Abstract Blazars are the brightest and most abundant persistent sources in the extragalactic γ -ray sky. Due to their significance, they are often observed across various energy bands, where the data ...of which can be used to explore potential correlations between emission at different energies, yielding valuable insights into the emission processes of their powerful jets. In this study we utilized IR data at 3.4 and 4.6 μ m from the Near-Earth Object Wide-field Infrared Survey Explorer Reactivation Mission, spanning 8 yr of observations, X-ray data from the Neil Gehrels Swift Observatory collected throughout the satellite’s lifetime, and 12 years of γ -ray measurements from the Fermi Large Area Telescope’s all-sky survey. Our analysis reveals that the IR spectral slope reliably predicts the peak frequency and maximum intensity of the synchrotron component of blazar spectral energy distributions, provided it is uncontaminated by radiation unrelated to the jet. A notable correlation between the IR and γ -ray fluxes was observed, with the BL Lacertae subclass of blazars displaying a strong correlation coefficient of r = 0.80. IR band variability is more pronounced in flat spectrum radio quasars than in BL Lacertae objects, with mean fractional variability values of 0.65 and 0.35, respectively. We also observed that the synchrotron peak intensity of intermediate-high-energy-peaked objects can forecast their detectability at very high γ -ray energies. We used this predicting power to identify objects in current catalogs that could meet the detection threshold of the Cerenkov Telescope Array extragalactic survey, which should encompass approximately 180 blazars.
ABSTRACT
High redshift blazars are among the most powerful non-explosive sources in the Universe and play a crucial role in understanding the evolution of relativistic jets. To understand these ...bright objects, we performed a detailed investigation of the multiwavelength properties of 79 γ-ray blazars with redshifts ranging from z = 2.0 to 2.5, using data from Fermi LAT, Swift XRT/UVOT, and NuSTAR observations. In the γ-ray band, the spectral analysis revealed a wide range of flux and photon indices, from 5.32 × 10−10 to 3.40 × 10−7 photon cm−2 s−1 and from 1.66 to 3.15, respectively, highlighting the diverse nature of these sources. The detailed temporal analysis showed that flaring activities were observed in 31 sources. Sources such as 4C+71.07, PKS 1329-049, and 4C + 01.02, demonstrated significant increase in the γ-ray luminosity and flux variations, reaching peak luminosity exceeding 1050 erg s−1. The temporal analysis extended to X-ray and optical/ultraviolet (UV) bands, showed clear flux changes in some sources in different observations. The time-averaged properties of high redshift blazars were derived through modeling the spectral energy distributions with a one-zone leptonic scenario, assuming the emission region is within the broad-line region (BLR) and the X-ray and γ-ray emissions are due to inverse Compton scattering of synchrotron and BLR-reflected photons. This modeling allowed us to constrain the emitting particle distribution, estimate the magnetic field inside the jet, and evaluate the jet luminosity, which is discussed in comparison with the disc luminosity derived from fitting the excess in the UV band.
ABSTRACT
The high redhsift blazars powered by supermassive black holes with masses exceeding 109 M⊙ have the highest jet power and luminosity and are important probes to test the physics of ...relativistic jets at the early epochs of the Universe. We present a multifrequency spectral and temporal study of high redshift blazar PKS 0537−286 by analysing data from Fermi-LAT, NuSTAR Swift XRT, and UVOT. Although the time averaged γ-ray spectrum of the source is relatively soft (indicating the high-energy emission peak is below the GeV range), several prominent flares were observed when the spectrum hardened and the luminosity increased above 1049 erg s−1. The X-ray emission of the source varies in different observations and is characterized by a hard spectrum ≤1.38 with a luminosity of >1047 erg s−1. The broad-band spectral energy distribution in the quiescent and flaring periods was modelled within a one-zone leptonic scenario assuming different locations of the emission region and considering both internal (synchrotron radiation) and external (from the disc, broad-line region, and dusty torus) photon fields for the inverse Compton scattering. The modelling shows that the most optimistic scenario, from the energy requirement point of view, is when the jet energy dissipation occurs within the broad-line region. The comparison of the model parameters obtained for the quiescent and flaring periods suggests that the flaring activities are most likely caused by the hardening of the emitting electron spectral index and shifting of the cut-off energy to higher values.
ABSTRACT
Blazars research is one of the hot topics of contemporary extragalactic astrophysics. That is because these sources are the most abundant type of extragalactic γ-ray sources and are ...suspected to play a central role in multimessenger astrophysics. We have used Swift$\_$xrtproc, a tool to carry out an accurate spectral and photometric analysis of the Swift-XRT data of all blazars observed by Swift at least 50 times between December 2004 and the end of 2020. We present a database of X-ray spectra, best-fit parameter values, count rates and flux estimations in several energy bands of over 31 000 X-ray observations and single snapshots of 65 blazars. The results of the X-ray analysis have been combined with other multifrequency archival data to assemble the broad-band Spectral Energy Distributions (SEDs) and the long-term light curves of all sources in the sample. Our study shows that large X-ray luminosity variability on different time-scales is present in all objects. Spectral changes are also frequently observed with a ‘harder-when-brighter’ or ‘softer-when-brighter’ behaviour depending on the SED type of the blazars. The peak energy of the synchrotron component (νpeak) in the SED of HBL blazars, estimated from the log-parabolic shape of their X-ray spectra, also exhibits very large changes in the same source, spanning a range of over two orders of magnitude in Mrk421 and Mrk501, the objects with the best data sets in our sample.
Multiwavelength study of high-redshift blazars Sahakyan, N; Israyelyan, D; Harutyunyan, G ...
