We presented in 2014 the very first data from a polarised gamma-ray beam between 1.7 and 74MeV. We now show the results of their analysis, and in particular the polarimetry measurements. With these ...results, we are establishing a new, high-performance way to do gamma-ray astronomy and, for the first time, polarimetry, in the e+e- pair regime.
We present a measurement of the cosmic-ray electron+positron spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the ...spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of 3.07±0.02(stat+syst)±0.04(energy measurement). An exponential cutoff lower than 1.8 TeV is excluded at 95% CL.
The dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are some of the most dark matter (DM) dominated objects known. We report on γ-ray observations of Milky Way dSphs based on six years ...of Fermi Large Area Telescope data processed with the new Pass8 event-level analysis. None of the dSphs are significantly detected in γ rays, and we present upper limits on the DM annihilation cross section from a combined analysis of 15 dSphs. These constraints are among the strongest and most robust to date and lie below the canonical thermal relic cross section for DM of mass ≲100 GeV annihilating via quark and τ-lepton channels.
ABSTRACT We present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in the 100 MeV-300 GeV range. Based on the first 4 yr of science data from the Fermi Gamma-ray Space ...Telescope mission, it is the deepest yet in this energy range. Relative to the Second Fermi LAT catalog, the 3FGL catalog incorporates twice as much data, as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse γ-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources above significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 238 sources are considered as identified based on angular extent or correlated variability (periodic or otherwise) observed at other wavelengths. For 1010 sources we have not found plausible counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. From source counts of Galactic sources we estimate that the contribution of unresolved sources to the Galactic diffuse emission is ∼3% at 1 GeV.
In the published version of the paper, errors were made in calculating the exposure time due to an analysis mistake. While they do not affect gas emissivities of the R CrA and Cepheus & Polaris flare ...regions significantly (the differences are within the systematic uncertainty), that of the Chamaeleon region is increased by approx.20%. Although we claimed a difference of ∼50% in gas emissivity among these molecular cloud regions in the original paper, it is decreased to ∼30% (comparable to the sum of the statistical and systematic uncertainties) in the revised analysis. Therefore, our conclusion of the original paper, that a small variation (approx. 20%) of the CR density in the solar neighborhood exists, is not supported by the data if we take these uncertainties into account. On the other hand, the obtained XCO and XAv values, and the masses of gas calculated from them are not changed significantly (the differences are within the statistical errors). Errors and corrections in the original paper are summarized below. 1. In the Abstract (lines 5-6) and Section 3 (lines 4-5 in the 3rd paragraph) in the original paper, the gamma -ray emissivity above 250 MeV for the Chamaeleon region should be (7.2 +/- 0.1stat +/- 1.0sys) × 10(exp −27) photons/s/sr/H-atom, not (5.9 +/-0.1stat +0.9−1.0sys) × 10(exp −27) photons/s/sr/H-atom. 2. In the Abstract (lines 8-10), "Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by approx.20% in the neighborhood of the solar system, even if we consider the systematic uncertainties." should be changed to "The energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth. Although the measured emissivities from 250 MeV to 10 GeV differ by approx.30% among these molecular cloud regions, the difference is not significant if we take the systematic uncertainty into account." 3. Table 1 and Figure 13, which show gas emissivities and spectra for the Chamaeleon region in the original paper, should be changed to the Table 1 and Figure 1 as shown below. 4. Figure 16, which compares Hi gas emissivities among several regions in the original paper, should be changed to Figure 2 as shown below. 5. The text from the line 13 to the last one in the first paragraph of Section 4.1, "The spectral shapes for the three regions..., indicating a difference of the CR density between the Chamaeleon and the others as shown in Figure 16." should be changed to the paragraph that follows. "The shaded area of each spectrum indicates the systematic uncertainty as described in Section 3. We note that the systematic uncertainty of the LAT effective area (5% at 100 MeV and 20% at 10 GeV; Rando et al. 2009) does not affect the relative value of emissivities. The effect of unresolved point sources is small; we have verified that the obtained emissivities are almost unaffected by decreasing the threshold for point sources from TS = 100 to TS = 50. We also confirmed that the residual excess of photons around (l = 280deg to 288deg, b = −20deg to −12deg; see the bottom panel of Figure 8) in the Chamaeleon region does not affect the local Hi emissivity very much. Thus the total systematic uncertainty is reasonably expressed by the shaded area shown in Fig. 1.
ABSTRACT The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy γ-rays. This paper describes the analysis of ...data taken during the first 62 months of the mission in the energy range 1-100 GeV from a 15° × 15° region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the γ-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ∼1 kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15° × 15° region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.
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