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— Comparison of the broadband SEDs of 3C 279 at the peak of γ-ray activity during the flares in 2013 December and 2014 April.
Source publication
The blazar 3C 279 exhibited twin $\gamma$-ray flares of similar intensity in
2013 December and 2014 April. In this work, we present a detailed
multi-wavelength analysis of the 2013 December flaring event. Multi-frequency
observations reveal the uncorrelated variability patterns with X-ray and
optical-UV fluxes peaking after the $\gamma$-ray maximum...
Citations
... The z-DCF method provides a conservative estimate for the cross correlation as a function of the time lag between unevenly sampled light curves. Furthermore, blazars often exhibit erratic flux variations with the same object sometimes showing correlated flux changes and uncorrelated variability during other epochs (e.g., 3C 279, Hayashida et al. 2015;Paliya et al. 2015Paliya et al. , 2016. Additionally, only flux upper limits could be derived during several epochs for various objects under consideration and that may somewhat bias the result as those upper limits would cover mainly the low states of the source. ...
Understanding the high-energy emission processes and variability patterns are two of the most challenging research problems associated with relativistic jets. In particular, the long-term (months to years) flux variability at very high energies (VHE >50 GeV) has remained an unexplored domain so far. This is possibly due to the decreased sensitivity of the Fermi Large Area Telescope (LAT) above a few GeV, hence low photon statistics, and observing constraints associated with the ground-based Cherenkov telescopes. This paper reports the results obtained from the 0.05−2 TeV Fermi-LAT data analysis of a sample of 29 blazars with the primary objective to explore their months-to-year-long very high-energy (VHE) flux variability behavior. This systematic search has led to, for the first time, the detection of significant flux variations in five blazars at the >99% confidence level, whereas eight of them exhibit variability, albeit at a lower confidence level (∼95%–99%). A comparison of the 0.05–2 TeV flux variations with that observed at 0.1–50 GeV band has revealed similar variability behavior for most of the sources. However, complex variability patterns that are not reflected contemporaneously in both energy bands were also detected, thereby providing tantalizing clues about the underlying radiative mechanisms. These results open up a new dimension to unravel the VHE emission processes operating in relativistic jets, hence sowing the seeds for their future observations with the upcoming Cherenkov Telescope Array.
... Hadronic model for blazar postulates that protons are accelerated to ultra-relativistic energies and dominate the high-energy emission through proton-synchrotron radiation (Aharonian 2000 ;M ücke et al. 2003 ) or photopion production via proton-proton or proton-photon interaction (Mannheim 1993 ), which results in the production of ultra-high-energy photons and neutrinos. The hybrid lepto-hadronic model has also been proposed in some cases to explain high-energy emission in blazar Paliya et al. 2016 ;Cerruti et al. 2019 ). ...
The correlation between optical and γ-ray flux variations in blazars reveals a complex behaviour. In this study, we present our analysis of the connection between changes in optical and γ-ray emissions in the blazar Ton 599 over a span of approximately 15 years, from August 2008 to March 2023. Ton 599 reached its highest flux state across the entire electromagnetic spectrum during the second week of January 2023. To investigate the connection between changes in optical and γ-ray flux, we have designated five specific time periods, labeled as epochs A, B, C, D, and E. During periods B, C, D, and E, the source exhibited optical flares, while it was in its quiescent state during period A. The γ-ray counterparts to these optical flares are present during periods B, C, and E, however during period D, the γ-ray counterpart is either weak or absent. We conducted a broadband spectral energy distribution (SED) fitting by employing a one-zone leptonic emission model for these epochs. The SED analysis unveiled that the optical-UV emission primarily emanated from the accretion disk in quiescent period A, whereas synchrotron radiation from the jet dominated during periods B, C, D, and E. Diverse correlated patterns in the variations of optical and γ-ray emissions, like correlated optical and γ-ray flares, could be accounted for by changes in factors such as the magnetic field, bulk Lorentz factor, and electron density. On the other hand, an orphan optical flare could result from increased magnetic field and bulk Lorentz factor.
... The MNRAS 527, 10575-10583 (2024) hadronic interpretation of high-energy spectral component involves hadron-initiated cascades, photo-meson/Bethe-Heitler process, etc. (see B öttcher et al. 2007 , and references therein for re vie w). Besides these, recent models involve the emission from both leptonic and hadronic origin to interpret the high-energy emission (lepto-hadronic models, Paliya et al. 2016 ). ...
