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1 INTRODUCTION Blazars, including BL Lac objects, highly polarized and optically violently variable quasars,and flat-spectrum radio quasars (FSRQs), are characterized by highly variable non-thermalemission which dominates their characteristics from radio to y-ray bands. The mechanismbelieved to be responsible for their broadband emission is synchrotron radiation followed by in-verse Compton (IC) scattering at higher energies (e.g. Blandford & Konigl 1979). Relativisticbeaming of a jet… 相似文献
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Neill Reid 《Monthly notices of the Royal Astronomical Society》2003,342(3):837-850
We present high-resolution echelle spectroscopy of 20 stars in 16 systems catalogued as members of the TW Hydrae association, and 16 stars identified as possible new members. We have calibrated the range of coronal and chromospheric activity expected for such young stars as a function of spectral type by combining our observations with literature data for field and open cluster stars. We also compute space motions for TWA members and candidate members with proper motion measurements, using two techniques to estimate distances to stars lacking direct trigonometric parallax measurements. The mean space motion of the four TWA members with known parallaxes is ( U , V , W : −10.0, −17.8, −4.6) km s−1 . 14 of the candidates have properties inconsistent with cluster membership; the remaining two are potential new members, although further observations are required to confirm this possibility. 相似文献
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Roberto F. Viotti Lucio Angelo Antonelli Sonja Rebecchi Corinne Rossi 《Journal of Astrophysics and Astronomy》2002,23(1-2):19-22
We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary
system η Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse,
this component was the same as outside eclipse, but for a large (×3.5) increase of NH
h
, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly,
at that time the iron 6.7 keV emission line was 40% stronger. BeppoSAX has for the first time found ahard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV
spectrum of η Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal
emission as an alternative model for the core source. 相似文献