Abstract The particle acceleration of blazar jets is crucial to high-energy astrophysics, yet the acceleration mechanism division in blazar subclasses and the underlying nature of these mechanisms ...remain elusive. In this work, we utilized the synchrotron spectral information (synchrotron peak frequency, log ν sy , and corresponding curvature, b sy ) of 2705 blazars from the literature and studied the subject of particle acceleration in blazar jets by analyzing the correlation between log ν sy and 1/ b sy . Our results suggested that the entire sample follows an energy-dependent probability acceleration (EDPA). Specifically, the low inverse Compton peak sources (LCPs) follow the mechanism of fluctuations of fractional gain acceleration (FFGA), while the high inverse Compton peak sources (HCPs) follow an acceleration mechanism of EDPA. Our results indicated that the separation between LCPs and HCPs results from the electron peak Lorentz factor ( γ p ), and the differentiation should originate from different acceleration mechanisms. Moreover, our study revealed a transition in the acceleration mechanism from FFGA to EDPA around log ν sy ∼ 15 through a detailed analysis of binned- log ν sy . The mechanism of FFGA dominates the particle acceleration in LCP jets because of stronger jets and the EDPA dominates the particle energy gain in the HCPs due to a more efficient acceleration process.
Abstract
Studies and constraints on the emission region are crucial to the blazar radiation mechanism. Yet previous works have mainly focused on individual sources. In this work, we make use of the ...largest and the latest spectral energy distribution fitting results in the literature to statistically study the blazar emission region properties in the framework of a one-zone leptonic model. Our results reveal: (1) that flat-spectrum radio quasars (FSRQs) show lower electron energy (
γ
p
≲ 1.6 × 10
3
) than BL Lacertae objects (BL Lacs) and tend to have a stronger magnetic field (
B
) and smaller electron-to-magnetic energy ratio (
U
e
/
U
B
) than BL Lacs; (2) we find that the electromagnetic equipartition would rather happen in the jets of BL Lacs than happen in the jets of FSRQs; (3) there are 682 blazars with a magnetic field weaker than the critical value for generating the Kelvin–Helmholtz instability, thus one-third of the blazars in our sample are able to produce this instability; and (4) the distance (
d
em
) between the emission region and the central black hole is on the scale of ∼0.1 pc, so the location of the emission region may be evenly distributed inside and outside the broad-line region.
Aiming to answer an interesting question on why some radio sources can be detected by Fermi-LAT but others cannot, we compare several parameters of Fermi-detected Fanaroff-Riley radio galaxies (FFRs) ...and non-Fermi-detected sources (NFFRs), including the optical absolute magnitude, 1.4 GHz radio luminosity, radio loudness, core dominance parameter, Doppler factor, and the mass of the central black hole. Significant differences are ascertained within these parameters between FFRs and NFFRs. Our findings suggest that FFRs are jet-dominant while NFFRs are disk-dominant sources, and NFFRs have a weaker beaming effect. Additionally, we predict the observed γ-ray flux for NFFRs, establishing that the reason why some NFFRs are not detectable arises from their γ-ray flux being below the sensitivity detection threshold of Fermi. We also discuss two sub-types of Fanaroff-Riley galaxies, namely FR I and FR II sources. We first propose a “changing-look” phenomenon in these radio sources and also investigate why FR IIs seem to be exclusive in γ-ray emission.
A sample including 664 blazars （301 Flat Spectrum Radio Quasars and 363 BL Lacs） with ）γ-ray data in both 1FGL and 2FGL catalogues were selected. The average values of both y-photon average energy ...and the photon spectral index for FSRQs, LBLs, IBLs and HBLs, follow the blazars sequence, FSRQs → LBLs →IBLs → HBLs. The slopes of correlation between photon spectral index and ）,-ray luminosity for 4 the sub-classes of blazars also follow the blazars sequence. Also, there was close an- ti-correlations between the difference of two ）,-ray photon spectral indices and the logarithm of the ratio of two y-ray luminosities from 2FGL and 1FGL catalogs. It implies that the spectrum becomes flat when the source becomes brighter in high energetic γ-ray band. Lastly, the Kolmogolov-Smirnov test （KS test） of the average γ-photon energy showed that HBLs differs from LBLs and FSRQs, while there was no clear difference between LBLs and FSRQs, which implied that the γ-ray emissions in LBLs and FSRQs may be a result of the same emission mechanism.
In this paper, a sample including 68 blazars （18 BL Lacs and 50 FSRQs） with known Doppler factors and superluminal velocity from our previous papers is presented. Both the Lorentz factors （/＇） and ...viewing angles （0） are estimated for the 68 sources The relationship between BL Lacs and FSRQs is also revisited using the two variables off＇and 0. The Lorenz factors are in the range of 2.33 to 64.07. The viewing angles are in the range of 0.04 to 24.56. The averaged value of the viewing angle for BL Lacs is slightly larger than that for FSRQs, while the averaged value of the Lorentz factor for BL Lacs is smaller than that for FSRQs.
