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The Cherenkov Telescope Array (CTA) will be the next generation gamma-ray observatory, open to the scientific community, to investigate the very high-energy emission from a large variety of celestial sources in the energy range 20 GeV - 300 TeV. The full array, distributed over two sites, one in the northern and one in the southern hemisphere, will provide whole-sky coverage and will improve by about one order of magnitude the sensitivity with respect to the current major arrays. CTA will investigate a much higher number of already known classes of sources, going to much larger distances in the Universe, performing population studies, accurate variability and spatially-resolved studies. Moreover, new light will be shed on possible new classes of high-energy sources, such as GRBs, cluster of Galaxies, Galactic binaries, and on fundamental physics. By pushing the high-energy limit to E>100 TeV it will allow a thorough exploration of the cut-off regime of the cosmic accelerators. We review the main CTA Key Science Projects, which will focus on major scientific cases, a clear advance beyond the current state of the art, and we discuss the production of legacy data-sets of high value to a wider community. [ABSTRACT FROM AUTHOR]

Recently, an alternative model based on white dwarfs pulsars has been proposed to explain a class of pulsars known as Soft Gamma Repeaters (SGR) and Anomalus X-Ray Pulsars (AXP) [1], usually named as magnetars. In this model, the magnetized white dwarfs can have surface magnetic field B ~ 107 - 1010 G and rotate very fast with angular frequencies Ω ~ 1 rad=s, allowing them to produce large electromagnetic (EM) potentials and generate electron-positron pairs. These EM potentials are comparable with the ones of neutron star pulsars with strong magnetic fields and even larger. In this study we consider two possible processes associated with the particle acceleration, both of them are common used to explain radio emission in neutron star pulsars: in the first process the pair production happens near to the star polar caps, i.e. inside of the light cylinder where magnetic field lines are closed; in the second one the creation of pair happens in the outer magnetosphere, i.e. far away of the star surface where magnetic field lines are open [2]. The analysis of the possibility of radio emission were done for 23 SGRs/AXPs of the McGill Online Magnetar Catalog [3] that contains the current information available on these sources. The results of this work show that the model where the particles production occur in the outer magnetosphere emission "o2" is the process compatible with the astronomical observations of absence of radio emission for almost all SGRs/AXPs when these sources are understood as white dwarf pulsars. Our work is a first attempted to find an explanation for the puzzle why for almost all the SGRs/AXPs was expected radio emission, but it was observed in only four of them. These four sources, as it was suggested recently [4], seem to belong to an high magnetic field neutron star pulsar category, different from all the others SGRs/AXPs that our work indicate to belong to a new class of white dwarf pulsars, very fast and magnetized. [ABSTRACT FROM AUTHOR]

We present the first detailed joint modelling of both the timing and spectral properties during the outburst decay of transient anomalous X-ray pulsars. We consider the two sources XTE J1810-197 and CXOU J164710.2-455216, and describe the source decline in the framework of a twisted magnetosphere model, using Monte Carlo simulations of magnetospheric scattering and mimicking localized heat deposition at the NS surface following the activity. Our results support a picture in which a limited portion of the star surface close to one of the magnetic poles is heated at the outburst onset. The subsequent evolution is driven both by the cooling/varying size of the heated cap and by a progressive untwisting of the magnetosphere. [ABSTRACT FROM AUTHOR]

We study the escape of cosmic-ray protons accelerated at a supernova remnant (SNR). We are interested in their propagation in the interstellar medium (ISM) after they leave the shock neighborhood where they are accelerated. We first compare the results of a simple model with observations of SNRs; cosmic-rays escaped from these SNRs seem to be illuminating molecular clouds around the SNRs. In this model, we take the diffusion coefficient for the cosmic-rays as a free parameter. We found that the coefficient around the SNRs is less than 1% of that away from them. Following this study, we construct a theoretical model, in which the diffusion coefficient is theoretically calculated. We found that the cosmic rays with energies of less than ∼TeV excite Alfvén waves around the SNR on a scale of the SNR itself. Thus, even if the cosmic rays can leave the shock, scattering by the waves prevents them from moving further away from the SNR. [ABSTRACT FROM AUTHOR]

