2,350 research outputs found
Unifying B2 radio galaxies with BL Lacertae objects
No full textIn an earlier paper we presented nuclear X-ray flux densities, measured with ROSAT, for the B2 bright sample of nearby low-luminosity radio galaxies. In this paper we construct a nuclear X-ray luminosity function for the B2 radio galaxies, and discuss the consequences of our results for models in which such radio galaxies are the parent population of BL Lacertae (BL Lac) objects. Based on our observations of the B2 sample, we use Monte Carlo techniques to simulate samples of beamed radio galaxies, and use the selection criteria of existing samples of BL Lac objects to compare our simulated results to what is observed. We find that previous analytical results are not applicable since the BL Lac samples are selected on beamed flux density. A simple model in which BL Lacs are the moderately beamed (gammasimilar to 3) counterparts of radio galaxies, with some random dispersion (similar to0.4 decades) in the intrinsic radio-X-ray relationship, can reproduce many of the features of the radio-selected and X-ray-selected BL Lac samples, including their radio and X-ray luminosity functions and the distributions of their radio-to-X-ray spectral indices. In contrast, models in which the X-ray and radio emission have systematically different beaming parameters cannot reproduce important features of the radio-galaxy and BL Lac populations, and recently proposed models in which the radio-to-X-ray spectral index is a function of source luminosity cannot in themselves account for the differences in the slopes of the radio- and X-ray-selected BL Lac luminosity functions. The redshift distribution and number counts of the X-ray-selected Einstein Medium Sensitivity Survey (EMSS) sample are well reproduced by our best models, supporting a picture in which these objects are beamed Fanaroff-Riley type I radio galaxies with intrinsic luminosities similar to those of the B2 sample. However, we cannot match the redshift distribution of the radio-selected 1-Jy sample, and it is likely that a population of Fanaroff-Riley type II radio galaxies is responsible for the high-redshift objects in this sample, in agreement with previously reported results on the sample's radio and optical emission-line properties.</p
On the relationship between BL Lacertae objects and radio galaxies.
No full textWe 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 (δ≳− 30°) 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 10 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. 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
Convergences in perfect BL-algebras
No full textThe aim of the paper is to investigate some concepts of convergence in the class of
perfect BL-algebras. Similarity convergence was developed by G. Georgescu and A. Popescu in
the case of the residuated lattices, while the convergence with a fixed regulator was studied
by Cernák for lattice-ordered groups and MV-algebras and by the author for residuated lattices. In this paper we study the similarity convergence and the convergence with a fixed regulator for the perfect BL-algebras. The main result is the construction of Cauchy completion of a perfect BL-algebra.Peer Reviewe
A Return to the Common Reader: Print Culture and the Novel, 1850-1900
No full textIn 1957, Richard Altick's groundbreaking work The English Common Reader transformed the study of book history. The collection aims to conceptualise some of the new directions that the field is taking fifty years afters the publication of this seminal work and to interrogate the category of the ‘common reader’ itself. What do we now mean by the term ‘common reader’? Is it still a useful term in book history and the sociology of literature? Though the history of mass readerships attests to a rise in literacy in the second half of the nineteenth century, and to snobberies and anxieties surrounding the development of a mass reading public, how did different institutional contexts, different groups of readers (such as women, soldiers, prisoners and radicals) and different forms of publication respond differently to the general trend of a growth in literacy? Were there groups of readers or forms of publication, for example, which complicate the picture of a growth in mass literacy and an elite fear of that growth? And who is to be included or excluded from the concept of the ‘common reader’? How did changing concepts of what constituted the ‘common reader’ in the first place contribute to the development of literary and print forms, educational institutions, and concepts of reading and readerships within the period? This privileging does not aim to disassociate the ‘common reader’ from Robert Darnton’s formulation of the author/publisher/reader circuit central to Book History, but rather to more closely analyse the multiple functions and interactions of the reader therein. Importantly, the interrogation of the concept of the ‘common reader’ is brought to bear, in every essay, on questions about the development of the novel in the period. The book offers important textual analyses of literary works by Dickens, Wilkie Collins, Ouida and a range of other popular novelists fruitfully bringing together Book History, print culture and literary methodologies in order to further research into the relationship between the social history of reading and the development of literature in the late nineteenth century. Bringing together a collection of essays, each of which explores distinctive cases of constructions of the ‘English common reader’, this book will further research in the sociology of literature by taking one of its fundamental categories of thought and exploring the complicated set of sociological, literary and historical assumptions and ideas which both underpin and contest it
