V. A. Dogiel, K. -S. Cheng, D. O. Chernyshov, W. -H. Ip, C. -M. Ko, V. Tatischeff
We discuss the origin of continuum and line X-ray emission observed in the direction the Galactic Center. We predict a significant flux of de-excitation gamma-ray lines in this direction, which can be produced by subrelativistic protons generated by accretion processes.
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Tibet AS-gamma collaboration has recently reported detection of gamma-rays with energies up to Peta-electronvolt from parts of the Galactic plane. We notice that the analysis of gamma-ray flux by the Tibet AS-gamma experiment also implies an upper bound on the diffuse gamma-ray flux from high Galactic latitudes(|b|>20 degrees) in the energy range between 100 TeV and 1 PeV. This bound is up to an order-of-magnitude stronger than previously derived bounds from GRAPES3, KASCADE and CASA-MIA experiments. We discuss the new TibetAS-gamma limit on high Galactic latitude gamma-ray flux in the context…
We describe an ongoing effort using the Fermi Large Area Telescope to search for gamma-ray emission from a source sample derived from published surveys of variable or transient galactic radio sources.
It is well known that the diffuse gamma-rays are produced by the collisions between the galactic cosmic rays with the stellar matter (Hayakawa-Morrison Hypothesis). In this paper the author tries to estimate the contribution of star flares in the low energy component of the diffuse component of the galactic gamma-rays. It is expected that high energy part of the disuse component of the galactic gamma-rays reflects the power spectrum of galactic cosmic rays with gamma= -2.75 (in differential). In the galactic disk and bulge, there are more than 100 billion stars. They might often make flare and…
The diffuse Galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission > 1 GeV relative to diffuse Galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called ``EGRET GeV excess''). The excess emission was observed in all directions on the sky, and a variety of explanations have been proposed, including beyond-the-Standard-Model scenarios like annih…
The diffuse Galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission > 1 GeV relative to diffuse Galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called ``EGRET GeV excess''). The excess emission was observed in all directions on the sky, and a variety of explanations have been proposed, including beyond-the-Standard-Model scenarios like annih…
Monochromatic gamma-rays are thought to be the smoking gun signal for identifying the dark matter annihilation. However, the flux of monochromatic gamma-rays is usually suppressed by the virtual quantum effects since dark matter should be neutral and does not couple with gamma-rays directly. In the work we study the detection strategy of the monochromatic gamma-rays in a future space-based detector. The monochromatic gamma-ray flux is calculated by assuming supersymmetric neutralino as a typical dark matter candidate. We discuss both the detection focusing on the Galactic center and in a scan …
Galactic diffuse TeV gamma-ray emission is produced by the interaction of high-energy cosmic-ray particles with matter and radiation in our Galaxy. The measurement of Galactic diffuse TeV gamma-ray emission would provide strong constraints on the acceleration and propagation of Galactic cosmic rays. The High Altitude Water Cherenkov (HAWC) Observatory, located in central Mexico at 4100 m above sea level, is sensitive to gamma rays between a few hundreds GeV and about 100 TeV. Thanks to its large field of view of 2 steradians and excellent background estimation, HAWC has a unique capability to …
In this talk, I shall update my 16-year old claim that all the (thousands of) observed GRBs - both long and short, repeating or (so far) not - come from the surfaces of Galactic neutron stars, often called 'magnetars', or 'throttled pulsars'.
