Marco Chiaberge

Structured jets in TeV BL Lac objects and radiogalaxies - Implications for the observed properties

TeV BL Lacertae objects require extreme relativistic bulk motions in the gamma-ray emission region, but at the VLBI scale their radio knots hardly move. The same sources show evidence, in radio, of a structure made of a fast spine plus a slow layer. We propose that this structure exists even on the spatial scale of regions responsible for the gamma-ray emission. One component sees the (beamed) radiation produced by the other, and this enhances the inverse Compton emission of both components. In addition, this allows the magnetic field to be nearly in equipartition with the emitting particles. The inverse Compton emission of the spine is anisotropic in its frame, possibly producing a deceleration of the spine by the Compton rocket effect. In this scenario, the slow layer is also a relatively strong high-energy emitter, and thus radiogalaxies become potentially detectable by GLAST.

Large-scale jets in active galactic nuclei: multiwavelength mapping

ABSTRA C T X-ray emission from large-scale extragalactic jets is likely to be as a result of inverse Compton scattering of relativistic particles off seed photons of both the cosmic microwave background field and the blazar nucleus. The first process dominates the observed highenergy emission of large-scale jets if the plasma is moving at highly relativistic speeds and if the jet is aligned with the line of sight, i.e. in powerful flat radio spectrum quasars. The second process is relevant when the plasma is moving at mildly bulk relativistic speeds, and can dominate the high-energy emission in misaligned sources, i.e. in radio galaxies. We show that this scenario satisfactorily accounts for the spectral energy distribution detected by Chandra from the jet and core of PKS 0637‐752.

Rapid variability in the synchrotron self-Compton model for blazars

ABSTRA C T Blazars are characterized by large amplitude and rapid variability, indicating that the electron distribution is changing rapidly, often on time-scales shorter than the light-crossing time. The emitting region is sufficiently compact to let radiative losses dominate the cooling of highenergy electrons. We study the time-dependent behaviour of the electron distribution after episodic electron injection phases, and calculate the observed synchrotron and self-Compton radiation spectra. Since photons produced in different parts of the source have different travel times, the observed spectrum is produced by the electron distribution at different stages of evolution. Even a homogeneous source then resembles an inhomogeneous one. Time delays between the light curves of fluxes at different frequencies are possible, as illustrated for the specific case of the BL Lac object Mrk 421.

X-Ray Emission of Markarian 421: New Clues from Its Spectral Evolution. II. Spectral Analysis and Physical Constraints

Mrk 421 was repeatedly observed with BeppoSAX in 1997 and 1998. The source showed a very rich phenomenology with remarkable spectral variability. This is the second of two papers presenting the results of a thorough temporal and spectral analysis of all the data available to us, focusing in particular on the flare of April 1998, which was simultaneously observed also at TeV energies. The spectral analysis and correlations are presented in this paper, while the data reduction and timing analysis are the content of the companion paper. The spectral evolution during the flare has been followed over few ks intervals, allowing us to detect for the first time the peak of the synchrotron component shifting to higher energies during the rising phase and then receding. This spectral analysis nicely confirms the delay of the flare at the higher energies, which in Paper I we quantified as a hard lag of a few ks. Furthermore, at the highest energies, evidence is found of variations of the inverse Compton component. The spectral and temporal information obtained challenge the simplest models currently adopted for the (synchrotron) emission and, most important, provide clues on the particle acceleration process. A scenario accounting for all the observational constraints is discussed, where electrons are injected at progressively higher energies during the development of the flare and the achromatic decay is ascribed to the source light crossing time exceeding the particle cooling timescales.

Chandra unveils a binary Active Galactic Nucleus in Mrk 463

We analyse Chandra, XMM‐Newton and Hubble Space Telescope (HST) data of the doublenucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk 463. The Chandra detection of two luminous (L2‐10 keV = 1.5 × 10 43 and 3.8 × 10 42 erg cm −2 s −1 ), unresolved nuclei in Mrk 463 indicates that this galaxy hosts a binary active galactic nucleus (AGN), with a projected separation of � 3.8 kpc (3.83 ± 0.01 arcsec). While the East nucleus was already known to be a type 2 Seyfert (and this is further confirmed by our Chandra detection of a neutral iron line), this is the first unambiguous evidence in favour of the AGN nature of the West nucleus. Mrk 463 is therefore the clearest case so far for a binary AGN, after NGC 6240.

Extreme synchrotron BL Lac objects - Stretching the blazar sequence

We performed an observational program with the X-ray satellite BeppoSAX to study objects with extreme synchrotron peak frequencies (nu_peak > 1 keV). Of the seven sources observed, four showed peak frequencies in the range 1-5 keV, while one (1ES 1426+428) displayed a flat power law spectrum (alpha= 0.92), locating its synchrotron peak at or above 100 keV. This is the third source of this type ever found, after Mkn 501 and 1ES 2344+514. Our data confirm the large nu_peak variability of this class of sources, compared with lower peaked objects. The high synchrotron peak energies, flagging the presence of high energy electrons, make the extreme BL Lacs also good candidates for TeV emission, and therefore good probes for the IR background.

How Complex is the Obscuration in Active Galactic Nuclei? New Clues from the Suzaku Monitoring of the X-Ray Absorbers in NGC 7582

We present the results of a Suzaku monitoring campaign of the Seyfert 2 galaxy, NGC7582. The source is characterized by very rapid (on timescales even lower than a day) changes of the column density of an inner absorber, together with the presence of constant components arising as reprocessing from a Compton-thick material. The best fitting scenario implies important modifications to the zeroth order view of Unified Models. While the existence of a pc-scale torus is needed in order to produce a constant Compton reflection component and an iron K

X-Ray Emission of Markarian 421: New Clues from Its Spectral Evolution. I. Temporal Analysis

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The BL Lac heart of Centaurus A

emission line, in this Seyfert 2 galaxy this is not viewed along the line of sight. On the other hand, the absorption of the primary continuum is due to another material, much closer to the BH, roughly at the distance of the BLR, which can produce the observed rapid spectral variability. On top of that, the constant presence of a

An optical spectroscopic survey of the 3CR sample of radio galaxies with z < 0.3. I. Presentation of the data ⋆

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