Low-energy cutoffs and hard X-ray spectra in high-z radio-loud quasars

The Suzaku view of RBS 315

F. Tavecchio, L. Maraschi, G. Ghisellini, Jun Kataoka, L. Foschini, R. M. Sambruna, G. Tagliaferri

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

We present the results from the Suzaku observation of the powerful radio-loud quasar RBS 315 (z = 2.69), for which a previous XMM-Newton observation showed an extremely flat X-ray continuum up to 10 keV (photon index Γ = 1.26) and indications of strong intrinsic absorption (NH ∼ 1022 cm-2, assuming neutral gas). The instrument for hard X-rays, HXD/PIN, allows us a detection of the source up to 50 keV. The broadband continuum (0.5-50 keV) can be well modeled with a power law with slope Γ = 1.5 (definitively softer than the continuum measured by XMM-Newton) above 1 keV with strong deficit of soft photons. The low-energy cutoff can be well fitted, either with intrinsic absorption (with column density NM ∼ 10 22 cm-1 in the quasar rest frame) or with a break in the continuum, with an extremely hard (Γ = 0.7) power law below 1 keV. We construct the spectral energy distribution of the source, using also opticalUV measurements obtained through a quasi-simultaneous observation with UVOT on board Swift observation. The shape of the SED is similar to that of other flat-spectrum radio quasars (FSRQs) with similar power, making this source an excellent candidate for the detection in 7-rays by the Gamma-Ray Large Area Space Telescope (GLAST). We model the SED with the synchrotron inverse Compton model usually applied to FSRQs, showing that the deficit of soft photons can be naturally interpreted as due to an intrinsic curvature of the spectrum near the low-energy end of the IC component, rather than to intrinsic absorption, although the latter possibility cannot be ruled out. We propose that in at least a fraction of the radio-loud QSOs at high redshift, the cutoff in the soft X-ray band can be explained in a similar way. Further studies are required to distinguish between the two alternatives.

Original languageEnglish
Pages (from-to)980-989
Number of pages10
JournalAstrophysical Journal
Volume665
Issue number2 I
DOIs
Publication statusPublished - 2007 Aug 10
Externally publishedYes

Fingerprint

quasars
cut-off
radio
continuums
radio spectra
energy
XMM-Newton telescope
power law
x rays
newton
photons
Fermi Gamma-ray Space Telescope
curvature
neutral gases
spectral energy distribution
rays
synchrotrons
indication
slopes
broadband

Keywords

  • Galaxies: Active
  • Galaxies: Jets
  • Quasars: Individual (RBS 315)
  • X-rays: Galaxies

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Tavecchio, F., Maraschi, L., Ghisellini, G., Kataoka, J., Foschini, L., Sambruna, R. M., & Tagliaferri, G. (2007). Low-energy cutoffs and hard X-ray spectra in high-z radio-loud quasars: The Suzaku view of RBS 315. Astrophysical Journal, 665(2 I), 980-989. https://doi.org/10.1086/519156

Low-energy cutoffs and hard X-ray spectra in high-z radio-loud quasars : The Suzaku view of RBS 315. / Tavecchio, F.; Maraschi, L.; Ghisellini, G.; Kataoka, Jun; Foschini, L.; Sambruna, R. M.; Tagliaferri, G.

In: Astrophysical Journal, Vol. 665, No. 2 I, 10.08.2007, p. 980-989.

Research output: Contribution to journalArticle

Tavecchio, F, Maraschi, L, Ghisellini, G, Kataoka, J, Foschini, L, Sambruna, RM & Tagliaferri, G 2007, 'Low-energy cutoffs and hard X-ray spectra in high-z radio-loud quasars: The Suzaku view of RBS 315', Astrophysical Journal, vol. 665, no. 2 I, pp. 980-989. https://doi.org/10.1086/519156
Tavecchio, F. ; Maraschi, L. ; Ghisellini, G. ; Kataoka, Jun ; Foschini, L. ; Sambruna, R. M. ; Tagliaferri, G. / Low-energy cutoffs and hard X-ray spectra in high-z radio-loud quasars : The Suzaku view of RBS 315. In: Astrophysical Journal. 2007 ; Vol. 665, No. 2 I. pp. 980-989.
@article{8f4a22efff884661b2bf3606a132b593,
title = "Low-energy cutoffs and hard X-ray spectra in high-z radio-loud quasars: The Suzaku view of RBS 315",
abstract = "We present the results from the Suzaku observation of the powerful radio-loud quasar RBS 315 (z = 2.69), for which a previous XMM-Newton observation showed an extremely flat X-ray continuum up to 10 keV (photon index Γ = 1.26) and indications of strong intrinsic absorption (NH ∼ 1022 cm-2, assuming neutral gas). The instrument for hard X-rays, HXD/PIN, allows us a detection of the source up to 50 keV. The broadband continuum (0.5-50 keV) can be well modeled with a power law with slope Γ = 1.5 (definitively softer than the continuum measured by XMM-Newton) above 1 keV with strong deficit of soft photons. The low-energy cutoff can be well fitted, either with intrinsic absorption (with column density NM ∼ 10 22 cm-1 in the quasar rest frame) or with a break in the continuum, with an extremely hard (Γ = 0.7) power law below 1 keV. We construct the spectral energy distribution of the source, using also opticalUV measurements obtained through a quasi-simultaneous observation with UVOT on board Swift observation. The shape of the SED is similar to that of other flat-spectrum radio quasars (FSRQs) with similar power, making this source an excellent candidate for the detection in 7-rays by the Gamma-Ray Large Area Space Telescope (GLAST). We model the SED with the synchrotron inverse Compton model usually applied to FSRQs, showing that the deficit of soft photons can be naturally interpreted as due to an intrinsic curvature of the spectrum near the low-energy end of the IC component, rather than to intrinsic absorption, although the latter possibility cannot be ruled out. We propose that in at least a fraction of the radio-loud QSOs at high redshift, the cutoff in the soft X-ray band can be explained in a similar way. Further studies are required to distinguish between the two alternatives.",
keywords = "Galaxies: Active, Galaxies: Jets, Quasars: Individual (RBS 315), X-rays: Galaxies",
author = "F. Tavecchio and L. Maraschi and G. Ghisellini and Jun Kataoka and L. Foschini and Sambruna, {R. M.} and G. Tagliaferri",
year = "2007",
month = "8",
day = "10",
doi = "10.1086/519156",
language = "English",
volume = "665",
pages = "980--989",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2 I",