It is well known that the temperature and optical depth of the Comptonising electrons of the corona of black hole binaries can be measured using spectroscopy in the 1 keV–1 MeV energy band. We emphasize recent developments in the modeling of high energy radiation processes which allow us to constrain other important physical parameters of the corona, such as the strength of magnetic field, or the temperature of the ions. In the prototypical source Cygnus X-1, the results appear to challenge current accretion models. [ABSTRACT FROM AUTHOR]

The complex structure of the light curves of Swift GRBs has made their interpretation and that of the blast wave caused by the burst, more difficult than in the pre-Swift era. We aim to constrain the blast wave parameters: electron energy distribution, p, density profile of the circumburst medium, k, and the continued energy injection index, q. We do so by comparing the observed multi-wavelength light curves and X-ray spectra of a Swift sample to the predictions of the blast wave model. We can successfully interpret all of the bursts in our sample of 10, except two, within the framework of the blast wave model, and we can estimate with confidence the electron energy distribution index for 6 of the sample. Furthermore we identify jet breaks in half of the bursts. A statistical analysis of the distribution of p reveals that, even in the most conservative case of least scatter, the values are not consistent with a single, universal value. The values of k suggest that the circumburst density profiles are not drawn from only one of the constant density or wind-like media populations. [ABSTRACT FROM AUTHOR]

We report on observations of correlated behavior between the prompt γ-ray and optical emission from GRB 080319B, which confirm that (i) they occurred within the same astrophysical source region and (ii) their respective radiation mechanisms were dynamically coupled. Our results, based upon a new cross-correlation function (CCF) methodology for determining the time-resolved spectral lag, are summarized as follows. First, the evolution in the arrival offset of prompt γ-ray photon counts between Swift-BAT 15–25 keV and 50–100 keV energy bands (intrinsic γ-ray spectral lag) appears to be anti-correlated with the arrival offset between prompt 15–350 keV γ-rays and the optical emission observed by TORTORA (extrinsic optical/γ-ray spectral lag), thus effectively partitioning the burst into two main episodes at ∼T+28±2 sec. Second, the rise and decline of prompt optical emission at ∼T+10±1 sec and ∼T+50±1 sec, respectively, both coincide with discontinuities in the hard to soft evolution of the photon index for a power law fit to 15–150 keV Swift-BAT data at ∼T+8±2 sec and ∼T+48±1 sec. These spectral energy changes also coincide with intervals whose time-resolved spectral lag values are consistent with zero, at ∼T+12±2 sec and ∼T+50±2 sec. These results, which are robust across heuristic permutations of Swift-BAT energy channels and varying temporal bin resolution, have also been corroborated via independent analysis of Konus-Wind data. This potential discovery may provide the first observational evidence for an implicit connection between spectral lags and GRB emission mechanisms in the context of canonical fireball phenomenology. Future work includes exploring a subset of bursts with prompt optical emission to probe the unique or ubiquitous nature of this result. [ABSTRACT FROM AUTHOR]

We use a new code to simulate the radiation and kinetic processes in the X-ray emitting region around accreting black holes and constrain the magnetic field and temperature of the hot protons in the corona of Cygnus X-1. In the hard state we find a magnetic field below equipartition with radiation, suggesting that the corona is not powered through magnetic field dissipation (as assumed in most accretion disc corona models). On the other hand, our results also point toward proton temperatures that are substantially lower than typical temperatures of the ADAF models. Finally, we show that in both spectral states Comptonising plasma could be powered essentially through power-law acceleration of non-thermal electrons, which are then partly thermalised by the synchrotron and Coulomb boiler. This suggests that, contrary to current beliefs, the corona of the HSS and that of the LHS could be of very similar nature. The differences between the LHS and HSS coronal spectra would then be predominantly caused by the strong disc soft cooling emission which is present in the HSS and absent in the LHS. [ABSTRACT FROM AUTHOR]

Gamma-ray binaries have been uncovered as a new class of Galactic objects in the very high energy sky (>100 GeV). The three systems known today have hard X-ray spectra (photon index ∼1.5), extended radio emission and a high luminosity in gamma-rays. Recent monitoring campaigns of LSI +61°303 in X-rays have confirmed variability in these systems and revealed a spectral hardening with increasing flux. In a generic one-zone leptonic model, the cooling of relativistic electrons accounts for the main spectral and temporal features observed at high energy. Persistent hard X-ray emission is expected to extend well beyond 10 keV. We explain how Simbol-X will constrain the existing models in connection with Fermi Space Telescope measurements. Because of its unprecedented sensitivity in hard X-rays, Simbol-X will also play a role in the discovery of new gamma-ray binaries, giving new insights into the evolution of compact binaries. [ABSTRACT FROM AUTHOR]

