scholarly journals Revealing the nature of the transient source MAXI J0637-430 through spectro-temporal analysis

2021 ◽  
Author(s):  
Blessy E Baby ◽  
G R Bhuvana ◽  
D Radhika ◽  
Tilak Katoch ◽  
Samir Mandal ◽  
...  
Keyword(s):  
Temporal Analysis ◽  
Spectral Fitting ◽  
Temporal Properties ◽  
Disc Model ◽  
Transient Source ◽  
Dominant State ◽  
Photon Index ◽  
Hard State ◽  
Band Limited ◽  
Hard Transition

Abstract We study the spectral and temporal properties of MAXI J0637-430 during its 2019-2020 outburst using NICER, AstroSat and Swift-XRT data. The source was in a disc dominant state within a day of its detection and traces out a ‘c’ shaped profile in the HID, similar to the ‘mini’-outbursts of the recurrent BHB 4U 1630-472. Energy spectrum is obtained in the 0.5 − 10 keV band with NICER and Swift-XRT, and 0.5 − 25 keV with AstroSat. The spectra can be modelled using a multicolour disc emission (diskbb) convolved with a thermal Comptonisation component (thcomp). The disc temperature decreases from 0.6 keV to 0.1 keV during the decay with a corresponding decrease in photon index (Γ) from 4.6 to 1.8. The fraction of Compton scattered photons (fcov) remains < 0.3 during the decay upto mid-January 2020 and gradually increases to 1 as the source reaches hard state. Power Density Spectra (PDS) generated in the 0.01-100 Hz range display no Quasi-periodic Oscillations (QPOs) although band-limited noise (BLN) is seen towards the end of January 2020. During AstroSat observations, Γ lies in the range 2.3 − 2.6 and rms increases from 11 to 20%, suggesting that the source was in an intermediate state till 21 November 2019. Spectral fitting with the relativistic disc model (kerrbb), in conjunction with the soft-hard transition luminosity, favour a black hole with mass 3 − 19 M⊙ with retrograde spin at a distance <15 kpc. Finally, we discuss the possible implications of our findings.

scholarly journals Simultaneous Multiwavelength Observations of the Low/Hard State of the X‐Ray Transient Source SWIFT J1753.5−0127

2007 ◽  
Vol 659 (1) ◽  
pp. 549-560 ◽  
Author(s):  
M. Cadolle Bel ◽  
M. Ribo ◽  
J. Rodriguez ◽  
S. Chaty ◽  
S. Corbel ◽  
...  
Keyword(s):  
X Ray ◽  
Transient Source ◽  
Hard State ◽  
Multiwavelength Observations

scholarly journals Discovery of a New X-ray Transient in Scorpius GRO J1655-40 ≡ X-ray Nova Scorpii 1994

1996 ◽  
Vol 165 ◽  
pp. 363-367
Author(s):  
W.S. Paciesas ◽  
S.N. Zhang ◽  
B.C. Rubin ◽  
B.A. Harmon ◽  
C.A. Wilson ◽  
...  
Keyword(s):  
Black Hole ◽  
High Resolution ◽  
Power Law ◽  
Radio Observations ◽  
X Ray ◽  
Black Hole Candidate ◽  
Radio Jets ◽  
Transient Source ◽  
Galactic Source ◽  
Photon Index

A bright transient X-ray source, GRO J1655-40 (X-ray Nova Scorpii 1994) was discovered with BATSE (the Burst and Transient Source Experiment) in late July 1994. More recently, the source also became a strong radio emitter, its rise in the radio being approximately anti-correlated with a decline in the hard X-ray intensity. High-resolution radio observations subsequent to this symposium showed evidence for superluminally expanding jets. Since the hard X-ray emission extends to at least 200 keV and we find no evidence of pulsations, we tentatively classify the source as a black-hole candidate. However, its hard X-ray spectrum is unusually steep (power-law photon index α ≃ −3) relative to most other black-hole candidates. In this regard, it resembles GRS 1915+105, the first galactic source to show superluminal radio jets.

Differentiating Cortical Areas Related to Pain Perception From Stimulus Identification: Temporal Analysis of fMRI Activity

1999 ◽  
Vol 81 (6) ◽  
pp. 2956-2963 ◽  
Author(s):  
A. Vania Apkarian ◽  
Aneela Darbar ◽  
Beth R. Krauss ◽  
Patricia A. Gelnar ◽  
Nikolaus M. Szeverenyi
Keyword(s):  
Impulse Response ◽  
Response Function ◽  
Pain Perception ◽  
Impulse Response Function ◽  
Temporal Analysis ◽  
Gradual Transition ◽  
Thermal Stimulus ◽  
Cortical Areas ◽  
Temporal Properties ◽  
Stimulus Identification