The recent detection of very high energy (VHE) emissions from flat spectrum radio quasars (FSRQs) at high redshifts has revealed that the universe is more transparent to VHE γ-rays than it was expected. It has also questioned the plausible VHE emission mechanism responsible for these objects. Particularly for FSRQs, the γ-ray emission is attributed to the external Compton process (EC). We perform a detailed spectral study of Fermi-detected FSRQ 3C 345 using synchrotron, synchrotron self Compton (SSC) and EC emission mechanisms. The simultaneous data available in optical, UV, X-ray, and γ-ray energy bands is statistically fitted under these emission mechanisms using the χ2-minimization technique. Three high flux states and one low flux state are chosen for spectral fitting. The broadband spectral energy distribution (SED) during these flux states is fitted under different target photon temperatures, and the model VHE flux is compared with the 50hr CTA sensitivity. Our results indicate a significant VHE emission could be attained during the high flux state from MJD 59635-59715 when the target photon temperature is within 900K to 1200K. Furthermore, our study shows a clear trend of variation in the bulk Lorentz factor of the emission region as the source transits through different flux states. We also note that during high γ-ray flux states, an increase in external photon temperature demands high bulk Lorentz factors, while this behaviour reverses in case of low γ-ray flux state.
... Such rapid variability demands a very compact emission region located well within the broad line emitting region of the quasar (Narayan & Piran 2012 ;Joshi, Marscher & B öttcher 2013 ). Ho we ver, the location of the emission region inferred from the broad-band SED modelling contradicts this since the γ -ray emission is better interpreted as EC/IR process (Sikora et al. 2009 ;Paliya et al. 2016 ). Besides, the frequent flaring episodes encountered from this source also raise the question of whether the source poses two definite flux states. ...
The long term broadband spectral study of Flat Spectrum Radio Quasars during different flux states has the potential to infer the emission mechanisms and the cause of spectral variations. To scrutinize this, we performed a detailed broadband spectral analysis of 3C 279 using simultaneous Swift-XRT/UVOT and Fermi-LAT observations spanning from August 2008 to June 2022. We also supplement this with the simultaneous NuSTAR observations of the source. The optical/UV, X-ray, and γ-ray spectra were individually fitted by a power-law to study the long term variation in the flux and the spectral indices. A combined spectral fit of simultaneous optical/UV and X-ray spectra was also performed to obtain the transition energy at which the spectral energy distribution is minimum. The correlation analysis suggests that the long term spectral variations of the source are mainly associated with the variations in the low energy index and the break energy of the broken power-law electron distribution which is responsible for the broadband emission. The flux distribution of the source represents a log-normal variability while the γ-ray flux distribution showed a clear double log-normal behaviour. The spectral index distributions were again normal except for γ-ray which showed a double-Gaussian behaviour. This indicates that the log-normal variability of the source may be associated with the normal variations in the spectral index. The broadband spectral fit of the source using synchrotron and inverse Compton processes indicates different emission processes are active at optical/UV, X-ray, and γ-rayenergies.
... Finally, another option is that hadronic processes might manifest themselves at certain activity states of the object. For example, its 2013 December flare (Paliya et al. 2016) and the minute-scale GeV flare in 2015 June (Petropoulou et al. 2017) both posed serious challenges to leptonic models, with the observed spectral and timing flux properties much more easily accommodated within a hadronic description. A detailed cross-correlation study of separate subsets of data for various stages of source activity is required to gain more insight into this problem. ...
Despite numerous studies, the origin of the γ -ray emission from blazars is still debated, in particular whether it is produced by leptonic or hadronic processes. In this study, we are testing the leptonic scenario for the flat-spectrum radio quasar 3C 279, assuming that the γ -ray emission is generated by inverse Compton scattering of external target photons from the broad-line region (IC-BLR scenario). For this purpose we use a 10 yr data set of the source consisting of the optical spectroscopy data from the Steward Observatory blazar monitoring program and Fermi Large Area Telescope γ -ray data. We search for a possible correlation between the Compton dominance and the emission-line luminosity using the discrete correlation function analysis. As a result, we find no significant correlation between these two quantities at any time lag value, while the emission-line luminosity displays a moderate correlation with the γ -ray flux at a zero time lag. We also reveal that the optical synchrotron continuum flux shows a pronounced correlation with the γ -ray flux, and therefore we interpret these results within the leptonic IC-BLR scenario where the variations in Compton dominance are primarily induced by changes in the magnetic field, rather than in the emission-line luminosity.
... where the CD is relatively low 3.4, nearly all prominent gamma-ray flares between 2008 and 2018 (including our patterns) are very likely of the EC origin (Larionov et al. 2020). Moreover, a detailed SED modeling shows that, for instance, the strongest flares during the fourth repetition of the pattern cannot be explained with a one-zone leptonic model (Hayashida et al. 2015;Paliya et al. 2016). The CD based indication of the EC nature of the gamma-ray emission only implies that the seed photons for the IC process are produced outside the emission zone. ...
