Emission Of 3C Research Articles

Pair Cascades at the Edge of the Broad-line Region Shaping the Gamma-Ray Spectrum of 3C 279

Abstract The blazar 3C 279 emits a flux of gamma rays that is variable on timescales as short as the light-crossing time across the event horizon of its central black hole. It is commonly reported that the spectral energy distribution (SED) does not show signs of pair attenuation due to interactions of the gamma rays with ambient ultraviolet photons, concluding that the gamma rays must originate from substructures in the jet outside of the broad-line region (BLR). We address the spectral signature imprinted by atomic emission lines on the gamma-ray spectrum produced by an inverse-Compton pair cascade in the photon field of the BLR. We determine with high precision the gamma-ray SED of 3C 279 using Fermi Large Area Telescope data from MJD 58129−58150 and simulate the pair cascade spectrum for three different injection terms. Satisfactory fits to the observational data are obtained. The obtained SED shows features imprinted by pair production on atomic emission line photons due to optically thick radiation transport, but lacking further exponential attenuation expected if the emission region would lie buried deep within the BLR. The SED of 3C 279 is consistent with an inverse-Compton pair cascade spectrum without exponential external pair absorption. Our findings support the view that the gamma-ray emission in 3C 279 originates from the edge of the BLR.

Excluding possible sites of high-energy emission in 3C 84

ABSTRACT The FR-I galaxy 3C 84, that is identified with the misaligned blazar NGC 1275, is well known as one of the very few radio galaxies emitting gamma-rays in the TeV range. Yet, the gamma-ray emission region cannot be pinpointed and the responsible mechanisms are still unclear. We calculate the optical absorption depth of high-energy photons in the broad-line region of 3C 84 depending on their energy and distance to the central black hole. Based on these calculations, a lower limit on the distance of the emission region from the central black hole can be derived. These lower limits are estimated for two broad-line region geometries (shell and ring) and two states of the source, the low state in 2016 October–December and a flare state in 2017 January. For the shell geometry, we can place the emission region outside the Ly α radius. For the ring geometry and the low flux activity, the minimal distance between the black hole, and the gamma-ray emission region is close to the Ly α radius. In the case of the flaring state (ring geometry), the results are not conclusive. Our results exclude the region near the central black hole as the origin of the gamma-rays detected by Fermi–LAT and Major Atmospheric Gamma-Ray Imaging Cherenkov. With these findings, we can constrain the theoretical models of acceleration mechanisms and compare the possible emission region to the source’s morphology resolved by radio images from the Very Long Baseline Array.

Non-thermal emission in lobes of radio galaxies – III. 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236

ABSTRACTRecent analyses of the broad spectral energy distributions (SEDs) of extensive lobes of local radio galaxies have confirmed the leptonic origin of their Fermi/Large Area Telescope γ-ray emission, significantly constraining the level of hadronic contribution. SEDs of distant (DL > 125 Mpc) radio-galaxy lobes are currently limited to the radio and X-ray bands, hence give no information on the presence of non-thermal (NT) protons but are adequate to describe the properties of NT electrons. Modelling lobe radio and X-ray emission in 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236, we fully determine the properties of intralobe NT electrons and estimate the level of the related γ-ray emission from Compton scattering of the electrons off the superposed cosmic microwave background, extragalactic background light, and source-specific radiation fields.

Focusing on the extended X-ray emission in 3C 459 with a Chandra follow-up observation

Aims. We investigated the X-ray emission properties of the powerful radio galaxy 3C 459 revealed by a recent Chandra follow-up observation carried out in October 2014 with a 62 ks exposure. Methods. We performed an X-ray spectral analysis from a few selected regions on an image obtained from this observation and also compared the X-ray image with a 4.9 GHz VLA radio map available in the literature. Results. The dominant contribution comes from the radio core but significant X-ray emission is detected at larger angular separations from it, surrounding both radio jets and lobes. According to a scenario in which the extended X-ray emission is due to a plasma collisionally heated by jet-driven shocks and not magnetically dominated, we estimated its temperature to be ∼0.8 keV. This hot gas cocoon could be responsible for the radio depolarization observed in 3C 459, as recently proposed also for 3C 171 and 3C 305. On the other hand, our spectral analysis and the presence of an oxygen K edge, blueshifted at 1.23 keV, cannot exclude the possibility that the X-ray radiation originating from the inner regions of the radio galaxy could be intercepted by some outflow of absorbing material intervening along the line of sight, as already found in some BAL quasars.

