arXiv subjects

Yuliang Xin

Publications and source records attributed to Yuliang Xin.

14 recordsLinked to original sources

arXiv2025

The GeV $γ$-ray emission from the composite SNR CTB 87

We report the GeV $γ$-ray emission around the composite supernova remnant (SNR) CTB 87 with more than 16 yrs PASS 8 data recorded by the Fermi Large Area Telescope. Two separate point sources with the different GeV spectra are identified in this region: one has a soft $γ$-ray spectrum, likely due to interactions between the SNR shock and molecular clouds (MCs); and another source with a hard GeV $γ$-ray spectrum aligns with the TeV spectrum of VER J2016+371, suggesting it as the GeV counterpart. Considering the observations of CTB 87 in the radio and X-ray bands, VER J2016+371 is proposed to originate from the pulsar wind nebula (PWN) associated with PSR J2016+3711. A leptonic model with a broken power-law electron distribution could explain the multi-wavelength data of VER J2016+371, with fitted parameters matching typical $γ$-ray PWNe. Deeper searching for the SNR shock of CTB 87 in other bands and the future TeV observations by LHAASO and CTA are crucial to reveal the nature of CTB 87.

astro-ph.HE↗

arXiv2024

Revision of the GeV $γ$-ray Emission in the Region of HESS J1813-178 with Fermi-LAT

HESS J1813-178 is one of the brightest and most compact TeV $γ$-ray sources, and whether its $γ$-ray emission is associated with supernova remnant (SNR), pulsar wind nebula (PWN) or young stellar cluster (YSC) is still under debate. By analysing the GeV $γ$-ray data in the field of HESS J1813-178 using 14 years of PASS 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT), we report the discovery of three different sources with different spectra in this region. The hard source with a power law spectral index of 2.11 $\pm$ 0.08 has a small size extension, which is spatially and spectrally coincident with the TeV $γ$-ray emission from HESS J1813-178. CO observations display the dense molecular clouds surrounding HESS J1813-178 in the velocity range of 45-60 km s$^{\rm -1}$. The possible origins of the $γ$-ray emission from HESS J1813-178 are discussed, including SNR G12.82-0.02, the PWN driven by the energetic X-ray pulsar PSR J1813-1749, and YSC Cl 1813-178. However, none of them can be ruled out clearly. Note that the maximum energy of protons in the hadronic model should exceed a few hundred TeV, which makes HESS J1813-178 to be a promising PeVatron. The detailed LHAASO data analysis about the morphology and spectrum would be helpful to investigate the origin of the $γ$-ray emission in this region and test its PeVatron nature.

astro-ph.HE↗

arXiv2023

Energy-Dependent Analyses of the Gamma-Ray Emission from HESS J1857+026 with Fermi-LAT

We report the discovery of energy-dependent morphology for the GeV gamma-ray emission from HESS J1857+026 with more than 13 years of {\it Fermi} Large Area Telescope (LAT) data. The GeV gamma-ray emission from this region is composed of two extended components. The hard component with an index of $1.74 \pm 0.07$ in the energy range of 0.5-500 GeV is spatially coincident with HESS J1857+026, and its 68\% containment radius varies from $\sim 0.44^\circ$ below 40 GeV to $\sim 0.30^\circ$ above 140 GeV. The hard GeV gamma-ray spectrum and the energy-dependent morphology of HESS J1857+026 make it favor a PWN origin, which is associated with the energetic pulsar, PSR J1856+0245. The soft component with an index of $2.70 \pm 0.16$ and another extended gamma-ray source detected in this region, 4FGL J1857.9+0313e with an index of $2.55 \pm 0.07$, are spatially coincidence with two molecular clumps in the northeast and southwest of HESS J1857+026, which favors the hadronic process, and the protons could be accelerated by the hypothetical SNR associated with PSR J1856+0245.

astro-ph.HE↗

arXiv2023

Detection of the extended $γ$-ray emission around supernova remnant DA 530 with Fermi-LAT

