Social Working

Montigny, Gerald A. J. de

doi:10.3138/9781442623361

Cited by 75 publications

(8 citation statements)

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“…EGRET has detected more than 65 active galactic nuclei (AGN) (Hartman et al 1999), almost all of which can be classified as blazars. The blazars seen by EGRET all share the common characteristic that they are radio-loud, flat spectrum sources, with radio spectral indices 0.6 > α > −0.6 (von Montigny et al 1995). Several of these blazars exhibit superluminal motion of components resolved with VLBI (e. g., 3C…”

Section: Discussionmentioning

confidence: 99%

Multiwavelength Examination of theCOS BField 2CG 075+00 Yields a Blazar Identification for 3EG J2016+3657

Mukherjee¹,

Gotthelf²,

Halpern³

et al. 2000

ApJ

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We present a high-energy study of the intriguing COS-B γ-ray field, 2CG 075+00, in order to search for possible counterparts. New EGRET data show that the COS-B emission probably corresponds to two localized γ-ray sources, 3EG J2016+3657 and 3EG J2021+3716. Spectral fits to these EGRET sources, assuming a power-law model, yield photon indices of ∼ 2 for each object. We examine archival ROSAT and ASCA X-ray data which overlap both EGRET error boxes, and find several point sources in the region to a flux limit of approximately 6.5 × 10 −13 erg cm −2 s −1 . We conclude that the most probable candidate for 3EG J2016+3657 is the compact, variable, flat-spectrum radio and millimeter source B2013+370 (G74.87+1.22) which has blazar-like properties.The other source, 3EG J2021+3716, remains unidentified.

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Section: Discussionmentioning

confidence: 99%

Multiwavelength Examination of theCOS BField 2CG 075+00 Yields a Blazar Identification for 3EG J2016+3657

Mukherjee¹,

Gotthelf²,

Halpern³

et al. 2000

ApJ

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“…is the observed flux between the lower and upper bandpass limits ǫ l , ǫ u ) typically drops by 3 orders of magnitude, so a 10 48 erg s −1 source only requires a 10 7 M ⊙ black hole. (ii) There is strong evidence for relativistic beaming in blazars (e.g., through the observation of superluminal jets (von Montigny et al 1995)). In fact, if blazars were not beamed, we would not be able to see any gamma-rays from them due to the high pair production opacity at the source; beaming reduces the luminosity/radius ratio by a factor δ p+1 , allowing photons to escape (Maraschi et al 1992).…”

Section: Gamma-ray Blazarsmentioning

confidence: 99%

Probing High‐Redshift Radiation Fields with Gamma‐Ray Absorption

2001

ApJ

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The next generation of gamma-ray telescopes may be able to observe gamma-ray blazars at high redshift, possibly out to the epoch of reionization. The spectrum of such sources should exhibit an absorption edge due to pair-production against UV photons along the line of sight. One expects a sharp drop in the number density of UV photons at the Lyman edge ǫ L . This implies that the universe becomes transparent after gamma-ray photons redshift below E ∼ (m e c 2 ) 2 /ǫ L ∼ 18GeV. Thus, there is only a limited redshift interval over which GeV photons can pair produce. This implies that any observed absorption will probe radiation fields in the very early universe, regardless of the subsequent star formation history of the universe. Furthermore, measurements of differential absorption between blazars at different redshifts can cleanly isolate the opacity due to UV emissivity at high redshift. An observable absorption edge should be present for most reasonable radiation fields with sufficient energy to reionize the universe. Lyα photons may provide an important component of the pair-production opacity. Observations of a number of blazars at different redshifts will thus allow us to probe the rise in comoving UV emissivity with time.