A Return to the Common Reader: Print Culture and the Novel, 1850-1900
No full textIn 1957, Richard Altick's groundbreaking work The English Common Reader transformed the study of book history. The collection aims to conceptualise some of the new directions that the field is taking fifty years afters the publication of this seminal work and to interrogate the category of the ‘common reader’ itself. What do we now mean by the term ‘common reader’? Is it still a useful term in book history and the sociology of literature? Though the history of mass readerships attests to a rise in literacy in the second half of the nineteenth century, and to snobberies and anxieties surrounding the development of a mass reading public, how did different institutional contexts, different groups of readers (such as women, soldiers, prisoners and radicals) and different forms of publication respond differently to the general trend of a growth in literacy? Were there groups of readers or forms of publication, for example, which complicate the picture of a growth in mass literacy and an elite fear of that growth? And who is to be included or excluded from the concept of the ‘common reader’? How did changing concepts of what constituted the ‘common reader’ in the first place contribute to the development of literary and print forms, educational institutions, and concepts of reading and readerships within the period? This privileging does not aim to disassociate the ‘common reader’ from Robert Darnton’s formulation of the author/publisher/reader circuit central to Book History, but rather to more closely analyse the multiple functions and interactions of the reader therein. Importantly, the interrogation of the concept of the ‘common reader’ is brought to bear, in every essay, on questions about the development of the novel in the period. The book offers important textual analyses of literary works by Dickens, Wilkie Collins, Ouida and a range of other popular novelists fruitfully bringing together Book History, print culture and literary methodologies in order to further research into the relationship between the social history of reading and the development of literature in the late nineteenth century. Bringing together a collection of essays, each of which explores distinctive cases of constructions of the ‘English common reader’, this book will further research in the sociology of literature by taking one of its fundamental categories of thought and exploring the complicated set of sociological, literary and historical assumptions and ideas which both underpin and contest it
A Return to the Common Reader: Print Culture and the Novel, 1850-1900
No full textIn 1957, Richard Altick's groundbreaking work The English Common Reader transformed the study of book history. The collection aims to conceptualise some of the new directions that the field is taking fifty years afters the publication of this seminal work and to interrogate the category of the ‘common reader’ itself. What do we now mean by the term ‘common reader’? Is it still a useful term in book history and the sociology of literature? Though the history of mass readerships attests to a rise in literacy in the second half of the nineteenth century, and to snobberies and anxieties surrounding the development of a mass reading public, how did different institutional contexts, different groups of readers (such as women, soldiers, prisoners and radicals) and different forms of publication respond differently to the general trend of a growth in literacy? Were there groups of readers or forms of publication, for example, which complicate the picture of a growth in mass literacy and an elite fear of that growth? And who is to be included or excluded from the concept of the ‘common reader’? How did changing concepts of what constituted the ‘common reader’ in the first place contribute to the development of literary and print forms, educational institutions, and concepts of reading and readerships within the period? This privileging does not aim to disassociate the ‘common reader’ from Robert Darnton’s formulation of the author/publisher/reader circuit central to Book History, but rather to more closely analyse the multiple functions and interactions of the reader therein. Importantly, the interrogation of the concept of the ‘common reader’ is brought to bear, in every essay, on questions about the development of the novel in the period. The book offers important textual analyses of literary works by Dickens, Wilkie Collins, Ouida and a range of other popular novelists fruitfully bringing together Book History, print culture and literary methodologies in order to further research into the relationship between the social history of reading and the development of literature in the late nineteenth century. Bringing together a collection of essays, each of which explores distinctive cases of constructions of the ‘English common reader’, this book will further research in the sociology of literature by taking one of its fundamental categories of thought and exploring the complicated set of sociological, literary and historical assumptions and ideas which both underpin and contest it
Convergences in perfect BL-algebras
No full textThe aim of the paper is to investigate some concepts of convergence in the class of
