Grupe, Dirk, Komossa, Stefanie, Gallo, Luigi C., Fabian, Andrew C., Larsson, Josefin, Pradhan, Anil K., ...
We report the discovery of strong soft X-ray emission lines and a hard continuum above 2 keV in the Narrow-Line Seyfert 1 galaxy Mrk 335 during an extremely low X-ray flux state. Mrk 335 was observed...
Grupe, Dirk, Komossa, Stefanie, Gallo, Luigi C., Fabian, Andrew C., Larsson, Josefin, Pradhan, Anil K., ...
Oelgoetz, Justin, Fontes, Christopher J., Zhang, Hong Lin, Pradhan, Anil K.
The General Spectral Modeling (GSM) code employs the quasi-static approximation, a standard, low-density methodology that assumes the ionization balance is separable from a determination of the...
Jain, Rajmal, Pradhan, Anil K., Joshi, Vishal, Shah, K. J., Trivedi, Jayshree J., Kayasth, S. L., ...
We present the first results from the "Low Energy Detector" payload of the "Solar X-ray Spectrometer (SOXS)" mission, which was launched onboard the GSAT-2 Indian spacecraft on 08 May 2003 by the...
Ionization Structure and Spectra of Iron in Gaseous Nebulae (2006)
Manuel A. Bautista, Anil K. Pradhan
Ionization Structure and Spectra of Iron in Gaseous Nebulae
Electron impact excitation of Helium-like ions up to n=4 levels including radiation damping (2006)
Delahaye, Franck, Pradhan, Anil K., Zeippen, Claude J.
Helium-like ions provide the most important X-ray spectral diagnostics in high temperature fusion and astrophysical plasmas. We previously presented computed collision strengths for O~VII including...
Chen, Guo-Xin, Pradhan, Anil K.
Efforts to benchmark astrophysical observations with X-ray laboratory measurements have been stymied by observed and measured differences of up to a factor of two in the ratio '3s/3d' of Fe XVII...
Pradhan, Anil K., Montenegro, Maximiliano, Nahar, Sultana N., Eissner, Werner
Based on new calculations we reconfirm the low and high density limits on the forbidden fine structure line ratio [O II] I(3729)/I(3726): lim_{N_ e} --> 0} = 1.5 and lim_{N_ e} --> \infty} = 0.35....
Studying the Variation of the Fine Structure Constant Using Emission Line Multiplets (2005)
Grupe, Dirk, Pradhan, Anil K., Frank, Stephan
As an extension of the method by Bahcall et al. (2004) to investigate the time dependence of the fine structure constant, we describe an approach based on new observations of forbidden line...
Nahar, Sultana N., Pradhan, Anil K.
We present new calculations for transition probabilities of Fe IV, with much more extensive datasets than heretofore available. The large-scale close coupling R-matrix calculations yield 1,798 LS...
The 6.7 keV KALPHA complex of He-like iron in transient plasmas (2004)
Oelgoetz, Justin, Pradhan, Anil K.
Time dependent numerical simulations of the K ALPHA complex of Fe XXV are carried out as a function of temperature/density/radiation field variations in high-temperature astrophysical and laboratory...
Resolution and accuracy of resonances in R-matrix cross sections (2004)
Delahaye, Franck, Nahar, Sultana N., Pradhan, Anil K, Zhang, Hong Lin
We investigate the effect of resonances in photoionization and recombination cross sections computed using the R-matrix method. Photoionization and recombination rates derived from high-resolution...
Molecular Hydrogen and [FeII] in Active Galactic Nuclei (2004)
Rodriguez-Ardila, Alberto, Pastoriza, Miriani G., Viegas, Sueli, Sigut, T. A. A., Pradhan, Anil K.
(Abridge) Near-infrared spectroscopy is used to study the kinematics and excitation mechanisms of the H2 and [FeII] gas in a sample of AGN. The H2 lines are unresolved in all objects in which they...
Sigut, T. A. A., Pradhan, Anil K., Nahar, Sultana N.
We present theoretical iron emission line strengths for physical conditions typical of Active Galactic Nuclei with Broad-Line Regions. The non-local thermodynamic equilibrium (NLTE) models include a...
