Rapid Gamma-Ray Variability of NGC 1275 Baghmanyan, V.; Gasparyan, S.; Sahakyan, N.
Astrophysical journal/The Astrophysical journal,
10/2017, Volume:
848, Issue:
2
Journal Article
Peer reviewed
Open access
We report on a detailed analysis of the γ-ray light curve of NGC 1275 using the Fermi Large Area Telescope data accumulated during 2008-2017. Major γ-ray flares were observed in 2015 October and 2016 ...December/2017 January when the source reached a daily peak flux of , achieving a flux of within 3 hr, which corresponds to an apparent isotropic γ-ray luminosity of . The most rapid flare had an e-folding time as short as hr, which had never been previously observed for any radio galaxy in γ-ray band. Also, γ-ray spectral changes were observed during these flares: in the flux versus photon index plane, the spectral evolution follows correspondingly a counterclockwise and a clockwise loop inferred from the light curve generated by an adaptive binning method. On 2016 December 30 and 2017 January 1 the X-ray photon index softened ( ) and the flux increased nearly ∼3 times as compared with the quiet state. The observed hour-scale variability suggests a very compact emission region ( ), implying that the observed emission is most likely produced in the subparsec-scale jet if the entire jet width is responsible for the emission. During the active periods, the γ-ray photon index hardened, shifting the peak of the high-energy spectral component to , making it difficult to explain the observed X-ray and γ-ray data in the standard one-zone synchrotron self-Compton model.
ABSTRACT
The observation of a very high-energy neutrino by IceCube (IceCube-170922A) and its association with the flaring blazar TXS 0506 + 056 provided the first multimessenger observations of ...blazar jets, demonstrating the important role of protons in their dynamics and emission. In this paper, we present SOPRANO (https://www.amsdc.am/soprano), a new conservative implicit kinetic code that follows the time evolution of the isotropic distribution functions of protons, neutrons, and the secondaries produced in photo-pion and photo-pair interactions, alongside with the evolution of photon and electron/positron distribution functions. SOPRANO is designed to study leptonic and hadronic processes in relativistic sources such as blazars and gamma-ray bursts. Here, we use SOPRANO to model the broadband spectrum of TXS 0506 + 056 and 3HSP J095507.9 + 355101, which are associated with neutrino events, and of the extreme flaring blazar 3C 279. The SEDs are interpreted within the guise of both a hadronic and a hybrid model. We discuss the implications of our assumptions in terms of jet power and neutrino flux.
ABSTRACT
The blazar PKS 0735+178 is possibly associated with multiple neutrino events observed by the IceCube, Baikal, Baksan, and KM3NeT neutrino telescopes while it was flaring in the γ-ray, X-ray, ...ultraviolet, and optical bands. We present a detailed study of this peculiar blazar to investigate the temporal and spectral changes in the multiwavelength emission when the neutrino events were observed. The analysis of Swift-XRT snapshots reveal a flux variability of more than a factor 2 in about 5 × 103 s during the observation on 2021 December 17. In the γ-ray band, the source was in its historical highest flux level at the time of the arrival of the neutrinos. The observational comparison between PKS 0735+178 and other neutrino source candidates, such as TXS 0506+056, PKS 1424+240, and GB6 J1542+6129, shows that all these sources share similar spectral energy distributions, very high radio and γ-ray powers, and parsec scale jet properties. Moreover, we present strong supporting evidence for PKS 0735+178 to be, like all the others, a masquerading BL Lac. We perform comprehensive modelling of the multiwavelength emission from PKS 0735+178 within one-zone lepto-hadronic models considering both internal and external photon fields and estimate the expected accompanying neutrino flux. The most optimistic scenario invokes a jet with luminosity close to the Eddington value and the interactions of ∼ PeV protons with an external UV photon field. This scenario predicts ∼0.067 muon and anti-muon neutrinos over the observed 3-week flare. Our results are consistent with the detection of one very high-energy neutrino like IceCube-211208A.
On the Multiwavelength Emission from CTA 102 Gasparyan, S.; Sahakyan, N.; Baghmanyan, V. ...
Astrophysical journal/The Astrophysical journal,
08/2018, Volume:
863, Issue:
2
Journal Article
Peer reviewed
Open access
We report on broadband observations of CTA 102 (z = 1.037) during the active states in 2016-2017. In the γ-ray band, Fermi-LAT observed several prominent flares that followed a harder-when-brighter ...behavior: the hardest photon index Γ = 1.61 0.10 being unusual for flat-spectrum radio quasars. The peak γ-ray flux above 100 MeV, observed on MJD 57,738.47 within 4.31 minutes, corresponds to an isotropic γ-ray luminosity of , comparable to the highest values observed from blazars so far. The analyses of the Swift UVOT/XRT data show an increase in the UV/optical and X-ray bands that is contemporaneous with the bright γ-ray periods. The X-ray spectrum observed by Swift XRT and NuSTAR during the γ-ray flaring period is characterized by a hard photon index of ∼1.30. The shortest e-folding time was 4.08 1.44 hr, suggesting a very compact emission region cm. We modeled the spectral energy distribution of CTA 102 in several periods (having different properties in UV/optical, X-ray, and γ-ray bands) assuming a compact blob inside and outside the BLR. We found that the high-energy data are better described when the infrared thermal radiation of the dusty torus is considered. In the flaring periods when the correlation between the γ-ray and UV/optical/X-ray bands is lacking, the γ-ray emission can be produced from the interaction of fresh electrons in a different blob, which does not make a dominant contribution at lower energies.
