Differential Energy Spectrum Research Articles

A wavelet based analysis of cosmic rays modulation

In this work we present estimated results of the Morlet wavelet analysis from the modulation of relative cosmic ray intensities, sunspot numbers, modulation potentials variabilities registered by Moscow and worldwide neutron monitors (NM). Unlike the conventional spectral analysis the wavelet transform are suitable tool for description of non-stationary processes containing multiscale features detection of singularities and analysis of transient phenomena [P. Kumar, E. Foufoula-Georgiou, Reviews of Geophysics 35 (4) (1977) 385–412]. Methods such as wavelets should be very suitable, thus it can be applied to the problem under consideration. On the other hand this approach is not frequently used for cosmic ray time series. Solar modulation of cosmic rays and their possible effect on cloud cover is the most complex candidate and remains hardest to test. However the yearly averages of cosmic ray intensities registered by Moscow NM from 1958 to 2007 are investigated to verify and explore 11-year cycles and other structures. Besides Time series of solar activity indicators such as sunspot number have been studied over the period 1810–2000 with Morlet wavelet method. The modulation potential ϕ often parametrising differential energy spectrum of galactic cosmic rays (GCR) is also used in this work to characterise solar modulation of GCRs. We have investigated the series of yearly values of the modulation potential ϕ of [I.G. Usoskin, K. Alanko-Huotari, G.A. Kovaltsov, K. Mursula, Heliospheric modulation of cosmic rays monthly reconstruction for 1951–2004, Journal of Geophysical Research 110 (2005) A12108] since 1951–2004 using the data of worldwide NM. Main results of the wavelet analysis and reconstruction suggest that the maximum of Morlet decomposition coefficients was found around the main 11–12 year cycle. However we have found for both solar activity indicator: the sunspot number and modulation potential a dominating period around 12–15 years. Magnitude of cycles is not absolutely the same but vary from cycle to cycle. The attempt of extrapolation has shown other periods of about 20–22, 27–30 years after the year 2007.

First direct measurement of jets in $\sqrt{s_{\mathit {NN}}}=200~\mbox{GeV}$ heavy ion collisions by STAR

We present the first measurement of reconstructed jets in ultra-relativistic heavy ion collisions. Utilizing the large coverage of the STAR Time Projection Chamber and Electromagnetic Calorimeter, we apply several modern jet reconstruction algorithms and background subtraction techniques and explore their systematic uncertainties in heavy ion events. The differential energy spectrum for inclusive jet production in central Au+Au collisions at \(\sqrt{s_{\mathit{NN}}}=200~\mbox{GeV}\) is presented. In order to assess the jet reconstruction biases, this spectrum is compared with the jet cross section measured in \(\sqrt{s}=200\) GeV p+p collisions scaled by the number of binary N–N collisions to account for nuclear geometric effects.

MAGIC observations of PG 1553+113 during a multiwavelength campaign in July 2006

The active galactic nucleus PG 1553+113 was observed by the MAGIC telescope in July 2006 during a multiwavelength campaign, in which telescopes in the optical, X-ray, and very high energies participated. Although the MAGIC data were affected by strong atmospheric absorption (calima), they were analyzed after applying a correction. In 8.5 hours, a signal was detected with a significance of 5.0 sigma. The integral flux above 150 GeV was (2.6 +/- 0.9)*10^{-7} ph/s/m^2. By fitting the differential energy spectrum with a power law, a spectral index of -4.1 +/- 0.3 was obtained.

Upper Limit on the Diffuse Flux of Ultrahigh Energy Tau Neutrinos from the Pierre Auger Observatory

The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of nu(tau) at EeV energies. Assuming an E(nu)(-2) differential energy spectrum the limit set at 90% C.L. is E(nu)(2)dN(nu)(tau)/dE(nu)<1.3 x 10(-7) GeV cm(-2) s(-1) sr(-1) in the energy range 2 x 10(17) eV< E(nu)< 2 x 10(19) eV.

