scholarly journals Timing and spectral analysis of 2S 1417−624 during its 2018 outburst

2021 ◽  
Author(s):  
M M Serim ◽  
Ö C Özüdoğru ◽  
Ç K Dönmez ◽  
Ş Şahiner ◽  
D Serim ◽  
...  
Keyword(s):  
Spectral Characteristics ◽  
Noise Spectrum ◽  
High Energy ◽  
Power Density Spectrum ◽  
Mode Switching ◽  
Model Parameters ◽  
Noise Component ◽  
Density Spectrum ◽  
X Ray ◽  
Spectral Changes

Abstract We investigate timing and spectral characteristics of the transient X-ray pulsar 2S 1417−624 during its 2018 outburst with NICER follow up observations. We describe the spectra with high-energy cut-off and partial covering fraction absorption (PCFA) model and present flux-dependent spectral changes of the source during the 2018 outburst. Utilizing the correlation-mode switching of the spectral model parameters, we confirm the previously reported sub-critical to critical regime transitions and we argue that secondary transition from the gas-dominated to the radiation pressure-dominated disc do not lead to significant spectral changes below 12 keV. Using the existing accretion theories, we model the spin frequency evolution of 2S 1417−624 and investigate the noise processes of a transient X-ray pulsar for the first time using both polynomial and luminosity-dependent models for the spin frequency evolution. For the first model, the power density spectrum of the torque fluctuations indicate that the source exhibits red noise component (Γ ∼ −2) within the timescales of outburst duration which is typical for disc-fed systems. On the other hand, the noise spectrum tends to be white on longer timescales with high timing noise level that indicates an ongoing accretion process in between outburst episodes. For the second model, most of the red noise component is eliminated and the noise spectrum is found to be consistent with a white noise structure observed in wind-fed systems.

scholarly journals Inertial oscillation modes of an inclined dipolar magnetosphere as a source of band-limited noise in X-ray pulsars

2020 ◽  
Vol 496 (1) ◽  
pp. 13-18
Author(s):  
Pavel Abolmasov ◽  
Anton Biryukov
Keyword(s):  
Equilibrium Points ◽  
Broad Band ◽  
Periodic Oscillation ◽  
Power Density Spectrum ◽  
Inertial Oscillation ◽  
Noise Component ◽  
Density Spectrum ◽  
X Ray ◽  
Field Lines ◽  
Band Limited

ABSTRACT Magnetic fields of strongly magnetized stars can trap conducting matter due to frozen-in condition. In the force-free regime, the motion of the matter along the field lines may be considered in the ‘bead on a wire’ approximation. Such a motion, if gravity and centrifugal forces are taken into account, has equilibrium points, some of which are stable. In most cases, stability is possible in about several per cent of the possible locations. Corresponding oscillation frequencies span the range from zero to $\sqrt{3}$ of the spin frequency. We suggest that this variability mode may be excited in some X-ray pulsars during the outbursts and create the peaked broad-band noise component near the break frequency in the power density spectrum, as well as produce some of the quasi-periodic oscillation features in this frequency range. Existence of this variability does not require any changes in mass accretion rate and involves only a small amount of matter infiltrating from the disc and magnetic flow due to interchange instabilities.

scholarly journals Properties of Faint X-ray Activity of XTE J1908+094 in 2019

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 25
Author(s):  
Debjit Chatterjee ◽  
Arghajit Jana ◽  
Kaushik Chatterjee ◽  
Riya Bhowmick ◽  
Sujoy Kumar Nath ◽  
...  
Keyword(s):  
Black Hole ◽  
Temporal Analysis ◽  
Power Density Spectrum ◽  
Periodic Oscillations ◽  
Telescope Array ◽  
Density Spectrum ◽  
X Ray ◽  
Black Hole Candidate ◽  
Short Period ◽  
Spectral State

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M⊙, with 90% confidence.

