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1.
We present a new population of radio quasars whose X-ray band, unlike previously known sources which have (flat) inverse Compton radiation, is characterized by (steep) synchrotron emission, with a broad-band spectral energy distribution similar to that of BL Lacs with high energy synchrotron peaks. We discuss how this new class was discovered, the class properties, and the implications of its existence for our understanding of jets and active galactic nuclei in general.  相似文献   

2.
We discuss the implications of the recent X-ray and TeV γ-ray observations of the PSR B1259–63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models of interaction of pulsar and stellar winds. We show that previously considered models have problems to account for the observed behaviour of the system. We develop a model in which the broad band emission from the binary system is produced in result of collisions of GeV–TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model the high energy γ-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton emission produced by low-energy (≤100 MeV) electrons from the decays of secondary charged π ± mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio emission components.   相似文献   

3.
In this work, we study the physical properties of the high-energy (HE) emission region by modeling the quasi-simultaneous multi-wavelength(MWL) spectral energy distributions (SEDs) of 27 Fermi-LAT detected low-synchrotron-peaked (LSP) blazars. We model the jets MWL SEDs in framework of a well accepted single-zone leptonic model including synchrotron self-Compton and external Compton (EC) processes for the jets in a state of equipartition between particle and magnetic field energy densities. In the model the GeV γ-ray spectrum is modeled by a combination of two different external Compton-scattered components: (i) EC scattering of photons coming from disk and broad line region (BLR), and (ii) EC scattering of photons originating from the dust tours (DT) and BLR. We find that the SEDs can be well reproduced by the equipartition model for the most majority of the sources, and the results are in agreement with many recent studies. Our results suggest that the SEDs modelling alone may not provide a significant constraint on the location of the HE emission region if we do not know enough about the physical properties of the external environment.  相似文献   

4.
We calculate the broad-band radio–X-ray spectra predicted by microblazar and microquasar models for ultraluminous X-ray sources (ULXs), exploring the possibility that their dominant power-law component is produced by a relativistic jet, even at near-Eddington mass accretion rates. We do this by first constructing a generalized disc–jet theoretical framework in which some fraction of the total accretion power, P a, is efficiently removed from the accretion disc by a magnetic torque responsible for jet formation. Thus, for different black hole masses, mass accretion rates and magnetic coupling strength, we self-consistently calculate the relative importance of the modified disc spectrum, as well as the overall jet emission due to synchrotron and Compton processes. In general, transferring accretion power to a jet makes the disc fainter and cooler than a standard disc at the same mass accretion rate; this may explain why the soft spectral component appears less prominent than the dominant power-law component in most bright ULXs. We show that the apparent X-ray luminosity and spectrum predicted by the microquasar model are consistent with the observed properties of most ULXs. We predict that the radio synchrotron jet emission is too faint to be detected at the typical threshold of radio surveys to date. This is consistent with the high rate of non-detections over detections in radio counterpart searches. Conversely, we conclude that the observed radio emission found associated with a few ULXs cannot be due to beamed synchrotron emission from a relativistic jet.  相似文献   

5.
Non-thermal emission from old supernova remnants   总被引：1，自引：0，他引：1  
We study the non-thermal emission from old shell-type supernova remnants (SNRs) on the frame of a time-dependent model. In this model, the time-dependent non-thermal spectra of both primary electrons and protons as well as secondary electron/positron (e±) pairs can be calculated numerically by taking into account the evolution of the secondary e± pairs produced from proton–proton (p–p) interactions as accelerated protons collide with the ambient matter in an SNR. The multiwavelength photon spectrum for a given SNR can be produced through leptonic processes such as electron/positron synchrotron radiation, bremsstrahlung and inverse Compton scattering as well as hadronic interaction. Our results indicate that the non-thermal emission of the secondary e± pairs is becoming more and more prominent when the SNR ages in the radiative phase because the source of the primary electrons has been cut off and the electron synchrotron energy loss is significant for a radiative SNR, whereas the secondary e± pairs can be produced continuously for a long time in the phase due to the large energy-loss time for the p–p interaction. We apply the model to two old SNRs, G8.7−0.1 and G23.3−0.3, and the predicted results can explain the observed multiwavelength photon spectra for the two sources.  相似文献   