Monthly notices of the Royal Astronomical Society,
10/2020, Volume:
498, Issue:
2
Journal Article
Peer reviewed
Open access
ABSTRACT
High-redshift blazars are among the most powerful objects in the Universe. The spectral and temporal properties of 33 distant blazars (z > 2.5) detected in the high-energy γ-ray band are ...investigated by analysing the Fermi-LAT and Swift Ultraviolet and Optical Telescope/X-ray Telescope (UVOT/XRT) data. The considered sources have soft time-averaged γ-ray spectra (Γγ ≥ 2.2) whereas those that have been observed in the X-ray band have hard X-ray spectra (ΓX = 1.01−1.86). The γ-ray flux of high-redshift blazars ranges from 4.84 × 10−10 to 1.50 × 10−7 photon cm−2 s−1 and the luminosity is within (0.10−5.54) × 1048 erg s−1 which during the γ-ray flares increases up to (0.1−1) × 1050 erg s−1. In the X-ray band, only the emission of PKS 0438−43, B2 0743+25, and TXS 0222+185 is found to vary in different Swift XRT observations whereas in the γ-ray band, the emission is variable for fourteen sources: the flux of B3 1343+451 and PKS 0537−286 changes in sub-day scales, that of PKS 0347−211 and PKS 0451−28 in day scales, while the γ-ray variability of the others is in week or month scales. The properties of distant blazar jets are derived by modelling the multiwavelength spectral energy distributions within a one-zone leptonic scenario assuming that the X-ray and γ-ray emissions are produced from inverse Compton scattering of synchrotron and dusty torus photons. From the fitting, the emission region size is found to be ≤0.05 pc and the magnetic field and the Doppler factor are correspondingly within 0.10−1.74 G and 10.0−27.4. By modelling the optical–UV excess, we found that the central black hole masses and accretion disc luminosities are within Ld ≃ (1.09−10.94) × 1046 erg s−1 and (1.69−5.35) × 109 M⊙, respectively.
ABSTRACT
We present long-term multiwavelength observations of blazar CTA 102 ($z$ = 1.037). Detailed temporal and spectral analyses of γ-ray, X-ray, and UV/optical data observed by Fermi-LAT, Swift ...XRT, NuSTAR, and Swift-UVOT over a period of 14 yr, between 2008 August and 2022 March, were performed. We found strong variability of source emission in all the considered bands; especially in the γ-ray band it exhibited extreme outbursts when the flux crossed the level of 10−5 photon cm−2 s−1. Using the Bayesian Blocks algorithm, we split the adaptively binned γ-ray light curve into 347 intervals of quiescent and flaring episodes and for each period built corresponding multiwavelength spectral energy distributions (SEDs), using the available data. Among the considered SEDs, 117 high-quality (quasi) contemporaneous SEDs, which have sufficient multiwavelength data, were modelled using jetset framework within a one-zone leptonic synchrotron and inverse-Compton emission scenario assuming the emitting region is within the broad-line region and considering internal and external seed photons for the inverse-Compton upscattering. As a result of modelling, the characteristics of the relativistic electron distribution in the jet as well as jet properties are retrieved and their variation in time is investigated. The applied model can adequately explain the assembled SEDs and the modelling shows that the data in the bright flaring periods can be reproduced for high Doppler boosting and magnetic field. The obtained results are discussed in the context of particle cooling in the emitting region.
We report the results of broadband observations of distant blazar PKS 0537-286 (z = 3.1) using data spanning more than ten years from the Fermi Large Area Telescope together with Swift UVOT/XRT ...archival data taken between 2005 and 2017. In the γ -ray band, the peak flux above 100 MeV, F
γ
= (6 23 ± 0 56) ∙ 10
-7
photon cm
-2
s
-1
observed on MJD 57874 within one week, corresponds to L
γ
= 2 46 ∙ 10
49
erg s
-1
isotropic γ -ray luminosity. The Swift XRT data analyses show that the X-ray emission is characterized by a significantly hard photon index, Γ
X-ray
≤ 1.3 , and an X-ray flux of 4 ∙ 10
-12
erg cm
-2
s
-1
, which is almost constant over twelve years. The spectral energy distribution is modeled within one-zone leptonic models assuming the emission region is within the broad-line region. The observed X-ray and γ -ray data are modeled as inverse Compton scattering of (i) only synchrotron photons and (ii) synchrotron and external photons on the electron population that produces the radioto-optical emission. The modeling shows that the nonthermal electrons in the jet of PKS 0537-286 have a hard power-law index (<1.9) and that the jet should be particle dominated with a luminosity within 10
45
-10
46
erg s
-1
.
The study of multiwavelength emission properties of blazar jets has the potential to shed light on the particle acceleration and emission mechanisms taking place in them. The emission of PKS 2155-304 ...(z = 0.116) and S5 0716+71 (z = 0.31) bright blazars in the optical/UV, X-ray and γ - ray bands is investigated by analyzing data from Fermi-LAT, Swift XRT and Swift UVOT telescopes. The multiwavelength light curves of both sources in these bands show multiple peaks when the flux increased substantially. In the optical/UV bands, the flux of both sources increased above 2·10-10 erg cm-2 s-1. The X-ray emission from PKS 2155-304 was characterized by a harder-when-brighter trend, whereas the y -ray emission from S5 0716+71 showed a moderated trend of softer-whenbrighter. The correlation analysis shows a strong correlation between the UV and y-ray emission of PKS 2155-304, while there is a correlation between the optical/UV and X-ray emission of S5 0716+71. The observed broadband spectral energy distribution of both sources as well as the observed variability and correlations can be accounted for within one-zone synchrotron/synchrotron-self-Compton models.
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