Differential Spectral Index Research Articles

Spatial and energy distribution of muons inγ-induced air showers

The FLUKA Monte Carlo program is used to calculate the effects of hadroproduction by primary gamma rays incident upon the Earth's atmosphere; for the results presented in this paper, only primary angles at $0\ifmmode^\circ\else\textdegree\fi{}$ from zenith are considered. The FLUKA code is believed to be quite accurate in reproducing experimental photon hadroproduction data in the 1 GeV to 10 TeV energy range studied. The charged pions which are so produced can decay to muons with sufficient energy to reach ground level. The number of these muons and their radial and energy distribution are studied for incident gamma ray energies from 1 GeV to 10 TeV. The number of these muons is not negligible; they can, in certain circumstances, be used to study potential sources of gamma rays such as gamma ray bursts. It is found, for example, that a 10 TeV incident primary gamma ray produces, on average, 3.4 muons which reach ground level; the gamma ray energy which produces the maximum number of muons at ground level depends on the spectral index of the primary gamma spectrum, a constant which describes how the primary gamma flux rises with decreasing primary energy. For example, for a differential spectral index of 2.7, there is a broad maximum number of muons coming from $\ensuremath{\approx}30$ GeV primary gamma ray energy.

Gamma‐Ray Observations of the Galactic Plane at EnergiesE > 500 GeV

In 1998 and 1999 the Whipple Observatory 10 m telescope was used to search for diffuse gamma ray emission from the Galactic Plane. No signifiant evidence of emission was found. Assuming the TeV emission profile matches EGRET observations above 1 GeV with a differential spectral index of 2.4, we derive an upper limit of {$\rm {3.0\cdot10^{-8}cm^{-2}s^{-1}sr^{-1}}$} for the average diffuse emission above {{$\rm500 GeV$}} in the galactic latitude range from {{$\rm-2^o$ to $\rm +2^o$}} at galactic longitude {{$\rm 40^o$}}. Comparisons with EGRET observations provide a lower limit of 2.31 for the differential spectral index of the diffuse emission, assuming there is no break in the spectrum between 30 GeV and 500 GeV. This constrains models for diffuse emission with a significant inverse Compton contribution.

Cosmic ray proton spectrum determined with the imaging atmospheric Cherenkov technique

The HEGRA system of 4 imaging atmospheric Cherenkov telescopes ~IACTs! has been used to determine the flux and the spectrum of cosmic ray protons over a limited energy range around 1.5 TeV. Although the IACT system is designed for the detection of g-rays with energies above 500 GeV, it has also a large detection area of .10 6 m 2 33 msr for primary protons of energies above 1 TeV and the capability to reconstruct the primary proton energy with a reasonable accuracy DE/E of 50% near this threshold. Furthermore, the principle of stereoscopic detection of air showers permits the effective suppression of air showers induced by heavier primaries already on the trigger level, and in addition on the software level by analysis of the stereoscopic images. The combination of both capabilities permits a determination of the proton spectrum almost independently of the cosmic ray chemical composition. The accuracy of our estimate of the spectral index at 1.5 TeV is limited by systematic uncertainties and is comparable to the accuracy achieved with recent balloon and space borne experiments. In this paper we describe in detail the analysis tools, namely the detailed Monte Carlo simulation, the analysis procedure and the results. We determine the local ~i.e., in the range of 1.5‐3 TeV! differential spectral index to be g p52.7260.02stat60.15syst and obtain an integral flux above 1.5 TeV of F (.1.5 TeV)53.160.6 stat61.2syst310 22 /s sr m 2 . @S0556-2821~99!04107-7#

Azimuthally controlled observation of heavy cosmic-ray primaries by means of the balloon-borne emulsion chamber