perfect BL-algebras. Similarity convergence was developed by G. Georgescu and A. Popescu in
the case of the residuated lattices, while the convergence with a fixed regulator was studied
by Cernák for lattice-ordered groups and MV-algebras and by the author for residuated lattices. In this paper we study the similarity convergence and the convergence with a fixed regulator for the perfect BL-algebras. The main result is the construction of Cauchy completion of a perfect BL-algebra.Peer Reviewe
A Kpc-scale radio polarization study of PG BL Lacs with the uGMRT
No full textWe present here uGMRT band 4 (~650 MHz) polarization images of 8 BL Lac objects belonging to the Palomar -Green (PG) 'blazar' sample. A large fraction of the sources (~63 per cent ) reveal core-halo radio structures with most of the polarization detected in the inner core-jet regions. PG1101 + 385 and PG2254 + 075 exhibit a 'spine -sheath structure' in polarization. The core-halo and 'spine -sheath' structures are consistent with the Unified Scheme suggestion that BL Lacs are the pole-on beamed counterparts of Fanaroff-Riley (FR) type I radio galaxies. PG1418 + 546 and PG0851 + 203 (OJ287) show the presence of terminal hotspots similar to FR type II radio galaxies. They were also found to be low-spectrally peaked BL Lacs, supportive of the 'blazar envelope' scenario for BL Lacs and quasars. Fractional polarization ranges from 1 to 13 per cent in the cores and 2 to 26 per cent in the inner jets/lobes of the sample BL Lacs. Compared to the varied radio morphology of quasars from the PG 'blazar' sample, the BL Lacs appear to be less diverse. A comparison of the inferred core magnetic (B-) field structures on arcsec(kpc-) scales w.r.t. the Very Long Baseline Interferometry jet direction does not reveal any preferred orientation, suggesting that if large-scale ordered B-fields exist, they do so on scales smaller than probed by the current observations. However, the presence of polarized emission on arcsec-scales suggests that any mixing of thermal plasma with the synchrotron emitting plasma is insufficient to fully depolarize the emission via the internal depolarization process.</p
A Kpc-scale Radio Polarization Study of PG BL Lacs with the uGMRT
No full textWe present here uGMRT band 4 (~650MHz) polarization images of 8 BL~Lac
objects belonging to the Palomar-Green (PG) `blazar' sample. A large fraction
of the sources (~63%) reveal core-halo radio structures with most of the
polarization detected in the inner core-jet regions. PG1101+385 and PG2254+075
exhibit a `spine-sheath structure' in polarization. The core-halo and
`spine-sheath' structures are consistent with the Unified Scheme suggestion
that BL~Lacs are the pole-on beamed counterparts of Fanaroff-Riley (FR) type I
radio galaxies. PG1418+546 and PG0851+203 (OJ287) show the presence of terminal
hotspots similar to FR type II radio galaxies. They were also found to be
low-spectrally peaked BL Lacs, supportive of the `blazar envelope' scenario for
BL~Lacs and quasars. Fractional polarization ranges from 1-13% in the cores and
2-26% in the inner jets/lobes of the sample BL Lacs. Compared to the varied
radio morphology of quasars from the PG `blazar' sample, the BL~Lacs appear to
be less diverse. A comparison of the inferred core magnetic (B-) field
structures on arcsec- (kpc-) scales w.r.t. the Very Long Baseline
Interferometry (VLBI) jet direction does not reveal any preferred orientation,
suggesting that if large-scale ordered B-fields exist, they do so on scales
smaller than probed by the current observations. However, the presence of
polarized emission on arcsec-scales suggests that any mixing of thermal plasma
with the synchrotron emitting plasma is insufficient to fully depolarize the
emission via the internal depolarization process.Comment: 17 pages; 12 figures; MNRAS accepte
Variations in the broad-band spectra of BL Lac objects: millimetre observations of an X-ray-selected sample
No full textObservations at millimetre wavelengths are presented for a representative sample of 22 X-ray-selected BL Lac objects (XBLs). This sample comprises 19 high-energy cut-off BL Lac objects (HBLs), 1 low-energy cut-off BL Lac object (LBL) and 2 ‘intermediate’ sources. Data for LBLs, which are mostly radio-selected BL Lac objects (RBLs), are taken from the literature. It is shown that the radio–millimetre spectral indices of HBLs inline image are slightly steeper than those of the LBLs inline image. A correlation exists between α5–230 and 230 GHz luminosity. While this correlation could be an artefact of comparing two populations of BL Lac objects with intrinsically different radio properties, it is also consistent with the predictions of existing unified schemes that relate BL Lac objects to Fanaroff–Riley class I radio galaxies.
The HBLs have significantly flatter submillimetre–X-ray spectral indices inline image than the LBLs inline image although the two intermediate sources also have intermediate values of α230–X∼−0.9. It is argued that this difference cannot be explained entirely by the viewing-angle hypothesis and requires a difference in physical-source parameters. The α230–X values for the HBLs are close to the canonical value found for large samples of radio sources and thus suggest that synchrotron radiation is the mechanism that produces the X-ray emission. As suggested by Padovani & Giommi, the inverse-Compton mechanism is likely to dominate in the LBLs requiring the synchrotron spectra of these sources to steepen or cut off at lower frequencies than those of the HBLs
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