scholarly journals Mass outflow of the X-ray emission line gas in NGC 4151

2020 ◽  
Vol 15 (S359) ◽  
pp. 131-135
Author(s):  
S. B. Kraemer ◽  
T. J. Turner ◽  
D. M. Crenshaw ◽  
H. R. Schmitt ◽  
M. Revalski ◽  
...  
Keyword(s):  
Emission Line ◽  
Total Mass ◽  
High Energy ◽  
Model Parameters ◽  
Zeroth Order ◽  
Space Telescope ◽  
X Ray ◽  
Ngc 4151 ◽  
Outflow Rate ◽  
Mass Outflow

AbstractWe have analyzed Chandra/High Energy Transmission Grating spectra of the X-ray emission line gas in the Seyfert galaxy NGC 4151. The zeroth-order spectral images show extended H- and He-like O and Ne, up to a distance r ˜ 200 pc from the nucleus. Using the 1st-order spectra, we measure an average line velocity ˜230 km s–1, suggesting significant outflow of X-ray gas. We generated Cloudy photoionization models to fit the 1st-order spectra; the fit required three distinct emission-line components. To estimate the total mass of ionized gas (M) and the mass outflow rates, we applied the model parameters to fit the zeroth-order emission-line profiles of Ne IX and Ne X. We determined an M ≍ 5.4 × 105Mʘ. Assuming the same kinematic profile as that for the [O III] gas, derived from our analysis of Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra, the peak X-ray mass outflow rate is approximately 1.8 Mʘ yr–1, at r ˜ 150 pc. The total mass and mass outflow rates are similar to those determined using [O III], implying that the X-ray gas is a major outflow component. However, unlike the optical outflows, the X-ray emitting mass outflow rate does not drop off at r > 100pc, which suggests that it may have a greater impact on the host galaxy.

scholarly journals Evolution of MAXI J1631–479 during the January 2019 outburst observed by INTEGRAL/IBIS

2020 ◽  
Vol 492 (3) ◽  
pp. 3657-3661 ◽  
Author(s):  
M Fiocchi ◽  
F Onori ◽  
A Bazzano ◽  
A J Bird ◽  
A Bodaghee ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Thermal Emission ◽  
Spectral Characteristics ◽  
Monitoring Program ◽  
High Energy ◽  
Thermal Electron ◽  
X Ray ◽  
Inverse Compton Scattering ◽  
Black Hole Candidate ◽  
Decay Times

ABSTRACT We report on a recent bright outburst from the new X-ray binary transient MAXI J1631–479, observed in January 2019. In particular, we present the 30–200 keV analysis of spectral transitions observed with INTEGRAL/IBIS during its Galactic plane monitoring program. In the MAXI and BAT monitoring period, we observed two different spectral transitions between the high/soft and low/hard states. The INTEGRAL spectrum from data taken soon before the second transition is best described by a Comptonized thermal component with a temperature of kTe ∼ 30 keV and a high-luminosity value of $L_{2-200\, \mathrm{keV}}\sim 3\times 10^{38}$ erg−1 (assuming a distance of 8 kpc). During the second transition, the source shows a hard, power-law spectrum. The lack of high energy cut-off indicates that the hard X-ray spectrum from MAXI J1631–479 is due to a non-thermal emission. Inverse Compton scattering of soft X-ray photons from a non-thermal or hybrid thermal/non-thermal electron distribution can explain the observed X-ray spectrum although a contribution to the hard X-ray emission from a jet cannot be determined at this stage. The outburst evolution in the hardness-intensity diagram, the spectral characteristics, and the rise and decay times of the outburst are suggesting that this system is a black hole candidate.

Coronal vertical structure variations in normal branch of GX 17+2: AstroSat’s SXT and LAXPC perspective

2020 ◽  
Vol 499 (2) ◽  
pp. 2214-2228
Author(s):  
S Malu ◽  
K Sriram ◽  
V K Agrawal
Keyword(s):  
Cross Correlation ◽  
Temporal Analysis ◽  
Light Curves ◽  
Power Density Spectrum ◽  
Large Area ◽  
Density Spectrum ◽  
X Ray ◽  
Correlation Studies ◽  
Reflection Model ◽  
Normal Branch

