scholarly journals AstroSat view of LMC X-2: evolution of broad-band X-ray spectral properties along a complete Z-track

2020 ◽  
Vol 497 (3) ◽  
pp. 3726-3733
Author(s):  
V K Agrawal ◽  
Anuj Nandi
Keyword(s):  
Optical Depth ◽  
Broad Band ◽  
Periodic Oscillation ◽  
Large Magellanic Cloud ◽  
Large Area ◽  
X Ray ◽  
Weak Evidence ◽  
First Results ◽  
Area X ◽  
Z Sources

ABSTRACT In this paper, we report the first results of the extragalactic Z-source Large Magellanic Cloud (LMC) X-2 obtained using the ∼140 ks observations with Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat. The Hardness-Intensity Diagram created with the LAXPC data revealed a complete Z-pattern of the source, showing all the three branches. We studied the evolution of the broad-band X-ray spectra in the energy range of 0.5–20.0 keV along the Z-track, a first such study of this source. The X-ray spectra of the different parts of the Z-pattern were well described by an absorbed Comptonized component. An absence of the accretion disc component suggests that the disc is most probably obscured by a Comptonized region. The best fit electron temperature (kTe) was found to be in the range of 1.7–2.1 keV and optical depth (τ) was found to be in the range of 13.2–17.5. The optical depth (τ) increased as the source moved from the normal/flaring branch (NB/FB) vertex to the upper part of the FB, suggesting a possible outflow triggered by a strong radiation pressure. The power density spectra (PDS) of HB and NB could be fitted with a pure power law of index α∼1.68 and 0.83, respectively. We also found a weak evidence of quasi-periodic oscillation (2.8σ) in the FB. The intrinsic luminosity of the source varied between (1.03–1.79) × 1038 erg s−1. We discuss our results by comparing with other Z-sources and the previous observations of LMC X-2.

scholarly journals AstroSat view of GRS 1915+105 during the soft state: detection of HFQPOs and estimation of mass and spin

2020 ◽  
Vol 499 (4) ◽  
pp. 5891-5901
Author(s):  
H Sreehari ◽  
Anuj Nandi ◽  
Santabrata Das ◽  
V K Agrawal ◽  
Samir Mandal ◽  
...  
Keyword(s):  
Broad Band ◽  
Power Spectra ◽  
Periodic Oscillation ◽  
High Energy ◽  
Energy Spectra ◽  
Large Area ◽  
X Ray ◽  
Soft State ◽  
Photon Index ◽  
Area X

ABSTRACT We report the results of AstroSat observations of GRS 1915+105 obtained using 100 ks Guaranteed Time during the soft state. The colour–colour diagram indicates a variability class of δ with the detection of high-frequency quasi-periodic oscillation (HFQPO) in the power density spectra. The HFQPO is seen to vary in the frequency range of 67.96–70.62 Hz with percentage rms ∼0.83–1.90 per cent and significance varying from 1.63 to 7.75. The energy dependent power spectra show that the HFQPO features are dominant only in 6–25 keV energy band. The broad-band energy spectra (0.7–50 keV) of Soft X-ray Telescope and Large Area X-ray Proportional Counter modelled with nthComp and powerlaw imply that the source has an extended corona in addition to a compact ‘Comptonizing corona’ that produces high-energy emission and exhibits HFQPOs. The broad-band spectral modelling indicates that the source spectra are well described by thermal Comptonization with electron temperature (kTe) of 2.07–2.43 keV and photon index (Γnth) between 1.73 and 2.45 with an additional powerlaw component of photon index (ΓPL) between 2.94 and 3.28. The norm of nthComp component is high (∼8) during the presence of strong HFQPO and low (∼3) during the absence of HFQPO. Further, we model the energy spectra with the kerrbb model to estimate the accretion rate, mass, and spin of the source. Our findings indicate that the source accretes at super-Eddington rate of $1.17\!-\!1.31~ \dot{M}_{\rm Edd}$. Moreover, we find the mass and spin of the source as 12.44–13.09 M⊙ and 0.990–0.997 with $90{{\ \rm per\ cent}}$ confidence suggesting that GRS 1915+105 is a maximally rotating stellar mass X-ray binary black hole source.

