排序方式： 共有24条查询结果，搜索用时 609 毫秒
1.
2.
3.
John R. Mattox 《Experimental Astronomy》1991,2(2):75-84
A Monte Carlo simulation shows that the EGRET gamma-ray telescope aboard the GRO satellite does not have sufficient sensitivity to detect linear polarization, even for 100% polarized gamma-ray sources. This is confirmed by analysis of calibration data. Several data selection techniques suggested to enhance polarization sensitivity have been evaluated and found to not significantly improve sensitivity.NRC/NAS RESEARCH ASSOCIATE 相似文献
4.
C. Brocksopp K. E. McGowan H. Krimm O. Godet P. Roming K. O. Mason N. Gehrels M. Still K. Page A. Moretti C. R. Shrader S. Campana J. Kennea 《Monthly notices of the Royal Astronomical Society》2006,365(4):1203-1214
We present Swift observations of the black hole X-ray transient, GRO J1655−40, during the recent outburst. With its multiwavelength capabilities and flexible scheduling, Swift is extremely well suited for monitoring the spectral evolution of such an event. GRO J1655−40 was observed on 20 occasions and data were obtained by all instruments for the majority of epochs. X-ray spectroscopy revealed spectral shapes consistent with the 'canonical' low/hard, high/soft and very high states at various epochs. The soft X-ray source (0.3–10 keV) rose from quiescence and entered the low/hard state, when an iron emission line was detected. The soft X-ray source then softened and decayed, before beginning a slow rebrightening and then spending ∼3 weeks in the very high state. The hard X-rays (14–150 keV) behaved similarly but their peaks preceded those of the soft X-rays by up to a few days; in addition, the average hard X-ray flux remained approximately constant during the slow soft X-ray rebrightening, increasing suddenly as the source entered the very high state. These observations indicate (and confirm previous suggestions) that the low/hard state is key to improving our understanding of the outburst trigger and mechanism. The optical/ultraviolet light curve behaved very differently from that of the X-rays; this might suggest that the soft X-ray light curve is actually a composite of the two known spectral components, one gradually increasing with the optical/ultraviolet emission (accretion disc) and the other following the behaviour of the hard X-rays (jet and/or corona). 相似文献
5.
Cdric Foellmi 《New Astronomy》2009,14(8):674-691
We examine the distance of the two galactic microquasars GRO J1655–40 and A 0620–00 which are potentially the two closest black holes to the Sun. We aim to provide a picture as wide and complete as possible of the problem of measuring the distance of microquasars in our Galaxy. The purpose of this work is to fairly and critically review in great detail every distance method used for these two microquasars in order to show that the distances of probably all microquasars in our Galaxy are much more uncertain than currently admitted. Moreover, we show that many confirmations of quantitative results are often entangled and rely on very uncertain measurements. We also present a new determination of the maximum distance of GRO J1655–40 using red clump giant stars, and show that it confirms our earlier result of a distance less than 2 kpc instead of 3.2 kpc. Because, it then becomes more likely that GRO J1655–40 could originate from the stellar cluster NGC 6242, located at 1.0 kpc, we review the distance estimations of A 0620–00, which is so far the closest black hole with an average distance of about 1.0 kpc. We show that the distance methods used for A 0620–00 are also problematic. Finally, we present a new analysis of spectroscopic and astrometric archival data on this microquasar, and apply the maximum distance method of Foellmi et al. [Foellmi, C., Depagne, E., Dall, T.H., Mirabel, I.F., 2006b. A&A 457, 249]. It appears that A 0620–00 could indeed be even closer to the Sun than currently estimated, and consequently would be the closest known black hole to the Sun. 相似文献
6.
7.
ROTSE‐IIId observations of the Be/X‐ray transient system KS 1947+300 obtained between September 2004 and December 2005 make it possible to study the correlation between optical and X‐ray activity. The optical outburst of 0.1 mag was accompanied by an increase of the X‐ray flux in the 2004 observations. A strong correlation between the optical and X‐ray light curves suggests that the neutron star directly accretes from the outflowing material of the Be star. The nearly zero time lag between X‐ray and optical light curves suggests a heating of the disk of Be star by X‐rays. No optical brightening and X‐ray enhancement was seen in the 2005 observations. There is no indication of an orbital modulation in the optical light curve. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
A. R. King 《Monthly notices of the Royal Astronomical Society》2000,312(3):L39-L41
I show that the Eddington limit implies a critical orbital period P crit (BH)≃2 d beyond which black hole LMXBs cannot appear as persistent systems. The unusual behaviour of GRO J1655–40 may result from its location close to this critical period. 相似文献
9.
Martin E.Beer PhilippPodsiadlowski 《Monthly notices of the Royal Astronomical Society》2002,331(2):351-360
We present ellipsoidal light-curve fits to the quiescent B , V , R and I light curves of GRO J1655–40 (Nova Scorpii 1994). The fits are based on a simple model consisting of a Roche-lobe-filling secondary and an accretion disc around the black hole primary. Unlike previous studies, no assumptions are made concerning the interstellar extinction or the distance to the source; instead these are determined self-consistently from the observed light curves. In order to obtain tighter limits on the model parameters, we used the distance determination from the kinematics of the radio jet as an additional constraint. We obtain a value for the extinction that is lower than was assumed previously; this leads to lower masses for both the black hole and the secondary star of 5.4±0.3 and 1.45±0.35 M⊙ , respectively. The errors in the determination of the model parameters are dominated by systematic errors, in particular arising from uncertainties in the modelling of the disc structure and uncertainties in the atmosphere model for the chemically anomalous secondary in the system. A lower mass of the secondary naturally explains the transient nature of the system if it is in either a late case A or early case B mass-transfer phase. 相似文献
10.