Steep Slopes and Preferred Breaks in GRB Spectra: the Role of Photospheres and Comptonization

The role of a photospheric component and of pair breakdown is examined in the internal shock model of gamma-ray bursts. We discuss some of the mechanisms by which they would produce anomalously steep low energy slopes, X-ray excesses and preferred energy breaks. Sub-relativistic comptonization should dominate in high comoving luminosity bursts with high baryon load, while synchrotron radiation dominates the power law component in bursts which have lower comoving luminosity or have moderate to low baryon loads. A photosphere leading to steep low energy spectral slopes should be prominent in the lowest baryon loadComment: ApJ'00, in press; minor revs. 10/5/99; (uses aaspp4.sty), 15 pages, 3 figure

The cutaneous 'rabbit' illusion affects human primary sensory cortex somatopically

We used functional magnetic resonance imaging (fMRI) to study neural correlates of a robust somatosensory illusion that can dissociate tactile perception from physical stimulation. Repeated rapid stimulation at the wrist, then near the elbow, can create the illusion of touches at intervening locations along the arm, as if a rabbit hopped along it. We examined brain activity in humans using fMRI, with improved spatial resolution, during this version of the classic cutaneous rabbit illusion. As compared with control stimulation at the same skin sites (but in a different order that did not induce the illusion), illusory sequences activated contralateral primary somatosensory cortex, at a somatotopic location corresponding to the filled-in illusory perception on the forearm. Moreover, the amplitude of this somatosensory activation was comparable to that for veridical stimulation including the intervening position on the arm. The illusion additionally activated areas of premotor and prefrontal cortex. These results provide direct evidence that illusory somatosensory percepts can affect primary somatosensory cortex in a manner that corresponds somatotopically to the illusory percept

HST STIS Ultraviolet Spectral Evidence of Outflow in Extreme Narrow-line Seyfert 1 Galaxies: II. Modeling and Interpretation

We present modeling to explore the conditions of the broad-line emitting gas in two extreme Narrow-line Seyfert 1 galaxies, using the observational results described in the first paper of this series. Photoionization modeling using Cloudy was conducted for the broad, blueshifted wind lines and the narrow, symmetric, rest-wavelength-centered disk lines separately. A broad range of physical conditions were explored for the wind component, and a figure of merit was used to quantitatively evaluate the simulation results. Of the three minima in the figure-of-merit parameter space, we favor the solution characterized by an X-ray weak continuum, elevated abundances, a small column density (log(N_H)\approx 21.4), relatively high ionization parameter (log(U)\approx -1.2 - -0.2), a wide range of densities (log(n)\approx 7 - 11), and a covering fraction of ~0.15. The presence of low-ionization emission lines implies the disk component is optically thick to the continuum, and the SiIII]/CIII] ratio implies a density of 10^10 - 10^10.25 cm^-3. A low ionization parameter (log(U)=-3) is inferred for the intermediate-ionization lines, unless the continuum is ``filtered'' through the wind before illuminating the intermediate-line emitting gas, in which case log(U)=-2.1. The location of the emission regions was inferred from the photoionization modeling and a simple ``toy'' dynamical model. A large black hole mass (1.3 x 10^8 M_\odot) radiating at 11% of the Eddington luminosity is consistent with the kinematics of both the disk and wind lines, and an emission radius of ~10^4 R_S is inferred for both. We compare these results with previous work and discuss implications.Comment: 45 pages, 15 figures (4 color), accepted for publication in ApJ, abstract shortene

Changing, priming, and acting on values: Effects via motivational relations in a circular model

Circular models of values and goals suggest that some motivational aims are consistent with each other, some oppose each other, and others are orthogonal to each other. The present experiments tested this idea explicitly by examining how value confrontation and priming methods influence values and value-consistent behaviors throughout the entire value system. Experiment 1 revealed that change in 1 set of social values causes motivationally compatible values to increase in importance, whereas motivationally incompatible values decrease in importance and orthogonal values remain the same. Experiment 2 found that priming security values reduced the better-than-average effect, but priming stimulation values increased it. Similarly, Experiments 3 and 4 found that priming security values increased cleanliness and decreased curiosity behaviors, whereas priming self-direction values decreased cleanliness and increased curiosity behaviors. Experiment 5 found that priming achievement values increased success at puzzle completion and decreased helpfulness to an experimenter, whereas priming with benevolence values decreased success and increased helpfulness. These results highlight the importance of circular models describing motivational interconnections between values and personal goals

Physical parameters of GRB 970508 and GRB 971214 from their afterglow synchrotron emission

We have calculated synchrotron spectra of relativistic blast waves, and find predicted characteristic frequencies that are more than an order of magnitude different from previous calculations. For the case of an adiabatically expanding blast wave, which is applicable to observed gamma-ray burst (GRB) afterglows at late times, we give expressions to infer the physical properties of the afterglow from the measured spectral features. We show that enough data exist for GRB970508 to compute unambiguously the ambient density, n=0.03/cm**3, and the blast wave energy per unit solid angle, E=3E52 erg/4pi sr. We also compute the energy density in electrons and magnetic field. We find that they are 12% and 9%, respectively, of the nucleon energy density and thus confirm for the first time that both are close to but below equipartition. For GRB971214, we discuss the break found in its spectrum by Ramaprakash et al. (1998). It can be interpreted either as the peak frequency or as the cooling frequency; both interpretations have some problems, but on balance the break is more likely to be the cooling frequency. Even when we assume this, our ignorance of the self-absorption frequency and presence or absence of beaming make it impossible to constrain the physical parameters of GRB971214 very well.Comment: very strongly revised analysis of GRB971214 and discussion, submitted to ApJ, 11 pages LaTeX, 4 figures, uses emulateapj.sty (included

