In this paper, we focus on the scientific case of Cygnus OB2, a northern sky young massive stellar cluster (YMSC) located towards the Cygnus X star-forming complex. We consider a model that assumes cosmic ray acceleration occurring only at the termination shock of the collective wind of the YMSC and address the question of whether, and under what hypotheses, hadronic emission by the accelerated particles can account for the observations of Cygnus OB2 obtained by Fermi-LAT, HAWC and LHAASO. In order to do so, we carefully review the available information on this source, also confronting different estimates of the relevant parameters with ad hoc developed simulations. Once other model parameters are fixed, the spectral and spatial properties of the emission are found to be very sensitive to the unknown properties of the turbulent magnetic field. Comparison with the data shows that our suggested scenario is incompatible with Kolmogorov turbulence. Assuming Kraichnan or Bohm type turbulence spectra, the model accounts well for the Very High Energy (VHE) data, but fails to reproduce the centrally peaked morphology observed by Fermi-LAT, suggesting that additional effects might be important for lower energy $γ$-ray emission. We discuss how additional progress can be made with a more detailed and extended knowledge of the spectral and morphological properties of the emission.
OB-associations and superbubbles being energetically essential galactic powerhouses are likely to be the important acceleration sites of galactic cosmic rays (CRs). The emission profile of gamma-ray sources related to superbubbles and stellar clusters indicates on continuous particle acceleration by winds of massive stars. One of the most luminous galactic gamma-ray sources is Cygnus Cocoon superbubble, observed by multiple instruments, such as Fermi-LAT, ARGO, and, recently, HAWC. We discuss a model of particle acceleration and transport in a superbubble to explain GeV-TeV gamma-ray spectrum …
The Cygnus Cocoon is the first gamma-ray superbubble powered by a massive stellar association, the OB2 association. It was postulated that the combined effects of the stellar winds of all the massive O-type stars of the OB2 association can accelerate the cosmic rays to PeV energy in the Cocoon. The conclusive proof of acceleration to PeV energy in the Cocoon will identify the stellar association as a PeV cosmic-ray accelerator, known as PeVatron. However, the Cocoon has been previously studied only up to 10 TeV. In this contribution, using 1343 days of High Altitude Water Cherenkov (HAWC) obse…
Star forming regions (SFRs) have been postulated as possible sources of cosmic rays (CRs) in our galaxy. One example of a gamma-ray source associated with an SFR is the Fermi-LAT cocoon, an extended region of gamma-ray emission in the Cygnus X region and attributed to a possible superbubble with freshly accelerated CRs. Because the emission region is surrounded by ionization fronts, it has been named the "Cygnus cocoon". CRs in the cocoon could have originated in the OB2 association and been accelerated at the interaction sites of stellar winds of massive O type stars. So far, there is no clea…
Cosmic rays with energies up to a few PeV are known to be accelerated within the Milky Way. Traditionally, it has been presumed that supernova remnants were the main source of very-high-energy cosmic rays but theoretically it is difficult to get protons to PeV energies and observationally there simply is no evidence to support the remnants as sources of hadrons with energies above a few tens of TeV. One possible source of protons with those energies is the Galactic Center region. Here we report observations of 1-100 TeV gamma rays coming from the 'Cygnus Cocoon', which is a superbubble surroun…
We explore electron pre-acceleration at high Mach-number nonrelativistic perpendicular shocks at, e.g., young supernova remnants, which are a prerequisite of further acceleration to very high energies via diffusive shock acceleration. Using fully kinetic particle-in-cell simulations of shocks and electron dynamics in them, we investigate the influence of shock-surfing acceleration at the shock foot on the nonthermal population of electrons downstream of the shock. The shock-surfing acceleration is followed by further energization at the shock ramp where the Weibel instability spawns a type of …
A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1
Julius-Maximilians-Universität Würzburg（维尔茨堡朱利叶斯-马克西米利安大学）；European Space Agency (ESA)（欧洲空间局）；Université Paris-Saclay（巴黎萨克雷大学）；Université Paris Cité（巴黎西岱大学）；Observatoire des Sciences de l’Univers de l’université Paris-Saclay（巴黎萨克雷宇宙科学观测站）；APC（粒子与宇宙学中心）；Dr. Karl Remeis-Observatory, Friedrich-Alexander-Universität Erlangen-Nürnberg（弗里德里希-亚历山大埃尔朗根-纽伦堡大学卡尔·雷梅斯天文台）
The X-ray spectra of X-ray binaries are dominated by emission of either soft or hard X-rays which defines their soft and hard spectral states. Cygnus X-3 is amongst the list of X-ray binaries that show quite complex behavior, with various distinct spectral states. Because of its softness and intrinsic low flux above typically 50 keV, very little is known about the hard X/soft gamma-ray (100-1000 keV) emission in Cygnus X-3. Using the whole INTEGRAL data base, we aim to explore the 3-1000 keV spectra of Cygnus X-3. This allows to probe this region with the highest sensitivity ever, and search f…