Observation of Gamma‐Ray Emission from the Galaxy M87 above 250 GeV with VERITAS1

The multiwavelength observation of the nearby radio galaxy M87 provides a unique opportunity to study in detail processes occurring in active galactic nuclei from radio waves to TeV γ-rays. Here we report the detection of γ-ray emission above 250 GeV from M87 in spring 2007 with the VERITAS atmospheric Cerenkov telescope array and discuss its correlation with the X-ray emission. The γ-ray emission is measured to be pointlike with an intrinsic source radius less than 4.5'. The differential energy spectrum is fitted well by a power-law function: dΦ/dE = (7.4 ± 1.3stat ± 1.5sys)(E/TeV)(− 2.31 ± 0.17stat ± 0.2sys) 10−9 m−2 s−1 TeV−1. We show strong evidence for a year-scale correlation between the γ-ray flux reported by TeV experiments and the X-ray emission measured by the ASM RXTE observatory, and discuss the possible short-timescale variability. These results imply that the γ-ray emission from M87 is more likely associated with the core of the galaxy than with other bright X-ray features in the jet.

Very high energy γ-ray observations of Mrk 501 using the TACTIC imaging γ-ray telescope during 2005–06

In this paper we report on the Markarian 501 results obtained during our TeV γ-ray observations from 11 March to 12 May 2005 and 28 February to 7 May 2006 for 112.5 h with the TACTIC γ-ray telescope. During 2005 observations for 45.7 h, the source was found to be in a low state and we have placed an upper limit of 4.62 × 10−12 photons cm−2 s−1 at 3σ level on the integrated TeV γ-ray flux above 1 TeV from the source direction. However, during 2006 observations for 66.8 h, detailed data analysis revealed the presence of a TeV γ-ray signal from the source with a statistical significance of 7.5σ above Eγ⩾ 1 TeV. The time-averaged differential energy spectrum of the source in the energy range 1–11 TeV is found to match well with the power-law function of the form (dΦ/dE = f0E−Γ) with f0 = (1.66 ± 0.52) × 10−11 cm−2 s−1 TeV−1 and Γ = 2.80 ± 0.27.

Cosmic ray spectrum obtained from the energy scattered by the particles of extensive air showers in the atmosphere and the galactic model

The differential energy spectrum of cosmic rays that is obtained on the basis of the measurements of Cherenkov radiation from extensive air showers in an energy range of 1015–1020 eV is compared with the model of the propagation of primary particles in the interstellar medium with fractal properties. It is found that the shape of the experimental spectrum is in good agreement with the shape of the calculated spectrum of “all particles” at 1015–1018 eV. The average mass composition of cosmic rays that is calculated on the basis of five components does not contradict the average mass composition obtained from the experimental data for several parameters in this energy range.

Unfolding of differential energy spectra in the MAGIC experiment

The paper describes the different methods, used in the MAGIC experiment, to unfold experimental energy distributions of cosmic ray particles ( γ -rays). Questions and problems related to the unfolding are discussed. Various procedures are proposed which can help to make the unfolding robust and reliable. The different methods and procedures are implemented in the MAGIC software and are used in most of the analyses.

Measurement of Very High Energy Gamma‐Ray Emission from Four Blazars Using the MAGIC Telescope and a Comparative Blazar Study

The thesis reports on the observation of very high energy gamma radiation from the active galactic nuclei (AGN) Mkn501, 1ES2344, PG1553, and BL Lacertae using the 17 m diameter MAGIC Cherenkov telescope. For the first time, flux variability on a time scale of minutes was observed for Mkn501, allowing the determination of a new limit on the quantum gravity energy scale. This limit is well compatible with the best limits inferred in the literature. 1ES2344 was for the first time observed in a low emission state, whose differential energy spectrum was deduced and whose properties are discussed. PG1553 and BL Lacertae were newly detected at gamma ray energies E>100 GeV. Further a comparative study of all blazar-type AGNs found at E>100 GeV is performed. The thesis also discusses the implementation of a fast repositioning system for the MAGIC telescope and the determination of differential fluxes in the MAGIC standard analysis and reconstruction software.

