-
A. A. Abdo,
M. Ackermann,
M. Ajello,
A. Allafort,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
K. Bechtol,
R. Bellazzini, [......],
N. Vilchez,
V. Vitale,
A. P. Waite,
E. Wallace,
P. Wang,
P. Weltevrede,
B. L. Winer,
K. S. Wood,
T. Ylinen,
and M. Ziegler
[show abstract]
[hide abstract]
ABSTRACT: Millisecond pulsars (MSPs) have been firmly established as a class of γ-ray emitters via the detection of pulsations above 0.1 GeV from eight MSPs by the Fermi Large Area Telescope (LAT). Using 13 months of LAT data, significant γ-ray pulsations at the radio period have been detected from the MSP PSR J0034–0534, making it the ninth clear MSP detection by the LAT. The γ-ray light curve shows two peaks separated by 0.274 ± 0.015 in phase which are very nearly aligned with the radio peaks, a phenomenon seen only in the Crab pulsar until now. The ≥0.1 GeV spectrum of this pulsar is well fit by an exponentially cutoff power law with a cutoff energy of 1.8 ± 0.6 ± 0.1 GeV and a photon index of 1.5 ± 0.2 ± 0.1, first errors are statistical and second are systematic. The near-alignment of the radio and γ-ray peaks strongly suggests that the radio and γ-ray emission regions are co-located and both are the result of caustic formation.
The Astrophysical Journal 03/2010; 712(2):957. · 6.02 Impact Factor
-
A A Abdo,
M Ackermann,
M Ajello,
L Baldini,
J Ballet,
G Barbiellini,
M G Baring,
D Bastieri,
B M Baughman,
K Bechtol, [......],
C Venter,
N Vilchez,
V Vitale,
A P Waite,
P Wang,
B L Winer,
K S Wood,
R Yamazaki,
T Ylinen,
M Ziegler
[show abstract]
[hide abstract]
ABSTRACT: Recent observations of supernova remnants (SNRs) hint that they accelerate cosmic rays to energies close to ~10(15) electron volts. However, the nature of the particles that produce the emission remains ambiguous. We report observations of SNR W44 with the Fermi Large Area Telescope at energies between 2 x 10(8) electron volts and 3 x10(11) electron volts. The detection of a source with a morphology corresponding to the SNR shell implies that the emission is produced by particles accelerated there. The gamma-ray spectrum is well modeled with emission from protons and nuclei. Its steepening above approximately 10(9) electron volts provides a probe with which to study how particle acceleration responds to environmental effects such as shock propagation in dense clouds and how accelerated particles are released into interstellar space.
Science 02/2010; 327(5969):1103-6. · 31.20 Impact Factor
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
A. Allafort,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
K. Bechtol,
R. Bellazzini, [......],
M. Kramer,
M. Kuss,
J. Lande,
L. Latronico,
M. Lemoine-Goumard,
Llena M. Garde,
F. Longo,
F. Loparco,
B. Lott,
others
Astrophysical Journal. 01/2010; 712(2):957-963.
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
W. B. Atwood,
M. Axelsson,
L. Baldini,
J. Ballet,
G. Barbiellini,
M. G. Baring,
D. Bastieri, [......],
A. S. Johnson,
R. P. Johnson,
T. J. Johnson,
W. N. Johnson,
S. Johnston,
T. Kamae,
G. Kanbach,
V. M. Kaspi,
H. Katagiri,
others
Astrophysical Journal Supplement Series. 01/2010; 187(2):460-494.
