XMM-Newton observations of the BL Lac MS 0737+7441

We report on the XMM-Newton observations of the BL Lac object MS 0737.9+7441 during the performance verification phase. A simple power-law fit provides an adequate description of the integrated spectrum in the 0.2-10 keV energy band. The photon index is slightly steeper in the EPIC pn data with 2.38+-0.01 compared to the EPIC MOS data (2.28+-0.01). The difference is most probably due to the present uncertainties in the calibration of the EPIC MOS and EPIC pn data sets. We report evidence for intrinsic absorption in the distant BL Lac above the Galactic column N_H,Gal=3.2*10^20 cm^-2 which is N_H,fit(z=0.315)= (2.70+-0.20)*10^20cm^-2 in the EPIC pn data and N_H,fit(z=0.315)= (3.25+-0.25)*10^20cm^-2 in the EPIC MOS data assuming neutral gas and solar abundances. The flux variations are found to be of the order of 10 %.Comment: 4 pages, 4 Figures, accepted for publication in the special A&A Letters issue for XMM-Newto

On the relationship between BL Lacertae objects and radio galaxies

We present deep radio images at 1.4 GHz of a large and complete sample of BL Lacertae objects (BL Lacs) selected from the Deep X-ray Radio Blazar Survey (DXRBS). We have observed 24 northern sources with the Very Large Array (VLA) in both its A and C configurations and 15 southern sources with the Australia Telescope Compact Array (ATCA) in its largest configuration. We find that in the DXRBS, as in the 1-Jy survey, which has a radio flux limit roughly ten times higher than the DXRBS, a considerable number (about a third) of BL Lacs can be identified with the relativistically beamed counterparts of Fanaroff-Riley type II (FR II) radio galaxies. We attribute the existence of FR II-BL Lacs, which is not accounted for by current unified schemes, to an inconsistency in our classification scheme for radio-loud active galactic nuclei (AGN). Taking the extended radio power as a suitable measure of intrinsic jet power, we find similar average values for low- (LBL) and high-energy peaked BL Lacs (HBL), contrary to the predictions of the blazar sequence.Comment: 21 pages, 10 figures, accepted by MNRA

Optical Nuclei of Radio-loud AGN and the Fanaroff-Riley Divide

We investigate the nature of the point-like optical ``cores'' that have been found in the centres of the host galaxies of a majority of radio galaxies by the Hubble Space Telescope. We examine the evidence that these optical cores are relativistically beamed, and look for differences in the behaviour of the cores found in radio galaxies of the two Fanaroff-Riley types. We also attempt to relate this behaviour to the properties of the optical nuclei in their highly beamed counterparts (the BL Lac objects and radio-loud quasars) as hypothesized by the simple Unified Scheme. Simple model-fitting of the data suggests that the emission may be coming from a non-thermal relativistic jet. It is also suggestive that the contribution from an accretion disk is not significant for the FRI objects and for the narrow-line radio galaxies of FRII type, while it may be significant for the Broad-line objects, and consistent with the idea that the FRII optical cores seem to suffer from extinction due to an obscuring torus while the FRI optical cores do not. These results are in agreement with the Unified Scheme for radio-loud AGNs.Comment: 16 pages including 7 figures and 6 tables, v3: Accepted for publication in A&

An X-ray selected sample of radio-loud quasars

We construct the first X-ray selected sample of broad line radio-loud AGN from the EMSS survey. In order to test unifying schemes for radio-loud objects, their spectral and statistical properties (both flat and steep spectrum objects) are examined and compared with those of other samples of blazars. The X-ray selection allows us to explore properties of radio-loud quasars 10-100 weaker in the radio band than classical samples. The most convincing interpretation of our results is that there are no radio-loud quasars whose synchrotron emission peak reaches the EUV-soft X-ray band at these (radio) flux levels. Moreover, due to the comparatively weak non-thermal emission, a quasi-thermal component appears to contribute at optical-UV energies. The detection of sources at low radio fluxes also reveals a large population of steep spectrum quasars and the lack of the predicted turnover in the quasar (radio) counts. The evolution of X-ray selected radio-loud quasars does not significantly differ from that of radio-selected ones, and flat spectrum and steep spectrum sources appear to behave quite similarly.Comment: 11 pages, 10 figures, accepted for publication in Astronomy & Astrophysic

