Related papers: The HRX-BL Lac sample - evolution of BL Lac object…
We report radio imaging and monitoring observations in the frequency range 0.235 - 2.7 GHz during the flaring mode of PKS 2155-304, one of the brightest BL Lac objects. The high sensitivity GMRT observations not only reveal extended…
We report results of a spectroscopic campaign carried out at the 10 m Gran Telescopio Canarias for a sample of 22 BL Lac objects detected (or candidates) at TeV energies, aimed to determine or constrain their redshift. This is of…
We investigate the temporal and colour variability of 897 blazars, comprising 455 BL Lacertae objects (BL Lacs) and 442 Flat Spectrum Radio Quasars (FSRQs), selected from the Roma-BZCAT catalogue, using the multi-band light curves from the…
We study the synchrotron component of the spectral energy distribution (SED) on the sample of 877 blazars using the ASDC SED Builder Tool with available broadband data from the literature. Our sample includes 423 flat-spectrum radio sources…
High-energy observations of extreme BL Lac objects, such as 1ES0229+200 or 1ES 0347-121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic background light and intergalactic magnetic…
A sample of 312 low-frequency peaked BL Lacertae objects (LBLs) and 694 flat spectrum radio quasars (FSRQs) with the parameters both redshift and $\gamma$-ray photon spectral index ($\Gamma _\gamma$) is compiled from the active galactic…
We present new BeppoSAX LECS, MECS, and PDS observations of four flat-spectrum radio quasars (FSRQ) having effective spectral indices alpha_ro and alpha_ox typical of high-energy peaked BL Lacs. Our sources have X-ray-to-radio flux ratios…
Using the sample of radio selected BL Lacertae objects (RBLs) and X-ray selected BL Lacertae objects (XBLs) presented by Sambruna et al. (1996), we calculated the luminosities of radio, optical and X-ray of each source and made the…
Aims: Intranight variation (or microvariation) is a common phenomenon of radio-loud BL Lac objects. However, it is not clear whether the recently found radio-quiet BL Lac objects have the same properties. The occurrence rate of intranight…
We present the analysis of archival data from ROSAT and ASCA of a serendipitous source PKS 2316-423. According to its featureless non-thermal radio/optical continuum, the object has been assumed as a BL Lac candidate in the literature. It…
Extreme high synchrotron peaked blazars (EHBLs) are amongst the most powerful accelerators found in nature. Usually the synchrotron peak frequency of an EHBL is above $10^{17}\,$Hz, i.e., lies in the range of medium to hard X-rays making…
One of the most important problem of the blazar astrophysics is to understand the physical origin of the blazar sequence. In this study, we focus on the GeV gamma-ray variability of blazars and evolution perspective we search the relation…
We have recently proposed a new simplified scenario where blazars are classified as flat-spectrum radio quasars (FSRQs) or BL Lacs according to the prescriptions of unified schemes, and to a varying combination of Doppler boosted radiation…
TeV-emitting BL Lac type blazars represent the extreme end of the blazar population. They are characterized by relatively weak jets and radiatively inefficient accretion disks. Particles accelerated in these jets experience fewer radiative…
We present the first observations at medium-hard X-rays with ASCA in 1998 August--November of four Flat Spectrum Radio Quasars (FSRQs), characterized by unusually steep soft X-ray spectra (photon index, \Gamma_{0.2-2.4 keV} \sim 2-2.5), as…
ROSAT observations of a large sample of bright gamma-ray (E > 100 MeV) blazars are presented. Results of a detailed spectral analysis in the soft $\sim$ 0.1-2.0 keV energy range are discussed in relation to the overall energy distribution…
Most of the extragalactic sources detected at TeV energies are BL Lac objects. They belong to the subclass of "high frequency peaked BL Lacs" (HBLs) exhibiting spectral energy distributions with a lower energy peak in the X-ray band; this…
We study the quasi-simultaneous near-IR, optical, UV, and X-ray photometry of eleven gamma-ray selected blazars for which redshift estimates larger than 1.2 have been recently provided. Four of these objects turn out to be high-power…
The LAT instrument, onboard the Fermi satellite, in its first three months of operation detected more than 100 blazars at more than the 10 sigma level. This is already a great improvement with respect to its predecessor, the instrument…
Context: BL Lacertae objects have been the targets for numerous recent multiwavelength campaigns, continuum spectral variability studies, and theoretical spectral and variability modeling. A meaningful interpretation of the results of such…