27 research outputs found
Spectral Evolutions in Gamma-Ray Burst Exponential Decays Observed with Suzaku WAM
This paper presents a study on the spectral evolution of gamma-ray burst
(GRB) prompt emissions observed with the Suzaku Wide-band All-sky Monitor
(WAM). By making use of the WAM data archive, 6 bright GRBs exhibiting 7
well-separated fast-rise-exponential-decay (FRED) shaped light curves are
presented and the evaluated exponential decay time constants of the
energy-resolved light curves from these FRED peak light curves are shown to
indicate significant spectral evolution. The energy dependence of the time
constants is well described with a power-law function tau(E) ~ E^gamma, where
gamma ~ -(0.34 +/- 0.12) in average, although 5 FRED peaks show consistent
value of gamma = -1/2 which is expected in synchrotron or inverse-Compton
cooling models. In particular, 2 of the GRBs were located with accuracy
sufficient to evaluate the time-resolved spectra with precise energy response
matrices. Their behavior in spectral evolution suggests two different origins
of emissions. In the case of GRB081224, the derived 1-s time-resolved spectra
are well described by a blackbody radiation model with a power-law component.
The derived behavior of cooling is consistent with that expected from radiative
cooling or expansion of the emission region. On the other hand, the other 1-s
time-resolved spectra from GRB100707A is well described by a Band GRB model as
well as with the thermal model. Although relative poor statistics prevent us to
conclude, the energy dependence in decaying light curve is consistent with that
expected in the former emission mechanism model.Comment: 11 pages, 7 figures, 5 tables. PASJ accepte
WIDGET: System Performance and GRB Prompt Optical Observations
The WIDeField telescope for Gamma-ray burst Early Timing (WIDGET) is used for
a fully automated, ultra-wide-field survey aimed at detecting the prompt
optical emission associated with Gamma-ray Bursts (GRBs). WIDGET surveys the
HETE-2 and Swift/BAT pointing directions covering a total field of view of 62
degree x 62 degree every 10 secounds using an unfiltered system. This
monitoring survey allows exploration of the optical emission before the
gamma-ray trigger. The unfiltered magnitude is well converted to the SDSS r'
system at a 0.1 mag level. Since 2004, WIDGET has made a total of ten
simultaneous and one pre-trigger GRB observations. The efficiency of
synchronized observation with HETE-2 is four times better than that of Swift.
There has been no bright optical emission similar to that from GRB 080319B. The
statistical analysis implies that GRB080319B is a rare event. This paper
summarizes the design and operation of the WIDGET system and the simultaneous
GRB observations obtained with this instrument.Comment: 19 pages, 11 figures, Accepted to appear in PAS
Spectral Properties of Prompt Emission of Four Short Gamma-Ray Bursts Observed by the Suzaku-WAM and the Konus-Wind
We have performed a joint analysis of prompt emission from four bright short
gamma-ray bursts (GRBs) with the Suzaku-WAM and the Konus-Wind experiments.
This joint analysis allows us to investigate the spectral properties of
short-duration bursts over a wider energy band with a higher accuracy. We find
that these bursts have a high E, around 1 MeV and have a harder
power-law component than that of long GRBs. However, we can not determine
whether these spectra follow the cut-off power-law model or the Band model. We
also investigated the spectral lag, hardness ratio, inferred isotropic
radiation energy and existence of a soft emission hump, in order to classify
them into short or long GRBs using several criteria, in addition to the burst
duration. We find that all criteria, except for the existence of the soft hump,
support the fact that our four GRB samples are correctly classified as
belonging to the short class. In addition, our broad-band analysis revealed
that there is no evidence of GRBs with a very large hardness ratio, as seen in
the BATSE short GRB sample, and that the spectral lag of our four short GRBs is
consistent with zero, even in the MeV energy band, unlike long GRBs. Although
our short GRB samples are still limited, these results suggest that the
spectral hardness of short GRBs might not differ significantly from that of
long GRBs, and also that the spectral lag at high energies could be a strong
criterion for burst classification.Comment: 23 pages, 6 figures, accepted for Publications of the Astronomical
Society of Japa
A multi band study of the optically dark GRB 051028
Observations were made of the optical afterglow of GRB 051028 with the Lulin
observatory's 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 absorption to find the limit of
GRB 051028's redshift, the expected 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.Comment: 5page, 5 figures, 1 table, accepted for publication in PASJ Letter.
