Synchrotron self-Compton Emission Models Research Articles

Stochastic acceleration in extreme TeV BL Lacs through MCMC

Extreme TeV BL Lacs are a class of blazars with unique spectral and temporal features that are not easily reproducible using standard one-zone models based on single shock acceleration. To account for their peculiar properties, we elaborated a two-step acceleration model in which a recollimation shock and the subsequent downstream turbulence energize non-thermal electrons. We applied the model to a sample of extreme TeV BL Lacs with well-characterized spectral energy distributions. Since we used several sources, we automatized the exploration of the parameter space. This allowed us to derive the parameter distributions and study the correlations among them. We numerically solved a system of two coupled nonlinear differential equations to obtain the non-thermal particles and turbulence spectra. We calculated the spectral energy distribution via the synchrotron self-Compton emission model. The automatization of the parameter space exploration is possible through a Markov chain Monte Carlo (MCMC) ensemble sampler, in our case emcee We derived well-defined posterior distributions for the parameters, showing that the model is well constrained by available data and demonstrating the suitability of our method. The cross-correlations among some of the physical parameters are not trivial.\ Therefore, we conclude that MCMC sampling is a key instrument for characterizing the complexity of our multiparameter phenomenological model.

Multiwavelength analysis and modeling of OJ 287 during 2017–2020

Context. The blazar OJ 287 has been proposed as binary black hole system based on its periodic optical outburst. Black hole binary systems are scarce among blazars with parsec scale jets, and hence this source is exciting to study Aims. The BL Lac OJ 287 is an interesting object for multiwavelength study due to its periodic outbursts. We analysed the optical, X-ray and γ-ray data of OJ 287 for the period of 2017–2020. There are several high states in optical–UV and X-ray frequencies during this period. Based on the observed variability in optical and X-ray frequencies, the entire period 2017–2020 is divided in five segments, in this paper referred as A, B, C, D, and E. A detailed temporal and spectral analysis is performed to understand the nature of the flaring activities of OJ 287. Methods. To understand the temporal variability in this source we studied the intraday and fractional variability for all the various states. In additon, fast variability time was also estimated in order to understand the nature of variability. Furthermore, the multiwavelength spectral energy distribution (SED) modeling was performed to know more about the physical processes responsible for the simultaneous broadband emission and the fast variability. Results. The Fermi-LAT observations show a moderate flux level of this source in γ-ray frequency throughout this period, though flux variability has been observed. The source has shown a strong flux variability in X-ray, optical, and UV during early 2017 and mid 2020 when the source was in very high state. A single-zone synchrotron self-Compton emission model is considered to model the SED, and this helps us to explore the nature of this BL Lac with binary supermassive black holes.

A synchrotron self-Compton emission model compared with the VHE spectrum of Crab Nebula, Geminga energy spectra and hadronic gamma-rays in the Tycho SNR

The Crab Nebula has an extraordinary broad spectrum, attributed to synchrotron radiation of electrons with energies from GeV to PeV. This continuous spectrum appears to terminate near 10 8 eV and photons, produced by relativistic electrons and positrons ( ∼ 10 15 eV ) via the Inverse Compton effect, form a new component of the spectrum in the GeV - TeV energy range. The spectrum of γ -rays from the Crab Nebula has been measured in the energy range 0.8 TeV to 11 TeV at the SHALON Alatoo Observatory by the atmospheric Cerenkov technique. The VHE spectral energy distribution of the Crab Nebula is compared with the predictions of a synchrotron self-Compton emission model in the energy range 0.8 TeV to 11 TeV (Hillas et al. 1998). Tycho's SNR has been observed by SHALON imaging Cherenkov telescope at Tien-Shan. This object, Ia SNR, has long been considered as a candidate for a CR hadron source in the Northern Hemisphere. The expected pion decay γ -flux, F γ ∼ E γ − 1 , extends up to > 30 TeV , whereas the IC γ -ray flux has a cutoff above a few TeV. So, the detection of γ -rays at energies of 10 - 40 TeV by SHALON is evidence for a hadron origin of the γ -rays.

