Some Ramifications of the Power-Law Spectral Index for Propagation Modeling.

1979 ◽  
Author(s):  
Charles L. Rino
Keyword(s):  
Spectral Index ◽  
Power Law ◽  
Propagation Modeling

scholarly journals The starburst galaxy NGC 253 revisited by H.E.S.S. and Fermi-LAT

2018 ◽  
Vol 617 ◽  
pp. A73 ◽  
Author(s):  
◽  
H. Abdalla ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
E. O. Angüner ◽  
...  
Keyword(s):  
Spectral Index ◽  
Power Law ◽  
Cosmic Ray ◽  
High Energy ◽  
Thick Target ◽  
Starburst Galaxy ◽  
Particle Accelerators ◽  
Power Law Distribution ◽  
Particle Population ◽  
Measurement Uncertainties

Context. NGC 253 is one of only two starburst galaxies found to emit γ-rays from hundreds of MeV to multi-TeV energies. Accurate measurements of the very-high-energy (VHE; E > 100 GeV) and high-energy (HE; E > 60 MeV) spectra are crucial to study the underlying particle accelerators, probe the dominant emission mechanism(s) and to study cosmic-ray interaction and transport. Aims. The measurement of the VHE γ-ray emission of NGC 253 published in 2012 by H.E.S.S. was limited by large systematic uncertainties. Here, the most up to date measurement of the γ-ray spectrum of NGC 253 is investigated in both HE and VHE γ-rays. Assuming a hadronic origin of the γ-ray emission, the measurement uncertainties are propagated into the interpretation of the accelerated particle population. Methods. The data of H.E.S.S. observations are reanalysed using an updated calibration and analysis chain. The improved Fermi–LAT analysis employs more than 8 yr of data processed using pass 8. The cosmic-ray particle population is evaluated from the combined HE–VHE γ-ray spectrum using NAIMA in the optically thin case. Results. The VHE γ-ray energy spectrum is best fit by a power-law distribution with a flux normalisation of (1.34 ± 0.14stat ± 0.27sys) × 10−13 cm−2 s−1 TeV1 at 1 TeV – about 40% above, but compatible with the value obtained in Abramowski et al. (2012). The spectral index Γ = 2.39 ± 0.14stat ± 0.25sys is slightly softer than but consistent with the previous measurement within systematic errors. In the Fermi energy range an integral flux of F(E > 60 MeV) = (1.56 ± 0.28stat ± 0.15sys) × 10−8 cm−2 s−1 is obtained. At energies above ∼3 GeV the HE spectrum is consistent with a power-law ranging into the VHE part of the spectrum measured by H.E.S.S. with an overall spectral index Γ = 2.22 ± 0.06stat. Conclusions. Two scenarios for the starburst nucleus are tested, in which the gas in the starburst nucleus acts as either a thin or a thick target for hadronic cosmic rays accelerated by the individual sources in the nucleus. In these two models, the level to which NGC 253 acts as a calorimeter is estimated to a range of fcal = 0.1 to 1 while accounting for the measurement uncertainties. The presented spectrum is likely to remain the most accurate measurements until the Cherenkov Telescope Array (CTA) has collected a substantial set of data towards NGC 253.

scholarly journals Spectral Index Versus Frequency and Models for the Continua of AGN and QSOs

1989 ◽  
Vol 134 ◽  
pp. 201-202
Author(s):  
Wayne A. Stein
Keyword(s):  
Accretion Disk ◽  
Spectral Index ◽  
Power Law ◽  
Spectral Distribution ◽  
Secondary Electron ◽  
Low Frequency ◽  
Spectral Indices ◽  
Ultraviolet Continuum ◽  
Electron Synchrotron ◽  
X Ray

