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We investigate properties of the emission region as revealed by drifting subpulses of opposite drift directions at different parts of a pulse profile by using the rotating carousel model in an obliquely rotating pulsar magnetosphere of multiple emission states. Subpulse emission is assumed coming from m discrete emission areas that are distributed around the magnetic axis on a rotating carousel. The flow rate of the emission areas is determined by the E × B drift in an emission state, designated by the parameter y , in which E and the associated flow rate are dependent on y . In this model, subpulses appear to drift in an emission state if a relative speed exists between the plasma flow and corotation, and the diversity in the drift rates and directions corresponds to the relative speed being different in different parts of a profile. We apply the model to three pulsars that exhibit drifting subpulses of opposite drift directions to identify the emission states and the values of m . Our results show that different drifting subpulses correspond to particular values of m and y , and the latter implies that different emission states can coexist and operate concurrently in an emission region. We find that m does not show clear dependency on either the obliquity angle or emission state. We demonstrate that subpulse arrangement may vary across an emission region meaning that it is not always uniform on a carousel. We discuss drifting subpulses of opposite drift directions and subpulse drift-rate switching in terms of different emission states in our model, and speculate that they may be two manifestations of the same underlying mechanism. [ABSTRACT FROM AUTHOR]

Extended Red Emission (ERE) is a widely observed optical emission process, present in a wide range of circumstellar and interstellar environments in the Milky Way galaxy as well as other galaxies. Definitive identifications of the ERE carriers and the ERE process are still a matter of debate. Numerous models have been proposed in recent decades, often developed without consideration of the growing body of observational constraints, which by now invalidate many of these models. This review focuses on the most well-established observational constraints which should help to delineate the way toward a generally accepted explanation of the ERE and an understanding of its place in the radiation physics of the interstellar medium. [ABSTRACT FROM AUTHOR]

The fourth Fermi Large Area Telescope Source Catalog (4FGL) lists over 5000 γ -ray sources with statistical significance above 4 σ . About 23% of the sources listed in this catalog are unidentified/unassociated γ -ray sources while ∼26% of the sources are classified as blazar candidates of uncertain type (BCUs), lacking optical spectroscopic information. To probe the blazar nature of candidate counterparts of UGSs and BCUs, we started our optical spectroscopic follow up campaign in 2012, which up to date account for more than 350 observed sources. In this paper, the tenth of our campaign, we report on the spectroscopic observations of 37 sources, mostly BCUs, whose observations were carried out predominantly at the Observatorio Astronómico Nacional San Pedro Mártir and the Southern Astrophysical Research Observatory between August 2018 and September 2019. We confirm the BL Lac nature of 27 sources and the flat spectrum radio quasar nature of three sources. The remaining ones are classified as six BL Lacs galaxy-dominated and one normal galaxy. We were also able to measure the redshifts for 20 sources, including 10 BL Lacs. As in previous analyses, the largest fraction of BCUs revealed to be BL Lac objects. [ABSTRACT FROM AUTHOR]

We collect a sample of 78 Fermi detected blazars with broad line region (BLR) data and the quasi-simultaneous multi-wave band data. By analyzing the sample, we find: (1) For whole blazar sample, there exist significant correlations between radio, $\gamma$ -ray luminosity and BLR luminosity. The slope of the best-fit linear regression equation is close to the theoretical value 1. Our results provided another support of jet-disk symbiosis. (2) For FSRQ sample, we find a significant correlation between radio luminosity and optical luminosity, and weaker correlations between X-ray luminosity and radio, optical luminosity. It indicates that the X-ray band radiation mechanism is slightly different from radio and optical bands. The X-ray emission is diluted by inverse Compton scattering (IC). There is a significant correlation between BLR luminosity and $\gamma$ -ray luminosity, but no correlations between X-ray luminosity and BLR, $\gamma$ -ray luminosity, which suggests that the seed soft photons are different for IC process. From these results we suggest that the X-ray band emission is diluted by synchrotron self-Compton (SSC) process, $\gamma$ -ray band emission is produced by external Compton (EC) process. [ABSTRACT FROM AUTHOR]