TeV Gamma and Cosmic Ray Production in Supernova Remnants

An information about high-energy CR population in SNRs can be obtained from gamma-ray observation. High-energy gamma-rays are produced by electronic and hadronic CR components in the inverse Compton (IC) scattering and in the hadronic collisions leading to pion production and subsequent decay respectively. SNe of type Ib and II are more numerous in our Galaxy. According to the theoretical prediction about 20 SNRs should be visible in the TeV gamma-rays whereas only two were detected up to now by SHALON, namely Tycho’s SNR and Geminga. The expected pion decay gamma-flux Fγ ∼ E−1 γ extends up to > 30TeV, whereas the IC gamma-ray flux has a cutoff above a few TeV. So, a detection of gamma-rays at energies of 10 40 TeV by SHALON is an evidence for hadron origin of the rays. An another class of objects considered as a particle accelerator in the Galaxy are Pulsar Wind Nebulae (PWN). One of them is Crab Nebula, observed through all bands of electromagnetic spectrum. Crab Nebula has an extraordinary broad spectrum, attributed to synchrotron radiation of electrons with energies from GeV to PeV. This continuous spectrum appears to terminate near 10 eV and photons, produced by relativistic electrons and positrons (∼ 10 eV) via Inverse Compton, form a new component of spectrum in GeV TeV energy range. The spectrum of gamma rays from the Crab Nebula has been measured in the energy range 0.8 TeV to 11 TeV at the SHALON Alatoo Observatory by the atmospheric Cerenkov technique. The integral energy spectrum is well described by the single power law I(> Eγ) ∝ E−1.44±0.07 γ . An image of gamma-ray emission from Crab Nebula by SHALON telescope is presented. The VHE spectral energy distribution of the Crab Nebula is compared with the predictions of a synchrotron self-Compton emission model in energy range 0.8 TeV to 11 TeV (Hillas et al. 1998).

Synoptic studies of 17 blazars detected in very high-energy γ-rays

Since 2002, the number of detected blazars at γ-ray energies above 100 GeV has more than doubled. I study 17 blazars currently known to emit E > 100 GeV γ-rays. Their intrinsic energy spectra are reconstructed by removing extragalactic background light attenuation effects. Luminosity and spectral slope in the E > 100 GeV region are then compared and correlated among each other, with X-ray, optical and radio data, and with the estimated black hole (BH) masses of the respective host galaxies. According to expectations from synchrotron self-Compton emission models, a correlation on the 3.6σ significance level between γ-ray and X-ray fluxes is found, while correlations between γ-ray and optical/radio fluxes are less pronounced. Further, a general hardening of the blazar spectra in the E > 100 GeV region with increasing γ-ray luminosity is observed, both for the full 17-source sample and for those sources which have been detected at distinct flux levels. This goes in line with a correlation of the γ-ray luminosity and the synchrotron peak frequency, which is also seen. Tests for possible selection effects reveal a hardening of the spectra with increasing redshift. The blazar γ-ray emission might depend on the mass of the central BH. The blazars under study do, however, show no correlation of the BH masses with the spectral index and the luminosity in the E > 100 GeV region. I also consider temporal properties of the X-ray and E > 100 GeV γ-ray flux. No general trends are found, except for the observation that the blazars with the most massive BHs do not show particularly high duty cycles. These blazars include Mkn 501 and PKS 2155−304, for which recently very fast flares have been reported. In general, very high-energy flare time-scales are not found to scale with the BH mass. As a specific application of the luminosity study, a constraint for the still undetermined redshift of the blazar PG 1553+113 is discussed.

HIGH ENERGY ASTROPHYSICS TESTS OF LORENTZ INVARIANCE VIOLATION

Observations of the multi-TeV spectra of the Mkn 501 and other nearby BL Lac objects exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having a flux level as determined by various astronomical observations. After correcting for such intergalactic absorption, these spectra can be explained within the framework of synchrotron self-Compton emission models. Stecker and Glashow have shown that the existence of this annihilation via electron-positron pair production puts strong constraints on Lorentz invariance violaition. Such constraints have important implications for some quantum gravity and large extra dimension models. A much smaller amount of Lorentz invariance violation has potential implications for understanding the spectra of ultrahigh energy cosmic rays.

Tests of quantum gravity and large extra dimensions models using high energy γ-ray observations

Observations of the multi-TeV spectra of the nearby BL objects Mkn 421 and Mkn 501 exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with infrared photons having a flux level as determined by various astronomical observations. After correction for this absorption effect, the derived intrinsic spectra of these multi-TeV sources can be explained within the framework of simple synchrotron self-Compton emission models. Stecker and Glashow have shown that the existence of such annihilations via electron–positron pair production interactions up to an energy of 20 TeV puts strong constraints on Lorentz invariance violation. Such constraints have important implications for quantum gravity models as well as models involving large extra dimensions. We also discuss the implications of observations of high energy γ-rays from the Crab Nebula on constraining quantum gravity models.

