Hard X-ray properties of blazars

We have considered all blazars observed in the X{ray band and for which the slope of the X{ray spectrum is available. We have collected 421 spectra of 268 blazars, including 12 archival unpublished ASCA spectra of 7 blazars whose analysis is presented here. The X{ray spectra of blazars show trends as a function of their power, conrming that the blazar overall energy distribution can be parameterized on the basis of one parameter only, i.e. the bolometric luminosity. This is conrmed by the relatively new hard (2{10 keV) X{ray data. Our results conrm the idea that in low power objects the X{ray emission mechanism is the synchrotron process, dominating both the soft and the hard X{ray emissions. Low energy peaked BL Lac objects are intermediate, often showing harder spectra in the hard X{ray band, suggesting that the synchrotron process dominates in the soft band, with the inverse Compton process dominating at high energies. The most powerful objects have X{ray spectra that are flat both in the soft and in the hard band, consistent with a dominating inverse Compton component.

[1]  G. Ghisellini,et al.  A jet model for the gamma-ray emitting blazar 3C 279 , 1992 .

[2]  E. Feigelson,et al.  Radio-loud active galaxies in the northern ROSAT All-Sky Survey. I. Radio identifications , 1996, astro-ph/9607058.

[3]  I. Hook,et al.  The extreme X-ray luminosity of the z = 4.72 radio-loud quasar GB 1428+4217 , 1997 .

[4]  G. Fossati,et al.  A unifying view of the spectral energy distributions of blazars , 1998 .

[5]  M. Elvis,et al.  ASCA and ROSAT X-Ray Spectra of High-Redshift Radio-loud Quasars , 1997 .

[6]  B. Wilkes,et al.  X-ray spectra of compact extragalactic radio sources , 1990 .

[7]  Simon L. Morris,et al.  Soft X-Ray Observations of a Complete Sample of X-Ray--selected BL Lacertae Objects: Erratum , 1996 .

[8]  T. Takahashi,et al.  ASCA Observations of Blazars and Multiband Analysis , 1998 .

[9]  Paolo Giommi,et al.  A Sample-oriented catalogue of BL Lacertae objects , 1995 .

[10]  Paul T. O'Brien,et al.  X-Ray Observations of the Broad-Line Radio Galaxy 3C 390.3 , 1997, astro-ph/9703013.

[11]  B. Savage,et al.  Ultraviolet and radio observations of Milky Way halo gas , 1992 .

[12]  T. Kii,et al.  AN X-RAY SURVEY OF QUASARS USING ASCA , 1997 .

[13]  G. Fossati,et al.  BeppoSAX Observations of the TeV Blazar Mkn 421 , 1998 .

[14]  T. Turner,et al.  The X-Ray Spectrum of the BL Lacertae Object EXO 055625-3838.6 , 1996 .

[15]  The RGB sample of intermediate BL lacertae objects , 1999, astro-ph/9905133.

[16]  A. Comastri,et al.  On the Soft X-Ray Spectra of γ-Loud Blazars , 1996, astro-ph/9612041.

[17]  Paolo Giommi,et al.  The X-Ray Spectra of Blazars: Analysis of the Complete EXOSAT Archive , 1994 .

[18]  R. Sambruna.  Soft X-Ray Properties of Flat-Spectrum Radio Quasars , 1997 .

[19]  C. Urry,et al.  Testing the Blazar Paradigm: ASCA Observations of Flat-Spectrum Radio Quasars with Steep Soft X-Ray Spectra , 1999, astro-ph/9912273.

[20]  Maarten Schmidt,et al.  VLA observations of objects in the Palomar Bright Quasar Survey , 1989 .

[21]  C. Urry,et al.  An X-Ray Absorption Feature in the BL Lacertae Object H1426+428 , 1997 .

[22]  Unifying models for X-ray selected and Radio selected BL Lac Objects , 1997, astro-ph/9704113.

[23]  ASCA and Contemporaneous Ground-based Observations of the BL Lacertae Objects 1749+096 and 2200+420 (BL Lac) , 1998, astro-ph/9810319.

[24]  Belinda J. Wilkes,et al.  Accurate galactic N(H) values towards quasars and AGN , 1989 .

[25]  C. Lawrence,et al.  Optical polarization of a complete sample of radio sources , 1991 .

[26]  P. J. Huggins,et al.  X-ray emission from red quasars , 1985 .

[27]  K. Nandra,et al.  A Peculiar Emission-Line Feature in the X-Ray Spectrum of the Quasar PKS 0637–752 , 1998, astro-ph/9807349.

[28]  C. Shrader,et al.  X-Ray Spectrum of the High-Polarization Quasar PKS 1510–089 , 1997, astro-ph/9708073.

[29]  J. Dickey,et al.  H I in the Galaxy , 1990 .

[30]  C. Impey,et al.  The optical polarization properties of quasars , 1990 .

[31]  P. Madau,et al.  ON THE ORIGIN OF THE GAMMA -RAY EMISSION IN BLAZARS , 1996 .

[32]  NUCLEAR PHYSICS B , 1994 .

[33]  Martin J. Rees,et al.  Comptonization of Diffuse Ambient Radiation by a Relativistic Jet: The Source of Gamma Rays from Blazars? , 1994 .

[34]  Felix J. Lockman,et al.  The Hubble Space Telescope Quasar Absorption Line Key Project. 10: Galactic H I 21 centimeter emission toward 143 quasars and active Galactic nuclei , 1995 .

[35]  A. Cimatti,et al.  BeppoSAX observations of 2‐Jy lobe‐dominated broad‐line sources ‐‐ I. The discovery of a hard X‐ray component , 1999, astro-ph/9901129.

[36]  Edward M. Murphy,et al.  Galactic H i Column Densities toward Quasars and Active Galactic Nuclei , 1996 .

[37]  P. Padovani,et al.  Relativistic bulk motion in active galactic nuclei , 1993 .