Bolometric luminosity is a basic physical parameter that is widely used in the study of blazars. Due to the lack of simultaneous full wavelength data, several estimators of the bolometric luminosity are being used in practice. In this paper, we study and evaluate the reliability and significance of six estimators, the $5\mbox{GHz}$ luminosity, the 1keV luminosity, the $\gamma$ -ray luminosity, the $5\mbox{GHz}$ luminosity + the 1keV luminosity, the $5\mbox{GHz}$ luminosity + the $\gamma$ -ray luminosity and the 1keV luminosity + the $\gamma$ -ray luminosity, by analyzing the linear correlations between the integrated bolometric luminosity and them. Our main results are as follows. (i) All the six estimators are reliable in the sense that they are all significant correlated with the bolometric luminosity. (ii) Ranking from the higher significance of the reliability to lower one the six estimators are the $5\mbox{GHz}$ luminosity + the $\gamma$ -ray luminosity, the 1keV luminosity + the $\gamma$ -ray luminosity, $\gamma$ -ray luminosity, the $5\mbox{GHz}$ luminosity + the 1keV luminosity, the $5\mbox{GHz}$ luminosity and the 1keV luminosity. (iii) We suggest that the bolometric luminosity can be well estimated by the $\gamma$ -ray luminosity using the best linear equation that given in this paper for Fermi FSRQs. (iv) According to the linear regressions obtained in the analysis, we provide calibration for each estimator. [ABSTRACT FROM AUTHOR]

Langmuir waves (LWs), which are believed to play a crucial role in the plasma emission of solar radio bursts, can be excited by streaming instability of energetic electron beams. However, solar hard X-ray observations imply that the energetic flare electrons usually have a power-law energy distribution with a lower energy cutoff. In this paper, we investigate LWs driven by the power-law electrons. The results show that power-law electrons with the steepness cutoff behavior can excite LWs effectively because of the population inversion distribution below the cutoff energy ( E). The growth rate of LWs increases with the steepness index ( δ) and decreases with the power-law index ( α). The wave number of the fastest growing LWs ( kλ), decreases with the characteristic velocity of the power-law electrons ( $v_{c}=\sqrt{2E_{c}/m_{e}}$) and increases with the thermal velocity of ambient electrons ( v). This can be helpful for us to understand better the physics of LWs and the dynamics of energetic electron beams in space and astrophysical plasmas. [ABSTRACT FROM AUTHOR]

This paper presents a modeling of the variable synchrotron emission in the BL Lacertae sources (BLLs). Flux variability is assumed to be a result of the interaction between a relativistic shock wave with a magnetized jet material. Long-term flares (of months to years durations) are modeled via the propagation of a plane relativistic shock wave though the emission zone of a cylindrical form with the radius R and length H. As for short-term bursts (lasting from days to weeks), they may result from shock passage through the jet inhomogeneities such as a shell of enhanced density downstream to a Mach disc, originated due to pressure imbalance between the jet and its ambient medium. Emitting particles (electrons) gain the energies, sufficient to produce synchrotron photons at optical-X-ray frequencies, via the first-order Fermi mechanism. Observation's frequency is the main parameter determining a rate of the increase/ decay of the emission via the characteristic decay time of emitting electrons. The magnetic field, assumed to be turbulent with an average field constant throughout the entire emission zone, is another key parameter determining the slope of a lightcurve corresponding to the flare-the higher strength the magnetic field has, the steeper the lightcurve is. The rest input parameters (shock speed, jet viewing angle, maximum/minimum energies of the electrons, particles' density etc.), as well the strength of average magnetic field, influence the energy output from a flare. [ABSTRACT FROM AUTHOR]

Investigations of the luminescence of frozen hydrocarbon particles of icy cometary halo have been made. The process of luminescence of icy particles in shortwavelength solar radiation field is considered. The comparative analysis of observed and laboratory data leads of 72 luminescent emission lines in the spectrum of 153P/Ikeya-Zhang comet. Several aspects of the problem are discussed. [ABSTRACT FROM AUTHOR]

New investigations of the photoluminescence of frozen hydrocarbon particles of icy cometary halo have been made. The process of photoluminescence of icy particles in the ultraviolet solar radiation field is considered. The comparative analysis of laboratory and observed data leads to the preliminary identification of some sixty eight photoluminescent emission features in the spectra of 109P/Swift–Tutle and 23P/Brorsen–Metcalf comets. Formulae are given for the calculation of the efficiency of the photoluminescence of icy organic particles in the cometary halo. [ABSTRACT FROM AUTHOR]

