Mu and Tau Neutrino Thermalization and Production in Supernovae: Processes and Timescales

We investigate the rates of production and thermalization of $\nu_\mu$ and $\nu_\tau$ neutrinos at temperatures and densities relevant to core-collapse supernovae and protoneutron stars. Included are contributions from electron scattering, electron-positron annihilation, nucleon-nucleon bremsstrahlung, and nucleon scattering. For the scattering processes, in order to incorporate the full scattering kinematics at arbitrary degeneracy, the structure function formalism developed by Reddy et al. (1998) and Burrows and Sawyer (1998) is employed. Furthermore, we derive formulae for the total and differential rates of nucleon-nucleon bremsstrahlung for arbitrary nucleon degeneracy in asymmetric matter. We find that electron scattering dominates nucleon scattering as a thermalization process at low neutrino energies ($\epsilon_\nu\lesssim 10$ MeV), but that nucleon scattering is always faster than or comparable to electron scattering above $\epsilon_\nu\simeq10$ MeV. In addition, for $\rho\gtrsim 10^{13}$ g cm$^{-3}$, $T\lesssim14$ MeV, and neutrino energies $\lesssim60$ MeV, nucleon-nucleon bremsstrahlung always dominates electron-positron annihilation as a production mechanism for $\nu_\mu$ and $\nu_\tau$ neutrinos.Comment: 29 pages, LaTeX (RevTeX), 13 figures, submitted to Phys. Rev. C. Also to be found at anonymous ftp site http://www.astrophysics.arizona.edu; cd to pub/thompso

Strong Water Absorption in the Dayside Emission Spectrum of the Planet HD 189733b

Recent observations of the extrasolar planet HD 189733b did not reveal the presence of water in the emission spectrum of the planet. Yet models of such 'Hot Jupiter' planets predict an abundance of atmospheric water vapour. Validating and constraining these models is crucial for understanding the physics and chemistry of planetary atmospheres in extreme environments. Indications of the presence of water in the atmosphere of HD 189733b have recently been found in transmission spectra, where the planet's atmosphere selectively absorbs the light of the parent star, and in broadband photometry. Here we report on the detection of strong water absorption in a high signal-to-noise, mid-infrared emission spectrum of the planet itself. We find both a strong downturn in the flux ratio below 10 microns and discrete spectral features that are characteristic of strong absorption by water vapour. The differences between these and previous observations are significant and admit the possibility that predicted planetary-scale dynamical weather structures might alter the emission spectrum over time. Models that match the observed spectrum and the broadband photometry suggest that heat distribution from the dayside to the night side is weak. Reconciling this with the high night side temperature will require a better understanding of atmospheric circulation or possible additional energy sources.Comment: 11 pages, 1 figure, published in Natur

Theoretical Spectral Models of the Planet HD 209458b with a Thermal Inversion and Water Emission Bands

We find that a theoretical fit to all the HD 209458b data at secondary eclipse requires that the dayside atmosphere of HD 209458b have a thermal inversion and a stratosphere. This inversion is caused by the capture of optical stellar flux by an absorber of uncertain origin that resides at altitude. One consequence of stratospheric heating and temperature inversion is the flipping of water absorption features into emission features from the near- to the mid-infrared and we see evidence of such a water emission feature in the recent HD 209458b IRAC data of Knutson et al. In addition, an upper-atmosphere optical absorber may help explain both the weaker-than-expected Na D feature seen in transit and the fact that the transit radius at 24 $\mu$m is smaller than the corresponding radius in the optical. Moreover, it may be a factor in why HD 209458b's optical transit radius is as large as it is. We speculate on the nature of this absorber and the planets whose atmospheres may, or may not, be affected by its presence.Comment: Accepted to the Astrophysical Journal Letters on August 28, 2007, six pages in emulateapj forma

Theoretical Interpretation of the Measurements of the Secondary Eclipses of TrES-1 and HD209458b

We calculate the planet-star flux-density ratios as a function of wavelength from 0.5 microns to 25 microns for the transiting extrasolar giant planets TrES-1 and HD209458b and compare them with the recent Spitzer/IRAC-MIPS secondary eclipse data in the 4.5, 8.0, and 24 micron bands. With only three data points and generic calibration issues, detailed conclusions are difficult, but inferences regarding atmospheric composition, temperature, and global circulation can be made. Our models reproduce the observations reasonably well, but not perfectly, and we speculate on the theoretical consequences of variations around our baseline models. One preliminary conclusion is that we may be seeing in the data indications that the day side of a close-in extrasolar giant planet is brighter in the mid-infrared than its night side, unlike Jupiter and Saturn. This correspondence will be further tested when the data anticipated in other Spitzer bands are acquired, and we make predictions for what those data may show.Comment: 15 pages, including 3 color figures, submitted to the Astrophysical Journa

