Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA NuSTAR observation of the low mass X-ray binary GX 349+2 throughout the Z-track
58
0
0.0
(
0
)
Added by
Benjamin Coughenour
Publication date
2017
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Although the most luminous class of neutron star low mass X-ray binaries, known as Z sources, have been well studied, their behavior is not fully understood. In particular, what causes these sources to trace out the characteristic Z-shaped pattern on color-color or hardness-intensity diagrams is not well known. By studying the physical properties of the different spectral states of these sources, we may better understand such variability. With that goal in mind, we present a recent NuSTAR observation of the Z source GX 349+2, which spans approximately 2 days, and covers all its spectral states. By creating a hardness-intensity diagram we were able to extract five spectra and trace the change in spectral parameters throughout the Z-track. GX 349+2 shows a strong, broad Fe K$alpha$ line in all states, regardless of the continuum model used. Through modeling of the reflection spectrum and Fe K$alpha$ line we find that in most states the inner disk radius is consistent with remaining unchanged at an average radius of 17.5 $R_g$ or 36.4 km for a canonical 1.4 $M_odot$ neutron star. During the brightest flaring branch, however, the inner disk radius from reflection is not well constrained.
rate research
Read More
Z 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 3-12, 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 Mdot into the disk: increase of Comptonization up the horizontal branch, transition from a standard thin disk to a slim disk up the normal branch, 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 Mdot along the entire Z track based on the thermal disk component. We also measure the upper kHz QPO frequency and find it to depend on the apparent inner disk radius R_in (prior to Compton scattering) approximately as frequency propto R_in^(-3/2), supporting the idenfitication of it as the Keplerian frequency at R_in. The horizontal branch oscillation is probably related to the dynamics in the inner disk as well, as both its frequency and R_in vary significantly on the horizontal branch but become relatively constant on the normal branch.
We report on a simultaneous NuSTAR and Swift observation of the neutron star low-mass X-ray binary 4U 1728-34. We identified and removed four Type I X-ray bursts during the observation in order to study the persistent emission. The continuum spectrum is hard and well described by a black body with $kT=$ 1.5 keV and a cutoff power law with $Gamma=$ 1.5 and a cutoff temperature of 25 keV. Residuals between 6 and 8 keV provide strong evidence of a broad Fe K$alpha$ line. By modeling the spectrum with a relativistically blurred reflection model, we find an upper limit for the inner disk radius of $R_{rm in}leq2 R_{rm ISCO}$. Consequently we find that $R_{rm NS}leq23$ km, assuming $M=1.4{mbox{$rm,M_{mathordodot}$}}$ and $a=0.15$. We also find an upper limit on the magnetic field of $Bleq2times10^8$ G.
We have analysed archived Ginga data on the Z source Sco X-2 (GX349+2). We present the first detailed investigation of its X-ray fast-time variability, as a function of position in the Z track. During the two-day observation over the period 5-7 March 1989, the source was in the so-called flaring branch, and the lower part of the so-called normal branch. We found broad peaked noise with a centroid frequency and width of ~4-7 Hz and ~6-12 Hz respectively. The peaked noise was strongest in the lower flaring branch, with a maximum fractional rms amplitude of ~3 %. We conclude that it is not a manifestation of atoll source high frequency noise, as had been suggested, and compare it with the power spectral features seen in other Z sources. We find that the peaked noise is markedly different to the quasi-periodic oscillations found in the normal and flaring branches of Sco X-1; however it bears some resemblance to that seen in the flaring branch of Cyg X-2 at low overall intensities.
We present the analysis of seven emph{Chandra} High Energy Transmission Grating Spectrometer and six simultaneous emph{RXTE} Proportional Counter Array observations of the persistent neutron star (NS) low-mass X-ray binary GX 13+1 on its normal and horizontal branches. Across nearly 10 years, GX 13+1 is consistently found to be accreting at $50-70$% Eddington, and all observations exhibit multiple narrow, blueshifted absorption features, the signature of a disk wind, despite the association of normal and horizontal branches with jet activity. A single absorber with standard abundances cannot account for all seven major disk wind features, indicating that multiple absorption zones may be present. Two or three absorbers can produce all of the absorption features at their observed broadened widths and reveal that multiple kinematic components produce the accretion disk wind signature. Assuming the most ionized absorber reflects the physical conditions closest to the NS, we estimate a wind launching radius of $7times10^{10}$ cm, for an electron density of $10^{12}$ cm$^{-3}$. This is consistent with the Compton radius and also with a thermally driven wind. Because of the sources high Eddington fraction, radiation pressure likely facilitates the wind launching.
We fit the observed high ionisation X-ray absorption lines in the neutron star binary GX13+1 with a full simulation of a thermal-radiative wind. This uses a radiation hydrodynamic code coupled to Monte Carlo radiation transfer to compute the observed line profiles from Hydrogen and Helium-like iron and Nickel, including all strong K{alpha} and K{beta} transitions. The wind is very strong as this object has a very large disc and is very luminous. The absorption lines from Fe K{alpha} are strongly saturated as the ion columns are large, so the line equivalent widths (EWs) depend sensitively on the velocity structure. We additionally simulate the lines including isotropic turbulence at the level of the azimuthal and radial velocities. We fit these models to the Fe xxv and xxvi absorption lines seen in the highest resolution Chandra third order HETGS data. These data already rule out the addition of turbulence at the level of the radial velocity of ~500 km/s. The velocity structure predicted by the thermal-radiative wind alone is a fairly good match to the observed profile, with an upper limit to additional turbulence at the level of the azimuthal velocity of ~100 km/s. This gives stringent constraints on any remaining contribution from magnetic acceleration.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