Origin of X-rays in the low state of the FSRQ 3C 273: evidence of inverse Compton emission

We analyze the 2.5--10 keV X-ray spectra of the luminous quasar 3C 273 and simultaneous observations in UV wavelengths from XMM--Newton between 2000 and 2015. The lowest flux level ever was observed in 2015. The continuum emission from 3C 273 is generally best described by an absorbed power-law but during extremely low states the addition of fluorescence from the K-shell iron line improves the fit. We study the spectral evolution of the source during its extended quiescent state and also examine connections between the X-ray and ultraviolet emissions, which have been seen in some, but not all, previous work. We detect a possible anti-correlation between these two bands during the low state that characterized 3C 273 for most of this period; however, this was not present during a flaring state. A harder-when-brighter trend for the X-ray spectrum was observed in these long-term observations of 3C 273 for the first time. We suggest that the X-ray emission in 3C 273 is the result of inverse Compton scattering of soft UV seed photons (emitted from the local environment of the AGN), most likely in a thermal corona. We can explain the significant temporal variation of the spectral continuum as an outcome of changing optical depth of the comptonizing medium, along the lines of the wind-shock model proposed by Courvoisier and Camenzind (1989).

Parsec-scale jet properties of the gamma-ray quasar 3C 286

The quasar 3C 286 is one of two compact steep-spectrum sources detected by the Fermi/Large Area Telescope. Here, we investigate the radio properties of the parsec(pc)-scale jet and its (possible) association with the gamma-ray emission in 3C 286. The Very Long Baseline Interferometry (VLBI) images at various frequencies reveal a one-sided core–jet structure extending to the south-west at a projected distance of ∼1 kpc. The component at the jet base showing an inverted spectrum is identified as the core, with a mean brightness temperature of 2.8 × 109 K. The jet bends at about 600 pc (in projection) away from the core, from a position angle of −135° to −115°. Based on the available VLBI data, we inferred the proper-motion speed of the inner jet as 0.013 ± 0.011 mas yr−1 (βapp = 0.6 ± 0.5), corresponding to a jet speed of about 0.5 c at an inclination angle of 48° between the jet and the line of sight of the observer. The brightness temperature, jet speed and Lorentz factor are much lower than those of gamma-ray-emitting blazars, implying that the pc-scale jet in 3C 286 is mildly relativistic. Unlike blazars in which gamma-ray emission is in general thought to originate from the beamed innermost jet, the location and mechanism of gamma-ray emission in 3C 286 may be different as indicated by the current radio data. Multiband spectrum fitting may offer a complementary diagnostic clue of the gamma-ray production mechanism in this source.

HINTS OF CORRELATION BETWEEN BROAD-LINE AND RADIO VARIATIONS FOR 3C 120

In the paper, we investigate correlation between broad-line and radio variations for broad-line radio galaxy 3C 120. By the z-transformed discrete correlation function method and the model-independent flux randomization/random subset selection (FR/RSS) Monte Carlo method, we find that the broad Hbeta line variations lead the 15 GHz variations. The FR/RSS method shows that the Hbeta line variations lead the radio variations by a factor of tau_{ob}=0.34 +/- 0.01 yr. This time lag can be used to locate the position of emitting region of radio outbursts in jet, on the order of ~ 5 light-years, from the central engine. This distance is much larger than the size of broad-line region. The large separation of the radio outburst emitting region from the broad-line region will observably influence the gamma-ray emission in 3C 120.

