Ritesh Ghosh | IUCAA - Academia.edu (original) (raw)

Papers by Ritesh Ghosh

A broad-band X-ray spectral study of the Seyfert 1 galaxy ESO 141–G055 with XMM–Newton and NuSTAR

Monthly Notices of the Royal Astronomical Society

We have extensively studied the broad--band X-ray spectra of the source ESO 141–G055 using all av... more We have extensively studied the broad--band X-ray spectra of the source ESO 141–G055 using all available XMM–Newton and NuSTAR observations. We detect a prominent soft excess below 2rm,,rmkeV2\rm \, \, {\rm keV}2rm,,rmkeV, a narrow Fe line, and a Compton hump ($\gt 10\rm \, \, {\rm keV}$). The origin of the soft excess is still debated. We used two models to describe the soft excess: the blurred reflection from the ionized accretion disc and the intrinsic thermal Comptonization model. We find that both of these models explain the soft excess equally well. We confirm that we do not detect any broad Fe line in the X-ray spectra of this source, although both the physical models prefer a maximally spinning black hole scenario (a > 0.96). This may mean that either the broad Fe line is absent or blurred beyond detection. The Eddington rate of the source is estimated to be lambdarm,Eddsim0.31\lambda _{\rm \, Edd}\sim 0.31lambdarm,Eddsim0.31. In the reflection model, the Compton hump has a contribution from both ionized and neutral reflecti...

Blazar Variability: A Study of Nonstationarity and the Flux–Rms Relation

The Astrophysical Journal

Monthly Notices of the Royal Astronomical Society

We present a broadband spectral study of the radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342 ... more We present a broadband spectral study of the radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342 based on multi-epoch observations performed with NuSTAR on 2014 March 15, and two simultaneous observations performed with Suzaku and Swift on 2009 July 26 and 2013 March 1. We found the presence of a strong soft X-ray excess emission, a broad but weak Fe line and hard X-ray excess emission. We used the blurred reflection (relxill) and the intrinsic disc Comptonization (optxagnf), two physically motivated models, to describe the broadband spectra and to disentangle the disk/corona and jet emission. The relxill model is mainly constrained by the strong soft X-ray excess although the model failed to predict this excess when fitted above 3 keV and extrapolated to lower energies. The joint spectral analysis of the three datasets above 3 keV with this model resulted in a high black hole spin (a > 0.9) and moderate reflection fraction R ∼ 0.5. The optxagnf model fitted to the two simultaneous datasets resulted in an excess emission in the UV band. The simultaneous UV-to-hard X-ray spectra of 1H 0323+342 are best described by a model consisting of a primary X-ray power-law continuum with Γ ∼ 1.8, a blurred reflection component with R ∼ 0.5, Comptonised disk emission as the soft X-ray excess, optical/UV emission from a standard accretion disk around a black hole of mass ∼ 10 7 M ⊙ and a steep power law (Γ ∼ 3 − 3.5) component, most likely the jet emission in the UV band. The fractional RMS variability spectra suggest that both the soft excess and the powerlaw component are variable in nature.

Monthly Notices of the Royal Astronomical Society

We have carried out a systematic X-ray spectral analysis of a sample of low luminosity quasars (L... more We have carried out a systematic X-ray spectral analysis of a sample of low luminosity quasars (LLQSO) to investigate the nature of the central engines of these sources. The opticallyselected LLQSO sample consists of close, known bright active galactic nuclei (AGN) which serves as an important link between the powerful quasars at higher redshift and local Seyfert galaxies. We find that although the bolometric luminosities of the LLQSOs are lower than those of the higher redshift quasars by almost an order of magnitude, their distribution of the Eddington rate λ Edd is similar. We detect a strong anti-correlation between α OX and L 2500Å , as has also been detected in several other quasar studies with large sample sizes, indicating that as the UV luminosity of the source increases, the X-ray luminosity decreases. We do not detect any significant neutral obscuration (N H 10 22 cm −2) in the X-ray spectra of the LLQSOs, and hence rule out obscuration as a possible cause for their lower luminosity. We conclude that the central engines of the LLQSOs function similarly to those of the higher redshift quasars, and the difference is possibly because of the fact that the LLQSOs have lower black hole masses. We do not find any correlation between the molecular gas in the host galaxies and accretion states of the AGN. This indicates that the presence of molecular gas in the host galaxies of the LLQSOs does not significantly influence the instantaneous accretion rates of their SMBHs.