The LAT instrument on the Fermi Gamma-Ray Space Telescope is performing an all-sky survey from 20 MeV to 300 GeV with unprecedented statistics and angular resolution. This is providing a wealth of new information on the non-thermal emission from the Galactic interstellar medium with implications for cosmic rays and Galactic structure. First results at intermediate latitudes have already shown good agreement with predictions based on direct measurements of cosmic rays, suggesting that at least the local (within about 1 kpc from the Sun) gamma-ray emission is understood. We will present the firs…
This conference proceedings is a write-up of the Gamma-ray Indirect rapporteur talk given at the 37th International Cosmic Ray Conference (ICRC 2021). In contrast to previous ICRCs, this years edition was held in a fully virtual format, with dedicated discussion sessions organised around specific scientific themes. Many of these topics span the two categories of Gamma-ray Indirect (GAI) and Gamma-ray Direct (GAD), observations of gamma-rays by ground-based and space-based facilities respectively. To cover this organisation by topic in a coherent manner, this GAI rapporteur contribution focuses…
Recently the H.E.S.S. collaboration announced the detection of an unidentified gamma-ray source with an off-set from the galactic plane of 3.5 degrees: HESS J1507-622. If the distance of the object is larger than about one kpc it would be physically located outside the galactic disk. The density profile of the ISM perpendicular to the galactic plane, which acts as target material for hadronic gamma-ray production, drops quite fast with increasing distance. This fact places distance dependent constraints on the energetics and properties of off-plane gamma-ray sources like HESS J1507-622 if a ha…
We demonstrate that young star clusters have a $γ$-ray surface brightness comparable to that of the diffuse Galactic emission (DGE), and estimate that their sky coverage in the direction of the inner Galaxy exceeds unity. We therefore suggest that they comprise a significant fraction of the DGE.
A discussion on the origin of the sub-PeV Galactic gamma-ray emission
本研究对比西藏ASγ与LHAASO的观测数据，分析亚PeV银河系伽马射线辐射的起源，指出弥散辐射可能占主导，已分辨源的贡献远低于60%的保守上限，需进一步开展单源能谱与弥散污染研究。
As of early 2009, latest results on Galactic sources (mainly shell-type and plerionic supernova remnants), as observed in the very-high-energy gamma-ray domain, are reviewed. A particular attention is given to those obtained with the H.E.S.S experiment during its Galactic Plane Survey which now covers the inner part of the Milky Way. From the well identified gamma-ray sources to those without any obvious counterpart and the putative Galactic diffuse emission, this observational window fully deserves to be celebrated during this International Year of Astronomy, as a new mean to image the Galaxy…
The Tibet ASgamma experiment just reported their measurement of sub-PeV diffuse gamma ray emission from the Galactic disk, with the highest energy up to 957 TeV. These gamma-rays are most likely the hadronic origin by cosmic ray interaction with interstellar gas in the Galaxy. This measurement provides direct evidence to the hypothesis that the Galactic cosmic rays can be accelerated beyond PeV energies. In this work, we try to explain the sub-PeV diffuse gamma-ray spectrum within cosmic rays diffusive propagation model. We find there is a tension between the sub-PeV diffuse gamma rays and the…
Galactic Science -- Rapporteur Talk of the 8th Heidelberg International Symposium on High Energy Gamma Ray Astronomy
本文总结了2024年米兰Gamma-2024国际会议上关于银河高能伽马射线天体物理的最新观测与理论进展。
The gluon condensation in the proton as a dynamical model is used to treat a series of unsolved puzzles in sub-TeV gamma ray spectra, they include the broken power-law of blazar's radiation, the hardening confusion of 1ES 1426+428, Mkn 501, and the recently recorded sub-TeV gamma spectra of GRB 180720B and GRB 190114C. We find that the above anomalous phenomena in gamma ray energy spectra can be understood with the simple broken power law based on a QCD gluon condensation effect.