Differentiating cortical areas related to pain perception from stimulus identification: temporal analysis of fMRI activity. In a recent functional magnetic resonance imaging study (fMRI), we reported the cortical areas activated in a thermal painful task and compared the extent of overlap between this cortical network and those activated during a vibrotactile task and a motor task. In the present study we examine the temporal properties of the cortical activations for all three tasks and use linear systems identification techniques to functionally differentiate the cortical regions identified in the painful thermal task. Cortical activity was examined in the contralateral middle third of the brain of 10 right-handed subjects, using echo-planar imaging and a surface coil. In another eight subjects the temporal properties of the thermal task were examined psychophysically. The fMRI impulse response function was estimated from the cortical activations in the vibrotactile and motor tasks and shown to correspond to earlier reports. Given the fMRI impulse response function and the time courses for the thermal stimulus and the associated pain ratings, predictor functions were generated. The correlation between these predictor functions and cortical activations in the painful thermal task indicated a gradual transition of information processing anteroposteriorly in the parietal cortex. Within this region, activity in the anterior areas more closely reflected thermal stimulus parameters, whereas activity more posteriorly was better related to the temporal properties of pain perception. Insular cortex at the level of the anterior commissure was the region best related to the thermal stimulus, and Brodmann’s area 5/7 was the region best related to the pain perception. The functional implications of these observations are discussed.

scholarly journals Spatio-temporal analysis of flood data from South Carolina

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Haigang Liu ◽  
David B. Hitchcock ◽  
S. Zahra Samadi
Keyword(s):  
South Carolina ◽  
Temporal Structure ◽  
Daily Rainfall ◽  
Temporal Analysis ◽  
The United States ◽  
Environmental Data ◽  
Temporal Properties ◽  
Proximity Matrix ◽  
Spatio Temporal ◽  
Emergency Decision

AbstractTo investigate the relationship between flood gage height and precipitation in South Carolina from 2012 to 2016, we built a conditional autoregressive (CAR) model using a Bayesian hierarchical framework. This approach allows the modelling of the main spatio-temporal properties of water height dynamics over multiple locations, accounting for the effect of river network, geomorphology, and forcing rainfall. In this respect, a proximity matrix based on watershed information was used to capture the spatial structure of gage height measurements in and around South Carolina. The temporal structure was handled by a first-order autoregressive term in the model. Several covariates, including the elevation of the sites and effects of seasonality, were examined, along with daily rainfall amount. A non-normal error structure was used to account for the heavy-tailed distribution of maximum gage heights. The proposed model captured some key features of the flood process such as seasonality and a stronger association between precipitation and flooding during summer season. The model is able to forecast short term flood gage height which is crucial for informed emergency decision. As a byproduct, we also developed a Python library to retrieve and handle environmental data provided by some main agencies in the United States. This library can be of general usefulness for studies requiring rainfall, flow, and geomorphological information over specific areas of the conterminous US.

scholarly journals ASCA Observations of the Crab-Like Pulsar PSR B0540 – 69

2000 ◽  
Vol 177 ◽  
pp. 343-346
Author(s):  
F. Nagase ◽  
T. Endo ◽  
M. Hirayama ◽  
N. Kawai ◽  
M. Itoh
Keyword(s):  
Spectral Analysis ◽  
High Stability ◽  
Pulse Frequency ◽  
Frequency Change ◽  
Archival Data ◽  
Crab Pulsar ◽  
The Past ◽  
Temporal Properties ◽  
Photon Index ◽  
Single Power

AbstractWe report on the spectral and temporal properties of the 50 ms pulsar PSR B0540–69 using ASCA archival data obtained during 1993 to 1995. From the spectral analysis it was found that the spectra of the whole (nebular and pulsed) emission and pulsed emission in the range 1-10 keV can be represented by a single power law of photon index, Γ = 2.00 ± 0.02 and Γpulsed= 1.7 ± 0.3 respectively. The parameters for pulse frequency change during 1993-1995 were obtained using the 9 pulse frequency measurements with ASCA. The parameters derived from the ASCA observations are consistent with the previous measurements, suggesting high stability of this pulsar, ΔΩ/Ω ≲ 0.5 × 10−7over the past 10 years. These results confirm similarity of this pulsar with the Crab pulsar.

scholarly journals Discovery of annular X-ray emission centered on MAXI J1421-613: Dust-scattering X-rays?

