Specific heat of the ideal gas obeying the generalized exclusion statistics

We calculate the specific heat of the ideal gas obeying the generalized exclusion statistics (GES) in the continuum model and the tight binding model numerically. In the continuum model of 3-d space, the specific heat increases with statistical parameter at low temperature whereas it decreases with statistical parameter at high temperature. We find that the critical temperature normalized by $\mu_f$ (Fermi energy) is 0.290. The specific heat of 2-d space was known to be independent of $g$ in the continuum model, but it varies with $g$ drastically in the tight-binding model. From its unique behavior, identification of GES particles will be possible from the specific heat.Comment: 14 pages, 9 figures, to be published in Eur. Phys. J. B, References and figures added, typos corrected, one section removed and two sections merge

Millimetre-VLBI Monitoring of AGN with Sub-milliarcsecond Resolution

Global millimetre VLBI allows detailed studies of the most central jet regions of AGN with unprecedent spatial resolution of a few 100-1000 Schwartzschild radii to be made. Study of these regions will help to answer the question how the highly relativistic AGN jets are launched and collimated. Since the early 1990s, bright mm-sources have been observed with global 3 mm VLBI. Here we present new images from an ongoing systematic analysis of the available observations. In particular, we focus on the structure and structural evolution of the best observed AGN jets, taking 3C 454.3 as a characteristic example. This core-dominated and highly variable quasar shows a complex morphology with individual jet components accelerating superluminally towards the outer structure. We briefly discuss the X-ray properties of 3C 454.3 and present its radio- to X-ray large-scale brightness distribution.Comment: 4 pages, 4 figures, Proceedings of the 7th EVN Symposium held in Toledo, Spain in October 2004, needs evn2004.cl

High-energy pulses and phase-resolved spectra by inverse Compton emission in the pulsar striped wind - Application to Geminga

(abridged) Although discovered 40 years ago, the emission mechanism responsible for the observed pulsar radiation remains unclear. However, the high-energy pulsed emission is usually explained in the framework of either the polar cap or the outer gap model. The purpose of this work is to study the pulsed component, that is the light-curves as well as the spectra of the high-energy emission, above 10 MeV, emanating from the striped wind model. Gamma rays are produced by scattering off the soft cosmic microwave background photons on the ultrarelativistic leptons flowing in the current sheets. We compute the time-dependent inverse Compton emissivity of the wind, in the Thomson regime, by performing three-dimensional numerical integration in space over the whole striped wind. The phase-dependent spectral variability is then calculated as well as the change in pulse shape when going from the lowest to the highest energies. Several light curves and spectra of inverse Compton radiation with phase resolved dependence are presented. We apply our model to the well-known gamma-ray pulsar Geminga. We are able to fit the EGRET spectra between 10 MeV and 10 GeV as well as the light curve above 100 MeV with good accuracy.Comment: Accepted by A&

ORFEUS-II Far-Ultraviolet Observations of 3C273: 1. Interstellar and Intergalactic Absorption Lines

We present the first intermediate-resolution (lambda / 3000) spectrum of the bright quasi-stellar object 3C273 at wavelengths between 900 and 1200 A. Observations were performed with the Berkeley spectrograph aboard the ORFEUS-SPAS II mission. We detect Lyman beta counterparts to previously-identified intergalactic Lyman-alpha features at cz = 19900, 1600, and 1000 km/s; counterparts to other putative Lyman-alpha clouds along the sight line are below our detection limit. The strengths of the two very low redshift Lyman-beta features, which are believed to arise in Virgo intracluster gas, exceed preflight expectations, suggesting that the previous determination of the cloud parameters may underestimate the true column densities. A curve-of-growth analysis sets a minimum H I column density of 4 E14/cm^2 for the 1600 km/s cloud. We find marginally significant evidence for Galactic H_2 along the sight line, with a total column density of about 1 E15/cm^2. We detect the stronger interstellar O VI doublet member unambiguously; the weaker member is blended with other features. If the Doppler b value for O VI is comparable to that determined for N V then the O VI column density is 7 +/- 2 E14/cm^2, significantly above the only previous estimate. The O VI / N V ratio is about 10, consistent with the low end of the range observed in the disk. Additional interstellar species detected for the first time toward 3C273 (at modest statistical significance) include P II, Fe III, Ar I, and S III.Comment: LaTeX file, 11 pages, 4 encapsulated PostScript figures. Uses aaspp4.sty and astrobib.sty. (Astrobib is available from http://www.stsci.edu/software/TeX.html .) The ORFEUS telescope is described at http://sag-www.ssl.berkeley.edu/orfeus/ . To appear in ApJ (Letters

SUMER: Solar Ultraviolet Measurements of Emitted Radiation

The SUMER (solar ultraviolet measurements of emitted radiation) experiment is described. It will study flows, turbulent motions, waves, temperatures and densities of the plasma in the upper atmosphere of the Sun. Structures and events associated with solar magnetic activity will be observed on various spatial and temporal scales. This will contribute to the understanding of coronal heating processes and the solar wind expansion. The instrument will take images of the Sun in EUV (extreme ultra violet) light with high resolution in space, wavelength and time. The spatial resolution and spectral resolving power of the instrument are described. Spectral shifts can be determined with subpixel accuracy. The wavelength range extends from 500 to 1600 angstroms. The integration time can be as short as one second. Line profiles, shifts and broadenings are studied. Ratios of temperature and density sensitive EUV emission lines are established

A Global 86GHz VLBI Survey of Compact Radio Sources

We present results from a large 86GHz global VLBI survey of compact radio sources. The main goal of the survey is to increase by factors of 3--5 the total number of objects accessible for future 3-mm VLBI imaging. The survey observations reach the baseline sensitivity of 0.1Jy and image sensitivity of better than 10 mJy/beam. The total of 127 compact radio sources have been observed. The observations have yielded images for 109 sources, extending the database of the sources imaged at 86GHz with VLBI observation by a factor of 5, and only 6 sources have not been detected. The remaining 12 objects have been detected but could not be imaged due to insufficient closure phase information. Radio galaxies are less compact than quasars and BL Lacs on sub-milliarcsecond scale. Flux densities and sizes of core and jet components of all imaged sources have been estimated using Gaussian model fitting. From these measurements, brightness temperatures have been calculated, taking into account resolution limits of the data. The cores of 70% of the imaged sources are resolved. The core brightness temperatures of the sources peak at $\sim 10^{11}$ K and only 1% have brightness temperatures higher than $10^{12}$ K. Cores of Intraday Variable (IDV) sources are smaller in angular size than non-IDV sources, and so yield higher brightness temperatures.Comment: 72 pages, 12 figures, accepted for publication in the Astronomical Journa

Nonlinear Radiation Pressure and Stochasticity in Ultraintense Laser Fields

The radiation force on a single electron in an ultraintense plane wave ($a = eE/mc\omega \sim 1$) is calculated and shown to be proportional to $a^4$ in the high-$a$ limit for arbitrary waveform and polarization. The cyclotron motion of an electron in a constant magnetic field and an ultraintense plane wave is numerically found to be quasiperiodic even in the high-$a$ limit if the magnetic field is not too strong, as suggested by previous analytical work. A strong magnetic field causes highly chaotic electron motion and the boundary of the highly chaotic region of parameter space is determined numerically. Applications to experiments and astrophysics are briefly discussed.Comment: 5 pages, 4 figures; uses RevTex, epsf macros. Corrected, expanded versio