Relativistic outflow drivesγ-ray emission in 3C 345

Aims: 3C345 was recently identified as a gamma-ray emitter, based on the first 20 months of Fermi-LAT data and optical monitoring. In this paper, a connection between the gamma-ray and optical variability of 3C345 and properties of its parsec-scale radio emission is investigated. Methods: The Fermi-LAT data of 3C345, covering an energy range of 0.1-300 GeV, were combined with 32 Very Long Baseline Array observations of the object made at 43.2 GHz in the period of January 2008 - March 2010. Results: The VLBA data reveal morphology and kinematics of the flow on scales of up to ~5 milliarcseconds (mas; deprojected linear distances of 380 parsecs). The brightness temperature, T_b(r), measured along the jet first decreases with distance proportional to r^-(0.95 +/-0.69) and later exhibits a break at ~0.3 mas, with T_b(r) proportional to r^-(4.11 +/-0.85) at larger separations. Variations of the gamma-ray, optical and parsec-scale radio emission show a similar long-term trend persistent during the entire VLBA monitoring period. The gamma-ray and optical variations on shorter time scales are related to structural changes in the jet on scales of ~0.3 mas (~23 parsecs, deprojected), with the gamma-ray and optical flares possibly related to the evolution of four distinct superluminal components identified in the flow. Conclusions: The observations indicate that both the quiescent and flaring components of the gamma-ray emission are produced in a region of the jet of ~23 pc in extent. This region may mark the Compton-loss dominated zone of the flow and its large extent may favor the synchrotron self-Compton mechanism for gamma-ray production in the relativistic jet of the quasar 3C345.

Molecular gas and continuum emission in 3C 48: evidence for two merger nuclei?

Received ; accepted Abstract. We present new interferometer observations of the CO(1-0) line and mm continuum emission from 3C48 — one of the nearest examples of a merger activating a quasar. Our new CO data show that most of the CO is not in a disk around the quasar 3C48, but rather in a second nucleus associated with the source 3C48A � 1 '' to the north-east, recently studied in the near-IR by Zuther et al. (2004). This main CO source has a strong velocity gradient (140km s −1 over about 1 '' ). Our new data also show a second, weaker CO source at the QSO itself. At 1.2mm, the continuum emission is elongated in the direction of the radio jet and towards 3C48A. We model the 1.2mm continuum with three different sources in 3C48 — the 3C48 QSO, the 3C48 jet, and the second nucleus 3C48A. We suggest that the unusually bright and extended nature of the jet may be due to its interaction with the second merger nucleus 3C48A.

Spectropolarimetry of broad Hα lines in radio galaxies: constraints on the geometry of the broad-line and scattering regions

We present optical spectropolarimetric observations of three radio-loud broad-line active galactic nuclei: 3C 332, 3C 351 and 4C 73.18, together with new observations of 3C 390.3, which we observed previously. Intrinsically polarized broad Hα emission was detected in 3C 332 and 3C 390.3 at levels of ∼3 per cent and ∼1 per cent, respectively. Significant polarization was not detected in 3C 351, while the polarization measured in 4C 73.18 (∼1 per cent) is consistent with foreground contamination by the galactic interstellar medium. Although 3C 332 and 3C 390.3 both exhibit ‘double-peaked’ broad Hα line profiles, their polarization properties differ significantly. The polarized Hα emission in 3C 332 has a similar profile to that seen in total flux and the continuum and line emission is polarized at 70° to the axis of the radio source. In 3C 390.3, however, the double peaks seen in total flux are suppressed in polarized flux and the Hα line and continuum are polarized at ∼5° to the axis of the radio emission. Comparison of these new observations of 3C 390.3 with data obtained 2 years previously reveals significant variations in both total and polarized flux. The implications of these observations for the relationship between the geometry of the broad-line region and that of the scattering medium are discussed. We argue that models in which the Hα emission arises in a relativistically rotating disc cannot easily explain the observed polarization properties of 3C 332 and, in particular, 3C 390.3. We consider instead a model in which the line emission originates in a bipolar outflow and present calculations showing that the observed polarization properties of 3C 390.3 can be broadly explained by scattering from the inner wall of an obscuring torus, while those of 3C 332 are consistent with scattering by particles situated above the poles of the torus. We outline a scheme in which either toroidal or polar scattering dominates in a given object, depending on the orientation of its radio jet axis to our line of sight.

