4 research outputs found
Gamma-Ray Burst Polarimeter - GAP - aboard the Small Solar Power Sail Demonstrator IKAROS
The small solar power sail demonstrator "IKAROS" is a Japanese engineering
verification spacecraft launched by H-IIA rocket on May 21, 2010 at JAXA
Tanegashima Space Center. IKAROS has a huge sail with 20 m in diameter which is
made of thin polyimide membrane. This sail converts the solar
radiation-pressure into the propulsion force of IKAROS and accelerates the
spacecraft. The Gamma-Ray Burst Polarimeter (GAP) aboard IKAROS is the first
polarimeter to observe the gamma-ray polarization of Gamma-Ray Bursts (GRBs)
during the IKAROS cruising phase. GAP is a tinny detector of 3.8 kg in weight
and 17 cm in size with an energy range between 50-300 keV. The GAP detector
also plays a role of the interplanetary network (IPN) to determine the GRB
direction. The detection principle of gamma-ray polarization is the anisotropy
of the Compton scattering. GAP works as the GRB polarimeter with the full
coincidence mode between the central plastic and the surrounding CsI detectors.
GAP is the first instrument, devoted for the observation of gamma-ray
polarization in the astronomical history. In this paper, we present the GAP
detector and its ground and onboard calibrations.Comment: Submitted to Publications of the Astronomical Society of Japan
(PASJ), 23 pages, 14 figure
Strict Limit on CPT Violation from Polarization of Gamma-Ray Bursts
We report the strictest observational verification of CPT invariance in the
photon sector, as a result of gamma-ray polarization measurement of distant
gamma-ray bursts (GRBs), which are brightest stellar-size explosions in the
universe. We detected the gamma-ray polarization of three GRBs with high
significance, and the source distances may be constrained by a well-known
luminosity indicator for GRBs. For the Lorentz- and CPT-violating dispersion
relation E_{\pm}^2=p^2 \pm 2\xi p^3/M_{Pl}, where \pm denotes different
circular polarization states of the photon, the parameter \xi is constrained as
|\xi|<O(10^{-15}). Barring precise cancellation between quantum gravity effects
and dark energy effects, the stringent limit on the CPT-violating effect leads
to the expectation that quantum gravity presumably respects the CPT invariance.Comment: 4 pages; accepted for publication in Physical Review Letters;
redshift estimates of GRBs changed (i.e z=0.382 was wrong for GRB 110721A)
and calculations of \xi limit improved from the previous versio