prantik nandi - Academia.edu (original) (raw)
Papers by prantik nandi
Monthly Notices of the Royal Astronomical Society
We present the results obtained from a detailed X-ray timing and spectral analysis of the Seyfert... more We present the results obtained from a detailed X-ray timing and spectral analysis of the Seyfert 2 galaxy NGC 6300 by using observations from the Suzaku observatory, theChandra X-ray Observatory and the Nuclear Spectroscopic Telescope Array(NuSTAR) mission between 2007 and 2016. We calculate the variance and the rms fractional variability of the source in different energy bands and we find variabilities in various energy bands. Spectral properties of the source are studied by using various phenomenological and physical models. The properties of the Compton clouds, reflection, Fe Kα line emission and soft X-ray excess are studied in detail. Several physical parameters of the source are extracted and investigated to establish the presence/absence of any correlation between them. We also investigate the nature of the circumnuclear ‘torus’ and we find that the torus is not uniform, but clumpy. The observed changes in the line-of-sight column density can be explained in terms of transit...
Monthly Notices of the Royal Astronomical Society
The evolution of variability properties of Galactic transient sources is a diagnostic tool to und... more The evolution of variability properties of Galactic transient sources is a diagnostic tool to understand various regimes of the accretion flow and its dynamics close to the central black hole. In this paper, we concentrate on the variability properties of the X-ray transient XTE J1650−500 and investigate the evolution of viscous delay, time lag, quasi-periodic oscillation (QPO) frequency, and their energy dependence throughout the rising phase as observed by Rossi X-ray Timing Explorer(RXTE) during its outburst in 2001. Our analysis reveals (1) a delay of 12 ± 1 d between 1 d-averaged hard (5–12 keV) and soft (1.5–3 keV) photon light curves as observed by RXTE/ASM; (2) QPOs with high rms values are observed in lower energy (4–8 keV) range; (3) the QPO frequencies and associated time lags were anticorrelated during the initial days of the rising phase, and later on, they were found to be correlated; (4) the time lags of Fe-line photons with respect to hard and soft photons remained a...
The Astrophysical Journal
The nature of lag variation of Galactic black holes remains enigmatic mostly because of nonlinear... more The nature of lag variation of Galactic black holes remains enigmatic mostly because of nonlinear and nonlocal physical mechanisms which contribute to the lag of the photons coming from the region close to the central black holes. One of the widely accepted major sources of the hard lag is the inverse Comptonization mechanism. However, exact reason or reasons for soft lags is yet to be identified. In this paper, we report a possible correlation between radio intensities of several outbursting Galactic black hole candidates and amounts of soft lag. The correlation suggests that the presence of major outflows or jets also change the disk morphology along the line of sight of the observer which produces soft lags.
Proceedings
X-ray time lags are complicated in nature. The exact reasons for complex lag spectra are as yet u... more X-ray time lags are complicated in nature. The exact reasons for complex lag spectra are as yet unknown. However, the hard lags, in general, are believed to be originated due to inverse Comptonization process. However, the origin of soft lags remained mischievous. Recent studies on “Disk–Jet Connections” revealed that the jets are also contributing in the X-ray spectral and timing properties in a magnitude which was more than what was predicted earlier. In this article, we first show an exact anticorrelation between X-ray time lag and radio flux for XTE J1550-546 during its 1998 outburst. We propose that the soft lags might be generated due to the change in the accretion disk structure along the line of sight during higher jet activity.
The Astrophysical Journal
We present X-ray spectral analysis of Seyfert 1.5 Active Galactic Nuclei (AGN) NGC 4151 using NuS... more We present X-ray spectral analysis of Seyfert 1.5 Active Galactic Nuclei (AGN) NGC 4151 using NuSTAR observation during 2012. This is the first attempt to fit an AGN data using the physical Two Component Advective flow (TCAF) solution. We disentangle the continuum emission properties of the source in the energy range 3.0 to 70.0 keV using the spectrum obtained from TCAF model. This model was used as an additive local model directly in XSPEC. Additionally, we used a power law (PL) component, to take care of possible X-ray contribution from the jet, which is not incorporated in the present version of TCAF. Our primary aim is to obtain the flow properties and the mass of the central supermassive black hole from the available archival data. Our best estimate of the average mass obtained from spectral fits of three observations, is M BH = 3.03 +0.26 −0.26 × 10 7 M ⊙. This is consistent with earlier estimations in the literature such as reverberation mapping, gas kinematics and stellar dynamics around black holes. We also discuss the accretion dynamics and the flow geometry on the basis of model fitted physical parameters. Model fitted disk accretion rate is found to be lower than the low angular momentum halo accretion rate, indicating that the source was in a hard state during the observation.
Monthly Notices of the Royal Astronomical Society
We present the long-term X-ray spectral and temporal analysis of a ‘bare-type AGN’ Ark 120. We co... more We present the long-term X-ray spectral and temporal analysis of a ‘bare-type AGN’ Ark 120. We consider the observations from XMM–Newton, Suzaku, Swift, and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of several physical parameters, such as the temperature and the optical depth of the electron cloud, the size of the Compton cloud, and the accretion properties for the last 15 yr. The spectral variations are explained from the changes in the accretion dynamics; (b) the X-ray time delay between 0.2–2 and 3–10 keV light-curves exhibited zero-delay in 2003, positive delay of 4.71 ± 2.1 ks in 2013, and negative delay of 2.90 ± 1.26 ks in 2014. The delays are explained considering Comptonization, reflection, and light-crossing time; (c) the long-term intrinsic luminosities, obtained using nthcomp, of the soft-excess and the primary continuum show a cor...
