arXiv subjects

C. W. Yang

Publications and source records attributed to C. W. Yang.

6 recordsLinked to original sources

arXiv2020

Compact Radio Emission from Nearby Galaxies with Mid-infrared Nuclear Outbursts

We present 5.5 GHz observations with the VLA of a sample of nearby galaxies with energetic nuclear outbursts at mid-infrared (MIR) bands. These observations reach a uniform depth down to a median rms of ~10 uJy, representing one of most sensitive searches for radio emission associated with nuclear transients. We detect radio emission in 12 out of 16 galaxies at a level of >5sigma, corresponding to a detection rate of 75%. Such a high detection is remarkably different from previous similar searches in stellar tidal disruption events. The radio emission is compact and not resolved for the majority of sources on scales of ~<0.5" (<0.9 kpc at z<0.1). We find the possibility of the star-formation contributing to the radio emission is low, but an AGN origin remains a plausible scenario, especially for sources that show evidence of AGN activity in their optical spectra. If the detections could represent radio emission associated with nuclear transient phenomenon such as jet or outflow, we use the blast wave model by analogy with the GRB afterglows to describe the evolution of radio light curves. In this context, the observations are consistent with a decelerating jet with an energy of ~10^{51-52} erg viewed at 30\degree-60\degree off-axis at later times, suggesting that powerful jets may be ubiquitous among MIR-burst galaxies. Future continuous monitoring observations will be crucial to decipher the origin of radio emission through detections of potential flux and spectral evolution. Our results highlight the importance of radio observations to constrain the nature of nuclear MIR outbursts in galaxies.

astro-ph.HE↗

arXiv2020

Multi-wavelength observations of the BL Lac object Fermi J1544-0649: one year after its awakening

We report observations of a transient source \fermi\ from radio to \grs. \fermi\ was discovered by the {\it Fermi-LAT} in May 2017. Follow-up {\it Swift-XRT} observations revealed three flaring episodes through March 2018, and the peak X-ray flux is about $10^3$ higher than the {\it ROSAT all-sky survey (RASS)} flux upper limit. Optical spectral measurements taken by the {\it Magellan 6.5-m telescope} and the {\it Lick-Shane telescope} both show a largely featureless spectrum, strengthening the BL Lac interpretation first proposed by \citet{Bruni18}. The optical and mid-infrared (MIR) emission goes to a higher state in 2018, when the flux in high energies goes down to a lower level. Our {\it RATAN-600m} measurements at 4.8~GHz and 8.2~GHz do not indicate any significant radio flux variation over the monitoring seasons in 2017 and 2018, nor deviate from the archival {\it NVSS} flux level. During GeV flaring times, the spectrum is very hard ($Γ_γ\sim$1.7) in the GeV band and at times also very hard (($Γ_{\rm X}\lesssim2$) in the X-rays, similar to a high-synchrotron-peak (or even an extreme) BL Lac object, making \fermi\ a good target for ground-based {\it Cherenkov telescopes}.

astro-ph.HE↗

arXiv2019

Capability of detecting low energy events in JUNO Central Detector

The Jiangmen Underground Neutrino Observatory (JUNO) is an experimental project designed to determine the neutrino mass ordering and probe the fundamental properties of the neutrino oscillations. The JUNO central detector is a spherical liquid scintillator detector with a diameter of 35.4 m and equipped with approximately 18,000 20-inch PMTs. A trigger threshold of 0.5 MeV can be easily achieved by using a common multiplicity trigger and can meet the requirements for measuring neutrino mass ordering. However, it is essential to further reduce the trigger threshold for detecting solar neutrinos and supernova neutrinos. A sophisticated trigger scheme is proposed to achieve a low energy threshold by reducing the level of low energy radioactivity and dark noise coincidence. With the new trigger scheme, the events rate of the central detector from different types of sources have been carefully studied by using a detailed detector simulation. It shows that the trigger threshold can be reduced to 0.2 MeV, or even 0.1 MeV, if the concentration of $^{14}$C in liquid scintillator can be well controlled.

physics.ins-det↗

arXiv2016

Constraints on Axion couplings from the CDEX-1 experiment at the China Jinping Underground Laboratory

We report the results of searches for solar axions and galactic dark matter axions or axion-like particles with CDEX-1 experiment at the China Jinping Underground Laboratory, using 335.6 kg-days of data from a p-type point-contact germanium detector. The data are compatible with the background model and no excess signals are observed. Limits of solar axions on the model independent coupling $g_{Ae}<2.5\times10^{-11}$ from Compton, bremsstrahlung, atomic-recombination and deexcitation channel and $g^{\text{eff}}_{AN}\times g_{Ae}<6.1\times10^{-17}$ from $^{57}$Fe M1 transition at 90 % confidence level are derived. Within the framework of the DFSZ and KSVZ models, our results exclude the axion mass heavier than 0.9 eV/c$^{2}$ and 173 eV/c$^{2}$, respectively. The derived constraints for dark matter axions below 1 keV improves over the previous results.

hep-ex↗

arXiv2014

Measurement of intrinsic radioactive backgrounds from Cs-137 and U/Th chains in CsI(Tl) crystals

The inorganic CsI(Tl) crystal scintillator is a candidate served as an anti-compton detector for China Dark matter EXperiment (CDEX). Studying the intrinsic radiopurity of CsI(Tl) crystal is an issue of major importance. The timing, energy and spatial correlations, as well as the capability of pulse shape discrimination provide powerful methods for the measurement of intrinsic radiopurities. The experimental design, detector performance and event-selection algorithms are described. A total of 359*3 kg-days data from three prototypes of CsI(Tl) crystals were taken at China Jinping underground laboratory where offers a good shielding environment. The contamination levels of internal isotopes from Cs-137, Th-232 and U-238 series, as well as the upper bounds of U-235 series are reported. Identification of the whole alpha8 peaks from U/Th decay chains and derivation of those corresponding quenching factors are achieved.

physics.ins-det↗

arXiv2014

Limits on light WIMPs with a germanium detector at 177 eVee threshold at the China Jinping Underground Laboratory

The China Dark Matter Experiment reports results on light WIMP dark matter searches at the China Jinping Underground Laboratory with a germanium detector array with a total mass of 20 g. The physics threshold achieved is 177 eVee ("ee" represents electron equivalent energy) at 50% signal efficiency. With 0.784 kg-days of data, exclusion region on spin-independent coupling with the nucleon is derived, improving over our earlier bounds at WIMP mass less than 4.6 GeV.

hep-ex↗