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“…When this explanation was suggested, only the relatively nearby quasar 3C 273 had been seen in high energy gamma rays [6] (E > 100 MeV ). Since the launch of the Compton Gamma Ray Observatory (CGRO) in 1991, its Energetic Gamma Ray Experiment Telescope (EGRET) has detected 33 bright AGN in high energy gamma rays [7], all of which seem to belong to the "blazar" class. Many more AGN including blazars, which are both bright and relatively close and which were within the EGRET field of view, have not been detected in high energy gamma rays, indicating that not all of these objects are so luminous in gamma rays, or their emission is highly beamed or has a low duty cycle.…”

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confidence: 99%

Origin of the High Energy Extragalactic Diffuse Gamma Ray Background

Dar

Shaviv

1995

Phys. Rev. Lett.

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Recent x-ray observations have discovered that groups and clusters of galaxies contain many more baryons in intergalactic gas than in stars. If high-energy cosmic rays are present there with an average intensity comparable to that observed in our Galaxy, they could produce the extragalactic diffuse gamma radiation.PACS nuInbers: 98.70. Rz, 98.62.Ra, 98.70.Vc Observations with the gamma ray satellite SAS-II have shown [1] that in addition to the galactic diffuse gamma radiation, which varies strongly with direction and can be explained by cosmic ray interactions in the galactic interstellar medium, there appears to be an unaccounted diffuse component which is isotropic at least on a coarse scale and fits well at low photon energies to the extragalactic hard x-ray background radiation.These two features suggest an extragalactic origin of this isotropic component [1]. Its spectrum in the energy range 35 -300 MeV was fitted [2] by a power law with a spectral index -2.35 03 and an intensity Ii, () 100 MeV) = (0.7 -2.3) X 10 s y cm 2 s 'sr ' at energies greater than 100 MeV. Recent analyses [3 -5] of observations with the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory (CGRO) have yielded similar results. For instance, a detailed analysis [3] of the high-quality data from "phase 1" of the EGRET observations obtained the result that the differential intensity of the GBR in the energy range 50 -10 GeV is well represented by dI =96' 10 E cm s 'sr 'GeV dF with n = 2.11~0.05. Equation (1) yields an intensity I~(F ) 100 MeV) = (1.1~0.05) X 10 s y cm 2 X s ' sr ' at energies greater than 100 MeV. Since cosmic ray interactions in the interstellar gas of our Milky Way (MW) galaxy explain [6,7] most of the gamma ray emission of the MW, it was suggested [8] that cosmic ray interactions in external galaxies may explain the extragalactic diffuse gamma background radiation (GBR). However, it was found that the summed emission from cosmic ray interactions in external galaxies falls short by a large factor ()20) in explaining the observed intensity of the GBR [9]. This can be seen easily:The total emissivity of the MW in high energy gamma rays (E ) 100 MeV) was estimated [6] to be L~()100 MeV) = 1.3 X 10 y s ', while its optical luminosity was estimated [10] to be LMw = (2.30 .6) X 10'OLO. The average luminosity density of the Universe was measured [11]to be pL = (1.83~0.35) X 10 hI. OMpc, where Ho = 100h kms ' Mpc ' is the Hubble constant. If the gamma ray and optical emis-(2) sivities of galaxies are approximately proportional to the galactic mass, then their ratio is approximately universal and equal to that of the MW. The intensity of the extragalactic GBR is then given by p, L,(oZ) I, ()F. ) = 4~HO I Mw It yields I~()100 MeV) = (2.6~0.8) X 10 y X cm s ' sr ', independent of the value of h. This intensity is smaller by a factor 30 -80 than the observed intensity of the GBR [12].Whereas the ratio of gas mass to stellar light for the MW is Ms"/LMw = 4.8 X 109 Mo/2. 3 X 10'o Lo = 0 21Mo/...

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Social Working

Cited by 75 publications

References 0 publications

Multiwavelength Examination of theCOS BField 2CG 075+00 Yields a Blazar Identification for 3EG J2016+3657

Multiwavelength Examination of theCOS BField 2CG 075+00 Yields a Blazar Identification for 3EG J2016+3657

Probing High‐Redshift Radiation Fields with Gamma‐Ray Absorption

Origin of the High Energy Extragalactic Diffuse Gamma Ray Background

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