Very High Energy Gamma-Ray Radiation from the Stellar Mass Black Hole Binary Cygnus X-1

We report on the results from the observations in very high energy band (VHE, E_gamma > 100 GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were performed with the MAGIC telescope, for a total of 40 hours during 26 nights, spanning the period between June and November 2006. Searches for steady gamma-ray signals yielded no positive result and upper limits to the integral flux ranging between 1 and 2% of the Crab nebula flux, depending on the energy, have been established. We also analyzed each observation night independently, obtaining evidence of gamma-ray signals at the 4.0 standard deviations (sigma) significance level (3.2 sigma after trial correction) for 154 minutes effective on-time (EOT) on September 24 between 20h58 and 23h41 UTC, coinciding with an X-ray flare seen by RXTE, Swift and INTEGRAL. A search for faster-varying signals within a night resulted in an excess with a significance of 4.9 sigma (4.1 sigma after trial correction) for 79 minutes EOT between 22h17 and 23h41 UTC. The measured excess is compatible with a point-like source at the position of Cygnus X-1, and excludes the nearby radio nebula powered by its relativistic jet. The differential energy spectrum is well fitted by an unbroken power-law described by dN/(dA dt dE) = (2.3+- 0.6) x 10^{-12} (E/1 TeV)^{-3.2 +- 0.6}. This is the first experimental evidence of VHE emission from a stellar-mass black hole, and therefore from a confirmed accreting X-ray binary.

The Energy Spectrum of the Blazar Markarian 421 above 130 GeV

Markarian 421 (Mrk 421) was the first blazar detected at gamma-ray energies above 300 GeV, and it remains one of only twelve TeV blazars detected to date. TeV gamma-ray measurements of its flaring activity and spectral variability have placed constraints on models of the high-energy emission from blazars. However, observations between 50 and 300 GeV are rare, and the high-energy peak of the spectral energy distribution (SED), predicted to be in this range, has never been directly detected. We present a detection of Mrk 421 above 100 GeV as made by the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) during a multiwavelength campaign in early 2004. STACEE is a ground-based atmospheric Cherenkov telescope using the wavefront sampling technique to detect gamma rays at lower energies than achieved by most imaging Cherenkov telescopes. We also outline a method for reconstructing gamma-ray energies using a solar heliostat telescope. This technique was applied to the 2004 data, and we present the differential energy spectrum of Mrk 421 above 130 GeV. Assuming a differential photon flux dN/dE proportional to E^-a, we measure a spectral index a = 2.1 +/- 0.2 (statistical) +0.2/-0.1 (systematic). Finally, we discuss the STACEE spectrum in the context of the multiwavelength results from the same epoch.

VHE γ‐Ray Observation of the Crab Nebula and its Pulsar with the MAGIC Telescope

We report about very high energy (VHE) gamma-ray observations of the Crab Nebula with the MAGIC telescope. The gamma-ray flux from the nebula was measured between 60 GeV and 9 TeV. The energy spectrum can be described by a curved power law dF/dE = f(0)(E/300 GeV)([a+b log)((E/300 GeV)])(10) with a flux normalization f(0) of (6.0 +/- 0.2(stat)) x 10(-10) cm(-2) s(-1) TeV-1, a = 2.31 +/- 0.06(stat), and b = 0.26 +/- 0.07(stat). The peak in the spectral energy distribution is estimated at 77 +/- 35 GeV. Within the observation time and the experimental resolution of the telescope, the gamma-ray emission is steady and pointlike. The emission's center of gravity coincides with the position of the pulsar. Pulsed gamma-ray emission from the pulsar could not be detected. We constrain the cutoff energy of the pulsed spectrum to be less than 27 GeV, assuming that the differential energy spectrum has an exponential cutoff. For a superexponential shape, the cutoff energy can be as high as 60 GeV.