The Iron Project and the RmaX Project (2003)
Ongoing activities under an international collaboration of atomic physicists and astrophysicists under the Iron Project and the RmaX Project, with applications to X-ray astronomy, are briefly...
Self-Consistent R-matrix Approach To Photoionization And Unified Electron-Ion Recombination (2003)
Nahar, Sultana N., Pradhan, Anil K.
A unified scheme using the R-matrix method has been developed for electron-ion recombination subsuming heretofore separate treatments of radiative and dielectronic recombination (RR and DR). The ab...
Nahar, Sultana N., Pradhan, Anil K.
Aimed at ionization balance and spectral analysis of UV and X-ray sources, we present self-consistent sets of photoionization cross sections, recombination cross sections, and rate coefficients for...
Nahar, Sultana N., Eissner, Werner, Chen, Guo-Xin, Pradhan, Anil K.
An extensive set of fine structure levels and corresponding transition probabilities for allowed and forbidden transitions in Fe XVII is presented. A total of 490 bound energy levels of Fe XVII of...
X-ray absorption via K-alpha resonance complexes in oxygen ions (2003)
Pradhan, Anil K., Chen, Guo Xin, Delahaye, Franck, Nahar, Sultana N., Oelgoetz, Justin
The K-alpha resonance complexes in oxygen ions O I - O VI are theoretically computed and resonance oscillator strengths and wavelengths are presented. The highly resolved photoionization cross...
Chen, Guo-Xin, Pradhan, Anil K., Eissner, W.
A comprehensive study of relativistic and resonance effects in electron impact excitation of (e+Fe XVII) is carried out using the BPRM method in the relativistic close coupling approximation. Two...
Predicted FeII Emission-Line Strengths from Active Galactic Nuclei (2002)
Sigut, T. A. A., Pradhan, Anil K.
We present theoretical FeII emission line strengths for physical conditions typical of Active Galactic Nuclei with Broad-Line Regions. The FeII line strengths were computed with a precise treatment...
X-Ray Resonance Opacity of Oxygen and Iron in AGN MCG--6-30-15 (2002)
Pradhan, Anil K., Chen, Guo-Xin, Delahaye, Franck, Nahar, Sultana N., Oelgoetz, Justin
Theoretical differential oscillator strengths related to monochromatic opacity due to K- and L-shell absorption from oxygen and iron ions are directly compared with the Chandra and Xmm-Newton spectra...
Delahaye, Franck, Pradhan, Anil K.
The primary X-ray diagnostic lines in He-like ions are mainly excited by electron impact from the ground level to the n = 2 levels, but at high temperatures n > 2 levels are also excited. In order to...
Influence of Resonances on Spectral Formation of X-Ray Lines in Fe XVII (2002)
Chen, Guo-Xin, Pradhan, Anil K.
New theoretical results from large-scale relativistic close coupling calculations reveal the precise effect of resonances in collisional excitation of x-ray lines of Ne-like Fe XVII. Employing the...
The K-alpha complex of He-like iron with dielectronic satellites (2001)
Oelgoetz, Justin, Pradhan, Anil K.
It is shown that the dielectronic satellites (DES) dominate X-ray spectral formation in the 6.7 keV K-alpha complex of Fe XXV at temperatures below that of maximum abundance in collisional ionization...
Pradhan, Anil K., Chen, Guo Xin, Nahar, Sultana N., Zhang, Hong Lin
Relativistic close coupling calculations are reported for unified electronic recombination of (e + C IV) including non-resonant and resonant recombination processes, radiative and dielectronic...
Zhang, Hong Lin, Nahar, Sultana N., Pradhan, Anil K.
Relativistic and channel coupling effects in photoionization and unified electronic recombination of Fe XVII are demonstrated with an extensive 60-level close coupling calculation using the...
Nahar, Sultana N., Pradhan, Anil K., Zhang, Hong Lin
Recently X-ray photoabsorption in KLL resonances of O VI was predicted [Pradhan, Astrophys.J. Lett. 545, L165 (2000)], and detected by the Chandra X-ray Observatory [Lee et al, Astrophys. J. {\it...
