The Fermi Large Area Telescope (LAT) First Source Catalog (1FGL) provided spatial, spectral, and temporal properties for a large number of gamma -ray sources using a uniform analysis method. After ...correlating with the most-complete catalogs of source types known to emit gamma rays, 630 of these sources are "unassociated" (i.e., have no obvious counterparts at other wavelengths). Here, we employ two statistical analyses of the primary gamma -ray characteristics for these unassociated sources in an effort to correlate their y-ray properties with the active galactic nucleus (AGN) and pulsar populations in 1FGL. Based on the correlation results, we classify 221 AGN-like and 134 pulsar-like sources in the 1FGL unassociated sources. The results of these source "classifications" appear to match the expected source distributions, especially at high Galactic latitudes. While useful for planning future multiwavelength follow-up observations, these analyses use limited inputs, and their predictions should not be considered equivalent to "probable source classes" for these sources. We discuss multiwavelength results and catalog cross-correlations to date, and provide new source associations for 229 Fermi-LAT sources that had no association listed in the 1FGL catalog. By validating the source classifications against these new associations, we find that the new association matches the predicted source class in ~80% of the sources.
We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the ...largest data sets ever used for this purpose. We use both archival interferometric 8.4 GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15 GHz measurements from the Owens Valley Radio Observatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using a surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the centimeter radio and the broadband (E > 100 MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability of <10--7 for the correlation appearing by chance. Using the OVRO data, we find that concurrent data improve the significance of the correlation from 1.6 X 10--6 to 9.0 X 10--8. Our large sample size allows us to study the dependence of correlation strength and significance on specific source types and gamma-ray energy band. We find that the correlation is very significant (chance probability < 10--7) for both flat spectrum radio quasars and BL Lac objects separately; a dependence of the correlation strength on the considered gamma-ray energy band is also present, but additional data will be necessary to constrain its significance.
The flat-spectrum radio quasar 3C454.3 underwent an extraordinary 5 day Delta *g-ray outburst in 2010 November when the daily flux measured with the Fermi Large Area Telescope (LAT) at photon ...energies E > 100 MeV reached (66 ? 2) X 10--6 photons cm--2 s--1. This is a factor of three higher than its previous maximum flux recorded in 2009 December and 5 times brighter than the Vela pulsar, which is normally the brightest source in the Delta *g-ray sky. The 3 hr peak flux was (85 ? 5)X10--6 photons cm--2 s--1, corresponding to an apparent isotropic luminosity of (2.1 ? 0.2)X1050 erg s--1, the highest ever recorded for a blazar. In this Letter, we investigate the features of this exceptional event in the Delta *g-ray band of the Fermi-LAT. In contrast to previous flares of the same source observed with the Fermi-LAT, clear spectral changes are observed during the flare.
Mercury emissions from some upstream gold mining areas and recent findings of high natural Hg levels in sediments motivated studies on the Hg cycle in the Minas Gerais state. The study presents the ...total mercury amount found in Geophagus brasiliensis' muscular tissue (wet weight) and sediments from Piracicaba River. Mercury was analyzed using acid digestion followed by determination of total mercury by cold vapour atomic absorption spectrophotometry. This study was also complemented with the analysis of the limnological parameters (water temperature, conductivity, total dissolved solids, suspended particles, pH, dissolved oxygen, maximum depth, photic index and total carbon). The mercury concentration in sediments samples was higher than the mercury concentration in muscular tissue of fish. The lowest Hg level measured in fish was 0.0147 μg g ⁻ ¹, while the highest was 0.101 μg g ⁻ ¹. In the sediment samples, the lowest and highest levels were 0.02 μg g ⁻ ¹ and 0.16 μg g ⁻ ¹, respectively. The Hg concentrations in fish and sediment were both under the maximum limit permitted by the World Health Organization.
We report on the discovery of >=100 MeV Delta *g-rays from the binary system PSR B1259--63/LS 2883 using the Large Area Telescope (LAT) on board Fermi. The system comprises a radio pulsar in orbit ...around a Be star. We report on LAT observations from near apastron to ~128 days after the time of periastron, tp , on 2010 December 15. No Delta *g-ray emission was detected from this source when it was far from periastron. Faint Delta *g-ray emission appeared as the pulsar approached periastron. At ~tp + 30 days, the >=100 MeV Delta *g-ray flux increased over a period of a few days to a peak flux 20-30 times that seen during the pre-periastron period, but with a softer spectrum. For the following month, it was seen to be variable on daily timescales, but remained at ~(1-4) X 10--6 cm--2 s--1 before starting to fade at ~tp + 57 days. The total Delta *g-ray luminosity observed during this period is comparable to the spin-down power of the pulsar. Simultaneous radio and X-ray observations of the source showed no corresponding dramatic changes in radio and X-ray flux between the pre-periastron and post-periastron flares. We discuss possible explanations for the observed Delta *g-ray-only flaring of the source.
Fermi/LAT observations of LS 5039 Ajello, M; Atwood, W. B; Baldini, L ...
The Astrophysical journal,
11/2009, Volume:
706, Issue:
1
Journal Article
Peer reviewed
Open access
The first results from observations of the high-mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. In this report, our results ...indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 ± 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV-300 GeV) of 4.9 ± 0.5(stat) ± 1.8(syst) ×10–7 photon cm–2 s–1, with a cutoff at 2.1 ± 0.3(stat) ± 1.1(syst) GeV and photon index Γ = 1.9 ± 0.1(stat) ± 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. Lastly, we suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.
We investigate the Fermi LAT gamma-ray and 15 GHz VLBA radio properties of a joint gamma-ray- and radio-selected sample of AGNs obtained during the first 11 months of the Fermi mission (2008 Aug 4 - ...2009 Jul 5). Our sample contains the brightest 173 AGNs in these bands above declination -30 deg. during this period, and thus probes the full range of gamma-ray loudness (gamma-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least four orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing gamma-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the gamma-ray emission in these BL Lacs over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED peak - gamma-ray loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQ) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lacs have generally lower Doppler factors than the lower-synchrotron peaked BL Lacs or FSRQs in our sample.
We have measured the gamma-ray emission spectrum of the Moon using the data collected by the Large Area Telescope onboard the Fermi satellite during its first seven years of operation, in the energy ...range from 30 MeV up to a few GeV. We have also studied the time evolution of the flux, finding a correlation with the solar activity. We have developed a full Monte Carlo simulation describing the interactions of cosmic rays with the lunar surface. The results of the present analysis can be explained in the framework of this model, where the production of gamma rays is due to the interactions of cosmic-ray proton and helium nuclei with the surface of the Moon. Finally, we have used our simulation to derive the cosmic-ray proton and helium spectra near Earth from the Moon gamma-ray data.
We present a measurement of the fundamental parameter of the standard model, the weak mixing angle sin2θℓeff which determines the relative strength of weak and electromagnetic interactions, in ...pp¯→Z/γ*→e+e- events at a center of mass energy of 1.96 TeV, using data corresponding to 9.7 fb-1 of integrated luminosity collected by the D0 detector at the Fermilab Tevatron. The effective weak mixing angle is extracted from the forward-backward charge asymmetry as a function of the invariant mass around the Z boson pole. The measured value of sin2θℓeff=0.23147±0.00047 is the most precise measurement from light quark interactions to date, with a precision close to the best LEP and SLD results.
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