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تسجيل مستخدم جديدFermi-LAT Search for Pulsar Wind Nebulae around gamma-ray Pulsars
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The high sensitivity of the Fermi-LAT (Large Area Telescope) offers the first opportunity to study faint and extended GeV sources such as pulsar wind nebulae (PWNe). After one year of observation the LAT detected and identified three pulsar wind nebulae: the Crab Nebula, Vela-X and the PWN inside MSH 15-52. In the meantime, the list of LAT detected pulsars increased steadily. These pulsars are characterized by high energy loss rates from ~3 times 10^{33} erg s$^{-1}$ to 5 times 10$^{38}$ erg s$^{-1}$ and are therefore likely to power a PWN. This paper summarizes the search for PWNe in the off-pulse windows of 54 LAT-detected pulsars using 16 months of survey observations. Ten sources show significant emission, seven of these likely being of magnetospheric origin. The detection of significant emission in the off-pulse interval offers new constraints on the gamma-ray emitting regions in pulsar magnetospheres. The three other sources with significant emission are the Crab Nebula, Vela-X and a new pulsar wind nebula candidate associated with the LAT pulsar PSR J1023-5746, coincident with the TeV source HESS J1023-575. We further explore the association between the H.E.S.S. and the Fermi source by modeling its spectral energy distribution. Flux upper limits derived for the 44 remaining sources are used to provide new constraints on famous PWNe that have been detected at keV and/or TeV energies.
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Pulsar Wind Nebulae (PWNe) represent the most numerous population of TeV sources in our Galaxy. These sources, some of which emit very-high-energy (VHE) gamma-rays, are believed to be related to the young and energetic pulsars that power highly magne
tized nebulae (a few $mu$G to a few hundred $mu$G). In this scenario, particles are accelerated to VHE along their expansion into the pulsar surroundings, or at the shocks produced in collisions of the winds with the surrounding medium. Those energetic pulsars can be traced using observations with the Fermi-LAT detector. The MAGIC Collaboration has carried out deep observations of PWNe around high spin-down power Fermi pulsars. We study the PWN features in the context of the already known TeV PWNe. We present here the analysis accomplished with three selected PWNe: PSR J0631+1036, PSR J1954+2838 and PSR J1958+2845.
The Large Area Telescope (LAT) on the Fermi satellite is the first gamma-ray instrument to discover pulsars directly via their gamma-ray emission. Roughly one third of the 117 gamma-ray pulsars detected by the LAT in its first three years were discov
ered in blind searches of gamma-ray data and most of these are undetectable with current radio telescopes. I review some of the key LAT results and highlight the specific challenges faced in gamma-ray (compared to radio) searches, most of which stem from the long, sparse data sets and the broad, energy-dependent point-spread function (PSF) of the LAT. I discuss some ongoing LAT searches for gamma-ray millisecond pulsars (MSPs) and gamma-ray pulsars around the Galactic Center. Finally, I outline the prospects for future gamma-ray pulsar discoveries as the LAT enters its extended mission phase, including advantages of a possible modification of the LAT observing profile.
The Large Area Telescope (LAT) on Fermi has detected ~150 gamma-ray pulsars, about a third of which were discovered in blind searches of the $gamma$-ray data. Because the angular resolution of the LAT is relatively poor and blind searches for pulsars
(especially millisecond pulsars, MSPs) are very sensitive to an error in the position, one must typically scan large numbers of locations. Identifying plausible X-ray counterparts of a putative pulsar drastically reduces the number of trials, thus improving the sensitivity of pulsar blind searches with the LAT. I discuss our ongoing program of Swift, XMM-Newton, and Chandra observations of LAT unassociated sources in the context of our blind searches for gamma-ray pulsars.
Context: Very-high-energy (VHE; E>100 GeV) {gamma}-ray emission from blazars inevitably gives rise to electron-positron pair production through the interaction of these {gamma}-rays with the Extragalactic Background Light (EBL). Depending on the magn
etic fields in the proximity of the source, the cascade initiated from pair production can result in either an isotropic halo around an initially beamed source or a magnetically broadened cascade flux. Aims: Both extended pair halo (PH) and magnetically broadened cascade (MBC) emission from regions surrounding the blazars 1ES 1101-232, 1ES 0229+200 and PKS 2155-304 were searched for, using VHE {gamma}-ray data taken with the High Energy Stereoscopic System (H.E.S.S.), and high energy (HE; 100 MeV<E<100 GeV) {gamma}-ray data with the Fermi Large Area Telescope (LAT). Methods: By comparing the angular distributions of the reconstructed gamma-ray events to the angular profiles calculated from detailed theoretical models, the presence of PH and MBC was investigated. Results: Upper limits on the extended emission around 1ES 1101-232, 1ES 0229+200 and PKS 2155-304 are found to be at a level of few percent of the Crab nebula flux above 1 TeV, depending on the assumed photon index of the cascade emission. Assuming strong Extra-Galactic Magnetic Field (EGMF) values, > 10$^{-12}$G, this limits the production of pair halos developing from electromagnetic cascades. For weaker magnetic fields, in which electromagnetic cascades would result in magnetically broadened cascades, EGMF strengths in the range (0.3 - 3)$times 10^{-15}$G were excluded for PKS 2155-304 at the 99% confidence level, under the assumption of a 1 Mpc coherence length.
We present a summary of the Fermi Pulsar Search Consortium (PSC), an international collaboration of radio astronomers and members of the Large Area Telescope (LAT) collaboration, whose goal is to organize radio follow-up observations of Fermi pulsars
and pulsar candidates among the LAT gamma-ray source population. The PSC includes pulsar observers with expertise using the worlds largest radio telescopes that together cover the full sky. We have performed very deep observations of all 35 pulsars discovered in blind frequency searches of the LAT data, resulting in the discovery of radio pulsations from four of them. We have also searched over 300 LAT gamma-ray sources that do not have strong associations with known gamma-ray emitting source classes and have pulsar-like spectra and variability characteristics. These searches have led to the discovery of a total of 43 new radio millisecond pulsars (MSPs) and four normal pulsars. These discoveries greatly increase the known population of MSPs in the Galactic disk, more than double the known population of so-called `black widow pulsars, and contain many promising candidates for inclusion in pulsar timing arrays.
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