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
W. B. Atwood,
M. Axelsson,
L. Baldini,
J. Ballet,
G. Barbiellini,
M. G. Baring,
D. Bastieri, [......],
M. Kramer,
F. Kuehn,
M. Kuss,
J. Lande,
L. Latronico,
S. H. Lee,
M. Lemoine-Goumard,
F. Longo,
F. Loparco,
others
[show abstract]
[hide abstract]
ABSTRACT: We report on gamma-ray observations of the Crab Pulsar and Nebula using 8 months of survey data with the Fermi Large Area Telescope (LAT). The high quality light curve obtained using the ephemeris provided by the Nancay and Jodrell Bank radio telescopes shows two main peaks stable in phase with energy. The first gamma-ray peak leads the radio main pulse by (281 +/- 12 +/- 21) mu s, giving new constraints on the production site of non-thermal emission in pulsar magnetospheres. The first uncertainty is due to gamma-ray statistics, and the second arises from the rotation parameters. The improved sensitivity and the unprecedented statistics afforded by the LAT enable precise measurement of the Crab Pulsar spectral parameters: cut-off energy at E(c) = (5.8 +/- 0.5 +/- 1.2) GeV, spectral index of Gamma = (1.97 +/- 0.02 +/- 0.06) and integral photon flux above 100 MeV of (2.09 +/- 0.03 +/- 0.18) x 10(-6) cm(-2) s(-1). The first errors represent the statistical error on the fit parameters, while the second ones are the systematic uncertainties. Pulsed gamma-ray photons are observed up to similar to 20 GeV which precludes emission near the stellar surface, below altitudes of around 4-5 stellar radii in phase intervals encompassing the two main peaks. A detailed phase-resolved spectral analysis is also performed: the hardest emission from the Crab Pulsar comes from the bridge region between the two gamma-ray peaks while the softest comes from the falling edge of the second peak. The spectrum of the nebula in the energy range 100 MeV-300 GeV is well described by the sum of two power laws of indices Gamma(sync) = (3.99 +/- 0.12 +/- 0.08) and Gamma(IC) = (1.64 +/- 0.05 +/- 0.07), corresponding to the falling edge of the synchrotron and the rising edge of the inverse Compton (IC) components, respectively. This latter, which links up naturally with the spectral data points of Cherenkov experiments, is well reproduced via IC scattering from standard magnetohydrodynamic nebula models, and does not require any additional radiation mechanism.
Astrophysical Journal. 01/2010; 708(2):1254-1267.
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
W. B. Atwood,
M. Axelsson,
L. Baldini,
J. Ballet,
G. Barbiellini,
M. G. Baring,
D. Bastieri, [......],
V. Vitale,
A. P. Waite,
E. Wallace,
P. Wang,
K. Watters,
P. Weltevrede,
B. L. Winer,
K. S. Wood,
T. Ylinen,
and M. Ziegler
[show abstract]
[hide abstract]
ABSTRACT: We report on γ-ray observations of the Crab Pulsar and Nebula using 8 months of survey data with the Fermi Large Area Telescope (LAT). The high quality light curve obtained using the ephemeris provided by the Nançay and Jodrell Bank radio telescopes shows two main peaks stable in phase with energy. The first γ-ray peak leads the radio main pulse by (281 ± 12 ± 21) μs, giving new constraints on the production site of non-thermal emission in pulsar magnetospheres. The first uncertainty is due to γ-ray statistics, and the second arises from the rotation parameters. The improved sensitivity and the unprecedented statistics afforded by the LAT enable precise measurement of the Crab Pulsar spectral parameters: cut-off energy at Ec = (5.8 ± 0.5 ± 1.2) GeV, spectral index of Γ = (1.97 ± 0.02 ± 0.06) and integral photon flux above 100 MeV of (2.09 ± 0.03 ± 0.18) × 10–6 cm–2 s–1. The first errors represent the statistical error on the fit parameters, while the second ones are the systematic uncertainties. Pulsed γ-ray photons are observed up to ~ 20 GeV which precludes emission near the stellar surface, below altitudes of around 4-5 stellar radii in phase intervals encompassing the two main peaks. A detailed phase-resolved spectral analysis is also performed: the hardest emission from the Crab Pulsar comes from the bridge region between the two γ-ray peaks while the softest comes from the falling edge of the second peak. The spectrum of the nebula in the energy range 100 MeV-300 GeV is well described by the sum of two power laws of indices Γsync = (3.99 ± 0.12 ± 0.08) and ΓIC = (1.64 ± 0.05 ± 0.07), corresponding to the falling edge of the synchrotron and the rising edge of the inverse Compton (IC) components, respectively. This latter, which links up naturally with the spectral data points of Cherenkov experiments, is well reproduced via IC scattering from standard magnetohydrodynamic nebula models, and does not require any additional radiation mechanism.