Chandradiscovery of extended non-thermal emission in 3C 207 and the spectrum of the relativistic electrons

We report on the Chandra discovery of large scale non–thermal emission features in the double lobed SSRL quasar 3C 207 (). These are: a diffuse emission well correlated with the western radio lobe, a bright one sided jet whose structure coincides with that of the eastern radio jet and an X-ray source at the tip of the jet coincident with the hot spot of the eastern lobe. The diffuse X-ray structure is best interpreted as inverse Compton (IC) scattering of the IR photons from the nuclear source and provides direct observational support to an earlier conjecture (Brunetti et al. [CITE]) that the spectrum of the relativistic electrons in the lobes of radio galaxies extends to much lower energies than those involved in the synchrotron radio emission. The X-ray luminous and spatially resolved knot along the jet is of particular interest: by combining VLA and Chandra data we show that a SSC model is ruled out, while the X-ray spectrum and flux can be accounted for by the IC scattering of the CMB photons (EIC) under the assumptions of a relatively strong boosting and of an energy distribution of the relativistic electrons as that expected from shock acceleration mechanisms. The X-ray properties of the hot spot are consistent with a SSC model. In all cases we find that the inferred magnetic field strength are lower, but close to the equipartition values. The constraints on the energy distribution of the relativistic electrons, imposed by the X-ray spectra of the observed features, are discussed. To this aim we derive in the Appendices precise semi–analytic formulae for the emissivities due to the SSC and EIC processes.

Relationship between X-ray and ultraviolet emission in 3C 273

In 3C 273, ultraviolet flux and X-ray flux measured by BATSE are not well correlated, contrarily to predictions of several models, unless the X-ray flux lags the UV emission by 1.75 yr. The absence of observed correlation at small lag cannot be due to spectral variability. A Comptonizing corona model is however compatible with all UV and X-ray observations covering the BATSE period.

ITAL]Hubble[/ITAL] [ITAL]Space[/ITAL] [ITAL]Telescope[/ITAL] Spectra of 3C 279: A Lyman Limit System at Low Redshift

We present Hubble Space Telescope (HST) Faint Object Spectrograph spectra of the blazar 3C 279 obtained during two recent optical outbursts of this source, maximizing the sensitivity to weak foreground absorption systems at far-UV wavelengths for this sight line. Eighteen absorption systems were detected above an observed 3 σ limiting equivalent width of ~0.3 A. These systems include an unusual, partially thick Lyman limit + C IV + Mg II system at zabs = 0.395. In retrospect, this Lyman limit system was detected in the cumulative IUE SWP scan of 3C 279 but was not noted previously. The column density (log NH = 16.8 cm-2), redshift (which places Lyα through the Lyman limit within the wavelength range observable with HST), location of the sight line ~20 h-1 kpc above the plane of an edge-on spiral galaxy, and apparent lack of velocity structure at 1 A resolution make this system an ideal candidate for a low-z measurement of the cosmic abundance of deuterium relative to hydrogen. Amazingly, this absorption system in 3C 279 (1253-055) differs by less than 100 km s-1 from the velocity of a known metal line/21 cm absorber in another quasar, PKS 1229-021 (zabs = 0.395) almost 7° (87.5 h-1 Mpc) away on the sky. The 3C 279 sight line also contains a time-variable absorber intrinsic to 3C 279 (outflow velocity of ~1200 km s-1) and a clump of four absorbers at z = 0.133–0.138. The 1996 epoch spectra, which immediately preceded a large flare at γ- and X-ray energies, showed the line flux of Lyα and N V emission in 3C 279 to be unchanged compared with an earlier epoch, despite a factor of 4 increase in the continuum emission level.

Time Variability Detected in the Gamma-Ray Emission of 3C 273 by OSSE

We report results of a 3 week observation of the quasar 3C 273 with the Oriented Scintillation Spectrometer Experiment (OSSE) instrument on the Compton Gamma Ray Observatory (CGRO). During the observation between 1994 August 31 and September 20, 3C 273 exhibited variability on timescales as short as 3-4 days in the 0.05-0.15 MeV energy range. This is the shortest measured variability of 3C 273 in this energy range. The measured flux at 100 keV is 2.40 ± 0.06 (×10-2 ph cm-2 s-1 MeV-1), which is the highest recorded flux for 3C 273 by OSSE in 5 years of monitoring and nearly twice as great as the previously recorded peak flux measured in 1991 June. While the flux varied by a factor of 1.7, no significant gamma-ray spectral evolution in the OSSE band was observed throughout the viewing period. The data for the full viewing period are described better with a broken power law than a single power law, with photon spectral index Γ = 1.62 ± 0.08 below a break at 300 ± 100 keV, and with a spectral index change of ΔΓ = 0.9+ 1.6−0.6. This break energy is significantly lower than the 1 MeV break reported by Johnson et al. in 1991 June.