We have exposed an emulsion chamber with an area of 1.22 m 2 on board of the balloon at an atmospheric depth of 8.9 g/cm 2 for 15.8 h, which has been azimuthally controlled within the accuracy of Δφ = 0.5°. With the use of the east-west asymmetry effect of arriving cosmic-ray primaries, we can obtain the energy spectra for individual elements in the kinetic energy range from a few GeV/nucleon up to ∼ 15 GeV/nucleon. We present also the energy spectra obtained by the opening-angle method for the higher energy region, 5–1000 GeV/nucleon, for the elements not lighter than silicon. We find that the energy spectra obtained by the former method continue smoothly to those obtained by the latter, indicating that the energy determination using the opening-angle method is performed correctly. We compare also the present results with those obtained by the previous work. We find that the iron flux is in nice agreement with that obtained by the previous observation, the differential spectral index being constant, ∼ 2.5, up to a few TeV/nucleon, while in the case of the silicon component, it is ∼ 2.7 for 10–1000 GeV/nucleon in this work, significantly harder than the previous one, ∼ 2.9. We also report the flux of the sub-iron component and its abundance ratio to the iron component. We find the abundance ratio of [Z = 21–25]/iron is slightly less than those obtained previously in the higher energy region, ≳ 100 GeV/n.

Jovian electron propagation in three dimensions of the heliosphere: The Ulysses Investigations

We report investigations of Jovian relativistic electrons in the interplanetary medium that provide new insights into both the physical processes by which the Jovian magnetosphere releases its trapped, relativistic electrons into the interplanetary medium, and the modes of their interplanetary propagation. These studies were dependent on the unique postencounter trajectory for Ulysses. The spacecraft remained close to the radial distance of Jupiter (∼5.2 AU) and moved southward on the duskside by only ∼12° in heliographic latitude and <8° in heliographic azimuth relative to Jupiter for the period of ∼100° days of this study. During this period the nominal Parker spiral interplanetary magnetic field with its alternating polarities sector structure established direct magnetic field line connections frequently between Jupiter and the spacecraft. These unique conditions made it possible to investigate in detail, for approximately four solar rotations, both the Jovian electron burst phenomenon and the continuous, diffusive interplanetary propagation of Jovian electrons. The Jovian electron burst phenomenon in the energy range 1‐20 MeV, with flux increasing up to 50 times the diffusive Jovian electron flux are now discovered to occur in both multiples of the planetary rotation period (∼10 hours) and occasionally in half rotation periods, namely, in sequences of 5‐, 10‐, 20‐, or 40‐hour intervals. Electrons in the burst are shown to stream from the magnetosphere and not the magnetotail to the spacecraft during times when the interplanetary magnetic field vector direction includes both Jupiter and the spacecraft. Over 90% of all electron bursts lasting ≥6 hours occurred during the positive magnetic field sector. The few bursts occurring in a negative sector (<10%) were associated with rapid changes in magnetic field orientation near a sector boundary. We found that the time for these burst sequences corresponded to either the dawnside or the duskside tilt of the magnetic dipole. This dawn‐dusk dipole tilt is in a plane approximately orthogonal to the Sun‐Jupiter line and aligned with the average interplanetary magnetic field direction at ∼5 AU. To interpret these measurements, we assumed that the release mechanism is intermittent reconnection of the interplanetary magnetic field with the opposite polarity of a component of the polar magnetospheric field. These experimental results appeared to exclude some models for electron release such as the magnetic anomaly model where the electrons are released into the magnetotail. The diffusive Jovian electron flux continuously present in the interplanetary medium confirmed the “10‐hour clock” variations of the differential energy spectral index found by Pioneer 10 in 1973. Present evidence indicates that this continuum of Jovian electrons with its 10‐hour rocking spectrum may be associated with the same release mechanism as the electron bursts.

Possible observation of 100 TeV gamma rays from the active galaxy Centaurus a

We have searched for evidence of ultra-high energy gamma rays from the active galaxy Centaurus A in the data set of the JANZOS experiment during the period 13 October 1987 to 18 January 1992. No significant DC excess was found from this source. Excess events were found, however, in the period 14 April – 3 June 1990. The duration of the excess, 48 days, and equivalent luminosity, ~ 10 43 erg s −1, are both similar to those measured previously for X-ray outbursts of Centaurus A. Furthermore, the events appear to exhibit the expected absorption feature at 200 TeV due to interactions with the 2.7 K background radiation, but the chance probability for the excess is at the 2% level. The equivalent time averaged flux during this period was (5.5 ± 1.5) × 10 −12 photons cm −2s −1 at energies ≥ 110 TeV, about 20 times as large as the upper lim of steady emission, assuming a differential spectral index of −2.0. Further observations are required to confirm the result