In the last decade multi-wavelength observations have demonstrated the importance of jets in the energy output of accreting black hole binaries. The observed correlations between the presence of a jet and the state of the accretion flow provide important information on the coupling between accretion and ejection processes. After a brief review of the properties of black hole binaries, I illustrate the connection between accretion and ejection through two particularly interesting examples. First, an INTEGRAL observation of Cygnus X-1 during a ‘mini-’ state transition reveals disc jet coupling on time scales of orders of hours. Second, the black hole XTEJ1118+480 shows complex correlations between the X-ray and optical emission. Those correlations are interpreted in terms of coupling between disc and jet on time scales of seconds or less. Those observations are discussed in the framework of current models. [ABSTRACT FROM AUTHOR]

Recent observations provide strong evidence for the BL Lac object OJ287 exhibiting a 11.6±0.5 yr periodicity with a double-peaked maxima in its optical flux variations. Several models have been proposed for the optical behavior. The 2005 November outburst in OJ287 gives us a surprising result since calculation based on the periodicity was predicting such an outburst in late 2006. Here we suggest a new model, it can not only explain the optical quasi-periodic behavior, but also the radio flares behavior which is and simultaneous with the optical flares. We propose that OJ287 is a binary pair of super-massive black holes, both of them creating a jet. The quasi-periodic double peaks would be due to the relativistic beaming effect on the emission coming from the double helix jets. We used “core flares” to explain the large lags between light curves at different frequencies, and the assumption of two jets appear to be merged with each other partly in the radio frequency emitting regions provides a viable interpretation that we can see only a broad maximum which contains two radio flares that we cannot distinguish. [ABSTRACT FROM AUTHOR]

Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties of Kepler’s SNR and, in particular, to predict the γ-eay spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical constraints for the total supernova (SN) explosion energy E sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler’s SN is a type Ia SN we determine for any given explosion energy E sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes it possible to make predictions for the expected γ-eay flux. Exploring the expected distance range we find that for a typical explosion energy E sn=1051 erg the expected energy flux of TeV γ-rays varies from 2×10−11 to 10−13 erg/(cm2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the γ-eay emission is dominated by π 0-decay γ-rays due to nuclear CRs. Therefore Kepler’s SNR represents a very promising target for instruments like H.E.S.S., CANGAROO and GLAST. A non-detection of γ-rays would mean that the actual source distance is larger than 7 kpc. [ABSTRACT FROM AUTHOR]

We report hard X-ray emission of the non-thermal supernova remnant G337.2+0.1. The source presents centrally filled and diffuse X-ray emission. A spectral study confirms that the column density of the central part of the object is about N H∼5.9(±1.5)×1022 cm−2 and its X-ray spectrum is well represented by a single power-law with a photon index Γ=0.96±0.56. Detailed spectral analysis indicates that the outer region is highly absorbed and quite softer than the inner region. Characteristics already observed in other well-known X-ray plerions. Based on the gathered information, we confirm the SNR nature of G337.2+0.1, and suggest that the central region of the source is a pulsar wind nebula (PWN), originated by an energetic though yet undetected pulsar. [ABSTRACT FROM AUTHOR]

Blazars are the most violent steady/recurrent sources of high-energy gamma-ray emission in the known Universe. They are prominent emitters of electromagnetic radiation throughout the entire electromagnetic spectrum. The observable radiation most likely originates in a relativistic jet oriented at a small angle with respect to the line of sight. This review starts out with a general overview of the phenomenology of blazars, including results from a recent multiwavelength observing campaign on 3C279. Subsequently, issues of modeling broadband spectra will be discussed. Spectral information alone is not sufficient to distinguish between competing models and to constrain essential parameters, in particular related to the primary particle acceleration and radiation mechanisms in the jet. Short-term spectral variability information may help to break such model degeneracies, which will require snap-shot spectral information on intraday time scales, which may soon be achievable for many blazars even in the gamma-ray regime with the upcoming GLAST mission and current advances in Atmospheric Cherenkov Telescope technology. In addition to pure leptonic and hadronic models of gamma-ray emission from blazars, leptonic/hadronic hybrid models are reviewed, and the recently developed hadronic synchrotron mirror model for TeV γ-ray flares which are not accompanied by simultaneous X-ray flares (“orphan TeV flares”) is revisited. [ABSTRACT FROM AUTHOR]

