An R-band photopolarimetric variability analysis of the TeV bright blazar W Comae between 2008 February 28 and 2013 May 17 is presented. The source showed a gradual tendency to decrease its mean flux level with a total change of 3 mJy. A maximum and minimum brightness states in the R band of 14.25+/-0.04 and 16.52+/-0.1 mag, respectively, were observed, corresponding to a maximum variation of {Delta}F=5.40 mJy. We estimated a minimum variability timescale of {Delta}t=3.3 days. A maximum polarization degree P=33.8%+/-1.6%, with a maximum variation of {Delta}P=33.2%, was found. One of our main results is the detection of a large rotation of the polarization angle from 78{deg} to 315{deg} ({Delta}{theta}~237{deg}) that coincides in time with the {gamma}-ray flare observed in 2008 June. This result indicates that both optical and {gamma}-ray emission regions could be co-spatial. During this flare, a correlation between the R-band flux and polarization degree was found with a correlation coefficient of r_F-p _=0.93+/-0.11. From the Stokes parameters, we infer the existence of two optically thin synchrotron components that contribute to the polarized flux. One of them is stable with a constant polarization degree of 11%. Assuming a shock-in jet model during the 2008 flare, we estimated a maximum Doppler factor {delta}_D_~27 and a minimum of {delta}_D_~16; a minimum viewing angle of the jet ~2.0{deg}; and a magnetic field B~0.12 G.
We present Chandra observations of nine high-redshift quasars (z=2.7-5.9) discovered by the Sloan Digital Sky Survey with weak or undetectable high-ionization emission lines in their UV spectra (WLQs). Adding archival X-ray observations of six additional sources of this class has enabled us to place the strongest constraints yet on the X-ray properties of this remarkable class of active galactic nuclei (AGNs). Although our data cannot rule out the possibility that the emission lines are overwhelmed by a relativistically boosted continuum, as manifested by BL Lac objects, we find that WLQs are considerably weaker in the X-ray and radio bands than the majority of BL Lacs found at much lower redshifts. If WLQs are high-redshift BL Lacs, then it is difficult to explain the lack of a large parent population of X-ray and radio bright weak-lined sources at high redshift. We also consider the possibility that WLQs are quasars with extreme properties, and in particular that the emission lines are suppressed by high accretion rates. Using joint spectral fitting of the X-ray spectra of 11 WLQs, we find that the mean photon index in the hard X-ray band is consistent with those observed in typical radio-quiet AGNs with no hint of an unusually steep hard-X-ray spectrum. This result poses a challenge to the hypothesis that WLQs have extremely high accretion rates, and we discuss additional observations required to test this idea.
The origin of high-energy emission in blazars jets (i.e., leptonic versus hadronic) has been a longstanding matter of debate. Here, we focus on one variant of hadronic models where proton synchrotron radiation accounts for the observed steady {gamma}-ray blazar emission. Using analytical methods, we derive the minimum jet power (P_j,min_) for the largest blazar sample analyzed to date (145 sources), taking into account uncertainties of observables and jet's physical parameters. We compare P_j,min_ against three characteristic energy estimators for accreting systems, i.e., the Eddington luminosity, the accretion disk luminosity, and the power of the Blandford-Znajek process, and find that P_j,min_ is about 2 orders of magnitude higher than all energetic estimators for the majority of our sample. The derived magnetic field strengths in the emission region require either large amplification of the jet's magnetic field (factor of 30) or place the {gamma}-ray production site at sub-pc scales. The expected neutrino emission peaks at ~0.1-10EeV, with typical peak neutrino fluxes ~10^-4^ times lower than the peak {gamma}-ray fluxes. We conclude that if relativistic hadrons are present in blazar jets, they can only produce a radiatively subdominant component of the overall spectral energy distribution of the blazar's steady emission.
This catalogue is an update of the previous versions. The recent release of the final release of the 2dF quasar catalogue and of the first part of the SLOAN catalogue, almost doubling the number of known QSOs, led us to prepare an updated version of our Catalogue of quasars and active nuclei, which now contains 48921 quasars, 876 BL Lac objects and 15069 active galaxies (including 11777 Seyfert 1). Like the tenth edition, it includes position and redshift as well as photometry (U, B, V) and 6 and 11 cm flux densities when available. The present edition this catalogue contains the quasars with measured redshift known prior to August 1st, 2003.
This catalogue is an update of the the previous versions. It contains 8609 (+172) quasars (defined as brighter than absolute B magnitude -23), 2833 (+978) AGNs (defined as fainter than absolute B magnitude -23), 220 (+49) BL Lac objects from 1662 (+176) references.
This catalogue is an update of the previous versions; as in the previous editions no information about absorption lines of X-ray properties are given, but absolute magnitudes are given, assuming Ho=50km/s/Mpc and q_0_=0. In this edition the 20cm radio flux is listed when available, in place of the 11cm flux. The present edition of this catalogue contains the quasars with measured redshift known prior to January 1st, 2006. It contains 85221 quasars, 1122 BL Lac objects and 21737 active galaxies (including 9628 Seyfert 1s), almost doubling the number listed in the 11th edition. Lists of known lensed quasars (table2.dat) and double quasars (table3.dat) are also given here.
This catalogue is a compilation of all known AGNs presented in a compact and convenient form. It is an update of the previous versions; and as in the previous editions no information about absorption lines of X-ray properties are given, but absolute magnitudes are given, assuming Ho=71km/s/Mpc and q_0_=0 (notice the change of cosmology: Ho was assumed to be 50km/s/Mpc in the previous editions). When available, the 20cm and 6cm radio flux are given. The present edition of this catalogue contains the quasars with measured redshift known prior to July 1st, 2009. It contains 133336 quasars, 1374 BL Lac objects and 34231 active galaxies (including 15627 Seyfert 1's), almost doubling the number listed in the 12th edition. Lists of known lensed quasars (table2.dat) and double quasars (table3.dat) are also given here.
This catalogue is an update of the previous versions. It contains 13214 (+1856) quasars (defined as brighter than absolute B magnitude -23), 4428 (+1094) AGNs (defined as fainter than absolute B magnitude -23) and 462 (+105) BL Lac objects from 2054 (+191) references.
This catalogue is an update of the previous versions. The recent publication of the first release of the 2dF quasar survey (Croom et al., 2001MNRAS.322L..29C, see Cat. <VII/223>) containing nearly 10,000 new QSOs, almost doubled the number of known such objects: there are now 23760 (+10546) quasars (defined as brighter than absolute B magnitude -23), 5751 (+1323) AGNs (defined as fainter than absolute B magnitude -23) of which 2765 are Seyfert 1, and 608 (+146) BL Lac objects from 2173 (+119) references. Like the ninth edition, it includes position and redshift as well as photometry (U, B, V) and 6 and 11 cm flux densities when available. The present edition this catalogue contains the quasars with measured redshift known prior to May 1st, 2001.
This catalogue is an update of the previous versions. It contains 11358 (+2759) quasars (defined as brighter than absolute B magnitude -23), 3334 (+501) AGNs (defined as fainter than absolute B magnitude -23) and 357 (+137) BL Lac objects from 1863 (+201) references.