The Astrophysical Journal

We have carried out an extensive X-ray spectral analysis of a sample of galaxies exhibiting molec... more We have carried out an extensive X-ray spectral analysis of a sample of galaxies exhibiting molecular outflows (MOX sample), to characterize the X-ray properties and investigate the effect of AGN on the dynamical properties of the molecular outflows. We find that the X-ray bolometric correction (L 2−10 keV /L AGN) of these sources ranges from ∼ 10 −4.5 to 10 −0.5 , with ∼ 70% of the sources below 10 −2 , implying a weak X-ray emission relative to the AGN bolometric luminosity (L AGN). However, the upper limit on the 2 − 10 keV luminosity (L 2−10 keV, 12µm) obtained from 12µm flux, following the correlation derived by Asmus et al., are ∼ 0.5 − 3 orders of magnitude larger than the L 2−10 keV values estimated using X-ray spectroscopy, implying a possibility that the MOX sources host normal AGN (not X-ray weak), and their X-ray spectra are extremely obscured. We find that both L 2−10 keV , and L AGN correlates strongly with the molecular outflow velocity as well as the mass outflow rates (Ṁ out), implying that the central AGN plays an important role in driving these massive outflows. However, we also find statistically significant positive correlations between the starburst emission and MO mass outflow rate, L Starburst vsṀ out , and L 0.6−2 keV vsṀ out , which implies that starbursts can generate and drive the molecular outflows. The correlations of MO velocity andṀ out with AGN luminosities are found to be stronger compared to those with the starburst luminosities. We conclude that both starbursts and AGN play crucial role in driving the large scale MO.

Monthly Notices of the Royal Astronomical Society

We have investigated the nature and origin of the Fe K emission lines in Mrk 205 using observatio... more We have investigated the nature and origin of the Fe K emission lines in Mrk 205 using observations with Suzaku and XMM–Newton, aiming to resolve the ambiguity between a broad emission line and multiple unresolved lines of higher ionization. We detect the presence of a narrow Fe K α emission line along with a broad-band Compton reflection hump at energies Egt10rm,,rmkeVE\gt 10\rm \, \, {\rm keV}Egt10rm,,rmkeV. These are consistent with reflected emission of hard X-ray photons off a Compton-thick material of NrmHge2.15times1024rm,,rmcm−2N_{\rm H}\ge 2.15\times 10^{24}\rm \, \, {\rm cm^{-2}}NrmHge2.15times1024rm,,rmcm−2. In addition we detect a partially covering ionized absorption with ionization parameter log(xi/rm,erg,cm,s−1)=1.9−0.5+0.1\log (\xi /\rm \, erg\, cm\, s^{-1})=1.9_{-0.5}^{+0.1}log(xi/rm,erg,cm,s−1)=1.9−0.5+0.1, column density NrmH=(5.6−1.9+2.0)times1022rm,,rmcm−2N_{\rm H}=(5.6_{-1.9}^{+2.0})\times 10^{22}\rm \, \, {\rm cm^{-2}}NrmH=(5.6−1.9+2.0)times1022rm,,rmcm−2, and a covering factor of 0.22−0.06+0.090.22_{-0.06}^{+0.09}0.22−0.06+0.09. We detect the presence of emission arising out of ionized disc reflection contributing in the soft and hard X-rays consistently in all the observations. We however, could n...

For most bright nearby AGN, we commonly detect He-like O VII emission lines at ∼ 0.56 keV. In thi... more For most bright nearby AGN, we commonly detect He-like O VII emission lines at ∼ 0.56 keV. In this work, I study the correlation between the O VII emission line strength and the instantaneous AGN ionizing luminosity (13.6 eV − 13.6 keV) in a sample of bright nearby AGN to understand the effect of L ion on the emission lines. I find two interesting results: 1. There is no significant correlation between O VII emission line normalization and L ion. 2. There is no strong emission line for very bright AGN (log L ion ≥ 45 erg s −1). The first result implies that there are several other physical factors apart from L ion that impact the emission line strength, such as the cloud density, and its distance from the central source. The second result may imply that a high luminosity AGN have blown off most of the material in its vicinity and the clouds that are emitting the emission lines are located further out, receiving less radiation and hence weak.