The Sedentary Multi-Frequency Survey. I. Statistical Identification and Cosmological Properties of HBL BL Lacs

We have assembled a multi-frequency database by cross-correlating the NVSS catalog of radio sources with the RASSBSC list of soft X-ray sources, obtaining optical magnitude estimates from the Palomar and UK Schmidt surveys as provided by the APM and COSMOS on-line services. By exploiting the nearly unique broad-band properties of High-Energy Peaked (HBL) BL Lacs we have statistically identified a sample of 218 objects that is expected to include about 85% of BL Lacs and that is therefore several times larger than all other published samples of HBLs. Using a subset (155 objects) that is radio flux limited and statistically well-defined we have derived the \vovm distribution and the LogN-LogS of extreme HBLs (fx/fr >= 3E-10 erg/cm2/s/Jansky) down to 3.5 mJy. We find that the LogN-LogS flattens around 20 mJy and that = 0.42 +/- 0.02. This extends to the radio band earlier results, based on much smaller X-ray selected samples, about the anomalous cosmological observational properties of HBL BL Lacs. A comparison with the expected radio LogN-LogS of all BL Lacs (based on a beaming model) shows that extreme HBLs make up roughly 2% of the BL Lac population, independently of radio flux. This result, together with the flatness of the radio logN-logS at low fluxes, is in contrast with the predictions of a recent model which assumes an anti-correlation between peak frequency and bolometric luminosity. The extreme fx/fr flux ratios and high X-ray fluxes of these BL Lacs makes them good candidate TeV sources, some of the brighter (and closer) ones possibly detectable with the current generation of Cerenkov telescopes.Comment: 11 pages, LaTeX, 6 ps figures. Accepted for publication in MNRA

Advances in imaging chest tuberculosis: blurring of differences between children and adults

This article reviews the ongoing role of imaging in the diagnosis of tuberculosis (TB) and its complications. A modern imaging classification of TB, taking into account both adults and children and the blurring of differences in the presentation patterns, must be absorbed into daily practice. Clinicians must not only be familiar with imaging features of TB but also become expert at detecting these when radiologists are unavailable. Communication between radiologists and clinicians with regard to local constraints, patterns of disease, human immunodeficiency virus (HIV) coinfection rates, and imaging parameters relevant for management (especially in drug resistance programs) is paramount for making an impact with imaging, and preserving clinician confidence. Recognition of special imaging, anatomic and vulnerability differences between children and adults is more important than trying to define patterns of disease exclusive to children

XMM-Newton spectroscopy of an X-ray selected sample of RL AGNs

This paper presents the X-ray spectroscopy of an X-ray selected sample of 25 radio-loud (RL) AGNs extracted from the XBSS sample. The main goal is to study the origin of the X-ray spectral differences usually observed between radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ AGNs has been also extracted from the same XBSS sample and studied together with the sample of RL AGNs. We have focused the analysis on the distribution of the X-ray spectral indices of the power-law component that models the large majority of the spectra in both samples. We find that the mean X-ray energy spectral index is very similar in the 2 samples and close to alpha_X~1. However, the intrinsic distribution of the spectral indices is significantly broader in the sample of RL AGNs. In order to investigate the origin of this difference, we have divided the RL AGNs into blazars and ``non-blazars'', on the basis of the available optical and radio information. We find strong evidence that the broad distribution observed in the RL AGN sample is mainly due to the presence of the blazars. Furthermore, within the blazar class we have found a link between the X-ray spectral index and the value of the radio-to-X-ray spectral index suggesting that the observed X-ray emission is directly connected to the emission of the relativistic jet. This trend is not observed among the ``non-blazars'' RL AGNs. This favours the hypothesis that, in these latter sources, the X-ray emission is not significantly influenced by the jet emission and it has probably an origin similar to the RQ AGNs. Overall, the results presented here indicate that the observed distribution of the X-ray spectral indices in a given sample of RL AGNs is strongly dependent on the amount of relativistic beaming present in the selected sources.Comment: 18 pages, 10 figures, accepted for publication in A&

Social Class

Discussion of class structure in fifth-century Athens, historical constitution of theater audiences, and the changes in the comic representation of class antagonism from Aristophanes to Menander

Reflection Groups, Generalized Schur Functions, and the Geometry of Majorization

1 online resource (PDF, 91 pages

Generating O(n) with Reflections

1 online resource (PDF, 10 pages