Multiwavelength Observations of the Extreme X-Ray-selected BL Lacertae Object PG 1553+11 (1ES 1553+113)

Intraday variability in X-ray selected BL Lacertae objects

We present a study of the intraday variability behaviour of two samples of X-ray selected BL Lac objects, the EMSS and EXOSAT samples consisting of 22 and 11 sources, respectively. In both samples we were able to detect intraday variability in less than 40% of the sources only. The duty cycle (the fraction of time, when a BL Lac object is variable) in X-ray selected BL Lac objects is 0.4 or les...

Spectral variability and multiwavelength studies of the high-frequency-peaked BL Lacertae object 1ES 0806+524 with the MAGIC telescopes

SAX and multiwavelength observations of BL Lacertae in 2000

We present two BeppoSAX observations of BL Lac (2200+420) as part of a multiwavelength campaign performed in 2000. The source was in different states of activity: in June, the X–ray spectrum was faint and hard (α ∼ 0.8), with positive residuals towards low energies. In October we detected the highest [2–10] keV flux ever measured for the source. During this observation, the spectrum was soft (α...

Multiwavelength Observations of the BL Lacertae Object PKS 2155 – 304 with XMM - Newton

The optical-UV and X-ray instruments on-board XMM-Newton provide an excellent opportunity to perform simultaneous observations of violently variable objects over a broad wavelength range. The UV and X-ray bright BL Lac object PKS 2155–304 has been repeatedly observed with XMM-Newton about twice per year. In this paper, we present a detailed analysis of the simultaneous multi-wavelength variabil...

Wide band X-ray and optical observations of the BL Lac object 1ES 1959+650 in high state

The blazar 1ES 1959+650 was observed twice by BeppoSAX in September 2001 simultaneously with optical observations. We report here the X-ray data together with the optical, RC magnitude, light curve since August 1995. The BeppoSAX observations were triggered by an active X-ray status of the source. The X-ray spectra are brighter than the previously published X-ray observations, although the sour...