Based upon Fermi 1FGL and EGRET 3EG samples, a sample including 79 blazars （53 FSRQs, 26 BL Lacs） is presented. It is investigated that the correlations between the ratio of EGRET to Fermi blazars ...g-ray flux densities and the spectral index differ for EGRET to Fermi blazars for three subclasses of high-frequency peaked BL Lacertae objects-HBL, low-frequency peaked BL Lacertae objects-LBL, and flat spectrum radio quasars-FSRQs. There is a consistent relationship between the ratio of the two γ-ray flux densities and the spectral index difference for the three subclasses. It suggests that the spectrum changed with the source brightness in the gamma-ray band. Both the spectral index difference and the correlation slopes follow a continuous sequence from FSRQs to LBLs to HBLs, which is consistent with the noted blazar sequence.
The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST) provides an increase in sensitivity and has detected rapid variability of gamma-ray sources. The variability ...time scales detected from the gamma-ray loud blazars by LAT and EGRET, and gamma-ray luminosity are used to estimate the central black hole masses. In this work, we find that the lower limits of central black hole masses are in a range of (0.3–24)×10
7
M
⊙
, which are compared with those obtained by other authors. Our results are consistent with other authors’ results. Also, the Lorentz factor,
Γ
, and the propagation angle,
θ
, are obtained for 18 blazars for which superluminal motions are known.
Abstract
Aiming to delineate the physical framework of blazars, we present an effective method to estimate four important parameters based on the idea proposed by Becker & Kafatos, including the ...upper limit of central black hole mass
M
, the Doppler factor
δ
, the distance along the axis to the site of the
γ
-ray production
d
(which then can be transformed into the location of
γ
-ray-emitting region
R
γ
) and the propagation angle with respect to the axis of the accretion disk Φ. To do so, we adopt an identical sample with 809 Fermi-LAT-detected blazars which had been compiled in Pei et al. These four derived parameters stepping onto the stage may shed new light on our knowledge regarding
γ
-ray blazars. With regard to the paper of Becker & Kafatos, we obtain several new perspectives, mainly in (1) putting forward an updated demarcation between BL Lacs and FSRQs based on the relation between broad-line region luminosity and disk luminosity both measured in Eddington units, i.e.,
L
disk
/
L
Edd
= 4.68 × 10
−3
, indicating that there are some differences between BL Lacs and FSRQs on the accretion power in the disk; (2) proposing that there is a so-called “appareling zone,” a potential transition field between BL Lacs and FSRQs where the changing-look blazars perhaps reside; (3) the location of
γ
-ray emission region is principally constrained outside the broad-line region, and for some BL Lacs are also away from the dusty molecular torus, which means the importance of emission components in the jet.
Beamed and Unbeamed Emission of γ-Ray Blazars Pei, Zhiyuan; Fan, Junhui; Yang, Jianghe ...
Publications of the Astronomical Society of the Pacific,
11/2020, Letnik:
132, Številka:
1017
Journal Article
Recenzirano
Odprti dostop
A two-component model of radio emission has been used to explain some radio observational properties of Active Galactic Nuclei (AGNs) and, in particular, of blazars. In this work, we extend the ...two-component idea to the γ-ray emission and assume that the total γ-ray output of blazars consists of relativistically beamed and unbeamed components. The basic idea leverages the correlation between the radio core-dominance parameter and the γ-ray beaming factor. To do so, we evaluate this correlation for a large sample of 584 blazars taken from the fourth source catalog of the Fermi Large Area Telescope (Fermi-LAT) and correlated their γ-ray core-dominance parameters with radio core-dominance parameters. The γ-ray beaming factor is then used to estimate the beamed and unbeamed components. Our analysis confirms that the γ-ray emission in blazars is mainly from the beamed component.
In a recent paper, we constructed the spectral energy distributions (SEDs) for 1425 Fermi blazars. We classify them as low synchrotron peak sources (LSPs) if log ν p ( Hz ) ≤ 14.0, intermediate ...synchrotron peak sources (ISPs) if 14.0 < log ν p ( Hz ) ≤ 15.3 , and high synchrotron peak sources (HSPs) if log ν p ( Hz ) > 15.3 . We obtain an empirical relation to estimate the synchrotron peak frequency, ν p Eq . from effective spectral indexes α o x and α r o as log ν p Eq . = 16 + 4.238 X if X < 0 , and log ν p Eq . = 16 + 4.005 Y if X > 0 , where X = 1.0 − 1.262 α r o − 0.623 α o x and Y = 1.0 + 0.034 α r o − 0.978 α o x . In the present work, we investigate the correlation between the peak frequency and the radio-to-X-ray spectral index, between peak luminosity (bolometric luminosity) and γ-ray/optical luminosity, and between peak luminosity and bolometric luminosity. Some discussion is presented.
PDF
