-
M Ackermann,
M Ajello,
A Allafort,
K Asano, W ~B Atwood,
L Baldini,
J Ballet,
G Barbiellini,
D Bastieri,
K Bechtol, [......],
V Vitale,
A Kienlin,
A ~P Waite,
E Wallace,
P Weltevrede,
B ~L Winer,
K ~S Wood,
M Wood,
Z Yang,
S Zimmer
apj. 03/2013; 765:54.
-
H J Pletsch,
L Guillemot,
H Fehrmann,
B Allen,
M Kramer,
C Aulbert,
M Ackermann,
M Ajello,
A de Angelis, W B Atwood, [......],
J Vandenbroucke,
V Vasileiou,
G Vianello,
V Vitale,
A P Waite,
B L Winer,
K S Wood,
M Wood,
Z Yang,
S Zimmer
[show abstract]
[hide abstract]
ABSTRACT: Millisecond pulsars, old neutron stars spun-up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such "recycled" rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311-3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found.
Science 10/2012; · 31.20 Impact Factor
-
The Fermi-LAT collaboration: M. Ackermann,
M. Ajello, W. B. Atwood,
L. Baldini,
G. Barbiellini,
D. Bastieri,
K. Bechtol,
R. Bellazzini,
R. D. Blandford,
E. D. Bloom, [......],
V. Vasileiou,
G. Vianello,
V. Vitale,
A. P. Waite,
E. Wallace,
K. S. Wood,
M. Wood,
Z. Yang,
G. Zaharijas,
S. Zimmer
[show abstract]
[hide abstract]
ABSTRACT: We have performed an analysis of the diffuse gamma-ray emission with the
Fermi Large Area Telescope in the Milky Way Halo region searching for a signal
from dark matter annihilation or decay. In the absence of a robust dark matter
signal, constraints are presented. We consider both gamma rays produced
directly in the dark matter annihilation/decay and produced by inverse Compton
scattering of the e+e- produced in the annihilation/decay. Conservative limits
are derived requiring that the dark matter signal does not exceed the observed
diffuse gamma-ray emission. A second set of more stringent limits is derived
based on modeling the foreground astrophysical diffuse emission using the
GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the
distribution of the cosmic-ray sources in the Galaxy, the index of the
injection cosmic-ray electron spectrum and the column density of the
interstellar gas are taken into account using a profile likelihood formalism,
while the parameters governing the cosmic-ray propagation have been derived
from fits to local cosmic-ray data. The resulting limits impact the range of
particle masses over which dark matter thermal production in the early Universe
is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic
ray anomalies as annihilation of dark matter.
05/2012;
-
M. Ackermann,
M. Ajello, W. B. Atwood,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
K. Bechtol,
R. Bellazzini,
B. Berenji, [......],
G. Vianello,
V. Vitale,
A. P. Waite,
P. Wang,
B. L. Winer,
K. S. Wood,
M. Wood,
Z. Yang,
M. Ziegler,
and S. Zimmer
[show abstract]
[hide abstract]
ABSTRACT: The γ-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse γ-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. To assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X CO factor, the ratio between integrated CO-line intensity and H2 column density, the fluxes and spectra of the γ-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as γ-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. We also provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.
The Astrophysical Journal 04/2012; 750(1):3. · 6.02 Impact Factor
-
M Ackermann,
M Ajello,
A Allafort, W ~B Atwood,
L Baldini,
G Barbiellini,
D Bastieri,
K Bechtol,
R Bellazzini,
P ~N Bhat, [......],
J Vandenbroucke,
V Vasileiou,
G Vianello,
V Vitale,
A Kienlin,
A ~P Waite,
C Wilson-Hodge,
D ~L Wood,
K ~S Wood,
Z Yang
apj. 04/2012; 748:151.
-
P. L. Nolan,
A. A. Abdo,
M. Ackermann,
M. Ajello,
A. Allafort,
E. Antolini, W. B. Atwood,
M. Axelsson,
L. Baldini,
J. Ballet, [......],
A. P. Waite,
E. Wallace,
P. Wang,
M. Werner,
B. L. Winer,
D. L. Wood,
K. S. Wood,
M. Wood,
Z. Yang,
and S. Zimmer
[show abstract]
[hide abstract]
ABSTRACT: We present the second catalog of high-energy γ-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely γ-ray-producing source classes.
