that future wide-field X-ray surveys will catch each year hundreds of supernovae in the act of exploding.

/pdf/an-extremely-luminous-x-ray-outburst-at-the-birth-of-a-3k4ifn2u7q.pdf

An extremely luminous X-ray outburst at the birth of a supernova

Massive stars end their short lives in spectacular explosions, supernovae, that synthesize new elements and drive galaxy evolution. Throughout history supernovae were discovered chiefly through their delayed optical light, preventing observations in the first moments (hours to days) following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the break-out of the supernova shock-wave from the progenitor, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We forecast that future wide-field X-ray surveys will catch hundreds of supernovae each year in the act of explosion, and thereby enable crucial neutrino and gravitational wave detections that may ultimately unravel the explosion mechanism.

G. Byrngelson

Papers

An extremely luminous X-ray outburst at the birth of a supernova

An Extremely Luminous X-ray Outburst Marking the Birth of a Normal Supernova