The observed spectral index as a function of frequency of QSO continua must be explained in models. It is generally increasing (F(ν) ∝ ν−α, α increasing) with higher frequency in the infrared (downward curvature). The visual to ultraviolet continuum has been shown to be a broken power law with F(ν) ∝ ν−0.5 at low frequency and a break to larger α at νo ∼ 3×1015 Hz. X-ray observations frequently exhibit a flat continuum with α < 1. One prominent example is 3C273 for which α1–3μm → 2, αvis ∼ 0.5 and αx ∼ 0.5. These spectral indices arise naturally in Secondary Electron Synchrotron Self-Compton (SESSC) models. Some accretion disk models approach these spectral indices for the visual-ultraviolet portion of the spectral distribution.

scholarly journals Two optical emission components with different variability in V404 Cygni

2016 ◽  
Vol 12 (S324) ◽  
pp. 43-44
Author(s):  
Yutaro Tachibana ◽  
Taketoshi Yoshii ◽  
Nobuyuki Kawai
Keyword(s):  
Spectral Index ◽  
Power Law ◽  
Time Domain ◽  
Optical Emission ◽  
Time Domain Analysis ◽  
Blackbody Radiation ◽  
Light Curves ◽  
Variable Component ◽  
Single Temperature ◽  
The Time Domain

AbstractV404 Cygni went into an outburst again on June 15, 2015 after 26 years of quietness. Soon after the notifications, we started intense optical observation campaign of this source. The spectral index between RC and IC-band was stable over the outburst, whereas that between g′ and RC-band varied violently. With the time domain analysis of the multi-color optical light curves, we successfully decomposed optical variations into three components: highly-variable component (HVC), little-variable component (LVC). The loci of the LVC in the color-color diagram is consistent with that of a single temperature blackbody radiation or a multi-color blackbody radiation from a standard accretion disk, while those of the HVC trace that of power-law spectra.

Power-law plateau and inverse symmetric inflation

2018 ◽  
Vol 27 (08) ◽  
pp. 1850087 ◽  
Author(s):  
Abdul Jawad ◽  
Shahid Chaudhary
Keyword(s):  
Scalar Field ◽  
Power Spectrum ◽  
Spectral Index ◽  
Power Law ◽  
Field Model ◽  
Chaplygin Gas ◽  
Generalized Chaplygin Gas ◽  
Planck Data ◽  
Inflationary Parameters ◽  
Ratio Versus

Warm generalized Chaplygin gas inflation is being studied by assuming power-law plateau and inverse symmetric potentials with standard scalar field model. We consider strong dissipative regime with generalized dissipative coefficient and extract the various inflationary parameters such as scalar power spectrum, spectral index, tensor-to-scalar ratio and running of spectral index. It is found that both inflationary potentials favor the strong dissipative regime. Also, we construct the [Formula: see text]–[Formula: see text] (running of spectral index versus spectral index) and [Formula: see text]–[Formula: see text] (tensor-to-scalar ratio versus spectral index) planes and found that the trajectories of these planes favor WMAP 7 [Formula: see text] WMAP 9 and latest Planck data.

scholarly journals k-essence for warm inflation on the brane

2017 ◽  
Vol 14 (06) ◽  
pp. 1750093 ◽  
Author(s):  
Lorenzo Sebastiani ◽  
Ratbay Myrzakulov
Keyword(s):  
Spectral Index ◽  
Power Law ◽  
General Class ◽  
Kinetic Term ◽  
Warm Inflation ◽  
Scalar Perturbations

In this paper, [Formula: see text]-inflation is analyzed in warm braneworld scenario. A general class of [Formula: see text]-essence models with power-law kinetic term is investigated and weak and strong dissipation regimes are studied. Scalar perturbations and spectral index are derived. The results are discussed and applied to specific examples.

