Observing Compact Stars with AstroSat

Bhattacharya, Dipankar

doi:10.1007/s12036-017-9461-x

Cited by 16 publications

(4 citation statements)

References 19 publications

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“…In addition, a multiplicative constant factor was included in the model combination to address uncertainties caused due to cross calibration between the SXT and LAXPC instruments. As prescribed by the POC, a systematic error of 3% was added to all spectral fits (Bhattacharya 2017). Further, a gain fit was performed with the slope of the gain frozen to unity and the offset left to vary to account for the non-linear change in the detector gain of the SXT instrument.…”

Section: Spectral Analysismentioning

confidence: 99%

Spectro-temporal and Type I X-ray burst analysis of GX 3$+$1 using \textit{AstroSat} observations

Thomas¹,

Gudennavar²,

G.³

2023

Preprint

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GX 3+1, an atoll type neutron star low-mass X-ray binary, was observed four times by Soft X-ray Telescope and The Large Area X-ray Proportional Counters on-board AstroSat between October 5, 2017 and August 9, 2018. The hardness-intensity-diagram of the source showed it to be in the soft spectral state during all the four observations. The spectra of the source could be adequately fit with a model consisting of blackbody (bbody) and power-law (powerlaw) components. This yielded the blackbody radius and mass accretion rate to be ∼8 km and ∼2 × 10 −9 M y −1 , respectively. In one of the observations, a Type I X-ray burst having a rise and e-folding time of 0.6 and 5.6 s, respectively, was detected. Time-resolved spectral analysis of the burst showed that the source underwent a photospheric radius expansion. The radius of the emitting blackbody in GX 3+1 and its distance were estimated to be 9.19 +0.97 −0.82 km and 10.17 +0.07−0.18 kpc, respectively. Temporal analysis of the burst yielded upper limits of the fractional RMS amplitude of 7%, 5% and 6% during burst start, burst maximum and right after the radius expansion phase, respectively.

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Section: Spectral Analysismentioning

confidence: 99%

Spectro-temporal and Type I X-ray burst analysis of GX 3$+$1 using \textit{AstroSat} observations

Thomas¹,

Gudennavar²,

G.³

2023

Preprint

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“…The constant factor here accounts for the uncertainties in the cross calibration between SXT and LAXPC-20 instruments. A systematic error of 3 per cent was added as prescribed by Bhattacharya (2017). Finally, a gain fit was performed with the slope of the gain fixed to unity and the offset left to vary to account for the non-linear change in the detector gain of the SXT instrument.…”

Section: Spectral Studies Using Astrosat Datamentioning

confidence: 99%

NuSTAR and AstroSat observations of GX 9+1: spectral and temporal studies

Thomas

Gudennavar

Bubbly

2023

Monthly Notices of the Royal Astronomical Society

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We have studied the spectro-temporal properties of the neutron star low mass X-ray binary GX 9+1 using data from NuSTAR/FPM and AstroSat/SXT and LAXPC. The hardness-intensity diagram of the source showed it to be in the soft spectral state during both observations. NuSTAR spectral analysis yielded an inclination angle (θ) = 29${^{+3}_{-4}}^{\circ }$ and inner disk radius (Rin) ≤ 19.01 km. Assuming that the accretion disk was truncated at the Alfvén radius during the observation, the upper limit of the magnetic dipole moment (μ) and the magnetic field strength (B) at the poles of the neutron star in GX 9+1 were calculated to be 1.45×1026 G cm3 and 2.08×108 G, respectively (for kA = 1). Flux resolved spectral analysis with AstroSat data showed the source to be in the soft spectral state (Fdisk/Ftotal ∼0.9) with a monotonic increase in mass accretion rate ($\dot{m}$) along the banana branch. The analysis also showed the presence of absorption edges at ∼1.9 and ∼2.4 keV, likely due to Si XIII and S XV, respectively. Temporal analysis with LAXPC-20 data in the 0.02 − 100 Hz range revealed the presence of noise components, which could be characterized with broad Lorentzian components.

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“…Further, a multiplicative constant factor was included to address uncertainties caused due to cross calibration of the SXT and LAXPC instruments. As prescribed by the POC, a systematic error of 3% was added to all spectral fit (Bhattacharya 2017). In addition to this, gain fit was performed for the SXT data to account for the non-linear change in the detector gain.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Spectral properties of soft X-ray transient MAXI J0637$-$430 using AstroSat

Thomas,

Gudennavar,

Misra

et al. 2022

Preprint

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Soft X-ray transients are systems that are detected when they go into an outburst, wherein their X-ray luminosity increases several orders of magnitude. These outbursts are markers of the poorly understood change in the spectral state of these systems from low/hard state to high/soft state. We report the spectral properties of one such soft X-ray transient: MAXI J0637−430, with data from the SXT and LAXPC instruments on-board AstroSat mission. The source was observed for a total of ∼ 60 ks over two observations on 8 th and 21 st November, 2019 soon after its discovery. Flux resolved spectral analysis of the source indicates the presence of a multi-colour blackbody component arising from the accretion disk and a thermal Comptonization component. The stable low temperature (∼ 0.55 keV ) of the blackbody component, points to a cool accretion disk with an inner disk radius of the order of a few hundred km. In addition, we report the presence of a relativistically broadened Gaussian line at 6.4 keV . The disk dominated flux and photon power law index of 2 and a constant inner disk radius indicate the source to be in the soft state. From the study we conclude that MAXI J0637−430 is a strong black hole X-ray binary candidate.

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Observing Compact Stars with AstroSat

Cited by 16 publications

References 19 publications

Spectro-temporal and Type I X-ray burst analysis of GX 3$+$1 using \textit{AstroSat} observations

Spectro-temporal and Type I X-ray burst analysis of GX 3$+$1 using \textit{AstroSat} observations

NuSTAR and AstroSat observations of GX 9+1: spectral and temporal studies

Spectral properties of soft X-ray transient MAXI J0637$-$430 using AstroSat

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