Detection of Exceptional X-Ray Spectral Variability in the TeV BL Lac 1ES 2344+514

We present the results of six BeppoSAX observations of 1ES 2344+514, five of which were taken within a week. 1ES 2344+514, one of the few known TeV BL Lac objects, was detected by the BeppoSAX Narrow Field Instruments between 0.1 to \~50 keV. During the first five closely spaced observations 1ES 2344+514 showed large amplitude luminosity variability, associated with spectacular spectral changes, particularly when compared to the last observation when the source was found to be several times fainter, with a much steeper X-ray spectrum. The energy dependent shape of the lightcurve and the spectral changes imply a large shift (factor of 30 or more in frequency) of the peak of the synchrotron emission. At maximum flux the peak was located at or above 10 keV, making 1ES 2344+514 the second blazar (after MKN501) with the synchrotron peak in the hard X-ray band. The shift, and the corresponding increase in luminosity, might be due to the onset of a second synchrotron component extending from the soft to the hard X-ray band where most of the power is emitted. Rapid variability on a timescale of approximately 5000 seconds has also been detected when the source was brightest.Comment: 7 pages, LaTeX, 6 PostScript figures. Accepted by MNRA

The Deep X-ray Radio Blazar Survey (DXRBS). II. New Identifications

We have searched the archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the WGACAT X-ray database with several publicly available radio catalogs, restricting our candidate list to serendipitous X-ray sources with a flat radio spectrum (alpha_r <= 0.70). This makes up the Deep X-ray Radio Blazar Survey (DXRBS). Here we present new identifications and spectra for 106 sources, including 86 radio-loud quasars, 11 BL Lacertae objects, and 9 narrow-line radio galaxies. Together with our previously published objects and already known sources, our sample now contains 298 identified objects: 234 radio-loud quasars (181 flat-spectrum quasars: FSRQ [alpha_r <= 0.50] and 53 steep-spectrum quasars: SSRQ), 36 BL Lacs, and 28 narrow-line radio galaxies. Redshift information is available for 96% of these. Thus our selection technique is ~ 90% efficient at finding radio-loud quasars and BL Lacs. Reaching 5 GHz radio fluxes ~ 50 mJy and 0.1-2.0 keV X-ray fluxes a few x 10^-14 erg/cm^2/s, DXRBS is the faintest and largest flat-spectrum radio sample with nearly complete (~ 85%) identification. We review the properties of the DXRBS blazar sample, including redshift distribution and coverage of the X-ray-radio power plane for quasars and BL Lacs. Additionally, we touch upon the expanded multiwavelength view of blazars provided by DXRBS. By sampling for the first time the faint end of the radio and X-ray luminosity functions, this sample will allow us to investigate the blazar phenomenon and the validity of unified schemes down to relatively low powers.Comment: 33 pages, 5 figures. Accepted for publication in MNRAS. Postscript file also available at http://www.stsci.edu/~padovani/survey.htm

Large-Scale Regular Morphological Patterns in the Radio Jet of NGC 6251

We report on large-scale, regular morphological patterns found in the radio jet of the nearby radio galaxy NGC 6251. Investigating morphological properties of this radio jet from the nucleus to a radial distance of $\sim$ 300 arcsec ($\approx$ 140 kpc) mapped at 1662 MHz and 4885 MHz by Perley, Bridle, & Willis, we find three chains, each of which consists of five radio knots. We also find that eight radio knots in the first two chains consist of three small sub-knots (the triple-knotty substructures). We discuss the observational properties of these regular morphological patterns.Comment: 8 figures, 15 pages, accepted for publication in A

X-Ray Spectral Variability of PKS 2005-489 During the Spectacular November 1998 Flare

We report on monitoring of the BL Lac object PKS 2005-489 by the Rossi X-ray Timing Explorer (RXTE) in October-December 1998. During these months, the source underwent a spectacular flare; at its peak on November 10, its 2-10 keV flux was $3.33 \times 10^{-10} {\rm ~erg ~cm^{-2} ~s^{-1}}$, over 30 times brighter than in quiescence. During the rising phase, the X-ray spectrum of PKS 2005-489 hardened considerably, reaching $\alpha = 1.32~ (F_\nu \propto \nu^{-\alpha})$ near maximum. During the declining phase, the X-ray spectrum steepened rapidly, reaching $\alpha = 1.82$, then became somewhat harder towards the end of December ($\alpha \sim 1.6$). While such behavior has been seen before, the simplicity, magnitude and duration of this flare allowed us to study it in great detail. We argue that this flare was caused by either the injection of particles into the jet or {\it in situ} particle acceleration, and that the spectral steepening which followed the flare maximum was the result of synchrotron cooling. Contrary to other recently observed blazar flares (e.g., Mkn 501, 3C 279, PKS 2155-304), our results do not imply a major shift in the location of the synchrotron peak during this flare.Comment: ApJ Letters in press, 6 pages, 2 figures Corrected reference

