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111.
Manuela Magliocchetti Steve J. Maddox Ed Hawkins John A. Peacock Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto de Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole A. Jackson Bryn Jones Ofer Lahav Ian Lewis Stuart Lumsden Peder Norberg Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,350(4):1485-1494
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Churyumov K. I. Luk'yanyk I. V. Vlassyuk V. V. Borisov N. V. 《Earth, Moon, and Planets》2002,90(1-4):141-146
We obtained spectra of comet C/1999 S4 (LINEAR) with the UAGS spectrograph(long slit and CCD) installed on the 1-m Zeiss reflector of the SAO of the RAS(Northern Caucuses, Nizhny Arkhyz) on July 23/24, 26/27 and 27/28, 2000. OnJuly 22/23, before the splitting of the cometary nucleus, several emission lines,such as C2, C3, CN, NH, CH, NH2, CO+, H2O+ wereclearly identified in the spectra. The inspections of the CCD spectra obtainedon July 27/28, 2000 reveals only very weak emission lines superimposed on thesolar reflection spectrum. From analyzing the surface brightness profile of C2 along the slit the velocity of separation of two secondary fragments (V = 10 km/h) and the energy of the fragment separation (E = 8.7 × 1015 erg) were estimated. A luminescence cometary continuum of 26% of the total continuum level is detected in the spectra of the comet at 5000 Å. Possible mechanisms of nucleus splitting are discussed. 相似文献
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R. Soria R. P. Fender D. C. Hannikainen A. M. Read I. R. Stevens 《Monthly notices of the Royal Astronomical Society》2006,368(4):1527-1539
We studied the radio source associated with the ultraluminous X-ray source in NGC 5408 ( L X ≈ 1040 erg s−1 ) . The radio spectrum is steep (index ≈−1 ), consistent with optically thin synchrotron emission, not with flat-spectrum core emission. Its flux density (≈0.28 mJy at 4.8 GHz, at a distance of 4.8 Mpc) was the same in the March 2000 and December 2004 observations, suggesting steady emission rather than a transient outburst. However, it is orders of magnitude higher than expected from steady jets in stellar-mass microquasar. Based on its radio flux and spectral index, we suggest that the radio source is either an unusually bright supernova remnant, or, more likely, a radio lobe powered by a jet from the black hole (BH). Moreover, there is speculative evidence that the source is marginally resolved with a radius ∼30 pc. A faint H ii region of similar size appears to coincide with the radio and X-ray sources, but its ionization mechanism remains unclear. Using a self-similar solution for the expansion of a jet-powered electron–positron plasma bubble, in the minimum-energy approximation, we show that the observed flux and (speculative) size are consistent with an average jet power ≈ 7 × 1038 erg s−1 ∼ 0.1 L X ∼ 0.1 L Edd , an age ≈105 yr, a current velocity of expansion ≈80 km s−1 . We briefly discuss the importance of this source as a key to understand the balance between luminosity and jet power in accreting BHs. 相似文献
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A. R. McDonald T. W. B. Muxlow A. Pedlar M. A. Garrett K. A. Wills S. T. Garrington P. J. Diamond P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2001,322(1):100-106
Observations of the starburst galaxy, M82, have been made with a 20-station global very long-baseline interferometry (VLBI) array at λ 18 cm. Maps are presented of the brightest young supernova remnants (SNR) in M82 and the wide-field mapping techniques used in making images over a field of view of ∼1 arcmin with 3-milliarcsecond resolution are discussed. A limit has been placed on the power-law deceleration of the young supernova remnant (SNR) 43.31+592 with an index greater than 0.73±0.11 from observations with the European VLBI Network. Using the global array we have resolved compact knots of radio emission in the source which, with future global observations, will enable better constraints to be placed on the expansion parameters of this SNR.
The latest global observations have also provided high-resolution images of the most compact radio source in M82, 41.95+575. We determine an upper limit to the radial expansion rate along the major axis of 2000 km s−1 . However, the new images also show structure resembling that of collimated ejection which brings into question the previous explanation of the source as being a result of the confinement of a supernova by a high-density circumstellar medium.
It is apparent that we are now able to image the brightest supernova remnants in M82 with a linear scale which allows direct comparison with galactic SNR such as Cassiopeia A. 相似文献
The latest global observations have also provided high-resolution images of the most compact radio source in M82, 41.95+575. We determine an upper limit to the radial expansion rate along the major axis of 2000 km s
It is apparent that we are now able to image the brightest supernova remnants in M82 with a linear scale which allows direct comparison with galactic SNR such as Cassiopeia A. 相似文献
120.
A. Caccianiga M.J.M. Marchã A. Thean J. Dennett-Thorpe 《Monthly notices of the Royal Astronomical Society》2001,328(3):867-872
We present and discuss the results of very-long baseline interferometry (VLBI, EVN) observations of three low-luminosity broad emission line active galactic nuclei (AGNs) carefully selected from a sample of flat-spectrum radio sources (CLASS). Based on the total and the extended radio power at 5 and at 1.4 GHz respectively, these objects should be technically classified as radio-quiet AGN and thus the origin of their radio emission is not clearly understood. The VLBI observations presented in this paper have revealed compact radio cores which imply a lower limit on the brightness temperature of about . This result rules out a thermal origin for the radio emission and strongly suggests an emission mechanism similar to that observed in more powerful radio-loud AGNs. Since, by definition, the three objects show a flat (or inverted) radio spectrum between 1.4 and 8.4 GHz, the observed radio emission could be relativistically beamed. Multi-epoch VLBI observations can confirm this possibility in two years' time. 相似文献