Implications of Gamma-Ray Transparency Constraints in Blazars: Minimum Distances and Gamma-Ray Collimation

We develop a general expression for the gamma-gamma absorption coefficient for gamma-rays propagating in an arbitrary direction at an arbitrary point in space above an X-ray emitting accretion disk. The X-ray intensity is assumed to vary as a power law in energy and radius between the outer disk radius and the inner radius, which is the radius of marginal stability for a Schwarzschild black hole. We use our result for the absorption coefficient to calculate the gamma-gamma optical depth for gamma-rays created at an arbitrary height and propagating at an arbitrary angle relative to the disk axis. As an application, we use our formalism to compute the minimum distance between the central black hole and the site of production of the gamma-rays detected by EGRET during the June 1991 flare of 3C 279. Our results indicate that the ``focusing'' of the gamma-rays along the disk axis due to pair production is strong enough to explain the observed degree of alignment in blazar sources. If the gamma-rays are produced isotropically in gamma-ray blazars, then these objects should appear as bright MeV sources when viewed along off-axis lines of sight.Comment: 23 pages, tex, figures available on request to [email protected]

International Ultraviolet Explorer Observations of the Aquarii Jet

Ultraviolet spectra were obtained with the International Ultraviolet Explorer of the newly discovered optical-radio jet feature in the symbiotic variable R Aquarii. The far-UV continuum of the jet is characterized by strong continuum which rises with decreasing wavelength in the 1200-2000 A wavelength range and is considerably different in appearance from the relatively flat continuum exhibited by ionized nebulosity in the central star. Prominent Si III] and Si II emission lines seen in the central region are virtually absent in the jet. This could reflect the depletion of silicon in the feature, the result of grain formation in material that has been ejected by the central star. Consistent with this interpretation is the overall excitation of the jet that suggests it is cooler than the nebulosity that engulfs the central UV object

Sporadic Mass Ejection in Red Supergiants

We have applied a general mechanism first proposed by J. A. Burke to red supergiants for determining the spin-down rate and angular momentum loss of rotating stars. This model relies principally on sporadic mass ejection, which is assumed to be the result of turbulent elements accelerating material in cool supergiant.atmospheres. Mass is preferentially expelled in the forward direction of rotation, resulting in a rapid loss of angular momentum on time scales of 1Q^4-10^6 years in the supergiant evolutionary phase. Such rotational breaking will occur if the turbulent elements have characteristic sizes a few percent of the stellar radius, and rms velocities one-third the escape speed of the star. This model predicts the formation of a cool silicate disk or torus around the star because of the preferred expulsion of material near equatorial regions of the supergiant

Mass Loss and OH Maser Emission from Mira Variables

We have estimated the mass, radius, and luminosity of 26 Mira variables that are known OH sources of radio emission at 1612 MHz. The time-independent solution of Salpeter\u27s stellar wind equation and a period-density relation are used to solve for basic stellar parameters, with the aid of the terminal expansion velocity of the OH maser cloud. Masses obtained from these calculations are consistent with other estimated values for masses of Mira variables. Good agreement is obtained when comparing the rate of mass loss as determined from Reimers\u27s semiempirical relation to estimates of the mass loss rate as deduced from theoretical models involving radiation pressure on grains. These calculations suggest a strong correlation between the mass loss rate and the pulsation period. Arguments concerning the general properties of silicate grains from radiation-pressure-driven stellar wind equations are discussed

The High-Energy Spectrum of Hot Accretion Disks

A hot, two-temperature accretion disk can be a strong γ-ray and relativistic particle source. This occurs when the accretion rate is high enough -- M/ M ≥ 3 X 10^-9 α γr^-1 for a canonical Kerr black hole-due to the high ion temperature in the inner disk. We present detailed photon and particle spectra for specific disk models. The predicted γ-ray flux is as high as 10% of the bolometric luminosity in sub-Eddington models. Most of the γ-radiation is continuous, due to the π^0 decay, emitted around 100 MeV but degraded to a few MeV in optically thick models. Spectral lines, due to positon annihilation or to excited nuclei, provide only a small amount of the primary γ-ray luminosity. The energy flux in - 35 MeV pairs is comparable to the γ-ray luminosity; Penrose effects provide a smaller number of - I Ge V pairs. Applications of the model both to galactic and extragalactic sources are discussed. Both the galactic center y-ray source and the extragalactic y-ray background (if it is due to discrete sources) may be due to this type of model

