Alkoholismus

Petry, J.

doi:10.1007/978-3-662-10776-8_74

Cited by 22 publications

(28 citation statements)

References 4 publications

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“…The spectrum given by eq. (3) connects the EGRET data at GeV energies to the TeV spectrum of the HEGRA collaboration (Petry, et al 1996) and follows the spectral steepening in the data above 1 TeV.…”

Section: The Opacity Of Intergalactic Space To the Iirfmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 82%

“…Observations of the γ-ray spectrum of the Crab Nebula from the same groups which have observed Mrk 421 both show agreement that the integral spectral index of the Crab Nebula is ∼1.7 at ∼ 1 TeV (Weekes, et al 1994;Petry, et al 1996). Furthermore, Petry, et al (1996) have shown that the spectrum of the Crab Nebula above 1 TeV is flatter than the corresponding spectrum of Mrk 421. The index of the integral spectrum of Mrk 421 of 2.8±0.6 derived by Petry, et al (1996) is significantly steeper than the value of ∼ 1 needed to connect the GeV and TeV data (see Figure 3).…”

Section: Discussionmentioning

confidence: 82%

“…Furthermore, Petry, et al (1996) have shown that the spectrum of the Crab Nebula above 1 TeV is flatter than the corresponding spectrum of Mrk 421. The index of the integral spectrum of Mrk 421 of 2.8±0.6 derived by Petry, et al (1996) is significantly steeper than the value of ∼ 1 needed to connect the GeV and TeV data (see Figure 3). While preliminary, the data of Mohanty, et al (1993) are also consistent with this conclusion.…”

Section: Discussionmentioning

confidence: 95%

“…In this paper, we calculate the absoption coefficient of intergalactic space using recent theoretical models of the spectral energy distribution (SED) of intergalactic low energy photons in conjunction with recent determinations of the IR background obtained by analysis of COBE data and galaxy counts. After giving our results on the γ-ray optical depth as a function of energy and redshift out to a redshift of 0.54, we apply our calculations to the high-energy γ-ray spectrum of Mrk 421 and compare our results with the published spectral data obtained by the HEGRA group (Petry, et al 1996) and the preliminary spectrum obtained by the Whipple group (Mohanty,et al 1993).…”

Section: Introductionmentioning

confidence: 98%

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On the Absorption of High‐Energy Gamma Rays by Intergalactic Infrared Radiation

Jager

1997

ApJ

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We present a new calculation of the intergalactic γ-ray pair-production absorption coefficient as a function of both energy and redshift up to the redshift of 3C279, z = 0.54.In reexamining this problem, we make use of new observational data on the intergalactic infrared radiation field (IIRF), together with recent theoretical models of the galactic spectral energy distributions of the IIRF from stars and dust reradiation and estimates of the IIRF from galaxy counts and COBE results. We present our results for two fairly well defined IIRF spectral energy distributions, one of which is within 1σ of our previous estimate of the IIRF at ∼ 20 µm. We then apply our results to the γ-ray spectrum of Mrk 421, and obtain good agreement with the observational data, including the recent results of the HEGRA group.Subject headings: γ-rays:theory -infrared:general -quasars:general -quasars:individual (Markarian 421, 3C279) very high energy γ-ray beams from blazars can be used to measure the intergalactic infrared radiation field, since pair-production interactions of γ-rays with intergalactic IR photons will attenuate the high-energy ends of blazar spectra. Determining the intergalactic IR field, in turn, allows us to model the evolution of the galaxies which produce it. As energy thresholds are lowered in both existing and planned ground-based air Cherenkov light detectors (Cresti 1996), cutoffs in the γ-ray spectra of more distant blazars are expected, owing to extinction by the IIRF. These can be used to explore the redshift dependence of the IIRF. Furthermore, by using blazars for a determination of attenuation as a function of redshift, combined with a direct observation of the IR background from the DIRBE detector on COBE, one can, in principle, measure of the Hubble constant H 0 at truly cosmological distances (Salamon, Stecker and De Jager 1994).The potential importance of the photon-photon pair-production process in high energy astrophysics was first pointed out by Nikishov (1961). Unfortunately, his early paper 3 overestimated the energy density of the IIRF by about three orders of magnitude. However, with the discovery of the cosmic microwave background radiation, Jelley (1966) and Gould and Schreder (1967) were quick to point out the opacity of the universe to photons of energy greater than 100 TeV. Stecker (1969) and Fazio and Stecker (1970) generalized these calculations to high redshifts, showing that photons originating at a redshift z will be absorbed above an energy of ∼ 100(1 + z) −2 TeV.An EGRET-strength "grazar" (observed γ-ray blazar) with a hard spectrum extending to multi-TeV energies is potentially detectable with ground-based telescopes (see the review on the Atmospheric Cherenkov Technique by Weekes (1988)). Pair-production interactions with the cosmic microwave background radiation (CBR) will not cut off the γ-ray spectrum of a low-redshift source below an energy of ∼ 100 TeV (see above). However, as pointed out in Paper I, even bright blazars at moderate redshifts (z > 0.1) will suffer absorpt...