The Southern Wide-field Gamma-ray Observatory (SWGO) is a proposed ground-based gamma-ray detector that will be located in the Southern Hemisphere and is currently in its design phase. In this contribution, we will outline the prospects for Galactic science with this Observatory. Particular focus will be given to the detectability of extended sources, such as gamma-ray halos around pulsars; optimisation of the angular resolution to mitigate source confusion between known TeV sources; and studies of the energy resolution and sensitivity required to study the spectral features of PeVatrons at th…
We present the first catalogs of the highest-energy (above 56 TeV and 100 TeV) gamma-ray sources seen by the High Altitude Water Cherenkov (HAWC) Observatory. The wide field-of-view of HAWC naturally lends itself to unbiased all-sky surveys and newly developed event-by-event gamma-ray energy reconstruction algorithms have allowed unprecedented energy resolution. The sources presented here are the highest-energy sources ever detected. All are coincident with known lower-energy gamma-ray sources within our Galaxy. These objects may have implications for the sources of Galactic cosmic rays; since…
Most of the diffuse Galactic GeV gamma-ray emission is produced via collisions of cosmic ray (CR) protons with ISM protons. As such the observed spectra of the gamma-rays and the CRs should be strongly linked. Recent observations of Fermi-LAT exhibit a hardening of the gamma-ray spectrum at around a hundred GeV, between the Sagittarius and Carina tangents, and a further hardening at a few degrees above and below the Galactic plane. However, standard CR propagation models that assume a time independent source distribution and a location independent diffusion cannot give rise to a spatially depe…
The High-Altitude Water Cherenkov Observatory, or HAWC, is carrying out an unbiased survey of cosmic rays and gamma rays from the Northern Hemisphere between 100 GeV and 100 TeV. HAWC is currently the only high-uptime wide-field TeV observatory in operation, and has a robust program to search for flares and other transient sources of gamma rays. The detector is also well suited to observe spatially extended regions of gamma-ray emission and cosmic-ray anisotropy. HAWC recently concluded its first year of data taking with the complete detector. The results include not only observations of many …
The Picard code for the numerical solution of the Galactic cosmic ray propagation problem allows for high-resolution models that acknowledge the 3D structure of our Galaxy. Picard was used to determine diffuse gamma-ray emission of the Galaxy over the energy range from 100 MeV to 100 TeV. We discuss the impact of a cosmic-ray source distribution aligned with the Galactic spiral arms for a range of such spiral-arm models. As expected, the impact on the gamma-ray emission is most distinct in the inverse-Compton channel, where imprints of the spiral arms are visible and yield predictions that are…
Recent astronomical observations reveal that Active Galactic Nuclei (AGN) are sources of high-energy radiation. For example, the Fermi-LAT and Hess telescopes have detected gamma-ray emissions from the cores of several types of AGN's. Even more, the Pierre Auger observatory has found a correlation of ultra-high energy cosmic ray events with the position of Active Galactic Nuclei, such as Centaurus A. In this way, according to particle physics, a flux of high-energy neutrinos should be expected from the interactions of cosmic and gamma-rays with the ambient matter and radiation at the source. I…
Various studies firmly establish the fact that gamma-ray observations can act as a unique probe to detect the possible cosmic ray (CR) sources, study the CR density distribution and explore the average properties of interstellar medium (ISM) such as the gas density profile of ISM. We use the DRAGON code to study different propagation models by incorporating realistic source distribution, Galactic magnetic field (GMF) and gas density profile, and finally obtain the proton distribution (both spatial and energy) in the Galaxy by fitting the locally observed CR spectra. The uncertainties in the mo…
The origin of the inner Galactic emission, measured by COMPTEL with a flux of $\sim 10^{-2} ~{\rm MeV~ cm}^{-2}~ {\rm s}^{-1}~ {\rm sr}^{-1}$ in the 1-30 MeV energy range from the inner Galactic region, has remained unsettled since its discovery. In this paper, we elaborate on a model of individual MeV gamma-ray sources unresolved by COMPTEL. This is conducted for sources crossmatched between the Swift-BAT and Fermi-LAT catalogs by interpolating the energy spectra in the hard X-ray and GeV gamma-ray ranges, as well as unmatched sources between the two catalogs. We find that the source contribu…
The IceCube Collaboration has recently reported evidence for a high-energy extraterrestrial neutrino flux. During two years of operation 28 events with energies between 30 TeV and 1.2 PeV were observed while only 10.6 events were expected from conventional atmospheric backgrounds. The hadronic interactions responsible for this IceCube excess will also produce a flux of high-energy gamma-rays that can serve as a probe of source direction and distance. We show that existing TeV to PeV diffuse gamma-ray limits support the interpretation that the IceCube excess is mostly of extragalactic origin. H…
The Large Area Telescope on the Fermi gamma-ray Space Telescope provides unprecedented sensitivity for all-sky monitoring of gamma-ray activity. It has detected a few Galactic sources, including 2 gamma-ray binaries and a microquasar. In addition, it is an adequate telescope to detect other transient sources. The observatory scans the entire sky every three hours and allows a general search for flaring activity on daily timescales. This search is conducted automatically as part of the ground processing of the data and allows a fast response to transient events, typically less than a day. Most …
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…
The supermassive black holes harboured in active galactic nuclei are at the origin of powerful jets which can emit copious amounts of gamma-rays. The exact interplay between the infalling matter, the black hole and the relativistic outflow is still poorly known, and this parallel session of the 12th Marcel Grossman meeting intended to offer the most up to date status of observational results with the latest generation of ground and space-based instruments, as well as the theoretical developments relevant for the field.
