A Long Observation of NGC 5548 by BeppoSAX: The High-Energy Cutoff, Intrinsic Spectral Variability, and a Truly Warm Absorber

NGC 5548 was observed by BeppoSAX in a single long (8 day) observation from 0.2 to 200 keV. We find (1) spectral variation of the source produced by a change of the intrinsic power-law slope; (2) a high-energy cutoff at Ec = 115 keV with a hint of change of Ec with flux; and (3) O VII and O VIII absorption K edges and a possible blended O VII-O VIII K?,? emission feature at 0.54 keV, inconsistent with a purely photoionized gas in equilibrium. We propose that the temperature of the absorbing and emitting gas is ~106 K so that both collisional ionization and photoionization contribute.

[1]  G. Ghisellini,et al.  X-Ray Variability and Correlations in the Two-Phase Disk-Corona Model for Seyfert Galaxies , 1996, astro-ph/9609050.

[2]  槙野 文命,et al.  New horizon of x-ray astronomy : first results from ASCA : Proceedings of the International conference on X-Ray Astronomy, March 8-11, 1994, Tokyo Metropolitan University , 1994 .

[3]  C. Reynolds,et al.  An X-ray spectral study of 24 type 1 active galactic nuclei , 1997 .

[4]  Michel Casse,et al.  Origin and evolution of the elements , 1993 .

[5]  A. Zdziarski,et al.  Angle-dependent Compton reflection of X-rays and gamma-rays , 1995 .

[6]  A. Fabian,et al.  The behaviour of compact non-thermal sources with pair production , 1989 .

[7]  S. Mathur,et al.  Testing Unified X-Ray/Ultraviolet Absorber Models with NGC 5548 , 1995 .

[8]  Bradley M. Peterson,et al.  ANISOTROPIC LINE EMISSION AND THE GEOMETRY OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI , 1992 .

[9]  H. Netzer.  Ionized absorbers, ionized emitters, and the X-ray spectrum of active galactic nuclei , 1993 .

[10]  Hagai Netzer,et al.  ASCA Observations of Seyfert 1 Galaxies. III. The Evidence for Absorption and Emission Due to Photoionized Gas , 1997, astro-ph/9708046.

[11]  K. Nandra,et al.  The complex variable soft X-ray spectrum of NGC 5548 , 1995 .

[12]  K. Nandra,et al.  GINGA observations of the X-ray spectra of Seyfert galaxies. , 1994 .

[13]  K. Nandra,et al.  A ROSAT observation of NGC 5548 , 1993 .

[14]  R. Mushotzky,et al.  A Confirmation of 2--40 keV Spectral Complexity in Seyfert Galaxies , 1995 .

[15]  Carl Heiles,et al.  The bell laboratories H I survey , 1992 .

[16]  D. Crenshaw,et al.  Intrinsic Absorption Lines in the Seyfert 1 Galaxy NGC 5548: Ultraviolet Echelle Spectra from the Space Telescope Imaging Spectrograph , 1999, astro-ph/9903439.

[17]  K. O. Mason,et al.  The Physics of Accretion onto Compact Objects , 1986 .

[18]  Cambridge,et al.  Ionized Absorbers in Active Galactic Nuclei: The Role of Collisional Ionization and Time-evolving Photoionization , 1998 .

[19]  H. Netzer.  X-Ray Lines in Active Galactic Nuclei and Photoionized Gases , 1996 .

[20]  M. Matsuoka,et al.  X-ray spectral signatures of very thick cold matter in the spectra of the Seyfert 1 galaxies NGC 7469 ad IC 4329A , 1990 .

[21]  A. Wandel,et al.  Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. I. Comparing the Photoionization and Reverberation Techniques , 1999 .

[22]  Atomic Data for Permitted Resonance Lines of Atoms and Ions from H to Si, and S, Ar, Ca, and Fe , 1996, atom-ph/9604003.

[23]  Cambridge,et al.  Resonant Absorption in the Active Galactic Nucleus Spectra Emerging from Photoionized Gas: Differences between Steep and Flat Ionizing Continua , 1998, astro-ph/9812392.

[24]  Giorgio Matt,et al.  98 12 39 2 v 1 2 1 D ec 1 99 8 Resonant Absorption in the AGN spectra emerging from photoionized gas : differences between steep and flat ionizing continua , 1998 .

[25]  Marcos Bavdaz,et al.  The low-energy concentrator spectrometer on-board the BeppoSAX X-ray astronomy satellite , 1997 .

[26]  Gerard A. Kriss,et al.  Ultraviolet variability of NGC 5548 : dynamics of the continuum production region and geometry of the broad-line region , 1991 .

[27]  A. Fabian,et al.  The effects of photoionization on X-ray reflection spectra in active galactic nuclei , 1993 .

[28]  M. Feroci,et al.  The high energy instrument PDS on-board the BeppoSAX X{ray astronomy satellite , 1997 .

[29]  T. Turner,et al.  The discovery of an O VII emission line in the ASCA spectrum of the Seyfert galaxy NGC 3783 , 1995 .

[30]  F. Haardt.  Anisotropic Comptonization in thermal plasmas : spectral distribution in plane-parallel geometry , 1993 .

[31]  S. Mathur,et al.  Multiple Velocity Components in the C IV Absorption Line of NGC 5548 , 1998, astro-ph/9901275.

[32]  R. Svensson.  The Nonthermal Pair Model for the X-Ray and Gamma-Ray Spectra from Active Galactic Nuclei , 1994 .

[33]  R. C. Butler,et al.  BeppoSAX, the wide band mission for X-ray astronomy , 1997 .