Ionization Structure and Spectra of Iron in Gaseous Nebulae (2001)
Bautista , Manuel A., Pradhan , Anil K.
We present a study of the emission spectra and the ionization structure of FeI--IV in gaseous nebulae. This work includes: (I) new atomic data; (II) a study of excitation mechanisms of [FeII],...
Unified Electronic Recombination Of Ne-like Fe XVII: Implications for Modeling X-Ray Plasmas (2000)
Pradhan, Anil K., Nahar, Sultana N., Zhang, Hong Lin
Unified recombination cross sections and rates are computed for (e + Fe XVIII) --> Fe XVII including non-resonant and resonant (radiative and di-electronic recombination, RR and DR) processes in an...
X-Ray Photoabsorption in KLL Resonances of O VI And Abundance Analysis (2000)
It is shown that photoabsorption via autoionizing resonances may be appreciable and used for abundance analysis. Analogous to spectral lines, the `resonance oscillator strength' f_r may be defined...
Nahar, Sultana N., Pradhan, Anil K., Zhang, Hong Lin
Photoionization and recombination cross sections and rate coefficients are calculated for Li-like Fe XXIV and He-like Fe XXV using the Breit-Pauli R-matrix (BPRM) method. A complete set of total and...
Chen, Guo Xin, Pradhan, Anil K.
Relativistic atomic structure calculations for electric dipole E1, electric quadrupole E2 and magnetic dipole M1 transition probabilities among the first 80 fine-structure levels of Fe VI, dominated...
Nahar, Sultana N., Pradhan, Anil K., Zhang, Hong Lin
The first complete set of unified cross sections and rate coefficients are calculated for photoionization and recombination of He- and Li-like ions using the relativistic Breit-Pauli R-matrix method....
Recent advances in theoretical atomic physics have enabled large-scale calculation of atomic parameters for a variety of atomic processes with high degree of precision. The development and...
Atomic data from the Iron Project.XLIII. Transition probabilities for Fe V (2000)
Nahar, Sultana N., Delahaye, Franck, Pradhan, Anil K., Zeippen, C. J.
An extensive set of dipole-allowed, intercombination, and forbidden transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM) method is used to calculate 1.46 x 10^6 oscillator...
Large-scale Breit-Pauli R-matrix calculations for transition probabilities of Fe V (2000)
Nahar, Sultana N., Pradhan, Anil K.
Ab initio theoretical calculations are reported for the electric (E1) dipole allowed and intercombination fine structure transitions in Fe V using the Breit-Pauli R-matrix (BPRM) method. We obtain...
Fluorescent Excitation of Spectral Lines in Planetary Nebulae (2000)
Chen, Guo Xin, Pradhan, Anil K.
Fluorescent excitation of spectral lines is demonstrated as a function of temperature-luminosity and the distance of the emitting region from the central stars of planetary nebulae. The electron...
Photoionization and recombination of Fe XIX (1999)
Zhang, Hong Lin, Pradhan, Anil K.
Photoionization cross sections and recombination rate coefficients are presented for the L-shell ground state fine structure levels $2s^22p^4 \ ^3P_{2,0,1}$ of Fe~XIX. Several sets of calculations...
Photoionization of Fe XV (1999)
Haque, Nasreen, Pradhan, Anil K.
Relativistic and resonance effects in the photoionization of Mg-like Fe~XV are investigated using the Breit-Pauli R-matrix Method (BPRM) at near-threshold and intermediate energies, complemented by...
Lyman Alpha Fluorescent Excitation of FeII in Active Galactic Nuclei (1998)
Sigut, T. A. A., Pradhan, Anil K.
We have calculated FeII emission line strengths for Active Galactic Nuclei Broad-Line Regions using precise radiative transfer and Iron Project atomic data. We improve the treatment of all previously...
Ionization Structure and Spectra of Iron in Gaseous Nebulae} (1997)
Bautista, Manuel A., Pradhan, Anil K.
The emission spectra and the ionization structure of the low ionization stages of iron, Fe I--IV, in gaseous nebulae are studied. This work includes: (i) new atomic data: photoionization cross...