Hard X‐Ray Emission from the Galactic Ridge

Yamasaki, Noriko Y.; Ohashi, T.; Takahara, Fumio; Yamauchi, Shigeo; Koyama, K.; Kamae, T.; Kaneda, Hidehiro; Makishima, Kazuo; Sekímoto, Yutaro; Hirayama, M.; Takahashi, Tadayuki; Yamagami, T.; Gunji, Shuichi; Tamura, T.; Miyazaki, Shota; Nomachi, M.

doi:10.1086/304097

Cited by 62 publications

(77 citation statements)

References 27 publications

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“…Therefore, on energetic grounds the LECRe scenario is plausible. The LECRe may be accelerated in supernovae remnants (e.g., Yamasaki et al 1997) or by ambient interstellar plasma turbulence (Schlickeiser 1997).…”

Section: Discussionmentioning

confidence: 99%

“…This is because the purely thermal models require a very hot gas (kT D 7 keV) that is uniformly produced and conÐned in the Galactic disk (a very contrived scenario). On the other hand, the presence of a nonthermal component for the emission is demonstrated by hard X-ray/soft c-ray observations of the Galactic background (e.g., Yamasaki et al 1997 ;Valinia & Marshall 1998 ;VKM00 ;Boggs et al 1999). The LECRe model along with a shock heated plasma component (both of which may have been created in supernovae explosions) provide a plausible explanation for the di †use Galactic background emission.…”

Section: Discussionmentioning

confidence: 99%

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On the Origin of the Iron K Line in the Spectrum of the Galactic X‐Ray Background

Valinia

Tatischeff

Arnaud

et al. 2000

ApJ

114

129

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We propose a mechanism for the origin of the Galactic ridge X-ray background that naturally explains the properties of the Fe K line, speciÐcally the detection of the centroid line energy below 6.7 keV and the apparent broadness of the line. Motivated by recent evidence of nonthermal components in the spectrum of the Galactic X-ray/c-ray background, we consider a model that is a mixture of thermal plasma components of perhaps supernova origin and nonthermal emission from the interaction of low-energy cosmic-ray electrons (LECRe) with the interstellar medium. The LECRe may be accelerated in supernova explosions or by ambient interstellar plasma turbulence. Atomic collisions of fast electrons produce characteristic nonthermal, narrow X-ray emission lines that can explain the complex Galactic background spectrum. Using the ASCA GIS archival data from the Scutum arm region, we show that a two-temperature thermal plasma model with kT D 0.6 and D2.8 keV, plus a LECRe component models the data satisfactorily. Our analysis rules out a purely nonthermal origin for the emission. It also rules out a signiÐcant contribution from low-energy cosmic-ray ions, because their nonthermal X-ray production would be accompanied by a nuclear c-ray line di †use emission exceeding the upper limits obtained using OSSE, as well as by an excessive Galaxy-wide Be production rate. The proposed model naturally explains the observed complex line features and removes the difficulties associated with previous interpretations of the data which evoked a very hot thermal component (kT D 7 keV).

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

On the Origin of the Iron K Line in the Spectrum of the Galactic X‐Ray Background

Valinia

Tatischeff

Arnaud

et al. 2000

ApJ

114

129

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“…A more detailed review of the previous works on the contribution of the discrete sources to the ridge spectrum can be found in Kaneda (1997) and Yamasaki (1996), and references therein. Finally, we point out that with the upcoming launch of AXAF, a more sensitive number-flux distribution of Galactic sources and their exact contribution to the diffuse Galactic background can be determined.…”

Section: Discrete Sourcesmentioning

confidence: 99%

“…al. 1982; EXOSAT [2-6 keV]: Warwick et al 1985;Tenma [2-11 keV]: ; Ginga [2-16 keV]: Yamasaki et al 1997; ASCA [0.5-10 keV]: Kaneda et al 1997). The presence of the 6.7 keV iron line in the spectrum discovered with Tenma has motivated the idea that part of the emission below 10 keV is due to a hot optically thin plasma of temperature 5−15 keV.…”

Section: Introductionmentioning

confidence: 99%

RXTEMeasurement of the Diffuse X‐Ray Emission from the Galactic Ridge: Implications for the Energetics of the Interstellar Medium

Valinia

Marshall

1998

ApJ

181

202

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The diffuse X-ray emission from the thin disk surrounding the Galactic midplane (the so-called Galactic ridge) was measured with RXTE PCA in order to determine the spatial extent, spectral nature, and origin of the emission. Spatial examination of the diffuse emission in the central 30 • of the plane in Galactic longitude reveals the presence of two components: a thin disk of full width ∼ < 0 • .5 centered roughly on the Galactic mid-plane, and a broad component which can be approximated as a Gaussian distribution with FWHM of about 4 • . Assuming an average distance of 16 kpc to the edge of the galaxy, a scale height of about 70 pc and 500 pc is derived for the thin and broad disk components, respectively. Spectral examination of the emission clearly reveals the presence of a hard power law tail above 10 keV and an emission line from He-like iron, indicating both thermal and possibly non-thermal origins for the diffuse emission. The averaged spectrum from the ridge in the 3−35 keV band can be modelled with a RaymondSmith plasma component of temperature ∼ 2−3 keV and a power law component of photon index ∼ 1.8. Based on this finding, we argue that the temperature of the hot phase of the Interstellar Medium (ISM) is less than the previously reported values of 5 − 15 keV.Motivated by the similarities between the characteristics of the thermal component of the Galactic ridge emission in our model and the thermal emission from supernova remnants (SNRs), we discuss the origin of the thermal emission in terms of a population of SNRs residing in the Galactic disk. We find that a 1 NAS/NRC Research Associate; valinia@milkyway.gsfc.nasa.gov 2 marshall@milkyway.gsfc.nasa.gov -2 -SN explosion rate of less than 5 per century is adequate to power the thermal emission from the ridge. The origin of the emission in the hard X-ray band modelled by a power law remains uncertain. Possible contributions from non-thermal bremsstrahlung of cosmic ray electrons and protons, inverse Compton scattering of energetic electrons from ambient microwave, infrared, and optical photons, non-thermal emission from SNRs, and emission from discrete X-ray sources are discussed. We speculate that bremsstrahlung of accelerated electrons and protons in SNR sites can play a significant role in producing the hard tail of the spectrum. Moreover, their collisional losses can play a major role in the ionization of the ISM.

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“…Through on board examination of the recorded waveforms, signals consistent with being fast scintillator light are selected from those mixed with slow/BGO scintillator light. This well-type phoswich detector technology was developed and used to reduce the cosmic rayinduced backgrounds by more than one order of magnitude for the WELCOME balloon experiments (Kamae et al [20,21]; Takahashi et al [22,23]; Gunji et al [24,25]; Miyazaki et al [26]; Yamasaki et al [27]). Based on this success, the technology has been applied to the Suzaku Hard X-ray Detector (Kamae et al [28]; Makishima et al [29]; Kokubun et al [30]).…”

Section: Pogolite Detectormentioning

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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Hard X‐Ray Emission from the Galactic Ridge

Cited by 62 publications

References 27 publications

On the Origin of the Iron K Line in the Spectrum of the Galactic X‐Ray Background

On the Origin of the Iron K Line in the Spectrum of the Galactic X‐Ray Background

RXTEMeasurement of the Diffuse X‐Ray Emission from the Galactic Ridge: Implications for the Energetics of the Interstellar Medium

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

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