The high-energy diffuse cosmic gamma-ray background radiation from blazars

view Abstract Citations (107) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The High-Energy Diffuse Cosmic Gamma-Ray Background Radiation from Blazars Stecker, F. W. ; Salamon, M. H. ; Malkan, M. A. Abstract We predict the spectrum and flux of the high-energy diffuse cosmic γ-ray background radiation produced by blazars. Our calculations are based on the Compton Observatory EGRET observations of high-energy gamma-rays from these objects, the Whipple observation of TeV γ- rays from Mrk 421, and radio population studies of flat-spectrum radio sources. Our statistical analysis gives the result Lgamma_ is proportional to L_radio_^1.2+/-0.1^, consistent with a linear correlation. We then use the radio luminosity function and redshift evolution to calculate the γ-ray background. We find that blazars cannot account for the flux level or steep spectrum of the background observed by SAS 2 in the sub-GeV range, but could likely provide the dominant background component in the multi-GeV energy range and above. We predict a differential photon spectral index for this component of ~2 up to ~10 GeV. Above that energy, the spectrum should gradually steepen owing to pair production by interactions of the γ-rays with intergalactic infrared photons. Using the calculations of this effect by Stecker, de Jager, & Salamon, we estimate a spectral index of ~3.5 for energies above a TeV. Publication: The Astrophysical Journal Pub Date: June 1993 DOI: 10.1086/186882 Bibcode: 1993ApJ...410L..71S Keywords: Background Radiation; Blazars; Diffuse Radiation; Energetic Particles; Galactic Cosmic Rays; Gamma Ray Astronomy; Active Galaxies; Quasars; Astrophysics; GAMMA RAYS: THEORY; GALAXIES: ACTIVE; GALAXIES: QUASARS: GENERAL full text sources ADS | data products SIMBAD (5) NED (1)

TeV gamma rays from 3C 279 - A possible probe of origin and intergalactic infrared radiation fields

The gamma-ray spectrum of 3C 279 during 1991 June exhibited a near-perfect power law between 50 MeV and over 5 GeV with a differential spectral index of -(2.02 +/- 0.07). If extrapolated, the gamma-ray spectrum of 3C 279 should be easily detectable with first-generation air Cerenkov detectors operating above about 0.3 TeV provided there is no intergalactic absorption. However, by using model-dependent lower and upper limits for the extragalactic infrared background radiation field, a sharp cutoff of the 3C 279 spectrum is predicted at between about 0.1 and about 1 TeV. The sensitivity of present air Cerenkov detectors is good enough to measure such a cutoff, which would provide the first opportunity to obtain a measurement of the extragalactic background infrared radiation field.

A search of the northern sky for ultra-high-energy point sources

view Abstract Citations (36) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Search of the Northern Sky for Ultra--High-Energy Point Sources Alexandreas, D. E. ; Berley, D. ; Biller, S. ; Burman, R. L. ; Cady, D. R. ; Chang, C. Y. ; Dingus, B. L. ; Dion, C. L. ; Dion, G. M. ; Ellsworth, R. W. ; Freedman, S. J. ; Fujikawa, B. K. ; Goodman, J. A. ; Haines, T. J. ; Hoffman, C. M. ; Krakauer, D. A. ; Kwok, P. W. ; Lu, X. -Q. ; Nagle, D. E. ; Potter, M. ; Sandberg, V. D. ; Sinnis, C. ; Stark, M. J. ; Vishwanath, P. R. ; Yodh, G. B. ; Zhang, W. P. Abstract A search has been made for steady emission of ultra-high-energy radiation from individual point sources over most of the northern sky. Over 2 x 10^8^ air showers induced by primary particles of energy greater than about 10 TeV were recorded from 1986 April until 1991 May by the CYGNUS air shower array. No statistically significant excess above the background from the isotropic flux of cosmic rays was found for any direction in the sky from 0^deg^ to 80^deg^ declination. In addition, 49 specific potential sources were examined, and none showed a statistically significant excess of events. 90% confidence level flux upper limits are established for the continuous emission from these sources; for a source that transits the zenith, a representative upper limit corresponds to an integral flux above 40 TeV of about 1.7 x 10^-13^ cm^-2^ s^-1^ (0.5% of the cosmic-ray flux within an angular area of 1.8 x 10^-3^ sr) assuming a power-law energy spectrum with a differential spectral index of -2.7. Publication: The Astrophysical Journal Pub Date: December 1991 DOI: 10.1086/186239 Bibcode: 1991ApJ...383L..53A Keywords: Cosmic Ray Showers; Gamma Rays; Northern Sky; Point Sources; Sky Surveys (Astronomy); Energy Spectra; Particle Energy; Particle Flux Density; Space Radiation; COSMIC RAYS: GENERAL; GAMMA RAYS: GENERAL full text sources ADS | data products SIMBAD (44) NED (2)

