Natsuki Kodaka

Suzaku X-Ray Imaging and Spectroscopy of Cassiopeia A

Suzaku X-ray observations of a young supernova remnant, Cassiopeia A, were carried out. K-shell transition lines from highly ionized ions of various elements were detected, including Chromium (Cr-K˛ at 5.61 keV). The X-ray continuum spectra were modeled in the 3.4–40 keV band, summed over the entire remnant, and were fitted with a simplest combination of the thermal bremsstrahlung and the non-thermal cut-off power-law models. The spectral fits with this assumption indicate that the continuum emission is likely to be dominated by non-thermal emission with a cut-off energy at >1 keV. The thermal-to-nonthermal fraction of the continuum flux in the 4–10 keV band is best estimated as 0.1. Non-thermal-dominated continuum images in the 4–14 keV band were made. The peak of the non-thermal X-rays appears at the western part. The peak position of the TeV -rays measured with HEGRA and MAGIC is also shifted at the western part with the 1-sigma confidence. Since the location of the X-ray continuum emission was known to be presumably identified with the reverse shock region, the possible keV–TeV correlations give a hint that the accelerated multi-TeV hadrons in Cassiopeia A are dominated by heavy elements in the reverse shock region.

OBSERVATIONS OF THE PROMPT GAMMA-RAY EMISSION OF GRB 070125

The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-Wind, RHESSI, Suzaku WAM, and Swift BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multipeaked emission over a period of about 1 minute. The total burst fluence as observed by Konus is -->1.79 ? 10?4 ergs cm?2 (20 keV-10 MeV). Using the spectroscopic redshift -->z = 1.548, we find that the burst is consistent with the Amati -->Epeak,i ? Eiso correlation. Assuming a jet opening angle derived from broadband modeling of the burst afterglow, GRB 070125 is a significant outlier to the Ghirlanda -->Epeak,i ? E? correlation. Its collimation-corrected energy release, -->E? = 2.5 ? 1052 ergs, is the largest yet observed.

A Multiband Study of the Optically Dark GRB 051028

Observations were made of the optical afterglow of GRB 051028 with the Lulin observatorys 1.0 m telescope and the WIDGET robotic telescope system. R band photometric data points were obtained on 2005 October 28 (UT), or 0.095-0.180 days after the burst. There is a possible plateau in the optical light curve around 0.1 days after the burst; the light curve resembles optically bright afterglows (e.g. GRB 041006, GRB 050319, GRB060605) in shape of the light curve but not in brightness. The brightness of the GRB 051028 afterglow is 3 magnitudes fainter than that of one of the dark events, GRB 020124. Optically dark GRBs have been attributed to dust extinction within the host galaxy or high redshift. However, the spectrum analysis of the X-rays implies that there is no significant absorption by the host galaxy. Furthermore, according to the model theoretical calculation of the Ly

Current Status of the Suzaku Wide‐band All‐sky Monitor (WAM)

\alpha

New probes of GRB prompt emission properties using wide-band spectroscopy by Suzaku Wide-band All-sky Monitor

absorption to find the limit of GRB 051028s redshift, the expected

Status of GRB Observations with the Suzaku Wideband All‐sky Monitor

R

The spectral properties of the GRB prompt gamma‐ray emission observed by the Suzaku Wide‐band All‐sky Monitor

band absorption is not high enough to explain the darkness of the afterglow. While the present results disfavor either the high-redshift hypothesis or the high extinction scenario for optically dark bursts, they are consistent with the possibility that the brightness of the optical afterglow, intrinsically dark.

Improvement of WIDGET

The Suzaku Wide‐band All‐sky Monitor (WAM) consists of 20 BGO anti‐coincidence scintillators for the Hard X‐ray Detector (HXD). The WAM has a wide field of view (FOV), about half of the whole sky, a large collecting area, 800 cm2, and broad‐band energy coverage from 50 to 5000 keV. Thus it has been designed to work as a gamma‐ray burst detector. For the three years since Suzaku launch in July 2005, the WAM has been working very well. About 500 GRBs have been detected through the end of 2008, corresponding to a detection rate of ∼140 GRBs per year. The current status of the WAM is presented in this paper.

Lyα EMITTERS AT z = 7 IN THE SUBARU/XMM-NEWTON DEEP SURVEY FIELD: PHOTOMETRIC CANDIDATES AND LUMINOSITY FUNCTION*

Although the afterglow observations in HETE‐2 and Swift era have revealed a lot of afterglow properties of gamma‐ray bursts (GRBs), we still have poor understanding of the prompt gamma‐ray emission, such as the emission mechanism of the prompt emission and differences between short and long duration GRBs. We have observed many prompt emission of GRBs by Suzaku Wide‐band All‐sky Monitor in wide energy range of 50–5000 keV, with very large effective area of 400 cm2 even at 1 MeV. Furthermore, a combination of the Suzaku/WAM and Swift data provides us not only wider energy range of 15–5000 keV but also redshift information even for some short GRBs. Thanks to these information, we can firstly investigate an intrinsic correlation for short GRBs like Epeak−Liso relation, and we can derive the same type of relation for time‐resolved spectra of long GRBs in finer time‐scale with higher statistics than ever before. These results could be used to discuss the differences between short and long GRBs, and our time‐res...

Design and in-orbit performance of the Suzaku Wide-band All-sky monitor

The Wide‐band All‐sky Monitor (WAM) is a made up of the large lateral BGO shield of the Hard X‐ray Detector (HXD) onboard Suzaku. Its large geometrical area of 800 cm2 per side, the large stopping power for the hard X‐rays and the wide‐field of view make the WAM an ideal detector for gamma‐ray bursts (GRBs) observations in the energy range of 50–5000 keV. In fact, the WAM has observed 288 GRBs confirmed by other satellites, till the end of May 2007.