We report the extended GeV $γ$-ray emission around the high Galactic latitude supernova remnant (SNR) DA 530 with the PASS 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT). The $γ$-ray spectrum in the energy range of 100 MeV - 1 TeV follows a power law model with an index of 2.23. The much more extended $γ$-ray emission than the radio shell of DA 530 and the spatial coincidence with the molecular cloud suggest that the $γ$-ray emission could be originated from the hadronic process, where the high energy protons are accelerated in and escaped from the shock of DA 530. With a steady-state injection model of protons, the $γ$-ray spectrum can be well fitted with the typical Galactic value for diffusion coefficient and the low energy content of the total escaped protons.

astro-ph.HE↗

arXiv2023

Discovery of an Extended $γ$-ray Emission around the Supernova Remnant Candidate associated with PSR J0837$-$2454

Motivated by the recent discovery of a low surface brightness diffuse emission, a supernova remnant (SNR) candidate, surrounding the young pulsar PSR~J0837--2454, we carry out a likelihood analysis of the $γ$-ray data obtained by the \emph{Fermi} Gamma-ray Space Telescope from August 2008 to November 2022. Using a 2D Gaussian spatial template, we detect a significant extended $γ$-ray emission with a 68\% containment radius of $\sim1^{\circ}.8$, which is spatially coincident with the new SNR candidate at $\sim12σ$ confidence level. The spectrum of the extended $γ$-ray emission, obtained in the energy range of 0.1-500.0 GeV, shows a significant spectral curvature at $\sim$1 GeV, with a log-parabola spectral shape. Several scenarios, such as the SNR, pulsar wind nebula, and pulsar halo, are discussed as the potential origins of the extended $γ$-ray emission, and our model fitting results are preferred for the SNR scenario.

astro-ph.HE↗

arXiv2022

GeV gamma-ray emission from pulsar wind nebula HESS J1356-645 with Fermi-LAT

HESS J1356-645 is considered to be a pulsar wind nebula (PWN) associated with the pulsar PSR J1357-6429. We reanalyze the GeV gamma-ray emission in the direction of HESS J1356-645 with more than 13 years of Fermi Large Area Telescope (LAT) data. The extended gamma-ray emission above 5 GeV is found to be spatially coincident with HESS J1356-645. The spectrum in the energy range of 1 GeV-1 TeV can be described by a power law with an index of $Γ=1.51\pm0.10$. The broadband spectrum of HESS J1356-645 can be reproduced by a leptonic model with a broken power-law electronic spectrum. In addition, we found evidence that the morphology of the GeV emission from HESS J1356-645 varies with energy, a behavior which is similar to that of the PWN Vela-X. More broadband observations will be helpful to study the energy-dependent characteristics of HESS J1356-645.

astro-ph.HE↗

arXiv2022

Revised the $γ$-ray emission from SNR CTB 109 with Fermi-LAT

CTB 109 is a middle-aged shell-type SNR with bright thermal X-ray emission. We reanalyze the GeV $γ$-ray emission from CTB 109 using thirteen years of Pass 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT). The $γ$-ray emission of CTB 109 shows a center bright morphology, which is well consistent with its thermal X-ray emission rather than the shell-type structure in the radio band. The spectral analysis shows an evident spectral curvature at $\sim$ several GeV for the GeV $γ$-ray spectrum, which can naturally explain the lack of TeV $γ$-ray emission from CTB 109. Although either a leptonic or a hadronic model could fit the multi-wavelength observations of CTB 109, the hadronic model is favored considering its $γ$-ray morphology and the spectral curvature of GeV spectrum. The unusual $γ$-ray spectrum of CTB 109 with other SNRs and the luminosity-diameter squared relation make CTB 109 to be distinguished both from the young-aged SNRs with hard GeV $γ$-ray spectra and several old-aged SNRs interacting with molecular clouds.

astro-ph.HE↗

arXiv2022

Detection of the extended $γ$-ray emission from the high Galactic latitude Calvera's SNR candidate

