499 research outputs found
The 2003 outburst of the X-ray transient H1743–322 : comparisons with the black hole microquasar XTE J1550–564
No full textThe bright X-ray transient H1743–322 was observed daily by the Rossi X-ray Timing Explorer during most of its eight-month outburst in 2003. We present a detailed spectral analysis and a supporting timing analysis of all of these data, and we discuss the behavior and evolution of the source in terms of the three principal X-ray states defined by Remillard and McClintock. These X-ray results are complemented by Very Large Array data obtained at six frequencies that provide quite complete coverage of the entire outburst cycle at 4.860 GHz and 8.460 GHz. We also present photometric data and finding charts for the optical counterpart in both outburst and quiescence. We closely compare H1743–322 to the well-studied black hole X-ray transient XTE J1550–564 and find the behaviors of these systems to be very similar. As reported elsewhere, both H1743–322 and XTE J1550–564 are relativistic jet sources and exhibit a pair of high-frequency quasi-periodic oscillations with a 3:2 frequency ratio. The many striking similarities between these two sources argue strongly that H1743–322 is a black hole binary, although presently no dynamical data exist to support this conclusion
THE SPECTRAL EVOLUTION ALONG THE Z TRACK OF THE BRIGHT NEUTRON STAR X-RAY BINARY GX 17+2
No full textZ sources are bright neutron star X-ray binaries, accreting at around the Eddington limit. We analyze the 68 RXTE observations (~270 ks) of Sco-like Z source GX 17+2 made between 1999 October 3 and 12, covering a complete Z track. We create and fit color-resolved spectra with a model consisting of a thermal multicolor disk, a single-temperature-blackbody boundary layer and a weak Comptonized component. We find that, similar to what was observed for XTE J1701-462 in its Sco-like Z phase, the branches of GX 17+2 can be explained by three processes operating at a constant accretion rate [dot over M] into the disk: increase of Comptonization up the horizontal branch (HB), transition from a standard thin disk to a slim disk up the normal branch (NB), and temporary fast decrease of the inner disk radius up the flaring branch. We also model the Comptonization in an empirically self-consistent way, with its seed photons tied to the thermal disk component and corrected for to recover the pre-Comptonized thermal disk emission. This allows us to show a constant [dot over M] along the entire Z track based on the thermal disk component. We also measure the upper kHz quasi-periodic oscillation frequency and find it to depend on the apparent inner disk radius R [subscript in] (prior to Compton scattering) approximately as frequency α R[superscript –3 over 2] [subscript in], supporting the identification of it as the Keplerian frequency at R [subscript in]. The HB oscillation is probably related to the dynamics in the inner disk as well, as both its frequency and R [subscript in] vary significantly on the HB but become relatively constant on the NB
GRS 1915+105 IN “SOFT STATE”: NATURE OF ACCRETION DISK WIND AND ORIGIN OF X-RAY EMISSION
No full textWe present the results from simultaneous Chandra HETGS and Rossi X-ray Timing Explorer (RXTE) observations of the microquasar GRS 1915+105 in its quasi-stable "soft state" (or State A) performed on 2007 August 14, several days after the state transition from "hard state" (State C). The X-ray flux increased with spectral hardening around the middle of the Chandra observation, after which the 67 Hz quasi-periodic oscillation (QPO) became significant. The HETGS spectra reveal at least 32 narrow absorption lines from highly ionized ions including Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, whose features are the deepest among those ever observed with Chandra from this source. By fitting to the absorption-line profiles by Voigt functions, we find that the absorber has outflow velocities of ≈150 and ≈500 km s–1 with a line-of-sight velocity dispersion of ≈70 and ≈200 km s[superscript –1] for the Si XIV and Fe XXVI ions, respectively. The larger velocity and its dispersion in heavier ions indicate that the wind has a nonuniform dynamical structure along the line of sight. The location of the absorber is estimated at ~(1-3) × 10[superscript 5] r [subscript g] (where r[subscript g] is the gravitational radius) from the source, consistent with thermally and/or radiation-driven winds. By taking into account narrow spectral features detected with Chandra, the continuum spectra obtained with RXTE in the 3-25 keV band can be well described with a thermal Comptonization with an electron temperature of ≈4 keV and an optical depth of ≈5 from seed photons from the standard disk extending down to (4-7)r [subscript g]. In this interpretation, most of the radiation energy is produced in the Comptonization corona, which completely covers the inner part of the disk. A broad (1σ width of ≈0.2 keV) iron-K emission line and a smeared edge feature are detected, which can be explained by reflection from the accretion disk at radii larger than 400r [subscript g] when an emissivity power law index of –3 is assumed.Japan. Ministry of Education, Culture, Sports, Science and Technology (Grants-in-Aid for Scientific Research 20540230, Global COE Program “The Next Generation of Physics, Spun from Universality and Emergence”
