A weak outburst of the millisecond X-ray pulsar SAX J1808.4-3658 in October 1996 as detected from RXTE slew data

Analysis of the RXTE slew data in October 1996 revealed a weak X-ray burst from the millisecond pulsar SAX J 1808.4-3658. The 3–20-keV energy spectrum of the source can be described by a power law with an index of 2.0 and a(3-to 20 keV) luminosity of ～1.4×10³⁵ erg s^?1 (the distance to the source was taken to be 2.5 kpc). Because of the short exposure time, we failed to detect weak pulsations at a frequency of 401 Hz in the source. The (2σ) upper limit of the pulse fraction is ～13%.     

A study of the new X-ray transient RXTE J2123−058 during its post-outburst state

We carried out I , R , V and B photometric observations of the neutron star X-ray binary RXTE J2123−058 shortly after the end of the X-ray outburst in mid-1998. We adopt the low-mass binary model to interpret our observations. After folding our data on the 0.24 821‐d orbital period, and correcting for the steady brightness decline following the outburst, we observed sinusoidal oscillations with hints of ellipsoidal modulations which became progressively more evident. Our data also show that the decline in brightness was faster in the V band than in the R and I bands. This suggests both the cooling of an irradiation-heated secondary star and the fading of an accretion disc over the nights of our observations.     

RXTE ASM的双SSC联合直接解调成像

利用直接解调成像方法对ＲＸＴＥ ＡＳＭ两个指向相同的扫描阴影照像机（ＳＳＣ）的观测,数据进行了联合成像分析,对Ｃｒａｂ天区的研究结果表明,联合成像对源的分辨能力比单ＳＳＣ成像有进上步提高,并且还对银心附近含多个源的一个天区进行了联合成像,分别计算了成像所得的３个Ｘ射线源的强度和位置坐标,并利用源与源之间的位置关系对ＲＸＴＥＡＳＭ定位定标中可能存在的系统误差作出估计,发现以直接解调成像法所得强源的定     

An upper limit on the X-ray luminosity of the microlensing black hole OGLE-1999-BUL-32

Having analyzed the 1999 scanning observations of the Galactic-center region with the PCA spectrometer onboard the RXTE observatory, we obtained upper limits on the flux from the microlensing black hole OGLE-1999-BUL-32 in 1999–2000. We show that the X-ray luminosity of this black hole did not exceed L _x ? 3 × 10³³(d/1kpc)² erg s^?1. Near the maximum amplification of the background star (on June 6, 1999), the upper limit was L _x ? 7 × 10³³(d/1kpc)² erg s^?1.     

The soft X-ray novae, black-hole candidates XTE J2012+381 and XTE J 1550-564

In 1998–1999, the X-ray transients XTE J2012+381 and XTE J1550-564 were observed with the TTM X-ray telescope onboard the Mir-Kvant astrophysical module. Spectral properties of these sources on the descent of the light curve after the secondary maxima of their outbursts are studied. Upper limits on the off-state flux are given. Comparison with other X-ray novae observed with the TTM telescope leads us to conclude that XTE J2012+381 and XTE J 1550-564 are soft X-ray novae. XTE J2012+381 probably belongs to the subclass of long-period X-ray transients.     

A ten-year-long peak of the X-ray flux from the burster 4U 1724-307 in the globular cluster Terzan 2: Evolution of the donor star or the influence of a third star?

We analyze observations of the burster 4U 1724-307 (1E 1724-3045) in the globular cluster Terzan 2 from 1971 until 2001. Uhuru, OSO-8, Einstein, and EXOSAT observations are used. In addition, we analyze data from the TTM telescope onboard the Mir/Kvant observatory and from the ASM and PCA instruments onboard the RXTE observatory. Based on PCA/RXTE scanning observations, we have mapped the sky in the Galactic-center region. The derived light curve of the burster 4U 1724-307 shows the source to be variable on a time scale of 30 years: over the first 20 years of observations (1970–1990), the source flux was approximately constant, while in the 1990s, it rose over ～5 years and declined over approximately the same period, approaching its original value. We discuss several scenarios to explain the behavior of the light curve, including the evolution of the mass outflow rate from the donor-star surface, the episodic appearance of a second source in the globular cluster, and gravitational microlensing. As one of the scenarios, we also consider the possibility that the passage of a third star affects the accretion rate in the binary 4U 1724-307. We show that if this event is responsible for the 10-year-long rise in the luminosity of the burster 4U 1724-307, then the size and period of this binary can be estimated.     

RXTE observations of the strongly absorbed sources IGR J16318-4848 and IGR J16358-4726

We analyzed the RXTE observations of two strongly absorbed sources, IGR J16318-4848 and IGR J16358-4726. We were able to obtain the 3–25 keV spectra of the sources by taking into account the contribution of the Galactic diffuse background to the X-ray flux recorded with the RXTE/PCA spectrometer. The spectra of the sources are well described by a power-law decrease of the photon flux with energy with a photon index of ～1 and strong photoabsorption. The photoabsorption column density n_HL for IGR J16318-4848 derived from the RXTE observation on March 14.1, 2003, is shown to be much higher than its value obtained by the XMM observatory on February 10.7, 2003. This result may suggest that the source has variable absorption that may depend on the orbital phase of the system. We point out that all of the three X-ray sources discovered by the INTEGRAL observatory in the region (l,b)～(336,0) (IGR J16318-4848, IGR J16320-4751, and IGR J16358-4726) have strong intrinsic photoabsorption and may be high-mass binaries. Their proximity to the region where the tangent to the Galactic spiral arm passes, i.e., to the region of enhanced concentration of young high-mass stars, can serve as an indirect confirmation of this assumption. If our assumption about the positions of the sources in the Norma spiral arm is valid, then we can roughly estimate their heliocentric distances: ～6–8 kpc.