arXiv subjects

Yi-Zhong Fan

Publications and source records attributed to Yi-Zhong Fan.

At least 181 records · Page 10Linked to original sources

arXiv2018

A Method of Alignment of the Plastic Scintillator Detector of DAMPE

The Plastic Scintillator Detector (PSD) of the DArk Matter Particle Explorer (DAMPE) is designed to measure cosmic ray charge (Z) and to act as a veto detector for gamma-ray identification. In order to fully exploit the charge identification potential of the PSD and to enhance its capability to identify the gamma ray events, we develop a PSD detector alignment method. The path length of a given track in the volume of a PSD bar is derived taking into account the shift and rotation alignment corrections. By examining energy spectra of corner-passing events and fully contained events, position shifts and rotations of all PSD bars are obtained, and found to be on average about 1mm and 0.0015 radian respectively. To validate the alignment method, we introduce the artificial shifts and rotations of PSD bars in the detector simulation. These shift and rotation parameters can be recovered successfully by the alignment procedure. As a result of the PSD alignment procedure, the charge resolution of the PSD is improved from $4\%$ to $8\%$ depending on the nuclei.

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arXiv2018

Active galactic nuclei with GeV activities and the PeV neutrino source candidate TXS 0506+056

On 2017 September 22 the IceCube neutrino observatory detected a track-like, very-high-energy event (IceCube-170922A) that is spatially associated with TXS 0506+056, a quasar at a redshift of $z=0.3365$. This source is characterized by the increased acitivies in a very wide energy range (from radio to TeV) during these days. To investigate the possible connection of the PeV neutrino emission with the GeV activity of blazars, in this work we select 116 bright sources and analyze their lightcurves and spectra. We focus on the sources displaying GeV activities. Among these blazars, TXS 0506+056 seems to be typical in many aspects but is distinguished by the very strong GeV activties. We suggest to search for neutrino outburst in the historical data of IceCube, as recently done for TXS 0506+056, from the directions of these more energetic and harder blazars with strong GeV activities.

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arXiv2018

Revisit of cosmic ray antiprotons from dark matter annihilation with updated constraints on the background model from AMS-02 and collider data

We study the cosmic ray antiprotons with updated constraints on the propagation, proton injection, and solar modulation parameters based on the newest AMS-02 data near the Earth and Voyager data in the local interstellar space, and on the cross section of antiproton production due to proton-proton collisions based on new collider data. We use a Bayesian approach to properly consider the uncertainties of the model predictions of both the background and the dark matter (DM) annihilation components of antiprotons. We find that including an extra component of antiprotons from the annihilation of DM particles into a pair of quarks can improve the fit to the AMS-02 antiproton data considerably. The favored mass of DM particles is about $60\sim100$ GeV, and the annihilation cross section is just at the level of the thermal production of DM ($\langleσv\rangle \sim O(10^{-26})$ cm$^3$~s$^{-1}$).

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arXiv2018

Search for gamma-ray emission from the nearby dwarf spheroidal galaxies with 9 years of Fermi-LAT data

In this work, we search for $γ$-ray emission from the directions of some nearby Milky Way dwarf spheroidal galaxies (dSphs) and candidates with the publicly-available Pass 8 data of Fermi-LAT. Our sample includes 12 sources with the distances $<50$ kpc. Very weak $γ$-ray excesses ($\sim 2σ$) are found in some dSphs/candidates, consistent with that reported in the previous literature. Intriguingly, the peak test statistic (TS) value of the weak emission from the direction of Reticulum II rises continually. If interpreted as dark matter (DM) annihilation, the peak TS value is 13.5 for the annihilation channel of $χχ\rightarrow τ^{+}τ^{-}$ and the DM mass of $m_χ\sim 16$ GeV. The combination of all these nearby sources yields a more significant (with local significance $> 4σ$) $γ$-ray signal.

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arXiv2018

Constraints on axion-like particle properties with very high energy gamma-ray observations of Galactic sources

Axion-like particles (ALPs) can oscillate to photons and vice versa in electromagnetic fields. The photon-ALP oscillation provides an attractive solution to the apparent transparency of the Universe to TeV photons. The allowed parameter regions for the ALP mass $m_{\rm a}\leq 10^{-7}$ eV have been tightly constrained by the Fermi-LAT and H.E.S.S observations of some extragalactic sources. In this work we show for the first time that the H.E.S.S observations of some TeV sources in the Galactic plane exclude the highest ALP mass region (i.e., $m_{\rm a}\sim {\rm a ~few\times 10^{-7}}$ eV) that accounts for the TeV transparency of the Universe. The upcoming CTA observations of the Galactic TeV sources are shown to be able to improve the constraints significantly.

