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Register a new userA Delayed Transition to the Hard State for 4U 1630-47 at the End of Its 2010 Outburst
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Authors
John A. Tomsick
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Here we report on Swift and Suzaku observations near the end of an outburst from the black hole transient 4U 1630-47 and Chandra observations when the source was in quiescence. 4U 1630-47 made a transition from a soft state to the hard state ~50 d after the main outburst ended. During this unusual delay, the flux continued to drop, and one Swift measurement found the source with a soft spectrum at a 2-10 keV luminosity of L = 1.07e35 erg/s for an estimated distance of 10 kpc. While such transients usually make a transition to the hard state at L/Ledd = 0.3-3%, where Ledd is the Eddington luminosity, the 4U 1630-47 spectrum remained soft at L/Ledd = 0.008/M10% (as measured in the 2-10 keV band), where M10 is the mass of the black hole in units of 10 solar masses. An estimate of the luminosity in the broader 0.5-200 keV bandpass gives L/Ledd = 0.03/M10%, which is still an order of magnitude lower than typical. We also measured an exponential decay of the X-ray flux in the hard state with an e-folding time of 3.39+/-0.06 d, which is much less than previous measurements of 12-15 d during decays by 4U 1630-47 in the soft state. With the ~100 ks Suzaku observation, we do not see evidence for a reflection component, and the 90% confidence limits on the equivalent width of a narrow iron Kalpha emission line are <40 eV for a narrow line and <100 eV for a line of any width, which is consistent with a change of geometry (either a truncated accretion disk or a change in the location of the hard X-ray source) in the hard state. Finally, we report a 0.5-8 keV luminosity upper limit of <2e32 erg/s in quiescence, which is the lowest value measured for 4U 1630-47 to date.
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We present an analysis of the RXTE observations of 4U 1630-47 during its outburst of 1998. The light curve and the spectral evolution of the outburst were distinctly different from the outbursts of the same source in 1996 and in 1999. Special emphasis of our analysis was on the observations taken during the initial rise of the flux and during the maximum of the outburst. The maximum of the outburst was divided into three plateaus, with almost constant flux within each plateau, and fast jumps between them. The spectral and timing parameters are stable for each individual plateau, but distinctly different between the plateaus. The variability detected on the first plateau is of special interest. During these observations the source exhibits quasi-regular modulations with period of ~10 - 20 s. Our analysis revealed significant differences in spectral and temporal behavior of the source at high and low fluxes during this period of time. The source behavior can be generally explained in the framework of the two-phase model of the accretion flow, involving a hot inner comptonization region and surrounding optically thick disk. The variability and spectral evolution of the source were similar to what was observed earlier for other X-ray Novae. We show that 4U 1630-47 has a variety of properties which are typical for Galactic black hole binaries, both transient and persistent. We argue that this system may be an intermediate case between different groups of black hole candidates.
We report on the detection with RXTE of variable high frequency features in the power spectra of the black hole candidate 4U 1630-47 during its 1998 outburst. We find high frequency features during the rise and the early decay of the outburst in the range of 100-300 Hz. The features are usually found to be broad, and have rms amplitudes of 2-8; their frequencies are correlated with count rate and anti-correlated with spectral hardness. Also, for the first time twin high frequency features are detected simultaneously, with a ratio in frequencies consistent with 1:4. Although some of the high frequency features are less coherent and stronger than found in other black hole sources, we show that they behave very similar to the high frequency features found in for instance XTE J1550-564.
Recent XMM-Newton observations of the black-hole candidate 4U 1630-47 during the 2012 outburst revealed three relativistically Doppler-shifted emission lines that were interpreted as arising from baryonic matter in the jet of this source. Here we reanalyse those data and find an alternative model that, with less free parameters than the model with Doppler-shifted emission lines, fits the data well. In our model we allow the abundance of S and Fe in the interstellar material along the line of sight to the source to be non solar. Among other things, this significantly impacts the emission predicted by the model at around 7.1 keV, where the edge of neutral Fe appears, and renders the lines unnecessary. The fits to all the 2012 XMM-Newton observations of this source require a moderately broad emission line at around 7 keV plus several absorption lines and edges due to highly ionised Fe and Ni, which reveal the presence of a highly-ionised absorber close to the source. Finally, our model also fits well the observations in which the lines were detected when we apply the most recent calibration files, whereas the model with the three Doppler-shifted emission lines does not.
We report the results from an X-ray and near-infrared observation of the Galactic black hole binary 4U 1630--47 in the very high state, performed with {it Suzaku} and IRSF around the peak of the 2012 September-October outburst. The X-ray spectrum is approximated by a steep power law, with photon index of 3.2, identifying the source as being in the very high state. A more detailed fit shows that the X-ray continuum is well described by a multi-color disc, together with thermal and non-thermal Comptonization. The inner disc appears slightly truncated by comparison with a previous high/soft state of this source, even taking into account energetic coupling between the disc and corona, although there are uncertainties due to the dust scattering correction. The near-infrared fluxes are higher than the extrapolated disc model, showing that there is a contribution from irradiation in the outer disk and/or the companion star at these wavelengths. Our X-ray spectra do not show the Doppler shifted iron emission lines indicating a baryonic jet which were seen four days previously in an XMM-Newton observation, despite the source being in a similar state. There are also no significant absorption lines from highly ionized irons as are seen in the previous high/soft state data. We show that the increased source luminosity is not enough on its own to make the wind so highly ionized as to be undetectable. This shows that the disc wind has changed in terms of its launch radius and/or density compared to the high/soft state.
We present the X-ray spectral and timing analysis of the transient black hole X-ray binary 4U 1630-47, observed with the AstroSat, Chandra and MAXI space missions during its soft X-ray outburst in 2016. The outburst, from the rising phase until the peak, is neither detected in hard X-rays (15-50 keV) by the Swift/BAT nor in radio. Such non-detection along with the source behavior in the hardness-intensity and color-color diagrams obtained using MAXI data confirm that both Chandra and AstroSat observations were performed during the high soft spectral state. The High Energy Grating (HEG) spectrum from the Chandra high-energy transmission grating spectrometer (HETGS) shows two strong, moderately blueshifted absorption lines at 6.705$_{-0.002}^{+0.002}$ keV and 6.974$_{-0.003}^{+0.004}$ keV, which are produced by Fe XXV and Fe XXVI in a low-velocity ionized disk wind. The corresponding outflow velocity is determined to be 366$pm$56 km/s. Separate spectral fits of Chandra/HEG, AstroSat/SXT+LAXPC and Chandra/HEG + AstroSat/SXT+LAXPC data show that the broadband continuum can be well described with a relativistic disk-blackbody model, with the disk flux fraction of $sim 0.97$. Based on the best-fit continuum spectral modeling of Chandra, AstroSat and Chandra+AstroSat joint spectra and using the Markov Chain Monte Carlo simulations, we constrain the spectral hardening factor at 1.56$^{+0.14}_{-0.06}$ and the dimensionless black hole spin parameter at 0.92 $pm$ 0.04 within the 99.7% confidence interval. Our conclusion of a rapidly-spinning black hole in 4U 1630-47 using the continuum spectrum method is in agreement with a previous finding applying the reflection spectral fitting method.
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