During the last decades, increasingly precise astronomical observations of the Galactic Centre (GC) region at radio, infrared, and X-ray wavelengths laid the foundations to a detailed understanding of the high energy astroparticle physics of this most remarkable location in the Galaxy. Recently, observations of this region in high energy (HE, 10 MeV - 100GeV) and very high energy (VHE, > 100 GeV) gamma rays added important insights to the emerging picture of the Galactic nucleus as a most violent and active region where acceleration of particles to very high energies -- possibly up to a PeV --…
A new extended gamma-ray source, which was named as Source A, in the southwest of Galactic supernova remnant (SNR) G306.3$-$0.9 was detected with a significance of $\sim$13$σ$ at the location of R.A. (J2000) = 13$^{\rm{h}}$ 17$^{\rm{m}}$ 52$^{\rm{s}\!\!}$.80, Decl. (J2000) = $-$63$^{\circ}$ 55$'$ 48$"\!\!$.00 using about 9 years of Fermi-LAT data. In order to investigate this unidentified gamma-ray source in multi-wavelengths, we performed Swift observations of Source A. In this presentation we summarize the published gamma-ray results, report about the recent ToO Swift observations of Source …
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…
Millisecond Pulsars in Globular Clusters and Implications for the Galactic Center Gamma-Ray Excess
研究银河系球状星团中的毫秒脉冲星伽马射线发射，以测量其光度函数。发现其平均光度及分布宽度，表明若银河系中心伽马射线过剩由类似脉冲星产生，则费米应已探测到更多源，但实际仅发现三个候选者，暗示可能需更暗的脉冲星解释。
We have simulated a Galactic population of young pulsars and compared with the Fermi LAT sample, constraining the birth properties, beaming and evolution of these spin-powered objects. Using quantitative tests of agreement with the distributions of observed spin and pulse properties, we find that short birth periods P_0 ~ 50ms and gamma-ray beams arising in the outer magnetosphere, dominated by a single pole, are strongly preferred. The modeled relative numbers of radio-detected and radio-quiet objects agree well with the data. Although the sample is local, extrapolation to the full Galaxy imp…
A new calculation of nuclear enhancement factor, used in estimation of Galactic diffuse gamma-ray flux from proton-proton interaction in order to take account of heavy nuclei included in cosmic-rays and interstellar matter, is presented by use of a Monte Carlo simulator, DPMJET-3. A new value of 1.8-2.0 in the energy range of 6-1000 GeV/nucleon, slightly increasing with kinetic energy of projectile cosmic rays, is about 20% larger than previous estimates.
We explore possible physical origin of correlation between radio wave and very-high-energy neutrino emission in active galactic nuclei (AGN), suggested by recently reported evidence for correlation between neutrino arrival directions and positions of brightest radio-loud AGN. We show that such correlation is expected if both synchrotron emitting electrons and neutrinos originate from decays of charged pions produced in proton-proton interactions in parsec-scale relativistic jet propagating through circum-nuclear medium of the AGN.