Constraints on Lorentz invariance violating quantum gravity and large extra dimensions models using high energy γ-ray observations

Observations of the multi-TeV spectra of the nearby BL objects Mkn 421 and Mkn 501 exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with infrared photons having a flux level as determined by various astronomical observations. After correction for this absorption effect, the derived intrinsic spectra of these multi-TeV sources can be explained within the framework of simple synchrotron self-Compton emission models. Stecker and Glashow have shown that the existence of such annihilations via electron–positron pair production interactions up to an energy of 20 TeV puts strong constraints on Lorentz invariance violation. Such constraints have important implications for Lorentz invariance violating (LIV) quantum gravity models as well as LIV models involving large extra dimensions. We also discuss the implications of observations of high energy γ-rays from the Crab Nebula on constraining quantum gravity models.

Complex X‐Ray Spectral Variability in Markarian 421 Observed withXMM‐Newton

The bright blazar Mrk 421 has been observed four times for uninterrupted durations of ~9-13 hr during the performance verification and calibration phases of the XMM-Newton mission. The source was strongly variable in all epochs, with variability amplitudes that generally increased to higher energy bands. Although the detailed relationship between soft (0.1-0.75 keV) and hard (2-10 keV) bands differed from one epoch to the next, in no case was there any evidence for a measurable interband lag, with robust upper limits of |τ| < 0.08 hr in the best-correlated light curves. This is in conflict with previous claims of both hard and soft lags of ~1 hr in this and other blazars. However, previous observations suffered a repeated 1.6 hr feature induced by the low-Earth orbital period, a feature that is not present in the uninterrupted XMM-Newton data. The new upper limit on |τ| leads to a lower limit on the magnetic field strength and Doppler factor of Bδ1/3 4.7 G, mildly out of line with the predictions from a variety of homogeneous synchrotron self-Compton emission models in the literature of Bδ1/3 = 0.2-0.8 G. Time-dependent spectral fitting was performed on all epochs, and no detectable spectral hysteresis was seen. We note, however, that the source exhibited significantly different spectral evolutionary behavior from one epoch to the next, with the strongest correlations in the first and last and an actual divergence between soft and hard X-ray bands in the third. This indicates that the range of spectral variability behavior in Mrk 421 is not fully described in these short snippets; significantly longer uninterrupted light curves are required and can be obtained with XMM-Newton.

The kinetic power and luminosity of parsec-scale radio jets - an argument for heavy jets

We present arguments indicating that radio jets are heavy (i.e. mainly composed of an electron-proton plasma), and that the non-thermal emitting particle distribution has a low-energy cut-off at about 50 MeV. The arguments are based on the comparison of physical properties of parsec-scale radio jets with values estimated on widely different scales, ranging from the central source supplying the jet to extended kpc-Mpc radio lobes. In particular, we use published VLBI size measures and spectral information on a large sample of sources and, applying the standard synchrotron self-Compton emission model, we estimate the bulk kinetic energy and the number flux of emitting particles in parsec-scale jets. The comparison of the former with the kinetic luminosity on extended scales and with the radiative luminosity supports the picture of stable jets efficiently supplying kinetic power to the extended structures

Resonant Compton cooling and annihilation line production in gamma-ray bursts

view Abstract Citations (2) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Resonant Compton Cooling and Annihilation Line Production in Gamma-Ray Bursts Preece, R. D. ; Harding, A. K. Abstract Attention is given to a synchrotron self-Compton emission model for gamma-ray bursts which produces narrow annihilation features for a variety of field strengths, primary electron injection energies, and injection rates. In this model, primary electrons are injected and cooled by synchrotron emission in a strong, homogeneous magnetic field, resulting in a pair cascade. Multiple resonant scattering with cyclotron photons efficiently traps and cools pairs in the ground state to an average energy where the Compton energy loss rate is zero, which is in agreement with previous estimates of a Compton temperature. The particle distributions in the ground state are determined by numerically solving the Fokker-Planck equation in the steady state. In the case of isotropic injection of primary electrons, a significant narrow-line feature appears in the overall emission. In the case of beamed injection, the annihilation line is broadened to the extent that it would not be observable. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/171017 Bibcode: 1992ApJ...386..308P Keywords: Annihilation Reactions; Compton Effect; Gamma Ray Bursts; Line Spectra; Astronomical Models; Astronomical Spectroscopy; Computational Astrophysics; Electron Distribution; Pair Production; Scattering Cross Sections; Space Radiation; GAMMA RAYS: BURSTS; LINE: FORMATION; RADIATION MECHANISMS: COMPTON AND INVERSE COMPTON full text sources ADS | data products SIMBAD (1)