Knots in Simulations of Magnetized Relativistic Jets

Bright features (knots) in extragalactic jets are commonly associated with reacceleration of charged particles in regions with shocks or strong compression. This letter presents a stagnation point-nozzle-Mach disk (SNM) morphology observed in time-dependent simulations of magnetized relativistic jets. The nozzles are remnants of an oscillation in the Mach disk at the hot spot. The results are compared with the jets of QSO 0800+608 and 3C 273. In particular, we suggest that these nozzles may explain the correlated optical and radio emission in 3C 273.

The X-Ray Emission of 3C 58 Revisited

We report on an observation of the youngest Crab-like supernova remnant, 3C 58, undertaken with the {ital ROSAT} high-resolution imager. The presence of a compact X-ray source at the center of the remnant, suggested by earlier observations, is confirmed, although aspect problems with the Observatory allow us to set only an upper limit on the size of the source of less than 10{double_prime}. We describe an efficient new algorithm for conducting period searches on sparsely sampled data with a relatively small number of photons, and use it to set an upper limit on the pulsed fraction of this source of 50{percent}. We show that the diffuse X-ray emission from the remnant is cospatial with the nonthermal radio emission and constrain the spectral parameters of the X-ray power-law fit. We go on to explore several models for the compact source, showing that Crab-like nonthermal pulses and thermal emission from the entire stellar surface are unlikely to explain the emission. Polar caps heated by magnetospheric discharges could be responsible for the observed X-rays. We conclude that the low X-ray pulsed fraction, inferred emitting area and temperature for the compact source, nebular luminosities in the X-ray and radio bands, and the known agemore » can all be reconciled if {ital P}{approximately}200 ms, {dot {ital P}}{approximately}4000{times}10{sup {minus}15} s s{sup {minus}1}, and {ital B}{approximately}3{times}10{sup 13} G, which would make this the highest magnetic field pulsar known. {copyright} {ital 1995 The American Astronomical Society.}« less

Relic radio emission in 3C 388

Relic radio emission in 3C 388

Beaming effect in the γ emission in 3C 279 and inverse Compton scattering

This paper gives a physical explanation of the high-energy γ emission (30MeV–10GeV) measured in 3C279. From the physical process of γ ray absorption in the γ-γ production of electron pairs, we derive the constraint that relativistic beaming effects must extist in the X-ray and γ-ray emitting regions. We calculate the high-energy γ-ray spectrum generated by inverse Compton emission and point out that, for a high-energy cutoff of the electron spectrum γ max > 10 5, inverse Compton spectrum of the observed low-energy spectrum of 3C 279 can account for its observed γ-ray spectrum.

Time variability in the gamma-ray emission of 3C 279

Following the initial detection of 3C 279 as an intense high-energy gamma-ray emitter during a 1991, June 16-28 observation, the EGRET instrument on the Compton Gamma Ray Observatory made a second observation during 1991, October 3-17. Low-sensitivity observations were also made during 1991, October 12-31 and 1992 April. The relatively intense June fluxes allowed the time structure to be determined down to the level of half-days. During this period a flux enhancement of about a factor of 4 is seen, lasting several days. The October exposures show fluxes somewhat below the minimum June flux, with no significant evidence of time variability. The 1992 April fluxes are well off the main instrument axis, and so the statistics are less compelling, but the evidence appears to show additional time variability. The observations are consistent with a model in which the gamma rays result from Compton scattering of low-energy photons by relativistic electrons in a jet.

Extended Lyman-alpha emission in 3C 326.1 - A 100 kiloparsec cloud of ionized gas at a redshift of 1.82

The discovery of a large cloud of ionized gas associated with the high-redshift radio source 3C 326.1 is reported; this cloud is the best candidate for a protogalaxy yet observed. The radio source is a small double without a detectable core which is encompassed by a cloud of ionized gas of approximately 100 kpc diameter and a redshift of 1.825. Two faint blue objects are located on the periphery of the cloud along with some very faint, extremely diffuse blue objects roughly coincident with the brightest regions of the cloud. The Ly-alpha emission from the cloud appears to have a large intrinsic width. Weak extended emission from semiforbidden C II and semiforbidden C III is seen, but C IV emission is not detected. The large equivalent width of Ly-alpha and the relative strengths of the carbon lines are consistent with H II region-type photoionization.