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Section: The Opacity Of Intergalactic Space To the Iirfmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 98%

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On the Absorption of High‐Energy Gamma Rays by Intergalactic Infrared Radiation

Jager

1997

ApJ

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Modeling the broadband spectra and variability of blazars

Böttcher

2004

New Astronomy Reviews

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A study of high energy emission from the TeV blazar Mrk 501 during multiwavelength observations in 1996

Kataoka

Mattox

Quinn

et al. 2000

Advances in Space Research

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We present the results of a multiwavelength campaign for Mrk 501 performed in March 1996 with ASCA, EGRET , Whipple, and optical telescopes. The X-ray flux observed with ASCA was 5 times higher than the quiescent level and gradually decreased by a factor of 2 during the observation in March 1996. In the X-ray band, a spectral break was observed around 2 keV. We report here for the first time the detection of high-energy γ-ray flux from Mrk 501 with EGRET with 3.5 σ significance (E > 100 MeV). Higher flux was also observed in April/May 1996, with 4.0 σ significance for E > 100 MeV, and 5.2 σ significance for E > 500 MeV. The γ-ray spectrum was measured to be flatter than most of the γ-ray blazars. We find that the multiband spectrum in 1996 is consistent with that calculated from a one-zone SSC model where X-rays are produced via synchrotron emission, and γ-rays via inverse Compton scattering of synchrotron photons in a homogeneous region. The flux of TeV γ-rays is consistent with the predictions of the model if the decrease of the Compton-scattering cross section in the Klein-Nishina regime is considered. In the context of this model, we investigate the values of the magnetic field strength and the beaming factor allowed by the observational results. We compare the March 1996 multiwavelength spectrum with that in the flare state in April 1997. Between these two epochs, the TeV flux increase is well correlated with that observed in keV range. The keV and TeV amplitudes during the April 1997 flare are accurately reproduced by a one-zone SSC model, assuming that the population of synchrotron photons in 1996 are scattered by the newly injected relativistic electrons, having maximum energies of γ max ∼ 6 × 10 6 . However, the TeV spectrum observed during March 1996 campaign is flatter than predicted by our models. We find that this cannot be explained by either higher order Comptonization or the contribution of the 'seed' IR photons from the host galaxy for the first-order external radiation Comptonization, but we cannot exclude possible effects of the IR photons that may arise in the parsec-size torus postulated to exist in AGN.

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Alkoholismus

Cited by 22 publications

References 4 publications

On the Absorption of High‐Energy Gamma Rays by Intergalactic Infrared Radiation

On the Absorption of High‐Energy Gamma Rays by Intergalactic Infrared Radiation

Modeling the broadband spectra and variability of blazars

A study of high energy emission from the TeV blazar Mrk 501 during multiwavelength observations in 1996

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