-
A. A. Abdo,
M. Ackermann,
W. B. Atwood,
L. Baldini,
J. Ballet,
G. Barbiellini,
M. G. Baring,
D. Bastieri,
B. M. Baughman,
K. Bechtol, [......],
V. Vitale,
A. P. Waite,
K. Watters,
K. S. Wood,
T. Ylinen,
M. Ziegler,
G. Hobbs,
M. Keith,
R. N. Manchester,
and P. Weltevrede
[show abstract]
[hide abstract]
ABSTRACT: Radio pulsar PSR J1028–5819 was recently discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic Gamma-Ray Experiment Telescope (EGRET) source 3EG J1027–5817. The spin-down power of this young pulsar is great enough to make it very likely the counterpart for the EGRET source. We report here the discovery of γ-ray pulsations from PSR J1028–5819 in early observations by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. The γ-ray light curve shows two sharp peaks having phase separation of 0.460 ± 0.004, trailing the very narrow radio pulse by 0.200 ± 0.003 in phase, very similar to that of other known γ-ray pulsars. The measured γ-ray flux gives an efficiency for the pulsar of ~10-20% (for outer magnetosphere beam models). No evidence of a surrounding pulsar wind nebula is seen in the current Fermi data but limits on associated emission are weak because the source lies in a crowded region with high background emission. However, the improved angular resolution afforded by the LAT enables the disentanglement of the previous COS-B and EGRET source detections into at least two distinct sources, one of which is now identified as PSR J1028–5819.
The Astrophysical Journal 03/2009; 695(1):L72. · 6.02 Impact Factor
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A. A. Abdo,
M. Ackermann,
W. B. Atwood,
M. Axelsson,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
B. M. Baughman,
K. Bechtol, [......],
M. L. Kocian,
F. Kuehn,
M. Kuss,
L. Latronico,
S. -H. Lee,
M. Lemoine-Goumard,
F. Longo,
F. Loparco,
B. Lott,
others
Astrophysical Journal. 01/2009; 697(1):934-941.
-
W. B. Atwood,
A. A. Abdo,
M. Ackermann,
W. Althouse,
B. Anderson,
M. Axelsson,
L. Baldini,
J. Ballet,
D. L. Band,
G. Barbiellini, [......],
L. Guillemot,
S. Guiriec,
G. Haller,
A. K. Harding,
P. A. Hart,
E. Hays,
S. E. Healey,
M. Hirayama,
L. Hjalmarsdotter,
others
Astrophysical Journal. 01/2009; 697(2):1071-1102.
-
A. A. Abdo,
M. Ackermann,
W. B. Atwood,
R. Bagagli,
L. Baldini,
J. Ballet,
D. L. Band,
G. Barbiellini,
M. G. Baring,
J. Bartelt, [......],
G. Hobbs,
R. E. Hughes,
G. Johannesson,
A. S. Johnson,
R. P. Johnson,
T. J. Johnson,
W. N. Johnson,
S. Johnston,
T. Kamae,
others
[show abstract]
[hide abstract]
ABSTRACT: The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new gamma-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E >= 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of Gamma = 1.51(-0.04)(+0.05) with an exponential cutoff at E(c) = 2.9 +/- 0.1 GeV. Spectral fits with generalized cutoffs of the form e(-(E/Ec)b) require b <= 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.
Astrophysical Journal. 01/2009; 696(2):1084-1093.