Formation of Power Law Tail with Spectral Index-5 Inside and Beyond the Heliosphere

2008 ◽  
Author(s):  
G. Gloeckler ◽  
L. A. Fisk ◽  
G. M. Mason ◽  
M. E. Hill ◽  
Gang Li ◽  
...  
Keyword(s):  
Spectral Index ◽  
Power Law

scholarly journals New mysteries and challenges from the Toothbrush relic: wideband observations from 550 MHz to 8 GHz

2020 ◽  
Vol 636 ◽  
pp. A30 ◽  
Author(s):  
K. Rajpurohit ◽  
M. Hoeft ◽  
F. Vazza ◽  
L. Rudnick ◽  
R. J. van Weeren ◽  
...  
Keyword(s):  
Mach Number ◽  
Spectral Index ◽  
Power Law ◽  
Galaxy Cluster ◽  
Radio Continuum ◽  
Published Data ◽  
Color Analysis ◽  
Wide Range ◽  
Shock Fronts ◽  
Spectral Shapes

Context. Radio relics are diffuse extended synchrotron sources that originate from shock fronts induced by galaxy cluster mergers. The particle acceleration mechanism at the shock fronts is still under debate. The galaxy cluster 1RXS J0603.3+4214 hosts one of the most intriguing examples of radio relics, known as the Toothbrush. Aims. In order to understand the mechanism(s) that accelerate(s) relativistic particles in the intracluster medium, we investigated the spectral properties of large-scale diffuse extended sources in the merging galaxy cluster 1RXS J0603.3+4214. Methods. We present new wideband radio continuum observations made with uGMRT and VLA. Our new observations, in combination with previously published data, allowed us to carry out a detailed high-spatial-resolution spectral and curvature analysis over a wide range of frequencies. Results. The integrated spectrum of the Toothbrush closely follows a power law over almost two orders of magnitude in frequency, with a spectral index of −1.16 ± 0.02. We do not find any evidence of spectral steepening below 8 GHz. The subregions of the Toothbrush also exhibit near-perfect power laws and identical spectral slopes, suggesting that the observed spectral index is rather set by the distribution of Mach numbers which may have a similar shape at different parts of the shock front. Indeed, numerical simulations show an intriguing similar spectral index, indicating that the radio spectrum is dominated by the average over the inhomogeneities within the shock, with most of the emission coming from the tail of the Mach number distribution. In contrast to the Toothbrush, the spectra of the fainter relics show a high-frequency steepening. Moreover, the integrated spectrum of the halo also follows a power law from 150 MHz to 3 GHz with a spectral index of −1.16 ± 0.04. We do not find any evidence for spectral curvature, not even in subareas of the halo. This suggest a homogeneous acceleration throughout the cluster volume. Between the “brush” region of the Toothbrush and the halo, the color-color analysis reveals emission that was consistent with an overlap between the two different spectral regions. Conclusions. None of the relic structures, that is, the Toothbrush as a whole or its subregions or the other two fainter relics, show spectral shapes consistent with a single injection of relativistic electrons, such as at a shock, followed by synchrotron aging in a relatively homogeneous environment. Inhomogeneities in some combination of Mach number, magnetic field strength, and projection effects dominate the observed spectral shapes.

Inflationary constraints in teleparallel gravity theory

2020 ◽  
pp. 2150027
Author(s):  
Shambel Sahlu ◽  
Joseph Ntahompagaze ◽  
Amare Abebe ◽  
David F. Mota
Keyword(s):  
Observational Data ◽  
Spectral Index ◽  
Power Law ◽  
Teleparallel Gravity ◽  
Gravity Models ◽  
Index Formula ◽  
Scalar Tensor Theory ◽  
Tensor Theory ◽  
Slow Roll ◽  
Inflationary Parameters

In this work, the cosmological inflationary parameters in the correspondence of teleparallel gravity for the scalar–tensor theory are investigated. After the review of [Formula: see text] and [Formula: see text] gravity cosmology, we use the slow-roll approximations to study the behavior of the inflationary parameters namely the spectral index [Formula: see text] and tensor-to-scalar ratio [Formula: see text], and a comparison with observational data for different paradigmatic [Formula: see text] gravity models such as exponential, Linder and power-law models is considered. We also consider the boundary term [Formula: see text] associated with these three models. The obtained behavior of the parameters under consideration shows that it is possible to constrain [Formula: see text] and [Formula: see text] models based on observational data.