hep-ph↗

arXiv2018

Total gravitational mass of the Galactic Double Neutron Star systems: evidence for a bimodal distribution

So far, in total 15 double neutron star systems (DNSs) with a reliable measurement of the total gravitational mass ($M_{\rm T}$) have been detected in the Galaxy. In this work we study the distribution of $M_{\rm T}$. The data prefer the double Gaussian distribution over a single Gaussian distribution and the low and high mass populations center at $M_{\rm T}\sim 2.58M_\odot$ and $\sim 2.72M_\odot$, respectively. The progenitor stars of GW170817 have a $M_{\rm T}=2.74^{+0.04}_{-0.01}M_\odot$, falling into the high mass population. With a local neutron star merger rate of $\sim 10^{3}~{\rm Gpc^{-3}~yr^{-1}}$, supposing the $M_{\rm T}$ of those merging neutron stars also follow the double Gaussian distribution, the upcoming runs of the advanced LIGO/Virgo will soon detect some events with a $M_{\rm T}\lesssim 2.6M_\odot$ that can effectively probe the equation of state of the neutron stars and the distribution function is expected to be reliably reconstructed in the next decade.

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arXiv2018

GW170817 and the prospect of forming supramassive remnants in neutron star mergers

The gravitational wave data of GW170817 favor the equation of state (EoS) models that predict compact neutron stars (NSs), consistent with the radius constraints from X-ray observations. Motivated by such a remarkable progress, we examine the fate of the remnants formed in NS mergers and focus on the roles of the angular momentum and the mass distribution of the binary NSs. In the mass shedding limit (for which the dimensionless angular momentum equals to the Keplerian value, i.e., $j=j_{\rm Kep}$), the adopted { seven EoS models, except H4 and ALF2,} yield supramassive NSs in more than half of the mergers. However, for $j\lesssim 0.7j_{\rm Kep}$, the presence or absence of a non-negligible fraction of supramassive NSs formed in the mergers depends sensitively on both the EoS and the mass distribution of the binary systems. The NS mergers with a total gravitational mass $\leq 2.6M_\odot$ are found to be able to shed valuable light on both the EoS model and the angular momentum of the remnants if supramassive NSs are still absent. We have also discussed the uncertainty on estimating the maximum gravitational mass of non-rotating NSs ($M_{\rm max}$) due to the unknown $j$ of the pre-collapse remnants. With the data of GW170817 and the assumption of the mass loss of $0.03M_\odot$, we have $M_{\rm max}<(2.19,~2.32)M_\odot$ (90\% confidence level) for $j=(1.0,~0.8)j_{\rm Kep}$, respectively.

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arXiv2018

A model explaining neutrino masses and the DAMPE cosmic ray electron excess

We propose a flavored $U(1)_{eμ}$ neutrino mass and dark matter~(DM) model to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only the first two lepton generations of the Standard Model are charged under the new $U(1)_{eμ}$ gauge symmetry. A vector-like fermion $ψ$, which is our DM candidate, annihilates into $e^{\pm}$ and $μ^{\pm}$ via the new gauge boson $Z'$ exchange and accounts for the DAMPE excess. We have found that the data favors a $ψ$ mass around 1.5~TeV and a $Z'$ mass around 2.6~TeV, which can potentially be probed by the next generation lepton colliders and DM direct detection experiments.

hep-ph↗

arXiv2018

Neutrinos from Choked Jets Accompanied by Type-II Supernovae

The origin of the IceCube neutrinos is still an open question. Upper limits from diffuse gamma-ray observations suggest that the neutrino sources are either distant or hidden from gamma-ray observations. It is possible that the neutrinos are produced in jets that are formed in the core-collapsing massive stars and fail to break out, the so-called choked jets. We study neutrinos from the jets choked in the hydrogen envelopes of red supergiant stars. Fast photo-meson cooling softens the neutrino spectrum, making it difficult to explain the PeV neutrinos observed by IceCube in a one-component scenario, but a two-component model can explain the spectrum. Furthermore, we predict that a newly born jet-driven type-II supernova may be observed to be associated with a neutrino burst detected by IceCube.