2020 ◽  
Vol 72 (2) ◽  
Author(s):  
Kumiko K Nobukawa ◽  
Masayoshi Nobukawa ◽  
Shigeo Yamauchi
Keyword(s):  
Time History ◽  
Rare Condition ◽  
X Rays ◽  
X Ray ◽  
Transient Source ◽  
Hydrogen Column Density ◽  
Photon Index ◽  
Absorbed Power ◽  
Short Time

Abstract We report the discovery of an annular emission of $\sim\!\! {3^{\prime }}\!-\!{9^{\prime }}$ radius around the center of a transient source, the X-ray burster MAXI J1421-613, in the Suzaku follow-up analysis. The spectrum of the annular emission shows no significant emission-line structure, and is well explained by an absorbed power-law model with a photon index of $\sim\!\! 4.2$. These features exclude the possibility that the annular emission is a shell-like component of a supernova remnant. The spectral shape, the time history, and the X-ray flux of the annular emission agree with the scenario that the emission is due to a dust-scattering echo. The annular emission is made under a rare condition of the dust-scattering echo, where the central X-ray source, MAXI J1421-613, exhibits a short time outburst with three X-ray bursts and immediately re-enters a long quiescent period. The distribution of the hydrogen column density along the annular emission follows that of the CO intensity, which means that MAXI J1421-613 is located behind the CO cloud. We estimate the distance to MAXI J1421-613 to be $\sim\!\! 3\:$kpc assuming that the dust layer responsible for the annular emission is located at the same position as the CO cloud.

NUSTAR and Swift observations of AMXP Swift J1756.9−2508 during its 2018 outburst

2019 ◽  
Vol 489 (4) ◽  
pp. 5858-5865
Author(s):  
Binay Rai ◽  
Bikash Chandra Paul
Keyword(s):  
Spectral Analysis ◽  
Power Law ◽  
Power Law Model ◽  
Pulse Profile ◽  
Spectral Parameters ◽  
Time Resolved ◽  
Pulse Phase ◽  
Photon Index ◽  
Hard State ◽  
Orbital Phase

ABSTRACT We present here the timing and spectral analysis of the accreting millisecond pulsar (AMXP) SwiftJ1756.9−2508 during its recent outburst in 2018 using Swift and NUSTAR observations. The simultaneous fitting of the Swift and NUSTAR spectra indicates that the source was in the hard state with a cut-off energy of about 74.58 keV. We also study in detail the pulse profile of the AMXP and its dependence on energy. The colour–colour diagram of the source is different from those previously reported. We performed phase- and time-resolved spectral analysis using NUSTAR data. Pulse phase-resolved spectra were fitted with a power-law model and significant changes in the spectral parameters with pulse phase were observed. The orbital phase and time-resolved spectra were fitted with a cut-off power-law model. The column density and photon index obtained from orbital phase spectral analysis were found to show some anticorrelation with the flux. Through time-resolved spectral analysis, we observed that the spectral parameters show positive correlation with each other and with the flux. We do not observe a softening of the spectrum with time. No emission lines or Compton bump were observed in the spectrum of the AMXP.

scholarly journals Accretion disc–jet couplings in X-ray binaries

2020 ◽  
Vol 495 (2) ◽  
pp. 2408-2415
Author(s):  
Pei-Xin Shen ◽  
Wei-Min Gu
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Flow Model ◽  
Accretion Disc ◽  
X Ray ◽  
Accretion Flow ◽  
Disc Model ◽  
Hard State ◽  
X Ray Binaries ◽  
Jet Power

ABSTRACT When the matter from a companion star is accreted towards the central compact accretor, i.e. a black hole (BH) or a neutron star (NS), an accretion disc and a jet outflow will form, providing bight X-ray and radio emission, which is known as X-ray binaries (XRBs). In the low/hard state, there exist disc–jet couplings in XRBs, but it remains uncertain whether the jet power comes from the disc or the central accretor. Moreover, black hole X-ray binaries (BHXRBs) have different properties compared with neutron star X-ray binaries (NSXRBs): quiescent BHXRBs are typically two to three orders of magnitude less luminous than NSXRBs in X-ray, whereas BHXRBs are more radio loud than NSXRBs. In observations, an empirical correlation has been established between radio and X-ray luminosity, $L_{\rm R} \propto L_{\rm X}^b$, where b ∼ 0.7 for BHXRBs and b ∼ 1.4 for non-pulsating NSXRBs. However, there are some outliers of BHXRBs showing unusually steep correlation as NSXRBs at higher luminosities. In this work, under the assumption that the origin of jet power is related to the internal energy of the inner disc, we apply our magnetized, radiatively efficient thin disc model and the well-known radiatively inefficient accretion flow model to NSXRBs and BHXRBs. We find that the observed radio/X-ray correlations in XRBs can be well understood by the disc–jet couplings.

scholarly journals Correlation of time lag and photon index in GX 339-4

2018 ◽  
Vol 614 ◽  
pp. L5 ◽  
Author(s):  
Nikolaos D. Kylafis ◽  
Pablo Reig
Keyword(s):  
Black Hole ◽  
Power Law ◽  
Time Lag ◽  
Radio Spectrum ◽  
X Ray ◽  
Inverse Compton Scattering ◽  
Photon Index ◽  
Hard State ◽  
Two Parameters ◽  
Soft Disk

