Swift observations of IBL and LBL objects

Abstract

BL Lacs are an enigmatic class of active galactic nuclei (AGNs), characterized by the non-thermal continuum typically attributed to synchrotron and inverse Compton emission. Depending on the frequency location of the maxima of these components, they are subdivided into three subclasses LBLs, IBLs, and HBLs. We present the results of a set of observations of eight BL Lac objects of LBL and IBL type performed by the XRT and UVOT detectors onboard the Swift satellite between January 2005 and November 2006. We are mainly interested in measuring the spectral parameters, and particularly the steepness between the UV and the X-ray band, useful for determining the classification of these sources. We compare the behavior of these sources with previous XMM-Newton, BeppoSAX obser- vations and with historical data in the X-ray and in the optical band. We are also interested in classifying the sources in our sample on the basis of the observations and comparing them with their classification presented in literature. We performed X-ray spectral analysis of observed BL Lac objects using a simple powerlaw and in a few cases the log-parabolic model. We also combined the UV emission with the low energy X-ray data to We used observational data to classify sources in our sample and derived parameters of their spectral energy distribution. We found that for the IBLs X-rays low states show features of the high energy component, usually interpreted as due to inverse Compton emission. Sources in our sample exhibit a range of temporal UV and X-ray behaviors, some objects having clear and neat correlated UV and X-ray variations (e.g. ON231) and other objects showing no clear (e.g. AO 0235+164) UV and X-ray correlation. Finally, we also note that our estimates of spectral curvature are in the range of that measured for the HBLs.

10 pages, 7 figures, published in A&A

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• Multi-band optical variability of the Blazar S5 0716+714 in outburst state during 2014-2015
• X-ray spectral components of the blazar and binary black hole candidate OJ 287 (2005-2020)
• Radio Weak BL Lac objects in the Fermi era
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• The Intrinsic Properties of Multiwavelength Energy Spectra for Fermi Teraelectronvolt Blazars
• Powerful high energy emission of the remarkable BL Lac object S5 0716+714
• MOMO IV: The complete Swift X-ray and UV/optical light curve and characteristic variability of the blazar OJ 287 during the last two decades
• Searching for gamma-ray blazar candidates among the unidentified INTEGRAL sources
• Swift observations of unidentified radio sources in the revised Third Cambridge Catalogue
• The $\gamma$-ray sky seen at X-ray energies I. Searching for the connection between X-rays and $\gamma$-rays in Fermi BL Lac objects
• MOMO V. Effelsberg, Swift and Fermi study of the blazar and supermassive binary black hole candidate OJ 287 in a period of high activity
• The $\gamma$-ray sky seen at X-ray energies II: the Swift hunt of Fermi BL Lac objects among unidentified gamma-ray sources
• Signature of stochastic acceleration and cooling processes in an outburst phase of the TeV blazar ON 231
• Powerful Radio Sources in the Southern Sky. II. A SWIFT X-Ray Perspective
• Raining in MKW 3s: a Chandra-MUSE analysis of X-ray cold filaments around 3CR 318.1
• Temporal and Spectral Variability of OJ 287 before the April--June 2020 Outburst
• Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2
• Swift-XRT follow-up analysis of unidentified hard X-ray sources