PASJ styl
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 \textit{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 multi-peaked emission over a
period of about one minute. The total burst fluence as observed by Konus is
erg/cm (20 keV--10 MeV). Using the spectroscopic
redshift , we find that the burst is consistent with the ``Amati''
correlation. Assuming a jet opening angle derived from
broadband modeling of the burst afterglow, GRB 070125 is a significant outlier
to the ``Ghirlanda'' correlation. Its
collimation-corrected energy release ergs is
the largest yet observed.Comment: 25 pages, 6 figures; accepted for publication in ApJ. Improved
spectral fits and energetics estimate
Spectral evolution of GRB 060904A 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 to 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 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.Comment: 19 pages, 9 figures, accepted for publication in PASJ (Suzaku 2nd
Special Issue
Synthesis and characterization of glycolate precursors to MTiO3 (M = Ni2+, Co2+, Zn2+)
Novel glycolate precursors to metal titanates MTiO3 (M = Ni2+, Co2+, Zn2+) were synthesized by heating metal acetate and titanium isopropoxide in ethylene glycol up to 190 °C during distilling the water to avoid hydrolysis of precursors. These glycolate precursors were characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), thermal analysis (TG-DTA), and scanning electron microscopy (SEM). The obtained three isostructural glycolate precursors were containing metal (Ni, Co, Zn), titanium, and ethylene glycol with a ratio of 1:1:4. The crystal growth processes of three precursors were different from each other. These precursors revealed homogeneous and well-defined rod-like structure with 0.5–3.0 μm in thickness and 4–20 μm in length. The obtained metal titanates were consisted of microrods with 0.4–1.5 μm in thickness and 2–15 μm in length
Landiolol, an ultra-short acting beta-1 blocker, for preventing postoperative lung cancer recurrence : study protocol for a phase III, multicenter randomized trial with two parallel groups of patients
Background: Recurrence of cancer after curative surgery is a major problem after most cancer treatments. Increased sympathetic activity during the perioperative period could promote cancer cell invasion to blood vessels and angiogenesis, resulting in cancer metastasis. Recent studies showed that use of beta blockers can be associated with the prolonged survival of patients with cancer. The objective of this study is to evaluate the preventive effects of landiolol hydrochloride, which is an ultra-short-acting beta-1-selective blocker that has been developed in Japan, on reducing recurrence of cancer after curative surgery for patients with lung cancer. Methods: The present study is a phase III, multicenter, randomized trial with two parallel groups of patients with lung cancer, comparing surgery alone and surgery with landiolol administration for three days during the perioperative period. A total of 400 patients will be enrolled from 12 Japanese institutions. The primary endpoint is two-year relapse-free survival and overall survival after curative surgery for lung cancer. The secondary endpoints are additional treatment after recurrence of cancer, safety events, and the incidence of postoperative complications. Discussion: The principal question addressed in this trial is whether landiolol can reduce recurrence of cancer after curative surgery for lung cancer
Spectral Evolutions in Gamma-Ray Burst Exponential Decays Observed with Suzaku WAM
This paper presents a study on the spectral evolution of gamma-ray burst (GRB) prompt emissions observed with the Suzaku Wide-band All-sky Monitor (WAM). By making use of the WAM data archive, 6 bright GRBs exhibiting 7 well-separated fast-rise-exponential-decay (FRED) shaped light curves are presented, and the evaluated exponential decay time constants of the energy-resolved light curves from these FRED peak light curves are shown to indicate significant spectral evolution. The energy dependence of the time constants is well described with a power-law function, τ(E) ∝Eγ, where γ∼−(0.34±0.12) on average, although 5 FRED peaks show a consistent value of γ=−1/2, which is expected in synchrotron or inverse-Compton cooling models. In particular, 2 of the GRBs were located with accuracy sufficient to evaluate the time-resolved spectra with precise energy response matrices. Their behavior in spectral evolution suggests two different origins of emissions. In the case of GRB 081224, the derived 1-s time-resolved spectra are well described by a blackbody radiation model with a power-law component. The derived behavior of cooling is consistent with that expected from radiative cooling or expansion of the emission region. On the other hand, the other 1-s time-resolved spectra from GRB 100707A is well described by a Band GRB model as well as with the thermal model. Although relative poor statistics prevent us to conclude, the energy dependence in the decaying light curve is consistent with that expected in the former emission mechanism model.Part of this work was financially supported by the Ministry of Education, Culture, Sports, Science and Technology, Grant-in-Aid for Scientific Research No. 22340039