Deep radio observations of galaxy clusters have revealed the existence of diffuse radio sources (“halos” and “relics”) related to the presence of relativistic electrons and weak magnetic fields in the intracluster volume. I will outline our current knowledge about the presence and properties of this non-thermal cluster component. Despite the recent progress made in observational and theoretical studies of the non-thermal emission in galaxy clusters, a number of open questions about its origin and its effects on the thermo-dynamical evolution of galaxy clusters need to be answered. I will show the importance of combining galaxy cluster observations by new-generation instruments such as LOFAR and Simbol-X. A deeper knowledge of the non-thermal cluster component, together with statistical studies of radio halos and relics, will allow to test the current cluster formation scenario and to better constrain the physics of large scale structure evolution. [ABSTRACT FROM AUTHOR]

The high kinetic energy outflowing in the jets of microquasars is delivered to the surrounding interstellar medium. This energy input can lead to the formation of bow shocks and cocoons that may emit from radio to gamma-ray energies. Evidence and hints of emission from jet/medium interactions have been reported for some sources, but little has been done regarding the theoretical modelisation of the resulting non-thermal emission. We have developed an analytical model for the interaction of microquasar jets with their surroundings based on those successfully applied in AGNs. Focusing on the adiabatic phase of the growing structures, we give estimations of the expected luminosities at high and very high energies, and study the detectability with present (MAGIC, HESS, VERITAS and GLAST) and future (CTA) gamma-ray observatories. [ABSTRACT FROM AUTHOR]

The very high energy γ-ray spectra of Pulsar Wind Nebulae are interpreted as due to inverse Compton scattering of ultrarelativistic electrons on the ambient photons, whereas their X-ray spectra are due to synchrotron emission. We investigate the relation between the γ- and X-ray emission and the pulsars’ spin-down luminosity and characteristic age. We find that the γ-to X-ray flux ratio of the nebulae is inversely proportional to the spin-down luminosity (∝Ė-1.9) and to the characteristic age (∝τc2.2) of the parent pulsar. We interpret these results as due to the evolution of the electron energy distribution and the nebular dynamics, supporting the idea of so-called relic pulsar wind nebulae. These empirical relations provide a new tool to classify unidentified diffuse γ-ray sources and to estimate the spin-down luminosity and characteristic age for four rotation powered pulsars with no detected pulsation from the X- and γ—ray properties of the associated pulsar wind nebulae. [ABSTRACT FROM AUTHOR]

We present simultaneous optical (BVRI) and X-ray (RXTE PCA) data on the quasar 3C279 from the day of the recent VHE detection by MAGIC and discuss the implications of the snap-shot spectral energy distribution (SED) for leptonic jet models of blazars. A one-zone synchrotron-self-Compton origin of the SED up to VHE γ-rays can be ruled out. The VHE emission could, in principle, be interpreted as Compton upscattering of external radiation (e.g., from the broad-line regions) in a one-zone leptonic model. However, such an interpretation would require either an unusually low magnetic field of B∼0.03 G, or (in order to achieve approximate equipartition between magnetic field at B∼0.25 G and relativistic electrons) an unrealistically high Doppler factor of Γ∼140. In addition, such a model fails to reproduce the observed X-ray flux. We therefore conclude that a simple one-zone, homogeneous leptonic jet model is not able to plausibly reproduce the SED of 3C279 including the recently detected VHE γ-ray emission. This as well as the lag of correlated variability in the optical with the VHE γ-ray emission suggests a multi-zone model in which the optical emission is produced in a different region than the VHE γ-ray emission. Alternatively, also a hadronic origin of the VHE γ-rays seems plausible. [ABSTRACT FROM AUTHOR]