We consider the synchrotron emission from relativistic shocks assuming that the radiating electrons cool rapidly (either through synchrotron or any other radiation mechanism). It is shown that the theory of synchrotron emission in the fast cooling regime can account for a wide range of spectral shapes. In particular, the magnetic field, which decays behind the shock front, brings enough flexibility to the theory to explain the majority of gamma-ray burst spectra even in the parameter-free fast cooling regime. Also, we discuss whether location of the peak in observed spectral energy distributions of gamma-ray bursts and active galactic nuclei can be made consistent with predictions of diffusive shock acceleration theory, and find that the answer is negative. This result is a strong indication that a particle injection mechanism, other than the standard shock acceleration, works in relativistic shocks. [ABSTRACT FROM AUTHOR]

Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of yet unidentified EGRET γ-ray sources with source populations appearing in star formation regions. This work re-considers the basic radiative processes and its properties that lead to high energy photon production in long-period massive star systems. We show that Klein–Nishina effects as well as the anisotropic nature of the inverse Compton scattering, the dominating leptonic emission process, likely yield spectral and variability signatures in the γ-ray domain at or above the sensitivity of current or upcoming gamma ray instruments like GLAST-LAT. In addition to all relevant radiative losses, we include propagation (such as convection in the stellar wind) as well as photon absorption effects, which a priori can not be neglected. The calculations are applied to WR 140 and WR 147, and predictions for their detectability in the γ-ray regime are provided. Physically similar specimen of their kind like WR 146, WR 137, WR 138, WR 112 and WR 125 may be regarded as candidate sources at GeV energies for near-future γ-ray experiments. Finally, we discuss several aspects relevant for eventually identifying this source class as a γ-ray emitting population. Thereby we utilize our findings on the expected radiative behavior of typical colliding wind binaries in the γ-ray regime as well as its expected spatial distribution on the γ-ray sky. [ABSTRACT FROM AUTHOR]

For the case of Tycho’s supernova remnant (SNR) we present the relation between the blast wave and contact discontinuity radii calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is so close to the shock radius that it can only be explained by efficient CR acceleration which in turn makes the medium more compressible. Together with the recently determined new value E sn=1.2×1051 erg of the SN explosion energy this also confirms our previous conclusion that a TeV γ-ray flux of (2–5)×10−13 erg/(cm2 s) is to be expected from Tycho’s SNR. Chandra measurements and the HEGRA upper limit of the TeV γ-ray flux together limit the source distance d to 3.3≤ d≤4 kpc. [ABSTRACT FROM AUTHOR]

Owing to effects arising from quantum electrodynamics (QED), magnetohydrodynamical fast modes of sufficient strength will break down to form electron-positron pairs while traversing the magnetospheres of strongly magnetised neutron stars. The bulk of the energy of the fast mode fuels the development of an electron-positron fireball. However, a small, but potentially observable, fraction of the energy (∼1033 erg) can generate a non-thermal distribution of electrons and positrons far from the star. This paper examines the cooling and radiative output of these particles. Small-scale waves may produce only the non-thermal emission. The properties of this non-thermal emission in the absence of a fireball match those of the quiescent, non-thermal radiation recently observed non-thermal emission from several anomalous X-ray pulsars and soft-gamma repeaters. Initial estimates of the emission as a function of angle indicate that the non-thermal emission should be beamed and therefore one would expect this emission to be pulsed as well. According to this model the pulsation of the non-thermal emission should be between 90 and 180 degrees out of phase from the thermal emission from the stellar surface. [ABSTRACT FROM AUTHOR]

Some recent developments in the study of relativistic jets in active galactic nuclei and microquasars are reviewed. While it has been well established for some time that extragalactic jets found in radio galaxies, quasars, and BL Lac objects are the site of ultrarelativistic particle acceleration, the recent identification of the Galactic jet source and microquasar LS~5039 as a source of very-high-energy gamma-ray emission has underlined the striking similarity between the two types of astrophysical jet sources. In this paper, I will present an overview of the dominant radiation and particle acceleration processes and observational tests to distinguish between such processes. The wide-ranging analogies between Galactic and extragalactic jets, but also their distinct differences, in particular those caused by the presence of the companion star in Galactic microquasar systems, will be exposed. [ABSTRACT FROM AUTHOR]

