scholarly journals The Sources of the Hard X-Ray Background

1996 ◽  
Vol 168 ◽  
pp. 263-270
Author(s):  
Giancarlo Setti ◽  
Andrea Comastri
Keyword(s):  
Energy Spectrum ◽  
Energy Density ◽  
Energy Flux ◽  
Large Fraction ◽  
Power Laws ◽  
Prima Facie ◽  
Folding Energy ◽  
Hard Component ◽  
X Ray ◽  
X Ray Background

The hard component (3 keV – ~ MeV) of the X-ray background (XRB) comprises the largest portion, ~ 90%, of the overall XRB intensity. The observed isotropy (the entire Galaxy is transparent above 3 keV) provides aprima facieevidence of its prevailing extragalactic nature. A large fraction (~ 75%) of the energy flux falls in the 3 – 100 keV band, the corresponding energy density being ≃ 5×10−5eV cm−3, of which 50% is confined to the narrower 3 – 20 keV band. Although the energy flux carried by the XRB is relatively small compared to other extragalactic backgrounds, it was soon realized that it cannot be accounted for in terms of sources and processes confined to the present epoch. An analysis of the combined observed spectra (Gruber 1992) concludes that, while a thermal bremsstrahlung with an e-folding energy = 41.13 keV accurately fits the data up to 60 keV, above this energy the sum of two power laws is required with normalizations such that at 60 keV the spectral index is ~ 1.6, gradually flattening to ~ 0.7 at MeV energies. It should also be noted that below 10 keV the XRB energy spectrum is well represented by a power law of index α = 0.4 (I∝E−α).

scholarly journals Pair Production in AGN

1989 ◽  
Vol 134 ◽  
pp. 194-196
Author(s):  
C. Done ◽  
A. C. Fabian
Keyword(s):  
Pair Production ◽  
Compton Scattering ◽  
Energy Flux ◽  
Large Fraction ◽  
Small Region ◽  
X Rays ◽  
X Ray ◽  
Electron Positron ◽  
Γ Rays ◽  
Radiant Power

The X-ray luminosity and variability of many AGN are sufficiently extreme that any hard γ-rays produced in the source will collide with the X-rays and create electron-positron pairs, rather than escape. A small region where vast amounts of energy are produced, such as an AGN, is an ideal place to accelerate particles to relativistic energies and so produce γ-rays by Compton scattering. The observed X-ray spectra of AGN are hard and indicate that most of the luminosity is at the highest energies so that absorption of the γ-rays represents a large fraction of the energy flux, which can then be re-radiated at lower energies. Pairs can thus effectively reprocess much of the radiant power in an AGN.

scholarly journals Optical Follow-Up Observations of ASCA Lynx Deep Survey

1998 ◽  
Vol 188 ◽  
pp. 471-472
Author(s):  
K. Ohta ◽  
M. Akiyama ◽  
K. Nakanishi ◽  
T. Yamada ◽  
K. Hayashida ◽  
...  
Keyword(s):  
Energy Density ◽  
Energy Band ◽  
X Ray ◽  
Preliminary Results ◽  
Deep Survey ◽  
X Ray Background

Since the bulk of the energy density of the Cosmic X-ray Background (CXB) resides in the harder energy band than that of the ROSAT band (0.5-2 keV) and since the X-ray sources identified in the ROSAT band have X-ray spectra softer than that of the CXB, investigation of nature of the X-ray sources at the harder energy band is indispensable to solve the origin of the CXB. However, only 2-3% of the CXB in the hard band (2-10 keV) had been resolved into discrete sources (Piccinotti et al. 1982, ApJ 253, 485). We present our preliminary results of optical follow-up observations of the ASCA Lynx deep survey.

scholarly journals The Multiwavelength AGN Population and the X-ray Background

2013 ◽  
Vol 9 (S304) ◽  
pp. 188-194
Author(s):  
Ezequiel Treister ◽  
Claudia M. Urry ◽  
Kevin Schawinski ◽  
Brooke D. Simmons ◽  
Priyamvada Natarajan ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Mass Density ◽  
Large Fraction ◽  
Supermassive Black Holes ◽  
X Rays ◽  
X Ray ◽  
Black Hole Growth ◽  
Hole Growth ◽  
X Ray Background