Gamma-ray emission from large structures is useful for tracing the propagation and distribution of cosmic rays throughout our Galaxy. For example, the search for gamma-ray emission from Giant Molecular Clouds may allow us to probe the flux of cosmic rays in distant galactic regions and to compare it with the flux measured at Earth. Also, the composition of the cosmic rays can be measured by separating the gamma-ray emission from hadronic or leptonic processes. In the case of emission from the Fermi Bubbles specifically, constraining the mechanism of gamma-ray production can point to their orig…
High-energy gamma-ray emission from the Galactic plane above ~100 MeV is composed of three main contributions: diffuse emission from cosmic ray interactions in the interstellar medium, emission from extended sources, such as supernova remnants and pulsar wind nebulae, and emission from isolated compact source populations. The diffuse emission and emission from the extended sources provide the dominant contribution to the flux almost everywhere in the inner Galaxy, preventing the detection of isolated compact sources. In spite of this difficulty, compact sources in the Galactic plane can be sin…
The high-energy radiation from short period binaries containing a massive star with a compact relativistic companion was detected from radio to TeV gamma rays. We show here that PeV regime protons can be efficiently accelerated in the regions of collision of relativistic outflows of a compact object with stellar winds in these systems. The accelerated proton spectra in the presented Monte Carlo model have an upturn in the PeV regime and can provide very hard spectra of sub-PeV photons and neutrinos by photo-meson processes in the stellar radiation field. Recent report of a possible sub-PeV gam…
Galactic cosmic rays reach energies of at least several PeV, and their interactions should generate $γ$-rays and neutrinos from decay of secondary pions. Therefore, Galactic sources have a guaranteed contribution to the total high-energy cosmic neutrino flux observed by IceCube. Assuming that the highest energy $γ$-rays are pionic, promising neutrino source candidates have been identified based on their spectra, and observing them is likely over the lifetime of the IceCube experiment. Here, we present the search for Galactic sources of high-energy cosmic neutrinos by focusing on sources identi…
A new extended gamma-ray source (PS J1934.5+1845) was detected with a significance of $\sim$13$σ$ at a location of 1$^{\circ}\!\!$.83 away from the radio location of the Galactic supernova remnant 3C 400.2 using about 9 years of Fermi-LAT data. The 68% containment radius of PS J1934.5+1845's extension was found to be 0$^{\circ}\!\!$.61 and PS J1934.5+1845 is showing a power-law type spectrum with a spectral index of $\sim$2.38. In this presentation we will summarize the gamma-ray analysis methods and report on the analysis results related to the extension and spectrum of PS J1934.5+1845.
We present a search in IceCube data for neutrino emission from Galactic TeV gamma-ray sources detected by the HAWC gamma-ray observatory. HAWC serves as the excellent instrument to complement IceCube with its energy range extending to very high energies. Assuming that the highest energy photons originate from the decay of pions, rather than from accelerated leptons, the very high energy gamma-rays observed by HAWC are expected to be correlated with neutrinos. Using eight years of IceCube data, we report on two analyses that investigate a possible neutrino--gamma ray correlation. The first is a…
The Galactic Center region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of non-thermal radiation. We present the analysis of the very-high-energy gamma-ray emission above 2 TeV of the region around the Galactic Center known as the Central Molecular Zone using 125 hours of data taken with the VERITAS imaging-atmospheric Cherenkov telescope between 2010 and 2018. This analysis employs new shower reconstruction algorithms and instrument response functions optimized for data taken at large zenith angles such as the Galactic Center sources…