GRB Energetics in the Swift Era

We examine the rest frame energetics of 76 gamma-ray bursts (GRBs) with known redshift that were detected by the Swift spacecraft and monitored by the satellite's X-ray Telescope (XRT). Using the bolometric fluence values estimated in Butler et al. 2007b and the last XRT observation for each event, we set a lower limit the their collimation corrected energy Eg and find that a 68% of our sample are at high enough redshift and/or low enough fluence to accommodate a jet break occurring beyond the last XRT observation and still be consistent with the pre-Swift Eg distribution for long GRBs. We find that relatively few of the X-ray light curves for the remaining events show evidence for late-time decay slopes that are consistent with that expected from post jet break emission. The breaks in the X-ray light curves that do exist tend to be shallower and occur earlier than the breaks previously observed in optical light curves, yielding a Eg distribution that is far lower than the pre-Swift distribution. If these early X-ray breaks are not due to jet effects, then a small but significant fraction of our sample have lower limits to their collimation corrected energy that place them well above the pre-Swift Eg distribution. Either scenario would necessitate a much wider post-Swift Eg distribution for long cosmological GRBs compared to the narrow standard energy deduced from pre-Swift observations. We note that almost all of the pre-Swift Eg estimates come from jet breaks detected in the optical whereas our sample is limited entirely to X-ray wavelengths, furthering the suggestion that the assumed achromaticity of jet breaks may not extend to high energies.Comment: 30 pages, 10 figures, Accepted to Ap

Theory for the Secondary Eclipse Fluxes, Spectra, Atmospheres, and Light Curves of Transiting Extrasolar Giant Planets

We have created a general methodology for calculating the wavelength-dependent light curves of close-in extrasolar giant planets (EGPs) as they traverse their orbits. Focussing on the transiting EGPs HD189733b, TrES-1, and HD209458b, we calculate planet/star flux ratios during secondary eclipse and compare them with the Spitzer data points obtained so far in the mid-infrared. We introduce a simple parametrization for the redistribution of heat to the planet's nightside, derive constraints on this parameter (P_n), and provide a general set of predictions for planet/star contrast ratios as a function of wavelength, model, and phase. Moreover, we calculate average dayside and nightside atmospheric temperature/pressure profiles for each transiting planet/P_n pair with which existing and anticipated Spitzer data can be used to probe the atmospheric thermal structure of severely irradiated EGPs. We find that the baseline models do a good job of fitting the current secondary eclipse dataset, but that the Spitzer error bars are not yet small enough to discriminate cleanly between all the various possibilities.Comment: 14 figures, 7 text pages (in two-column emulateapj format); Accepted to the Ap.J. June 26, 2006; one cosmetic change made to astro-ph version

Analysis of the X-ray Emission of Nine Swift Afterglows

The X-ray light-curves of 9 Swift XRT afterglows (050126, 050128, 050219A, 050315, 050318, 050319, 050401, 050408, 050505) display a complex behaviour: a steep t^{-3.0 \pm 0.3} decay until ~400 s, followed by a significantly slower t^{-0.65+/-0.20} fall-off, which at 0.2--2 d after the burst evolves into a t^{-1.7+/-0.5} decay. We consider three possible models for the geometry of relativistic blast-waves (spherical outflows, non-spreading jets, and spreading jets), two possible dynamical regimes for the forward shock (adiabatic and fully radiative), and we take into account a possible angular structure of the outflow and delayed energy injection in the blast-wave, to identify the models which reconcile the X-ray light-curve decay with the slope of the X-ray continuum for each of the above three afterglow phases. By piecing together the various models for each phase in a way that makes physical sense, we identify possible models for the entire X-ray afterglow. The major conclusion of this work is that a long-lived episode of energy injection in the blast-wave, during which the shock energy increases at t^{1.0+/-0.5}, is required for five afterglows and could be at work in the other four as well. Optical observations in conjunction with the X-ray can distinguish among these various models. Our simple tests allow the determination of the location of the cooling frequency relative to the X-ray domain and, thus, of the index of the electron power-law distribution with energy in the blast-wave. The resulting indices are clearly inconsistent with an universal value.Comment: 10 pages, minor changes, to be published in the MNRA

Experimental study of acoustic displays of flight parameters in a simulated aerospace vehicle

Evaluating acoustic displays of target location in target detection and of flight parameters in simulated aerospace vehicle

The rapid decline of the prompt emission in Gamma-Ray Bursts

Many gamma ray bursts (GRBs) have been observed with the Burst-Alert and X-Ray telescopes of the Swift satellite. The successive `pulses' of these GRBs end with a fast decline and a fast spectral softening, until they are overtaken by another pulse, or the last pulse's decline is overtaken by a less rapidly-varying `afterglow'. The fast decline-phase has been attributed, in the currently-explored standard fireball model of GRBs, to `high-latitude' synchrotron emission from a collision of two conical shells. This high latitude emission does not explain the observed spectral softening. In contrast, the temporal behaviour and the spectral evolution during the fast-decline phase agree with the predictions of the cannonball model of GRBs.Comment: Four added figures comparing the evolution of the inferred effective photon spectral index during the fast decline phase of the prompt emission in 14 selected Swift GRBS and the cannonball (CB) model predictio