}

TY - JOUR

T1 - Low-energy cutoffs and hard X-ray spectra in high-z radio-loud quasars

T2 - The Suzaku view of RBS 315

AU - Tavecchio, F.

AU - Maraschi, L.

AU - Ghisellini, G.

AU - Kataoka, Jun

AU - Foschini, L.

AU - Sambruna, R. M.

AU - Tagliaferri, G.

PY - 2007/8/10

Y1 - 2007/8/10

N2 - We present the results from the Suzaku observation of the powerful radio-loud quasar RBS 315 (z = 2.69), for which a previous XMM-Newton observation showed an extremely flat X-ray continuum up to 10 keV (photon index Γ = 1.26) and indications of strong intrinsic absorption (NH ∼ 1022 cm-2, assuming neutral gas). The instrument for hard X-rays, HXD/PIN, allows us a detection of the source up to 50 keV. The broadband continuum (0.5-50 keV) can be well modeled with a power law with slope Γ = 1.5 (definitively softer than the continuum measured by XMM-Newton) above 1 keV with strong deficit of soft photons. The low-energy cutoff can be well fitted, either with intrinsic absorption (with column density NM ∼ 10 22 cm-1 in the quasar rest frame) or with a break in the continuum, with an extremely hard (Γ = 0.7) power law below 1 keV. We construct the spectral energy distribution of the source, using also opticalUV measurements obtained through a quasi-simultaneous observation with UVOT on board Swift observation. The shape of the SED is similar to that of other flat-spectrum radio quasars (FSRQs) with similar power, making this source an excellent candidate for the detection in 7-rays by the Gamma-Ray Large Area Space Telescope (GLAST). We model the SED with the synchrotron inverse Compton model usually applied to FSRQs, showing that the deficit of soft photons can be naturally interpreted as due to an intrinsic curvature of the spectrum near the low-energy end of the IC component, rather than to intrinsic absorption, although the latter possibility cannot be ruled out. We propose that in at least a fraction of the radio-loud QSOs at high redshift, the cutoff in the soft X-ray band can be explained in a similar way. Further studies are required to distinguish between the two alternatives.

AB - We present the results from the Suzaku observation of the powerful radio-loud quasar RBS 315 (z = 2.69), for which a previous XMM-Newton observation showed an extremely flat X-ray continuum up to 10 keV (photon index Γ = 1.26) and indications of strong intrinsic absorption (NH ∼ 1022 cm-2, assuming neutral gas). The instrument for hard X-rays, HXD/PIN, allows us a detection of the source up to 50 keV. The broadband continuum (0.5-50 keV) can be well modeled with a power law with slope Γ = 1.5 (definitively softer than the continuum measured by XMM-Newton) above 1 keV with strong deficit of soft photons. The low-energy cutoff can be well fitted, either with intrinsic absorption (with column density NM ∼ 10 22 cm-1 in the quasar rest frame) or with a break in the continuum, with an extremely hard (Γ = 0.7) power law below 1 keV. We construct the spectral energy distribution of the source, using also opticalUV measurements obtained through a quasi-simultaneous observation with UVOT on board Swift observation. The shape of the SED is similar to that of other flat-spectrum radio quasars (FSRQs) with similar power, making this source an excellent candidate for the detection in 7-rays by the Gamma-Ray Large Area Space Telescope (GLAST). We model the SED with the synchrotron inverse Compton model usually applied to FSRQs, showing that the deficit of soft photons can be naturally interpreted as due to an intrinsic curvature of the spectrum near the low-energy end of the IC component, rather than to intrinsic absorption, although the latter possibility cannot be ruled out. We propose that in at least a fraction of the radio-loud QSOs at high redshift, the cutoff in the soft X-ray band can be explained in a similar way. Further studies are required to distinguish between the two alternatives.

KW - Galaxies: Active

KW - Galaxies: Jets

KW - Quasars: Individual (RBS 315)

KW - X-rays: Galaxies

UR - http://www.scopus.com/inward/record.url?scp=35348944020&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=35348944020&partnerID=8YFLogxK

U2 - 10.1086/519156

DO - 10.1086/519156

M3 - Article

VL - 665

SP - 980

EP - 989

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 I

ER -