The Astrophysical Journal 12/2009; 708(2):1254. · 6.02 Impact Factor
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
W. B. Atwood,
M. Axelsson,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
B. M. Baughman, [......],
M. Kuss,
J. Lande,
L. Latronico,
M. Lemoine-Goumard,
M. Livingstone,
F. Longo,
F. Loparco,
B. Lott,
M. N. Lovellette,
others
Astrophysical Journal Letters. 01/2009; 699(2):L102-L107.
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
W. B. Atwood,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
M. Battelino,
B. M. Baughman, [......],
M. Kramer,
F. Kuehn,
M. Kuss,
J. Lande,
L. Latronico,
S. -H. Lee,
M. Lemoine-Goumard,
F. Longo,
F. Loparco,
others
Astrophysical Journal. 01/2009; 700(2):1059-1066.
-
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.
-
R. Atkins,
W. Benbow,
D. Berley,
M. L. Chen,
D. G. Coyne,
R. S. Delay,
B. L. Dingus,
D. E. Dorfan,
R. W. Ellsworth, C. Espinoza, [......],
G. W. Sullivan,
T. N. Thompson,
T. Tumer,
K. Wang,
M. O. Wascko,
S. Westerhoff,
D. A. Williams,
T. Yang,
G. B. Yodh,
and (The
Milagro Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The Milagrito water Cerenkov detector near Los Alamos, New Mexico, was operated as a sky monitor at energies of a few TeV between 1997 February and 1998 May, including the period of the strong, long-lasting 1997 flare of Markarian 501. Milagrito served as a test run for the full Milagro detector. An event excess with a significance of 3.7 σ from Markarian 501 was observed, in agreement with expectations.
The Astrophysical Journal 12/2008; 525(1):L25. · 6.02 Impact Factor
-
D A Smith,
L. Guillemot,
F. Camilo,
I. Cognard,
D. Dumora, C. Espinoza,
P. C. C. Freire,
E. V. Gotthelf,
A. K. Harding,
G. B. Hobbs, [......],
A. Noutsos,
S. M. Ransom,
M. S. E. Roberts,
R. W. Romani,
B. W. Stappers,
G. Theureau,
D. J. Thompson,
S. E. Thorsett,
N Wang,
P. Weltevrede
[show abstract]
[hide abstract]
ABSTRACT: We describe a comprehensive pulsar monitoring campaign for the Large Area Telescope (LAT) on the {\em Fermi Gamma-ray Space Telescope} (formerly GLAST). The detection and study of pulsars in gamma rays give insights into the populations of neutron stars and supernova rates in the Galaxy, into particle acceleration mechanisms in neutron star magnetospheres, and into the ``engines'' driving pulsar wind nebulae. LAT's unprecedented sensitivity between 20 MeV and 300 GeV together with its 2.4 sr field-of-view makes detection of many gamma-ray pulsars likely, justifying the monitoring of over two hundred pulsars with large spin-down powers. To search for gamma-ray pulsations from most of these pulsars requires a set of phase-connected timing solutions spanning a year or more to properly align the sparse photon arrival times. We describe the choice of pulsars and the instruments involved in the campaign. Attention is paid to verifications of the LAT pulsar software, using for example giant radio pulses from the Crab and from PSR B1937+21 recorded at Nan\c{c}ay, and using X-ray data on PSR J0218+4232 from XMM-Newton. We demonstrate accuracy of the pulsar phase calculations at the microsecond level. Data Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ .
