A simple physical model for long-duration gamma-ray bursts (GRBs) is used to fit the redshift (z) and the jet opening angle distributions measured with earlier GRB missions and with Swift. The effect of different sensitivities for GRB triggering is sufficient to explain the difference in the z distributions of the pre-Swift and Swift samples, with mean redshifts of hzi ffi 1:5 and hzi ffi 2:7, respectively. Assuming that the emission properties of GRBs do not change with time, we find that the data can only be fitted if the comoving rate density of GRB sources exhibits positive evolution to z k 3Y5. The mean intrinsic beaming factor of GRBs is found to range from %34 to 42, with the Swift average opening half-angle h j i $ 10 , compared to the pre-Swift average of h j i $ 7 . Within the uniform jet model, the GRB luminosity function is /L À3:25 Ã , as inferred from our best fit to the opening angle distribution. Because of the unlikely detection of several GRBs with z P 0:25, our analysis indicates that low-redshift GRBs represent a different population of GRBs than those detected at higher redshifts. Neglecting possible metallicity effects on GRB host galaxies, we find that %1 GRB occurs every 600,000 yr in a local L Ã spiral galaxy like the Milky Way. The fraction of high-redshift GRBs is estimated at 8% Y12% and 2.5%Y6% at z ! 5 and z ! 7, respectively, assuming continued positive evolution of the GRB rate density to high redshifts.

We present a spectral analysis of a ∼ 30 d, near-continuous observation of the Seyfert 1 galaxy NGC 7469 with RXTE. Daily integrations show strong spectral changes during the observation. Our main result is that we find the X-ray spectral index to be correlated with the UV flux. Furthermore, the broad-band X-ray photon flux is also correlated with the UV continuum. These correlations point towards a model in which the X-rays originate via thermal Comptonization of UV seed photons. Furthermore, the UV is also correlated with the extrapolation of the X-ray power law into the soft X-ray/EUV region. Our data analysis therefore re-opens the possibility the the UV photons and their variability arise from reprocessing, as long as the primary source of heating is photo-electric absorption in the reprocessor, rather than Compton downscattering, A coherent picture of the X-ray/UV variability can therefore be constructed whereby absorption and reprocessing of EUV/soft X-rays in a standard accretion disk produce a variable seed photon distribution which are in turn up-scattered into the X-ray band. We also find a significant correlation between the 2-10 keV flux and the 6.4 keV iron Kα line suggesting that at least some portion of the line originates within ∼ 1 lt day of the X-ray continuum source. Neither the power law photon index nor the Compton reflection component are correlated with the 2-10 keV flux. The latter is not correlated -2with the iron Kα line flux either. We do find an apparent correlation between the X-ray spectral index and the strength of the Compton reflection component. In an Appendix we show, however, that this can be produced by a combination of statistical and systematic errors. We conclude the apparent variations in the Compton reflection component may be an artifact of these effects.

Stochastic acceleration of charged particles due to interactions with magnetohydrodynamic (MHD) plasma waves is the dominant process leading to the formation of the high-energy electron and ion distributions in a variety of astrophysical systems. Collisions with the waves influence both the energization and the spatial transport of the particles, and therefore it is important to treat these two aspects of the problem in a self-consistent manner. We solve the representative Fokker-Planck equation to obtain a new, closed-form solution for the timedependent Green's function describing the acceleration and escape of relativistic ions interacting with Alfvén or fast-mode waves characterized by momentum diffusion coefficient D(p) ∝ p q and mean particle escape timescale t esc (p) ∝ p q−2 , 1

The structure of the inner region of an advection-dominated accretion disk around a nonrotating black hole is explored by applying asymptotic analysis in the region just outside the event horizon. We assume that the viscous transport is described by the standard Shakura-Sunyaev prescription throughout the disk, including the inner region close to the horizon. One of our goals is to explore the self-consistency of this assumption by analyzing the causality of the viscous transport near the black hole. The effects of general relativity are incorporated in an approximate manner by utilizing a pseudo-Newtonian gravitational potential. Analysis of the conservation equations yields unique asymptotic forms for the behaviors of the radial inflow velocity, density, sound speed, and angular velocity. The specific behaviors are determined by three quantities, namely, the accreted specific energy, the accreted specific angular momentum, and the accreted specific entropy. The additional requirement of passage through a sonic point further constrains the problem, leaving only two free parameters. Our detailed results confirm that the Shakura-Sunyaev viscosity yields a well-behaved flow structure in the inner region that satisfies the causality constraint. We also show that the velocity distribution predicted by our pseudo-Newtonian model agrees with general relativity in the vicinity of the horizon. The asymptotic expressions we derive therefore yield useful physical insight into the structure of advection-dominated disks, and they also provide convenient boundary conditions for the development of global models via numerical integration of the conservation equations. Although we focus here on advection-dominated flows, the results we obtain are also applicable to disks that lose matter and energy, provided that the loss rates become negligible close to the event horizon.