The Fermi-LAT data accumulated over 7 years of γ-ray observations, together with the high resolution gas (CO & HI) and the dust opacity maps, are used to study the emissivity of γ-rays induced by interactions of cosmic rays (CRs) with the interstellar medium. Based on the dust opacity templates, the γ-ray emissivity was measured for 36 segments of the Galactic plane. Furthermore, the γ-ray emissivity was evaluated in six Galactocentric rings. Both the absolute emissivity and the energy spectra of γ-rays derived in the interval 0.2-100 GeV show significant variations along the galactic plane. The density of CRs, derived under the assumption that γ-rays are predominately produced in CR interactions with the interstellar gas, is characterised by a strong radial dependence. In the inner Galaxy the CR density substantially exceeds the density in the outer parts of the Galaxy: by a factor of a few at 10 GeV, and by more than an order of magnitude at 1 TeV. Remarkably, the energy distribution of CRs appears to be substantially harder than the energy spectrum obtained from direct measurements of local CRs. At the same time, the flux and the energy spectrum of multi-GeV protons derived from γ-ray data in the outskirts of the Galaxy is quite close to the measurements of local CRs.
X-ray observations suggest high compactness of coronae in active galactic nuclei as well as in X-ray binaries. The compactness of the source implies a strong radial dependence in the illumination of the accretion disc. This will, for any reasonable radial profile of the density, lead to a radial profile of the disc ionisation. Svoboda et al. (2012) showed on a single example that assuming a radially-structured ionisation profile of the disc can cause an artificial increase of the radial-emissivity parameter. We further investigate how the X-ray spectra are modified and quantify this effect for…
Very steep reflection emissivity profiles in the inner part of accretion disks are commonly found in the analysis of X-ray observations of black hole binaries and AGN, but there is some debate about their exact origin. While steep reflection emissivity profiles can be naturally produced by compact coronae close to black holes, the measured radial emissivity parameter can be further increased by the radial disk ionization profile when the theoretical model assumes a disk with constant ionization. In this paper, we implement the possibility of a radial disk ionization profile in the reflection m…
Physically motivated AGN emissivity profiles and their effects on quasar microlensing signatures. 1. Multi-epoch accretion disc size inference
IFPU - Institute for Fundamental Physics of the Universe（基础物理宇宙研究所）；SISSA - International School for Advanced Studies（国际高等研究院）；INAF - Osservatorio Astronomico di Trieste（的里雅斯特天文台）；Center for Astrophysics and Cosmology, University of Nova Gorica（新戈里察大学天体物理学与宇宙学中心）
We revisit calculations of the X-ray emission from warm-hot intergalactic medium (WHIM) with particular focus on contribution from the resonantly scattered cosmic X-ray background (CXB). If the significant part of the CXB emission is resolved into point sources, the properties of the WHIM along the line of sight are recorded in the absorption lines in the stacked spectrum of resolved sources and in the emission lines in the remaining diffuse signal. For the strongest resonant lines, this implies a factor of $\sim30$ boost in emissivity compared to the intrinsic emissivity over the major part o…
This article reviews a few topics relevant to Galactic cosmic-ray astrophysics, focusing on the recent AMS-02 data release and Fermi Large Area Telescope data on the diffuse Galactic gamma-ray emissivity. Calculations are made of the diffuse cosmic-ray induced p+p --> pi^0 --> 2 gamma spectra, normalized to the AMS-02 cosmic-ray proton spectrum at ~ 10 - 100 GV, with and without a hardening in the cosmic-ray proton spectrum at rigidities R >~ 300 GV. A single power-law momentum "shock" spectrum for the local interstellar medium cosmic-ray proton spectrum cannot be ruled out from the gamma-ray …