Variable Ultraviolet Emission in SY Muscae

Following the enhancement in ultraviolet flux which we reported previously, we have continued monitoring the symbiotic variable SY Muscae with the International Ultraviolet Explorer (JUE). Over the course of one year, the prominent emission lines of N v, 0 v, C rv, He II appear to be gradually decreasing in absolute intensity. This appears to coincide with a steady decline in electron density in the emission line forming region, as suggested from the Sim] :\1892 and Cm] :\1909 intensity ratio. Our data is consistent with a sudden ejection event in which material expelled from the surface of a hot Teff = 65 000 K sub dwarf has exposed the underlying UV continuum of the star. A number of strong emission lines that are photoexcited by the intense radiation field of the secondary also exhibit broad pedestal emission that suggest turbulent velocities of -150-300 km s- 1 in an expanding shell or possibly in an accretion disc. The radical change of the UV emission properties observed in SY Muscae indicates that our initial observations of this object were obtained during preliminary stages of mass ejection

IUE Observations of the Peculiar Star RX Puppis

We have obtained the first high-dispersion observations of RX Pup in the wavelength region 1200-2000 A with the International Ultraviolet Explorer. RX Pup has been classified a symbiotic star and has been compared to slow novae as well as to 11 Carinae. The anomalies that we observed in high-excitation lines in RX Pup such as He II, 0 III], C III], C IV, and Si IIIl that show split line profiles, Doppler displaced multiple components, and possible inverse P Cygni profiles inN III] and N IV J suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion. The continuum observed by us in low dispersion is fairly flat in the wavelength region 1200-2000 A and rises toward longer wavelengths in the region 2000-3200 A. It cannot be due to a star earlier than AO II. Alternatively it may be from an accretion disk. We find electron densities in the line-emitting region in the range 109-1011 em- 3 , temperatures in the range 10,000-20,000 K, and linear sizes :S a few x 1013 em. We find that the photoionizing radiation may be due to the presence of an unseen, hot subdwarf with most probable effective temperature in the range 75,000-90,000 K. Alternatively it may be due to an accretion disk around a secondary with boundary layer temperature -105 K. Short-range as well as long-range monitoring of this very interesting object in the far-UV would be very helpful in understanding the nature of its peculiar properties and the connection between slow novae and symbiotic stars

Migration, Environment and Public Health: Theory and Interdisciplinary Research from a Regional Science Perspective

As regional climate evolves into new climatic states in different parts of the world, humanity will be facing increasing issues associated with migration environment and health concerns. Challenges of major hazards and impacts on human societies, involving water resources, agriculture, economy and energy issues are central issues. This paper examines the generalization of Tiebout’s model in our understanding of the forced environmental migration of the Great Planes farmers to California during the Dust Bowl period in 1931-1939. The paper considers the issues of public health that arose from this migration after the arrival and settlement of the Okies in California. Settlement of the migrants in California was more bitter than the migration itself, prompting John Steinbeck to write his award winning novel of the journey in the “Grapes of Wrath.” Among many health risks in their new environment a relatively unappreciated and unpublicized airborne fungus causing Valley fever when inhaled emerged. Valley fever was, and is today, highly endemic in California’s San Joaquin Valley where many of the Okies remained, staying for employment in agriculture and working the fertile soil that harbored the fungus. The vast majority of migrants into the San Joaquin Valley had been infected, but we know today that most who were, did not report it. A very high percentage of migrants did become infected when a few statistics emerged, such as 25% of the population of one migrant camp were diagnosed with the disease. Many migrants fought the disease only to die later in the 1940s and 1950s. The destiny of the migrants was not exposed in books or mass media until the early 1960s. Many migrants escaped infection when they left the fields for employment in the factories and manufacturing supporting the World War II effort. Other reasons for this historical silence were the Great Depression, those who went to war, the Cold War era, and the Californian farmers themselves who kept the infection secret. The second generation migrants or the “survivors” from Valley fever infection exposed the destiny of their parents in the Californian farms in the mass media in the early 1960s and later on Internet webpages and blogs in the 1980s. We examine the general implications and lessons learned from these historical cases

Using transport coefficients of cosmic rays in turbulent magnetic fields to determine hybrid viscosity in hot accretion disks around AGN

The nature of the viscosity operative in hot, two-temperature accretion disks around AGN has been a long-standing, unsolved problem. It has been previously suggested that protons, in conjunction with the turbulent magnetic field that is likely to exist in the accretion disk, might be crucial in providing this viscosity. Several authors have recently determined diffusion coefficients for charged particles (cosmic rays) propagating in turbulent magnetic fields by means of extensive Monte Carlo simulations. We use the diffusion coefficients for protons determined by these simulations to find the effective mean free path for protons in hot accretion disks. This in turn yields good estimates of the viscosity due to energetic protons embedded in the turbulent magnetic field of a hot, two-temperature accretion disk. We combine this with a simple two-temperature accretion disk model to determine the Shakura-Sunyaev $\alpha$ viscosity parameter arising out of this mechanism. We find that protons diffusing in the turbulent magentic field embedded in a hot accretion d isk provide a physically reasonable source of viscosity in hot accretion disks around AGN.Comment: submitted to proceedings of the 29th International Cosmic Ray Conf., Aug 3-10 2005, Pun