[Show abstract][Hide abstract] ABSTRACT: A precise measurement of the proton flux in primary cosmic rays with rigidity (momentum/charge) from 1 GV to 1.8 TV is presented based on 300 million events. Knowledge of the rigidity dependence of the proton flux is important in understanding the origin, acceleration, and propagation of cosmic rays. We present the detailed variation with rigidity of the flux spectral index for the first time. The spectral index progressively hardens at high rigidities.
[Show abstract][Hide abstract] ABSTRACT: We present a measurement of the cosmic ray (e[superscript +] + e[superscript -]) flux in the range 0.5 GeV to 1 TeV based on the analysis of 10.6 million (e[superscript +] + e[superscript -]) events collected by AMS. The statistics and the resolution of AMS provide a precision measurement of the flux. The flux is smooth and reveals new and distinct information. Above 30.2 GeV, the flux can be described by a single power law with a spectral index γ = -3.170 ± 0.008(stat + syst) ± 0.008(energy scale).
[Show abstract][Hide abstract] ABSTRACT: Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ∼30 GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons.
[Show abstract][Hide abstract] ABSTRACT: A precision measurement by AMS of the positron fraction in primary cosmic rays in the energy range from 0.5 to 500 GeV based on 10.9 million positron and electron events is presented. This measurement extends the energy range of our previous observation and increases its precision. The new results show, for the first time, that above ∼200 GeV the positron fraction no longer exhibits an increase with energy.
[Show abstract][Hide abstract] ABSTRACT: We present the results from a multiwavelength campaign on the TeV blazar 1ES 1959+650, performed in 2006 May. Data from the optical, UV, soft- and hard-X-ray, and very high energy (VHE) gamma-ray (E > 100 GeV) bands were obtained with the Suzaku and Swift satellites, the MAGIC telescope, and other ground-based facilities. The source spectral energy distribution (SED), derived from Suzaku and MAGIC observations at the end of 2006 May, shows the usual double hump shape, with the synchrotron peak at a higher flux level than the Compton peak. With respect to historical values, during our campaign the source exhibited a relatively high state in X-rays and optical, while in the VHE band it was at one of the lowest level so far recorded. We also monitored the source for flux spectral variability on a time window of 10 days in the optical-UV and X-ray bands and 7 days in the VHE band. The source varies more in the X-ray than in the optical band, with the 2-10 keV X-ray flux varying by a factor of ~2. The synchrotron peak is located in the X-ray band and moves to higher energies as the source gets brighter, with the X-ray fluxes above it varying more rapidly than the X-ray fluxes at lower energies. The variability behavior observed in the X-ray band cannot be produced by emitting regions varying independently and suggests instead some sort of "standing shock" scenario. The overall SED is well represented by a homogeneous one-zone synchrotron inverse Compton emission model, from which we derive physical parameters that are typical of high-energy peaked blazars.
The Astrophysical Journal 12/2008; 679(2):1029. DOI:10.1086/586731 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the discovery of very high energy (VHE) γ-ray emission from the BL Lacertae object 1ES 1011+496. The observation was triggered by an optical outburst in 2007 March and the source was observed with the MAGIC telescope from 2007 March to May. Observing for 18.7 hr, we find an excess of 6.2 σ with an integrated flux above 200 GeV of (1.58 ± 0.32) × 10-11 photons cm-2 s-1. The VHE γ-ray flux is >40% higher than in 2006 March-April (reported elsewhere), indicating that the VHE emission state may be related to the optical emission state. We have also determined the redshift of 1ES 1011+496 based on an optical spectrum that reveals the absorption lines of the host galaxy. The redshift of z = 0.212 makes 1ES 1011+496 the most distant source observed to emit VHE γ-rays to date.