Long-term gamma-ray variability of a non-blazar Active Galactic Nucleus (AGN) PKS 0521-36 is investigated by using Fermi-LAT pass 8 data covering from 2008 August to 2021 March. The results show that the histogram of the gamma-ray fluxes follows a log-normal distribution. Interestingly, in the analysis of about 5.8-year (from MJD 56317 to 58447) LAT data between two outbursts (occurring during 2012 October and 2019 May respectively), a quasi-periodic oscillation (QPO) with a period of about 1.1 years (about 5 sigma of significance) is found in the Lomb-Scargle Periodogram (LSP), the Weighted W…
The High Energy Stereoscopic System (H.E.S.S.) has revealed many TeV (10 12 eV) gamma-ray sources along the Galactic Plane and around 30 percent of these sources remain unidentified. The morphology and dynamics of dense gas coincident and surrounding the gamma-ray emission can provide clues about the nature of the TeV emission. The H2O Southern Galactic Plane Survey (HOPS) undertaken with the Mopra radio telescope, includes several dense gas tracers, such as NH3 (n,n) transitions and HC3N (3-2), star formation tracers including H2O masers, and radio recombination lines which trace ionised gas.…
We perform a search for sources of gamma-rays with energies E>100 GeV at low Galactic latitudes |b|<10 deg using the data of Fermi telescope. To separate compact gamma-ray sources from the diffuse emission from the Galaxy, we use the Minimal Spanning Tree method with threshold of 5 events in inner Galaxy (Galactic longitude |l|<60 deg) and of 3 events in outer Galaxy. Using this method, we identify 22 clusters of very-high-energy (VHE) gamma-rays, which we consider as "source candidates". 3 out of 22 event clusters are expected to be produced in result of random coincidences of arrival directi…
Kes 69, 3C 396, and 3C 400.2 are mixed-morphology (MM) Galactic supernova remnants (SNRs), where Kes 69 and 3C 396 are interacting with molecular clouds (MCs). Previous X-ray studies showed that the emission from these SNRs is thermal. It has been suggested that MM SNRs interacting with MCs are potential candidates for recombining plasma (RP) in X-rays and hadronic gamma-ray emission. Recently, Chandra observations revealed signs of RP in 3C 400.2. Our preliminary analyses show that the X-ray emission of NW and SE region of 3C 400.2 arises from recombining plasma. We detected GeV gamma-ray emi…
Galactic Diffuse Gamma-Ray and Neutrino Emission from Cosmic-Ray Interactions in Stellar Atmospheres
通过耦合恒星演化模型和宇宙线输运，首次系统评估恒星作为强子靶的累积贡献，发现其对银河系弥散伽马射线背景可忽略，但在超高能段成为不可减除的局域背景。
The inner region of the Milky Way is one of the most interesting and complex regions of the gamma-ray sky. The intense interstellar emission and resolved point sources, as well as potential contributions by other sources such as unresolved source populations and dark matter, complicate the interpretation of the data. In this paper the Fermi LAT team analysis of a 15x15 degree region about the Galactic centre is described. The methodology for point-source detection and treatment of the interstellar emission is given. In general, the bulk of the gamma-ray emission from this region is attributabl…
We present Chandra ACIS-I X-ray observations of 0FGL J1311.9-3419 and 0FGL J1653.4-0200, the two brightest high Galactic latitude (|b|>10 deg) gamma-ray sources from the 3 month Fermi-LAT bright source list that are still unidentified. Both were also detected previously by EGRET, and despite dedicated multi-wavelength follow-up, they are still not associated with established classes of gamma-ray emitters like pulsars or radio-loud active galactic nuclei. X-ray sources found in the ACIS-I fields of view are catalogued, and their basic properties are determined. These are discussed as candidate …
The GPSP Atlas: High-resolution Galactic Photon Survival Probability Atlas for Very-High- and Ultra-High-Energy Gamma-Ray Astronomy
本研究构建了首个覆盖1 TeV至10 PeV的GPSP星图，基于GALPROP模型生成，可用于伽马射线衰减计算，还扩展至LIV场景，为银河PeV天文学研究提供了公开基础。
The spectral shapes of Galactic gamma-ray source
针对地面伽马射线望远镜（含LHAASO）发布的TeV/PeV能区银河系源目录，研究发现其能谱均弯曲且30TeV上下斜率差异显著，累积能谱随能量软化，为理解其起源这一高能天体物理关键挑战提供观测基础。
The number of millisecond pulsars (MSPs) observed in Milky Way globular clusters has increased explosively in recent years, but the underlying population is still uncertain due to observational biases. We use state-of-the-art $N$-body simulations to study the evolution of MSP populations in dense star clusters. These cluster models span a wide range in initial conditions, including different initial masses, metallicities, and virial radii, which nearly cover the full range of properties exhibited by the population of globular clusters in the Milky Way. We demonstrate how different initial clus…