The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence of the companion star. Both orbital-phase dependent γγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST mission. [ABSTRACT FROM AUTHOR]

Jet models for the high-energy emission of Galactic X-ray binary sources have regained significant interest with detailed spectral and timing studies of the X-ray emission from microquasars, the recent detection by the HESS collaboration of very-high-energy γ-rays from the microquasar LS 5039, and the earlier suggestion of jet models for ultraluminous X-ray sources observed in many nearby galaxies. Here we study the synchrotron and Compton signatures of time-dependent electron injection and acceleration, and adiabatic and radiative cooling in the jets of Galactic microquasars. [ABSTRACT FROM AUTHOR]

Astrophysical jets seem to gain strength disproportionate to the power of their associated accretion flow, making low-luminosity sources ideal targets for studies of the role of outflows. Radio/X-ray correlations have supported the case for a strong relationship between the jets and the hard X-ray emitting regions, and here we explore the strongest scenario where the base of the jets subsumes the role of the corona. The properties of coronae, as inferred from spectral models, are very similar to what is empirically required at jet bases assuming conservation laws hold. We present a few preliminary fits to simultaneous radio and X-ray datasets from our GX 339−4 and Cyg X-1 campaigns. The fits are performed in detector space, and include a jet plus thermal disk continuum model, with added Gaussian line and non-relativistic reflection features similar to the approach of other X-ray models. We find that we can fit the entire radio through X-ray spectrum quite well, with any deviation occurring in the line/reflection region. The results suggest that a jet/corona unification can provide a reasonable description of the data. Future work will benefit from a more complex approach to the disk feedback features. [ABSTRACT FROM AUTHOR]

In recent years, significant evidence for the similar nature of active galactic nuclei (AGN) and X-ray binaries (XRBs) has been gathered. We describe a unification scheme for accreting black holes following the idea that weakly accreting systems may be jet dominated. This is tested with the radio/X-ray correlation of XRBs and AGN. The established correlation is further used to diagnose ultra-luminous X-ray sources. For higher accretion rates, we explore high-power jets and the effect of Compton cooling of the jet by the accretion disk. [ABSTRACT FROM AUTHOR]

Blazars are the only (with one or two exceptions) extragalactic objects which were detected and identified at gamma-ray energies so far. It is suspected that most of the unidentified gamma-ray sources may be the blazars as well. Because the entire electromagnetic spectrum of these objects is dominated by non-thermal radiation from relativistically moving jets, the effects such as the Klein-Nishina regime in the Compton scattering may play a major role in shaping some parts of the blazar spectrum. Within the framework of external radiation Compton model, we present how these effect influence the spectra of blazars for which the production of gamma rays is dominated by Comptonization of external radiation. [ABSTRACT FROM AUTHOR]

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 #8A is an O6+O5.5 binary system with a period of about 21.9 days. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to ?-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative ?-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+4118. [ABSTRACT FROM AUTHOR]

Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550-564 has been recently discovered withChandraby Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with the well-known Sedov evolutionary phaseR?t2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gamma-ray burst remnants, is shown to be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around the source is well below the canonical valuenISM~1 cm-3. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta. [ABSTRACT FROM AUTHOR]

Suprathermal proton bremsstrahlung (SPB) of energetic protons is an important source of high-energy X-ray and gamma-ray photons in the interstellar medium. We calculate the suprathermal bremsstrahlung radiation power and the associated energy loss rate of the radiating protons. Also the mean photon energy from the SPB process is derived which can be used to construct a monochromatic approximation of the radiation power. The SPB power is the starting point for the quantitative modelling of theoretical SPB radiation spectra in cosmic sources. [ABSTRACT FROM AUTHOR]

