Flux density measurements of a complete sample of faint blazars

We performed observations with the Effelsberg 100-m radio telescope to measure flux densities and polarised emission of sources selected from the "Deep X-ray Radio Blazar Survey" (DXRBS) to better define their spectral index behaviour in the radio band, with the aim to construct a homogeneous sample of blazars. Sources were observed at four different frequencies with the Effelsberg 100-m telescope. We complemented these measurements with flux density data at 1.4GHz derived from the NRAO VLA Sky Survey.The spectral indices of a sample of faint blazars were computed making use of almost simultaneous measurements. Sixty-six percent of the sources can be classified as "bona fide" blazars. Seven objects show a clearly inverted spectral index. Seventeen sources previously classified as flat spectrum radio quasars (FSRQs) are actually steep spectrum radio quasars (SSRQs). The flux densities obtained with the Effelsberg 100-m telescope at 5GHz are compared with the flux densities listed in the Green Bank GB6 survey and in the Parkes-MIT-NRAO PMN catalogue. About 43% of the sources in our sample exhibit flux density variations on temporal scales of 19 or 22 years. We confirm that 75 out of 103 sources of the DXRBS are indeed FSRQs. Twenty-seven sources show a spectral index steeper than -0.5 and should be classified as SSRQs. Polarised emission was detected for 36 sources at 4.85GHz. The median value of the percentage of polarised emission is (5.8+-0.9$)%. Five sources show rotation measure (RM) values >200 rad m^-2.Comment: Accepted for publication in Astronomy and Astrophysic

A Flare in the Jet of Pictor A

A Chandra X-ray imaging observation of the jet in Pictor A showed a feature that appears to be a flare that faded between 2000 and 2002. The feature was not detected in a follow-up observation in 2009. The jet itself is over 150 kpc long and a kpc wide, so finding year-long variability is surprising. Assuming a synchrotron origin of the observed high-energy photons and a minimum energy condition for the outflow, the synchrotron loss time of the X-ray emitting electrons is of order 1200 yr, which is much longer than the observed variability timescale. This leads to the possibility that the variable X-ray emission arises from a very small sub-volume of the jet, characterized by magnetic field that is substantially larger than the average over the jet.Comment: 12 pages, 3 figures, to appear in Ap. J. Letter

Absorption of short-pulse electromagnetic energy by a resistively loaded straight wire

Absorption of short-pulse electromagnetic energy by a resistively loaded straight wire is examined. Energy collected by the wire, load energy, peak load currents, and peak load voltages are found for a wide range of parameters, with particular emphasis on nuclear electromagnetic pulse (EMP) phenomena. A series of time-sequenced plots is used to illustrate pulse propagation on wires when loads and wire ends are encountered. (auth

Absorption of short-pulse electromagnetic energy by a resistively loaded straight wire

Absorption of short-pulse electromagnetic energy by a resistively loaded straight wire is examined. Energy collected by the wire, load energy, peak load currents, and peak load voltages are found for a wide range of parameters, with particular emphasis on nuclear electromagnetic pulse (EMP) phenomena. A series of time-sequenced plots is used to illustrate pulse propagation on wires when loads and wire ends are encountered. (auth

Testing the blazar spectral sequence: X-ray selected blazars

We present simultaneous optical and X-ray data from Swift for a sample of FSRQs selected from the EMSS survey. We present also a complete analysis of Swift and INTEGRAL data on 4 blazars recently discussed as possibly challenging the trends of the "blazar spectral sequence". The SEDs of all these objects are modelled in terms of a general theoretical scheme leading to an estimate of the jets' physical parameters. Our results show that, in the case of the EMSS broad line blazars, X-ray selection does not lead to find sources with synchrotron peaks in the UV/X-ray range, as was the case for X-ray selected BL Lacs. Instead, for a wide range of radio powers all the sources with broad emission lines show similar SEDs, with synchrotron components peaking below the optical/UV range. Of the remaining 4 "anomalous" blazars, two highly luminous sources with broad lines, claimed to possibly emit synchrotron X-rays, are shown to be better described with IC models for their X-ray emission. For one source with weak emission lines (a BL Lac object) a synchrotron peak in the soft X-ray range is confirmed, while for the fourth source, exhibiting lines typical of NLSy1s, no evidence of X-ray emission from a relativistic jet is found. We reexamine the original "blazar spectral sequence" and suggest that the photon ambient, in which the particle acceleration and emission occur, is likely the main factor determining the shape of the blazar SED.Comment: 11 figures and 6 tables. Accepted for publication in MNRA