Context. Black hole transients, as a class, exhibit during their outbursts a correlation between the time lag of hard photons with respect to softer ones and the photon index of the hard X-ray power law. The correlation is not very tight and therefore it is necessary to examine it source by source. Aims. The objective of the present work is to investigate in detail the correlation between the time lag and the photon index in GX 339-4, which is the best studied black hole transient. Methods. We have obtained RXTE energy spectra and light curves and have computed the photon index and the time lag of the 9–15 keV photons with respect to the 2–6 keV photons. The observations cover the first stages of the hard state, the pure hard state, and the hard-intermediate state. Results. We have found a tight correlation between time lag and photon index Γ in the hard and hard-intermediate states. At low Γ, the correlation is positive; it becomes negative at high Γ By assuming that the hard X-ray power-law index Γ is produced by inverse Compton scattering of soft disk photons in the jet, we have reproduced the entire correlation by varying two parameters in the jet: the radius of the jet at its base R0 and the Thomson optical depth along the jet τ∥. We have found that as the luminosity of the source increases, R0 initially increases and then decreases. This behavior is expected in the context of the Cosmic Battery. Conclusions. Our jet model nicely explains the correlation with reasonable values of the parameters R0 and τ∥ These parameters also correlate between themselves. As a further test of our model, we predict the break frequency in the radio spectrum as a function of the photon index during the rising part of an outburst.

scholarly journals Fermi-LAT observation of nonblazar AGNs

2018 ◽  
Vol 614 ◽  
pp. A6 ◽  
Author(s):  
N. Sahakyan ◽  
V. Baghmanyan ◽  
D. Zargaryan
Keyword(s):  
Power Law ◽  
Radio Galaxies ◽  
High Energy ◽  
Type I ◽  
Large Area ◽  
Instrument Response Function ◽  
Temporal Properties ◽  
Flux Variability ◽  
Photon Index ◽  
Ngc 1275

Context. Fermi Large Area Telescope (Fermi-LAT) has recently detected γ-ray emission from active galactic nuclei (AGN) that do not show clear evidence for optical blazar characteristics or have jets pointing away from the observer (nonblazar AGNs). These are interesting γ-ray emitters providing an alternative approach to studying high energy emission processes. Aims. This paper investigates the spectral and temporal properties of γ-ray emission from nonblazar AGNs using the recent Fermi-LAT observational data. Methods. The data collected by Fermi-LAT during 2008–2015, from the observations of 26 nonblazar AGNs, including 11 Fanaroff–Riley Type I (FRI) and ten FRII radio galaxies and steep spectrum radio quasars (SSRQs) and five narrow line seyfert 1s (NLSy1s) are analysed using the new PASS 8 event selection and instrument response function. Possible spectral changes above GeV energies are investigated with a detailed spectral analysis. Light curves generated with normal and adaptive time bins are used to study the γ-ray flux variability. Results. Non-blazar AGNs have a γ-ray photon index in the range of 1.84–2.86 and a flux varying from a few times 10−9 photon cm−2 s−1 to 10−7 photon cm−2 s−1. Over long time periods, the power law provides an adequate description of the γ-ray spectra of almost all sources. Significant curvature is observed in the γ-ray spectra of NGC 1275, NGC 6251, SBS 0846 + 513, and PMN J0948 + 0022 and their spectra are better described by log parabola or by the power law with exponential cut-off models. The γ-ray spectra of PKS 0625-25 and 3C 380 show a possible deviation from a simple power-law shape, indicating a spectral cut-off around the observed photon energy of Ecut = 131.2 ± 88.04 GeV and Ecut = 55.57 ± 50.74 GeV, respectively. Our analysis confirms the previous finding of an unusual spectral turnover in the γ-ray spectrum of Cen A: the photon index changes from Γ = 2.75 ± 0.02 to 2.31 ± 0.1 at 2.35 ± 0.08 GeV. In the Γ−Lγ plane, the luminosity of nonblazar AGNs is spread in the range of (1041–1047) erg s−1, where those with the lowest luminosity are FRI radio galaxies (but typically appear with a harder photon index) and those with the highest luminosity have are SSRQs/NLSY1s (with softer photon indexes). We confirm the previously reported short-timescale flux variability of NGC 1275 and 3C 120. The γ-ray emission from NLSY1s, 1H 0323 + 342, SBS 0846 + 513, and PMN J0948 + 0022 is variable, showing flares in short scales sometimes accompanied by a moderate hardening of their spectra (e.g., for MJD 56146.8 the γ-ray photon index of SBS 0846 + 513 was Γ = 1.73 ± 0.14). Non-blazar AGNs 3C 111, Cen A core, 3C 207, 3C 275.1, 3C 380, 4C + 39.23B, PKS 1502 + 036, and PKS 2004-447 show a long-timescale flux variability in the γ-ray band.

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