We report the extended GeV $γ$-ray emission that spatially associated with the high Galactic latitude supernova remnant (SNR) candidate - Calvera's SNR with the Pass 8 data recorded by the {\em Fermi} Large Area Telescope. The $γ$-ray spectrum of Calvera's SNR between 100 MeV and 1 TeV shows an evident ($\sim$ 3.4$σ$) spectral curvature at several tens of GeV. The multi-wavelength data can be fitted with either a leptonic model or a hadronic one. However, the leptonic model exhibits the inconsistent between the flat radio spectrum and the hard GeV $γ$-ray spectrum of Calvera's SNR. For the hadronic model, the spectral index of protons should be harder than 1.6. And the total energy of protons is fitted to be more than one order of magnitude higher than the explosion energy of a typical supernova, which also challenges the hadronic model. The evident spectral curvature and the absence of non-thermal X-ray emission from Calvera's SNR makes it to be an interesting source bridging young-aged SNRs with bright non-thermal X-ray emission and old-aged SNRs interacting with molecular clouds.

astro-ph.HE↗

arXiv2021

TeV cosmic ray nuclei acceleration in shell-type supernova remnants with hard $γ$-ray spectra

The emission mechanism for hard $γ$-ray spectra from supernova remnants (SNRs) is still a matter of debate. Recent multi-wavelength observations of TeV source HESS J1912+101 show that it is associated with an SNR with an age of $\sim 100$ kyrs, making it unlikely produce the TeV $γ$-ray emission via leptonic processes. We analyzed Fermi observations of it and found an extended source with a hard spectrum. HESS J1912+101 may represent a peculiar stage of SNR evolution that dominates the acceleration of TeV cosmic rays. By fitting the multi-wavelength spectra of 13 SNRs with hard GeV $γ$-ray spectra with simple emission models with a density ratio of GeV electrons to protons of $\sim 10^{-2}$, we obtain reasonable mean densities and magnetic fields with a total energy of $\sim 10^{50}$ ergs for relativistic ions in each SNR. Among these sources, only two of them, namely SN 1006 and RCW 86, favor a leptonic origin for the $γ$-ray emission. The magnetic field energy is found to be comparable to that of the accelerated relativistic ions and their ratio has a tendency of increase with the age of SNRs. These results suggest that TeV cosmic rays mainly originate from SNRs with hard $γ$-ray spectra.

astro-ph.HE↗

arXiv2020

Hadronic vs leptonic models for $γ$-ray emission from VER J2227+608

Recent observations of VER J2227+608 reveal a broken power $γ$-ray spectrum with the spectral index increasing from $\sim 1.8$ in the GeV energy range to $\sim 2.3$ in the TeV range. Such a spectral break can be attributed to radiative energy loss of energetic electrons in the leptonic scenario for the $γ$-ray emission, which, in combination with characteristic age of the nearby pulsar, can be used to constrain magnetic field in the emission region. We show that the radio and X-ray observations can also be explained in such a scenario. In the hadronic scenario, the spectral break can be attributed to diffusion of energetic ions in a turbulent medium and detailed spectral measurement can be used to constrain the diffusion coefficient. These two models, however, predict drastically different spectra above 100 TeV, which will be uncovered with future high-resolution observations, such as LHAASO and/or CTA.

astro-ph.HE↗

arXiv2019

Evolution of High-energy Particle Distribution in Supernova Remnants

The spectra fits to a sample of 34 supernova remnants (Zeng et al., 2019) are updated. $γ$-ray spectra of 20 supernova remnants (SNRs) with a soft TeV spectrum are further analyzed. We found that 17 of them can be fitted in the hadronic scenario with a single power-law ion distribution with an index of $\sim$ 2.6, which is significantly softer than the ion distribution inferred from $γ$-ray observations of star-burst galaxies. If Galactic cosmic rays are mostly produced by SNRs, this result suggests that SNRs in star-burst galaxies may never reach the phase with a soft $γ$-ray spectra or escape of high-energy particles from SNRs before they reach this phase with a soft $γ$-ray spectrum dominates the contribution of SNRs to Galactic cosmic rays.

astro-ph.HE↗

arXiv2019

VER J2227+608: A Hadronic PeVatron Pulsar Wind Nebula?