Cross-linguistic study of vocal pathology: perceptual features of spasmodic dysphonia in French-speaking subjects

Clinical characterisation of Spasmodic Dysphonia of the adductor type (SD) in French speakers by Klap and colleagues (1993) appears to differ from that of SD in English. This perceptual analysis aims to describe the phonetic features of French SD. A video of 6 French speakers with SD supplied by Klap and colleagues was analysed for frequency of phonatory breaks, pitch breaks, harshness, creak, breathiness and falsetto voice, rate of production, and quantity of speech output. In contrast to English SD, the French speaking SD patients demonstrated no evidence pitch breaks, but phonatory breaks, harshness and breathiness were prominent features. This verifies the French authors’ (1993) clinical description. These findings suggest that phonetic properties of a specific language may affect the manifestation of pathology in neurogenic voice disorders

The Blazar Sequence: Validity and Predictions

The "blazar sequence" posits that the most powerful BL Lacertae objects and flat-spectrum radio quasars should have relatively small synchrotron peak frequencies, nu_peak, and that the least powerful such objects should have the highest nu_peak values. This would have strong implications for our understanding of jet formation and physics and the possible detection of powerful, moderately high-redshift TeV blazars. I review the validity of the blazar sequence by using the results of very recent surveys and compare its detailed predictions against observational data. I find that the blazar sequence in its simplest form is ruled out. However, powerful flat-spectrum radio quasars appear not to reach the nu_peak typical of BL Lacs. This could indeed be related to some sort of sequence, although it cannot be excluded that it is instead due to a selection effect.Comment: 9 pages, 4 figures, invited talk at the Workshop "The Multi-messenger approach to high energy gamma-ray sources", Barcelona, Spain, July 4-7, 2006, to appear in the proceeding

Stochastic Flux-Freezing and Magnetic Dynamo

We argue that magnetic flux-conservation in turbulent plasmas at high magnetic Reynolds numbers neither holds in the conventional sense nor is entirely broken, but instead is valid in a novel statistical sense associated to the "spontaneous stochasticity" of Lagrangian particle tra jectories. The latter phenomenon is due to the explosive separation of particles undergoing turbulent Richardson diffusion, which leads to a breakdown of Laplacian determinism for classical dynamics. We discuss empirical evidence for spontaneous stochasticity, including our own new numerical results. We then use a Lagrangian path-integral approach to establish stochastic flux-freezing for resistive hydromagnetic equations and to argue, based on the properties of Richardson diffusion, that flux-conservation must remain stochastic at infinite magnetic Reynolds number. As an important application of these results we consider the kinematic, fluctuation dynamo in non-helical, incompressible turbulence at unit magnetic Prandtl number. We present results on the Lagrangian dynamo mechanisms by a stochastic particle method which demonstrate a strong similarity between the Pr = 1 and Pr = 0 dynamos. Stochasticity of field-line motion is an essential ingredient of both. We finally consider briefly some consequences for nonlinear MHD turbulence, dynamo and reconnectionComment: 29 pages, 10 figure

The role of the synchrotron component in the mid infrared spectrum of M 87

We study in detail the mid-infrared Spitzer-IRS spectrum of M 87 in the range 5 to 20 micron. Thanks to the high sensitivity of our Spitzer-IRS spectra we can disentangle the stellar and nuclear components of this active galaxy. To this end we have properly subtracted from the M 87 spectrum, the contribution of the underlying stellar continuum, derived from passive Virgo galaxies in our sample. The residual is a clear power-law, without any additional thermal component, with a zero point consistent with that obtained by high spatial resolution, ground based observations. The residual is independent of the adopted passive template. This indicates that the 10 micron silicate emission shown in spectra of M 87 can be entirely accounted for by the underlying old stellar population, leaving little room for a possible torus contribution. The MIR power-law has a slope alpha ~ 0.77-0.82 (S$_\nu\propto\nu^{-\alpha}$), consistent with optically thin synchrotron emission.Comment: 5 pages, 4 figures, accepted for publication in ApJ main journa