THE PHYSICS OF THE “HEARTBEAT” STATE OF GRS 1915+105
No full textWe present the first detailed phase-resolved spectral analysis of a joint Chandra High-Energy Transmission Grating Spectrometer and Rossi X-ray Timing Explorer observation of the ρ variability class in the microquasar GRS 1915+105. The ρ cycle displays a high-amplitude, double-peaked flare that recurs roughly every 50 s and is sometimes referred to as the "heartbeat" oscillation. The spectral and timing properties of the oscillation are consistent with the radiation pressure instability and the evolution of a local Eddington limit in the inner disk. We exploit strong variations in the X-ray continuum, iron emission lines, and the accretion disk wind to probe the accretion geometry over nearly six orders of magnitude in distance from the black hole. At small scales (1-10 R [subscript g]), we detect a burst of bremsstrahlung emission that appears to occur when a portion of the inner accretion disk evaporates due to radiation pressure. Jet activity, as inferred from the appearance of a short X-ray hard state, seems to be limited to times near minimum luminosity, with a duty cycle of ~10%. On larger scales (10[superscript 5]-10[superscript 6] R [subscript g]), we use detailed photoionization arguments to track the relationship between the fast X-ray variability and the accretion disk wind. For the first time, we are able to show that changes in the broadband X-ray spectrum produce changes in the structure and density of the accretion disk wind on timescales as short as 5 s. These results clearly establish a causal link between the X-ray oscillations and the disk wind and therefore support the existence of a disk-jet-wind connection. Furthermore, our analysis shows that the mass-loss rate in the wind may be sufficient to cause long-term oscillations in the accretion rate, leading to state transitions in GRS 1915+105
X-RAY REFLECTION SPECTROSCOPY OF THE BLACK HOLE GX 339–4: EXPLORING THE HARD STATE WITH UNPRECEDENTED SENSITIVITY
No full textWe analyze simultaneously six composite RXTE spectra of GX 339–4 in the hard state comprising 77 million counts collected over 196 ks. The source spectra are ordered by luminosity and span the range 1.6%–17% of the Eddington luminosity. Crucially, using our new tool pcacorr, we re-calibrate the data to a precision of 0.1%, an order of magnitude improvement over all earlier work. Using our advanced reflection model relxill, we target the strong features in the component of emission reflected from the disk, namely, the relativistically broadened Fe K emission line, the Fe K edge, and the Compton hump. We report results for two joint fits to the six spectra: For the first fit, we fix the spin parameter to its maximal value (a* = 0.998) and allow the inner disk radius R[subscript in] to vary. Results include (i) precise measurements of R[subscript in], with evidence that the disk becomes slightly truncated at a few percent of Eddington and (ii) an order-of-magnitude swing with luminosity in the high energy cutoff, which reaches >890 keV at our lowest luminosity. For the second fit, we make the standard assumption in estimating spin that the inner edge of the accretion disk is located at the innermost stable circular orbit (R[subscript in] = R[subscript ISCO]) and find a* = 0.95[+0.03 over -0.05] (90% confidence, statistical). For both fits, and at the same level of statistical confidence, we estimate that the disk inclination is i = 48° ± 1° and that the Fe abundance is super-solar, A[subscript Fe] = 5 ± 1
Recommended from our members
Men's Relay team, 1949
No full textFront Row- Zeleny, Fulmer, DeLoid, R. Howell; Back Row- Remillard, Brown, Coach Sannell
Recommended from our members
Men's Track team, 1949
No full textBack-Coach Sannella, Schmitt, Althen, Sherman, Sasek, Remillard; Middle- Zeleny, Barna, Carpenter, Leonard, East, H. Howell, Willard, R. Howard; Front- Roberts, Herman, DeLoid, Brown, Madwed, Reid, Lovell, Dewir
"A New Hedge Fund Replication Method with the Dynamic Optimal Portfolio"
No full textThis paper provides a new hedge fund replication method, which extends Kat and Palaro (2005) and Papageorgiou, Remillard and Hocquard (2008) to multiple trading assets with both long and short positions. The method generates a target payoff distribution by the cheapest dynamic portfolio. It is regarded as an extension of Dybvig (1988) to continuous-time framework and dynamic portfolio optimization where the dynamic trading strategy is derived analytically by applying Malliavin calculus. It is shown that the cost minimization is equivalent to maximization of a certain class of von Neumann-Morgenstern utility functions. The method is applied to the replication of a CTA/Managed Futures Index in practice.
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