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arXiv2018

Short GRBs: opening angles, local neutron star merger rate and off-axis events for GRB/GW association

The jet breaks in the afterglow lightcurves of short gamma-ray bursts (SGRBs), rarely detected so far, are crucial for estimating the half-opening angles of the ejecta ($θ_{\rm j}$) and hence the neutron star merger rate. In this work we report the detection of jet decline behaviors in GRB 150424A and GRB 160821B and find $θ_{\rm j}\sim 0.1$ rad. Together with five events reported before 2015 and other three "identified" recently (GRB 050709, GRB 060614 and GRB 140903A), we have a sample consisting of nine SGRBs and one long-short GRB with reasonably estimated $θ_{\rm j}$. In particular, three {\it Swift} bursts in the sample have redshifts $z\leq 0.2$, with which we estimate the local neutron star merger rate density {to be $\sim 1109^{+1432}_{-657}~{\rm Gpc^{-3}~yr^{-1}}$ or $162^{+140}_{-83} {\rm Gpc^{-3}yr^{-1}}$ if the narrowly-beamed GRB 061201 is excluded}. Inspired by the typical $θ_{\rm j}\sim 0.1$ rad found currently, we further investigate whether the off-beam GRBs (in the uniform jet model) or the off-axis events (in the structured jet model) can significantly enhance the GRB/GW association or not. For the former the enhancement is at most moderate, while for the latter the enhancement can be much greater and a high GRB/GW association probability of $\sim 10\%$ is possible. We also show that the data of GRB 160821B may contain a macronova/kilonova emission component with a temperature of $\sim 3100$ K at $\sim 3.6$ days after the burst and more data are needed to ultimately clarify.

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arXiv2018

Searching for spectral oscillations due to photon-axionlike particle conversion using the Fermi-LAT observations of bright supernova remnants

Axionlike-particles (ALPs) are one promising type of dark matter candidate particle that may generate detectable effects on $γ$-ray spectra other than the canonical weakly interacting massive particles. In this work we search for such oscillation effects in the spectra of supernova remnants caused by the photon-ALP conversion, using the Fermi Large Area Telescope data. Three bright supernova remnants, IC443, W44, and W51C, are analyzed. The inclusion of photon-ALP oscillations yields an improved fit to the $γ$-ray spectrum of IC443, which gives a statistical significance of $4.2σ$ in favor of such spectral oscillation. However, the best-fit parameters of ALPs ($m_{a}=6.6\,{\rm neV}$, $g_{aγ}=13.4 \times 10^{-11}\,{\rm GeV}^{-1}$) are in tension with the upper bound ($g_{aγ}< 6.6 \times 10^{-11}\,{\rm GeV}^{-1}$) set by the CAST experiment. It is difficult to explain the results using the systematic uncertainties of the flux measurements. We speculate that the "irregularity" displayed in the spectrum of IC443 may be due to the superposition of the emission from different parts of the remnant.

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arXiv2018

New Bounds on Axion-Like Particles From the Fermi Large Area Telescope observation of PKS $2155-304$

The axion-like particle (ALP)-photon mixing in the magnetic field around $γ$-ray sources or along the line-of-sight could induce oscillation between photons and ALPs, which then causes irregularities in the $γ$-ray spectra. In this work we try to search for such spectral irregularities in the spectrum of PKS $2155-304$ using 8.6 years of the Fermi Large Area Telescope (Fermi-LAT) data. No significant evidence for the presence of ALP-photon oscillation is obtained, and the parameter space of ALPs is constrained. The exclusion region sensitively depends on the poorly known magnetic field of host galaxy cluster of PKS $2155-304$. If the magnetic field is as high as $\sim 10~{\rm μG}$, the "hole"-like parameter region allowed in Ref.~\cite{Fermi} can be ruled out.

hep-ph↗

arXiv2018

How Special Is GRB 170817A?

GRB 170817A is the first short gamma-ray burst (GRB) with direct detection of the gravitational-wave radiation and also the spectroscopically identified macronova emission (i.e., AT 2017gfo). The prompt emission of this burst, however, is underluminous in comparison with the other short GRBs with known redshift. In this work, we examine whether GRB 170817A is indeed unique. We firstly show that GRB 130603B/macronova may be the on-axis "analogs" of GRB 170817A/AT 2017gfo, and the extremely dim { but long-lasting} afterglow emission of GRB 170817A may suggest a low number density ($\sim 10^{-5}~{\rm cm^{-3}}$) of its circumburst medium { and a structured outflow}. We then discuss whether GRB 070923, GRB 080121, GRB 090417A, GRB 111005A, and GRB 170817A form a new group of very nearby underluminous GRBs originated from neutron star mergers. If the short events GRB 070923, GRB 080121, and GRB 090417A are indeed at a redshift of $\sim 0.076,~0.046,~0.088$, respectively, their isotropic energies of the prompt emission are $\sim 10^{47}$ erg and thus comparable to the other two events. The non-detection of optical counterparts of GRB 070923, GRB 080121, GRB 090417A, and GRB 111005A, however, strongly suggests that the macronovae from neutron star mergers are significantly diverse in luminosities or, alternatively, there is the other origin channel (for instance, the white dwarf and black hole mergers). We finally suggest that GW170817/GRB 170817A are likely not alone and similar events will be detected by the upgraded/upcoming gravitational-wave detectors and the electromagnetic monitors.

