Green's matrix for Compton reflection of polarized radiation from cold matter

Poutanen, Juri; Nagendra, K. N.; Svensson, Roger

doi:10.1093/mnras/283.3.892

Cited by 61 publications

(53 citation statements)

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“…These affects have been carefully considered by Matt et al (2015) in their study of the NuSTAR data on NGC5506. The exponential cutoff energy is measured at 720 +130 −190 keV whereas the COMPPS model (Poutanen, Nagendra & Svensson 1996) gives a temperature of 270 keV. Matt et al (2015) also remind us of the comment by Gilli, Comastri & Hasinger (2007) that the mean value of E cut for AGN must lie below 300 keV, in order not to saturate the X-ray Background at 100 keV.…”

Section: Resultsmentioning

confidence: 96%

“…The results for the NuSTAR sample (CAT1) are plotted in lated this by generating Comptonization spectra using COMPPS (Poutanen, Nagendra & Svensson 1996) in a spherical geometry for a seed photon tenperature of 10 eV, a Thomson depth τ = 1 and a set of temperatures (40 keV, 60 keV, 70 keV, 80 keV, 90 keV, 100 keV, 120 keV, 150 keV, 200 keV) (Fig. 3).…”

Section: Resultsmentioning

confidence: 99%

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Properties of AGN coronae in theNuSTARera

Fabian

Lohfink

Kara

et al. 2015

Mon. Not. R. Astron. Soc.

370

433

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The focussing optics of NuSTAR have enabled high signal-to-noise spectra to be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic Black Hole Binaries (BHB). Spectral modelling then allows robust characterization of the spectral index and upper energy cutoff of the coronal power-law continuum, after accounting for reflection and absorption effects. Spectral-timing studies, such as reverberation and broad iron line fitting, of these sources yield coronal sizes, often showing them to be small and in the range of 3 to 10 gravitational radii in size. Our results indicate that coronae are hot and radiatively compact, lying close to the boundary of the region in the compactness -temperature (Θ − ℓ) diagram which is forbidden due to runaway pair production. The coincidence suggests that pair production and annihilation are essential ingredients in the coronae of AGN and BHB and that they control the shape of the observed spectra.

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

Properties of AGN coronae in theNuSTARera

Fabian

Lohfink

Kara

et al. 2015

Mon. Not. R. Astron. Soc.

370

433

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“…Evidence for this reflection component is provided by a fluorescent Fe-line at ∼6.4 keV, an Fe absoption edge at 7 keV, and a broad "hump" at ∼10-200 keV (Lightman & White [77]). While the primary emission is not expected to be significantly polarised as it arises via multiple Compton scatterings, the reflection component is expected to display significant intrinsic polarisation (Matt [78]; Poutanen et al [79]). The observed degree of polarisation is also dependent on the inclination of the system, giving polarimetry the potential to derive inclinations of XRB systems, which is often difficult by other means.…”

Section: Accereting Black Holesmentioning

confidence: 99%

PoGOLite – A high sensitivity balloon-borne soft gamma-ray polarimeter

Kamae

Andersson

Arimoto

et al. 2008

Astroparticle Physics

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We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200 mCrab point-like sources between 25 keV and 80 keV in one 6 hour flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high-energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. Synchrotron radiation, inverse Compton scattering and propagation through high magnetic fields are likely to produce high degrees of polarisation in the energy band of the instrument. We demonstrate, through tests at accelerators, with radioactive sources and through computer simulations, that PoGOLite will be able to detect degrees of polarisation as predicted by models for several classes of high-energy sources. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles while securing a large effective area has been the greatest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow field of view (FWHM = 1.25 msr, 2.0 degrees × 2.0 degrees) obtained with detector cells and the use of thick background shields warrant a large effective area for polarisation measurements (∼228 cm 2 at E = 40 keV) without sacrificing the signal-to-noise ratio. Simulation studies for an atmospheric overburden of 3-4 g/cm 2 indicate that neutrons and gamma-rays entering the PDC assembly through the shields are dominant backgrounds. Off-line event selection based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a ∼100 mCrab source between 25 keV and 50 keV. A 6 hour observation of the Crab pulsar will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5σ significance; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. Long-duration flights will measure the dependence of the polarisation across the cyclotron absorption line in Hercules X-1. A scaled-down instrument will be flown as a pathfinder mission from the north of Sweden in 2010. The first science flight is planned to take place shortly thereafter.Key words: Instrumentation: detectors, Techniques: polarimetric, Pulsars: general, X-ray: binaries, Stars: neutron, Galaxies: active PACS: 95.30. Gv, 95.55.Ka, 95.55.Qf, 95.75.Hi, 95.85.Pw, 97.60Gv, 97.60.Lf, 97.80.Jp, 98.54.Cm

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“…It incorporates exact Green's functions accounting for the angular dependence of the outgoing (observed) reflected spectrum and different ionization states of the reflecting medium, while being self-consistent regarding the ionization balance only up to a reflector temperature of order 0.1 keV [17]. If the incident spectrum is anisotropic as expected, e.g., in the case of magnetic flares on the surface of accretion disks [18][19][20][21], the reflected spectrum should be computed using Green's functions that account for angular dependence of both incident and reflected radiation [22].…”

Section: Spectral Modelsmentioning

confidence: 99%

Modeling X/γ-ray spectra of Galactic black holes and Seyferts

Poutanen¹

1998

AIP Conference Proceedings

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Abstract. Recent high quality broad-band X-ray and gamma-ray observations of Galactic black holes by ASCA, Ginga, RXTE, and CGRO show that the spectra cannot be described by simple thermal Comptonization models (even including a fully relativistic treatment). Multi-component models accounting for Comptonization by thermal and non-thermal electrons, Compton reflection of X/γ-rays from cold matter, and emission of the optically thick accretion disk are required. In this review, I discuss recent advances in the spectral modeling of Galactic black holes and Seyferts and the codes available for such an analysis. SPECTRAL MODELSAlready at the time of the discoveries in the early 1970s of the first X-rays sources it was realized that the most efficient process to produce large X-ray/γ-ray (Xγ hereafter) luminosities is Comptonization of soft seed photons by a hot rarefied electron gas (e.g., [1]). Detailed calculations of thermal Comptonization spectra were carried out by Monte-Carlo [2-4] and analytical methods [1,[5][6][7]. Analytical formulae describing spectra emerging from an optically thick cloud of nonrelativistic electrons have been derived by solving the Kompaneets equation [8] in a "double" diffusion approximation (in optical depth and frequency) [7] and have been used extensively during last twenty years to fit the Xγ data. Only recently the data has become good enough to require a more accurate theoretical description of Comptonized spectra. The usefulness of generalizations of the analytical formulae to a mildly-relativistic gas and an optically thin media [9] is disputable [10] and not trivial, since both electron and photon energies can be of order ∼ m e c 2 . No analytical formulae exist for Comptonized spectra for non-Maxwellian electron distribution (except for power-law distributions of electrons in the optically thin limit). Monte-Carlo simulations unfortunately, are still too slow to be implemented into the standard software for the Xγ data analysis (e.g. XSPEC), but on the other hand give the possibility to consider arbitrary geometries.All this makes attractive the use of numerical methods capable in solving relativistic kinetic equations for Compton scattering on electrons of arbitrary energy

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Green's matrix for Compton reflection of polarized radiation from cold matter

Cited by 61 publications

References 0 publications

Properties of AGN coronae in theNuSTARera

Properties of AGN coronae in theNuSTARera

PoGOLite – A high sensitivity balloon-borne soft gamma-ray polarimeter

Modeling X/γ-ray spectra of Galactic black holes and Seyferts

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