-
M. de Naurois,
J. Holder,
R. Bazer-Bachi,
H. Bergeret,
P. Bruel,
A. Cordier,
G. Debiais,
J.-P. Dezalay,
D. Dumora,
E. Durand, [......],
J. Québert,
R. C. Rannot,
T. Reposeur,
L. Rob,
P. Roy,
T. Sako,
P. Schovanek,
D. A. Smith,
P. Snabre,
and A. Volte
[show abstract]
[hide abstract]
ABSTRACT: We have converted the former solar electrical plant THEMIS (French Pyrenees) into an atmospheric Cerenkov detector called CELESTE, which records gamma rays above 30 GeV (7 × 1024 Hz). Here we present the first sub-100 GeV detection by a ground-based telescope of a gamma-ray source, the Crab Nebula, in the energy region between satellite measurements and imaging atmospheric Cerenkov telescopes. At our analysis threshold energy of 60 ± 20 GeV we measure a gamma-ray rate of 6.1 ± 0.8 minute-1. Allowing for 30% systematic uncertainties and a 30% error on the energy scale yields an integral gamma-ray flux of I(E > 60GeV) = 6.2 × 10-6 photons m-2 s-1. The analysis methods used to obtain the gamma-ray signal from the raw data are detailed. In addition, we determine the upper limit for pulsed emission to be less than 12% of the Crab flux at the 99% confidence level, in the same energy range. Our result indicates that if the power law observed by EGRET is attenuated by a cutoff of form e, then E0 < 26 GeV. This is the lowest energy probed by a Cerenkov detector and leaves only a narrow range unexplored beyond the energy range studied by EGRET.
The Astrophysical Journal 12/2008; 566(1):343. · 6.02 Impact Factor
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F Aharonian,
A G Akhperjanian,
K-M Aye,
A R Bazer-Bachi,
M Beilicke,
W Benbow,
D Berge,
P Berghaus,
K Bernlöhr,
C Boisson, [......],
C Stegmann,
J-P Tavernet,
R Terrier,
C G Théoret,
M Tluczykont,
G Vasileiadis,
C Venter,
P Vincent,
H J Völk,
S J Wagner
[show abstract]
[hide abstract]
ABSTRACT: X-ray binaries are composed of a normal star in orbit around a neutron star or stellar-mass black hole. Radio and x-ray observations have led to the presumption that some x-ray binaries called microquasars behave as scaled-down active galactic nuclei. Microquasars have resolved radio emission that is thought to arise from a relativistic outflow akin to active galactic nuclei jets, in which particles can be accelerated to large energies. Very high energy gamma-rays produced by the interactions of these particles have been observed from several active galactic nuclei. Using the High Energy Stereoscopic System, we find evidence for gamma-ray emission of >100 gigaelectron volts from a candidate microquasar, LS 5039, showing that particles are also accelerated to very high energies in these systems.
Science 08/2005; 309(5735):746-9. · 31.20 Impact Factor
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F Aharonian,
A G Akhperjanian,
K-M Aye,
A R Bazer-Bachi,
M Beilicke,
W Benbow,
D Berge,
P Berghaus,
K Bernlöhr,
C Boisson, [......],
R Terrier,
C G Théoret,
M Tluczykont,
D J van der Walt,
G Vasileiadis,
C Venter,
P Vincent,
B Visser,
H J Völk,
S J Wagner
[show abstract]
[hide abstract]
ABSTRACT: Very high energy gamma-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (HESS) reveals a population of eight previously unknown firmly detected sources of very high energy gamma-rays. At least two have no known radio or x-ray counterpart and may be representative of a new class of "dark" nucleonic cosmic ray sources.
Science 04/2005; 307(5717):1938-42. · 31.20 Impact Factor
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F Aharonian,
AG Akhperjanian,
KM Aye,
AR Bazer-Bachi,
M Beilicke,
W Benbow,
D Berge,
P Berghaus,
K Bernlohr,
O Bolz, [......],
C Stegmann,
JP Tavernet,
CG Theoret,
M Tluczykont,
DJ Walt,
G Vasileiadis,
P Vincent,
B Visser,
HJ Volk,
SJ Wagner
Astronomy & Astrophysics. 01/2005; 430(3):865-875.
