16648604
The Redshift and the Ordinary Host Galaxy of GRB 970228
The gamma-ray burst of 1997 February 28 (GRB 970228) ushered in the discovery of the afterglow phenomenon. Despite intense study of the nearby galaxy, however, the nature of this galaxy and the distance to the burst eluded the community. Here we present the measurement of the redshift of the galaxy, the putative host galaxy of GRB 970228, and, based on its spectroscopic and photometric properties, identify the galaxy as a subluminous but otherwise normal galaxy at redshift z = 0.695 undergoing a modest level of star formation. At this redshift, the GRB released an isotropic-equivalent energy of (1.4 ± 0.3) × 1052 ergs (20-2000 keV rest frame). We find no evidence that the host is significantly bluer or is forming stars more vigorously than the general field population. In fact, by all accounts in our analysis (color-magnitude, magnitude-radius, star formation rate, and Balmer-break amplitude), the host properties appear typical for faint blue field galaxies at comparable redshifts.
8913778
Spitzer Observations of the New Luminous Red Nova M85 OT2006-1
M85 OT2006-1 is the latest and most brilliant addition to the small group of known luminous red novae (LRNe). An identifying characteristic of the previously detected events (M31 RV, V4332 Sgr, and V838 Mon) was a spectral redward evolution connected with an emerging infrared component following the optical decay. Here we report on the discovery of a similar feature in Keck NIRC and Spitzer photometry of M85 OT2006-1 6 months posteruption. We find that its 2.1-22 μm spectral energy distribution is best described by a blackbody with effective temperature T_(eff) = 950 ± 150 K and bolometric luminosity L = 2.9^(+0.4)_(-0.5) × 10^5 L_⊙. Assuming spherical geometry, the blackbody effective radius, R = 2.0^(+0.6)_(-0.4) × 10^4 R_⊙, and corresponding expansion velocity, v = 870^(+260)_(-180) km s^(-1), are remarkably similar to the properties of M31 RV 70 days after its eruption. Furthermore, we propose a search strategy for LRNe in the local universe making use of the longevity of their infrared excess emission and discuss the expected number of events in the Spitzer Infrared Nearby Galaxies Survey.
11026035
The Incidence of Dwarf Novae in Large Area Transient Searches
Understanding and quantifying the contribution of known classes of transient and variable sources is an important lesson to be learned from the manifold of precursor programs of the near-future large synoptic sky survey programs such as SkyMapper, Pan-STARRS, and LSST. With this goal in mind, we undertook photometric and spectroscopic follow-up observations of four recently reported unidentified transients. For two sources, WFI J132813.7-214237 and WFI J161953.3+031909, we show that unfortunate coincidences led to their previous designation as transients. While the former is now interpreted as the spatial coincidence of a solar system object with a faint background star, the latter is merely a cataclysmic variable unfortunately caught in and out of eclipse. The third candidate, ROTSE3 J160213.1-021311.7, is identified as an SU UMa type dwarf nova with quiescent brightness of R ~ 22.7 and an outburst amplitude of ~5 mag. The fourth event, SDSS-SN 15207, similarly shows evidence for a dwarf nova origin. Our main conclusion is that cataclysmic variables in their various avatars will contribute moderately to the population of transient objects.