11/2008;
-
Atkins,
W Benbow,
D Berley,
M-L Chen,
DG Coyne,
RS Delay,
BL Dingus,
DE Dorfan,
RW Ellsworth, C Espinoza, [......],
AJ Smith,
GW Sullivan,
TN Thompson,
OT Tumer,
K Wang,
MO Wascko,
S Westerhoff,
DA Williams,
T Yang,
GB Yodh
[show abstract]
[hide abstract]
ABSTRACT: Milagrito, a large, covered water-Cherenkov detector, was the world's first air-shower-particle detector sensitive to cosmic gamma rays below 1 TeV. It served as a prototype for the Milagro detector and operated from February 1997 to May 1998. This paper gives a description of Milagrito, a summary of the operating experience, and early results that demonstrate the capabilities of this technique.
Nuclear Instruments and Methods in Physics Research Section A. 07/2000; 449:478-499.
-
R Atkins,
W Benbow,
D Berley,
ML Chen,
DG Coyne,
RS Delay,
BL Dingus,
DE Dorfan,
RW Ellsworth, C Espinoza, [......],
AJ Smith,
GW Sullivan,
TN Thompson,
T Tumer,
K Wang,
MO Wascko,
S Westerhoff,
DA Williams,
T Yang,
GB Yodh
[show abstract]
[hide abstract]
ABSTRACT: The Milagrito water Cerenkov detector near Los Alamos, New Mexico, was operated as a sky monitor at
energies of a few TeV between 1997 February and 1998 May, including the period of the strong, long lasting
1997 flare of Markarian 501. Milagrito served as a test run for the full Milagro detector. An event excess with
a significance of 3.7 j from Markarian 501 was observed, in agreement with expectations.
The Astrophysical Journal 11/1999; 525:L25-L28. · 6.02 Impact Factor
-
R. E. Mischke,
V. Armijo,
J. K. Black,
R. D. Bolton,
S. Carius,
M. D. Cooper, C. Espinoza,
G. W. Hart,
G. E. Hogan,
L. E. Piilonen,
J. Sandoval,
S. Schilling
[show abstract]
[hide abstract]
ABSTRACT: The construction of MWPCs for the MEGA experiment at LAMPF are described. The chambers are cylindrical, low mass (3 à 10â»â´ radiation lengths), and are designed to operate at high rates (3 à 10â´ /mm²/s). Several novel construction techniques have been developed and custom electronics have been designed to help achieve the required performance, which corresponds to that needed at high luminosity colliders. 4 refs., 3 figs.
-
R. Atkins,
W. Benbow,
D. Berley,
M.-L. Chen,
D.G. Coyne,
R.S. Delay,
B.L. Dingus,
D.E. Dorfan,
R.W. Ellsworth, C. Espinoza, [......],
A.J. Smith,
G.W. Sullivan,
T.N. Thompson,
O.T. Tumer,
K. Wang,
M.O. Wascko,
S. Westerhoff,
D.A. Williams,
T. Yang,
G.B. Yodh
[show abstract]
[hide abstract]
ABSTRACT: Milagrito, a large, covered water-Cherenkov detector, was the world's first air-shower-particle detector sensitive to cosmic gamma rays below 1 TeV. It served as a prototype for the Milagro detector and operated from February 1997 to May 1998. This paper gives a description of Milagrito, a summary of the operating experience, and early results that demonstrate the capabilities of this technique.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
-
M.D Cooper,
V Armijo,
J.K Black,
R.D Bolton,
S Carius, C Espinoza,
G Hart,
G.E Hogan,
A Gonzales,
M.A Kroupa, [......],
C.A Gagliardi,
R.E Tribble,
X.-L Tu,
R.J Fisk,
D.D Koetke,
R.W Manweiler,
P.M Nord,
S Stanislaus,
L.E Piilonen,
Y.D Zhang
[show abstract]
[hide abstract]