Fermi-LAT observations provide continuous and regularly-sampled measurements of gamma-ray photon flux for hundreds of blazars. Many of these light curves, spanning almost 15 years, have been thoroughly examined for periodicity in multiple studies. However, the possibility that blazars may exhibit irregularly repeating flaring patterns in their gamma-ray light curves has not been systematically explored. In this study, we aim to find repeating episodes of flaring activity in the 100 brightest blazars using Fermi-LAT light curves with various integration times. We use a Bayesian Blocks representation to convert the time series into strings of symbols and search for repeating sub-strings using a fuzzy search algorithm. As a result, we identify 27 repeated episodes in the gamma-ray light curves of 10 blazars. We find that the patterns are most likely produced in structured jets composed of a fast spine and a slower sheath. When individual emission features propagate in the spine, they scatter seed photons produced in the non-uniform sheath through the inverse Compton mechanism, resulting in a set of gamma-ray flares with a similar profile every such passage. Additionally, we explore the theoretically-predicted possibility that the spine-sheath structure facilitates the production of high-energy neutrinos in blazar jets. Using the catalogue of track-like events detected by the IceCube neutrino telescope, we find evidence supporting this hypothesis at a $3.5\sigma$ significance level.
... Finally, another option is that hadronic processes might manifest themselves at certain activity states of the object. For example, its December 2013 flare (Paliya et al. 2016), or the minutescale GeV flare in June 2015 (Petropoulou et al. 2017) both posed serious challenges to leptonic models, with the observed spectral and timing flux properties much more easily accommodated within a hadronic description. A detailed cross-correlation study of separate subsets of data for various stages of source activity is required to gain more insight into this problem. ...
Despite numerous studies, the origin of the gamma-ray emission from blazars is still debated, in particular whether it is produced by leptonic or hadronic processes. In this study, we are testing the leptonic scenario for the Flat Spectrum Radio Quasar (FSRQ) 3C 279, assuming that the gamma-ray emission is generated by inverse Compton scattering of external target photons from Broad Line Region (IC-BLR scenario). For this purpose we use a 10-year data set of the source consisting of the optical spectroscopy data from the Steward Observatory blazar monitoring program and Fermi-LAT gamma-ray data. We search for a possible correlation between the Compton dominance and the emission line luminosity using the discrete correlation function (DCF) analysis. As a result, we find no significant correlation between these two quantities at any time lag value, while the emission line luminosity displays a moderate correlation with the gamma-ray flux at a zero time lag. We also reveal that the optical synchrotron continuum flux shows a pronounced correlation with the gamma-ray flux, and therefore we interpret these results within the leptonic IC-BLR scenario where the Compton dominance variations are primarily induced by changes in the magnetic field, rather than in the emission line luminosity.
... Blazar 3C 279 is an FSRQ source profusely emitting in hard X-rays and γ -rays. Highly variable across a wide range of spectral bands (see Hayashida et al. 2015 ;Paliya et al. 2016 , and the references therein), it is one of the few FSRQs detected abo v e 100 GeV (MAGIC Collaboration 2008 ). The source reveals a compact, milliarcsecondscale radio core ejecting radio knots with a bulk Lorentz factor = 15.5 ± 2.5, in a direction making an angle θ obs = 2.1 ± 1.1 • to the line of sight (Jorstad et al. 2004(Jorstad et al. , 2005. ...
Flaring episodes in blazars represent one of the most violent processes observed in extra-galactic objects. Studies of such events shed light on the energetics of the physical processes occurring in the innermost regions of blazars, which cannot otherwise be resolved by any current instruments. In this work, we present some of the largest and most rapid flares captured in the optical band in the blazars 3C 279, OJ 49, S4 0954+658, TXS 1156+295 and PG 1553+113. The source flux was observed to increase by nearly ten times within a timescale of a few weeks. We applied several methods of time series analysis and symmetry analysis. Moreover, we also performed searches for periodicity in the light curves of 3C 279, OJ 49 and PG 1553+113 using the Lomb-Scargle method and found plausible indications of quasi-periodic oscillations (QPOs). In particular, the 33- and 22-day periods found in 3C 279, i.e. a 3:2 ratio, are intriguing. These violent events might originate from magnetohydrodynamical instabilities near the base of the jets, triggered by processes modulated by the magnetic field of the accretion disc. We present a qualitative treatment as the possible explanation for the observed large amplitude flux changes in both the source-intrinsic and source-extrinsic scenarios.
