Gamma-ray bursts (GRBs) are the most brilliant objects in the Universe but efforts to estimate the total energy released in the explosion -- a crucial physical quantity -- have been stymied by their unknown geometry: spheres or cones. We report on a comprehensive analysis of GRB afterglows and derive their conical opening angles. We find that the gamma-ray energy release, corrected for geometry, is narrowly clustered around 5x10**50 erg. We draw three conclusions. First, the central engines of GRBs release energies that are comparable to ordinary supernovae, suggesting a connection. Second, the wide variation in fluence and luminosity of GRBs is due entirely to a distribution of opening angles. Third, only a small fraction of GRBs are visible to a given observer and the true GRB rate is at least a factor of 500 times larger than the observed rate.Comment: Nature, submitte

We describe the target selection and resulting properties of a spectroscopic sample of luminous, red galaxies (LRG) from the imaging data of the Sloan Digital Sky Survey (SDSS). These galaxies are selected on the basis of color and magnitude to yield a sample of luminous, intrinsically red galaxies that extends fainter and further than the main flux-limited portion of the SDSS galaxy spectroscopic sample. The sample is designed to impose a passively-evolving luminosity and restframe color cut to a redshift of 0.38. Additional, yet more luminous, red galaxies are included to a redshift of ∼ 0.5. Approximately 12 of these galaxies per square degree are targeted for spectroscopy, so the sample will number over 100,000 with the full survey. SDSS commissioning data indicate that the algorithm efficiently selects luminous (M g * ≈ −21.4), red galaxies, that the spectroscopic success rate is very high, and that the resulting set of galaxies is approximately volume-limited out to z = 0.38. When the SDSS is complete, the LRG spectroscopic sample will fill over 1h −3 Gpc 3 with an approximately homogeneous population of galaxies and will therefore be well suited to studies of large-scale structure and clusters out to z = 0.5. 20 Called bright, red galaxies (BRG), in analogy to brightest cluster galaxies, in earlier papers and documentation.

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.

There is increasingly strong evidence that gamma-ray bursts (GRBs) are associated with star-forming galaxies and occur near or in the star-forming regions of these galaxies. These associations provide indirect evidence that at least the long GRBs detected by BeppoSAX are a result of the collapse of massive stars. The recent evidence that the light curves and the spectra of the afterglows of GRB 970228 and GRB 980326 appear to contain a supernova component, in addition to a relativistic shock-wave component, provides more direct clues that this is the case. We show that, if many GRBs are indeed produced by the collapse of massive stars, GRBs and their afterglows provide a powerful probe of the very high redshift universe. We Ðrst establish that GRBs and their afterglows are both detectable out to (z Z 5) very high redshifts. We then show that one expects GRBs to occur out to at least z B 10, and possibly to z B 15È20, redshifts that are far larger than those expected for the most distant quasars. This implies that there are large numbers of GRBs with peak photon number Ñuxes below the detection thresholds of BATSE and HET E 2, and even below the detection threshold of Swift. The mere detection of very high redshift GRBs would give us our Ðrst information about the earliest generations of stars. We show that GRBs and their afterglows can be used as beacons to locate core-collapse supernovae at redshifts z ? 1 and to study the properties of these supernovae. We describe the expected properties of the absorptionline systems and the Lya forest in the spectra of GRB afterglows and discuss various strategies for determining the redshifts of very high redshift GRBs. We then show how the absorption-line systems and the Lya forest visible in the spectra of GRB afterglows can be used to trace the evolution of metallicity in the universe and to probe the large-scale structure of the universe at very high redshifts. Finally, we show how measurement of the Lya break in the spectra of GRB afterglows can be used to constrain, or possibly measure, the epoch at which reionization of the universe occurred by using the Gunn-Peterson test.