Fermi observations of Cassiopeia and Cepheus: diffuse gamma-ray emission in the outer Galaxy
本文分析了费米大天区望远镜在银河系第二象限100度< l < 145度和-15度< b < +30度区域测量到的星际伽马射线辐射。这一区域包括仙后座、仙王座和北极星耀斑的显著的古尔德带云，以及更远距离的原子和分子复合体，如英仙座臂中与NGC 7538相关的复合体。而且每个星系中都存在大质量的复合体，这使得这个区域非常适合探测宇宙射线和太阳圈以外的星际介质。古尔德带中气体的伽马射线发射率光谱与基于当地测量的宇宙射线光谱的预期一致。伽马射线发射率从古尔德带到英仙座臂逐渐降低，但测量到的梯度比宇宙射线源在银河系内部达到峰值的预期要平坦，这一点由天文学家提出。我们发现Xco=N（H2）/W（CO）的转换因子从古尔德带的（0.87 +- 0.05）10^20 cm^-2（K km s^-1）^-1增加到英仙座臂的（1.9 +- 0.2）10^20 cm^-2（K km s^-1）^-1。在古尔德带中，通过相关的过量尘埃和伽马射线发射，发现了没有被无线电和微波探测正确追踪的暗气体：其质量约为CO追踪质量的50%。
The dynamical production of low-mass X-ray binaries and brighter cataclysmic variables (CVs) in dense globular clusters is well-established. We investigate how the X-ray emissivity of fainter X-ray binaries (principally CVs and coronally active binaries) varies between different environments. We compile calculations (largely from the literature) of the X-ray emissivity of old stellar populations, including open and globular clusters and several galaxies. We investigate three literature claims of unusual X-ray sources in low-density stellar populations. We show that a suggested quiescent neutro…
The diffuse hard X-ray emission that fills the Galactic center, bulge, and ridge is believed to arise from unresolved populations of X-ray binary systems. However, the identity of the dominant class of accreting objects in each region remains unclear. Recent studies of Fe line properties and the low-energy (<10 keV) X-ray continuum of the bulge indicate a major population fraction of non-magnetic cataclysmic variables (CVs), in particular quiescent dwarf novae. This is in contrast to previous high-energy (>10 keV) X-ray measurements of the bulge and ridge, which indicate a dominant population …
We develop a broadband spectral model, agnsli}, to describe super-Eddington black hole accretion disc spectra. This is based on the slim disc emissivity, where radial advection keeps the surface luminosity at the local Eddington limit, resulting in L(r)~ r^{-2} rather than the r^{-3} expected from the Novikov-Thorne (standard, sub-Eddington) disc emissivity. Wind losses should also be important but these are expected to produce a similar radiative emissivity. We assume that the flow is radially stratified, with an outer standard disc, an inner hot Comptonising region and an intermediate warm C…
Recent direct measurements of Galactic cosmic ray spectra by balloon/space-borne detectors reveal spectral hardenings of all major nucleus species at rigidities of a few hundred GV. The all-sky diffuse gamma-ray emissions measured by the Fermi Large Area Telescope also show spatial variations of the intensities and spectral indices of cosmic rays. These new observations challenge the traditional simple acceleration and/or propagation scenario of Galactic cosmic rays. In this work we propose a spatially-dependent diffusion scenario to explain all these phenomena. The diffusion coefficient is as…
The nearby Orion-Eridanus superbubble, which was blown by multiple supernovae several Myr ago, has likely produced cosmic rays. Its turbulent medium, still energised by massive stars, can impact cosmic-ray transport locally. The gamma rays produced in cosmic-ray interactions with interstellar gas were used to compare the GeV to TeV cosmic-ray spectrum in the superbubble and in other regions near the Sun. We used ten years of Fermi-LAT data in the 0.25-63 GeV energy range to study the closer (Eridanus) end of the superbubble. We modelled the spatial and spectral distributions of the gamma rays …
We present a novel interpretation of the $γ$-ray diffuse emission measured by Fermi-LAT and H.E.S.S. in the Galactic center (GC) region and the Galactic ridge (GR). In the first part we perform a data-driven analysis based on PASS8 Fermi-LAT data: we extend down to few GeV the spectra measured by H.E.S.S. and infer the primary cosmic-ray (CR) radial distribution between 0.1 and 3 TeV. In the second part we adopt a CR transport model based on a position-dependent diffusion coefficient. Such behavior reproduces the radial dependence of the CR spectral index recently inferred from the Fermi-LAT o…
