XTE J1739-302 is a transient X-ray source with unusually short outbursts, lasting on the order of hours. Here we give a summary of X-ray observations we have made of this object in outburst with the ...Rossi X-Ray Timing Explorer (RXTE) and at a low level of activity with the Chandra X-Ray Observatory, as well as observations made by other groups. Visible and infrared spectroscopy of the mass donor of XTE J1739-302 are presented in a companion paper. The X-ray spectrum is hard both at low levels and in outburst, but somewhat variable, and there is strong variability in the absorption column from one outburst to another. Although no pulsation has been observed, the outburst data from multiple observatories show a characteristic timescale for variability on the order of 1500-2000 s. The Chandra localization (R.A. = 17 super(h)39 super(m)11 58, decl. = -3020' 37 6, J2000.0) shows that despite being located less than 2 from the Galactic center and highly absorbed, XTE J1739-302 is actually a foreground object with a bright optical counterpart. The combination of a very short outburst timescale and a supergiant companion is shared with several other recently discovered systems, forming a class we designate as supergiant fast X-ray transients (SFXTs). Three persistently bright X-ray binaries with similar supergiant companions have also produced extremely short, bright outbursts: Cyg X-1, Vela X-1, and 1E 1145.1-6141.
Long term variability of Cygnus X–1 Pottschmidt, K.; Wilms, J.; Nowak, M. A. ...
Astronomy and astrophysics (Berlin),
09/2003, Letnik:
407, Številka:
3
Journal Article
The variable cyclotron line in GX 301-2 Kreykenbohm, I.; Wilms, J.; Coburn, W. ...
Astronomy and astrophysics (Berlin),
12/2004, Letnik:
427, Številka:
3
Journal Article
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We present pulse phase resolved spectra of the hypergiant high mass X-ray binary GX 301-2. We observed the source in 2001 October with RXTE continuously for a total on-source time of almost 200 ks. ...We model the continuum with both, a heavily absorbed partial covering model and a reflection model. In either case we find that the well known cyclotron resonant scattering feature (CRSF) at ~35 keV is – although present at all pulse phases – strongly variable over the pulse: the line position varies by 25% from 30 keV in the fall of the secondary pulse to 38 keV in the fall of the main pulse where it is deepest. The line variability implies that we are seeing regions of magnetic field strength varying between $3.4\times 10^{12}$ G and $4.2\times 10^{12}$ G.
We present pulse phase-resolved X-ray spectra of the high mass X-ray binary Vela X-1 using the Rossi X-ray Timing Explorer. We observed Vela X-1 in 1998 and 2000 with a total observation time of ~90 ...ksec. We find an absorption feature at $23.3^{+1.3}_{-0.6}~ke\kern -0.09em V$ in the main pulse, that we interpret as the fundamental cyclotron resonant scattering feature (CRSF). The feature is deepest in the rise of the main pulse where it has a width of $7.6^{+4.4}_{-2.2}~ke\kern -0.09em V$ and an optical depth of $0.33^{+0.06}_{-0.13}$. This CRSF is also clearly detected in the secondary pulse, but it is far less significant or undetected during the pulse minima. We conclude that the well known CRSF at $50.9^{+0.6}_{-0.7}~ke\kern -0.09em V$, which is clearly visible even in phase-averaged spectra, is the first harmonic and not the fundamental. Thus we infer a magnetic field strength of $B=2.6\times 10^{12}$ G.
We present the analysis of the approximately three-year long Rossi X-ray Timing Explorerd (RXTE) campaign for monitoring the canonical soft state black-hole candidates LMC X-1 and LMC X-3. In ...agreement with previous observations, we find that the spectra of both sources can be well-described by the sum of a multi-temperature disc blackbody and a power law. In contrast to LMC X-1, which does not exhibit any periodic spectral changes, we find that LMC X-3 exhibits strong spectral variability on time-scales of days to weeks. The variability pattern observed with the RXTE All Sky Monitor reveals that the variability is more complicated than the 99- or 198-d periodicity discussed by Cowley et al. For typical ASM count rates, the luminosity variations of LMC X-3 are due to changes of the phenomenological disc blackbody temperature, kTin, between ∼1 to ∼1.2keV. During episodes of especially low luminosity (ASM count rates ≲0.6countss−1; four such periods are discussed here), kTin strongly decreases until the disc component is undetectable, and the power law significantly hardens to a photon index of Γ ∼ 1.8. These changes are consistent with state changes of LMC X-3 from the soft state to the canonical hard state of galactic black holes. We argue that the long-term variability of LMC X-3 might be owing to a wind-driven limit cycle, such as that discussed by Shields et al.
The variable cyclotron line in GX301-2 KREYKENBOHM, I; WILMS, J; COBURN, W ...
Astronomy and astrophysics (Berlin),
12/2004, Letnik:
427, Številka:
3
Journal Article
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