Since the discovery of cosmic rays (CRs) over a century ago, their origin has remained a mystery and a key research question. Recently, the LHAASO experiment identified the first CR super-acceleration source, the Cygnus bubble, which can accelerate CRs to energies exceeding 10 PeV. A pertinent question is: how much does the Cygnus bubble contribute to the CR spectrum observed on Earth? With the aim of answering that question, a 3D propagation analysis was conducted on CRs in this study. The Cygnus bubble was incorporated into our propagation model in order to determine its contributions to the observed spectra. First, we calculated the spectrum and spatial morphology of the Cygnus bubble to reproduce the observed LHAASO data. Subsequently, we calculated the diffuse $γ$-ray emissions produced by the CRs from the Cygnus bubble and the energy spectrum of the cosmic ray particles near Earth after propagation. Finally, we utilized a CR spatial-dependent propagation model to calculate the large-scale CR energy spectrum and the resulting diffuse $γ$-ray emissions. Our results indicate that: (1) the Cygnus bubble contributes minimally to the CR spectrum observed on Earth, (2) the emissions produced by the CR particles from the Cygnus bubble dominates the diffuse $γ$-ray emissions in that region, (3) the structural fluctuations of the diffuse $γ$-ray emissions observed by LHAASO are likely due to the local CR halo. We anticipate that LHAASO will identify more CR halo sources to validate our model.
Microquasar Cygnus X-3 as the PeVatron powering the Cygnus Bubble
University of Science and Technology of China（中国科学技术大学）；Yerevan State University（埃里温国立大学）；TIANFU Cosmic Ray Research Center（天府宇宙线研究中心）；Max-Planck-Institut for Nuclear Physics（马克斯·普朗克核物理研究所）
The Cygnus\,OB2 region, $\sim 3.5-5~\text{Myr}$ old, contains one of the most significant populations of massive stars of the Milky Way. Such stars substantially contribute to producing large scale soft ($<2~\text{keV}$) diffuse X-ray emission. We also detected hard ($>3~\text{keV}$) diffuse X-ray emission in the direction of the pulsar PSR\,J2032+4127. The torus-shaped emission spans a $\approx 3'\times 2'$ jet-like structure. It is spatially coincident with the Fermi $γ$-ray source 4FGL\,J2032.3+4127. We suggest that the hard diffuse X-ray emission is the pulsar wind nebula bearing the pulsa…
We present a large-scale study of diffuse X-ray emission in the nearby massive stellar association Cygnus OB2 as part of the Chandra Cygnus OB2 Legacy Program. We used 40 Chandra X-ray ACIS-I observations covering $\sim$1.0 deg$^2$. After removing 7924 point-like sources detected in our survey, background-corrected X-ray emission, the adaptive smoothing reveals large-scale diffuse X-ray emission. Diffuse emission was detected in the sub-bands Soft [0.5 : 1.2] and Medium [1.2 : 2.5], and marginally in the Hard [2.5 : 7.0] keV band. From X-ray spectral analysis of stacked spectra we compute a to…
Suppressed diffusion and gamma-ray emission from the Cygnus bubble
Gran Sasso Science Institute (GSSI)（格兰萨索科学研究所）；INFN-Laboratori Nazionali del Gran Sasso (LNGS)（意大利国家核物理研究所格兰萨索国家实验室）；INAF-Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切尔天文台）
It has been pointed out in arXiv:2211.17057 that our recent (published) paper might be revised, due to an incorrect evaluation of the diffusion coefficients, $D(E)$, employed in the calculations. Unfortunately, there is no indication as to where the incorrectness might be. Here we offer the opportunity to be more specific, by providing the community with the whole description of the equations involved in the calculation of $D(E)$, which is missing in the {\tt arXiv} note. In this context, we mention that no \textit{ad hoc} parameterisation has been used in our paper. Furthermore, any assumptio…
Very recently, diffuse gamma rays with $0.1\,{\rm PeV}<E_γ<1\,\rm PeV$ have been discovered from the Galactic disk by the Tibet air shower array and muon detector array (Tibet AS+MD array). While the measured sub-PeV flux may be compatible with the hadronic origin in the conventional Galactic cosmic ray propagation model, we find that it is in possible tension with the non-detection of Galactic neutrino emissions by the IceCube neutrino telescope. We further find that the presence of an extra cosmic ray component of relatively hard spectrum, which is probably related to the Cygnus Cocoon regio…
