1,721,431 research outputs found
A gamma-ray pulsar timing array constrains the nanohertz gravitational wave background
No full textAfter large galaxies merge, their central supermassive black holes are expected to form binary systems. Their orbital motion should generate a gravitational wave background (GWB) at nanohertz frequencies. Searches for this background use pulsar timing arrays, which perform long-term monitoring of millisecond pulsars at radio wavelengths. We used 12.5 years of Fermi Large Area Telescope data to form a gamma-ray pulsar timing array. Results from 35 bright gamma-ray pulsars place a 95% credible limit on the GWB characteristic strain of 1.0 × 10 −14 at a frequency of 1 year –1 . The sensitivity is expected to scale with t obs , the observing time span, as t obs − 13 / 6 . This direct measurement provides an independent probe of the GWB while offering a check on radio noise models.A gamma-ray pulsar timing array After galaxies merge, the supermassive black holes (SMBHs) at their centers are expected to form binaries that emit gravitational waves at nanohertz frequencies. Numerous SMBH binaries throughout the Universe should combine to produce a gravitational wave background. Existing searches for this signal use radio observations of pulsars as sensitive clocks and look for small shifts in the pulse timings. The Fermi-LAT Collaboration implemented a pulsar timing array using gamma rays and achieved a sensitivity close to that of the radio approaches. The results set an independent upper limit on the gravitational wave background, which is subject to different noise sources. —KTSA pulsar timing array is implemented using gamma rays, setting a limit on the nanohertz gravitational wave background
The Fermi Gamma Ray Space Telescope discovers the Pulsar in the Young Galactic Supernova-Remnant CTA 1
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Simultaneous observations of PKS 2155-304 with H.E.S.S., Fermi, RXTE and ATOM: spectral energy distributions and variability in a low state
No full textMeasurement of the Cosmic Ray e+ plus e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope
No full textDiscovery of Pulsed Gamma Rays from the Young Radio Pulsar PSR J1028-5819 with the Fermi Large Area Telescope
No full textFermi-LAT observations of the gamma-ray emission from the quiescent sun - first 6 years in orbit
No full textThe quiescent sun is a steady source of high energy gamma-ray emission due to the interactions of cosmic ray (CR) protons and electrons with matter and photons in the solar environment. Such interactions lead to two components of the emission with distinctly different spatial distributions and spectra: a point-like emission from the solar disk due to the CR cascades in the solar atmosphere, and the extended emission from the inverse Compton (IC) scattering of CR electrons off solar photons that is coming from the whole heliosphere. The Fermi-LAT Collaboration has reported the detection of the gamma-ray emission from the quiescent sun in a previous publication, based on the first 18 months of observations. In this paper we present the results of the first 6 years of observations. The new Pass 8 event-level analysis was applied to the data set. Significantly larger photon statistics and better instrument performance allow us to explore both components of the emission in greater details and let us better comparisons of data with current models of the IC component. Moreover, the longer period of observations allows us to study the variations of the emission over the solar cycle
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