The Astrophysical Journal 12/2008; 667(1):L21. DOI:10.1086/521982 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: All but three (M87, BL Lac, and 3C 279) extragalactic sources detected so far at very high energy γ-rays belong to the class of high-frequency-peaked BL Lac objects. This suggested to us a systematic scan of candidate sources with the MAGIC telescope, based on the Donato et al. compilation of X-ray blazars. The observations took place from 2004 December to 2006 March and cover northern sky sources visible under small zenith distances zd < 30° at culmination, constraining the declination to –2° to +58°. The sensitivity of the search was planned for detecting X-ray-bright [F(1 keV) > 2 μ Jy ] sources emitting at least the same energy flux at 200 GeV as at 1 keV. To avoid strong γ-ray attenuation close to the energy threshold, source redshift was constrained to z < 0.3. Of the 14 sources observed, 1ES 1218+304 (for the first time at VHE) and 1ES 2344+514 (strong detection in a low flux state) were detected in addition to the known bright TeV blazars Mrk 421 and Mrk 501. A marginal excess of 3.5 σ from the position of 1ES 1011+496 was observed and then confirmed as a VHE γ-ray source by a second MAGIC observation triggered by a high optical state. For the remaining sources, we present 99% c.l. upper limits on the integral flux 200 GeV. We characterize the HBL sample (including all HBLs detected at VHE so far) by looking for correlations between their multifrequency spectral indices determined from simultaneous optical, archival X-ray, and radio luminosities, finding that VHE-emitting HBLs do not seem to constitute a unique subclass. The HBLs' absorption-corrected γ-ray luminosities at 200 GeV are generally not higher than their X-ray luminosities at 1 keV.
The Astrophysical Journal 12/2008; 681(2):944. DOI:10.1086/587499 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on very high energy γ-ray observations with the MAGIC Telescope of the pulsar PSR B1951+32 and its associated nebula, CTB 80. Our data constrain the cutoff energy of the pulsar to be less than 32 GeV, assuming the pulsed γ-ray emission to be exponentially cut off. In the case that the cutoff follows a superexponential behavior, the cutoff energy can be as high as ~60 GeV. The upper limit on the flux of pulsed γ-ray emission above 75 GeV is 4.3 × 10-11 photons cm-2 s-1, and the upper limit on the flux of steady emission above 140 GeV is 1.5 × 10-11 photons cm-2 s-1. We discuss our results in the framework of recent model predictions and other studies.
The Astrophysical Journal 12/2008; 669(2):1143. DOI:10.1086/521807 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report about very high energy (VHE) γ-ray observations of the Crab Nebula with the MAGIC telescope. The γ-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 = f0(E/300 GeV)[a+blog10(E/300 GeV)] with a flux normalization f0 of (6.0 ± 0.2stat) × 10−10 cm−2 s−1 TeV−1, a = − 2.31 ± 0.06stat, and b = − 0.26 ± 0.07stat. 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 γ-ray emission is steady and pointlike. The emission's center of gravity coincides with the position of the pulsar. Pulsed γ-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.
The Astrophysical Journal 12/2008; 674(2):1037. DOI:10.1086/525270 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We observed the first known very high energy (VHE) γ-ray-emitting unidentified source, TeV J2032+4130, for 94 hr with the MAGIC telescope. The source was detected with a significance of 5.6 σ. The flux, position, and angular extension are compatible with the previous ones measured by the HEGRA telescope system 5 years ago. The integral flux amounts to (4.5 ± 0.3stat ± 0.35sys) × 10−13 photons cm−2 s−1 above 1 TeV. The source energy spectrum, obtained with the lowest energy threshold to date, is compatible with a single power law with a hard photon index of Γ = –2.0 ± 0.3stat ± 0.2sys.
The Astrophysical Journal 12/2008; 675(1):L25. DOI:10.1086/529520 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Until April 2007 the Major Atmospheric Gamma ray Imaging Cherenkov (MAGIC) telescope used a 300 MSamples/s flash analog-to-digital converter (FADC) system to sample the shaped photomultiplier tube (PMT) signals produced by the captured Cherenkov photons of air showers. Different algorithms to reconstruct the signal from the read-out samples (extractors) have been implemented and are described and compared. Criteria based on the obtained charge and time resolution/bias are defined and used to judge the different extractors, by applying them to calibration, cosmic and pedestal signals. The achievable charge and time resolution have been derived as functions of the number of incident photo-electrons.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/2008; 594(3-594):407-419. DOI:10.1016/j.nima.2008.06.043 · 1.22 Impact Factor