Studies Of The Band Component Of Radiation Spectrum Of The Gamma-ray Bursts Prompt Emission Phase

Observationally,the main component of the radiation energy spectrum of the prompt emission of the Gamma Ray Bursts(GRBs)usually can be well fitted by the exponentially jointed broken power law(i.e.the so-called Band function),which imply that the synchrotron radiation generated by the non-thermal relativistic electrons may be the promising mechanism of the prompt emission.However,there are indeed some problem within the synchrotron scenario.One of them is the famous “fast-cooling problem”,that is to say,in a classical GRBs environment,the low energy radiation spectrum generated by the fastcooling electrons is much softer than a typical observed one.In this thesis,we find that this problem may be able to be alleviated by considering an timeincreasing high energy electrons injection rate within the synchrotron radiation mechanism.We study the radiation spectrum of the Poynting-flux-dominated jet with an increasing high energy electron injection rate.It is found that the Band function can be reproduced by the synchrotron radiation spectrum with an increasing electron injection rate.At the same time,our studies also reveal that a Poynting-flux dominated jet with a larger emission radius,a shorter magnetic reconnection region length,or a lower minimum injected energy would prefer to form a Band-like radiation spectrum.In addition,the increasing electron injection rate would generate a bump-shape low energy electron spectrum,which may be the key for the Band function within synchrotron radiation scenario.Except for our study,many researchers have also proposed other different mechanisms to produce the Band-like synchrotron radiation spectrum.Comparing with the traditional fast-cooling electron spectrum,they usually invoke an electron spectrum with a special low-energy regime to generate the synchrotron radiation.Thus,how to estimate the shape of the low-energy electron spectrum from the observation is the key question for producing the Band synchrotron radiation spectrum,as we stressed above.For this purpose,we creatively propose a method to directly estimate the electron spectrum for the prompt emission,as possible as not specifying any prior certain-physical model for electron spectrum.In this method,an empirical function(i.e.,a four-order Bézier curve jointed with a linear function at high energy)is applied to describe the electron spectrum in log–log coordinates.It is found that our empirical function can well mimic the electron spectra obtained in many numerical calculations or simulations.Then,our method can figure out the electron spectrum for the prompt emission without specifying a model.By employing our method on observations,taking GRB180720 B and GRB 160509 A as examples,it is found that the obtained electron spectra are generally different from that in the standard fast-cooling scenario and even a broken power law.Moreover,the morphology of electron spectra in its low-energy regime varies with time in a burst and even in a pulse.Our proposed method provides a valuable way to confront the synchrotron radiation mechanism with observations.