A broad-band X-ray spectral study of the Seyfert 1 galaxy ESO 141–G055 with XMM–Newton and NuSTAR

Monthly Notices of the Royal Astronomical Society

We have extensively studied the broad--band X-ray spectra of the source ESO 141–G055 using all av... more We have extensively studied the broad--band X-ray spectra of the source ESO 141–G055 using all available XMM–Newton and NuSTAR observations. We detect a prominent soft excess below 2rm,,rmkeV2\rm \, \, {\rm keV}2rm,,rmkeV, a narrow Fe line, and a Compton hump ($\gt 10\rm \, \, {\rm keV}$). The origin of the soft excess is still debated. We used two models to describe the soft excess: the blurred reflection from the ionized accretion disc and the intrinsic thermal Comptonization model. We find that both of these models explain the soft excess equally well. We confirm that we do not detect any broad Fe line in the X-ray spectra of this source, although both the physical models prefer a maximally spinning black hole scenario (a > 0.96). This may mean that either the broad Fe line is absent or blurred beyond detection. The Eddington rate of the source is estimated to be lambdarm,Eddsim0.31\lambda _{\rm \, Edd}\sim 0.31lambdarm,Eddsim0.31. In the reflection model, the Compton hump has a contribution from both ionized and neutral reflecti...

Blazar Variability: A Study of Nonstationarity and the Flux–Rms Relation

The Astrophysical Journal

Monthly Notices of the Royal Astronomical Society

We present a broadband spectral study of the radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342 ... more We present a broadband spectral study of the radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342 based on multi-epoch observations performed with NuSTAR on 2014 March 15, and two simultaneous observations performed with Suzaku and Swift on 2009 July 26 and 2013 March 1. We found the presence of a strong soft X-ray excess emission, a broad but weak Fe line and hard X-ray excess emission. We used the blurred reflection (relxill) and the intrinsic disc Comptonization (optxagnf), two physically motivated models, to describe the broadband spectra and to disentangle the disk/corona and jet emission. The relxill model is mainly constrained by the strong soft X-ray excess although the model failed to predict this excess when fitted above 3 keV and extrapolated to lower energies. The joint spectral analysis of the three datasets above 3 keV with this model resulted in a high black hole spin (a > 0.9) and moderate reflection fraction R ∼ 0.5. The optxagnf model fitted to the two simultaneous datasets resulted in an excess emission in the UV band. The simultaneous UV-to-hard X-ray spectra of 1H 0323+342 are best described by a model consisting of a primary X-ray power-law continuum with Γ ∼ 1.8, a blurred reflection component with R ∼ 0.5, Comptonised disk emission as the soft X-ray excess, optical/UV emission from a standard accretion disk around a black hole of mass ∼ 10 7 M ⊙ and a steep power law (Γ ∼ 3 − 3.5) component, most likely the jet emission in the UV band. The fractional RMS variability spectra suggest that both the soft excess and the powerlaw component are variable in nature.

Monthly Notices of the Royal Astronomical Society

We have carried out a systematic X-ray spectral analysis of a sample of low luminosity quasars (L... more We have carried out a systematic X-ray spectral analysis of a sample of low luminosity quasars (LLQSO) to investigate the nature of the central engines of these sources. The opticallyselected LLQSO sample consists of close, known bright active galactic nuclei (AGN) which serves as an important link between the powerful quasars at higher redshift and local Seyfert galaxies. We find that although the bolometric luminosities of the LLQSOs are lower than those of the higher redshift quasars by almost an order of magnitude, their distribution of the Eddington rate λ Edd is similar. We detect a strong anti-correlation between α OX and L 2500Å , as has also been detected in several other quasar studies with large sample sizes, indicating that as the UV luminosity of the source increases, the X-ray luminosity decreases. We do not detect any significant neutral obscuration (N H 10 22 cm −2) in the X-ray spectra of the LLQSOs, and hence rule out obscuration as a possible cause for their lower luminosity. We conclude that the central engines of the LLQSOs function similarly to those of the higher redshift quasars, and the difference is possibly because of the fact that the LLQSOs have lower black hole masses. We do not find any correlation between the molecular gas in the host galaxies and accretion states of the AGN. This indicates that the presence of molecular gas in the host galaxies of the LLQSOs does not significantly influence the instantaneous accretion rates of their SMBHs.

