arXiv subjects

J. Z. Wang

Publications and source records attributed to J. Z. Wang.

36 records · Page 2Linked to original sources

arXiv2021

Inflight performance of the GECAM Gamma-ray and Charge particle Detectors

The GECAM mission consists of two identical microsatellites (GECAM-A and GECAM-B). Each satellite is equipped with 25 gamma-ray detectors (GRD) and 8 charged particle detectors (CPD). The main scientific objective of the GECAM mission is to detect gamma-ray bursts (GRBs) associated with the gravitational wave events produced by the merging of binary compact stars. After the launch on Dec. 10, 2020 , we carried out a series of on orbit tests. This paper introduces the test results of the GECAM-B satellite. According to the in-flight performance, the energy band for gamma-ray detection of GECAM-B is from about 7 keV to 3.5 MeV. GECAM-B can achieve prompt localization of GRBs. For the first time, GECAM-B realized a quasi-real-time transmission of trigger information using Beidou-3 RDSS. Keywords GECAM, gamma-ray burst, gravitational wave, GRD, CPD

physics.ins-det↗

arXiv2021

The SiPM Array Data Acquisition Algorithm Applied to the GECAM Satellite Payload

The Gravitational Wave Burst High-energy Electromagnetic Counterpart All-sky Monitor (GECAM), consists of 2 small satellites that each contain 25 LaBr3 (lanthanum bromide doped with cerium chloride) detectors and 8 plastic scintillator detectors. The detector signals are read out using a silicon photomultiplier (SiPM) array. In this study, an acquisition algorithm for in-orbit real-time SiPM array data is designed and implemented, and the output event packet is defined. Finally, the algorithm's efficacy for event acquisition is verified.

astro-ph.IM↗

arXiv2021

Ground-based calibration and characterization of GRD of GECAM: 8-160 keV

As the main detector of the GECAM satellite, the calibration of the energy response and detection efficiency of the GRD detector is the main content of the ground-based calibration. The calibration goal requires the calibrated energy points to sample the full energy range (8 keV-2 MeV) as much as possible. The low energy band (8-160 keV) is calibrated with the X-ray beam, while the high energy band (>160 keV) with radioactive sources. This article mainly focuses on the calibration of the energy response and detection efficiency in the 8-160 keV with a refined measurement around the absorption edges of the lanthanum bromide crystal. The GRD performances for different crystal types, data acquisition modes, working modes, and incident positions are also analyzed in detail. We show that the calibration campaign is comprehensive, and the calibration results are generally consistent with simulations as expected.

astro-ph.IM↗

arXiv2021

GECAM detection of a bright type-I X-ray burst from 4U 0614+09: confirmation its spin frequency at 413 Hz

One month after launching Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM), a bright thermonuclear X-ray burst from 4U~0614+09, was observed on January 24, 2021. We report the time-resolved spectroscopy of the burst and a burst oscillation detection at 413 Hz with a fractional amplitude 3.4\% (rms). This coincides with the burst oscillation previously discovered with \textit{Swift}/BAT \citep{Strohmayer2008}, and therefore confirms the spin frequency of this source. This burst is the brightest one in the normal bursts (except the superburst) ever detected from 4U~0614+09, which leads to an upper limit of distance estimation as 3.1 kpc. The folded light curve during the burst oscillation shows a multi-peak structure, which is the first case observed during a single burst oscillation in nonpulsating sources. The multi-peak profile could be due to additional harmonics of the burst oscillation, which is corresponding to several brighter/fainter spots at the stellar surface.

astro-ph.HE↗

arXiv2021

Measurement of the cosmic ray helium energy spectrum from 70 GeV to 80 TeV with the DAMPE space mission

The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the DArk Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of $4.3σ$. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out.

astro-ph.HE↗

arXiv2020

A systematic observational study on Galactic interstellar ratio 18O/17O: I. C18O and C17O J=1-0 data analysis