-
F A Aharonian,
A G Akhperjanian,
K-M Aye,
A R Bazer-Bachi,
M Beilicke,
W Benbow,
D Berge,
P Berghaus,
K Bernlöhr,
O Bolz, [......],
C Stegmann,
J-P Tavernet,
C G Théoret,
M Tluczykont,
D J Van Der Walt,
G Vasileiadis,
P Vincent,
B Visser,
H J Völk,
S J Wagner
[show abstract]
[hide abstract]
ABSTRACT: A significant fraction of the energy density of the interstellar medium is in the form of high-energy charged particles (cosmic rays). The origin of these particles remains uncertain. Although it is generally accepted that the only sources capable of supplying the energy required to accelerate the bulk of Galactic cosmic rays are supernova explosions, and even though the mechanism of particle acceleration in expanding supernova remnant (SNR) shocks is thought to be well understood theoretically, unequivocal evidence for the production of high-energy particles in supernova shells has proven remarkably hard to find. Here we report on observations of the SNR RX J1713.7 - 3946 (G347.3 - 0.5), which was discovered by ROSAT in the X-ray spectrum and later claimed as a source of high-energy gamma-rays of TeV energies (1 TeV = 10(12) eV). We present a TeV gamma-ray image of the SNR: the spatially resolved remnant has a shell morphology similar to that seen in X-rays, which demonstrates that very-high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks.
Nature 12/2004; 432(7013):75-7. · 36.28 Impact Factor
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F. Aharonian,
A.G. Akhperjanian,
K.-M. Aye,
A.R. Bazer-Bachi,
M. Beilicke,
W. Benbow,
D. Berge,
P. Berghaus,
K. Bernlöhr,
O. Bolz, [......],
C. Stegmann,
J.-P. Tavernet,
C.G. Théoret,
M. Tluczykont,
D.J. van der Walt,
G. Vasileiadis,
P. Vincent,
B. Visser,
H.J. Volk,
S.J. Wagner
[show abstract]
[hide abstract]
ABSTRACT: H.E.S.S.—the high energy stereoscopic system—is a new system of large atmospheric Cherenkov telescopes for GeV/TeV astronomy. Each of the four telescopes of 107 m2 mirror area is equipped with a 960-pixel photomultiplier-tube camera. This paper describes the methods used to convert the photomultiplier signals into the quantities needed for Cherenkov image analysis. Two independent calibration techniques have been applied in parallel to provide an estimation of uncertainties. Results on the long-term stability of the H.E.S.S. cameras are also presented.
Astroparticle Physics. 01/2004;
-
F. Piron,
A. Djannati-Atai,
M. Punch,
J.-P. Tavernet,
A. Barrau,
R. Bazer-Bachi,
L.-M. Chounet,
G. Debiais,
B. Degrange,
J.-P. Dezalay, [......],
C. Gouiffes,
B. Khelifi,
I. Malet,
C. Masterson,
G. Mohanty,
E. Nuss,
C. Renault,
M. Rivoal,
L. Rob,
S. Vorobiov
[show abstract]
[hide abstract]
ABSTRACT: The γ-ray emission above 250 GeV from the BL Lac object Markarian
421 has been observed by the CAT Cherenkov Imaging Telescope since
December, 1996. In 2000 and 2001, the source showed an activity much
higher than during the previous 3 years. Results on the source
variability and on its energy spectrum obtained from observations during
years 2000 and 2001 are reported.
07/2001; 7:2601.
-
B. Khelifi,
A. Barrau,
R. Bazer-Bachi,
L.-M. Chounet,
G. Debiais,
B. Degrange,
J.-P. Dezalay,
A. Djannati-Ataie,
P. Espigat,
B. Fabre, [......],
I. Malet,
C. Masterson,
G. Mohanty,
E. Nuss,
M. Punch,
C. Renault,
M. Rivoal,
L. Rob,
J.-P. Tavernet,
S. Vorobiov
[show abstract]
[hide abstract]
ABSTRACT: The recent evidence of TeV γ-ray emission from the Supernova
Remnant (SNR) Cassiopeia A (Aharonian et al., 2001) demonstrates the
interesting nature of these sources as candidate accelerators of cosmic
rays. The observed TeV γ-ray emission may be produced by
high-energy electrons and/or nuclei accelerated by shock fronts within
the SNR. Here we report on observations by the CAT imaging Cherenkov
telescope on the SNRs CTA 1 and IC443 during the years 2000-01. We also
present our observations of the plerion CTB 80 during the same period.
