We report the detection of GeV gamma -ray emission from the supernova remnant (SNR) Puppis A with the Fermi Gamma-Ray Space Telescope. Puppis A is among the faintest SNRs yet detected at GeV ...energies, with a luminosity of only 2.7 x 10 super(34) (D/2.2 kpc) super(2) erg s super(-1) between 1 and 100 GeV. The gamma -ray emission from the remnant is spatially extended, with a morphology matching that of the radio and X-ray emission, and is well described by a simple power law with an index of 2.1. We attempt to model the broadband spectral energy distribution (SED), from radio to gamma -rays, using standard nonthermal emission mechanisms. To constrain the relativistic electron population we use 7 years of Wilkinson Microwave Anisotropy Probe data to extend the radio spectrum up to 93 GHz. Both leptonic- and hadronic-dominated models can reproduce the nonthermal SED, requiring a total content of cosmic-ray electrons and protons accelerated in Puppis A of at least W sub(CR) approximately (1-5) x 10 super(49) erg.
In this paper, we present the Fermi All-sky Variability Analysis (FAVA), a tool to systematically study the variability of the gamma-ray sky measured by the Large Area Telescope on board the Fermi ...Gamma-ray Space Telescope.For each direction on the sky, FAVA compares the number of gamma-rays observed in a given time window to the number of gamma-rays expected for the average emission detected from that direction. This method is used in weekly time intervals to derive a list of 215 flaring gamma-ray sources. We proceed to discuss the 27 sources found at Galactic latitudes smaller than 10 and show that, despite their low latitudes, most of them are likely of extragalactic origin.
Numerical simulations based on the LambdaCDM model of cosmology predict a large number of as yet unobserved Galactic dark matter satellites. We report the results of a Large Area Telescope (LAT) ...search for these satellites via the gamma -ray emission expected from the annihilation of weakly interacting massive particle (WIMP) dark matter. Some dark matter satellites are expected to have hard gamma -ray spectra, finite angular extents, and a lack of counterparts at other wavelengths. We sought to identify LAT sources with these characteristics, focusing on gamma -ray spectra consistent with WIMP annihilation through the bb channel. We found no viable dark matter satellite candidates using one year of data, and we present a framework for interpreting this result in the context of numerical simulations to constrain the velocity-averaged annihilation cross section for a conventional 100 GeV WIMP annihilating through the bb channel.
Context. Recent Suzaku X-ray observations of the ejecta-dominated supernova remnant W49B have shown that there is a clear indication in the global spectrum for overionized plasma, whose physical ...origin is still under debate. Aims. In order to ascertain the physical origin of this rapidly cooling plasma, we focus on its spatial localization within the X-ray emitting ejecta. Methods. We confirm a saw-edged excess (interpreted as a strong radiative recombination continuum) in the global spectrum above 8 keV, which emerges above the ionization-equilibrium model. We produce a hardness-ratio map to determine where the plasma is overionized and perform a spectral analysis of the regions with and without strong overionization. Results. We find that the overionized plasma is localized in the center of the remnant and in its western jet, while it is not detected in the bright eastern jet, where the expansion of the ejecta is hampered by their interaction with a dense interstellar cloud. Conclusions. The location of overionized plasma suggests that the inner ejecta are rapidly cooling by expansion, unlike the outer ejecta, for which expansion is hampered by interstellar clouds seen in H2.
We present the analysis of Fermi Large Area Telescope gamma -ray observations of HB 21 (G89.0+4.7). We detect significant gamma -ray emission associated with the remnant; the flux > 100 MeV is 9.4 + ...or - 0.8 (stat) + or - 1.6 (syst) x 10 super(-11) erg cm super(-2) s super(-1). HB 21 is well modeled by a uniform disk centered at l = 88degrees.75 + or - 0degrees.04, b = +4degrees.65 + or - 0degrees.06 with a radius of 1degrees.19 + or - 0degrees.06. The gamma -ray spectrum shows clear evidence of curvature, suggesting a cutoff or break in the underlying particle population at an energy of a few GeV. We complement gamma -ray observations with the analysis of the WMAP 7 yr data from 23 to 93 GHz, achieving the first detection of HB 21 at these frequencies. In combination with archival radio data, the radio spectrum shows a special break, which helps to constrain the relativistic electron spectrum, and, in turn, parameters of simple non-thermal radiation models. In one-zone models multi wavelength data favor the origin of gamma rays from nucleon-nucleon collisions. A single population of electrons cannot produce both gamma rays through bremsstrahlung and radio emission through synchrotron radiation. A predominantly inverse-Compton origin of the gamma -ray emission is disfavored because it requires lower interstellar densities than are inferred for HB 21. In the hadronic-dominated scenarios, accelerated nuclei contribute a total energy of ~3 x 10 super(49) erg, while, in a two-zone bremsstrahlung-dominated scenario, the total energy in accelerated particles is ~1 x 10 super(49) erg.
