Continuum radiation from active galactic nuclei

Bregman, Joel N.

doi:10.1007/bf00872765

Cited by 83 publications

(53 citation statements)

References 260 publications

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“…This assumes a different origin of the X-ray emission for HBLs and LBLs: namely, an extension of the synchrotron emission likely responsible for the lower energy continuum in the former and inverse Compton (SSC: synchrotron self-Compton) emission in the latter. This would be consistent with the peak of the emitted power being at lower energies for LBLs, suggestive of an extra component taking over at higher frequencies (see Bregman 1990 and references therein). A crucial test of our hypothesis (and in general of any other model wishing to explain the existence of two BL Lac classes) is then the analysis of the spectral shape of the X-ray emission of a large sample of BL Lacs including both HBLs and LBLs.…”

Section: Introductionsupporting

confidence: 65%

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The Rosat X-Ray Spectra of BL Lacertae Objects

Padovani

Giommi²

1996

Extragalactic Radio Sources

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We study the X-ray spectra of 85 BL Lacertae objects using the hardness ratios as given in the WGA catalogue of ROSAT sources. This sample includes all WGA BL Lacs with high-quality data and comprises about 50 per cent of presently known BL Lacs. We find that BL Lacs have energy power-law spectral indices between 0 and 3 with a mean value α x ∼ 1.4. Significant differences, however, are present between high-energy cutoff BL Lacs (HBLs), normally selected in the X-ray band, and lowenergy cutoff BL Lacs (LBLs), generally found in radio surveys. HBLs have steeper X-ray spectral slopes (α x ∼ 1.5) well correlated with α ox , and anti-correlated with the X-ray-to-radio flux ratio and cutoff frequency, with convex overall broad-band spectra. LBLs, on the other hand, have flatter X-ray spectra (α x ∼ 1.1) and concave optical-X-ray continuum. We interpret these results in terms of different mechanisms being responsible for the X-ray emission in the two classes, namely synchrotron and inverse Compton for HBLs and LBLs respectively. The observed differences are consistent with the hypothesis that HBLs and LBLs are powered by essentially the same non-thermal engines differing mainly in their synchrotron cutoff energy.

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Section: Introductionsupporting

confidence: 65%

“…Their multifrequency spectra are in fact fairly smooth over a wide frequency range, suggestive of a common emission process, and lack the thermal features characteristic of the other, more common, AGN, like dust emission in the infrared and (possibly) disk emission in the ultraviolet band (e.g., Bregman 1990).…”

Section: Introductionmentioning

confidence: 99%

The Rosat X-Ray Spectra of BL Lacertae Objects

Padovani

Giommi²

1996

Extragalactic Radio Sources

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“…Commonly, this increase is referred to as a "blue bump", which could be due to emission from an accretion disk (e.g. Bregman 1990). …”

Section: Spectral Energy Distributionsmentioning

confidence: 99%

“…Such an increase in the spectrum of a quasar is commonly referred to thermal emission from an accretion disk (e.g. Bregman 1990), but in that case, although the observations are separated by ∼30 years, the component should not be so strongly variable. A similar behaviour was observed in AO 0235+164, where a variable UV-to-soft-X-ray bump was found (Raiteri et al 2005.…”

Section: −089mentioning

confidence: 99%

Multi-frequency monitoring of γ-ray loud blazars

Bach¹,

Raiteri²,

Villata³

et al. 2006

A&A

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Context. Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how the energy is extracted from the central black hole in radio-loud active galactic nuclei. Aims. Crucial information is provided by broad-band spectral energy distributions (SEDs), their trends with luminosity and correlated multi-frequency variability. With this study we plan to obtain a database of contemporaneous radio-to-optical spectra of a sample of blazars, which are and will be observed by current and future high-energy satellites. Methods. Since December 2004 we are performing a monthly multi-frequency radio monitoring of a sample of 35 blazars at the antennas in Medicina and Noto. Contemporaneous near-IR and optical observations for all our observing epochs are organised. Results. Until June 2006 about 4000 radio measurements and 5500 near-IR and optical measurements were obtained. Most of the sources show significant variability in all observing bands. Here we present the multi-frequency data acquired during the first eighteen months of the project, and construct the SEDs for the best-sampled sources.

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“…In the optical-UV band, the emission is characterized by the "big blue bump", which is present from about 10 nm to 0.3 μm (Sanders et al 1989;Bregman 1990;Zhou et al 1997). This emission is thought to come from an optically thick accretion disk (Shakura & Sunyaev 1973).…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength campaign on Mrk 509

Boissay

Paltani

Ponti

et al. 2014

A&A

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Active galactic nuclei (AGN) are the most luminous persistent objects in the universe. The X-ray domain is particularly important because the X-ray flux represents a significant fraction of the bolometric emission from such objects and probes the innermost regions of accretion disks, where most of this power is generated. An excess of X-ray emission below ∼2 keV, called soft-excess, is very common in Type 1 AGN spectra. The origin of this feature remains debated. Originally modeled with a blackbody, there are now several possibilities to model the soft-excess, including warm Comptonization and blurred ionized reflection. In this paper, we test ionized-reflection models on Mrk 509, a bright Seyfert 1 galaxy for which we have a unique data set, in order to determine whether it can be responsible for the strong soft-excess. We use ten simultaneous XMM-Newton and INTEGRAL observations performed every four days. We present here the results of the spectral analysis, the evolution of the parameters, and the variability properties of the X-ray emission. The application of blurred ionized-reflection models leads to a very strong reflection and an extreme geometry, but fails to reproduce the broad-band spectrum of Mrk 509. Two different scenarios for blurred ionized reflection are discussed: stable geometry and lamp-post configuration. In both cases we find that the model parameters do not follow the expected relations, indicating that the model is fine-tuned to fit the data without physical justification. A large, slow variation in the soft-excess without a counterpart in the hard X-rays could be explained by a change in ionization of the reflector. However, such a change does not naturally follow from the assumed geometrical configuration. Warm Comptonization remains the most probable origin of the soft-excess in this object. Nevertheless, it is possible that both ionized reflection and warm Comptonization mechanisms can explain the soft-excess in all objects, one dominating the other one, depending on the physical conditions of the disk and the corona.

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Continuum radiation from active galactic nuclei

Cited by 83 publications

References 260 publications

The Rosat X-Ray Spectra of BL Lacertae Objects

The Rosat X-Ray Spectra of BL Lacertae Objects

Multi-frequency monitoring of γ-ray loud blazars

Multiwavelength campaign on Mrk 509

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