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arXiv2018

Fermi Large Area Telescope detection of gamma-ray emission from the direction of supernova iPTF14hls

The remnant of supernova explosion is widely believed to be the acceleration site of high-energy cosmic ray particles. The acceleration timescale is, however, typically very long. Here we report the detection of a variable $γ$-ray source with the Fermi Large Area Telescope, which is positionally and temporally consistent with a peculiar supernova, iPTF14hls. A quasi-stellar object SDSS J092054.04+504251.5, which is probably a blazar according to the infrared data, is found in the error circle of the $γ$-ray source. More data about the $γ$-ray source and SDSS J092054.04+504251.5 are needed to confirm their association. On the other hand, if the association between the $γ$-ray source and the supernova is confirmed, this would be the first time to detect high-energy $γ$-ray emission from a supernova, suggesting very fast particle acceleration by supernova explosions.

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arXiv2018

Detection of the Characteristic Pion-Decay Signature in the Molecular Clouds

The $γ$-ray emission from molecular clouds is widely believed to have a hadronic origin, while unequivocal evidence is still lacking. In this work, we analyze the Fermi-LAT Pass 8 publicly available data accumulated from 2008 August 4 to 2017 June 29 and report the significant detection of a characteristic $π^0$-decay feature in the $γ$-ray spectra of the molecular clouds Orion A and Orion B. This detection provides a direct evidence for the hadronic origin of their $γ$-ray emission.

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arXiv2018

GRB 111005A at Z = 0.0133 and the Prospect of Establishing Long-short GRB/GW Association

GRB 111005A, one long duration gamma-ray burst (GRB) occurred within a metal-rich environment that lacks massive stars with $M_{\rm ZAMS}\geq 15M_\odot$, is not coincident with supernova emission down to stringent limit and thus should be classified as a "long-short" GRB (lsGRB; also known as SN-less long GRB or hybrid GRB), like GRB 060505 and GRB 060614. In this work we show that in the neutron star merger model, the non-detection of the optical/infrared emission of GRB 111005A requires a sub-relativistic neutron-rich ejecta with the mass of $\leq 0.01~M_\odot$, (significantly) less massive than that of GRB 130603B, GRB 060614 and GRB 050709. The lsGRBs are found to have a high rate density and the neutron star merger origin model can be unambiguously tested by the joint observations of the second generation gravitational wave (GW) detectors and the full-sky gamma-ray monitors such as Fermi-GBM and the proposing GECAM. If no lsGRB/GW association is observed in 2020s, alternative scenarios have to be systematically investigated. With the detailed environmental information achievable for the very-nearby events, a novel kind of merger or explosion origin may be identified.

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arXiv2018

Is the gamma-ray emission around the Coma galaxy cluster a dark matter origin?

Recently, gamma-ray emission in the direction of Coma, with a TS value of $\sim 40$, has been reported. In this work we will discuss the possibility of such a residual emission coming from dark matter annihilation. Our results show that the gamma-ray emission within the Coma region is also spatially correlated to the mass distribution derived from weak gravitational lensing measurements very well. However the dark matter models are not supported by the spectral analysis results and constraints by observations of other targets. Thus we derive the upper limits of the dark matter annihilation cross section according to the observation of the Coma region.

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arXiv2017

Detection of GeV $γ$-ray emission in the direction of HESS J1731-347 with Fermi-LAT

We report the detection of GeV $γ$-ray emission from supernova remnant HESS J1731-347 using 9 years of {\it Fermi} Large Area Telescope data. We find a slightly extended GeV source in the direction of HESS J1731-347. The spectrum above 1 GeV can be fitted by a power-law with an index of $Γ= 1.77\pm0.14$, and the GeV spectrum connects smoothly with the TeV spectrum of HESS J1731-347. Either a hadronic-leptonic or a pure leptonic model can fit the multi-wavelength spectral energy distribution of the source. However, the hard GeV $γ$-ray spectrum is more naturally produced in a leptonic (inverse Compton scattering) scenario, under the framework of diffusive shock acceleration. We also searched for the GeV $γ$-ray emission from the nearby TeV source HESS J1729-345. No significant GeV $γ$-ray emission is found, and upper limits are derived.

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