Monthly Notices of the Royal Astronomical Society
We present the results obtained from a detailed X-ray timing and spectral analysis of the Seyfert... more We present the results obtained from a detailed X-ray timing and spectral analysis of the Seyfert 2 galaxy NGC 6300 by using observations from the Suzaku observatory, theChandra X-ray Observatory and the Nuclear Spectroscopic Telescope Array(NuSTAR) mission between 2007 and 2016. We calculate the variance and the rms fractional variability of the source in different energy bands and we find variabilities in various energy bands. Spectral properties of the source are studied by using various phenomenological and physical models. The properties of the Compton clouds, reflection, Fe Kα line emission and soft X-ray excess are studied in detail. Several physical parameters of the source are extracted and investigated to establish the presence/absence of any correlation between them. We also investigate the nature of the circumnuclear ‘torus’ and we find that the torus is not uniform, but clumpy. The observed changes in the line-of-sight column density can be explained in terms of transit...
Monthly Notices of the Royal Astronomical Society
The evolution of variability properties of Galactic transient sources is a diagnostic tool to und... more The evolution of variability properties of Galactic transient sources is a diagnostic tool to understand various regimes of the accretion flow and its dynamics close to the central black hole. In this paper, we concentrate on the variability properties of the X-ray transient XTE J1650−500 and investigate the evolution of viscous delay, time lag, quasi-periodic oscillation (QPO) frequency, and their energy dependence throughout the rising phase as observed by Rossi X-ray Timing Explorer(RXTE) during its outburst in 2001. Our analysis reveals (1) a delay of 12 ± 1 d between 1 d-averaged hard (5–12 keV) and soft (1.5–3 keV) photon light curves as observed by RXTE/ASM; (2) QPOs with high rms values are observed in lower energy (4–8 keV) range; (3) the QPO frequencies and associated time lags were anticorrelated during the initial days of the rising phase, and later on, they were found to be correlated; (4) the time lags of Fe-line photons with respect to hard and soft photons remained a...
The Astrophysical Journal
The nature of lag variation of Galactic black holes remains enigmatic mostly because of nonlinear... more The nature of lag variation of Galactic black holes remains enigmatic mostly because of nonlinear and nonlocal physical mechanisms which contribute to the lag of the photons coming from the region close to the central black holes. One of the widely accepted major sources of the hard lag is the inverse Comptonization mechanism. However, exact reason or reasons for soft lags is yet to be identified. In this paper, we report a possible correlation between radio intensities of several outbursting Galactic black hole candidates and amounts of soft lag. The correlation suggests that the presence of major outflows or jets also change the disk morphology along the line of sight of the observer which produces soft lags.
Proceedings
X-ray time lags are complicated in nature. The exact reasons for complex lag spectra are as yet u... more X-ray time lags are complicated in nature. The exact reasons for complex lag spectra are as yet unknown. However, the hard lags, in general, are believed to be originated due to inverse Comptonization process. However, the origin of soft lags remained mischievous. Recent studies on “Disk–Jet Connections” revealed that the jets are also contributing in the X-ray spectral and timing properties in a magnitude which was more than what was predicted earlier. In this article, we first show an exact anticorrelation between X-ray time lag and radio flux for XTE J1550-546 during its 1998 outburst. We propose that the soft lags might be generated due to the change in the accretion disk structure along the line of sight during higher jet activity.
The Astrophysical Journal
We present X-ray spectral analysis of Seyfert 1.5 Active Galactic Nuclei (AGN) NGC 4151 using NuS... more We present X-ray spectral analysis of Seyfert 1.5 Active Galactic Nuclei (AGN) NGC 4151 using NuSTAR observation during 2012. This is the first attempt to fit an AGN data using the physical Two Component Advective flow (TCAF) solution. We disentangle the continuum emission properties of the source in the energy range 3.0 to 70.0 keV using the spectrum obtained from TCAF model. This model was used as an additive local model directly in XSPEC. Additionally, we used a power law (PL) component, to take care of possible X-ray contribution from the jet, which is not incorporated in the present version of TCAF. Our primary aim is to obtain the flow properties and the mass of the central supermassive black hole from the available archival data. Our best estimate of the average mass obtained from spectral fits of three observations, is M BH = 3.03 +0.26 −0.26 × 10 7 M ⊙. This is consistent with earlier estimations in the literature such as reverberation mapping, gas kinematics and stellar dynamics around black holes. We also discuss the accretion dynamics and the flow geometry on the basis of model fitted physical parameters. Model fitted disk accretion rate is found to be lower than the low angular momentum halo accretion rate, indicating that the source was in a hard state during the observation.
Monthly Notices of the Royal Astronomical Society
We present the long-term X-ray spectral and temporal analysis of a ‘bare-type AGN’ Ark 120. We co... more We present the long-term X-ray spectral and temporal analysis of a ‘bare-type AGN’ Ark 120. We consider the observations from XMM–Newton, Suzaku, Swift, and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of several physical parameters, such as the temperature and the optical depth of the electron cloud, the size of the Compton cloud, and the accretion properties for the last 15 yr. The spectral variations are explained from the changes in the accretion dynamics; (b) the X-ray time delay between 0.2–2 and 3–10 keV light-curves exhibited zero-delay in 2003, positive delay of 4.71 ± 2.1 ks in 2013, and negative delay of 2.90 ± 1.26 ks in 2014. The delays are explained considering Comptonization, reflection, and light-crossing time; (c) the long-term intrinsic luminosities, obtained using nthcomp, of the soft-excess and the primary continuum show a cor...