Detection of Very High Energy Radiation from the BL Lacertae Object PG 1553+113 with the MAGIC Telescope

In 2005 and 2006, the MAGIC telescope observed very high energy gamma-ray emission from the distant BL Lac object PG 1553 + 113. The overall significance of the signal was 8.8 sigma for 18.8 hr of observation time. The light curve shows no significant flux variations on a daily timescale; the flux level during 2005 was, however, significantly higher compared to 2006. The differential energy spectrum between similar to 90 and 500 GeV is well described by a power law with photon index. Gamma = 4.2 +/- 0.3. The combined 2005 and 2006 energy spectrum provides an upper limit of z = 0.74 on the redshift of the object.

Excitation modes ofHe6from proton collisions

The cross section for inelastic scattering of Borromean halo nuclei from protons is evaluated using the Multiple Scattering expansion of the Total transition amplitude (MST) formalism. Differential cross sections and energy spectra are shown for $p$-$^{6}\mathrm{He}$ at 700 MeV/nucleon. The role of spin flip excitations is analyzed.

The disappearance of anomalous protons at Voyager 1 and Voyager 2 in the outer heliosphere between 1998 and 2002

In 1998 and 1999 at V1 and V2 in the outer heliosphere between 55 and 75 AU, large intensities of anomalous H were observed with a peak in the differential energy spectrum at ∼25 MeV. Subsequently, in 2000 and 2001 when these spacecraft were 5–10 AU further out, these intensities were greatly reduced by 11‐year modulation effects, so that by the beginning of 2002 anomalous H had completely disappeared beneath the E1.0 spectrum of galactic H at low energies. The modulation between 1998 and 2002 produced intensity changes of galactic H similar to those observed at the Earth in the same time period except that the changes at V1 and V2 were much smaller. The intensity change at V2 was also larger than that at V1. For anomalous H, however, the intensity changes at V1 and V2 were a factor of 10–20 times larger than those for galactic H, so that by the end of 2001 the anomalous H intensities were less than 1% of their 1998 values. Also, during one time period in late 2001 there was a large reduction of anomalous H at both V1 and V2 with no corresponding change in galactic H. These different intensity changes between galactic and anomalous H provide an insight into particle transport, drift, and acceleration processes in the region near the heliospheric termination shock, which is located just beyond V1. Radial gradient comparisons in 1998 and also at the times of reduced anomalous H intensities imply that most of the intensity reduction of anomalous H apparently occurred at ∼90 AU or beyond. This could indicate source changes in the anomalous H spectra but most likely is a measure of changes in the “connection” between V1 and V2 and the source region, such as might be caused by changing drift patterns and particle entry into the heliosphere.

Discovery of very high energy γ-ray emission from the BL Lacertae object H 2356-309 with the HESS Cherenkov telescopes

The extreme synchrotron BL Lac object H2356-309, located at a redshift of z = 0.165, was observed from June to December 2004 with a total exposure of approx. 40 h live-time with the H.E.S.S. (High Energy Stereoscopic System) array of atmospheric-Cherenkov telescopes (ACTs). Analysis of this data set yields, for the first time, a strong excess of 453 gamma-rays (10 standard deviations above background) from H2356-309, corresponding to an observed integral flux above 200 GeV of I(>200GeV) = (4.1+-0.5) 10^12 cm^-2.s^-1 (statistical error only). The differential energy spectrum of the source between 200 GeV and 1.3 TeV is well-described by a power law with a normalisation (at 1 TeV) of N_0 = (3.00 +- 0.80_stat +- 0.31_sys) 10^-13 cm^-2.s^-1.TeV^-1 and a photon index of Gamma = 3.09 +- 0.24_stat +- 0.10_sys. H2356-309 is one of the most distant BL Lac objects detected at very-high-energy gamma-rays so far. Results from simultaneous observations from ROTSE-III (optical), RXTE (X-rays) and NRT (radio) are also included and used together with the H.E.S.S. data to constrain a single-zone homogeneous synchrotron self-Compton (SSC) model. This model provides an adequate fit to the H.E.S.S. data when using a reasonable set of model parameters.

