[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. · 6.73 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. · 6.73 Impact Factor
[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. · 6.73 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. · 6.73 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. · 6.73 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. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Alpha Magnetic Spectrometer (AMS), whose final version AMS-02 is to be installed on the International Space Station (ISS) for at least 3 years, is a detector designed to measure charged cosmic ray spectra with energies up to the TeV region and with high energy photon detection capability up to a few hundred GeV. It is equipped with several subsystems, one of which is a proximity focusing RICH detector with a dual radiator (aerogel+NaF) that provides reliable measurements for particle velocity and charge. The assembly and testing of the AMS RICH is currently being finished and the full AMS detector is expected to be ready by the end of 2008. The RICH detector of AMS-02 is presented. Physics prospects are briefly discussed.
[show abstract][hide abstract] ABSTRACT: The nearby dwarf spheroidal galaxy Draco with its high mass to light ratio is one of the most auspicious targets for indirect dark matter (DM) searches. Annihilation of hypothetical DM particles can result in high-energy γ-rays, e.g. from neutralino annihilation in the supersymmetric framework.
The Astrophysical Journal 02/2008; 679(1). · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The AMS detector, to be installed on the International Space Station, includes a Ring Imaging Cerenkov detector with two different radiators, silica aerogel (n=1.05) and sodium fluoride (n=1.334). This detector is designed to provide very precise measurements of velocity and electric charge in a wide range of cosmic nuclei energies and atomic numbers. The detector geometry, in particular the presence of a reflector for acceptance purposes, leads to complex Cerenkov patterns detected in a pixelized photomultiplier matrix. The results of different reconstruction methods applied to test beam data as well as to simulated samples are presented. To ensure nominal performances throughout the flight, several detector parameters have to be carefully monitored. The algorithms developed to fulfill these requirements are presented. The velocity and charge measurements provided by the RICH detector endow the AMS spectrometer with precise particle identification capabilities in a wide energy range. The expected performances on light isotope separation are discussed.
[show abstract][hide abstract] ABSTRACT: We report on VHE γ-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 < 32 GeV, assuming the pulsed γ-ray emission to be exponentially cutoff. The upper limit on the flux of pulsed γ-ray emission > 75 GeV is 4.3 · 10 −11 photons cm −2 sec −1 and the upper limit on the flux of steady emission > 140 GeV is 1.5 · 10 −11 photons cm −2 sec −1 . We discuss our results in the framework of recent model predictions and other studies.
[show abstract][hide abstract] ABSTRACT: During its first data cycle, between 2005 and the beginning of 2006, the fast repositioning system of the MAGIC telescope allowed the observation of nine different gamma-ray bursts as possible sources of very high energy γ-rays. These observations were triggered by alerts from Swift, HETE-2, and INTEGRAL; they started as quickly as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending on the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events using the standard analysis chain of MAGIC. For the bursts with measured redshifts, the upper limits are compatible with a power-law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the metagalactic radiation field.
The Astrophysical Journal 01/2007; 667:358-366. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The MAGIC collaboration observed BL Lacertae for 22.2 hr during 2005 August to December and for 26 hr during 2006 July to September. The source is the historical prototype and eponym of a class of low-frequency-peaked BL Lacertae (LBL) objects. A very high energy (VHE) gamma-ray signal was discovered with a 5.1 sigma excess in the 2005 data. Above 200 GeV, an integral flux of (0.6+/-0.2)×10-11 cm-2 s-1 was measured, corresponding to approximately 3% of the Crab flux. The differential spectrum between 150 and 900 GeV is rather steep with a photon index of -3.6 +/- 0.5. The light curve shows no significant variability during the observations in 2005. For the first time a clear detection of VHE gamma-ray emission from an LBL object was obtained with a signal below previous upper limits. The 2006 data show no significant excess. This drop in flux follows the observed trend in optical activity.
The Astrophysical Journal 01/2007; 666:L17-L20. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The MAGIC collaboration has observed very high energy gamma-ray emission from the AGN 1ES 2344+514. A gamma-ray signal corresponding to an 11 σ excess and an integral flux of (2.38 ± 0.30stat ± 0.70syst) × 10-11 cm-2 s-1 above 200 GeV has been obtained from 23.1 hr of data taking between 2005 August 3 and 2006 January 1. The data confirm the previously detected gamma-ray emission from this object during a flare seen by the Whipple collaboration in 1995 and the evidence (below 5 σ significance level) from long-term observations conducted by the Whipple and HEGRA groups. The MAGIC observations show a relatively steep differential photon spectrum that can be described by a power law with a photon index of α = -2.95 ± 0.12stat ± 0.2syst between 140 GeV and 5.4 TeV. The observations reveal a low-flux state, about 6 times below the 1995 flare seen by Whipple and comparable with the previous Whipple and HEGRA long-term measurements. During the MAGIC observations no significant time variability was observed.
The Astrophysical Journal 01/2007; 662:892-899. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The fast repositioning system of the MAGIC Telescope has allowed during its first data cycle, between 2005 and the beginning of year 2006, observing nine different GRBs as possible sources of very high energy gammas. These observations were triggered by alerts from Swift, HETE-II, and Integral; they started as fast as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending upon the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events, using the standard analysis chain of MAGIC. For the bursts with measured redshift, the upper limits are compatible with a power law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the Metagalactic Radiation Field (MRF). Comment: 25 pages, 9 figures, final version accepted by ApJ. Changet title to "MAGIC upped limits on the VERY high energy emission from GRBs", re-organized chapter with description of observation, removed non necessaries figures, added plot of effective area depending on zenith angle, added an appendix explaining the upper limit calculation, added some references