6.
Chandra ACIS observations of PKS 0521−365 find that the X-ray emission of this BL Lac object consists of emission from an unresolved core, a diffuse halo and a 2-arcsec jet feature coincident with the inner radio/optical jet. A comparison with a new ATCA 8.6-GHz map also finds X-ray emission from the bright hotspot south-east of the nucleus. The jet spectrum, from radio to X-ray, is probably synchrotron emission from an electron population with a broken power-law energy distribution, and resembles the spectra seen from the jets of low-power (FR I) radio galaxies. The hotspot X-ray flux is consistent with the expectations of synchrotron self-Compton emission from a plasma close to equipartition, as seen in studies of high-power (FR II) radio galaxies. While the angular structure of the halo is similar to that found by an analysis of the ROSAT High Resolution Imager image, its brightness is seen to be lower with Chandra , and the halo is best interpreted as thermal emission from an atmosphere of similar luminosity to the haloes around FR I radio galaxies. The X-ray properties of PKS 0521−365 are consistent with it being a foreshortened, beamed, radio galaxy.  相似文献   

7.
Flat radio spectra with large brightness temperatures at the core of active galactic nuclei and X-ray binaries are usually interpreted as the partially self-absorbed bases of jet flows emitting synchrotron radiation. Here we extend previous models of jets propagating at large angles to our line of sight to self-consistently include the effects of energy losses of the relativistic electrons due to the synchrotron process itself and the adiabatic expansion of the jet flow. We also take into account energy gains through self-absorption. Two model classes are presented. The ballistic jet flows, with the jet material travelling along straight trajectories, and adiabatic jets. Despite the energy losses, both scenarios can result in flat emission spectra; however, the adiabatic jets require a specific geometry. No re-acceleration process along the jet is needed for the electrons. We apply the models to observational data of the X-ray binary Cygnus X-1. Both models can be made consistent with the observations. The resulting ballistic jet is extremely narrow with a jet opening angle of only 5 arcsec. Its energy transport rate is small compared to the time-averaged jet power and therefore suggests the presence of non-radiating protons in the jet flow. The adiabatic jets require a strong departure from energy equipartition between the magnetic field and the relativistic electrons. These models also imply a jet power of two orders of magnitude higher than the Eddington limiting luminosity of a  10-M⊙  black hole. The models put strong constraints on the physical conditions in the jet flows on scales well below achievable resolution limits.  相似文献   

8.
HST observations have shown that low-redshift 3CR radio galaxies often exhibit a point-like optical component positionally coincident with the GHz-frequency radio core. In this paper we discuss the correlation between the luminosities of the radio, optical and X-ray cores in these objects, and argue that all three components have a common origin at the base of the relativistic jets. In unified models, FR I radio galaxies should appear as dimmed, redshifted versions of BL Lac objects. We show that such models are consistent with the spectral energy distributions of the radio galaxies only if the nuclear X-ray emission in radio galaxies is inverse Compton in origin.  相似文献   

9.
3C 84 is a well-known supermassive black hole that can be used to explore jet and accretion physics. In this work, we model the multiwavelength spectral energy distribution (SED) of the 3C 84, and find that the SED is difficult to fit with pure advection dominated accretion flow (ADAF) or pure jet model. Using a coupled ADAF-jet model to fit the SED of 3C 84, it is found that the radio emission and the millimeter emission can be naturally reproduced by the synchrotron radiation of nonthermal electrons in the jet, and that the X-ray emission may predominantly come from inverse Compton radiation from electrons in ADAF. According to the Rotation Measure (RM) obtained by the polarization observation, we consider the possible location of the polarizing source and found that the calculated RM in the jet is roughly consistent with the observational constraints. These results will help us better understand jets produced by black holes.  相似文献   

10.
We present results for the first three low-power radio galaxies from the B2 bright sample to have been observed with Chandra . Two have kiloparsec-scale radio jets, and in both Chandra resolves jet X-ray emission, and detects soft X-ray core emission and an X-ray-emitting galaxy-scale atmosphere of luminosity a few ×1041 erg s−1. These are the first detections of X-ray jets in low-power radio galaxies more distant than Centaurus A and M87. The cooling time of the galaxy-scale gas implies mass infall rates of the order of 1 M⊙ yr−1. The gas pressure near the jets is comparable to the minimum pressure in the jets, implying that the X-ray-emitting gas may play an important role in jet dynamics. The third B2 radio galaxy has no kiloparsec-scale radio jet, and here only soft X-ray emission from the core is detected. The ratio of X-ray to radio flux is similar for the jets and cores, and the results favour a synchrotron origin for the emission. Kiloparsec-scale radio jets are detected in the X-ray in ∼7-ks exposures with Chandra more readily than in the optical via Hubble Space Telescope snapshot surveys.  相似文献   