Recently, the MAGIC collaboration reported evidence for a delay in the arrival times of photons of different energies during a γ-ray flare from the blazar Markarian 501 on 2005 July 9. We describe the observed delayed high-energy emission by applying a homogeneous synchrotron self-Compton (SSC) model under the assumption that the blob, containing relativistic electrons, was observed in its acceleration phase. This modified SSC model predicts the appearance of a γ-ray flare first at lower energies and subsequently at higher energies. Based on the reported time delay, we predict a delay on the order of 1 h if observed between 10 GeV and 100 GeV, which can be tested in the future by simultaneous flare observations using, e.g., the Fermi Gamma-Ray Telescope and Cerenkov telescopes. [ABSTRACT FROM AUTHOR]

We estimate the radiation produced at high energies by the cluster of galaxies Abell 3376, which is characterized by double opposite, giant ringlike radio structures. These recently detected radio relics support the presence of relativistic particles that are assumed to be accelerated in-situ by a diffusive shock mechanism. We calculate the spectral energy distribution resulting from the most relevant non-thermal processes (synchrotron radiation, inverse Compton (IC) scattering, relativistic Bremsstrahlung, and inelastic proton-proton collisions). From our specific model, we find that the major radiative component at high energies is IC scattering. Hadronic interactions would yield a minor contribution to the overall non-thermal emission, but would dominate at ultra-high energies. The nearby cluster Abell 3376 might be detectable at gamma-rays by GLAST satellite and Cherenkov arrays. [ABSTRACT FROM AUTHOR]

We report on observations of correlated behavior between the prompt γ-ray and optical emission from GRB 080319B, which (i) strongly suggest that they occurred within the same astrophysical source region and (ii) indicate that their respective radiation mechanisms were most likely dynamically coupled. Our preliminary results, based upon a new cross-correlation function (CCF) methodology for determining the time-resolved spectral lag, are summarized as follows. First, the evolution in the arrival offset of prompt γ-ray photon counts between Swift-BAT 15–25 keV and 50–100 keV energy bands (intrinsic γ-ray spectral lag) appears to be anti-correlated with the arrival offset between prompt 15–350 keV γ-rays and the optical emission observed by TORTORA (extrinsic γ-ray/optical lag), thus effectively partitioning the burst into two main episodes at ∼T+28±2 sec. Second, prompt optical emission is nested within intervals of both (a) trivial intrinsic γ-ray spectral lag (∼T+12±2 and ∼T+50±2 sec) with (b) discontinuities in the hard to soft evolution of the photon index for a power law fit to 15–150 keV Swift-BAT data (∼T+8±2 and ∼T+48±1 sec), both of which coincide with the rise (∼T+10±1 sec) and decline (∼T+50±1 sec) of prompt optical emission. This potential discovery, robust across heuristic permutations of BAT energy channels and varying temporal bin resolution, provides the first observational evidence for an implicit connection between spectral lag and the dynamics of shocks in the context of canonical fireball phenomenology. [ABSTRACT FROM AUTHOR]

We discuss the origin of ultra-high energy cosmic rays in light of the latest observational results from the Pierre Auger Observatory, highlighting potential astrophysical sources such as active galactic nuclei, gamma-ray bursts, and clusters of galaxies. Key issues include their energy budget, the acceleration and escape of protons and nuclei, and their propagation in extragalactic radiation and magnetic fields. We briefly address the prospects for Telescope Array and future facilities such as JEM-EUSO, and also emphasize the importance of multi-messenger X-ray and gamma-ray signatures in addition to neutrinos as diagnostic tools for source identification. [ABSTRACT FROM AUTHOR]

Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences for the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as standard candles. Here we address the issue of X-ray breaks which are possibly ‘hidden’ and hence the light curves are misinterpreted as being single power-laws. We show how a number of precedents, including GRB 990510 & GRB 060206, exist for such hidden breaks and how, even with the well sampled light curves of the Swift era, these breaks may be left misidentified. We do so by synthesising X-ray light curves and finding general trends via Monte Carlo analysis. Furthermore, in light of these simulations, we discuss how to best identify achromatic breaks in afterglow light curves via multi-wavelength analysis. [ABSTRACT FROM AUTHOR]

We present a comprehensive multiwavelength analysis of the bright, long duration gamma-ray burst GRB 070125, comprised of observations in γ-ray, X-ray, optical, millimeter and centimeter wavebands. Radio light curves show rapid flux variations, which are interpreted as due to interstellar scintillation, and are used to derive an upper limit of 2.4×1017 cm on the radius of the fireball. Radio light curves and spectra suggest that the afterglow shock wave is moving in a dense medium. Our broadband modeling favors a constant density profile for the circumburst medium over a wind-like profile (R-2). GRB 070125 is a burst with high radiative efficiency (>60%). [ABSTRACT FROM AUTHOR]