We report the detection of GeV $γ$-ray emission from the very-high-energy (VHE) $γ$-ray source VER J2227+608 associated with the "tail" region of SNR G106.3+2.7. The GeV $γ$-ray emission is extended and spatially coincident with molecular clouds traced by CO emission. The broadband GeV to TeV emission of VER J2227+608 can be well fitted by a single power-law function with an index of 1.90$\pm$0.04, without obvious indication of spectral cutoff toward high energies. The pure leptonic model for the $γ$-ray emission can be marginally ruled out by the X-ray and TeV data. In the hadronic model, the low energy content of CRs and the hard $γ$-ray spectrum, in combination with the center-bright source structure, suggest that VER J2227+608 may be powered by the PWN instead of shocks of the SNR. And the cutoff energy of the proton distribution needs to be higher than $\sim$ 400 TeV, which makes it an attractive PeVatron candidate. Future observations by the upcoming Large High Altitude Air Shower Observatory (LHAASO) and the Cherenkov Telescope Array in the north (CTA-North) could distinguish these models and constrain the maximum energy of cosmic rays in supernova remnants.

astro-ph.HE↗

arXiv2018

Evolution of high-energy particle distribution in Supernova Remnants

Supernova remnants (SNRs) have been considered as the dominant contributors to Galactic cosmic rays. However, the relation between high-energy particles trapped in SNRs and cosmic rays observed at the Earth remains obscure. In this paper, we fit the spectral energy distributions of 35 SNRs with a simple one-zone emission model and analyze correlations of model parameters to uncover the evolution of high-energy particle distribution in SNRs. We find that (1) the particle distribution in general can be described by a broken power-law function with a high-energy cutoff for all SNRs; (2) the low-energy spectrum becomes harder and the break energy decreases with aging of SNRs, (3) for most middle-age SNRs, the energy loss timescale of electrons at the high-energy cutoff is approximately equal to the age of the corresponding remnant implying quenching of very high-energy electron acceleration; for young SNRs, this energy loss timescale is shorter than the age of SNRs implying continuous electon acceleration at the cutoff energy; and for a few old age SNRs, the energy loss timescale is longer than the corresponding age which may suggest escaping of higher energy particles from SNRs. Finally, we comment on the implications of these results on the SNR origin of Galactic cosmic rays.

astro-ph.HE↗

arXiv2016

Evolution of High-Energy Particle Distribution in Mature Shell-Type Supernova Remnants

Multi-wavelength observations of mature supernova remnants (SNRs), especially with recent advances in gamma-ray astronomy, make it possible to constrain energy distribution of energetic particles within these remnants. In consideration of the SNR origin of Galactic cosmic rays and physics related to particle acceleration and radiative processes, we use a simple one-zone model to fit the nonthermal emission spectra of three shell-type SNRs located within 2 degrees on the sky: RX J1713.7-3946, CTB 37B, and CTB 37A. Although radio images of these three sources all show a shell (or half-shell) structure, their radio, X-ray, and gamma-ray spectra are quite different, offering an ideal case to explore evolution of energetic particle distribution in SNRs. Our spectral fitting shows that 1) the particle distribution becomes harder with aging of these SNRs, implying a continuous acceleration process, and the particle distributions of CTB 37A and CTB 37B in the GeV range are harder than the hardest distribution that can be produced at a shock via the linear diffusive shock particle acceleration process, so spatial transport may play a role; 2) the energy loss timescale of electrons at the high-energy cutoff due to synchrotron radiation appears to be always a bit (within a factor of a few) shorter than the age of the corresponding remnant, which also requires continuous particle acceleration; 3) double power-law distributions are needed to fit the spectra of CTB 37B and CTB 37A, which may be attributed to shock interaction with molecular clouds.

astro-ph.HE↗