scholarly journals Variation of the Solar Flare Energy Spectrum Over the 11-Year Activity Cycle

1989 ◽  
Vol 104 (2) ◽  
pp. 255-258 ◽  
Author(s):  
V.V. Kasinsky ◽  
R.T. Sotnikova
Keyword(s):  
Energy Spectrum ◽  
Solar Flare ◽  
Spectral Index ◽  
Power Law ◽  
Activity Cycle ◽  
Energy Spectra ◽  
Cycle Phase ◽  
X Ray ◽  
Flux Data ◽  
Flare Energy

AbstractBased on X-ray (1-8 Å) flux data for 1977-1987, the integral spectra of solar flare energy were computed. The energy spectra were approximated by a power law N(E) α; E~n, with N being the number of flares with energy in excess of E. It is shown that the spectral index (β) varies systematically with the 11-year cycle phase.

Solar Energetic Electron Events Associated with Hard X-ray Flares 

2021 ◽  
Author(s):  
Wen Wang ◽  
Linghua Wang ◽  
Sam Krucker ◽  
Glenn M. Mason ◽  
Yang Su ◽  
...  
Keyword(s):  
Spectral Index ◽  
Power Law ◽  
Heliocentric Distance ◽  
Energetic Electron ◽  
High Energy ◽  
Thick Target ◽  
The Other ◽  
Ion Acceleration ◽  
X Ray ◽  
Positive Correlation

&lt;p&gt;&lt;span&gt;We investigate 16 solar energetic electron (SEE) events measured by WIND/3DP with a double power-law spectrum and the associated western hard X-ray (HXR) flares measured by RHESSI with good count statistics, from 2002 February to 2016 December. In all 16 cases, the presence of an SEE power-law spectrum extending down to &lt;/span&gt;&lt;span&gt;6&lt;/span&gt;&lt;span&gt;5 keV at 1 AU implies that the SEE source would be high in the corona, at a heliocentric distance of &lt;/span&gt;&lt;span&gt;&gt;&lt;/span&gt;&lt;span&gt;1.3 &lt;/span&gt;&lt;span&gt;solar radii&lt;/span&gt;&lt;span&gt;, while the footpoint or footpoint-like emissions shown in HXR images suggest that the observed HXRs are likely produced mainly by thick target bremsstrahlung processes very low in the corona. &lt;/span&gt;&lt;span&gt;We find that in 8 cases (the other 8 cases), the power-law spectral index of HXR-producing electrons, estimated under the relativistic thick-target bremsstrahlung model, is significantly larger than (similar to) the observed high-energy spectral index of SEEs, with a positive correlation. In addition, the estimated number of SEEs is only &lt;/span&gt;&lt;span&gt;&amp;#8764;&lt;/span&gt;&lt;span&gt;10&lt;/span&gt;&lt;span&gt;-&lt;/span&gt;&lt;span&gt;4 &lt;/span&gt;&lt;span&gt;- &lt;/span&gt;&lt;span&gt;10&lt;/span&gt;&lt;span&gt;-&lt;/span&gt;&lt;span&gt;2 &lt;/span&gt;&lt;span&gt;of the estimated number of HXRproducing electrons at energies above 30 keV, but also with a positive correlation. &lt;/span&gt;&lt;span&gt;These results suggest that in these cases, SEEs are likely formed by upward-traveling electrons from an acceleration source high in the corona, while their downward-traveling counterparts may undergo a secondary acceleration before producing HXRs via thick-target bremsstrahlung processes. In addition, the associated &lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;He&lt;/span&gt;&lt;span&gt;=&lt;/span&gt;&lt;span&gt;4&lt;/span&gt;&lt;span&gt;He ratio is positively correlated with &lt;/span&gt;&lt;span&gt;the observed high-energy spectral index of SEEs&lt;/span&gt;&lt;span&gt;, indicating a possible relation of the &lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;He ion acceleration with high-energy SEEs&lt;/span&gt;&lt;/p&gt;

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