Diffuse gamma-ray emission from interstellar clouds results largely from cosmic ray (CR) proton collisions with ambient gas, regardless of the gas state, temperature, or dust properties of the cloud. The interstellar medium is predominantly transparent to both CRs and gamma-rays, so GeV emission is a unique probe of the total gas column density. The gamma-ray emissivity of a cloud of known column density is then a measure of the impinging CR population and may be used to map the kpc-scale CR distribution in the Galaxy. To this end, we test a number of commonly used column density tracers to ev…
Diffuse radio emission was detected around the soft gamma-ray repeater SGR 1806-20, after its 2004 powerful giant flare. We study the possible extended X-ray emission at small scales around SGR 1806-20, in two observations by the High Resolution Camera Spectrometer (HRC-S) on board of the Chandra X-ray Observatory: in 2005, 115 days after the giant flare, and in 2013, during quiescence. We compare the radial profiles extracted from data images and PSF simulations, carefully considering various issues related with the uncertain calibration of the HRC PSF at sub-arcsecond scales. We do not see s…
The "GeV-excess" of the diffuse gamma-rays in the halo is studied with a template fit based on energy spectra for each possible process of gamma-ray emission. Such a fit allows to determine the background and signal simultaneously, so the Galactic Disk can be included in the analysis. We find evidence that the "excess", characterised by a gamma-ray spectrum peaking at 2 GeV, is much stronger in Molecular Clouds in the disk than the "GeV-excess" observed up to now in the halo. The possible reason why the emissivity of Molecular Clouds peaks at 2 GeV are the energy losses and magnetic cutoffs in…
In this paper we present RELXILLDGRAD_NK, a relativistic reflection model in which the electron density of the accretion disk is allowed to have a radial power-law profile. The ionization parameter has also a non-constant radial profile and is calculated self-consistently from the electron density and the emissivity. We show the impact of the implementation of the electron density gradient in our model by analyzing a NuSTAR spectrum of the Galactic black hole in EXO 1846-031 during its last outburst in 2019 and a putative future observation of the same source with Athena and eXTP. For the NuST…
The interaction of cosmic rays with the gas contained in our Galaxy is a guaranteed source of diffuse high energy neutrinos. We provide expectations for this component by considering different assumptions for the cosmic ray distribution in the Galaxy which are intended to cover the large uncertainty in cosmic ray propagation models. We calculate the angular dependence of the diffuse galactic neutrino flux and the corresponding rate of High Energy Starting Events in IceCube by including the effect of detector angular resolution. Moreover we discuss the possibility to discriminate the galactic c…
Simulating the LOcal Web (SLOW) -- VI: Gamma-ray Emission in the Local Universe
The University of Chicago（芝加哥大学）；Ludwig-Maximilians-Universität München（慕尼黑大学）；Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Univ. Lille, CNRS, Centrale Lille, UMR 9189 CRIStAL（里尔大学）；Université Paris-Saclay（巴黎萨克雷大学）
Globular clusters (GCs) are the ideal environment for the formation of neutron stars (NSs) and millisecond pulsars (MSPs). NSs origin and evolution provide a useful information on stellar dynamics and evolution in star clusters, and are among the most interesting astrophysical objects, being precursors of several high-energy phenomena such as gravitational waves and gamma-ray bursts. Due to a large velocity kick that they receive at birth, most of the NSs escape the local field, affecting the evolution and dynamics of their parent cluster. In this paper, we study the origin and dynamical evolu…
