In the past decade, the most successful approach to search for millisecond pulsars (MSPs) has been to use acceleration searches to look for radio pulsations in the error bars of Gamma-ray sources identified by the Large Area Telescope (LAT) aboard the Fermi Satellite. However, 1000s of gamma-ray sources found by LAT still remain unassociated with any astrophysical object. It is believed that...
PSR J2021+4026 in the Cygnus region is one of the most interesting radio-quiet pulsars detected by Fermi-LAT. This source, thought to be associated with the Gamma Cygni supernova remnant, is the first isolated gamma-ray pulsar that exhibited clear evidence of variability, with a simultaneous flux and spindown change first occurred in October 2011. After a long recovery phase, in August 2015...
In the last decade, Fermi LAT has provided an amazing roadmap to assist with pulsar searches conducted in other parts of the electromagnetic system. Indeed, multiple surveys have used Fermi unidentified sources with pulsar-like structures as their targets. Following this strategy, we present in this poster a survey conducted using the MeerKAT telescope to find energetic new pulsars associated...
PSR J0218+4232 is one of the most energetic millisecond pulsars (MSP) known and has been considered as one of the best candidates for very high energy (>100 GeV) γ-ray emission. It has a period of 2.3 ms in a 2-day orbit with a ∼ 0.2M⊙ white dwarf companion. With a characteristic age τ <0.5 Gyr it is one of the youngest MSPs known, with an extremely strong magnetic field at the light cylinder...
Gamma rays from the quiet Sun are produced by Cosmic Rays (CRs) interacting with its surface (disk component) and with its photon field (spatially extended inverse-Compton component, IC). IC is maximum close to the Sun and it extends over the whole sky. Monitoring the IC component with Fermi-LAT allows to obtain information on CR electrons close to the Sun and in the heliosphere for different...
Wolf-Rayet (WR) stars are massive evolved stars undergoing advanced nuclear burning in their cores and possess strong stellar winds. WR stars -- and in particular WR binary systems -- are also predicted to be potential emitters of gamma rays. Although details of the high-energy emission mechanisms are not well-understood, a majority of the emission is likely due to strong shocks produced by...
LS 5039 is one of the best-observed gamma-ray binaries with non-thermal emission ranging from soft X-rays to VHE gamma-ray. Explaining the observed anti-correlation between the X-ray/VHE and the HE gamma-ray bands, while accounting for its complex spectral features, has become a challenge for current modelling efforts.
We investigate this system in a wind-driven context, where non-thermal...
The gamma-ray emission from stars is induced by the interaction of cosmic rays with stellar atmospheres and photon fields. This emission is expected to come in two components: a stellar disk emission, where gamma-rays are mainly produced in atmospheric showers generated by hadronic cosmic rays, and an extended halo emission, where the high density of soft photons in the surroundings of stars...
Superorbital periods in Roche-lobe overflowing X-ray binaries such as Her X-1 have been known for some time. These can be understood as being related to the presence of an accretion disk. However, more recently a number of HMXBs accreting from the wind of their supergiant companion, where the presence of a persistent accretion disk is unlikely, have also been found to show superorbital...
The ability of the Fermi Large Area Telescope to identify pulsar-like gamma-ray sources has sparked a huge increase in discoveries of "Spider" millisecond pulsar binaries (Black Widows and Redbacks). These systems are characterised by long radio eclipses due to scattering and absorption by diffuse intra-binary material that has been evaporated from the companion star's surface. Unlike radio...
Synchrotron radio emission from non-relativistic jets powered by massive protostars has been reported, indicating the presence of relativistic electrons and mG magnetic fields. We study diffusive shock acceleration and magnetic field amplification in protostellar jets with speeds between 300 and 1000 km/s. We show that the magnetic field in the synchrotron emitter can be amplified by the...
Supernova remnants (SNRs) are widely believed to be one of the main candidates for the origin of Galactic cosmic rays. Very-high-energy gamma-ray emission observed from a number of SNRs suggests that particles are indeed accelerated to high energies by shock in remnants. However, it is extremely difficult to discriminate which particles are responsible for this emission as both protons...
Gamma-ray binaries are a class of high-mass binary systems which are distinguished by their spectral energy distributions peaking above 1 MeV. Gamma-ray binaries consist of an O or B type companion and an orbiting compact object which is either a neutron star or a black hole. Generally in these systems the nature of the compact object is unknown except for two cases, namely PSR B1259-63 and...
The Fermi data imply that the gamma-ray observables, i.e., the gamma-ray luminosity, spectral cut-off energy, stellar surface magnetic field, and spin-down power obey a relation that represents a 3D plane in the 4D log-space. This observed fundamental plane (FP) is remarkably close to the theoretical relation that is obtained, assuming that the pulsar gamma-ray emission is due to curvature...
