Flat Spectrum Radio Quasar 3C Research Articles

Modelling the very high energy flare of 3C 279 using one-zone leptonic model

We model the simultaneous observations of the flat spectrum radio quasar 3C 279 at radio, optical, X-ray and very high energy (VHE) gamma ray energies during 2006 flare using a simple one zone leptonic model. We consider synchrotron emission due to cooling of a non-thermal electron distribution in an equipartition magnetic field and inverse Compton emission due to the scattering off synchrotron photons (SSC) and external soft photons (EC) by the same distribution of electrons. We show that the VHE gamma ray flux cannot be explained by SSC process thereby suggesting the EC mechanism as a plausible emission process at this energy. The EC scattering of BLR photons to VHE energies will be in Klein-Nishina regime predicting a steep spectrum which is contrary to the observations. However the infrared photons from the dusty torus can be boosted to VHE energies with the scattering process remaining in the Thomson regime. Though EC process can successfully explain the observed VHE flux, it require a magnetic field much lower than the equipartition value to reproduce the observed X-ray flux. Hence we attribute the X-ray emission due to SSC process. We derive the physical parameters of 3C 279 considering the above mentioned emission processes. In addition we assume the size of emission region constrained by a variability timescale of one day. This model can successfully reproduce the broadband spectrum of 3C 279 but predicts substantially large flux at MeV-GeV energies.

FLARING PATTERNS IN BLAZARS

Blazars radiate from relativistic jets launched by a supermassive black hole along our line of sight; the subclass of FSRQs exhibits broad emission lines, a telltale sign of a gas-rich environment and high accretion rate, contrary to the other subclass of the BL Lacertae objects. We show that this dichotomy of the sources in physical properties is enhanced in their flaring activity. The BL Lac flares yielded spectral evidence of being driven by further acceleration of highly relativistic electrons in the jet. Here we discuss spectral fits of multi-lambda data concerning strong flares of the two flat spectrum radio quasars 3C 454.3 and 3C 279 recently detected in gamma rays by the AGILE and Fermi satellites. We find that optimal spectral fits are provided by external Compton radiation enhanced by increasing production of thermal seed photons by growing accretion. We find such flares to trace patterns on the jet power - electron energy plane that diverge from those followed by flaring BL Lacs, and discuss why these occur.

FERMI GAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE GAMMA-RAY OUTBURST FROM 3C454.3 IN NOVEMBER 2010

The flat-spectrum radio quasar 3C 454.3 underwent an extraordinary 5-day gamma-ray outburst in November 2010 where the daily flux measured with the Fermi Large Area Telescope (LAT) at photon energies E>100 MeV reached (66+/-2) x 10^-6 ph cm^-2 s^-1. This is a factor of 3 higher than its previous maximum flux recorded in December 2009 and ~5 times brighter than the Vela pulsar, which is normally the brightest source in the gamma-ray sky. The 3-hr peak flux was (85+/-5) x 10^-6 ph cm^-2 s^-1, corresponding to an apparent isotropic luminosity of 2.1+/-0.2 10^50 erg s^-1, the highest ever recorded for a blazar. In this paper, we investigate the features of this exceptional event in the gamma-ray band of the Fermi-LAT. In contrast to previous flares of the same source observed with the Fermi-LAT, clear spectral changes are observed during the flare.

FERMI GAMMA-RAY SPACE TELESCOPEOBSERVATIONS OF GAMMA-RAY OUTBURSTS FROM 3C 454.3 IN 2009 DECEMBER AND 2010 APRIL

The flat spectrum radio quasar 3C~454.3 underwent an extraordinary outburst in December 2009 when it became the brightest gamma-ray source in the sky for over one week. Its daily flux measured with the Fermi Large Area Telescope at photon energies E>100 MeV reached F = 22+/-1 x 10^-6 ph cm^-2 s^-1, representing the highest daily flux of any blazar ever recorded in high-energy gamma-rays. It again became the brightest source in the sky in 2010 April, triggering a pointed-mode observation by Fermi. The correlated gamma-ray temporal and spectral properties during these exceptional events are presented and discussed. The main results show flux variability over time scales less than 3 h and very mild spectral variability with an indication of gradual hardening preceding major flares. No consistent loop pattern emerged in the gamma-ray spectral index vs flux plane. A minimum Doppler factor of ~ 15 is derived, and the maximum energy of a photon from 3C 454.3 is ~ 20 GeV. The spectral break at a few GeV is inconsistent with Klein-Nishina softening from power-law electrons scattering Ly_alpha line radiation, and a break in the underlying electron spectrum in blazar leptonic models is implied.