Observation of the AGN 1ES1959 + 650 with the MAGIC telescope

The AGN 1ES1959+650 has been observed with the MAGIC telescope in September and October 2004. The MAGIC Telescope is a low energy threshold IACT with, which is well suited for observations of weak γ-ray sources with soft spectra. During the first observations by MAGIC, 1ES1959+650 was in a low state of activity both in X-ray and in optical wavelengths. The analysis of VHE γ-ray data showed a ∼8σ significant signal, while no strong variation of emission during the examined period has been found. The mean measured γ-ray flux was ∼17% of Crab Nebula above 300 GeV. The measured differential energy spectrum between 150 GeV and 2 TeV can be described by a power law function of spectral index α = (2.72±0.14).

Discovery of Very High Energy Gamma Rays from 1ES 1218+30.4

The MAGIC collaboration has studied the high peaked BL-Lac object 1ES1218+30.4 at a redshift z = 0.182, using the MAGIC imaging air Cherenkov telescope located on the Canary island of La Palma. A gamma-ray signal was observed with 6.4sigma significance. The differential energy spectrum for an energy threshold of 120GeV can be fitted by a simple power law yielding F_E(E) = (8.1+-2.1)*10^-7 (E/250GeV)^(-3.0+-0.4) TeV^-1 m^-2 s^-1. During the six days of observation in January 2005 no time variability on time scales of days was found within the statistical errors. The observed integral flux above 350GeV is nearly a factor two below the the upper limit reported by the Whipple Collaboration in 2003.

Primary proton spectrum around the knee observed by the Tibet air-shower experiment

Simultaneous observation of γ-families and their accompanying air showers was performed at Yangbajing (4300 m above sea level) in Tibet with the emulsion chambers and burst detectors which were linked with the Tibet-II air-shower array. For three years operation, we observed 177 γ-families (∑ E γ > 20 TeV) accompanying air showers with the size N e > 2 × 10 5. Using this data and the simulation code CORSIKA, we obtained the primary proton spectrum in the energy range of 10 15–10 16 eV. The slope of the observed spectrum is steeper than that extrapolated smoothly from the lower energy region below 10 14 eV, irrespective of the interaction models assumed in the simulation. The uncertainty of the absolute flux of protons due to the interaction model dependence involved in the simulation codes is at most 30%, which is much weaker than results of other air-shower experiments. Our experiment shows low intensity of light components (proton and helium) independent of the interaction models suggesting that the main component responsible for making the knee structure of the all-particle spectrum is composed of nuclei heavier than helium. This is the first measurement of the differential energy spectra of primary protons by selecting them event by event at the knee energy region.

Spectra and solar energetic protons over 20 GeV in Bastille Day event

Solar energetic particles (SEPs) from large solar flares give important information about the physical process in the solar corona and the heliosphere. Several observations have indicated that solar protons could sometimes be accelerated to at least tens of GeV, even hundreds of GeV, in intense solar energetic process. We studied the solar proton differential energy spectra with energy range of 1–500 MeV at several time intervals during Bastille Day event. It was shown that the spectra could be fitted by a power law function before flare and after flare the power law spectra still existed above 30 MeV although spectra became softer with time. There was a spectral “knee” occurring at ∼30 MeV. We constructed a solar proton differential spectrum from 30 MeV to 3 GeV at peak flux time 10:30 UT and fitted it in the same manner. On the basis of a supposition of having the same power law spectrum in higher energy, we calculated the solar proton integrated fluxes in energy range of from 500 MeV to 20 GeV and compared them with other results obtained from experimental, modelling and theoretical calculations in other big historic SEP events. A Monte Carlo simulation was carried out for a primary proton beam at the top of the atmosphere producing secondary muons on the ground. Based on the simulation, possibility of registering the solar energetic proton beams with energies over 20 GeV was discussed.