11.
The large mechanical luminosity of the jets of GRS 1915+105 should give rise to luminous emission regions, similar to those observed in radio galaxies, where the jets interact with the gas surrounding the source. However, no radio synchrotron emission of the expected morphology has been found. Here we present the results of a study suggesting that radio bremsstrahlung from the compressed and heated ISM in front of the jets should be detectable, while the synchrotron lobes may be too faint. We identify these jet impact sites with two well-known IRAS regions. This identification suggests a distance of GRS 1915+105 of 6.5± 1.6 kpc, significantly closer than the usually assumed distance of 11–12 kpc. We discuss the implications of this reduced distance estimate. The non-detection of the synchrotron radio lobes implies a significant fraction of non-radiating particles, possibly protons, in the jets. The apparent motion of small-scale jet components is not superluminal, so if superluminal motion is required for an object to be termed a microquasar, GRS 1915+105 actually does not qualify. The mass of the black hole in the system is increased to 21± 9 M⊙, while the mechanical luminosity of the jets is reduced to 14% of the Eddington luminosity.  相似文献   

12.
We present a model which describes the evolution of the energy spectrum of relativistic electrons in supernova remnants, with radiation losses of electrons taken into account. The model can be used to calculate the synchrotron X-ray emission from supernova remnants in the uniform interstellar medium and in the uniform interstellar magnetic field. The importance of various factors in the variations of spatial distributions of nonthermal electrons and their synchrotron emissive capacity is demonstrated. We analyze the errors which arise in the magnetic field strength when it is estimated with the use of the models which ignore the detailed pattern of the evolution of the magnetic field and the electron spectrum behind the shock front in the remnant. The evolution of synchrotron emission spectrum and the ratio between the synchrotron radio and X-ray fluxes from supernova remnants are calculated.  相似文献   

13.
We have observed emission from the nucleus of the closest radio galaxy, Centaurus A, from the radio to the gamma-ray band. We construct, for the first time, its overall spectral energy distribution (SED) which appears to be intriguingly similar to those of blazars, showing two broad peaks located in the far-infrared band and at ∼0.1 MeV respectively. The whole nuclear emission of Centaurus A is successfully reproduced with a synchrotron self-Compton model. The estimated physical parameters of the emitting source are similar to those of BL Lacs, except for a much smaller beaming factor, as qualitatively expected when a relativistic jet is orientated at a large angle to the line of sight. These results represent strong evidence that Centaurus A is indeed a misoriented BL Lac, and provide strong support in favour of the unification scheme for low-luminosity radio-loud active galactic nuclei. Modelling of the SED of Centaurus A also provides further and independent indications of the presence of velocity structures in sub-parsec-scale jets.  相似文献   

14.
We present model fits to spectral energy distributions in the optical and near-infrared of >100 flat-spectrum radio quasars from the Parkes Half-Jansky Flat-spectrum Sample. We find that ∼40 per cent of the sources have power-law spectral energy distributions (SEDs), while a similar number show evidence for two primary components: a blue power law and optical synchrotron emission. The blue power law is similar to the dominant component observed in the spectra of optically selected quasars. There is strong evidence that the synchrotron component has a turnover in the ultraviolet–optical rest frame of the spectrum. In the remaining sources, it is likely that the synchrotron peaks at longer wavelengths. This mixture of two components is supported by optical polarization measurements in a subgroup of the sources. The sources with power-law SEDs show evidence for an excess number of red power-law slopes compared with optically selected quasars. There are additional spectral components in some of the sources, such as dust and the underlying galaxy, which have not been considered here.  相似文献   

15.
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16.
We have observed the prototypical wide-angle tail (WAT) radio galaxy 3C 465 with Chandra and XMM–Newton . X-ray emission is detected from the active nucleus and the inner radio jet, as well as a small-scale, cool component of thermal emission, a number of the individual galaxies of the host cluster (Abell 2634), and the hotter thermal emission from the cluster itself. The X-ray detection of the jet allows us to argue that synchrotron emission may be an important mechanism in other well-collimated, fast jets, including those of classical double radio sources. The bases of the radio plumes are not detected in the X-ray, which supports the model in which these plumes are physically different from the twin jets of lower-power radio galaxies. The plumes are in fact spatially coincident with deficits of X-ray emission on large scales, which argues that they contain little thermal material at the cluster temperature, although the minimum pressures throughout the source are lower than the external pressures estimated from the observed thermal emission. Our observations confirm both spatially and spectrally that a component of dense, cool gas with a short cooling time is associated with the central galaxy. However, there is no evidence for the kind of discontinuity in external properties that would be required in many models of the jet–plume transition in WATs. Although the WAT jet–plume transition appears likely to be related to the interface between this central cool component and the hotter intracluster medium, the mechanism for WAT formation remains unclear. We revisit the question of the bending of WAT plumes, and show that the plumes can be bent by plausible bulk motions of the intracluster medium, or by motion of the host galaxy with respect to the cluster, as long as the plumes are light.  相似文献   

