2002/01/18 by M. Ravasio, G. Tagliaferri, G. Ghisellini +23
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics and Cosmic Phenomena #BL Lac object #Blazar #Earth Systems and Cosmic Evolution #Flare #Flux (metallurgy) #Light curve #Line (geometry) #Magnetic field #Scientific Research and Discoveries #Spectral line #Synchrotron #astro-ph
paper · pdf · doi:10.1051/0004-6361:20011828
19 pages, 6 figures, accepted by Astronomy & Astrophysics
arxiv created 2002/01/18 · openalex publication_date 2002/03/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report on two BeppoSAX observations of BL Lac (2200+420) performed respectively in June and December 1999, as part of a ToO program to monitor blazars in high states of activity. During both runs the source has been detected up to 100 keV, but it showed quite different spectra: in June it was concave with a very hard component above 5–6 keV (; ); in December it was well fitted by a single power law (). During the first BeppoSAX observation BL Lac showed an astonishing variability episode: the 0.3–2 keV flux doubled in ~ min, while the flux above 4 keV was almost constant. This frequency–dependent event is one of the shortest ever recorded for BL Lac objects and places lower limits on the dimension and magnetic field of the emitting region and on the energy of the synchrotron radiating electrons. A similar but less extreme behaviour is detected also in optical light curves, that display non-simultaneous, smaller fluctuations of ∼ in 20 min. We fit the spectral energy distributions with a homogeneous, one-zone model to constrain the emission region in a very simple but effective SSC + external Compton scenario, highlighting the importance of the location of the emitting region with respect to the Broad Line Region and the relative spectral shape dependence. We compare our data with historical radio to γ-ray Spectral Energy Distributions.