ABSTRACT We performed spectro-temporal analysis in the 0.8–50 keV energy band of the neutron star Z source GX 17+2 using AstroSat Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) data. The source was found to vary in the normal branch (NB) of the hardness–intensity diagram. Cross-correlation studies of LAXPC light curves in soft and hard X-ray band unveiled anticorrelated lags of the order of few hundred seconds. For the first time, cross-correlation studies were performed using SXT soft and LAXPC hard light curves and they exhibited correlated and anticorrelated lags of the order of a hundred seconds. Power density spectrum displayed normal branch oscillations (NBOs) of 6.7–7.8 Hz (quality factor 1.5–4.0). Spectral modelling resulted in inner disc radius of ∼12–16 km with Γ ∼ 2.31–2.44 indicating that disc is close to the innermost stable circular orbit and a similar value of disc radius was noticed based on the reflection model. Different methods were used to constrain the corona size in GX 17+2. Using the detected lags, corona size was found to be 27–46 km (β = 0.1, β = vcorona/vdisc) and 138–231 km (β = 0.5). Assuming the X-ray emission to be arising from the boundary layer (BL), its size was determined to be 57–71 km. Assuming that BL is ionizing the disc’s inner region, its size was constrained to ∼19–86 km. Using NBO frequency, the transition shell radius was found to be around 32 km. Observed lags and no movement of the inner disc front strongly indicate that the varying corona structure is causing the X-ray variation in the NB of Z source GX 17+2.

scholarly journals Radiative Processes and Geometry of Spectral States of Black-hole Binaries

2000 ◽  
Vol 195 ◽  
pp. 153-170 ◽  
Author(s):  
A. A. Zdziarski
Keyword(s):  
Black Hole ◽  
High Energy ◽  
Power Density Spectrum ◽  
Main Process ◽  
Density Spectrum ◽  
Black Hole Binaries ◽  
Nonthermal Electrons ◽  
Radiative Processes ◽  
Soft State ◽  
Spectral States

I review radiative processes responsible for X-ray emission in the hard (low) and soft (high) spectral states of black-hole binaries. The main process in the hard state appears to be thermal Comptonization (in a hot plasma) of blackbody photons emitted by a cold disk. This is supported by correlations between the spectral index, the strength of Compton reflection, and the peak frequencies in the power-density spectrum, as well as by the frequency-dependence of Fourier-resolved spectra. Spectral variability may then be driven by the variable truncation radius of the disk. The soft state appears to correspond to the smallest truncation radii. However, the lack of high-energy cutoffs observed in the soft state implies that its main radiative process is Compton scattering of disk photons by nonthermal electrons. The bulk-motion Comptonization model for the soft state is shown to be ruled out by the data.

scholarly journals A non-linear mathematical model for the X-ray variability of the microquasar GRS 1915+105 – III. Low-frequency quasi-periodic oscillations

2020 ◽  
Vol 497 (1) ◽  
pp. 405-415
Author(s):  
E Massaro ◽  
F Capitanio ◽  
M Feroci ◽  
T Mineo
Keyword(s):  
Mathematical Model ◽  
Equilibrium Points ◽  
Low Frequency ◽  
Input Function ◽  
Power Density Spectrum ◽  
Periodic Oscillations ◽  
Density Spectrum ◽  
X Ray ◽  
Almost All ◽  
The Mathematical Model

ABSTRACT The X-ray emission from the microquasar GRS 1915+105 shows, together with a very complex variability on different time-scales, the presence of low-frequency quasi-periodic oscillations (LFQPOs) at frequencies lower than ∼30 Hz. In this paper, we demonstrate that these oscillations can be consistently and naturally obtained as solutions of a system of two ordinary differential equations, which is able to reproduce almost all variability classes of GRS 1915+105. We modified the Hindmarsh–Rose model and obtained a system with two dynamical variables x(t), y(t), where the first one represents the X-ray flux from the source, and an input function J(t), whose mean level J0 and its time evolution is responsible of the variability class. We found that for values of J0 around the boundary between the unstable and the stable interval, where the equilibrium points are of spiral type, one obtains an oscillating behaviour in the model light curve similar to the observed ones with a broad Lorentzian feature in the power density spectrum and, occasionally, with one or two harmonics. Rapid fluctuations of J(t), as those originating from turbulence, stabilize the LFQPOs, resulting in a slowly amplitude modulated pattern. To validate the model, we compared the results with real RXTE data, which resulted remarkably similar to those obtained from the mathematical model. Our results allow us to favour an intrinsic hypothesis on the origin of LFQPOs in accretion discs ultimately related to the same mechanism responsible for the spiking limit cycle.