The Astrophysical Journal Supplement Series 03/2012; 199(2):31. · 13.46 Impact Factor
-
M Ackermann,
M Ajello,
A Allafort, W B Atwood,
L Baldini,
G Barbiellini,
D Bastieri,
K Bechtol,
R Bellazzini,
B Berenji, [......],
J Vandenbroucke,
V Vasileiou,
G Vianello,
V Vitale,
A P Waite,
B L Winer,
K S Wood,
M Wood,
Z Yang,
S Zimmer
[show abstract]
[hide abstract]
ABSTRACT: We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 GeV. We confirm that the fraction rises with energy in the 20-100 GeV range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.
Physical Review Letters 01/2012; 108(1):011103. · 7.37 Impact Factor
-
M Ackermann,
M Ajello,
A Albert, W B Atwood,
L Baldini,
J Ballet,
G Barbiellini,
D Bastieri,
K Bechtol,
R Bellazzini, [......],
V Vitale,
A P Waite,
P Wang,
B L Winer,
K S Wood,
M Wood,
Z Yang,
S Zimmer,
M Kaplinghat,
G D Martinez
[show abstract]
[hide abstract]
ABSTRACT: Satellite galaxies of the Milky Way are among the most promising targets for dark matter searches in gamma rays. We present a search for dark matter consisting of weakly interacting massive particles, applying a joint likelihood analysis to 10 satellite galaxies with 24 months of data of the Fermi Large Area Telescope. No dark matter signal is detected. Including the uncertainty in the dark matter distribution, robust upper limits are placed on dark matter annihilation cross sections. The 95% confidence level upper limits range from about 10(-26) cm3 s(-1) at 5 GeV to about 5×10(-23) cm3 s(-1) at 1 TeV, depending on the dark matter annihilation final state. For the first time, using gamma rays, we are able to rule out models with the most generic cross section (∼3×10(-26) cm3 s(-1) for a purely s-wave cross section), without assuming additional boost factors.
Physical Review Letters 12/2011; 107(24):241302. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We quantitatively establish the sensitivity to the detection of young to middle-aged, isolated, gamma-ray pulsars through blind searches of Fermi Large Area Telescope (LAT) data using a Monte Carlo simulation. We detail a sensitivity study of the time-differencing blind search code used to discover gamma-ray pulsars in the first year of observations. We simulate 10,000 pulsars across a broad parameter space and distribute them across the sky. We replicate the analysis in the Fermi LAT First Source Catalog to localize the sources, and the blind search analysis to find the pulsars. We analyze the results and discuss the effect of positional error and spin frequency on gamma-ray pulsar detections. Finally, we construct a formula to determine the sensitivity of the blind search and present a sensitivity map assuming a standard set of pulsar parameters. The results of this study can be applied to population studies and are useful in characterizing unidentified LAT sources.
The Astrophysical Journal 11/2011; 742(2):126. · 6.02 Impact Factor
-
A ~A Abdo,
M Ackermann,
M Ajello, W ~B Atwood,
M Axelsson,
L Baldini,
J Ballet,
G Barbiellini,
M ~G Baring,
D Bastieri,
al
apjs. 03/2011; 193:22.
-
M. Ajello, W. B. Atwood,
L. Baldini,
G. Barbiellini,
D. Bastieri,
R. Bellazzini,
B. Berenji,
R. D. Blandford,
E. D. Bloom,
E. Bonamente, [......],
S. Ritz,
T. L. Schalk,
C. Sgro,
J. Siegal-Gaskins,
E. J. Siskind,
P. D. Smith,
G. Spandre,
P. Spinelli,
D. J. Suson,
others
Physical Review D. 01/2011; 84(3).
-
A A Abdo,
M Ackermann,
M Ajello, W B Atwood,
L Baldini,
J Ballet,
G Barbiellini,
D Bastieri,
K Bechtol,
R Bellazzini, [......],
M Sasada,
V I Shenavrin,
S N Shore,
G K Skinner,
J Sokoloski,
M Stroh,
A M Tatarnikov,
M Uemura,
G M Wahlgren,
M Yamanaka
[show abstract]
[hide abstract]
ABSTRACT: Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce pi(0) decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.