20207808
DISCOVERY OF A COSMOLOGICAL, RELATIVISTIC OUTBURST VIA ITS RAPIDLY FADING OPTICAL EMISSION
We report the discovery by the Palomar Transient Factory (PTF) of the transient source PTF11agg, which is distinguished by three primary characteristics: (1) bright (Rpeak = 18.3mag), rapidly fading (ΔR = 4mag in Δt = 2 days) optical transient emission; (2) a faint (R = 26.2 ± 0.2mag), blue (g � − R = 0.17 ± 0.29mag) quiescent optical counterpart; and (3) an associated year-long, scintillating radio transient. We argue that these observed properties are inconsistent with any known class of Galactic transients (flare stars, X-ray binaries, dwarf novae), and instead suggest a cosmological origin. The detection of incoherent radio emission at such distances implies a large emitting region, from which we infer the presence of relativistic ejecta. The observed properties are allconsistentwiththepopulationoflong-durationgamma-raybursts(GRBs),markingthefirsttimesuchanoutburst has been discovered in the distant universe independent of a high-energy trigger. We searched for possible highenergy counterparts to PTF11agg, but found no evidence for associated prompt emission. We therefore consider three possible scenarios to account for a GRB-like afterglow without a high-energy counterpart: an “untriggered” GRB (lack of satellite coverage), an “orphan” afterglow (viewing-angle effects), and a “dirty fireball” (suppressed high-energy emission). The observed optical and radio light curves appear inconsistent with even the most basic predictions for off-axis afterglow models. The simplest explanation, then, is that PTF11agg is a normal, on-axis long-durationGRBforwhichtheassociatedhigh-energyemissionwassimplymissed.However,wehavecalculated the likelihood of such a serendipitous discovery by PTF and find that it is quite small (≈2.6%). While not definitive, we nonetheless speculate that PTF11agg may represent a new, more common (>4 times the on-axis GRB rate at 90% confidence) class of relativistic outbursts lacking associated high-energy emission. If so, such sources will be uncovered in large numbers by future wide-field optical and radio transient surveys.
14167939
Detecting Outer Planets in Edge-on Orbits: Combining Radial Velocity and Astrometric Techniques
The astrometric and radial velocity techniques of extrasolar planet detection attempt to detect the periodic reflex motion of the parent star by extracting this periodic signal from a time-sampled set of observations. The extraction is generally accomplished using periodogram analysis or the functionally equivalent technique of least-squares fitting of sinusoids. In this paper, we use a frequentist approach to examine the sensitivity of the least-squares technique when applied to a combination of radial velocity and astrometric observations. We derive an analytical expression for the sensitivity and show that the combined approach yields significantly better sensitivity than either technique on its own. We discuss the ramifications of this result to upcoming astrometric surveys with the Full-Sky Astrometric Mapping Explorer, the Keck Interferometer, and the Space Interferometry Mission.
28576228
CORE-COLLAPSE SUPERNOVAE FROM THE PALOMAR TRANSIENT FACTORY: INDICATIONS FOR A DIFFERENT POPULATION IN DWARF GALAXIES
We use the first compilation of 72 core-collapse supernovae (SNe) from the Palomar Transient Factory (PTF) to study their observed subtype distribution in dwarf galaxies compared to giant galaxies. Our sample is the largest single-survey, untargeted, spectroscopically classified, homogeneous collection of core-collapse events ever assembled, spanning a wide host-galaxy luminosity range (down to M_r ≈ –14 mag) and including a substantial fraction (>20%) of dwarf (M_r ≥ –18 mag) hosts. We find more core-collapse SNe in dwarf galaxies than expected and several interesting trends emerge. We use detailed subclassifications of stripped-envelope core-collapse SNe and find that all Type I core-collapse events occurring in dwarf galaxies are either SNe Ib or broad-lined SNe Ic (SNe Ic-BL), while "normal" SNe Ic dominate in giant galaxies. We also see a significant excess of SNe IIb in dwarf hosts. We hypothesize that in lower metallicity hosts, metallicity-driven mass loss is reduced, allowing massive stars that would have appeared as "normal" SNe Ic in metal-rich galaxies to retain some He and H, exploding as Ib/IIb events. At the same time, another mechanism allows some stars to undergo extensive stripping and explode as SNe Ic-BL (and presumably also as long-duration gamma-ray bursts). Our results are still limited by small-number statistics, and our measurements of the observed N(Ib/c)/N(II) number ratio in dwarf and giant hosts (0.25^(+0.3)_(–0.15) and 0.23^(+0.11)_(–0.08), respectively; 1σ uncertainties) are consistent with previous studies and theoretical predictions. As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed via the dwarf-galaxy SN population.