The Astrophysical Journal

We have carried out an extensive X-ray spectral analysis of a sample of galaxies exhibiting molec... more We have carried out an extensive X-ray spectral analysis of a sample of galaxies exhibiting molecular outflows (MOX sample), to characterize the X-ray properties and investigate the effect of AGN on the dynamical properties of the molecular outflows. We find that the X-ray bolometric correction (L 2−10 keV /L AGN) of these sources ranges from ∼ 10 −4.5 to 10 −0.5 , with ∼ 70% of the sources below 10 −2 , implying a weak X-ray emission relative to the AGN bolometric luminosity (L AGN). However, the upper limit on the 2 − 10 keV luminosity (L 2−10 keV, 12µm) obtained from 12µm flux, following the correlation derived by Asmus et al., are ∼ 0.5 − 3 orders of magnitude larger than the L 2−10 keV values estimated using X-ray spectroscopy, implying a possibility that the MOX sources host normal AGN (not X-ray weak), and their X-ray spectra are extremely obscured. We find that both L 2−10 keV , and L AGN correlates strongly with the molecular outflow velocity as well as the mass outflow rates (Ṁ out), implying that the central AGN plays an important role in driving these massive outflows. However, we also find statistically significant positive correlations between the starburst emission and MO mass outflow rate, L Starburst vsṀ out , and L 0.6−2 keV vsṀ out , which implies that starbursts can generate and drive the molecular outflows. The correlations of MO velocity andṀ out with AGN luminosities are found to be stronger compared to those with the starburst luminosities. We conclude that both starbursts and AGN play crucial role in driving the large scale MO.

Monthly Notices of the Royal Astronomical Society

We have investigated the nature and origin of the Fe K emission lines in Mrk 205 using observatio... more We have investigated the nature and origin of the Fe K emission lines in Mrk 205 using observations with Suzaku and XMM–Newton, aiming to resolve the ambiguity between a broad emission line and multiple unresolved lines of higher ionization. We detect the presence of a narrow Fe K α emission line along with a broad-band Compton reflection hump at energies Egt10rm,,rmkeVE\gt 10\rm \, \, {\rm keV}Egt10rm,,rmkeV. These are consistent with reflected emission of hard X-ray photons off a Compton-thick material of NrmHge2.15times1024rm,,rmcm−2N_{\rm H}\ge 2.15\times 10^{24}\rm \, \, {\rm cm^{-2}}NrmHge2.15times1024rm,,rmcm−2. In addition we detect a partially covering ionized absorption with ionization parameter log(xi/rm,erg,cm,s−1)=1.9−0.5+0.1\log (\xi /\rm \, erg\, cm\, s^{-1})=1.9_{-0.5}^{+0.1}log(xi/rm,erg,cm,s−1)=1.9−0.5+0.1, column density NrmH=(5.6−1.9+2.0)times1022rm,,rmcm−2N_{\rm H}=(5.6_{-1.9}^{+2.0})\times 10^{22}\rm \, \, {\rm cm^{-2}}NrmH=(5.6−1.9+2.0)times1022rm,,rmcm−2, and a covering factor of 0.22−0.06+0.090.22_{-0.06}^{+0.09}0.22−0.06+0.09. We detect the presence of emission arising out of ionized disc reflection contributing in the soft and hard X-rays consistently in all the observations. We however, could n...

For most bright nearby AGN, we commonly detect He-like O VII emission lines at ∼ 0.56 keV. In thi... more For most bright nearby AGN, we commonly detect He-like O VII emission lines at ∼ 0.56 keV. In this work, I study the correlation between the O VII emission line strength and the instantaneous AGN ionizing luminosity (13.6 eV − 13.6 keV) in a sample of bright nearby AGN to understand the effect of L ion on the emission lines. I find two interesting results: 1. There is no significant correlation between O VII emission line normalization and L ion. 2. There is no strong emission line for very bright AGN (log L ion ≥ 45 erg s −1). The first result implies that there are several other physical factors apart from L ion that impact the emission line strength, such as the cloud density, and its distance from the central source. The second result may imply that a high luminosity AGN have blown off most of the material in its vicinity and the clouds that are emitting the emission lines are located further out, receiving less radiation and hence weak.