Recent observations of the diffuse Galactic gamma-ray emission by the Fermi-LAT satellite have shown significant deviations from models which assume the same diffusion properties for cosmic rays (CR) throughout the Galaxy. We explore the possibility that a fraction of this diffuse Galactic emission could be due to hadronic interactions of CRs self-confined in the region around their sources. In fact, freshly accelerated CRs that diffuse away from the acceleration region can trigger the streaming instability able to amplify magnetic disturbance and to reduce the particle diffusion. When this ha…
We investigate the gamma-ray and X-ray emission from the transient gamma-ray source Fermi J0035+6131, which was discovered with the Fermi Large Area Telescope (LAT) near the Galactic plane at $b=1.3^\circ$, and we discuss potential multi-wavelength counterparts of the gamma-ray source. Our analysis of over 9 years of Fermi LAT data revealed two flaring events lasting 10-30 hr during which the gamma-ray flux increased by a factor of >300 compared to the long-term average. We also analyzed X-ray data obtained with XMM-Newton and Swift and identified several sources with a hard X-ray spectrum ins…
The spectral data on the diffuse Galactic gamma-rays, at medium and high latitudes (|b| > 10) and energies of 1-100 GeV, recently published by the Fermi Collaboration are used to produce a novel study on the gamma-ray emissivity in the Galaxy. We focus on analyzing the properties of propagation of cosmic rays (CRs), using the publicly available DRAGON code. We critically address some of the models for the interstellar HI and H2 gas distributions commonly used in the literature, as well as test a variety of propagation models. Each model assumes a distinct global profile for the diffusion and t…
Dark matter annihilation in Galactic substructure will produce diffuse gamma-ray emission of remarkably constant intensity across the sky, making it difficult to disentangle this Galactic dark matter signal from the extragalactic gamma-ray background. We show that if Galactic dark matter contributes a modest fraction of the measured emission in an energy range accessible to the Fermi Gamma-ray Space Telescope, the energy dependence of the angular power spectrum of the total measured emission could be used to confidently identify gamma rays from Galactic dark matter substructure.
Radiatively inefficient accretion flows (RIAFs) in low-luminosity active galactic nuclei (LLAGNs) have been suggested as cosmic-ray and neutrino sources that may largely contribute to the observed diffuse neutrino intensity. We show that this scenario naturally predicts hadronic multi-TeV gamma-ray excesses around Galactic centers. The protons accelerated in the RIAF in Sagittarius A$^*$ (Sgr A$^*$) escape and interact with dense molecular gas surrounding Sgr A$^*$, which is known as the central molecular zone (CMZ), and produce gamma rays as well as neutrinos. Based on a theoretical model tha…
We report on the discovery of two gamma-ray sources at E > 200 GeV with VERITAS: RX J0648.7+1516 and VER J0521+211. Both sources are located at low galactic latitudes (|b| < 10 deg), and were previously classified as active galactic nuclei of unknown type. The discovery and characterization of gamma-ray emission together with follow-up optical spectroscopy permitted the identification of RX J0648.7+1516 and VER J0521+211 as BL Lac-type blazars. In the case of RX J0648.7+1516, a spectroscopic redshift of z = 0.179 was derived.
Dark matter annihilation in Galactic substructure produces diffuse gamma-ray emission of remarkably constant intensity across the sky, and in general this signal dominates over the smooth halo signal at angles greater than a few tens of degrees from the Galactic Center. The large-scale isotropy of the emission from substructure suggests that it may be difficult to extract this Galactic dark matter signal from the extragalactic gamma-ray background. I show that dark matter substructure induces characteristic small-scale anisotropies in the diffuse emission which may provide a robust means of di…
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