scholarly journals A variable-frequency HFQPO in GRS 1915+105 as observed with AstroSat

2019 ◽  
Vol 489 (1) ◽  
pp. 1037-1043 ◽  
Author(s):  
Tomaso M Belloni ◽  
Dipankar Bhattacharya ◽  
Pietro Caccese ◽  
Varun Bhalerao ◽  
Santosh Vadawale ◽  
...  
Keyword(s):  
Periodic Oscillation ◽  
Large Area ◽  
Quasi Periodic Oscillation ◽  
X Ray ◽  
Phase Lags ◽  
Time Variations ◽  
Area X ◽  
First Time ◽  
Observation Period

ABSTRACT From the analysis of more than 92 ks of data obtained with the Large Area X-Ray Proportional Counter (LAXPC) instrument onboard AstroSat we have detected a clear high-frequency quasi-periodic oscillation (HFQPO) whose frequency varies between 67.4 and 72.3 Hz. In the classification of variability classes of GRS 1915+105, at the start of the observation period the source was in class ω and at the end the variability was that of class μ: both classes are characterized by the absence of hard intervals and correspond to disc-dominated spectra. After normalization to take into account time variations of the spectral properties as measured by X-ray hardness, the QPO centroid frequency is observed to vary along the hardness–intensity diagram, increasing with hardness. We also measure phase lags that indicate that HFQPO variability at high energies lags that at lower energies and detect systematic variations with the position on the hardness–intensity diagram. This is the first time that (small) variations of the HFQPO frequency and lags are observed to correlate with other properties of the source. We discuss the results in the framework of existing models, although the small (7 per cent) variability observed is too small to draw firm conclusions.

scholarly journals Estimation of the black hole spin in LMC X-1 using AstroSat

2020 ◽  
Vol 498 (3) ◽  
pp. 4404-4410
Author(s):  
Sneha Prakash Mudambi ◽  
A Rao ◽  
S B Gudennavar ◽  
R Misra ◽  
S G Bubbly
Keyword(s):  
Black Hole ◽  
Broad Band ◽  
Spectral Studies ◽  
Large Area ◽  
Mass Source ◽  
Orbital Inclination ◽  
X Ray ◽  
Soft State ◽  
Galactic Black Hole ◽  
Area X

ABSTRACT LMC X-1, a persistent, rapidly rotating, extra-galactic, black hole X-ray binary (BHXB) discovered in 1969, has always been observed in its high soft state. Unlike many other BHXBs, the black hole mass, source distance, and binary orbital inclination are well established. In this work, we report the results of simultaneous broad-band spectral studies of LMC X-1 carried out using the data from Soft X-ray Telescope and Large Area X-ray Proportional Counter aboard AstroSat as observed on 2016 November 26 and 2017 August 28. The combined spectrum was modelled with a multicolour blackbody emission (diskbb), a Gaussian along with a Comptonization component (simpl) in the energy range 0.7–30.0 keV. The spectral analysis revealed that the source was in its high soft state (Γ = 2.67$^{+0.24}_{-0.24}$ and Γ = 2.12$^{+0.19}_{-0.20}$) with a hot disc (kTin = 0.86$^{+0.01}_{-0.01}$ and kTin = 0.87$^{+0.02}_{-0.02}$). Thermal disc emission was fitted with a relativistic model (kerrbb) and spin of the black hole was estimated to be 0.93$^{+0.01}_{-0.01}$ and 0.93$^{+0.04}_{-0.03}$ (statistical errors) for the two Epochs through X-ray continuum-fitting, which agrees with the previous results.

A large area X-ray imager with online linearization and noise suppression

2011 ◽  
Author(s):  
T. He ◽  
R. Durst ◽  
B. L. Becker ◽  
J. Kaercher ◽  
G. Wachter
Keyword(s):  
Noise Suppression ◽  
Large Area ◽  
X Ray ◽  
Area X

scholarly journals A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state

2019 ◽  
Vol 486 (2) ◽  
pp. 2964-2975 ◽  
Author(s):  
Bari Maqbool ◽  
Sneha Prakash Mudambi ◽  
R Misra ◽  
J S Yadav ◽  
S B Gudennavar ◽  
...  
Keyword(s):  
Time Lag ◽  
Broad Band ◽  
Propagation Model ◽  
Large Area ◽  
Temporal Behaviour ◽  
X Ray ◽  
Single Temperature ◽  
Hard State ◽  
Band Spectra ◽  
Energy Dependent