AbstractIn order to fully understand galaxy formation we need to know when in the cosmic history are supermassive black holes (SMBHs) growing more intensively, in what type of galaxies this growth is happening and what fraction of these sources are invisible at most wavelengths due to obscuration. Active Galactic Nuclei (AGN) population synthesis models that can explain the spectral shape and intensity of the cosmic X-ray background (CXRB) indicate that most of the SMBH growth occurs in moderate-luminosity (LX~ 1044 erg/s) sources (Seyfert-type AGN), at z~ 0.5−1 and in heavily obscured but Compton-thin, NH~ 1023cm−2, systems. However, this is not the complete history, as a large fraction of black hole growth does not emit significantly in X-rays either due to obscuration, intrinsic low luminosities or large distances. The integrated intensity at high energies indicates that a significant fraction of the total black hole growth, 22%, occurs in heavily-obscured systems that are not individually detected in even the deepest X-ray observations. We further investigate the AGN triggering mechanism as a function of bolometric luminosity, finding evidence for a strong connection between significant black hole growth events and major galaxy mergers from z~ 0 to z~ 3, while less spectacular but longer accretion episodes are most likely due to other (stochastic) processes. AGN activity triggered by major galaxies is responsible for ~60% of the total black hole growth. Finally, we constrain the total accreted mass density in supermassive black holes at z > 6, inferred via the upper limit derived from the integrated X-ray emission from a sample of photometrically selected galaxy candidates. We estimate an accreted mass density <1000 M⊙Mpc−3 at z~ 6, significantly lower than the previous predictions from some existing models of early black hole growth and earlier prior observations.

Pulsed X-Ray Annealing of Arsenic-Implanted Silicon

1981 ◽  
Vol 4 ◽  
Author(s):  
T. W. Sigmon ◽  
D. E. Osias ◽  
R. L. Schneider ◽  
C. Gilman ◽  
G. Dahlbacka
Keyword(s):  
Energy Density ◽  
Structural Properties ◽  
Energy Flux ◽  
High Energy ◽  
Wafer Surface ◽  
X Rays ◽  
Density Range ◽  
X Ray ◽  
Large Numbers ◽  
Unique Capability

ABSTRACTIn this paper we report experiments on annealing of arsenic-implanted silicon using a pulsed imploding-plasma X-ray source. Silicon wafers of <100> orientation were implanted with arsenic ions at 50 keV to a dose of 3.5 ∼ 1015 cm−2 and exposed to a single 50 ns pulse of X-rays in the energy density range of 0.15 to 0.55 J/cm2 The characteristic X-ray absorptiog coeificient in silicon for these experiments was 1.6 ∼ 10 cm−1, resulting in most of the energy being absorbed in the first 100 nm of the wafer surface.For wafers annealed in the energy density range of 0.3 to 0.4 J/cm2 backscattering and channeling measurements show recovery of the crystallinity of the damaged layer with incorporation of about 86% of the implanted arsenic onto substitutional lattice positions. Evidence of redistribution and flattening of the arsenic profile in the annealed wafer was observed in the backscattering data and confirmed by SIMS profiling. Detailed results on the electrical and structural properties of these annealed layers will be presented. High energy pulsed X-ray sources offer the unique capability of simultaneously exposing large numbers of wafers to an extremely uniform energy flux at much higher efficiencies than conventional lasers.

scholarly journals Radio Emission from Extended Shell-Like SNRs

1998 ◽  
Vol 188 ◽  
pp. 249-250
Author(s):  
A.I. Asvarov
Keyword(s):  
Radio Emission ◽  
Thin Shell ◽  
Large Fraction ◽  
Radiative Cooling ◽  
Interstellar Space ◽  
Low Density ◽  
Shell Formation ◽  
X Ray ◽  
Cooling Effects ◽  
X Ray Background

Observations of the soft X-Ray background and interstellar UV absorption lines have indicated that a large fraction of interstellar space is filled with a high temperature low density “coronal” gas. In such low density environments SNRs will expand up to 200 pc in radius without thin shell formation which occurs due to radiative cooling effects. Such SNRs can occupy a large fraction of volume of Galaxy and can be the main source of background emissions. In the present work we examine the evolution of the radio emission of shell-like SNR evolving in the hot ISM.

scholarly journals The Shape of Soft X-ray Spectra of Quasars

1989 ◽  
Vol 134 ◽  
pp. 175-176
Author(s):  
D. A. Schwartz ◽  
Y. Qian ◽  
W. H. Tucker
Keyword(s):  
Flux Density ◽  
Power Laws ◽  
Seyfert Galaxies ◽  
Background Spectrum ◽  
X Ray ◽  
The Mean ◽  
X Ray Background ◽  
Image Position ◽  
Two Parameters ◽  
Lines Of Evidence

Several lines of evidence suggest that the x-ray spectra of quasars are not simple, exact power laws: 1. when Wilkes and Elvis (1987) analyzed quasars as power laws they found an absorption less than that due to our galaxy; 2. The mean 0.3 to 3.5 keV spectral index is steeper than the mean for the 2 to 20 keV range; 3. although several lines of evidence argue that AGN provide a significant portion (perhaps all) of the x-ray background, the diffuse background spectrum does not agree with the x-ray power-law indices measured for quasars or Seyfert galaxies. Schwartz and Tucker (1988) have suggested that all the above conflicts are reconciled if the slope in the Log(flux density) vs. Log(energy) plot flattens continuously with increasing energy. In this paper we utilize one particular parameterization suggested for the flux density, which we call the “log-slope” model: where f is the flux density, K a normalization parameter which is not of interest here, and a and b are the two parameters of our fit.