Context. Although numerous archival XMM-Newton observations existed towards the Small Magellanic Cloud (SMC) before 2009, only a fraction of the whole galaxy had been covered. Aims. Between May 2009 ...and March 2010, we carried out an XMM-Newton survey of the SMC, to ensure a complete coverage of both its bar and wing. Thirty-three observations of 30 different fields with a total exposure of about one Ms filled the previously missing parts. Methods. We systematically processed all available SMC data from the European Photon Imaging Camera. After rejecting observations with very high background, we included 53 archival and the 33 survey observations. We produced images in five different energy bands. We applied astrometric boresight corrections using secure identifications of X-ray sources and combined all the images to produce a mosaic covering the main body of the SMC. Results. We present an overview of the XMM-Newton observations, describe their analysis, and summarise our first results, which will be presented in detail in follow-up papers. Here, we mainly focus on extended X-ray sources, such as supernova remnants (SNRs) and clusters of galaxies, that are seen in our X-ray images. Conclusions. Our XMM-Newton survey represents the deepest complete survey of the SMC in the 0.15 − 12.0 keV X-ray band. We propose three new SNRs that have low surface brightnesses of a few 10-14 erg cm-2 s-1 arcmin-2 and large extents. In addition, several known remnants appear larger than previously measured at either X-rays or other wavelengths extending the size distribution of SMC SNRs to larger values.
Context. The Large Magellanic Cloud (LMC) is to date the only normal external galaxy that has been detected in high-energy gamma rays. High-energy gamma rays trace particle acceleration processes and ...gamma-ray observations allow the nature and sites of acceleration to be studied. Aims. We characterise the distribution and sources of cosmic rays in the LMC from analysis of gamma-ray observations. Methods. We analyse 11 months of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope and compare it to tracers of the interstellar medium and models of the gamma-ray sources in the LMC. Results. The LMC is detected at 33σ significance. The integrated >100 MeV photon flux of the LMC amounts to (2.6 ± 0.2) × 10-7 ph cm-2 s-1 which corresponds to an energy flux of (1.6 ± 0.1) × 10-10 erg cm-2 s-1, with additional systematic uncertainties of $\la$16%. The analysis reveals the massive star forming region 30 Doradus as a bright source of gamma-ray emission in the LMC in addition to fainter emission regions found in the northern part of the galaxy. The gamma-ray emission from the LMC shows very little correlation with gas density and is rather correlated to tracers of massive star forming regions. The close confinement of gamma-ray emission to star forming regions suggests a relatively short GeV cosmic-ray proton diffusion length. Conclusions. The close correlation between cosmic-ray density and massive star tracers supports the idea that cosmic rays are accelerated in massive star forming regions as a result of the large amounts of kinetic energy that are input by the stellar winds and supernova explosions of massive stars into the interstellar medium.
We report the discovery of two millisecond pulsars in a search for radio pulsations at the positions of Fermi-Large Area Telescope sources with no previously known counterparts, using the Nancay ...Radio Telescope. The two millisecond pulsars, PSRs J2017+0603 and J2302+4442, have rotational periods of 2.896 and 5.192 ms and are both in binary systems with low-eccentricity orbits and orbital periods of 2.2 and 125.9 days, respectively, suggesting long recycling processes. Gamma-ray pulsations were subsequently detected for both objects, indicating that they power the associated Fermi sources in which they were found. The gamma-ray light curves and spectral properties are similar to those of previously detected gamma-ray millisecond pulsars. Detailed modeling of the observed radio and gamma-ray light curves shows that the gamma-ray emission seems to originate at high altitudes in their magnetospheres. Additionally, X-ray observations revealed the presence of an X-ray source at the position of PSR J2302+4442, consistent with thermal emission from a neutron star. These discoveries along with the numerous detections of radio-loud millisecond pulsars in gamma rays suggest that many Fermi sources with no known counterpart could be unknown millisecond pulsars.
A search for new sources below 100 MeV in the Fermi-LAT data Principe, G.; Malyshev, D.; Ballet, J. ...
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
12/2019, Volume:
30, Issue:
Suppl 1
Journal Article
Peer reviewed
The
Fermi
Large Area Telescope (LAT) has discovered more than 3000 sources between 100 MeV and 300 GeV (3FGL), including over 200
γ
-ray pulsars. The majority of these pulsars have their spectral ...energy peaks (in
ν
F
ν
) above 1 GeV. There exists another population of very energetic, young rotation-powered pulsars having non-thermal hard X-ray emission with spectral energy distributions (SEDs) peaking around 1 MeV, but having no detected emission by
Fermi
LAT above 100 MeV. Previous analyses of point sources in the gamma ray range were done only below 30 MeV (COMPTEL) or above 100 MeV (
Fermi
-LAT). Below 30 MeV, the imaging Compton telescope (COMPTEL) detected 26 steady sources in the energy range from 0.75 to 30 MeV. Since the
Fermi
LAT detects gamma rays down to 20 MeV, we create a list of sources detected in the energy range between 30 MeV and 100 MeV, using PGWave, a background-independent tool that makes use of a wavelet transform. This closes a gap of point source analysis between the COMPTEL catalog and the
Fermi
-LAT catalog and provides information and constraint for this missing MeV pulsar population.
To assess the efficiency of a medium-pressure UV reactor under full-scale water treatment plant (WTP) conditions on the infectivity of Cryptosporidium parvum oocysts in an Naval Medical Research ...Institute (NMRI) suckling mice infectivity model. Six/seven-day-old mice were administered orally 2-10 x 10⁴Cryptosporidium parvum oocysts. Compared with nonirradiated oocysts, 40 mJ cm⁻² UV irradiation of ingested oocysts resulted 7 days later in a 3·4-4·0 log₁₀ reduction in the counts of small intestine oocysts, using a fluorescent flow cytometry assay. Present data extend to industrial conditions previous observations of the efficiency of UV irradiation against Cryptosporidium parvum oocyst in vivo development. Present results suggest that in WTP conditions, a medium-pressure UV reactor is efficient in reducing the infectivity of Cryptosporidium parvum oocysts, one of the most resistant micro-organisms present in environmental waters.
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