Recent calculations indicate that the cohesive energy of condensed matter increases with magnetic field strength and becomes very significant at magnetar-like fields (e.g., 10 keV at 3×1014 G for zero-pressure condensed iron). This implies that for sufficiently strong magnetic fields and/or low temperatures, the neutron star surface may be in a condensed state with little gas or plasma above it. Such surface condensation may lead to the formation of a charge-depleted acceleration zone (“vacuum gap”) in the magnetosphere above the stellar polar cap. Using the latest results on the cohesive property of magnetic condensed matter, we quantitatively determine the conditions for vacuum gap formation in magnetic neutron stars. We also study the physics of pair cascades in the (Ruderman-Sutherland type) vacuum gap model for photon emission by accelerating electrons and positrons due to both curvature radiation and resonant/nonresonant inverse Compton scattering. Our calculations of the condition of cascade-induced vacuum breakdown and the related pulsar death line/boundary generalize previous works to the superstrong field regime. [ABSTRACT FROM AUTHOR]

A large sample of about two hundred pulsars have been observed to study their subpulse modulation at an observing wavelength of (when achievable) both 21 and 92 cm using the Westerbork Synthesis Radio Telescope. For 57 pulsars drifting subpulses are discovered for the first time and are confirmed for many others. This leads to the conclusion that it could well be that the drifting subpulse mechanism is an intrinsic property of the emission mechanism itself, although for some pulsars it is difficult or impossible to detect. It appears that the youngest pulsars have the most disordered subpulses and the subpulses become more and more organized into drifting subpulses as the pulsar ages. Drifting subpulses are in general found at both frequencies and the measured values of P3 at the two frequencies are highly correlated, showing the broadband nature of this phenomenon. Also the modulation indices measured at the two frequencies are clearly correlated, although at 92 cm they are on average possibly higher. The correlations with the modulation indices are argued to be consistent with the picture in which the radio emission is composed out of a drifting subpulse signal plus a quasi-steady signal which becomes, on average, stronger at high observing frequencies. There is no obvious correlation found between P3 and the pulsar age (or any other pulsar parameter) contrary to reports in the past. [ABSTRACT FROM AUTHOR]

We find that the color indices of the optical afterglow (OA) of the short GRB050709 are consistent with those of the ensemble of 25 OAs of the long GRBs. This suggests that the spectral profiles of the OAs of both kinds of GRB are similar to each other and that the reddening inside their host galaxies is quite small (EB–V < 0.2). The k-corrected R band absolute magnitude of the OA of GRB050709 in (t - T0)rest = 2.13 days (i.e. in the rest frame of the GRB) is MR ≈ -16.7, which is considerably fainter than that of the ensemble of the OAs of the long GRBs studied by [13]. This can suggest that the properties of a fireball do not depend very much on the phenomenon which originated it while the intensities differ considerably. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We find that the behaviour of the color indices of the optical afterglows (OAs) of GRBs can be divided into several intervals during the first several tens of days. We present an analysis of the color variations in the very early phases of the OAs and their relation to those of the ensemble of 25 OAs studied by [8]. Our analysis of the Swift/UVOT observations of the very early phase of the OA of GRB050922C reveals chromatic variations which possibly suggest a multi-component, rapidly varying spectral profile during t - T0 < 0.01 days. The colors of this OA do not show any significant intrinsic extinction and put constraints on the changes of the extinction caused by the GRB and/or its OA. We argue that the ensemble of OAs studied here is not reddened. A very broad range of their redshifts (0.17 < z < 3.5) suggests that these GRBs presumably occur in the different times of the evolution of their host galaxies, and hence in the regions with different metallicity and dust content. Although several mechanisms can play a role, our finding shows that all of them must be able to provide a negligible extinction for the events analysed here. We briefly discuss also the implications for the orphan afterglows. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