Gamma-ray flux upper limits are given for positions coincident with
EGRET detections of each source.
07/2001; 6:2444.
-
M. de Naurois,
J. Holder,
R. Bazer-Bachi,
H. Bergeret,
P. Bruel,
A Cordier,
G. Debiais,
J. P. Dezalay,
D. Dumora,
E. Durand, [......],
J. Quebert,
R. C. Rannot,
T. Reposeur,
L. Rob,
P Roy,
T Sako,
P. Schovanek,
D A Smith,
P. Snabre,
A Volte
[show abstract]
[hide abstract]
ABSTRACT: We have converted the former solar electrical plant THEMIS (French Pyrenees) into an atmospheric Cherenkov detector called CELESTE, which records gamma rays above 30 GeV (7E24 Hz). Here we present the first sub-100 GeV detection by a ground based telescope of a gamma ray source, the Crab nebula, in the energy region between satellite measurements and imaging atmospheric Cherenkov telescopes. At our analysis threshold energy of 60 +/- 20 GeV we measure a gamma ray rate of 6.1 +/- 0.8 per minute. Allowing for 30% systematic uncertainties and a 30% error on the energy scale yields an integral gamma ray flux of I(E>60 GeV) = 6.2^{+5.3}_{-2.3} E-6 photons m^-2 s^-1. The analysis methods used to obtain the gamma ray signal from the raw data are detailed. In addition, we determine the upper limit for pulsed emission to be <12% of the Crab flux at the 99% confidence level, in the same energy range. Our result indicates that if the power law observed by EGRET is attenuated by a cutoff of form e^{-E/E_0} then E_0 < 26 GeV. This is the lowest energy probed by a Cherenkov detector and leaves only a narrow range unexplored beyond the energy range studied by EGRET. Comment: 34 pages, accepted by the Astrophysical Journal
07/2001;
-
F. Piron,
A. Djannati-Atai,
M. Punch,
J P Tavernet,
A. Barrau,
R. Bazer-Bachi,
L.-M. Chounet,
G. Debiais,
B. Degrange,
J. P. Dezalay, [......],
C. Gouiffes,
B. Khelifi,
I. Malet,
C. Masterson,
G. Mohanty,
E. Nuss,
C. Renault,
M. Rivoal,
L. Rob,
S. Vorobiov
[show abstract]
[hide abstract]
ABSTRACT: The gamma-ray emission above 250 GeV from the BL Lac object Markarian 421 was observed by the CAT Cherenkov imaging telescope between December, 1996, and June, 2000. In 1998, the source produced a series of small flares, making it the second extragalactic source detected by CAT. The time-averaged differential spectrum has been measured from 0.3 to 5 TeV, which is well fitted with a power law with an index of -2.88+-0.12(stat)+-0.06(syst). In 2000, the source showed an unprecedented activity, with variability time-scales as short as one hour, as for instance observed during the night between 4 and 5 February. The 2000 time-averaged spectrum measured is compatible with that of 1998, but some indication of a spectral curvature is found between 0.3 and 5 TeV. The possibility of TeV spectral hardening during flares is also discussed, and the results are compared to those obtained on the other TeV BL Lac, Markarian 501. Comment: Latex2e, 11 pages, 7 figures, accepted for publication in Astronomy & Astrophysics
06/2001;
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G. Mohanty,
L.-M. Chounet,
B. Degrange, P. Fleury,
G. Fontaine,
L. Iacoucci,
F. Piron,
R. Bazer-Bachi,
J.-P. Dezalay,
I. Malet, [......],
K. Schahmaneche,
J.-P. Tavernet,
L. Rob,
A. Djannati-Ataï,
P. Espigat,
M. Punch,
P. Goret,
C. Gouiffes,
I. A. Grenier,
D. Ellison
[show abstract]
[hide abstract]
ABSTRACT: Supernova remnants (SNR) can be broadly classified into two types: plerionic or plasma-filled SNR, like the Crab Nebula, and shell-type SNR, like Cassiopeia A (Cas A). VHE observations of the Crab Nebula and Cas A made with the CAT atmospheric Cherenkov imaging telescope are used to constrain models for production of gamma rays in SNR. For both plerionic and shell-type SNR, these observations serve primarily to impose a limit on the magnetic field in the region where the particles are accelerated. © 2000 American Institute of Physics.