Science 08/2010; 329(5993):817-21. · 31.20 Impact Factor
-
A. A. Abdo,
M. Ackermann,
M. Ajello,
A. Allafort,
E. Antolini, W. B. Atwood,
M. Axelsson,
L. Baldini,
J. Ballet,
G. Barbiellini, [......],
S. J. Fegan,
E. C. Ferrara,
W. B. Focke,
P. Fortin,
M. Frailis,
Y. Fukazawa,
S. Funk,
P. Fusco,
F. Gargano,
D. Gasparrini
[show abstract]
[hide abstract]
ABSTRACT: The data analyzed for the 1FGL catalog were obtained during 2008 August
4-2009 July 4. The total live time included is 245.6 days.
(4 data files).
VizieR Online Data Catalog. 06/2010; 218:80405.
-
[show abstract]
[hide abstract]
ABSTRACT: The Fermi Gamma-ray Space Telescope (Fermi) was launched on 11 June 2008 and began its first year sky survey on 11 August 2008. The Large Area Telescope (LAT), a wide field-of-view pair-conversion telescope covering the energy range from 20 MeV to more than 300 GeV, is the primary instrument on Fermi. While this review focuses on results obtained with the LAT, the Gamma-ray Burst Monitor (GBM) complements the LAT in its observations of transient sources and is sensitive to x-rays and γ-rays with energies between 8 keV and 40 MeV. During the first year in orbit, the Fermi LAT has observed a large number of sources that include active galaxies, pulsars, compact binaries, globular clusters, supernova remnants as well as the Sun, the Moon and the Earth. The GBM and LAT together have uncovered surprising characteristics in the high-energy emission of gamma-ray bursts that have been used to set significant new limits on violations of Lorentz invariance. The Fermi LAT has also made important new measurements of the Galactic diffuse radiation and has made precise measurements of the spectrum of cosmic-ray electrons and positrons from 20 GeV to 1 TeV.
Reports on Progress in Physics 06/2010; 73(7):074901. · 14.72 Impact Factor
-
A A Abdo,
M Ackermann,
M Ajello,
A Allafort,
E Antolini, W B Atwood,
M Axelsson,
L Baldini,
J Ballet,
G Barbiellini, [......],
V Vitale,
A P Waite,
E Wallace,
P Wang,
K Watters,
B L Winer,
K S Wood,
Z Yang,
T Ylinen,
M Ziegler
[show abstract]
[hide abstract]
ABSTRACT: We present a catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), during the first 11 months of the science phase of the mission, which began on 2008 August 4. The First Fermi-LAT catalog (1FGL) contains 1451 sources detected and characterized in the 100 MeV to 100 GeV range. Source detection was based on the average flux over the 11 month period, and the threshold likelihood Test Statistic is 25, corresponding to a significance of just over 4 sigma. The 1FGL catalog includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and power-law spectral fits as well as flux measurements in five energy bands for each source. In addition, monthly light curves are provided. Using a protocol defined before launch we have tested for several populations of gamma-ray sources among the sources in the catalog. For individual LAT-detected sources we provide firm identifications or plausible associations with sources in other astronomical catalogs. Identifications are based on correlated variability with counterparts at other wavelengths, or on spin or orbital periodicity. For the catalogs and association criteria that we have selected, 630 of the sources are unassociated. Care was taken to characterize the sensitivity of the results to the model of interstellar diffuse gamma-ray emission used to model the bright foreground, with the result that 161 sources at low Galactic latitudes and toward bright local interstellar clouds are flagged as having properties that are strongly dependent on the model or as potentially being due to incorrectly modeled structure in the Galactic diffuse emission.
The Astrophysical Journal Supplement Series 06/2010; 188:405-436. · 13.46 Impact Factor
-
A A Abdo,
M Ackermann,
M Ajello, W B Atwood,
L Baldini,
J Ballet,
G Barbiellini,
D Bastieri,
B M Baughman,
K Bechtol, [......],
V Vitale,
A P Waite,
E Wallace,
P Wang,
B L Winer,
K S Wood,
T Ylinen,
M Ziegler,
M J Hardcastle,
D Kazanas
[show abstract]
[hide abstract]
ABSTRACT: The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.