About one thousand extragalactic large-scale jets are known, and a few tens of them are confirmed sources of infrared, optical, or X-ray photons. Multiwavelength emission comming directly from these outflows is always non-thermal in origin. This fact constitutes a primary difficulty in extracting unknown parameters of large-scale jets, since the non-thermal featureless continua do not allow to infer undoubtfully (or even at all) bulk velocities and composition of the radiating plasma. In addition, arcsecond spatial resolution, limited sensitivity and narrow energy bands of the best high-frequency telescopes like Spitzer, Hubble and Chandra, preclude precise constraints on the spectral and morphological properties of the discussed objects. Nevertheless, new multiwavelength observations have substantially enriched our knowledge on extragalactic large-scale jets, in many aspects, however, by means of challenging previous predictions and expectations. In this short contribution I will concentrate on the following issue: what can be learned by analyzing broad-band emission of the discussed objects about particle acceleration processes acting thereby and about jet internal parameters. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We determine the color indices of SN 2006aj/GRB060218 from the UVOT observations (including the cosmic UV), supplemented by the ground-based data. This turns out to be a much better tool than the analysis of the lightcurves themselves. We show a rapid and complicated evolution of the colors and lightcurves of this transient for t-T0<25 days. The very large difference between the values and time evolution of the color indices of the early optical afterglow (OA) and SN 2006aj speaks against the influence of a possible prolonged early OA on the supernova light. In our interpretation, the light contribution of the outer layers of SN 2006aj became increasingly prominent in UV already at t-T0≈0.55 d. We find that SN 2006aj systematically possesses a significant light excess in U with respect to the canonical SN 1998bw. The outer layers of SN 2006aj underwent the largest evolution among the considered SNe. We interpret this as due to the fact that we observed simultaneously the different regions of SN 2006aj in the initial phase. A hot ‘hole’ caused by the emerging jet was surrounded by cooler layers further away from the axis of the jet. The line blanketing undergoes only small variations and the UV emitting area tends to shrink during the evolution of SN 2006aj over the time interval investigated. No variations of the reddening caused by the dust destruction even in the very initial phase of the OA are present. [ABSTRACT FROM AUTHOR]

We investigate the luminosity and colors of the optical afterglow (OA) of GRB060218 during t-T0<2 days in the context of the OAs of long GRBs. The R-band absolute magnitude -19.5 at (t-T0)rest = 1.5 d places this event below or at the lower end of the statistical distribution of the spectrally homogeneous ensemble of 23 OAs of long GRBs which we considered in our previous work [13, 14]. We find that the color indices of this phase are not consistent with those of the ensemble of OAs of GRBs, but their time evolution is. No variations of reddening even in the initial phase of these OAs are present. We argue that the optical and UV emission is not a simple continuation (Rayleigh-Jeans tail) of the X-ray emission. We also show that although both GRB060218 and XRF030723 possess a very soft gamma-ray spectrum, sorting them to X-ray flashes, the color indices of their early OAs are mutually discordant. [ABSTRACT FROM AUTHOR]

We performed a detailed calculation of gamma-ray burst (GRB) prompt emission in the framework of the internal shock scenario, focusing on the high energy (GeV) bands. In order to follow the evolution of the ultrarelativistic inhomogeneous wind, we combined a model for the dynamics of internal shocks with a detailed calculation of the radiative processes occurring in the shocked medium. We present the resulting synthetic GRB light curves and spectra. We show the spectral evolution that can be expected for different sets of microphysics parameters and parameters of the dynamical evolution, and how the relative importance of synchrotron and inverse Compton components is varying during a burst. [ABSTRACT FROM AUTHOR]

During the last few years there were discovered and deeply examined several transient neutron stars (Part Time Radio Pulsars). It is already well accepted that these objects are rotating neutron stars. But their extraordinary features (burst-like behavior) made necessary revision of well accepted models of pulsar interior structure. Nowadays most popular model for part time radio pulsars is precessing pulsar model, which is the subject of big discussion. We assume that these objects are pulsars with specific spin parameters. An important feature of our model, naturally explaining most of the properties of these neutron stars, is presence of very low frequency, nearly transverse drift waves propagating across the magnetic field and encircling the open field lines region of the pulsar magnetosphere. [ABSTRACT FROM AUTHOR]