AIP Conference Proceedings. 04/2000; 510(1):77-81.
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A. Djannati-Atai,
F. Piron,
A. Barrau,
L. Iacoucci,
M. Punch,
J P Tavernet,
R. Bazer-Bachi,
H. Cabot,
L.-M. Chounet,
G. Debiais, [......],
G. Mohanty,
E. Nuss,
E Paré,
J. Québert,
K. Ragan,
C. Renault,
M. Rivoal,
L. Rob,
K. Schahmaneche,
D A Smith
[show abstract]
[hide abstract]
ABSTRACT: The BL Lac object Mrk 501 went into a very high state of activity during 1997, both in VHE gamma-rays and X-rays. We present here results from observations at energies above 250 GeV carried out between March and October 1997 with the CAT Cerenkov imaging Telescope. The average differential spectrum between 30 GeV and 13 TeV shows significant curvature and is well represented by phi_0 * E_TeV^{-(alpha + beta*log10(E_TeV))}, with: phi_0 = 5.19 +/- 0.13 {stat} +/- 0.12 {sys-MC} +1.66/-1.04 {sys-atm} * 10^-11 /cm^2/s/TeV alpha = 2.24 +/- 0.04 {stat} +/- 0.05 {sys} beta = 0.50 +/- 0.07 {stat} (negligible systematics). The TeV spectral energy distribution of Mrk 501 clearly peaks in the range 500 GeV-1 TeV. Investigation of spectral variations shows a significant hardness-intensity correlation with no measurable effect on the curvature. This can be described as an increase of the peak TeV emission energy with intensity. Simultaneous and quasi-simultaneous CAT VHE gamma-ray and BeppoSAX hard X-ray detections for the highest recorded flare on 16th April and for lower-activity states of the same period show correlated variability with a higher luminosity in X-rays than in gamma-rays. The observed spectral energy distribution and the correlated variability between X-rays and gamma-rays, both in amplitude and in hardening of spectra, favour a two-component emission scheme where the low and high energy components are attributed to synchrotron and inverse Compton (IC) radiation, respectively.
07/1999;
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W B Atwood,
S Ritz,
P. Anthony,
E. D. Bloom,
P. E. Bosted,
J Bourotte,
C. Chaput,
X Chen,
D. L. Chenette,
D. Engovatov, [......],
P Nolan,
J. P. Norris,
M. Oreglia,
J. F. Ormes,
B.F. Phlips,
A. Pocar,
H F W Sadrozinski,
Z. Szalata,
D. J. Thompson,
W. F. Tompkins
[show abstract]
[hide abstract]
ABSTRACT: A beam test of GLAST (Gamma-ray Large Area Space Telescope) components was performed at the Stanford Linear Accelerator Center in October, 1997. These beam test components were simple versions of the planned flight hardware. Results on the performance of the tracker, calorimeter, and anti-coincidence charged particle veto are presented.