The Cygnus Loop (G74.0-8.5) is a very well-known nearby supernova remnant (SNR) in our Galaxy. Thanks to its large size, brightness, and angular offset from the Galactic plane, it has been studied in detail from radio to $γ$-ray emission. The $γ$ -rays probe the populations of energetic particles and their acceleration mechanisms at low shock speeds. We present an analysis of the $γ$-ray emission detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope over 11 years in the region of the Cygnus Loop. We performed detailed morphological and spectral studies of the $γ$-ra…
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…
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）
Cutoff energy in a synchrotron radiation spectrum of a supernova remnant (SNR) contains a key parameter of ongoing particle acceleration. We systematically analyze 11 young SNRs, including all historical SNRs, to measure the cutoff energy, thus shedding light on the nature of particle acceleration at the early stage of SNR evolution. The nonthermal (synchrotron) dominated spectra in filament-like outer rims are selectively extracted and used for spectral fitting because our model assumes that accelerated electrons are concentrated in the vicinity of the shock front due to synchrotron cooling. …
From GeV to PeV: Orbital Modulation and Wind-Regulated Ultrahigh-energy Emission in Cygnus~X-3
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文学和天体物理学重点实验室（南京大学））；Tianfu Cosmic Ray Research Center（天府宇宙线研究中心）；State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）
Star-forming regions may play an important role in the life cycle of Galactic cosmic rays. Gamma-ray observations of Cygnus X have revealed the presence of an excess of hard-spectrum gamma-ray emission, possibly related to a cocoon of freshly accelerated particles. Based on ~13 years of observations with the Fermi-Large Area Telescope (LAT), we performed an improved spectro-morphological characterisation of the residual emission including the cocoon. The best-fit model for the cocoon includes two main emission components: an extended component FCES G78.74+1.56, described by a 2D Gaussian of ex…
We report observations of gamma-ray emissions with energies in the 100 TeV energy region from the Cygnus region in our Galaxy. Two sources are significantly detected in the directions of the Cygnus OB1 and OB2 associations. Based on their positional coincidences, we associate one with a pulsar PSR J2032+4127 and the other mainly with a pulsar wind nebula PWN G75.2+0.1 with the pulsar moving away from its original birthplace situated around the centroid of the observed gamma-ray emission. This work would stimulate further studies of particle acceleration mechanisms at these gamma-ray sources.
Synchrotron radio emission from non-relativistic jets powered by massive protostars has been reported, indicating the presence of relativistic electrons and magnetic fields of strength ~0.3-5 mG. We study diffusive shock acceleration and magnetic field amplification in protostellar jets with speeds between 300 and 1500 km/s. We show that the magnetic field in the synchrotron emitter can be amplified by the non-resonant hybrid (Bell) instability excited by the cosmic-ray streaming. By combining the synchrotron data with basic theory of Bell instability we estimate the magnetic field in the sync…
The magnetic field in the X-ray corona of Cygnus X-1
BH双星的硬、软光谱态（HS和SS）的电子分布不同，可能是由动力学过程引起的，也可能是由于日冕中物理条件的变化而引起的。在日冕中存在磁场的情况下，即使加速机制会产生非热分布，电子分布也会出现热分布。这是由于通过同步加速器自吸收的快速和有效的热化。我们已经分析了6年的观测数据天鹅座X-1的INTEGRAL天文台和生产12个高质量的，堆叠的宽带硬X射线光谱代表的整个范围内的光谱形状观察。然后，我们拟合这些光谱与混合热/非热康普顿化模型和研究的物理参数的吸积流跨越光谱过渡的演变。特别是，我们使用的BELM模型来约束的磁场在日冕通过其对日冕发射的影响。事实上，X射线日冕的热电子产生软（光学-UV）同步辐射，其然后被康普顿化并且可以通过康普顿冷却影响电子的温度。我们发现在SS中，辐射主要由盘光子的康普顿化所控制，磁场最多为1 E +06 G量级。在硬态下，数据与纯同步自康普顿模型一致。如果在HS中观察到的几百keV以上的非热过剩是在与热康普顿化的主体相同的区域中产生的，则我们得到日冕磁场的上限约为1 E +05 G。另一方面，如果在不同的位置产生非热过剩，则HS中对磁场的约束有所放松，上限上升到1 E +07 G。我们讨论这些限制的背景下，目前的吸积流模型。
3D simulations of young core-collapse supernova remnants undergoing efficient particle acceleration
在我们的银河系内，超新星遗迹被认为是宇宙射线的主要来源。然而，重要的问题仍然是关于强子和轻子成分的份额，以及超新星能量的一部分被引导到这些成分中。我们解决这样的问题，通过数值模拟的手段相结合的冲击波的动力学处理与粒子加速。执行3D模拟使我们能够生成热发射和非热发射的合成投影图和光谱，可以与多波长观测（无线电，X射线和伽马射线）进行比较。超新星有不同的类型，虽然它们的能量收支是相同的，但它们的残余物有不同的性质，因此可能以不同的方式对银河宇宙射线池做出贡献。我们的第一个模拟集中在热核超新星，像第谷的SNR，通常发生在一个基本上不受干扰的介质。在这里，我们提出了我们的核心坍缩超新星的三维模拟，如Cas A SNR，发生在一个更复杂的介质轴承的祖先恒星的风的印记。
Particle acceleration to suprathermal energies in strong astrophysical shock waves is a widespread phenomenon, generally explained by diffusive shock acceleration. Such shocks can also amplify upstream magnetic field considerably beyond simple compression. The complex plasma physics processes involved are often parameterized by assuming that shocks put some fraction $ε_e$ of their energy into fast particles, and another fraction $ε_B$ into magnetic field. Modelers of shocks in supernovae, supernova remnants, and gamma-ray bursters, among other locations, often assume typical values for these f…
Galactic sites of acceleration of cosmic rays to energies of order 10^15 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In November 2020, the IceCube neutrino observatory reported an ~150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1-sigma (post trial) excess of a…
