Classification of radiating compact stars

A classification of compact stars, depending on the electron distribution in velocity space and the density profiles characterizing their magnetospheric plasma, is proposed. Fast pulsars, such as NP 0532, X-ray sources such as Sco-X1, and slow pulsars are suggested as possible evolutionary stages of similar objects. The heating mechanism of Sco-X1 is discussed in some detail

Thermo-Rotational Instability in Plasma Disks Around Compact Objects

Differentially rotating plasma disks, around compact objects, that are imbedded in a ``seed'' magnetic field are shown to develop vertically localized ballooning modes that are driven by the combined radial gradient of the rotation frequency and vertical gradients of the plasma density and temperature. When the electron mean free path is shorter than the disk height and the relevant thermal conductivity can be neglected, the vertical particle flows produced by of these modes have the effect to drive the density and temperature profiles toward the ``adiabatic condition'' where $\eta_{T}\equiv(dlnT/dz)/(dlnn/dz)=2/3$. Here $T$ is the plasma temperature and $n$ the particle density. The faster growth rates correspond to steeper temperature profiles $(\eta_{T}>2/3)$ such as those produced by an internal (e.g., viscous) heating process. In the end, ballooning modes excited for various values of $\eta_{T}$ can lead to the evolution of the disk into a different current carrying configuration such as a sequence of plasma rings

Closure Relations for Electron-Positron Pair-Signatures in Gamma-Ray Bursts

We present recipes to diagnose the fireball of gamma-ray bursts (GRBs) by combining observations of electron-positron pair-signatures (the pair-annihilation line and the cutoff energy due to the pair-creation process). Our recipes are largely model-independent and extract information even from the non-detection of either pair-signature. We evaluate physical quantities such as the Lorentz factor, optical depth and pair-to-baryon ratio, only from the observable quantities. In particular, we can test whether the prompt emission of GRBs comes from the pair/baryonic photosphere or not. The future-coming Gamma-Ray Large Area Space Telescope (GLAST) satellite will provide us with good chances to use our recipes by detecting or non-detecting pair-signatures.Comment: 7 pages, 4 figures, accepted for publication in ApJ, with extended discussions. Conclusions unchange

Simultaneous X-Ray and Gamma-Ray Observations of TeV Blazars: Testing Synchro-Compton Emission Models and Probing the Infrared Extragalactic Background

The last years have seen a revolution in ground-based gamma-ray detectors. We can now detect the spectra of nearby TeV blazars like Mrk 421 and 501 out to approximately 20 TeV, and during the strongest flares, we can now follow fluctuations in these spectra on timescales close to the shortest ones likely in these objects. We point out that this represents a unique opportunity. Using these and future detectors in combination with broadband X-ray satellites like SAX and RXTE, we will be able to simultaneously follow all significant X-ray/gamma-ray variations in a blazar's emission. This will provide the most stringent test yet of the synchrotron-Compton emission model for these objects. In preparation for the data to come, we present sample SSC model calculations using a fully self-consistent, accurate code to illustrate the variability behavior one might see (the range of behavior is wider than many expect) and to show how good timing information can probe physical conditions in the source. If the model works, i.e., if X-ray/TeV variations are consistent with being produced by a common electron distribution, then we show it is possible to robustly estimate the blazar's intrinsic TeV spectrum from its X-ray spectrum. Knowing this spectrum, we can then determine the level of absorption in the observed spectrum. Constraining this absorption, due to gamma-ray pair production on diffuse radiation, provides an important constraint on the infrared extragalactic background intensity. Without the intrinsic spectrum, we show that detecting absorption is very difficult and argue that Mrk 421 and 501, as close as they are, may already be absorbed by a factor 2 at approximately 3 TeV. This should not be ignored when fitting emission models to the spectra of these objects.Comment: 12 pages, 3 figures; final version for ApJ Letters; minor revisions from previous version (some wording changed+panels a&b in figure 2 were swapped

Fast growing double tearing modes in a tokamak plasma

Configurations with nearby multiple resonant surfaces have broad spectra of linearly unstable coupled tearing modes with dominant high poloidal mode numbers m. This was recently shown for the case of multiple q = 1 resonances [Bierwage et al., Phys. Rev. Lett. 94 (6), 65001 (2005)]. In the present work, similar behavior is found for double tearing modes (DTM) on resonant surfaces with q >= 1. A detailed analysis of linear instability characteristics of DTMs with various mode numbers m is performed using numerical simulations. The mode structures and dispersion relations for linearly unstable modes are calculated. Comparisons between low- and higher-m modes are carried out, and the roles of the inter-resonance distance and of the magnetic Reynolds number S_Hp are investigated. High-m modes are found to be destabilized when the distance between the resonant surfaces is small. They dominate over low-m modes in a wide range of S_Hp, including regimes relevant for tokamak operation. These results may be readily applied to configurations with more than two resonant surfaces.Comment: 11 pages, 15 figure