We present results of a population synthesis of millisecond pulsars from the Galactic disk. Excluding globular clusters, we model the spatial distribution of millisecond pulsars by assuming their birth in the Galactic disk with a random kick velocity and evolve them to the present within the Galactic potential. We assume that ordinary and millisecond pulsars are standard candles described with a common radio emission model that invokes a new relationship between radio core and cone emission suggested by recent studies. In modeling the radio emission beams, we explore the relativistic effects of time delay, aberration and sweepback of the open field lines. While these effects are essential in understanding pulse profiles, the phase-averaged flux is adequately described without a relativistic model. We use a polar cap acceleration model for the γ-ray emission. We present the preliminary results of our recent study and the implications for observing millisecond pulsars with GLAST and AGILE. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Large Area Telescope (LAT) instrument onboard GLAST offers a tremendous opportunity for future blazar studies. In order to fully benefit from its capabilities and to maximize the scientific return from the LAT, it is of great importance to conduct dedicated multi-frequency monitoring campaigns that will result comprehensive observations. Consequently, we initiated an effort to conduct a GLAST-dedicated, quasi-simultaneous, broad-band flux-density (and polarization) monitoring of potential GLAST blazars with the Effelsberg and OVRO radio telescopes (11 cm to 7 mm wavelength). Here, we present a short overview of these activities which will complement the multi-wavelengths activities of the GLAST/LAT collaboration towards the ‘low-energy’ radio bands. Further we will give a brief outlook including the extension of this coordinated campaign towards higher frequencies and future scientific aims. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