Search for gamma rays from the supernova 1987A at energies greater than 100 TeV.

We searched for ultrahigh-energy γ rays emitted by the supernova 1987A with a new cosmic-ray facility installed at the Black Birch Range in New Zealand. The observations from 13 October to 3 December 1987 suggest no clear clustering of events around the direction of the supernova. We conclude that an upper limit on the flux γ rays of energies greater than 100 TeV is 1.1×10−12 cm−2 s−1 (95% confidence limit) for a differential spectral index α=2.0 and source distance d=50 kpc. This value gives an upper bound on the γ-ray luminosity of the supernova of 5.5×1038 erg s−1 for 1014–1017 eV.Received 19 January 1988DOI:https://doi.org/10.1103/PhysRevLett.60.1110©1988 American Physical Society

On the possibility of observations of high energy neutrino and gamma-ray fluxes from SN1987A

We estimate the production of high energy neutrino and gamma-ray signals through interactions of protons and subsequent decay of secondaries in the shell of SN1987a. We also discuss the absorption of the gamma-ray signals, the detection limits and the existing and proposed experiments in the Southern hemisphere, TeV and PeV gamma-ray signals will be detectable if the total proton luminosity of the supernova is greater than 10 39 erg/s and the differential spectral index γ of the accelerated protons is not steeper than 2.4. The detection of neutrino induced muons from the supernova will only be possible if the total proton luminosity exceeds 10 42 erg/s.

The Acceleration of Galactic Cosmic Rays

Although it is clear that cosmic rays are of considerable astrophysical significance we know surprisingly little about their origin(s), their mode(s) of propagation and escape from the galaxy, and even of their general properties. Practically nothing is known of the composition and energy spectra of different species at energies below about 200 MeV/nucleon as a consequence of solar modulation, which has a significant effect on the observed spectra at energies up to about 10 GeV/ nucleon. The energy spectra of ions (especially protons) appear to be well approximated by a power law (differential spectral index γ ~ 2.6) in the range 1010–1015 eV/nucleon. At higher energies (up to ~ 1020 eV/nucleon) both the spectrum and the composition of the ion component are less well known, however it is significant that the anisotropy, as evidenced from the sidereal diurnal variation, increases substantially, suggesting that perhaps an extragalactic origin must be considered.

Low energy γ-ray spectrum of NGC4151

Following the first detection of X-ray emission from the Seyfert galaxy NGC41511, later observations2–4 have demonstrated that the X-ray spectrum up to 100 keV may be described by a power law having a differential spectral index 1<α<1.6 with a turnover at low energies caused by photoelectric absorption. Recently the results of an observation of this galaxy in the energy range 25–190 keV (ref. 5) have shown it to have a very hard spectrum with α≅0.9. Here more detailed results of the original observation of NGC4151 (ref. 6) using the MISO telescope are presented.

The small anisotropy and the rigidity spectrum of the March 30, 1969 solar flare event

A study of the March 30, 1969 solar flare event is presented utilizing data obtained from the world-wide network of neutron monitors. Although, to a good first approximation, the solar flare radiation displayed a high degree of isotropy at the orbit of the earth, it is deduced that a small anisotropy from East of the earth-sun line was present at the time of maximum enhancement of the event. This small deduced anisotropy does not, however, preclude the use of a method, based on isotropic particle propagation, to calculate the rigidity spectral index of the flare-induced radiation. Use of such a method determines the differential rigidity spectral index to be 3.9 ± 0.1.