Cosmic-ray (CR) diffusion is the result of the interaction of such charged particles against magnetic fluctuations. These fluctuations originate from large-scale turbulence cascading towards smaller spatial scales, decomposed into three different modes, as described by $magneto-hydro-dynamics$ (MHD) theory. As a consequence, the description of particle diffusion strongly depends on the model describing the injected turbulence. Moreover, the amount of energy assigned to each of the three modes is in general not equally divided, which implies that diffusion properties might be different from one…
High energy emissions near particle accelerators provide unique windows to probe the particle acceleration and ensuing escape process determined by local medium properties, particularly the turbulence properties. It has been demonstrated both theoretically and observationally that particle diffusion in local environment can differ from the averaged values inferred from the CR global propagation in the Galaxy determined by local medium, particularly magnetic field and turbulence. A recent publication by Fornieri & Zhang (2022) computed particle transport employing the formalism of fast modes sc…
Multimessenger Concordance for the Cygnus Region as the Source of the Cosmic-Ray Knee
Gran Sasso Science Institute（格兰萨索科学研究所）；INFN, Laboratori Nazionali del Gran Sasso（意大利国家核物理研究所，格兰萨索国家实验室）；The Pennsylvania State University（宾夕法尼亚州立大学）；Yukawa Institute for Theoretical Physics（京都大学汤川理论物理研究所）；University of L’Aquila（拉奎拉大学）；INAF Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；Shanghai Jiao Tong University（上海交通大学）
Identification of a Large-Scale Diffuse Gamma-Ray Structure in the Southern Galactic Hemisphere
School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）；Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台暗物质与空间天文重点实验室）
The Fermi Bubbles were discovered about a decade ago in the {\it Fermi}-LAT data as a double-lobe structure extending up to 55 deg. in Galactic latitudes above and below the Galactic Center. At the moment their origin is still unknown. The H.E.S.S. collaboration is currently performing the first ever survey in TeV gamma rays of the Milky Way inner region: the Inner Galaxy Survey. This survey is intended to achieve the best sensitivity to faint and diffuse emissions in a region of several degrees around the Galactic Centre. It provides an unprecedented sensitivity to dark matter signals, new di…
The enhanced star forming activity, typical of starburst galaxies, powers strong galactic winds expanding on kiloparsec (kpc) scales and characterized by bubble structures. Here we discuss the possibility that particle acceleration may take place at the termination shock of such winds. We calculate the spectrum of accelerated particles and their maximum energy, that turns out to range up to a few hundred petaelectronvolt (PeV) for typical values of the parameters. Cosmic rays accelerated at the termination shock are advected towards the edge of the bubble excavated by the wind and eventually e…
Interstellar dust permeates our Galaxy and plays an important role in many physical processes in the diffuse and dense regions of the interstellar medium. High-resolution X-ray spectroscopy, coupled with modelling based on laboratory dust measurements, provides a unique probe to investigate the interstellar dust properties along our line of sight towards Galactic X-ray sources. Here, we focus on the oxygen content of the interstellar medium through its absorption features in the X-ray spectra. To model the dust features, we perform a laboratory experiment using the electron microscope facility…