... The source of external seed photons could be the accretion disc (Dermer & Schlickeiser 1993 ;Boettcher, Mause & Schlickeiser 1997 ), the broad-line region or BLR (Sikora, Begelman & Rees 1994 ;Ghisellini & Madau 1996 ), and the dusty torus or DT (Bła żejowski et al. 2000 ;Ghisellini & Tavecchio 2008 ). Apart from the leptonic model, the high-energy peak has been explained by hadronic (M ücke et al. 2003 ; B öttcher et al. 2013 ) and lepto-hadronic Paliya et al. 2016 ) model as well in many blazars. In the hadronic model, the high-energy peak of SED is produced by the proton-photon or proton-proton interactions inside the jets. ...
... The flaring period can vary, depending upon the cause of the flare, and in the leptonic scenario, it is expected to be flaring in all wavebands simultaneously. But, we also sometimes observe a time delay between emissions in different wavebands, which challenges the standard one-zone leptonic emission model (Hovatta et al. 2015 ;Paliya et al. 2016,Cerruti et al. 2017,Xue et al. 2019,Prince, Gupta & Nalew ajk o 2019Das, Prince & Gupta 2021 ;Boula & Mastichiadis 2022 ). The fast flux variability is another important property of these sources. ...
One of the most important questions in blazar physics is the origin of broadband emission and fast-flux variation. In this work, we studied the broadband temporal and spectral properties of a TeV blazar 1ES 1727+502 and explore the one-zone synchrotron-self Compton (SSC) model to fit the broadband spectral energy distribution (SED). We collected the long-term (2014-2021) multiband data which includes both the low and high flux states of the source. The entire light curve is divided into three segments of different flux states and the best-fit parameters obtained by broadband SED modeling corresponding to three flux states were then compared. The TeV blazar 1ES 1727+502 has been observed to show the brightest flaring episode in X-ray followed by optical-UV and gamma-ray. The fractional variability estimated during various segments behaves differently in multiple wavebands, suggesting a complex nature of emission in this source. This source has shown a range of variability time from days scale to month scale during this long period of observations between 2014-2021. A ‘harder-when-brighter’ trend is not prominent in X-ray but seen in optical-UV and an opposite trend is observed in γ-ray. The complex nature of correlation among various bands is observed. The SED modeling suggests that the one-zone SSC emission model can reproduce the broadband spectrum in the energy range from optical-UV to very high energy γ-ray.
... The source of external seed photons could be the accretion disk (Dermer & Schlickeiser 1993, Boettcher et al. 1997, the broad-line region or BLR (Sikora et al. 1994, Ghisellini & Madau 1996, and the dusty torus or DT (Błażejowski et al. 2000, Ghisellini & Tavecchio 2008. Apart from the leptonic model, the high energy peak has been explained by hadronic (Mücke et al. 2003, Böttcher et al. 2013) and leptohadronic , Paliya et al. 2016) model as well in many blazars. In hadronic model, the high energy peak of spectral energy distribution (SED) is produced by the proton-photon or proton-proton interactions inside the jets. ...
... The flaring period can vary depending upon the cause of the flare and in leptonic scenario it is expected to be flaring in all wavebands simultaneously. But, we also sometimes observe a time delay between emissions in different wavebands, which challenges the standard one-zone leptonic emission model (Hovatta et al. 2015, Paliya et al. 2016,Cerruti et al. 2017,Xue et al. 2019, Das et al. 2021, Boula & Mastichiadis 2022. The fast flux variability is another important property of these sources. ...
One of the most important questions in blazar physics is the origin of broadband emission and fast-flux variation. In this work, we studied the broadband temporal and spectral properties of a TeV blazar 1ES 1727+502 and explore the one-zone synchrotron-self Compton (SSC) model to fit the broadband spectral energy distribution (SED). We collected the long-term (2014-2021) multiband data which includes both the low and high flux states of the source. The entire light curve is divided into three segments of different flux states and the best-fit parameters obtained by broadband SED modeling corresponding to three flux states were then compared. The TeV blazar 1ES 1727+502 has been observed to show the brightest flaring episode in X-ray followed by optical-UV and gamma-ray. The fractional variability estimated during various segments behaves differently in multiple wavebands, suggesting a complex nature of emission in this source. This source has shown a range of variability time from days scale to month scale during this long period of observations between 2014-2021. A "harder-when-brighter" trend is not prominent in X-ray but seen in optical-UV and an opposite trend is observed in gamma-ray. The complex nature of correlation among various bands is observed. The SED modeling suggests that the one-zone SSC emission model can reproduce the broadband spectrum in the energy range from optical-UV to very high energy gamma-ray.