THE EXTRAORDINARY GAMMA-RAY FLARE OF THE BLAZAR 3C 454.3

We present the gamma-ray data of the extraordinary flaring activity above 100 MeV from the flat spectrum radio quasar 3C 454.3 detected by AGILE during the month of December 2009. 3C 454.3, that has been among the most active blazars of the FSRQ type since 2007, was detected in the gamma-ray range with a progressively rising flux since November 10, 2009. The gamma-ray flux reached a value comparable with that of the Vela pulsar on December 2, 2009. Remarkably, between December 2 and 3, 2009 the source more than doubled its gamma-ray emission and became the brightest gamma-ray source in the sky with a peak flux of F_{\gamma,p} = (2000 \pm 400) x 10^-8 ph cm^-2 s^-1 for a 1-day integration above 100 MeV. The gamma-ray intensity decreased in the following days with the source flux remaining at large values near F \simeq (1000 \pm 200) x 10^-8 ph cm^-2 s^-1 for more than a week. This exceptional gamma-ray flare dissipated among the largest ever detected intrinsic radiated power in gamma-rays above 100 MeV (L_{\gamma, source, peak} \simeq 3 x 10^46 erg s^-1, for a relativistic Doppler factor of {\delta} \simeq 30). The total isotropic irradiated energy of the month-long episode in the range 100 MeV - 3 GeV is E_{\gamma,iso} \simeq 10^56 erg. We report the intensity and spectral evolution of the gamma-ray emission across the flaring episode. We briefly discuss the important theoretical implications of our detection.

Constraining the location of the emitting region in Fermi blazars through rapid γ-ray variability

Abstract We consider the 1.5-yr Fermi/Large Area Telescope (LAT) light curves (E>100 MeV) of the flat spectrum radio quasars 3C454.3 and PKS1510−089, which show high activity in this period of time. We characterize the duty cycle of the source by comparing the time spent by the sources at different flux levels. We consider in detail the light curves covering periods of extreme flux. The large number of high-energy photons collected by LAT in these events allows us to find evidence of variability on time-scales of a few hours. We discuss the implications of significant variability on such short time-scales that challenge the scenario recently advanced in which the bulk of the γ-ray luminosity is produced in regions of the jet at large distances (tens of parsec) from the black hole.

ON THE BREAK IN THEFERMI-LARGE AREA TELESCOPE SPECTRUM OF 3C 454.3

Fermi Gamma ray Space Telescope observations of the flat spectrum radio quasar 3C~454.3 show a spectral-index change $\Delta \Gamma \cong 1.2\pm 0.3$ at break energy $E_{br} \approx 2.4\pm0.3$ GeV. Such a sharp break is inconsistent with a cooling electron distribution and is poorly fit with a synchrotron self-Compton model. We show that a combination of two components, namely the Compton-scattered disk and broad-line region (BLR) radiations, explains this spectral break and gives a good fit to the quasi-simultaneous radio, optical/UV, X-ray, and $\gamma$-ray spectral energy distribution observed in 2008 August. A sharp break can be produced independent of the emitting region's distance from the central black hole if the BLR has a gradient in density $\propto R^{-2}$, consistent with a wind model for the BLR.

Implications of Bulk Velocity Structures in AGN Jets

Abstract Synchrotron self-Compton (SSC) models and External Compton (EC) models of AGN jets with continually longitudinal and transverse bulk velocity structures have been constructed. The observed spectra show complex and interesting patterns in different velocity structures and viewing angles. These models were used to calculate the synchrotron and inverse Compton spectra of two typical BL Lac objects (BLO) (Mrk 421 and 0716$+$714) and (one) Flat Spectrum Radio Quasars (FSRQs) (3C 279), and to discuss the implications of jet bulk velocity structures in a unification of the BLO and FR I radio galaxies (FRI). By calculating the synchrotron spectra and SSC spectra of BL Lac object jets with continually bulk velocity structures, we have found that the spectra are much different from those in jets with a uniform velocity structure under increasing viewing angles. The unification of BLO and FRI is less constrained by the viewing angles, and would be imprinted by velocity structures intrinsic to the jets, themselves. By considering jets with bulk velocity structures constrained by the apparent speed, we discuss the velocity structures imprinted on the observed spectra for different viewing angles. We find that the spectra are greatly impacted by longitudinal velocity structures, because the volume elements are compressed or expanded. Finally, we present the EC spectra of FSRQs and FR II radio galaxies (FRII), and find that they are weakly affected by the velocity structures compared to synchrotron and SSC spectra.