Abstract We report the results from analysis of six observations of Cygnus X-1 by Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat, when the source was in the hard spectral state as revealed by the broad-band spectra. The spectra obtained from all the observations can be described by a single-temperature Comptonizing region with disc and reflection components. The event mode data from LAXPC provides unprecedented energy dependent fractional root mean square (rms) and time-lag at different frequencies which we fit with empirical functions. We invoke a fluctuation propagation model for a simple geometry of a truncated disc with a hot inner region. Unlike other propagation models, the hard X-ray emission (>4 keV) is assumed to be from the hot inner disc by a single-temperature thermal Comptonization process. The fluctuations first cause a variation in the temperature of the truncated disc and then the temperature of the inner disc after a frequency dependent time delay. We find that the model can explain the energy dependent rms and time-lag at different frequencies.

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.

Balloon Observations of Several Southern X-Ray Sources

1979 ◽  
Vol 3 (5) ◽  
pp. 349-350 ◽  
Author(s):  
J. G. Greenhill ◽  
M. L Duldig ◽  
M. W. Emery ◽  
A. G. Fenton ◽  
K. B. Fenton ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Transient Increase ◽  
Large Area ◽  
Gamma Ray Burst ◽  
X Ray ◽  
The University ◽  
Area X

The University of Tasmania balloon-borne large area X-ray telescope was flown from Alice Springs on 20 November 1978. A number of known X-ray sources were observed and a transient increase believed to be a gamma ray burst was detected.

New large-area x-ray image sensor

1998 ◽  
Author(s):  
Donald R. Ouimette ◽  
Sol Nudelman ◽  
Richard S. Aikens
Keyword(s):  
Image Sensor ◽  
Large Area ◽  
X Ray ◽  
Area X

scholarly journals High Speed, High Resolution and Large Area X-ray Imaging Using Silicon Drift Detectors

2011 ◽  
Vol 17 (S2) ◽  
pp. 892-893 ◽  
Author(s):  
R Terborg ◽  
J Berlin ◽  
T Salge
Keyword(s):  
High Resolution ◽  
High Speed ◽  
Large Area ◽  
X Ray ◽  
X Ray Imaging ◽  
Silicon Drift Detectors ◽  
Area X

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

scholarly journals Study of recent outburst in the Be/X-ray binary RX J0209.6−7427 with AstroSat: a new ultraluminous X-ray pulsar in the Magellanic Bridge?

2020 ◽  
Vol 495 (3) ◽  
pp. 2664-2672 ◽  
Author(s):  
Amar Deo Chandra ◽  
Jayashree Roy ◽  
P C Agrawal ◽  
Manojendu Choudhury
Keyword(s):  
Energy Band ◽  
Spectral Characteristics ◽  
Spectral Studies ◽  
X Rays ◽  
Energy Bands ◽  
Large Area ◽  
Pulse Profile ◽  
X Ray ◽  
Outburst Energy ◽  
Area X

ABSTRACT We present the timing and spectral studies of RX J0209.6–7427 during its rare 2019 outburst using observations with the Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) instruments on the AstroSat satellite. Pulsations having a periodicity of 9.29 s were detected for the first time by the NICER mission in the 0.2–10 keV energy band and, as reported here, by AstroSat over a broad energy band covering 0.3–80 keV. The pulsar exhibits a rapid spin-up during the outburst. Energy resolved folded pulse profiles are generated in several energy bands in 3–80 keV. To the best of our knowledge this is the first report of the timing and spectral characteristics of this Be binary pulsar in hard X-rays. There is suggestion of evolution of the pulse profile with energy. The energy spectrum of the pulsar is determined and from the best-fitting spectral values, the X-ray luminosity of RX J0209.6−7427 is inferred to be 1.6 × 1039 erg s−1. Our timing and spectral studies suggest that this source has features of an ultraluminous X-ray pulsar in the Magellanic Bridge. Details of the results are presented and discussed in terms of the current ideas.

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