The interstellar oxygen isotopic ratio of 18O/17O can reflect the relative amount of the secular enrichment by ejecta from high-mass versus intermediate-mass stars. Previous observations found a Galactic gradient of 18O/17O, i.e., low ratios in the Galactic center and large values in the Galactic disk, which supports the insideout formation scenario of our Galaxy. However, the observed objects are not many and, in particular, not so many at large galactocentric distances. Thus we started a systematic study on Galactic interstellar 18O/17O, through observations of C18O and C17O multi-transition lines toward a large sample of 286 sources (at least one order of magnitude larger than previous ones), from the Galactic center region to the far outer Galaxy (~22 kpc). Here we present our observations of J=1-0 lines of C18O and C17O, with the ARO12m and the IRAM 30m telescope. We detected successfully both C18O and C17O 1-0 lines for 34 sources among our IRAM30m sample of 50 targets and for 166 sources among our ARO12m sample of 260 targets. The C18O optical depth effect on our ratio results, evaluated by fitting results of C17O spectra with hyperfine components and our RADEX non-LTE model calculation for the strongest source, was found to be insignificant. Beam dilution does not seem to be a problem either, which was supported by the fact of no systematic variation between the isotopic ratio and the heliocentric distance, and consistent measured ratios from two telescopes for most of those detected sources. Our results, though there are still very few detections made for sources in the outer Galaxy, confirm the apparent 18O/17O gradient of 18O/17O = (0.10+-0.03)R_GC+(2.95+-0.30), with a Pearson's rank correlation coefficient R = 0.69. This is supported by the newest Galactic chemical evolution model including the impact of massive stellar rotators and novae.

astro-ph.GA↗

arXiv2019

Measurement of the cosmic-ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite

The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with two and a half years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time an experiment directly measures the cosmic ray protons up to ~100 TeV with a high statistics. The measured spectrum confirms the spectral hardening found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee, and sheds new light on the origin of Galactic cosmic rays.

astro-ph.HE↗

arXiv2019

The on-orbit calibration of DArk Matter Particle Explorer

The DArk Matter Particle Explorer (DAMPE), a satellite-based cosmic ray and gamma-ray detector, was launched on December 17, 2015, and began its on-orbit operation on December 24, 2015. In this work we document the on-orbit calibration procedures used by DAMPE and report the calibration results of the Plastic Scintillator strip Detector (PSD), the Silicon-Tungsten tracKer-converter (STK), the BGO imaging calorimeter (BGO), and the Neutron Detector (NUD). The results are obtained using Galactic cosmic rays, bright known GeV gamma-ray sources, and charge injection into the front-end electronics of each sub-detector. The determination of the boundary of the South Atlantic Anomaly (SAA), the measurement of the live time, and the alignments of the detectors are also introduced. The calibration results demonstrate the stability of the detectors in almost two years of the on-orbit operation.

astro-ph.IM↗

arXiv2019

The Potential of FAST in Detecting Celestial Hydroxyl Masers and Related Science Topics

The Five Hundred Meter Aperture Spherical Radio Telescope (FAST) will make contributions to the study of Galactic and extragalactic masers. The telescope, now finished construction and commissioning in China, has an innovative design that leads to the highest sensitivity of any single dish telescope in the world. FAST's potential for OH megamaser research is discussed, including the sky density of masers detectable in surveys. The scientific impact expected from FAST maser studies is also discussed.

astro-ph.GA↗

arXiv2019

Multi-outcome homodyne detection in a coherent-state light interferometer

The Cramér-Rao bound plays a central role in both classical and quantum parameter estimation, but finding the observable and the resulting inversion estimator that saturates this bound remains an open issue for general multi-outcome measurements. Here we consider multi-outcome homodyne detection in a coherent-light Mach-Zehnder interferometer and construct a family of inversion estimators that almost saturate the Cramér-Rao bound over the whole range of phase interval. This provides a clue on constructing optimal inversion estimators for phase estimation and other parameter estimation in any multi-outcome measurement.