Radiation Front Sweeping the Ambient Medium of Gamma-Ray Bursts

Gamma-ray bursts (GRBs) are emitted by relativistic ejecta from powerful cosmic explosions. Their light curves suggest that the gamma-ray emission occurs at early stages of the ejecta expansion, well before it decelerates in the ambient medium. If so, the launched gamma-ray front must overtake the ejecta and sweep the ambient medium outward. As a result a gap is opened between the ejecta and the medium that surfs the radiation front ahead. Effectively, the ejecta moves in a cavity until it reaches a radius R_{gap}=10^{16}E_{54}^{1/2} cm where E is the isotropic energy of the GRB. At R=R_{gap} the gap is closed, a blast wave forms and collects the medium swept by radiation. Further development of the blast wave is strongly affected by the leading radiation front: the front plays the role of a precursor where the medium is loaded with e+- pairs and preaccelerated just ahead of the blast. It impacts the emission from the blast at R < R_{load}=5R_{gap} (the early afterglow). A spectacular observational effect results: GRB afterglows should start in optical/UV and evolve fast (< min) to a normal X-ray afterglow. The early optical emission observed in GRB 990123 may be explained in this way. The impact of the front is especially strong if the ambient medium is a wind from a massive progenitor of the GRB. In this case three phenomena are predicted: (1) The ejecta decelerates at R<R_{load} producing a lot of soft radiation. (2) The light curve of soft emission peaks at t_{peak}=40(1+z)E_{54}^{1/2}(Gamma_{ej}/100)^{-2} s where Gamma_{ej} is the Lorentz factor of the ejecta. Given measured redshift z and t_{peak}, one finds Gamma_{ej}. (3) The GRB acquires a spectral break at 5 - 50 MeV because harder photons are absorbed by radiation scattered in the wind.Comment: 20 pages, accepted to Ap

The AGN Obscuring Torus -- End of the "Doughnut" Paradigm?

Unified schemes of active galactic nuclei (AGN) require an obscuring dusty torus around the central engine. The compact sizes (only a few pc) determined in recent high-resolution observations require that the obscuring matter be clumpy and located inside the region where the black-hole gravity dominates over the galactic bulge. This location is in line with the scenario depicting the torus as the region of the clumpy wind coming off the accretion disk in which the clouds are dusty and optically thick. We study here the outflow scenario within the framework of hydromagnetic disk winds, incorporating the cloud properties determined from detailed modeling of the IR emission from clumpy tori. We find that torus clouds were likely detected in recent water maser observations of NGC 3079. In the wind scenario, the AGN main dynamic channel for release of accreted mass seems to be switching at low luminosities from torus outflow to radio jets. The torus disappears when the bolometric luminosity decreases below about \E{42} erg/sec because the accretion onto the central black hole can no longer sustain the required cloud outflow rate. This disappearance seems to have been observed in both LINERs and radio galaxies. With further luminosity decrease, suppression of cloud outflow spreads radially inward from the disk's dusty, molecular region into its atomic, ionized zone, resulting in disappearance of the broad emission line region at lower luminosities, yet to be determined.Comment: ApJ Letters, to be publishe

Formation and Disruption of Cosmological Low Mass Objects

We investigate the evolution of cosmological low mass (low virial temperature) objects and the formation of the first luminous objects. First, the `cooling diagram' for low mass objects is shown. We assess the cooling rate taking into account the contribution of H_2, which is not in chemical equilibrium generally, with a simple argument of time scales. The reaction rates and the cooling rate of H_2 are taken from the recent results by Galli & Palla (1998). Using this cooling diagram, we also estimate the formation condition of luminous objects taking into account the supernova (SN) disruption of virialized clouds. We find that the mass of the first luminous object is several times 10^7 solar mass, because smaller objects may be disrupted by the SNe before they become luminous. Metal pollution of low mass (Ly-alpha) clouds also discussed. The resultant metallicity of the clouds is about 1/1000 of the solar metallicity.Comment: 11 pages, 2 figures, To appear in ApJ

Topological regluing of rational functions

Regluing is a topological operation that helps to construct topological models for rational functions on the boundaries of certain hyperbolic components. It also has a holomorphic interpretation, with the flavor of infinite dimensional Thurston--Teichm\"uller theory. We will discuss a topological theory of regluing, and trace a direction in which a holomorphic theory can develop.Comment: 38 page

Cosmic Renaissance: The First Sources of Light

I review recent progress in understanding the formation of the first stars and quasars. The initial conditions for their emergence are given by the now firmly established model of cosmological structure formation. Numerical simulations of the collapse and fragmentation of primordial gas indicate that the first stars formed at redshifts z ~ 20 - 30, and that they were predominantly very massive, with M_* > 100 M_sun. Important uncertainties, however, remain. Paramount among them is the accretion process, which builds up the final stellar mass by incorporating part of the diffuse, dust-free envelope into the central protostellar core. The first quasars, on the other hand, are predicted to have formed later on, at z ~ 10, in more massive dark matter halos, with total masses, ~ 10^8 M_sun, characteristic of dwarf galaxies.Comment: 16 pages, 7 figures, invited review, to appear in PASP, Feb. 200