ﻻ يوجد ملخص باللغة العربية
We analyze 9 years of PASS 8 $textit{Fermi}$-LAT data in the 60$-$500 MeV range and determine flux upper limits (UL) for 17 gamma-ray dark pulsars as a probe of axions produced by nucleon-nucleon Bremsstrahlung in the pulsar core. Using a previously published axion decay gamma-ray photon flux model for pulsars which relies on a high core temperature of 20 MeV, we improve the determination of the UL axion mass ($m_a$), at 95 percent confidence level, to 9.6 $times$ 10$^{-3}$ eV, which is a factor of 8 improvement on previous results. We show that the axion emissivity (energy loss rate per volume) at realistic lower pulsar core temperatures of 4 MeV or less is reduced to such an extent that axion emissivity and the gamma-ray signal becomes negligible. We consider an alternative emission model based on energy loss rate per mass to allow $m_a$ to be constrained with $Fermi$-LAT observations. This model yields a plausible UL $m_a$ of 10$^{-6}$ eV for pulsar core temperature $<$ 0.1 MeV but knowledge of the extent of axion to photon conversion in the pulsar $B$ field would be required to make a precise UL axion mass determination. The peak of axion flux is likely to produce gamma-rays in the $leq$ 1 MeV energy range and so future observations with medium energy gamma-ray missions, such as AMEGO and e-ASTROGAM, will be vital to further constrain UL $m_a$.
We present precise phase-connected pulse timing solutions for 16 gamma-ray-selected pulsars recently discovered using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope plus one very faint radio pulsar (PSR J1124-5916) that is more
We apply the axion-photon conversion mechanism to the 130 GeV $gamma$-ray line observed by the Fermi satellite. Near the Galactic center, some astrophysical sources and/or particle dark matter can produce energetic axions (or axionlike particles), an
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
We report the analysis of the first deep optical observations of three isolated $gamma$-ray pulsars detected by the {em Fermi Gamma-ray Space Telescope}: the radio-loud PSR, J0248+6021 and PSR, J0631+1036, and the radio-quiet PSR, J0633+0632. The lat
Observations of pulsars with the Large Area Telescope (LAT) on the Fermi satellite have revolutionized our view of the gamma-ray pulsar population. For the first time, a large number of young gamma-ray pulsars have been discovered in blind searches o