quant-ph↗

arXiv2018

In-flight performance of the DAMPE silicon tracker

DAMPE (DArk Matter Particle Explorer) is a spaceborne high-energy cosmic ray and gamma-ray detector, successfully launched in December 2015. It is designed to probe astroparticle physics in the broad energy range from few GeV to 100 TeV. The scientific goals of DAMPE include the identification of possible signatures of Dark Matter annihilation or decay, the study of the origin and propagation mechanisms of cosmic-ray particles, and gamma-ray astronomy. DAMPE consists of four sub-detectors: a plastic scintillator strip detector, a Silicon-Tungsten tracKer-converter (STK), a BGO calorimeter and a neutron detector. The STK is composed of six double layers of single-sided silicon micro-strip detectors interleaved with three layers of tungsten for photon conversions into electron-positron pairs. The STK is a crucial component of DAMPE, allowing to determine the direction of incoming photons, to reconstruct tracks of cosmic rays and to estimate their absolute charge (Z). We present the in-flight performance of the STK based on two years of in-flight DAMPE data, which includes the noise behavior, signal response, thermal and mechanical stability, alignment and position resolution.

astro-ph.IM↗

arXiv2018

Internal alignment and position resolution of the silicon tracker of DAMPE determined with orbit data

The DArk Matter Particle Explorer (DAMPE) is a space-borne particle detector designed to probe electrons and gamma-rays in the few GeV to 10 TeV energy range, as well as cosmic-ray proton and nuclei components between 10 GeV and 100 TeV. The silicon-tungsten tracker-converter is a crucial component of DAMPE. It allows the direction of incoming photons converting into electron-positron pairs to be estimated, and the trajectory and charge (Z) of cosmic-ray particles to be identified. It consists of 768 silicon micro-strip sensors assembled in 6 double layers with a total active area of 6.6 m$^2$. Silicon planes are interleaved with three layers of tungsten plates, resulting in about one radiation length of material in the tracker. Internal alignment parameters of the tracker have been determined on orbit, with non-showering protons and helium nuclei. We describe the alignment procedure and present the position resolution and alignment stability measurements.

physics.ins-det↗

arXiv2017

Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

High energy cosmic ray electrons plus positrons (CREs), which lose energy quickly during their propagation, provide an ideal probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been directly measured up to $\sim 2$ TeV in previous balloon- or space-borne experiments, and indirectly up to $\sim 5$ TeV by ground-based Cherenkov $γ$-ray telescope arrays. Evidence for a spectral break in the TeV energy range has been provided by indirect measurements of H.E.S.S., although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range $25~{\rm GeV}-4.6~{\rm TeV}$ by the DArk Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The majority of the spectrum can be properly fitted by a smoothly broken power-law model rather than a single power-law model. The direct detection of a spectral break at $E \sim0.9$ TeV confirms the evidence found by H.E.S.S., clarifies the behavior of the CRE spectrum at energies above 1 TeV and sheds light on the physical origin of the sub-TeV CREs.