With the anticipated launch of GLAST, the existing X-ray telescopes, and the enhanced capabilities of the new generation of TeV telescopes, developing tools for modeling the variability of high energy sources such as blazars is becoming a high priority. We point out the serious, innate problems one zone synchrotron-self Compton models have in simulating high energy variability. We then present the first steps toward a multi zone model where non-local, time delayed Synchrotron-self Compton electron energy losses are taken into account. By introducing only one additional parameter, the length of the system, our code can simulate variability properly at Compton dominated stages, a situation typical of flaring systems. As a first application, we were able to reproduce variability similar to that observed in the case of the puzzling ‘orphan’ TeV flares that are not accompanied by a corresponding X-ray flare. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The two interpretations suggested for the Chandra-detected X-ray emission of the large scale jets of powerful quasars are external Compton (EC) scattering off the cosmic microwave background (CMB) photons (EC/CMB) and synchrotron emission from a population of electrons separate from those producing the radio — IR emission. Here we present a way to discriminate between the two models based on a fundamental difference they have: the production of synchrotron X-rays requires multi — TeV electrons, while the EC/CMB model requires a cutoff in the electron energy distribution (EED) below TeV energies. This has significant implications for the γ-ray emission predicted by these two models, that can be tested through GeV and TeV observations of the nearby bright quasar 3C 273. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In spring/summer 2006 the BL Lac object Mrk 421 reached its largest ever recorded flux in the X-rays, up to about one tenth of Crab in the 2.0–10.0 keV band, and showed a synchrotron SED peak at approximately 10 keV. We present results of a spectral analysis of three observations performed by the UVOT, the XRT and the BAT telescopes on board the SWIFT satellite. According to the widely accepted SSC scenario, the expected flux in the GLAST LAT instrument, for such a bright X-ray state, should result in a counting statistics sufficient for a determination of the gamma-ray spectral shape. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The question of a possible redshift-dependence of γ-ray absorption due to γγ-pair production of jet photons in the accretion disk and BLR radiation field in strong-line quasars is investigated. For this relevant aspects of cosmological black hole and quasar evolution are applied to the expected pair production opacity of GeV-photons in those sources. I demonstrate that for positively evolving and non-evolving accretion rates over cosmological time, detectable γ-ray optical depths originating within the AGN system will show a redshift-dependence in the LAT energy range with larger opacity from sources at higher redshifts. This introduces ambiguities in the interpretation of spectral absorption features, and complicates approaches for estimating the evolution of the extragalactic background light by probing the γ-ray horizon when using blazars whose external photon fields are involved in γ-ray production. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We investigate a magnetized plasma in which injected high energy gamma-rays annihilate on a soft photon field, that is provided by the synchrotron radiation of the created pairs. For a very wide range of magnetic fields, this process involves gamma-rays between 0.3 GeV and 30 TeV. We derive a simple dynamical system for this process, analyze its stability to runaway production of soft photons and pans, and find conditions for it to automatically quench by reaching a steady state with an optical depth to photon-photon annihilation larger than unity. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We discuss the contribution of kiloparsec-scale jets in FR I radio galaxies to the diffuse γ-ray background radiation. The analyzed γ-ray emission comes from inverse-Compton scattering of starlight photon fields by the ultrarelativistic electrons whose synchrotron radiation is detected from such sources at radio, optical and X-ray energies. We find that these objects, under the minimum-power hypothesis (corresponding to a magnetic field of 300 μG in the brightest knots of these jets), can contribute about one percent to the extragalactic γ-ray background measured by EGRET. We point out that this result already indicates that the magnetic fields in kpc-scale jets of low-power radio galaxies are not likely to be smaller than 10 μG on average, as otherwise the extragalactic γ-ray background would be overproduced. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Evidence for orbital modulation of the very high energy (VHE) γ-ray emission from the high-mass X-ray binary and microquasar LS 5039 has recently been reported by the HESS collaboration. The observed flux modulation was found to go in tandem with a change in the GeV – TeV spectral shape, which may partially be a result of γγ absorption in the intense radiation field of the massive companion star. In a recent paper [1], I have presented a parameter study of the γγ absorption effects in this system. For a range of plausible locations of the VHE γ-ray emission region and the allowable range of viewing angles, the de-absorbed, intrinsic VHE γ-ray spectra and total VHE photon fluxes and luminosities were calculated and compared to luminosity constraints based on Bondi-Hoyle limited wind accretion onto the compact object in LS 5039. It was found that (1) it is impossible to choose the viewing angle and location of the VHE emission region in a way that the intrinsic spectra in superior and inferior conjunction are identical; (2) if the VHE luminosity is limited by wind accretion from the companion star and the system is viewed at an inclination angle of i > 40°, the emission is most likely beamed by a larger Doppler factor than inferred from the dynamics of the large-scale radio outflows; (3) the still poorly constrained viewing angle between the line of sight and the jet axis is most likely substantially smaller than the maximum of ∼ 64° inferred from the lack of eclipses. (4) Consequently, the compact object is more likely to be a black hole rather than a neutron star. (5) There is a limited range of allowed configurations for which the expected VHE neutrino flux would actually anti-correlate with the observed VHE γ-ray emission. If hadronic models for the γ-ray production in LS 5039 apply, a solid detection of the expected VHE neutrino flux and its orbital modulation with km3 scale water-Cherenkov neutrino detectors might require the accumulation of data over more than 3 years. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present results of a pulsar population synthesis of normal pulsars in the Galactic plane. Over the past several years, a program has been developed to simulate pulsar birth, evolution, and emission using Monte Carlo techniques. We model the spatial distribution of pulsars by assuming they are born with a random kick velocity and then evolved within the Galactic potential. We assume that pulsars are standard candles and invoke a new relationship between core and cone emission suggested by recent studies, which we also apply to millisecond pulsars. From our studies of radio pulsars that have clearly identifiable core and cone components, in which we fit the polarization sweep as well as the pulse profiles to constrain the viewing geometry, we develop a model describing the ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are more cone-dominated than in our previous studies. We use both a low and high altitude slot gap model for describing the gamma-ray emission. We also include gamma-ray emission from an outer-gap model to compare the statistics of radio-loud and radio-quiet gamma-ray pulsars on the same footing as pulsars from our slot gap, polar cap model. We present results of our recent study and the implications for observing these pulsars with GLAST and AGILE. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We consider propagation of relativistic heavy nuclei injected by a young pulsar into the radiation field of a massive companion. If the binary system is compact enough, the nuclei suffer multiple photodisintegrations in collisions with thermal photons coming from the massive star. Some neutrons and protons, dissolved from the nuclei, can collide with the massive star producing neutrinos. Due to the propagation effects of charged particles (protons from nuclei and their surviving remnants) in the magnetic field of the massive star, some hadrons can impinge onto the massive star surface at the angles larger than the obscuring angle of the massive star. We calculate the fluxes of neutrinos, produced by these hadrons, as a function of the viewing angle measured from the plane of the binary system. It is found that significant fluxes of neutrinos should be also expected in the case of non-eclipsing binary systems, i.e. at angles larger than corresponding to the obscuring angle of the massive star. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]