118523006
Modelling the clustering of dark matter haloes in resummed perturbation theories
We address the issue of the cosmological bias between matter and galaxy distributions, looking at dark matter haloes as a first step to characterize galaxy clustering. Starting from the linear density field at high redshift, we follow the centre-of-mass trajectory of the material that will form each halo at late times (protohalo). We adopt a fluid-like description for the evolution of perturbations in the protohalo distribution, which is coupled to the matter density field via gravity. We present analytical solutions for the density and velocity fields, in the context of renormalized perturbation theory. We start from the linear solution, then compute one-loop corrections for the propagator and the power spectrum. Finally, we analytically resum the propagator, and we use a suitable extension of the time-renormalization-group method to resum the power spectrum. For halo masses M < 1014 h−1 M⊙, our results at z= 0 are in good agreement with N-body simulations. Our model is able to predict the halo–matter cross-spectrum with an accuracy of 5 per cent up to k≈ 0.1 h Mpc−1 approaching the requirements of future galaxy redshift surveys.
14909136
Remarks on the generalized Chaplygin gas
We develop an action formulation for the generalized Chaplygin gas (GCG). The most general form for the nonrelativistic GCG action is derived consistent with the equation of state. We also discuss a relativistic formulation for GCG by providing a detailed analysis of the Poincare algebra.
18639894
Nonconservation of energy-momentum tensor in classical Liouville theory
where Ah is the area of the horizon. In this context, the classical Liouville theory [4] has gained considerable importance owing to the work of Solodukhin [5]. He showed that the computation of the black hole entropy can be carried out at the classical level. He observed that the 4-dimensional Einstein-Hilbert action can be reduced to an effective 2-dimensional theory, with fixed boundary conditions on the horizon, by performing a dimensional reduction with the ansatz of spherical symmetry and writing the metric in conformally flat form. This action can then be transformed to a form similar to the classical Liouville theory which in turn admits a Virasoro algebra near the horizon with a nontrivial classical central charge. The computation of this central charge then allows to determine the black hole entropy from the Cardy formula [6]. This approach was then used to study thermodynamic properties of black hole with a bifurcate killing horizon [7]. However, it is a well known fact from general field theoretic considerations [8, 9] that a central charge is related to diffeomorphism anomaly manifested as a nonconservation of the energy-momentum tensor. This relation is discussed from quantum considerations. The central charge and the diffeomorphism anomaly reveal different manifestations of the same phenomenon – a breakdown of classical symmetry upon the process of quantisation. Since the central charge is obtained [5, 7] in a classical Liouville theory, a natural question that arises is whether, in such a theory, there is a diffeomorphism anomaly. The principal objective of this paper is to show that this is indeed true. In this paper, we show explicitly that if we consider terms in the expansion of the metric, near the horizon, beyond leading order, then it leads to a diffeomorphism anomaly which is compatible with the fact that the theory has a nontrivial classical central charge. The computation of this anomaly has in fact been done to all orders. To begin with, we consider a four-dimensional spherically symmetric metric of the form
13913623
Hawking fluxes, back reaction and covariant anomalies
Starting from the chiral covariant effective action approach of Banerjee and Kulkarni (2008 Phys. Lett. B 659 827), we provide a derivation of the Hawking radiation from a charged black hole in the presence of gravitational back reaction. The modified expressions for charge and energy flux, due to the effect of one-loop back reaction are obtained.
118387184
Higher order WKB corrections to black hole entropy in brick wall formalism
We calculate the statistical entropy of a quantum field with an arbitrary spin propagating on the spherical symmetric black hole background by using the brick wall formalism at higher orders in the WKB approximation. For general spins, we find that the correction to the standard Bekenstein–Hawking entropy depends logarithmically on the area of the horizon. Furthermore, we apply this analysis to the Schwarzschild and Schwarzschild–AdS(dS) black holes and discuss our results.