High-energy emission as a test of the prior emission model for gamma-ray burst afterglows (2009)
Murase, Kohta, Toma, Kenji, Yamazaki, Ryo, Nagataki, Shigehiro, Ioka, Kunihito
We study high-energy gamma-ray afterglow emission from gamma-ray bursts (GRBs) in the prior emission model, which is proposed to explain the plateau phase of the X-ray afterglow. This model predicts...
An up-scattered cocoon emission model of Gamma-Ray Burst high-energy lags (2009)
Toma, Kenji, Wu, Xue-Feng, Meszaros, Peter
The Fermi Gamma-ray Space Telescope recently detected the most energetic gamma-ray burst so far, GRB 080916C, and reported its detailed temporal properties in an extremely broad spectral range: (i)...
Zhang, Bing, Zhang, Bin-Bin, Virgili, Francisco J., Liang, En-Wei, Kann, D. Alexander, Wu, Xue-Feng, ...
(Abridged) The highest redshift (z=6.7) gamma-ray burst (GRB) 080913 recently detected by Swift is an intrinsically short, hard GRB. It would be recognized by BATSE as a short/hard GRB should it have...
The Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRB 080319B (2009)
Stamatikos, Michael, Ukwatta, Tilan N., Sakamoto, Takanori, Dhuga, Kalvir S., Toma, Kenji, Pe'er, Asaf, ...
We report on observations of correlated behavior between the prompt gamma-ray and optical emission from GRB 080319B, which confirm that (i) they occurred within the same astrophysical source region...
Statistical Properties of Gamma-Ray Burst Polarization (2008)
Toma, Kenji, Sakamoto, Takanori, Zhang, Bing, Hill, Joanne E., McConnell, Mark L., Bloser, Peter F., ...
The emission mechanism and the origin and structure of magnetic fields in gamma-ray burst (GRB) jets are among the most important open questions concerning the nature of the central engine of GRBs....
Toma, Kenji, Ioka, Kunihito, Nakamura, Takashi
The late-time optical/radio afterglows of $\gamma$-ray bursts (GRBs) are believed to be synchrotron emission of electrons accelerated in relativistic collisionless shocks propagating in the ambient...
Unstable GRB photospheres and electron-positron annihilation lines (2007)
Ioka, Kunihito, Murase, Kohta, Toma, Kenji, Nagataki, Shigehiro, Nakamura, Takashi
We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can reproduce the observed non-thermal spectra with high radiative efficiencies, >50%. Internal dissipation below a photosphere...
Toma, Kenji, Ioka, Kunihito, Sakamoto, Takanori, Nakamura, Takashi
The gamma-ray burst (GRB) 060218 has ~ 10^5 times lower luminosity than typical long GRBs, and is associated with a supernova (SN). The radio afterglow displays no jet break, so that this burst might...
Ioka, Kunihito, Toma, Kenji, Yamazaki, Ryo, Nakamura, Takashi
Most X-ray afterglows of gamma-ray bursts (GRBs) observed by the Swift satellite have a shallow decay phase t^{-1/2} in the first few hours. This is not predicted by the standard afterglow model and...
Shallow Decay of Early X-ray Afterglows from Inhomogeneous Gamma-Ray Burst Jets (2005)
Toma, Kenji, Ioka, Kunihito, Yamazaki, Ryo, Nakamura, Takashi
Almost all the X-ray afterglows of gamma-ray bursts (GRBs) observed by the Swift satellite have a shallow decay phase in the first thousands of seconds. We show that in an inhomogeneous jet...
Tail Emission of Prompt Gamma-Ray Burst Jets (2005)
Yamazaki, Ryo, Toma, Kenji, Ioka, Kunihito, Nakamura, Takashi
Tail emission of the prompt gamma-ray burst (GRB) is discussed using a multiple emitting sub-shell (inhomogeneous jet, sub-jets or mini-jets) model, where the whole GRB jet consists of many emitting...
Ep-Eiso Correlation in a Multiple Subjet Model of Gamma-Ray Bursts (2005)
Toma, Kenji, Yamazaki, Ryo, Nakamura, Takashi
We perform Monte Carlo simulations to study Ep-Eiso correlation in the context of a multiple subjet model (or inhomogeneous jet model) for gamma-ray bursts (GRBs), X-ray--rich GRBs (XRRs), and X-ray...
A Unified Model for Gamma-Ray Bursts (2005)
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi, Toma, Kenji
A possible unified model of short and long gamma-ray bursts (GRBs), X-ray rich GRBs, and X-ray flashes is proposed. It is assumed that the jet of a GRB consists of many emitting sub-shells (i.e., an...
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi, Toma, Kenji
We propose a possible unified model of short and long gamma-ray bursts (GRBs), X-ray rich GRBs, and X-ray flashes. The jet of a GRB is assumed to consist of multiple sub-jets or sub-shells (i.e., an...
A Possible Origin of Bimodal Distribution of Gamma-Ray Bursts (2004)
Toma, Kenji, Yamazaki, Ryo, Nakamura, Takashi
We study the distribution of the durations of gamma-ray bursts (GRBs) in the unified model of short and long GRBs recently proposed by Yamazaki, Ioka, and Nakamura. Monte Carlo simulations show clear...