ABSTRACT: A design for extremely low mass, high-resolution multiwire proportional chambers (MWPC) was achieved by the MEGA collaboration in its experiment to search for the lepton family number violating decay μ→eγ. To extend the present branching ratio limit by over an order of magnitude, these MWPCs were operated in high particle fluxes. They showed minimal effects of aging, and evidenced spatial and energy resolutions for the orbiting positrons from muon decay which were consistent with our design parameters. The unique features of these chambers, their assembly into the MEGA positron spectrometer, and their performance during the experiment are described in this paper.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
W B Atwood,
M. Axelsson,
L Baldini,
J. Ballet,
G. Barbiellini,
M. G. Baring,
D. Bastieri, [......],
V Vitale,
A P Waite,
E. Wallace,
P Wang,
K. Watters,
P. Weltevrede,
B. L. Winer,
K. S. Wood,
T. Ylinen,
M Ziegler
[show abstract]
[hide abstract]
ABSTRACT: We report on γ -ray observations of the Crab Pulsar and Nebula using 8 months of survey data with the Fermi Large Area Telescope (LAT). The high quality light curve obtained using the ephemeris provided by the Nan¸cay and Jodrell Bank radio telescopes shows two main peaks stable in phase with energy. The first γ -ray peak leads the radio main pulse by (281 ± 12 ± 21) μs, giving new constraints on the production site of non-thermal emission in pulsar magnetospheres. The first uncertainty is due to γ -ray statistics, and the second arises from the rotation parameters. The improved sensitivity and the unprecedented statistics afforded by the LAT enable precise measurement of the Crab Pulsar spectral parameters: cut-off energy at Ec = (5.8 ± 0.5 ± 1.2) GeV, spectral index of Γ = (1.97 ± 0.02 ± 0.06) and integral photon flux above 100 MeV of (2.09 ± 0.03 ± 0.18) × 10−6 cm−2 s−1. The first errors represent the statistical error on the fit parameters, while the second ones are the systematic uncertainties. Pulsed γ -ray photons are observed up to ∼20 GeV which precludes emission near the stellar surface, below altitudes of around 4–5 stellar radii in phase intervals encompassing the two main peaks. A detailed phase-resolved spectral analysis is also performed: the hardest emission from the Crab Pulsar comes from the bridge region between the two γ -ray peaks while the softest comes from the falling edge of the second peak. The spectrum of the nebula in the energy range 100 MeV–300 GeV is well described by the sum of two power laws of indices Γsync = (3.99 ± 0.12 ± 0.08) and ΓIC = (1.64 ± 0.05 ± 0.07), corresponding to the falling edge of the synchrotron and the rising edge of the inverse Compton (IC) components, respectively. This latter, which links up naturally with the spectral data points of Cherenkov experiments, is well reproduced via IC scattering from standard magnetohydrodynamic nebula models, and does not require any additional radiation mechanism.
Astrophysical Journal.
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
L Baldini,
J. Ballet,
G. Barbiellini,
M. G. Baring,
D. Bastieri,
B. M. Baughman,
K. Bechtol, [......],
C. Venter,
N. Vilchez,
V Vitale,
A P Waite,
P Wang,
B. L. Winer,
K. S. Wood,
R. Yamazaki,
T. Ylinen,
M Ziegler
Science, v.327, 1103-1106 (2010).
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
W B Atwood,
M. Axelsson,
L Baldini,
J. Ballet,
G. Barbiellini,
M. G. Baring,
D. Bastieri, [......],
V Vitale,
A P Waite,
P Wang,
N Wang,
K. Watters,
P. Weltevrede,
B. L. Winer,
K. S. Wood,
T. Ylinen,
M Ziegler
Astrophysical Journal Supplement Series, v.187, 460-494 (2010).
