| Gamma-Ray Bursts (hereafter GRBs) is the extreme astrophysics phenomenon after the big bang in the universe. Generally it can light up the whole universe in a short time such as less than thousand seconds with its intense gamma rays. Compared number of> 1 GeV photons are emitted both in the burst phase and afterglow phase devoted by Fermi, although we do not distinguish their origin clearly. Another one issue is of star forming phenomenon, a basic process to form our universe, specially at some starburst galaxies(the starbursts) in which nucleons can be accelerated to high energy or ultra high energy (cosmic rays, hereafter CRs) due to star-forming and star-burst actives. High energy gamma rays are thus to be enhanced significantly when those CRs collide with surrounding giant molecule gases, which also become an interest object in Fermi’s history and have been detected at several starbursts. Prompt emission, afterglow emission of GRBs detected by Fermi, also the variation of light curve and spectral feature of the starbursts, thus are analyzed and discussed of my recent works.Review on GRBs including observations, correlations, models and polarization are firstly present in chapter 1. A brief introduction of the star formation rate and properties of gamma rays from the starbursts are given secondly. Finally we review the instruments onboard Fermi, then list abundantly progresses of study both in GRBs and the starbursts benefited from Fermi.In chapter 2, bulk lorentz factors of outflow from GRBs are calculated assuming the existed high energy spectral cutoff/break caused by the pair-production absorption. By searching GRBs with high energy cutoff from the completed sample between Aug 2008 and Oct 2014,6 bursts are founded to have a cutoff significantly over a Band function. Two correlations are tested, i.e, lorentz factor- isotropic luminosity, lorentz factor-isotropic energy, both of which result in a strong positive correlation that indicate the more powerful for GRBs, the more faster for its jets.In chapter 3, a comprehensive study for late high energy gamma ray emission are performed for two GRBs, i.e, GRB 130427A and GRB 130907A. For GRB 130427A, energy flux derived from synchrotron model can not attain the observational data in the energy above～2 GeV at several hundred seconds after GBM onset, and for GRB 130907A, maximum photon energy accelerated with synchrotron model also can not reach the 55 GeV photon at time of 5 hours after burst trigger. A natural interpretation is that these photons share an different origin. With broadband model, a synchrotron plus a synchrotron-self Compton model can be accepted for both observations.Considering high energy gamma ray from the starbursts to be detected with three years more than observations using in first results reported by Fermi team in 2012, we search for them in 7 nearby star-forming galaxies in Chapter 4. NGC 2146 is ensured a detection with 5.5 σ above 100 MeV, which is also a luminous infrared galaxy and thus strength the link between the gamma-ray emission and the death of massive stars.In chapter 5, a conclusion for my works are summarized. Finally, research prospect-s for GRBs and the star bursts are listed. Some concerning issues including very high energy emission, neutrino emission are to be detected in future for starbursts, and dark matter also should be shed light on. |
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