The<i>ASCA</i>spectrum of the<i>z</i> = 4.72 blazar GB 1428+4217

Fabian, A. C.; Iwasawa, K.; Celotti, A.; Brandt, W. N.; McMahon, R. G.; Hook, I.

doi:10.1046/j.1365-8711.1998.29511483.x

Cited by 30 publications

(48 citation statements)

References 5 publications

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“…In Fig. 9 the contour plots for the two critical parameters of the model – the gas column density and the ionization state – are shown for the BeppoSAX , ASCA and ROSAT PSPC data (Fabian et al 1997, 1998). A common range of (marginally consistent) parameters, around and column densities of ∼, can be found for the three data sets.…”

Section: Discussionmentioning

confidence: 99%

“…High‐redshift active galactic nuclei (AGN) are powerful tools with which to study the physical and cosmological evolution of massive black holes and their relationship with their host galaxies. A particularly interesting class is formed by several high‐redshift , X‐ray‐bright, radio‐loud quasars (Fabian et al 1997, 1998; Moran & Helfand 1997; Zickgraf et al 1997; Hook & McMahon 1998), which present characteristics typical of blazars. Interestingly, their X‐ray spectra have recently been found systematically to show the presence of spectral flattening in the soft X‐ray band.…”

Section: Introductionmentioning

confidence: 99%

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The blazar GB 1428+4217: a warm absorber at z = 4.72?

Fabian

Celotti

Iwasawa

et al. 2001

Monthly Notices of the Royal Astronomical Society

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BeppoSAX observations of the high‐redshift (z=4.72) blazar GB 1428+4217 confirm the presence of a complex soft X‐ray spectrum first seen with the ROSAT PSPC. Flattening below a rest‐frame energy of 5 keV can be accounted for by absorption from an equivalent column density of (cold) gas with NH∼8×1022 cm−2. Below 2 keV a (variable) excess of a factor of ∼20 above the extrapolated absorbed spectrum is also detected. These findings are consistent with and extend to higher redshifts the correlation between increasing soft X‐ray flattening and increasing z, previously pointed out for large samples of radio‐loud quasars. We propose that such features, including X‐ray absorption and soft excess emission as well as absorption in the optical spectra, can be satisfactorily accounted for by the presence of a highly ionized nuclear absorber with column NH∼1023 cm−2, with properties possibly related to the conditions in the nuclear regions of the host galaxy. High‐energy X‐ray emission consistent with the extrapolation of the medium‐energy spectrum is detected up to ∼300 keV (rest frame).

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The blazar GB 1428+4217: a warm absorber at z = 4.72?

Fabian

Celotti

Iwasawa

et al. 2001

Monthly Notices of the Royal Astronomical Society

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“…In all cases the Ñuxes from di †erent observations agree to within the measurement uncertainty of D30%, and no Ñux variations over time are detected. The quasar GB 1428]4217 has six ROSAT observations and was found to vary by a factor of 2 over a timescale of 2 weeks (or less), which corresponds to less than 2.5 days in the sourceÏs rest frame, a result not unexpected in that this quasar is a Ñat-spectrum radio-loud blazar (Fabian et al 1998(Fabian et al , 1999.…”

Section: èèèèèèèèèèèèèèèmentioning

confidence: 97%

The X-Ray Properties of [CLC][ITAL]z[/ITAL][/CLC] > 4 Quasars

Kaspi

Brandt

Schneider

2000

The Astronomical Journal

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We report on a search for X-ray emission from quasars with redshifts greater than 4 using the ROSAT public database. Our search has doubled the number of z [ 4 quasars detected in X-rays from six to 12. Most of those known prior to this work were radio-loud and X-rayÈselected sources ; our study increases the number of X-rayÈdetected, optically selected z [ 4 quasars from one to seven. We present their basic X-ray properties and compare these with those of lower redshift quasars. We do not Ðnd any evidence for strong broadband spectral di †erences between optically selected z [ 4 quasars and those at lower redshifts.

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“…However, there are some objects with such hard X-ray spectra (Malizia et al 2000 ;Fabian et al 1998) that they can only be explained if But even in these cases, c b ? 1. as long as at least some pair content is required.…”

Section: Ow-energy Injection Break and Pair Contentmentioning

confidence: 99%

Comptonization of Infrared Radiation from Hot Dust by Relativistic Jets in Quasars

Błażejowski

Sikora

Moderski

et al. 2000

ApJ

426

300

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We demonstrate the importance of near-infrared radiation from hot dust for Compton cooling of electrons/positrons in quasar jets. In our model, we assume that the nonthermal radiation spectra observed in optically violent variable (OVV) quasars are produced by relativistic electrons/positrons accelerated in thin shells that propagate down the jet with relativistic speeds. We show that the Comptonization of the near-IR Ñux is likely to dominate the radiative output of OVV quasars in the energy range from tens of keV up to hundreds of MeV, where it exceeds that produced by Comptonization of the UV radiation reprocessed and rescattered in the broad emission line (BEL) region. The main reason for this lies in the fact that the jet encounters the ambient IR radiation over a relatively large distance as compared to the distance where the energy density of the BEL light peaks. In the soft to mid-energy X-ray band, the spectral component resulting from Comptonization of the near-IR radiation joins smoothly with the synchrotron self-Compton component, which may be responsible for the soft X-ray Ñux. At the highest observed c-ray energies, in the GeV range, Comptonization of broad emission lines dominates over other components.

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TheASCAspectrum of thez = 4.72 blazar GB 1428+4217

Cited by 30 publications

References 5 publications

The blazar GB 1428+4217: a warm absorber at z = 4.72?

The blazar GB 1428+4217: a warm absorber at z = 4.72?

The X-Ray Properties of [CLC][ITAL]z[/ITAL][/CLC] > 4 Quasars

Comptonization of Infrared Radiation from Hot Dust by Relativistic Jets in Quasars

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