Science 04/2010; 328(5979):725-9. · 31.20 Impact Factor
-
A A Abdo,
M Ackermann,
M Ajello, W B Atwood,
L Baldini,
J Ballet,
G Barbiellini,
D Bastieri,
B M Baughman,
K Bechtol, [......],
T L Usher,
V Vasileiou,
N Vilchez,
V Vitale,
A P Waite,
P Wang,
B L Winer,
K S Wood,
T Ylinen,
M Ziegler
[show abstract]
[hide abstract]
ABSTRACT: We report on the first Fermi Large Area Telescope (LAT) measurements of the so-called "extragalactic" diffuse gamma-ray emission (EGB). This component of the diffuse gamma-ray emission is generally considered to have an isotropic or nearly isotropic distribution on the sky with diverse contributions discussed in the literature. The derivation of the EGB is based on detailed modeling of the bright foreground diffuse Galactic gamma-ray emission, the detected LAT sources, and the solar gamma-ray emission. We find the spectrum of the EGB is consistent with a power law with a differential spectral index gamma = 2.41 +/- 0.05 and intensity I(>100 MeV) = (1.03 +/- 0.17) x 10(-5) cm(-2) s(-1) sr(-1), where the error is systematics dominated. Our EGB spectrum is featureless, less intense, and softer than that derived from EGRET data.
Physical Review Letters 03/2010; 104(10):101101. · 7.37 Impact Factor
-
A A Abdo,
M Ackermann,
M Ajello, W B Atwood,
L Baldini,
J Ballet,
G Barbiellini,
D Bastieri,
K Bechtol,
R Bellazzini, [......],
T L Usher,
V Vasileiou,
N Vilchez,
V Vitale,
A P Waite,
P Wang,
B L Winer,
K S Wood,
T Ylinen,
M Ziegler
[show abstract]
[hide abstract]
ABSTRACT: Dark matter (DM) particle annihilation or decay can produce monochromatic gamma rays readily distinguishable from astrophysical sources. gamma-ray line limits from 30 to 200 GeV obtained from 11 months of Fermi Large Area Space Telescope data from 20-300 GeV are presented using a selection based on requirements for a gamma-ray line analysis, and integrated over most of the sky. We obtain gamma-ray line flux upper limits in the range 0.6-4.5x10{-9} cm{-2} s{-1}, and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.
Physical Review Letters 03/2010; 104(9):091302. · 7.37 Impact Factor
-
A. A. Abdo,
M. Ackermann,
M. Ajello, W. B. Atwood,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
K. Bechtol,
R. Bellazzini, [......],
V. Vitale,
A. P. Waite,
P. Wang,
B. L. Winer,
K. S. Wood,
T. Ylinen,
M. Ziegler,
James S. Bullock,
Manoj Kaplinghat,
and Gregory D. Martinez
[show abstract]
[hide abstract]
ABSTRACT: We report on the observations of 14 dwarf spheroidal galaxies (dSphs) with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky γ-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected γ-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dSphs, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant γ-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the γ-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10–9 photons cm–2 s–1. Using recent stellar kinematic data, the γ-ray flux limits are combined with improved determinations of the dark matter density profile in eight of the 14 candidate dwarfs to place limits on the pair-annihilation cross section of WIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g., in models where supersymmetry breaking occurs via anomaly mediation. The γ-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e + e – data, including low-mass wino-like neutralinos and models with TeV masses pair annihilating into muon-antimuon pairs.
The Astrophysical Journal 02/2010; 712(1):147. · 6.02 Impact Factor
-
The Fermi LAT Collaboration,
A. A. Abdo,
M. Ackermann,
M. Ajello, W. B. Atwood,
L. Baldini,
J. Ballet,
G. Barbiellini,
D. Bastieri,
K. Bechtol, [......],
T. L. Usher,
V. Vasileiou,
N. Vilchez,
V. Vitale,
A. P. Waite,
P. Wang,
B. L. Winer,
K. S. Wood,
T. Ylinen,
M. Ziegler
[show abstract]
[hide abstract]
ABSTRACT: Dark matter (DM) particle annihilation or decay can produce monochromatic
$\gamma$-rays readily distinguishable from astrophysical sources. $\gamma$-ray
line limits from 30 GeV to 200 GeV obtained from 11 months of Fermi Large Area
Space Telescope data from 20-300 GeV are presented using a selection based on
requirements for a $\gamma$-ray line analysis, and integrated over most of the
sky. We obtain $\gamma$-ray line flux upper limits in the range $0.6-4.5\times
10^{-9}\mathrm{cm}^{-2}\mathrm{s}^{-1}$, and give corresponding DM annihilation
cross-section and decay lifetime limits. Theoretical implications are briefly
discussed.
01/2010;
