Spectral evolution of pks 2155-304 observed with bepposax during an active gamma-ray phase

We present the results of BeppoSAX observations of PKS 2155-304 during an intense gamma-ray flare. The source was in a high X-ray state. A temporal analysis of the data reveals a tendency of the amplitude of variations to increase with energy and the presence of a soft lag with a timescale of the order 103 s. A curved continuum spectrum, with no evidence of spectral features, extends up to ~50 keV, while there is indication of a flatter component emerging at higher energies, consistent with the interpretation of the broadband spectral energy distribution (SED) due to synchrotron self-Compton emission from a single region. Notably, the fitting of the SED with such a model is consistent with an interpretation of the detected soft lag due to radiative cooling, supporting the idea that radiation losses play an important role in variability. The observed shifts of the SED peaks between the lowest and highest flux levels can be accounted for by an increase of the "break" energy in the relativistic particle spectrum. The model predicts emission at TeV energies in good agreement with the recently reported detection.

[1]  Milano,et al.  Constraints on the Physical Parameters of TeV Blazars , 1998, astro-ph/9809051.

[2]  J. Bregman,et al.  Optical and radio variability in blazars , 1992 .

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

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

[5]  Santina Piraino,et al.  The high pressure gas scintillation proportional counter on-board the BeppoSAX X-ray astronomy satellite , 1997 .

[6]  P. Padovani,et al.  UNIFIED SCHEMES FOR RADIO-LOUD ACTIVE GALACTIC NUCLEI , 1995, astro-ph/9506063.

[7]  E. Feigelson,et al.  Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 3: Ground-based observations in 1991 November , 1995 .

[8]  Paolo Giommi,et al.  The Connection between X-Ray-- and Radio-selected BL Lacertae Objects , 1995 .

[9]  C. Megan Urry,et al.  VARIABILITY OF ACTIVE GALACTIC NUCLEI , 1997 .

[10]  Paul S. Smith,et al.  Multiwavelength Monitoring of the BL Lacertae Object PKS 2155–304 in 1994 May. III. Probing the Inner Jet through Multiwavelength Correlations , 1997, astro-ph/9704194.

[11]  J. G. Stacy,et al.  High-Energy Gamma Rays from the BL Lacertae Object PKS 2155–304 , 1995 .

[12]  C. Urry,et al.  A ubiquitous absorption feature in the X-ray spectra of BL Lacertae objects , 1991 .

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

[14]  A. Kinney,et al.  The Colorado IUE active galaxy survey. I - Blazars , 1992 .

[15]  A. E. Blaugrund,et al.  The mean life of the 210 keV state in Pt195 , 1965 .

[16]  C. Dermer.  On Spectral and Temporal Variability in Blazars and Gamma-Ray Bursts , 1998, astro-ph/9805289.

[17]  Noriko Y. Yamasaki,et al.  ASCA Observation of an X-Ray/TeV Flare from the BL Lacertae Object Markarian 421 , 1996 .

[18]  R Edelson,et al.  The Discrete Correlation Function: a New Method for Analyzing Unevenly Sampled Variability Data , 1988 .

[19]  R. Schlickeiser,et al.  Nonthermal Compton and Synchrotron Processes in the Jets of Active Galactic Nuclei , 1997 .

[20]  P. M. Chadwick,et al.  Very High Energy Gamma Rays from PKS 2155–304 , 1998, astro-ph/9810209.

[21]  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 .

[22]  A. P. Marscher,et al.  Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 4: Multiwavelength analysis , 1995 .

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

[24]  J. E. Pesce,et al.  Multiwavelength Monitoring of the BL Lacertae Object PKS 2155–304 in 1994 May. II. The IUE Campaign , 1997, astro-ph/9706300.

[25]  C. Canizares,et al.  A sharp X-ray absorption feature in the BL Lacertae object PKS 2155-304 , 1984 .