Research On The Cosmic-ray Sources Using The Gamma-ray Observations

Cosmic rays(CR)have been studied for more than a hundred years since they were discovered in 1912.However,their origin is still unknown well.With the development of CR observations,more questions about CR have been raised.CR are mainly composed of relativistic protons and helium nuclei,of which the production and propagation are usually accompanied by the production of gamma rays,so it is very effective to discuss cosmic rays from the gamma ray window.Using the large area telescope(LAT)boarded on the Fermi satellite,knowledge of candidate sources of cosmic ray such as blazar,gamma-ray bursts,supernova remnants(SNR),pulsar clouds(PWN),and starforming galaxies has been greatly updated.In this paper,candidates for Mpc-scale galaxy clusters,kpc-scale star-forming galaxies,and pc-scale SNR and PWN cosmic ray sources were selected,and their observations at Ge V band were used to explore the properties of these candidate.Mpc-scale extended radio radiation has been widely observed in galaxy clusters,thus confirming the existence of cosmic leptons in galaxy clusters.It is generally believed that relativistic lepton within inter cluster media(ICM)is accelerated by structureforming shock wave and turbulent,which the CR hadron is expected to accelerate and inject into the ICM similar to CR leptons.The Ge V emission associated with the these CR particles is expected,but has no significant detection.Based on Unbinned analysis method,we firstly detected Ge V emission from the direction of the Coma cluster(> 5?),which shows a spatial morphology roughly coincident with the center radio halo,with an apparent excess at the southwest of the cluster.The central part of Ge V emission is extended at the confidence level of > 2?.Interpreting he gamma-ray emission as arising from CR proton interaction,we infer that the volume-averaged value of the CR to thermal pressure ration in the Coma cluster is ~ 2%.Within star-forming galaxies,Ge V emission is generated from CRs interaction with gas or radiation fields,which is an important window to explore the acceleration and propagation of cosmic rays in the galaxy.We searched for Ge V radiation from starforming galaxies in a sample and detected Ge V emission from galaxies M33 and Arp299.Based on the empirical relationship between infrared and gamma-ray luminosity,we believe that Ge V eimssion from these two galaxies results from the interaction of cosmic rays with gas and radiation fields in the galaxies.For M33 galaxy,The Ge V emission is likely to be offset from the galactic center at the confidence level of >2?,which is associated with the large HII ionization region NGC 604 in the northeast direction of the galaxy spatially.For Arp 299,we found that there may be a significant flux variability at 3? significant level,indicating that part of the Ge V emission may come from the obscured AGN activity in the galactic center.At the pc scale,the shock wave driven by the interaction between a supernova ejecta and the circumstellar medium can accelerate the CR particles(cosmic ray leptons and hadrons)that generate SNR Ge V emission.Here we report a serendipitous discovery of a fading Ge V gamma-ray source in spatial coincidence with one of the nearest and brightest supernova—SN2004dj from our gamma-ray survey of nearby starforming galaxies with Fermi-LAT.We interpret this gamma-ray emission arising from the supernova ejecta interacting with a surrounding high-density shell,which decelerates the ejecta and converts ~ 1% of the SN kinetic energy to relativistic protons.The interaction between the pulsar wind and the circumstellar medium can drive the terminal shock wave,thus accelerating the CR leptons which can generate Ge V PWN.These leptons also escape out of the PWN region to earth,which may be attributed to the positron excess.Nearby pulsars Geminga/PWN and PSR B0656+14/PWN are discussed as candidates extendly.In 2017,HAWC Observatory detected Te V extended emission(Te V Nebulae)from these two PWN,which resulted in relatively low electron diffusion coefficient.Therefore,based on the framework of single-zone model,they exclude that the positron excess are contributed by these two nearby pulsars/PWN.However,in the two-zone model,it could not be excluded.We searched for Ge V emission associated with Te V Nebulae and found no any significant Ge V emission.According to the Ge V flux upper limits,we also ruled out that nearby Geminga/PWN and PSR B0656 + 14/PWN as a dominant contribution to the positron excess in the framework of two-zone model.