1,745,056 research outputs found
The Parsec-Scale Jet of PKS 0637-752
No full textChandra observations of the quasar PKS 0637-752 during its checkout phase resulted in the unexpected detection of a luminous kiloparsec-scale X-ray jet. The apparent superluminal speed of this jet on the parsec-scale, based on two VSOP and four ground-based observations, has proven crucial to understanding the X-ray production in the arcsec-scale jet. We present here for the first time the full details of the ground-based observations used to determine the parsec-scale jet speed, describe the results of a third VSOP observation, and examine the reported jet speed in the light of more recent ground-based VLBI observations. We find some evidence of increased source activity coincident with extrapolated epochs of jet component ejection, although the monitoring of the source is relatively sparse and the ejection epochs are not tightly constrained. We also construct the spectral energy distribution for the nucleus of PKS 0637-752 and show that it can be modelled well in terms of a one-zone synchrotron self-Compton model of an electron-positron jet with a Doppler factor of ∼ 10, consistent with the results of the VLBI observations. © 2006. Astronomical Society of Japan
Space VLBI Observations of Southern Hemisphere Gamma-Ray and Non-Gamma-Ray AGN: First Results for PKS 0637-752
No full textWe present the first results from our VSOP proposal, "γ-ray loud and quiet AGN with VSOP and SHEVE at 5 GHz". This project is aimed at determining what, if anything, differentiates γ-ray-identified radio sources from similar strong, flat-spectrum radio sources which have not been identified as sources of greater than 100 MeV γ-rays. Five VSOP observations have been successfully completed as part of this project during VSOP AO1. One observation has been correlated thus far, a 4.970 GHz observation of PKS 0637-752 from 1997 November 21. We present the VSOP image for PKS 0637-752 and make comparisons between the space VLBI image and ground-based VLBI and Australia Telescope Compact Array (ATCA) images, as well as present ATCA flux density monitoring at 4.8 GHz. A brightness temperature for PKS 0637-752 of 0.7×10 12 K has been determined from the VSOP data and a tentative apparent superluminal speed, from comparison to the ground-based VLBI image, of ∼9c. © 2000 COSPAR. Published by Elsevier Science Ltd
Rapeseed: an alternative crop for Idaho
No full textBulletin no. 752 Moscow, Idaho :University of Idaho, College of Agriculture, Agriculture Experiment Station, 1994-02-01. Author(s): Melfi, J. A.; Withers, Russell V
Periodic structure in the megaparsec-scale jet of pks 0637-752
No full textWe present 18GHz Australia Telescope Compact Array imaging of the megaparsec-scale quasar jet PKS 0637-752 with angular resolution ~0.58". We draw attention to a spectacular train of quasi-periodic knots along the inner 11" of the jet, with average separation 1.1 arcsec (7.6kpc projected). We consider two classes of model to explain the periodic knots: those that involve a static pattern through which the jet plasma travels (e.g., stationary shocks) and those that involve modulation of the jet engine. Interpreting the knots as re-confinement shocks implies the jet kinetic power Qjet ~ 1046erg s-1, but the constant knot separation along the jet is not expected in a realistic external density profile. For models involving modulation of the jet engine, we find that the required modulation period is 2 x 103 yr τ 5 yr. The lower end of this range is applicable if the jet remains highly relativistic on kiloparsec scales, as implied by the IC/CMB model of jet X-ray emission. We suggest that the periodic jet structure in PKS 0637-752 may be analogous to the quasi-periodic jet modulation seen in the microquasar GRS 1915+105, believed to result from limit cycle behavior in an unstable accretion disk. If variations in the accretion rate are driven by a binary black hole, the predicted orbital radius is 0.7 pc ≲ a ≲ 30 pc, which corresponds to a maximum angular separation of ~0.1-5 mas
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Commento all'art. 752 c.p.c.
No full textIl contributo verte sul procedimento di apposizione dei sigilli disciplinato dagli artt. 752 ss. c.p.c
Inscriptions 752 à 764
No full textInscriptions 752 à 764. In: Revue épigraphique du Midi de la France, tome 2, N°52, 1889. pp. 403-413
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