17.
A hypothesis is being put forward that the formation of jets in the nuclei of radio galaxies is due to a high-speed energy excretion (explosion) in the accretion disk around a massive black hole. The explosion can be induced, for example, by a fall of the star into the black hole. For the accretion disk featuring an exponential high-density distribution, an asymmetrical explosion can be obtained: the shock front moves in the direction of decreasing the density accelerately and achieves the relativistic velocity swiftly, carrying away the most fraction of the explosion energy. Radio emission of the jet involves synchrotron radiation of relativistic electrons which are accelerated by such shock wave in the magnetic field driven up by the shock front.  相似文献   

18.
Microquasar (MQ) jets are sites of particle acceleration and synchrotron emission. Such synchrotron radiation has been detected coming from jet regions of different spatial scales, which for the instruments at work nowadays appear as compact radio cores, slightly resolvedradio jets, or (very) extended structures (e.g. Mirabel and Rodríguez, 1999; Fender, 2001; Corbel et al., 2002). Because of the presence of relativistic particles and dense photon, magnetic and matter fields, these outflows are also the best candidates to generate the very high-energy (VHE) gamma-rays detected coming from two of these objects, LS 5039 and LS I +61 303 (Aharonian, 2005; Aharonian et al., 2006a; and Albert, 2006, respectively), and may be contributing significantly to the X-rays emitted from the MQ core (e.g. Markoff et al., 2001; Bosch-Ramon et al., 2005a). In addition, beside electromagnetic radiation, jets at different scales are producing some amount of leptonic and hadronic cosmic rays (CR), and evidences of neutrino production in these objects may be eventually found. In this work, we review on the different physical processes that may be at work in or related to MQ jets. The jet regions capable to produce significant amounts of emission at different wavelengths have been reduced to the jet base, the jet at scales of the order of the size of the system orbital semi-major axis, the jet middle scales (the resolved radio jets), and the jet termination point. The surroundings of the jet could be sites of multiwavelength emission as well, deserving also an insight. We focus on those scenarios, either hadronic or leptonic, in which it seems more plausible to generate both photons from radio to VHE and high-energy neutrinos. We briefly comment as well on the relevance of MQ as possible contributors to the galactic CR in the GeV–PeV range.  相似文献   

19.
We derive accretion rate functions (ARFs) and kinetic luminosity functions (KLFs) for jet-launching supermassive black holes. The accretion rate as well as the kinetic power of an active galaxy is estimated from the radio emission of the jet. For compact low-power jets, we use the core radio emission while the jet power of high-power radio-loud quasars is estimated using the extended low-frequency emission to avoid beaming effects. We find that at low luminosities the ARF derived from the radio emission is in agreement with the measured bolometric luminosity function (BLF) of active galactic nucleus (AGN), i.e. all low-luminosity AGN launch strong jets. We present a simple model, inspired by the analogy between X-ray binaries (XRBs) and AGN, that can reproduce both the measured ARF of jet-emitting sources as well as the BLF. The model suggests that the break in power-law slope of the BLF is due to the inefficient accretion of strongly sub-Eddington sources. As our accretion measure is based on the jet power it also allows us to calculate the KLF and therefore the total kinetic power injected by jets into the ambient medium. We compare this with the kinetic power output from supernova remnants (SNRs) and XRBs, and determine its cosmological evolution.  相似文献   

20.
1 INTRoDUCTIONB1azars are rwho-loud AGNs characterized by emissions of strong and raPidiy wriablenOllthermal radiation over the elltire electromagntic spectrum. Syndritron ehasha followedby inverse ComPton scattering in a re1aivistic jet and beamd inio one directiOn is generallythought to be the IneCha8m powering these Objects (Kollgaard 1994; Urry & Paded 1995).All blazars have a sPectral energy distribution (SED) with tWO peak8 in a uFv rePesentation(von Montigny et al. 1995; S…  相似文献   

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