A microspectroscopic study of cap damage in annealed RE-doped AlN-capped GaN

2005 ◽  
Vol 892 ◽  
Author(s):  
Emilio Nogales ◽  
K. Lorenz ◽  
K. Wang ◽  
I.S. Roqan ◽  
R.W. Martin ◽  
...  
Keyword(s):  
Surface Defects ◽  
Light Emission ◽  
Lattice Mismatch ◽  
High Energy ◽  
Annealing Atmosphere ◽  
X Ray ◽  
Electron Probe Microanalyzer ◽  
Annealing Temperatures ◽  
Spectral Changes ◽  
Microscopic Surface

AbstractIntegrated AlN nanocaps are used to protect gallium nitride epilayers during high temperature annealing treatments following high-energy implantation of rare earth (RE) ions. Cracks formed in thicker caps due to the lattice mismatch between AlN and GaN lead to the creation of microscopic surface defects at annealing temperatures higher than around 1200 °C. GaN dissociates locally to produce holes in the caps. Simultaneous cathodoluminescence/wavelength dispersive X-ray microanalysis in a modified electron probe microanalyzer allows study of the compositional and light emission variations near these microscopic defects. The intensity of the 5D0 – 7F2 transition related emission is enhanced and spectral changes can be observed, which indicate changes in the structure and/or composition of a very thin layer that forms the walls of holes in the caps. We also report some preliminary observations on the influence of the annealing atmosphere (nitrogen or ammonia) on cap damage.

Mechanical behaviour of jute fibre-reinforced polyester composite: Characterization of damage mechanisms using acoustic emission and microstructural observations

2019 ◽  
Vol 53 (24) ◽  
pp. 3377-3394 ◽  
Author(s):  
Adem Alia ◽  
Gilbert Fantozzi ◽  
Nathalie Godin ◽  
Hocine Osmani ◽  
Pascal Reynaud
Keyword(s):  
Acoustic Emission ◽  
Matrix Cracking ◽  
Power Density Spectrum ◽  
Damage Mechanisms ◽  
Density Spectrum ◽  
X Ray ◽  
Time Frequency ◽  
Pull Out ◽  
Fibre Matrix

The present work deals with the mechanical characterization of a woven jute fabrics reinforced polyester resin composite. Two stacking sequences were considered: [0]8 and [+45/−45]2S. In-situ acoustic emission technique, X-ray computed tomography (X-ray CT) and post-mortem microscopic observations were used to characterise the damage mechanisms and to follow their evolutions during uniaxial tension. The microstructural analysis and X-ray CT revealed the following damage modes for the two lay-ups: fibre-matrix debondings which constitute the dominant mechanism, matrix crackings and fibre breakages and pull-outs. The acoustic emission data were processed using an unsupervised pattern recognition technique which combines principal components analysis and k-means optimized by a genetic algorithm. Both temporal and frequential features of acoustic emission signals were considered. The Laplacian score and dendrogram were used to determine the relevant and uncorrelated descriptors for clustering. Three clusters of events were obtained and the waveforms of each one were examined. Furthermore, the frequency contents of signals of each cluster were accurately investigated using power density spectrum and smoothed pseudo Wigner-Ville time-frequency distribution and the discrepancies between clusters are highlighted. Cluster 1 (Cl 1) characterized by signals of low frequency and intermediate amplitude, cluster 2 (Cl 2) characterized by signals of higher frequency and an amplitude similar to that of Cl 1 and cluster 3 (Cl 3) characterized by signals of higher amplitude. A correlation between the clusters and the damage mechanisms was established by means of interrupted tensile tests: Cl 1 is assigned to the matrix cracking, Cl 2 to the fibre-matrix debonding and Cl 3 to the fibre breakage and pull-out. The kinetic of evolution of each damage mode was monitored for the two stacking sequences.

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