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
We present the γ-ray observations of the flat-spectrum radio quasar PKS 1441+25 (z = 0.939), using the Fermi large Area Telescope data accumulated during 2015 January – December. A γ-ray ...flare was observed in January 24, when the flux increased up to (2.22 ± 0.38) × 10−6 photon cm−2 s−1 with the flux-doubling time-scale being as short as ∼1.44 d. The spectral analysis shows that from 2015 April 13 to April 28, the MeV-to-GeV photon index has hardened and changes in the range of Γ = (1.73 − 1.79) for most of the time. The hardest photon index of Γ = 1.54 ± 0.16 has been observed on MJD 57 131.46 with 11.8σ which is not common for flat-spectrum radio quasars. For the same period the γ-ray spectrum shows a possible deviation from a simple power-law shape, indicating a spectral cutoff at E
cut = 17.7 ± 8.9 GeV. The spectral energy distributions during quiescent and flaring states are modelled using one-zone leptonic models that include the synchrotron, synchrotron self Compton and external inverse Compton processes; the model parameters are estimated using the Markov Chain Monte Carlo method. The emission in the flaring states can be modelled assuming that either the bulk Lorentz factor or the magnetic field has increased. The modelling shows that there is a hint of hardening of the low-energy index (∼1.98) of the underlying non-thermal distribution of electrons responsible for the emission in 2015 April. Such hardening agrees with the γ-ray data, which pointed out a significant γ-ray photon index hardening on 2015 April 13 to 28.
Context. Important information on the evolution of a jet can be obtained by comparing the physical state of the plasma at its propagation through the broad-line region (where the jet is most likely ...formed) into the intergalactic medium, where it starts to decelerate significantly. Aims. We compare the constraints on the physical parameters in the innermost (≤pc) and outer (≥kpc) regions of the 3C 120 jet by means of a detailed multiwavelength analysis and theoretical modeling of their broadband spectra. Methods. The data collected by Fermi LAT (γ-ray band), Swift (X-ray and ultraviolet bands), and Chandra (X-ray band) are analyzed together and the spectral energy distributions are modeled using a leptonic synchrotron and inverse Compton model, taking into account the seed photons originating inside and outside the jet. The model parameters are estimated using the Markov chain Monte Carlo method. Results. The γ-ray flux from the inner jet of 3C 120 was characterized by rapid variation from MJD 56 900 to MJD 57 300. Two strong flares were observed on April 24, 2015, when within 19.0 min and 3.15 h the flux was as high as (7.46 ± 1.56) × 10-6 photon cm-2 s-1 and (4.71 ± 0.92) × 10-6 photon cm-2 s-1, respectively, with ≥10σ. During these flares the apparent isotropic γ-ray luminosity was Lγ ≃ (1.20−1.66) × 1046 erg s-1 which is not common for radio galaxies. The broadband emission in the quiet and flaring states can be described as synchrotron self-Compton emission, while inverse Compton scattering of dusty torus photons cannot be excluded for the flaring states. The X-ray emission from the knots can be reproduced by inverse Compton scattering of cosmic microwave background photons only if the jet is highly relativistic (even when δ = 10,Ue/UB is still ≥80). These extreme requirements can be somewhat softened assuming the X-rays are from the synchrotron emission of a second population of very high energy electrons. Conclusions. We found that the jet power estimated at two scales is consistent, suggesting that the jet does not suffer severe dissipation, it simply becomes radiatively inefficient.
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 Modeling the multiwavelength spectral energy distributions (SEDs) of blazars provides key insights into the underlying physical processes responsible for the emission. While SED modeling ...with self-consistent models is computationally demanding, it is essential for a comprehensive understanding of these astrophysical objects. We introduce a novel, efficient method for modeling the SEDs of blazars by the mean of a convolutional neural network (CNN). In this paper, we trained the CNN on a leptonic model that incorporates synchrotron and inverse Compton emissions, as well as self-consistent electron cooling and pair creation–annihilation processes. The CNN is capable of reproducing the radiative signatures of blazars with high accuracy. This approach significantly reduces the computational time, thereby enabling real-time fitting to multiwavelength data sets. As a demonstration, we used the trained CNN with MultiNest to fit the broadband SEDs of Mrk 421 and 1ES 1959+650, successfully obtaining their parameter posterior distributions. This novel framework for fitting the SEDs of blazars will be further extended to incorporate more sophisticated models based on external Compton and hadronic scenarios, allowing for multimessenger constraints in the analysis. The models will be made publicly available via a web interface at the Markarian Multiwavelength Data Center to facilitate self-consistent modeling of multimessenger data from blazar observations.
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.
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