arXiv subjects

T. Tamba

Publications and source records attributed to T. Tamba.

5 recordsLinked to original sources

arXiv2025

Gamma-Ray and AntiMatter Survey(GRAMS) experiment

The Gamma-Ray and AntiMatter Survey (GRAMS) is a next-generation experiment using a Liquid Argon Time Projection Chamber (LArTPC) detector to measure MeV gamma rays and antiparticles. MeV gamma-ray observations are important for understanding multi-messenger and time-domain astronomy, enabling exploration of the universe's most potent events, such as supernovae and neutron star mergers. Despite the significance of MeV gamma-rays, GRAMS could also explore the so-called 'MeV gap' region to improve MeV gamma-ray measurement sensitivity that was restricted by the challenge of accurately reconstructing Compton events. Aside from gamma-ray detection, the GRAMS proposed method also serves as an antiparticle spectrometer, targeting the low-energy range of cosmic antinuclei measurements. This work will provide updates on the current status and progress towards the prototype balloon flight with a small-scale LArTPC (pGRAMS) scheduled for early 2026, as well as the recent progress on antihelium-3 sensitivity calculation.

hep-ex↗

arXiv2025

Antihelium-3 Sensitivity for the GRAMS Experiment

The Gamma-Ray and AntiMatter Survey (GRAMS) is a next-generation balloon/satellite mission utilizing a Liquid Argon Time Projection Chamber (LArTPC) detector to measure both MeV gamma rays and antinuclei produced by dark matter annihilation or decay. The GRAMS can identify antihelium-3 events based on the measurements of X-rays and charged pions from the decay of the exotic atoms, Time of Flight (TOF), energy deposition, and stopping range. This paper shows the antihelium-3 sensitivity estimation using a GEANT4 Monte Carlo simulation. For the proposed long-duration balloon (LDB) flight program (35 days $ \times $ 3 flights) and future satellite mission (2-year observation / 10-year observation), the sensitivities become 1.47 $\times$ 10$^{-7}$ [m$^2$ s sr GeV/n]$^{-1}$ and 1.55 $\times$ 10$^{-9}$ [m$^2$ s sr GeV/n]$^{-1}$ / $3.10\times10^{-10}$ [m$^2$ s sr GeV/n]$^{-1}$, respectively. The results indicate that GRAMS can extensively investigate various dark matter models through the antihelium-3 measurements.

hep-ex↗

arXiv2024

First operation of LArTPC in the stratosphere as an engineering GRAMS balloon flight (eGRAMS)

GRAMS (Gamma-Ray and AntiMatter Survey) is a next-generation balloon/satellite experiment utilizing a LArTPC (Liquid Argon Time Projection Chamber), to simultaneously target astrophysical observations of cosmic MeV gamma-rays and conduct an indirect dark matter search using antimatter. While LArTPCs are widely used in particle physics experiments, they have never been operated at balloon altitudes. An engineering balloon flight with a small-scale LArTPC (eGRAMS) was conducted on July 27th, 2023, to establish a system for safely operating a LArTPC at balloon altitudes and to obtain cosmic-ray data from the LArTPC. The flight was launched from the Japan Aerospace Exploration Agency's (JAXA) Taiki Aerospace Research Field in Hokkaido, Japan. The total flight duration was 3 hours and 12 minutes, including a level flight of 44 minutes at a maximum altitude of 28.9 km. The flight system was landed on the sea and successfully recovered. The LArTPC was successfully operated throughout the flight, and about 0.5 million events of the cosmic-ray data including muons, protons, and Compton scattering gamma-ray candidates, were collected. This pioneering flight demonstrates the feasibility of operating a LArTPC in high-altitude environments, paving the way for future GRAMS missions and advancing our capabilities in MeV gamma-ray astronomy and dark matter research.

astro-ph.IM↗

arXiv2023

Gas selection for Xe-based LCP-GEM detectors onboard the CubeSat X-ray observatory NinjaSat

We present a gas selection for Xe-based gas electron multiplier (GEM) detectors, Gas Multiplier Counters (GMCs) onboard the CubeSat X-ray observatory NinjaSat. To achieve an energy bandpass of 2-50 keV, we decided to use a Xe-based gas mixture at a pressure of 1.2 atm that is sensitive to high-energy X-rays. In addition, an effective gain of over 300 is required for a single GEM so that the 2 keV X-ray signal can be sufficiently larger than the electrical noise. At first, we measured the effective gains of GEM in nine Xe-based gas mixtures (combinations of Xe, Ar, CO2, CH4, and dimethyl ether; DME) at 1.0 atm. The highest gains were obtained with Xe/Ar/DME mixtures, while relatively lower gains were obtained with Xe/Ar/CO2, Xe/Ar/CH4, and Xe+quencher mixtures. Based on these results, we selected the Xe/Ar/DME (75%/24%/1%) mixture at 1.2 atm as the sealed gas for GMC. Then we investigated the dependence of an effective gain on the electric fields in the drift and induction gaps ranging from 100-650 V cm$^{-1}$ and 500-5000 V cm$^{-1}$, respectively, in the selected gas mixture. The effective gain weakly depended on the drift field while it was almost linearly proportional to the induction field: 2.4 times higher at 5000 V cm$^{-1}$ than at 1000 V cm$^{-1}$. With the optimal induction and drift fields, the flight model GMC achieves an effective gain of 460 with an applied GEM voltage of 590 V.

astro-ph.IM↗

arXiv2021

Discovery of 40.5 ks Hard X-ray Pulse-Phase Modulations from SGR 1900+14

X-ray timing properties of the magnetar SGR 1900+14 were studied, using the data taken with Suzaku in 2009 and NuSTAR in 2016, for a time lapse of 114 ks and 242 ks, respectively. On both occasions, the object exhibited the characteristic two-component spectrum. The soft component, dominant in energies below $\sim 5$ keV, showed a regular pulsation, with a period of $P=5.21006$ s as determined with the Suzaku XIS, and $P=5.22669$ with NuSTAR. However, in $\gtrsim 6$ keV where the hard component dominates, the pulsation became detectable with the Suzaku HXD and NuSTAR, only after the data were corrected for periodic pulse-phase modulation, with a period of $T=40-44$ ks and an amplitude of $\approx 1$ s. Further correcting the two data sets for complex energy dependences in the phase-modulation parameters, the hard X-ray pulsation became fully detectable, in 12-50 keV with the HXD, and 6-60 keV with NuSTAR, using a common value of $T=40.5 \pm 0.8$ ks. Thus, SGR 1900+14 becomes a third example, after 4U 0142+61 and 1E 1547$-$5408, to show the hard X-ray pulse-phase modulation, and a second case of energy dependences in the modulation parameters. The neutron star in this system is inferred to perform free precession, as it is axially deformed by $\approx P/T =1.3 \times 10^{-4}$ presumably due to $\sim 10^{16}$ G toroidal magnetic fields. As a counter example, the Suzaku data of the binary pulsar 4U 1626-67 were analyzed, but no similar effect was found. These results altogether argue against the accretion scenario for magnetars.

astro-ph.HE↗