We present a possible Cepheid-like luminosity estimator for the long gamma-ray bursts based on the variability of their light curves. To construct the luminosity estimator, we use CGRO/BATSE data for 13 bursts, W ind/Konus data for Ðve bursts, Ulysses/GRB data for one burst, and NEAR/XGRS data for one burst. Spectroscopic redshifts, peak Ñuxes, and high-resolution light curves are available for 11 of these bursts ; partial information is available for the remaining nine bursts. We Ðnd that the isotropic equivalent peak luminosities L of these bursts positively correlate with a rigorously constructed measure V of the variability of their light curves. We Ðt to these data a model that accommodates both intrinsic scatter (statistical variance) and extrinsic scatter (sample variance). We Ðnd that If one L D V 3.3~0 1 . . 9 1 . excludes GRB 980425 from the Ðt, on the grounds that its association with SN 1998bw at a redshift of z \ 0.0085 is not secure, the luminosity estimator spans B2.5 orders of magnitude in L , and the slope of the correlation between L and V is positive with a probability of 1 [ (1.4 ] 10~4) (3.8 p). Although GRB 980425 is excluded from this Ðt, its L and V values are consistent with the Ðtted model, which suggests that GRB 980425 may well be associated with SN 1998bw and that GRB 980425 and the cosmological bursts may share a common physical origin. If one includes GRB 980425 in the Ðt, the luminosity estimator spans B6.3 orders of magnitude in L , and the slope of the correlation is positive with a probability of 1 [ (9.3 ] 10~7) (4.9 p). In either case, the luminosity estimator yields best-estimate luminosities that are accurate to a factor of B4, or best-estimate luminosity distances that are accurate to a factor of B2. Regardless of whether GRB 980425 should be included in the Ðt, its light curve is unique in that it is much less variable than the other B17 light curves of bursts in our sample for which the signal-tonoise ratio is reasonably good.

During the second observing run of the Laser Interferometer gravitationalwave Observatory (LIGO) and Virgo Interferometer, a gravitational-wave signal consistent with a binary neutron star coalescence was detected on 2017 August 17th (GW170817), quickly followed by a coincident short gamma-ray burst trigger by the Fermi satellite. The Distance Less Than 40 (DLT40) Mpc supernova search performed pointed follow-up observations of a sample of galaxies regularly monitored by the survey which fell within the combined LIGO+Virgo localization region, and the larger Fermi gamma ray burst error box. Here we report the discovery of a new optical transient (DLT17ck, also known as SSS17a; it has also been registered as AT 2017gfo) spatially and temporally coincident with GW170817. The photometric and spectroscopic evolution of DLT17ck are unique, with an absolute peak magnitude of M r = -15.8 ± 0.1 and an r−band decline rate of 1.1 mag/d. This fast evolution is generically consistent with kilonova models, which have been predicted as the optical counterpart to binary neutron star coalescences. Analysis of archival DLT40 data do not show any sign of transient activity at the location of DLT17ck down to r∼19 mag in the time period between 8 months and 21 days prior to GW170817. This discovery represents the beginning of a new era for multi-messenger astronomy opening a new path to study and understand binary neutron star coalescences, short gamma-ray bursts and their optical counterparts.

Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently. Backward integrations of their orbits indicated that they separated gently with low relative velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process may explain their formation-critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primary's spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.

We present ultraviolet, optical and near-infrared observations of the interacting transient SN 2009ip, covering the period from the start of the outburst in 2012 October until the end of the 2012 observing season. The transient reached a peak magnitude of M V = −17.7 mag, with a total integrated luminosity of 1.9 × 10 49 erg over the period of 2012 August-December. The light curve fades rapidly, dropping by 4.5 mag from the V-band peak in 100 d. The optical and near-infrared spectra are dominated by narrow emission lines with broad electron scattering wings, signalling a dense circumstellar environment, together with multiple components of broad emission and absorption in H and He at velocities in the range 0.5-1.2 × 10 4 km s −1 . We see no evidence for nucleosynthesized material in SN 2009ip, even in late-time pseudonebular spectra. We set a limit of <0.02 M on the mass of any possible synthesized 56 Ni from the late-time light curve. A simple model for the narrow Balmer lines is presented and used to derive number densities for the circumstellar medium in the range ∼10 9 -10 10 cm −3 . Our * Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of programme 188.D-3003 (PESSTO).