S. Okuno

Spectral Evolution of GRB060904A Observed with Swift and Suzaku- Possibility of Inefficient Electron Acceleration

We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku satellites. We found rapid spectral softening during both the prompt tail phase and the decline phase of an X-ray flare in the BAT and XRT data. The observed spectra were fit by power-law photon indices which rapidly changed from

Suzaku and Swift observations for X‐ray afterglows; Investigation into the electron acceleration in the internal/external shocks

\Gamma = 1.51^{+0.04}_{-0.03}

Automated 1.3m Near-Infrared Telescope System triggered by Gamma-Ray Burst

to

The Suzaku-Swift Joint Observation of the Early X-Ray Afterglow of GRB060105

\Gamma = 5.30^{+0.69}_{-0.59}

The Suzaku-Swift Joint Observation of the Early X-Ray Afterglow of GRB060105(Chapter 1. Gamma Ray Bursts, Cosmic Rays and Neutrino, The Extreme Universe in the Suzaku Era)

within a few hundred seconds in the prompt tail. This is one of the steepest X-ray spectra ever observed, making it quite difficult to explain by simple electron acceleration and synchrotron radiation. Then, we applied an alternative spectral fitting using a broken power-law with exponential cutoff (BPEC) model. It is valid to consider the situation that the cutoff energy is equivalent to the synchrotron frequency of the maximum energy electrons in their energy distribution. Since the spectral cutoff appears in the soft X-ray band, we conclude the electron acceleration has been inefficient in the internal shocks of GRB 060904A. These cutoff spectra suddenly disappeared at the transition time from the prompt tail phase to the shallow decay one. After that, typical afterglow spectra with the photon indices of 2.0 are continuously and preciously monitored by both XRT and Suzaku/XIS up to 1 day since the burst trigger time. We could successfully trace the temporal history of two characteristic break energies (peak energy and cutoff energy) and they show the time dependence of

Strategy of the Suzaku gamma-ray burst observations

\propto t^{-3} \sim t^{-4}

GRB 060801: Kanazawa optical observation.

while the following afterglow spectra are quite stable. This fact indicates that the emitting material of prompt tail is due to completely different dynamics from the shallow decay component. Therefore we conclude the emission sites of two distinct phenomena obviously differ from each other.

GRB 060807: kanazawa r-band observation.

We have performed ToO observations for three bright GRBs with the Japanese X‐ray satellite “Suzaku”. Suzaku strongly supports the follow‐up observations by Swift, especially in the late time afterglow phase, with its capabilities of larger effective area and wider energy band compared with Swift/XRT. In this presentation, mainly focusing on the X‐ray afterglow of GRB 060904A, we introduce these ToO observation results. In GRB 060904A, we found rapid spectral softening with the photon indices from 1.5 to 5.3 during the steep decay (prompt tail) phase in the BAT and XRT data. This ultra soft spectra suddenly disappeared at the transition time from the prompt tail phase to the shallow decay one. After that, typical afterglow spectra with the photon indices of 2.0 are continuously and preciously monitored by both XRT and Suzaku/XIS up to 1 day since the burst trigger time. To explain this ultra soft spectra, we introduce a spectral cutoff model instead of power‐law, and investigate the possibility of the maxi...

GRB 060108: ISAS early observations and near IR upper limit.

The design for robotic telescopes to observe Gamma-Ray Burst (GRB) afterglows and the results of observations are presented. Quickly fading bright GRB flashes and afterglows provide a good tool to study an extremely early universe. However, most large ground-based telescopes cannot afford to follow-up the afterglows and flashes quickly within a few hours since a GRB explosion. We re-modeled the existing middle-class 1.3 m &slasho; telescope of the near infrared band at ISAS in Japan to match for the above requirement. We also set a small telescope of 30 cm diameter with a conventional CCD. These telescopes can monitor afterglows quickly within a few minutes in J, H, Ks and R band with a grism spectrometer.