Estimating the redshift of PKS 0447-439 through its GeV-TeV emission

Context. Blazars are radio-loud active galactic nuclei (AGN) with a jet pointing at small angles towards the observer. The overall emitted spectrum is typically non-thermal, and in some cases the emission and/or absorption lines are so faint as to prevent the determination of the redshift based on optical spectroscopy methods. PKS 0447-439 is a bright blazar recently detected at very high energy. The redshift of the source is still disputed: a recent spectral analysis reports only a lower limit of z > 1.246, which contradicts the previous measure of z = 0.205 reported in the literature. Aims. We aim to give a redshift estimate of the blazar PKS 0447-439 based on combined GeV (Fermi/LAT) and TeV (H.E.S.S.) observations. Methods. Taking into account the absorption of TeV photons by the interaction with the extragalactic background light (EBL), we applied the method we developed in a previous work to derive the redshift of PKS 0447-439. Moreover, we compiled the overall spectral energy distribution (SED) using optical-UV, soft X-ray, and -ray data, nearly simultaneous to the H.E.S.S. observations at TeV energies. Finally we modelled the spectral energy distribution (SED) within the framework of a homogeneous, leptonic synchrotron self-Compton (SSC) model. Results. Using the recent TeV spectrum measured by H.E.S.S. we obtain for PKS 0447-439 a redshift of zrec = 0.20 \pm 0.05, which is our estimate on the source distance. This value agrees very well with the value reported in the literature and confirms that our method can be successfully used to constrain blazars distances. Assuming this distance, the SED can be well fitted with the above mentioned model. The physical parameters that we find suggest a strongly matter-dominated jet. Conclusions. Our analysis confirms that the redshift of PKS 0447-439 is likely 0.2, and supports the result present in the literature.Comment: 5 pages, 3 figures. A&A in pres

Dynamical Black Hole Masses of BL Lac Objects from the Sloan Digital Sky Survey

We measure black hole masses for 71 BL Lac objects from the Sloan Digital Sky Survey with redshifts out to z~0.4. We perform spectral decompositions of their nuclei from their host galaxies and measure their stellar velocity dispersions. Black hole masses are then derived from the black hole mass - stellar velocity dispersion relation. We find BL Lac objects host black holes of similar masses, ~10^{8.5} M_sun, with a dispersion of 0.4 dex, similar to the uncertainties on each black hole measurement. Therefore, all BL Lac objects in our sample have the same indistinguishable black hole mass. These 71 BL Lac objects follow the black hole mass - bulge luminosity relation, and their narrow range of host galaxy luminosities confirm previous claims that BL Lac host galaxies can be treated as standard candles. We conclude that the observed diversity in the shapes of BL Lac object spectral energy distributions is not strongly driven by black hole mass or host galaxy properties.Comment: 9 pages, 5 figures, 1 table. Accepted for publication in MNRA

The blazar S5 0014+813: a real or apparent monster?

A strong hard X-ray luminosity from a blazar flags the presence of a very powerful jet. If the jet power is in turn related to the mass accretion rate, the most luminous hard X-ray blazars should pinpoint the largest accretion rates, and therefore the largest black hole masses. These ideas are confirmed by the Swift satellite observations of the blazar S5 0014+813, at the redshift z=3.366. Swift detected this source with all its three instruments, from the optical to the hard X-rays. Through the construction of its spectral energy distribution we are confident that its optical-UV emission is thermal in origin. Associating it to the emission of a standard optically thick geometrically thin accretion disk, we find a black hole mass of 40 billion solar masses, radiating at 40% the Eddington value. The derived mass is among the largest ever found. Super-Eddington slim disks or thick disks with the presence of a collimating funnel can in principle reduce the black hole mass estimate, but tends to produce spectra bluer than observed.Comment: 5 pages, 2 figures, accepted for publication as a letter in MNRAS after minor revisio