Nearly one third of the sources in the Fermi-LAT catalogs lacks a lower energy counterpart, hence being referred as unidentified/unassociated gamma-ray sources (UGSs). In order to firmly classify them, dedicated multifrequency follow-up campaigns are necessary. These will permit to unveil their nature and identify the fraction that could belong to the class of active galaxies known as blazars that is the largest population of extragalactic γ -ray sources. In Fermi-LAT catalogs there are also gamma-ray sources associated with multifrequency blazar-like objects known as Blazars Candidates of Uncertain type (i.e., BCUs) for which follow up spectroscopic campaigns are mandatory to confirm their blazar nature. Thus, in 2013 we started an optical spectroscopic campaign to identify blazar-like objects potential counterparts of UGSs and BCUs. Here we report the spectra of 31 additional targets observed as part of our follow up campaign. Thirteen of them are BCUs for which we acquired spectroscopic observations at Observatorio Astrofísico Guillermo Haro (OAGH) and at Southern Astrophysical Research Observatory (SOAR) telescopes, while the rest has been identified thanks to the archival observations available from the Sloan Digital Sky Survey (SDSS). We confirm the blazar nature of all BCUs: three of them are in blazar of quasar type (BZQs) while the remaining ones can be spectroscopically classified as BL Lac objects (BZBs). Then we also discovered 18 BL Lac objects lying within the positional uncertainty regions of UGSs that could be their potential counterparts. [ABSTRACT FROM AUTHOR]

In the present paper, we discuss theoretical interpretation of the X-ray and gamma-ray emission of the extremely bright pulsar PSR J0540-6919, in the Large Magellanic cloud. The source of the high frequency emission is assumed to be the synchrotron radiation, which is generated near the light cylinder during the quasi-linear stage of the cyclotron instability developed in this region. The emitting particles are the particles of the primary beam, with the Lorentz factors of the order of γ b ∼ 10 7 that provide generation of the gamma-ray emission with the photon energy up to 10 GeV and the secondary plasma electrons with γ t ∼ 10 5 , emitting in the X-ray domain. The theoretical synchrotron radiation spectra obtained in the framework of the model provide natural explanation of the observed photon spectra showing power-law indices 2.2 for gamma-rays and 1.55 for the X-rays. The present model provides natural explanation for pulse-aligned emission peaks at different frequencies and smearing of two-peak pulse profile at higher frequencies that is clearly observed in radio domain. [ABSTRACT FROM AUTHOR]

In the present work we consider energy accumulation mechanism in relativistic electron-positron plasma in the magnetosphere of pulsars. In the light cylinder vicinity the waves propagating almost across the magnetic field lines are generated. Due to their propagation characteristics, these waves spend significantly long time in the resonance region and as a result accumulate the energy of resonant plasma particles. The accumulated energy is transmitted in the parallel direction of the magnetic field lines as soon as the non-linear plasma processes start to operate. As a result the direction of propagation of waves changes and the waves with accumulated energy can exit the pulsar magnetosphere. It is suggested that when the propagation angles of the mentioned waves becomes small with respect to the magnetic field lines, the waves can be observed as Giant Radio Pulses. [ABSTRACT FROM AUTHOR]

In this paper, we compile the very-high-energy and high-energy spectral indices of 43 BL Lac objects from the literature. Based on a simple math model, ΔΓobs=αz+β, we present evidence for the origin of an observed spectral break that is denoted by the difference between the observed very-high-energy and high-energy spectral indices, ΔΓobs. We find by linear regression analysis that α≠0 and β≠0. These results suggest that the extragalactic background light attenuation and the intrinsic curvature dominate on the GeV-TeV γ-ray energy spectral break of BL Lac objects. We argue that the extragalactic background light attenuation is an exclusive explanation for the redshift evolution of the observed spectral break. [ABSTRACT FROM AUTHOR]

We study the multi-wavelength emission features of PKS 0447-439 in the frame of the one-zone homogeneous lepto-hadronic model. In this model, we assumed that the steady power-laws with exponential cut-offs distributions of protons and electrons are injected into the source. The non-linear time-dependent kinematic equations, describing the evolution of protons, electrons and photons, are defined; these equations self-consistently involve synchrotron radiation of protons, photon-photon interaction, synchrotron radiation of electron/positron pairs, inverse Compton scattering and synchrotron self-absorption. The model is applied to reproduce the multi-wavelength spectrum of PKS 0447-439. Our results indicate that the spectral energy distribution (SED) of PKS 0447-439 can be reproduced well by the model. In particular, the GeV-TeV emission is produced by the synchrotron radiation of relativistic protons. The physically plausible solutions require the magnetic strength 10G≲B≲100G. We found that the observed spectrum of PKS 0447-439 can be reproduced well by the model whether z=0.16 or z=0.2, and the acceptable upper limit of redshift is z=0.343. [ABSTRACT FROM AUTHOR]