06/1999;
-
B. Giebels,
R. Bazer-Bachi,
H. Bergeret,
A Cordier,
G. Debiais,
M. de Naurois,
J. P. Dezalay,
D. Dumora,
P. Eschstruth,
P. Espigat,
B. Fabre, P. Fleury,
N. Herault,
I. Malet,
B. Merkel,
C. Meynadier
[show abstract]
[hide abstract]
ABSTRACT: The CELESTE experiment will be an Atmospheric Cherenkov detector designed to bridge the gap in energy sensitivity between current satellite and ground-based gamma-ray telescopes, 20 to 300 GeV. We present test results made at the former solar power plant, Themis, in the French Pyrenees. The tests confirm the viability of using a central tower heliostat array for Cherenkov wavefront sampling. 1 e-mail: giebels@cenbg.in2p3.fr 2 Visiting from McGill University, Montreal, Canada. 3 Deceased. Preprint submitted to Elsevier Preprint 27 October 1 INTRODUCTION The CELESTE experiment uses the Electricit'e de France central receiver solar power plant at Themis (N. 42.50 ffi , E. 1.97 ffi , 1650 m. a.s.l.) as a gamma-ray telescope [1]. The project is fully funded and will begin observations in early 1998 with 18 heliostats, growing to 40 in the following year. Figure 1 sketches the principal of the CELESTE approach. This paper describes test results accumulated during the design and co...
11/1998;
-
A. Barrau,
R. Bazer-Bachi,
E. Beyer,
M Cerutti,
L.-M. Chounet,
G. Debiais,
B. Degrange,
H. Delchini,
J. P. Denance,
G. Descotes, [......],
S. Le Bohec,
I. Malet,
C. Meynadier,
J. P. Mols,
P. Mora de Freitas,
R Morano,
G. Morinaud,
F. Munz,
K. Ragan,
L. Rob
[show abstract]
[hide abstract]
ABSTRACT: The CAT (Cherenkov Array at Th'emis) imaging telescope, equipped with a veryhigh -definition camera (546 fast phototubes with 0:12 ffi spacing surrounded by 54 Preprint submitted to Elsevier Preprint 31 March larger tubes in two guard rings) started operation in Autumn 1996 on the site of the former solar plant Th'emis (France). Using the atmospheric Cherenkov technique, it detects and identifies very high energy fl-rays in the range 250 GeV to a few tens of TeV. The instrument, which has detected three sources (Crab nebula, Markarian 421 and Markarian 501), is described in detail. Key words: Gamma-Ray Astronomy, Atmospheric Cherenkov detector 1 Introduction The recent development of Very-High-Energy Gamma-Ray Astronomy is essentially due to Atmospheric Cherenkov Telescopes (ACT). Since 1988, two arrays of Cherenkov detectors, ASGAT [1] and THEMISTOCLE [2] have been operated on the site of the former solar plant "Th'emis", close to Font-Romeu in the French Pyrenees. They consist of...
05/1998;
-
S. Le Bohec,
B. Degrange,
M. Punch,
A. Barrau,
L.-M. Chounet,
G. Debiais,
J. P. Dezalay,
A. Djannati-Atai,
D. Dumora,
P. Espigat, [......],
F. Munz,
Y Pons,
K. Ragan,
C. Renault,
M. Rivoal,
L. Rob,
P. Schovanek,
D Smith,
J P Tavernet,
J Vrana
[show abstract]
[hide abstract]
ABSTRACT: A new method of shower-image analysis is presented which appears very powerful as applied to those Cherenkov Imaging Telescopes with very high definition imaging capability. It provides hadron rejection on the basis of a single cut on the image shape, and simultaneously determines the energy of the electromagnetic shower and the position of the shower axis with respect to the detector. The source location is Preprint submitted to Elsevier Preprint 31 March also reconstructed for each individual fl-ray shower, even with one single telescope, so for a point source the hadron rejection can be further improved. As an example, this new method is applied to data from the CAT (Cherenkov Array at Th'emis) imaging telescope, which has been operational since Autumn, 1996. Key words: Gamma-Ray Astronomy, Atmospheric Cherenkov detector 1 Introduction Most of the recent progress in ground-based fl-ray Astronomy has been obtained from Atmospheric Cherenkov Telescopes (ACT) using the imaging techni...
05/1998;
