Other
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010acasn..51..105y&link_type=abstract
Acta Astronomica Sinica, vol. 51, no.1, p. 105-107
Other
Gamma Rays: Bursts, Radiation Mechanisms: Non-Thermal, Stars: Neutron, Neutrinos, Relativity
Scientific paper
Gamma-ray bursts (GRBs), which are generally followed by long-lasting low-frequency afterglow emission, are short and intense pulses of gamma-rays observed from the sky in arbitrary directions. In order to observe the multi-wavelength emission at the early afterglow phase and even the prompt emission phase, NASA launched the Swift satellite on Nov. 20th 2004. Swift can localize GRBs within about 10 seconds. A brief review on the recent progress in observations and theories in the Swift era is given in Chapter 1. This paper focuses on the features of the early afterglows and the multi-wavelength prompt emission. In Chapters 2 and 3, we try to explain the shallow-decaying X-ray afterglows and X-ray flares, both of which are unaccountable in the standard afterglow model. (1) It is widely accepted that the shallow decay phase indicates a continuous energy injection into the GRB blast wave, and this energy could be released from the central engine after the burst. Based on the knowledge of the evolution of a pulsar wind, we argue that the injected flow interacting with the GRB blast wave is an ultra-relativistic kinetic-energy flow (i.e., wind) rather than pure electromagnetic waves. Therefore, a relativistic wind bubble (RWB) including a pair of shocks will be formed. Our numerical calculations and the fitting results show that the emission from an RWB can well account for the X-ray shallow decay phase. (2) For the X-ray flares that are attributed to some intermediate late activities of the central engine, we analyze the detailed dynamics of late internal shocks which directly produce the flare emission. Comparing the theoretical results with the lower limits of the observational luminosities and the profiles of the flare light curves, we find some constraints on the properties of the pre-collision shells, which are directly determined by the central object. In Chapter 4, we investigate the high-energy afterglow emission during the shallow decay phase in two models, i.e., RWB model and the model with a wide radially spread of Lorentz factors in GRB ejecta (RSE model). We provide a unified description of the dynamics of these two models and calculate the high-energy emission by considering the inverse-Compton (IC) scattering between the electrons and low-energy synchrotron photons. Our results show that, in both models, there is a plateau (even a hump) in high-energy light curves during the shallow decay phase. In particular, the high-energy flux predicted by the RWB model is about one order of magnitude higher than what predicted by the RSE model. These observational signatures would be used to discriminate between these two different energy-injection models. In addition, a similar study on high-energy emission due to the IC mechanism in the late internal shock model shows that the high-energy flares accompanying with the relatively brighter X-ray flares could be detected by Fermi/LAT.
In Chapter 5, neutrino emission from early afterglows of GRB 060218-like GRBs is concerned and neutrinos are expected to be produced from photon-pion interactions in a GRB blast wave which propagates into a dense wind. Relativistic protons are accelerated by an external shock, while target photons are basically provided by the thermal emission from the supernova shock breakout and its IC-scattered component. Because of the estimated high occurrence rate of the low-luminosity GRBs, it will be more possible to detect afterglow neutrinos from a single nearby GRB event of this type by IceCube. In Chapter 6, we show that the synchrotron emissions respectively produced by the internal forward and reverse shocks could peak at two quite different energy bands if the Lorentz factors of these two types of shocks are significantly different with each other (e.g., the former is Newtonian and the latter is relativistic). Then we investigate whether this scenario is applicable to the case of GRB 080319B and find that a bimodal distribution of the Lorentz factors of shells, peaking at about 400 and 105, is required. In addition, this scenario predicts an accompanying IC GeV emission with a luminosity comparable to (not much higher than) that of the synchrotron MeV emission, which can be tested by the Fermi observations in future. In Chapter 7, considering the effects of reheating due to r-mode dissipation, magnetic braking and accretion, we carefully investigate the long-term spins and thermal evolutions of isolated neutron stars and neutron stars in low-mass X-ray binaries. The role of the r-mode-induced differential rotation on the evolution of neutron stars is taken into account. Finally, we give some discussions and an outlook in Chapter 8.
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