97 research outputs found
Study of Negative-Ion TPC Using {\mu}-PIC for Directional Dark Matter Search
Negative-ion time projection chambers(TPCs) have been studied for low-rate
and high-resolution applications such as dark matter search experiments.
Recently, a full volume fiducialization in a self-triggering TPC was realized.
This innovative technology demonstrated a significant reduction in the
background with MWPC-TPCs. We studied negative-ion TPC using the {\mu}-PIC+GEM
system and obtained sufficient gas gain with CSgas and SF gas at
low pressures. We expect an improvement in detector sensitivity and angular
resolution with better electronics
Background contributions in the electron-tracking Compton camera onboard SMILE-2+
The Mega electron volt (MeV) gamma-ray observation is a promising diagnostic
tool for observing the universe. However, the sensitivity of MeV gamma-ray
telescopes is limited due to peculiar backgrounds, restricting the application
of MeV gamma rays for observation. Identification of backgrounds is crucial for
designing next-generation telescopes. Therefore, herein, we assessed the
background contribution in the electron-tracking Compton camera (ETCC) on board
the SMILE- 2+ balloon experiment. This assessment was performed using the Monte
Carlo simulation. The results revealed that the background below 400 keV
existed due to the atmospheric gamma-ray background, the
cosmic-ray/secondary-particle background, and the accidental background. On the
other hand, the unresolved background component, which was not likely to be
relevant to direct Compton-scattering events in the ETCC, was confirmed above
400 keV. Overall, this study demonstrated that the Compton-kinematics test
provides a powerful tool to remove the background and principally improves the
signal-to-noise ratio at 400 keV by an order of magnitude.Comment: 11 pages, 18 figure
Sumo Puff: Tidal Debris or Disturbed Ultra-Diffuse Galaxy?
We report the discovery of a diffuse stellar cloud with an angular extent
, which we term "Sumo Puff", in data from the Hyper
Suprime-Cam Subaru Strategic Program (HSC-SSP). While we do not have a redshift
for this object, it is in close angular proximity to a post-merger galaxy at
redshift and is projected within a few virial radii (assuming
similar redshifts) of two other galaxies, which we use to
bracket a potential redshift range of . The object's light
distribution is flat, as characterized by a low Sersic index (). It
has a low central -band surface brightness of mag
arcsec, large effective radius of (
kpc at and kpc at ), and an elongated
morphology (). Its red color () is consistent with a
passively evolving stellar population and similar to the nearby post-merger
galaxy, and we may see tidal material connecting Sumo Puff with this galaxy. We
offer two possible interpretations for the nature of this object: (1) it is an
extreme, galaxy-size tidal feature associated with a recent merger event, or
(2) it is a foreground dwarf galaxy with properties consistent with a quenched,
disturbed ultra-diffuse galaxy. We present a qualitative comparison with
simulations that demonstrates the feasibility of forming a structure similar to
this object in a merger event. Follow-up spectroscopy and/or deeper imaging to
confirm the presence of the bridge of tidal material will be necessary to
reveal the true nature of this object.Comment: 10 pages, 5 figures, submitted to PASJ for the HSC-SSP special issu
Development of Convolutional Neural Networks for an Electron-Tracking Compton Camera
Electron-tracking Compton camera, which is a complete Compton camera with
tracking Compton scattering electron by a gas micro time projection chamber, is
expected to open up MeV gamma-ray astronomy. The technical challenge for
achieving several degrees of the point spread function is the precise
determination of the electron-recoil direction and the scattering position from
track images. We attempted to reconstruct these parameters using convolutional
neural networks. Two network models were designed to predict the recoil
direction and the scattering position. These models marked 41degrees of the
angular resolution and 2.1mm of the position resolution for 75keV
electron simulation data in Argon-based gas at 2atm pressure. In addition,
the point spread function of ETCC was improved to 15degrees from
22degrees for experimental data of 662keV gamma-ray source. These
performances greatly surpassed that using the traditional analysis
A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam Survey
We report the discovery of a new ultra-faint dwarf satellite companion of the
Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru
Strategic Program. This new satellite, Virgo I, which is located in the
constellation of Virgo, has been identified as a statistically significant (5.5
sigma) spatial overdensity of star-like objects with a well-defined main
sequence and red giant branch in their color-magnitude diagram. The
significance of this overdensity increases to 10.8 sigma when the relevant
isochrone filter is adopted for the search. Based on the distribution of the
stars around the likely main sequence turn-off at r ~ 24 mag, the distance to
Virgo I is estimated as 87 kpc, and its most likely absolute magnitude
calculated from a Monte Carlo analysis is M_V = -0.8 +/- 0.9 mag. This stellar
system has an extended spatial distribution with a half-light radius of 38
+12/-11 pc, which clearly distinguishes it from a globular cluster with
comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites
known and is located beyond the reach of the Sloan Digital Sky Survey. This
demonstrates the power of this survey program to identify very faint dwarf
satellites. This discovery of VirgoI is based only on about 100 square degrees
of data, thus a large number of faint dwarf satellites are likely to exist in
the outer halo of the Milky Way.Comment: typos are corrected, 6 pages, 4 figures, accepted for publication in
Ap
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