Observations of SN 1987A from Ginga

1988 ◽  
Vol 7 (4) ◽  
pp. 479-485
Author(s):  
H. Inoue
Keyword(s):  
Energy Spectrum ◽  
Time Variable ◽  
Soft Component ◽  
X Rays ◽  
Hard Component ◽  
X Ray ◽  
Sn 1987A

AbstractResults of the observations of SN 1987A from Ginga are presented. The first detection of X-rays from the SN 1987A was July, 1987. The energy spectrum is quite unnusual for any of the known classes of X-ray sources, and apparently consists of two seperate components; a soft and a hard component. The soft component is significantly time-variable, and also showed a flarelike increase in January, 1988. Whereas, the intensity of the hard component has remained fairly stationary for more than 300 days. The origins of the two components are also discussed.

scholarly journals X-Ray Observation of SN1987A from Ginga

1988 ◽  
Vol 108 ◽  
pp. 399-405
Author(s):  
Y. Tanaka
Keyword(s):  
Energy Spectrum ◽  
Time Variable ◽  
Soft Component ◽  
Hard Component ◽  
X Ray

AbstractAn unusual hard X-ray source was discovered in an error box of 0.2° × 0.3° including SN1987A from the X-ray astronomy satellite Ginga. The energy spectrum is quite unusual for any known classes of X-ray source, and apparently consists of two separate components, a soft component and a very hard component. This source is considered to be identified with SN1987A. The X-ray emergence occurred in July, 1987, or possibly even earlier. The soft component is significantly time-variable and also showed a flare-like increase in January, 1988, while the intensity of the hard component has remained relatively unchanged for more than 200 days.

scholarly journals The Extragalactic X-Ray and γ-ray Backgrounds

1990 ◽  
Vol 139 ◽  
pp. 345-356
Author(s):  
G. Setti
Keyword(s):  
Big Bang ◽  
Prima Facie ◽  
Baryon Density ◽  
Primordial Nucleosynthesis ◽  
X Ray ◽  
Γ Ray ◽  
X Ray Background ◽  
Seyfert Type ◽  
Number Of Authors

The long-standing problem of the origin of the extragalactic X-ray background (XRB) is reviewed. Although the shape of the spectrum in the 3–100 keV interval is suggestive of an optically thin bremsstrahlung at ~ 40 keV, the interpretation in terms of a hot intergalactic gas (IGG) requires a rather extreme energy supply and a gas density conflicting with the baryon density upper limit derived from primordial nucleosynthesis calculations in the standard hot big-bang model. A summary discussion of the estimated contributions from the integrated X-ray emission of known classes of extragalactic discrete sources at a reference energy of 2 keV is given. Although these estimates are still uncertain, the subtraction of a “minimum” contribution drastically modifies the 40 keV thermal shape, which is the prima facie evidence of a hot IGG. AGNs are the main contributors. Low luminosity AGNs (Seyfert type 1 nuclei) at redshift z = 1 − 2 may in fact saturate the 2 keV XRB, but their observed hard X-ray spectra are on the average unlike (much too steep) that of the XRB. This has led a number of authors to postulate new classes of sources and some exotic models which are briefly summarized. However, if a recently proposed unified scheme of AGNs holds, then the bulk of the XRB intensity can be explained independently of the observed spectral differences and with a mild cosmological evolution. The origin of the extragalactic γ-ray background is briefly commented upon in the concluding remarks.

scholarly journals ROSAT Observations of B and Be Stars

1994 ◽  
Vol 162 ◽  
pp. 189-199
Author(s):  
Joseph P. Cassinelli ◽  
David H. Cohen
Keyword(s):  
Large Fraction ◽  
Emission Measure ◽  
X Rays ◽  
Be Stars ◽  
Hard Component ◽  
B Stars ◽  
X Ray ◽  
Wind Speeds ◽  
Sky Survey ◽  
Wind Theory

We present results from a survey of X-ray emission properties of near main-sequence B stars, including several Be and β Cephei stars. The main conclusions of our survey are: 1) The X-rays are soft, probably because the shock velocity jumps are small since the terminal wind speeds are small. 2) A major fraction of the wind emission measure is hot, assuming wind theory estimates for the density distribution. A large fraction of the wind is not expected to be hot in current wind shock models. 3) A hard component is found to be present in τ Sco; possible causes are discussed. 4) For the Be stars, the X-rays emission is from a normal B-star wind that is coming from the poles as in the WCD model of Be stars. 5) None of the stars, including the β Cep stars, show noticeable variability in their X-rays. For the normal B stars we conclude from the lack of variability that the shocks are in the form of fragments in the wind instead of spherical shells. 6) Our observations suggest that all B stars are X-ray sources and that there is a basal amount of X-ray luminosity of about 10-8.5Lboi. The hot component in τ Sco and the high X-ray luminosity of B stars detected in the all-sky survey suggests that there is a source of X-ray emission in addition to wind shocks in some B stars.

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