BeppoSAX observations of 1-Jy BL Lacertae objects – I |
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Authors: | Paolo Padovani †‡ Luigi Costamante Paolo Giommi Gabriele Ghisellini rea Comastri Anna Wolter Laura Maraschi Gianpiero Tagliaferri C Megan Urry |
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Institution: | 1Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA;2Universitàdegli Studi di Milano, Milano, Italy;3BeppoSAX Science Data Center, ASI, Via Corcolle 19, I-00131 Roma, Italy;4Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate, Italy;5Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna, Italy;6Osservatorio Astronomico di Brera, Via Brera 28, I-20121 Milano, Italy |
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Abstract: | We present new BeppoSAX observations of seven BL Lacertae objects selected from the 1-Jy sample plus one additional source. The collected data cover the energy range (observer's frame), reaching ~50 keV for one source (BL Lac). All sources characterized by a peak in their multifrequency spectra at infrared/optical energies (i.e., of the low-energy peaked BL Lac type, LBL) display a relatively flat X-ray spectrum, which we interpret as inverse Compton emission. Four objects (two-thirds of the LBLs) show some evidence for a low-energy steepening, which is probably due to the synchrotron tail merging into the inverse Compton component around ~ . If this were generally the case with LBLs, it would explain why the ROSAT spectra of our sources are systematically steeper than the BeppoSAX ones . The broad-band spectral energy distributions fully confirm this picture, and a synchrotron inverse Compton model allows us to derive the physical parameters (intrinsic power, magnetic field, etc.) of our sources. Combining our results with those obtained by BeppoSAX on BL Lacs covering a wide range of synchrotron peak frequency, ν peak, we confirm and clarify the dependence of the X-ray spectral index on ν peak originally found in ROSAT data. |
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Keywords: | galaxies: active BL Lacertae objects: general X-rays: galaxies |
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