Measuring the diffuse Galactic gamma-ray flux in the TeV range is difficult for ground-based gamma-ray telescopes because of the residual cosmic-ray background, which is higher than the gamma-ray flux by several orders of magnitude. Its detection is also challenging for space-based telescopes because of low signal statistics. We characterize the diffuse TeV flux from the Galaxy using decade-long exposures of the Fermi Large Area Telescope. Considering that the level of diffuse Galactic emission in the TeV band approaches the level of residual cosmic-ray background, we estimated the level of re…
We report the detection of high-energy gamma-ray signal towards the young star-forming region, W40. Using 10-year Pass 8 data from the Fermi Large Area Telescope (Fermi-LAT), we extracted an extended gamma-ray excess region with a significance of about 18sigma. The radiation has a spectrum with a photon index of 2.49 +/- 0.01. The spatial correlation with the ionized gas content favors the hadronic origin of the gamma-ray emission. The total cosmic-ray (CR) proton energy in the gamma-ray production region is estimated to be the order of 10^47 erg. However, this could be a small fraction of the…
One of the brightest regions of diffuse gamma-ray emission in the northern sky is the Cygnus star-forming region, where one can assume the most energetic processes are taking place. The Dragonfly Nebula (MGRO J2019+37) is one of the brightest sources in the Cygnus region. First discovered by MILAGRO, it was later resolved into two sources by VERITAS: the faint point-like source VER J2016+371 and the bright extended source VER J2019+368. The latter accounts for the bulk of the MGRO J2019+37 emission, with the spectrum among the hardest in the TeV range. We report the results of a dedicated MAGI…
We present results from deep observations towards the Cygnus region using 300 hours of very-high-energy (VHE) $γ$-ray data taken with the VERITAS Cherenkov telescope array and over seven years of high-energy $γ$-ray data taken with the Fermi satellite at an energy above 1 GeV. As the brightest region of diffuse $γ$-ray emission in the northern sky, the Cygnus region provides a promising area to probe the origins of cosmic rays. We report the identification of a potential Fermi-LAT counterpart to VER J2031+415 (TeV J2032+4130), and resolve the extended VHE source VER J2019+368 into two source c…
After discovery of the Fermi bubbles, giant structures observed in radio to X-rays have been discussed as possi- ble evidence of past activities in the Galactic Center (GC). We report here on the analysis of Suzaku data pointing around the Loop I arc. The diffuse X-ray emission was well represented by the three-component model: (1) an unabsorbed thermal plasma with kT ~ 0.1 keV either from the Local Hot Bubble (LHB) and/or solar wind charge exchange (SWCX), (2) an absorbed thermal plasma regarded as a contribution from the Loop I and the Galactic halo (GH), and (3) an absorbed power-law compon…
The nature of the $γ$-ray emission from the \emph{Fermi} bubbles is unknown. Both hadronic and leptonic models have been formulated to explain the peculiar $γ$-ray signal observed by the Fermi-LAT between 0.1-500~GeV. If this emission continues above $\sim$30~TeV, hadronic models of the \emph{Fermi} bubbles would provide a significant contribution to the high-energy neutrino flux detected by the IceCube observatory. Even in models where leptonic $γ$-rays produce the \emph{Fermi} bubbles flux at GeV energies, a hadronic component may be observable at very high energies. The combination of IceCu…
Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport
GRAPPA Institute, University of Amsterdam（阿姆斯特丹大学 GRAPPA 研究所）；Department of Physics and Astronomy, San Francisco State University（旧金山州立大学物理与天文系）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo（东京大学宇宙物理数学研究所）
The $^{26}$Al Gamma-ray Line from Massive-Star Regions
当在已知距离和严格限制的恒星星族中研究特定恒星群时，对源自超新星核合成的放射性扩散余辉中的伽马射线进行测量被认为是测试模型的实验室。已被用于此类研究的区域包括天鹅座、船底座、猎户座和天蝎座-半人马座。猎户座区域是猎户座OB 1星协及其子群的所在地，距离约为450秒差距。我们报道了用INTEGRAL/SPI探测该区域的$^{26}$ Al γ射线。
The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100 deg on the sky, is still being debated. The northern-most part of Loop I, known as the North Polar Spur (NPS), is the brightest arm and is even clearly visible in the ROSAT X-ray sky map. In this paper, we present a comprehensive review on the X-ray observations of the Fermi bubbles and …