MODELING OF NON-HBL VHE γ-RAY BLAZARS

This is a summary of recent modeling results of three newly detected TeV blazars of the intermediate BL Lac object (IBL) and flat-spectrum radio quasar (FSRQ) sub-classes: W Comae, 3C 66A, and 3C 279. For model fits to the spectral energy distributions of W Comae and 3C 66A, a non-negligible contribution from a source of soft radiation external to the jets of these blazars is strongly preferred over pure synchrotron-self-Compton or synchrotron-proton-blazar models, respectively. This indicates that IBLs are truly intermediate between the "classical" TeV blazars (high-frequency-peaked BL Lac objects) and FSRQs. The VHE γ-ray detection of the FSRQ 3C 279 poses severe challenges for leptonic models, and seems to favor a hadronic origin of the high-energy emission. However, even a hadronic model suffers from problems with extreme energy requirements.

PHYSICS INSIGHTS FROM RECENT MAGIC AGN OBSERVATIONS

The total set of the 14 active galactic nuclei detected by MAGIC so far includes well-studied bright blazars like Mkn 501, the giant radio galaxy M 87, but also the distant flat-spectrum radio quasar 3C 279, and an intriguing gamma-ray source in the 3C 66A/B region, whose energy spectrum is not compatible with the expectations from 3C 66A. Besides scheduled observations, so far MAGIC succeeded in discovering TeV gamma rays from three blazars following triggers from high optical states. I report selected highlights from recent MAGIC observations of extragalactic TeV gamma-ray sources, emphasizing and discussing the new physics insights the MAGIC observations were able to contribute.

High energy variability of 3C 273 during the AGILE multiwavelength campaign of December 2007–January 2008

We report the results of a 3-weeks multi-wavelength campaign on the flat spectrum radio quasar 3C 273 carried out with the AGILE gamma-ray mission, covering the 30 MeV -50 GeV and 18-60 keV, the REM observatory (covering the near-IR and optical), Swift (near-UV/Optical, 0.2-10 keV and 15-50 keV), INTEGRAL (3 - 200 keV) and Rossi XTE (2-12 keV). This is the first observational campaign including gamma-ray data, after the last EGRET observations, more than 8 years ago. Our study was carried out using simultaneous light curves of the source flux from all the involved instruments, in the different energy ranges, in search for correlated variability. Then a time-resolved SED was used for a detailed physical modelling of the emission mechanisms. The source was detected in gamma-rays only in the second week of our campaign. We found indication of a possible anti-correlation between the emission at gamma-rays and at soft and hard X-rays, supported by the complete set of instruments. Instead, optical data do not show short term variability. Only in two EGRET observations (in 1993 and 1997) 3C 273 showed intra-observation variability in gamma-rays. The SED with almost simultaneous data, partially covers the regions of the synchrotron emission, the big blue bump, and the inverse-Compton. The soft X-ray emission is consistent with combined SSC and EC mechanisms, while hard X and gamma-ray emissions are compatible with EC from thermal photons of the disk. The time evolution of the SED is well interpreted and modelled in terms of an acceleration episode of the electrons population, leading to a shift in the IC peak towards higher energies.

Broad‐Line Radio Galaxies: Jet Contribution to the Nuclear X‐Ray Continuum

It is shown that for broad-line radio galaxies the strength of the nonthermal beamed radiation, when present, is always smaller than the accretion flow by a factor of <0.7 in the 2-10 keV band. This result has been obtained using the procedure adopted for disentangling the flat-spectrum radio quasar 3C 273. Although this implies a significantly smaller nonthermal flux in radio galaxies when compared to blazars, the jet component, if present, could be important at very high energies and thus easily detectable with GLAST.