摘要:

The XMM-Newton X-ray observatory pointed the galactic black hole candidate and microquasar GRS 1758-258 in September 2000 for about 10 ks during a program devoted to the scan of the Galactic Center regions. Preliminary results from EPIC MOS camera data are presented here. The data indicate that the source underwent a state transition from its standard low-hard state to an intermediate state. For the first time in this source the ultra-soft component of the accretion disk, which black hole binaries display in intermediate or high-soft states, was clearly detected and measured thanks to the high spectral capabilities of XMM-Newton. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419372

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We analyze a set of three RXTE Target of Opportunity observations of the Galactic microquasar GRS1915+105,observed in April 2000. We concentrate on the timing properties of the source, and examine the properties of a low frequency QPO, with its harmonic, in several energy ranges. The source was found in two different states of the spectro/temporal classification of Belloni &etal; (2000), and exhibited in the three observations a strong, low frequency QPO together with a strong harmonic. We discuss the properties of the QPO, of its harmonic and of their spectral behavior in the framework of the Accretion Ejection Instability (AEI) (Tagger & Pellat, 1999; Varnie`re, Rodriguez & Tagger, 2001; Rodriguez &etal;, 2001). ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419373

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The most popular models for the complex phase and time lags in the rapid aperiodic variability of Galactic X-ray binaries are based Comptonization of soft seed photons in a hot corona, where small-scale flares are induced by flares of the soft seed photon input (presumably from a cold accretion disc). However, in their original version, these models have neglected the additional cooling of the coronal plasma due to the increased soft seed photon input, and assumed a static coronal temperature structure. In this paper, our Monte-Carlo/Fokker-Planck code for time-dependent radiation transfer and electron energetics is used to simulate the self-consistent coronal response to the various flaring scenarios that have been suggested to explain phase and time lags observed in some Galactic X-ray binaries. It is found that the predictions of models involving slab-coronal geometries are drastically different from those deduced under the assumption of a static corona. However, with the inclusion of coronal cooling they may even be more successful than in their original version in explaining some of the observed phase and time lag features. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419374

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We present results from a monitoring campaign on Cyg X-1 during a large X-ray flare. During this period, the spectrum of the source evolved significantly: the higher the soft flux the steeper the spectrum. The evolution follows a simple pattern of pivoting around 8–10 keV, which is similar to that observed in the 1996 state transition. The power density spectrum during the flare is typical of the source during a spectral state transition, so do the correlations among temporal properties and the spectral properties. Therefore, an X-ray flare and a spectral state transition appear to be similar phenomenon and the difference seems to be only quantitative. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419375

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We observed Cyg X-1 contiguously with RXTE over one 5.6-day binary orbit. Many X-ray dips were detected in the X-ray light curves, which lie mostly between orbital phases 0.8 and 1.2 (with phase 0.0 or 1.0 defined as the times of superior conjunction of the black hole), but dips were also seen at other orbital phases. We discovered that the dips fall into two distinct categories, based on their spectral properties. One (common) type exhibits additional energy-dependent attenuation of X-ray emission at the lowest energies during a dip, which is characteristic of photoelectric absorption, but the other type shows nearly energy-independent attenuation up to at least 20 keV. Moreover, the former seems to occur around superior conjunction but the latter almost at the opposite side of the binary orbit (around phase 0.6), based on limited statistics. Therefore, the first type of dips are likely caused by density enhancement in an inhomogeneous wind of the companion star, while the second type might be due to partial obstruction of an extended X-ray emitting region by an optically thick trailing tidal stream. Such a tidal stream has been shown to exist in hydrodynamic simulations of wind accretion in high-mass X-ray binaries. We also made an attempt to quantifying the varying amount of absorbing material along the line of sight over the orbit. The column density does seem to be higher, on average, around superior conjunction, but large uncertainties in the measurements make it difficult to draw any definitive conclusions. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419376

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We consider the production of 2.223 MeV radiation resulting from the capture of neutrons in the atmosphere of the secondary in an X-ray binary system, the neutrons being produced in the accretion disk around the compact primary star and radiated in all directions. We have considered several accretion disk models (ADAF, ADIOS, SLE, Uniform-Temperature) and a variety of parameters (accretion rate, mass of the compact object, mass, temperature, and composition of the secondary star, distance between the two objects, etc.). The neutron production rates are calculated by a network of nuclear reactions in the accretion disk, and this is handled by a reaction-rate formulation taking into account the structure equations given by each accretion model. The processes undergone by the neutrons in the atmosphere of the companion star are studied in detail, including thermalization, elastic and inelastic scatterings, absorption, escape from the surface, decay, and capture by protons. The radiative transfer of the 2.22 MeV photons is treated separately, taking into consideration the composition and density of the star’s atmosphere. We compute neutron production rates in each model and set of parameters. The final flux of the 2.22 MeV radiation that can be detected from earth is calculated taking into account the distance to the source, the direction of observation with respect to the binary system frame, and the rotation of the source, as this can lead to an observable periodicity in the flux. We have produced spectra of the line, where rotational Doppler shift effects can lead to changes in the spectra that are measurable by INTEGRAL’s spectrometer (SPI). ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419377

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The Galactic Microquasar GRS1915+105was observed by the Narrow Field Instruments on-board BeppoSAX in two pointings during year 2000. We present the preliminary results of wide-band study of the observed variability, carried out also with the wavelet analysis. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419378

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We have used observations from CGRO to study the variation in the MeV emission of Cygnus X-1 between its low and high X-ray states. These data provide a measurement of the spectral variability above 1 MeV. The high state MeV spectrum is found to be much harder than that of the low state MeV spectrum. In particular, the power-law emission seen at hard X-ray energies in the high state spectrum (with a photon spectral index of 2.6) is found to extend out to at least 5 MeV, with no evidence for any cutoff. Here we present the data and describe our efforts to model both the low state and high state spectra using a hybrid thermal/nonthermal model in which the emission results from the Comptonization of an electron population that consists of both a thermal and nonthermal component. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419379

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Special and general relativistic effects on the X-ray emissions, especially the continuum spectra, from the accretion disks around black holes are investigated using the ray-tracing method. Because both the special and general relativistic effects are more important at distances closer to the black hole, the relativistic modifications to the emitted X-ray spectra are more significant at higher energies. In a simple accretion disk precession model, the relativistic effects can account for the energy dependence of the QPO amplitude and phase-lags observed in several black hole binaries. The dramatic QPO phase-lag transitions only show up when the central black hole is spinning rapidly. The narrow distribution of the observed system inclination angles of black hole binaries may be due to the selection effect caused by the relativistic effects around black holes. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419380

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Understanding the properties of the hot corona is very important for studying the accretion disks in black hole X-ray binary systems. Using the Monte-Carlo technique to simulate the inverse Compton scattering process between disk photons and electrons in the hot corona, we have produced two table models in the XSPEC package. Applying the models to the broad-band BeppoSAX observations of the black hole candidate XTEJ2012+381,we demonstrate the power of this table model. Our results indicate that the electron distribution in the corona has a powerlaw shape with a spectral index around 4 and the size of the corona is just several tens of gravitational radius and the inclination angle of the disk is around 60 degrees. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419381

出版商:AIP    

年代:1901

数据来源: AIP