astro-ph.HE↗

arXiv2017

Millimeter Observations of the disk around GW Ori

The GW Ori system is a pre-main sequence triple system (GW Ori A/B/C) with companions (GW Ori B/C) at $\sim$1 AU and $\sim$8 AU, respectively, from the primary (GW Ori A). The primary of the system has a mass of 3.9 $M_{\odot}$, but shows a spectral type of G8. Thus, GW Ori A could be a precursor of a B star, but it is still at an earlier evolutionary stage than Herbig Be stars. GW Ori provides us an ideal target for experiments and observations (being a "blown-up" upscaled Solar System with a very massive "sun" and at least two "upscaled planets"). We present the first spatially-resolved millimeter interferometric observations of the disk around the triple pre-main-sequence system GW Ori, obtained with the the Submillimeter Array, both in continuum and in the $^{12}{\rm CO} J=2-1$, $^{13}{\rm CO} J=2-1$, and ${\rm C^{18}O} J=2-1$ lines. These new data reveal a huge, massive, and bright disk in the GW Ori system. The dust continuum emission suggests a disk radius around 400 AU. But, the $^{12}{\rm CO} J=2-1$ emission shows much more extended disk with a size around 1300 AU. Due to the spatial resolution ($\sim$1$"$), we cannot detect the gap in the disk which is inferred from spectral energy distribution (SED) modeling. We characterize the dust and gas properties in the disk by comparing the observations with the predictions from the disk models with various parameters calculated with a Monte Carlo radiative transfer code RADMC-3D. The disk mass is around 0.12 $M_{\odot}$, and the disk inclination with respect to the line of sight is around $\sim$ 35$^\circ$. The kinematics in the disk traced by the CO line emission strongly suggest that the circumstellar material in the disk is in Keplerian rotation around GW Ori. Tentatively substantial ${\rm C^{18}O}$ depletion in gas phase is required to explain the characteristics of the line emission from the disk.

astro-ph.SR↗

arXiv2014

The silicon matrix for the prototype for the Dark Matter Particle Explorer

A new generation detector for the high energy cosmic ray - the DAMPE(DArk Matter Particle Explorer) is a satellite based project. Its main object is the measurement of energy spectrum of cosmic ray nuclei from 100GeV to 100TeV, the high energy electrons and gamma ray from 5GeV to 10TeV. A silicon matrix detector described in this paper, is employed for the sea level cosmic ray energy and position detection while the prototype testing of the DAMPE. This matrix is composed by the 180 silicon PIN detectors, which covers an area of 32*20 cm2. The primary testing results are shown including MIPs energy spectrum and the position sensitive map.

physics.ins-det↗

arXiv2002

Precise Measurements of Atmospheric Muon Fluxes with the BESS Spectrometer

The vertical absolute fluxes of atmospheric muons and muon charge ratio have been measured precisely at different geomagnetic locations by using the BESS spectrometer. The observations had been performed at sea level (30 m above sea level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada. The vertical cutoff rigidities in Tsukuba (36.2 N, 140.1 E) and in Lynn Lake (56.5 N, 101.0 W) are 11.4 GV and 0.4 GV, respectively. We have obtained vertical fluxes of positive and negative muons in a momentum range from 0.6 to 20 GeV/c with systematic errors less than 3 % in both measurements. By comparing the data collected at two different geomagnetic latitudes, we have seen an effect of cutoff rigidity. The dependence on the atmospheric pressure and temperature, and the solar modulation effect have been also clearly observed. We also clearly observed the decrease of charge ratio of muons at low momentum side with at higher cutoff rigidity region.

astro-ph↗

arXiv2002

Measurements of Cosmic-ray Low-energy Antiproton and Proton Spectra in a Transient Period of the Solar Field Reversal

The energy spectra of cosmic-ray low-energy antiprotons and protons have been measured by BESS in 1999 and 2000, during a period covering the solar magnetic field reversal. Based on these measurements, a sudden increase of the antiproton to proton flux ratio following the solar magnetic field reversal was observed, and it generally agrees with a drift model of the solar modulation.

astro-ph↗

arXiv2000

Precise Measurement of Cosmic-Ray Proton and Helium Spectra with the BESS Spectrometer

We report cosmic-ray proton and helium spectra in energy ranges of 1 to 120 GeV and 1 to 54 GeV/nucleon, respectively, measured by a balloon flight of the BESS spectrometer in 1998. The magnetic-rigidity of the cosmic-rays was reliably determined by highly precise measurement of the circular track in a uniform solenoidal magnetic field of 1 Tesla. Those spectra were determined within overall uncertainties of +-5 % for protons and +- 10 % for helium nuclei including statistical and systematic errors.

astro-ph↗