The nature of the GeV gamma-ray Galactic center excess (GCE) in the data of Fermi-Large Area Telescope (LAT) is still to be unveiled. We present a new analysis of the inner Galaxy Fermi-LAT data at energies above 10 GeV, based on an innovative method which combines the skyFACT adaptive template fitting with and the 1pPDF pixel-count statistics. We find a strong evidence for the GCE also at high energies, $σ> 5$ regardless of the GCE spatial template. Remarkably, our fits prefer the bulge morphological model over the dark matter one at high significance, and show no evidence for an additional dark matter template on top of the bulge component. Through the 1pPDF analysis, we find that the model best describing the gamma-ray data requires a smooth, diffuse GCE following a bulge morphology, together with sub-threshold point sources. The 1pPDF fit reconstructs a consistent population of faint point sources down at least to $10^{-12}$ ph cm$^{-2}$ s$^{-1}$. Between $10^{-12}$ ph cm$^{-2}$ s$^{-1}$ and $10^{-11}$ ph cm$^{-2}$ s$^{-1}$ the 1pPDF measures a number of point sources significantly higher than the ones in the Fermi 4FGL catalog. The robustness of our results brings further support to the attempt of explaining, at least partially, the high-energy tail of the GCE in terms of a population of point sources, likely corresponding to millisecond pulsars.
With the Fermi-LAT data quite a few research groups have reported a spatially extended GeV $γ$-ray excess surrounding the Galactic Center (GC). The physical origin of such a GeV excess is still unclear and one interesting possibility is the inverse Compton scattering of the electrons/positrons from annihilation of self-interacting dark matter (SIDM) particles with the interstellar optical photons. In this work we calculate the morphology of such a kind of $γ$-ray emission. For the annihilation channel of $\barχχ\rightarrow ϕϕ\rightarrow e^{+}e^{-}e^{+}e^{-}$, the inverse Compton scattering (IC…
We show that the soft X-ray excess in the Coma cluster can be explained by a cosmic background of relativistic axions converting into photons in the cluster magnetic field. We provide a detailed self-contained review of the cluster soft X-ray excess, the proposed astrophysical explanations and the problems they face, and explain how a 0.1-1 keV axion background naturally arises at reheating in many string theory models of the early universe. We study the morphology of the soft excess by numerically propagating axions through stochastic, multi-scale magnetic field models that are consistent wit…
Excess GeV gamma rays from the Galactic Center (GC) have been measured with the Fermi Large Area Telescope (LAT). The presence of the GC excess (GCE) appears to be robust with respect to changes in the diffuse galactic background modeling. The three main proposals for the GCE are an unresolved population of millisecond pulsars (MSPs), outbursts of cosmic rays from the GC region, and self-annihilating dark matter (DM). The injection of secondary electrons and positrons into the interstellar medium (ISM) by an unresolved population of MSPs or DM annihilations can lead to observable gamma-ray emi…
One of the main, unresolved questions about the nature of quasars is the position of the acceleration site responsible for the highest energies. The attempt to investigate this question in the energy regime with the highest resolution, the radio band, has the downside that no theoretical model exists that can connect these two regimes. The model in this work tries to shrink this gap by extending the general synchrotron self Compton (SSC) model up to length scales in the order of the resolution of radio observations. The resulting spectral energy distributions (SED) show a qualitative improveme…
Predefined spatial templates to describe the background of $γ$-ray emission from astrophysical processes, like cosmic ray interactions, are used in previous searches for the $γ$-ray signatures of annihilating galactic dark matter. In this proceeding, we investigate the GeV excess in the inner Galaxy using an alternative approach, in which the astrophysical components are identified solely by their spectral and morphological properties. We confirm the reported GeV excess and derive related parameters for dark matter interpretation, which are consistent with previous results. We investigate the …
Recently, a spatially extended excess of gamma rays collected by the Fermi-LAT from the inner region of the Milky Way has been detected by different groups and with increasingly sophisticated techniques. Yet, any final conclusion about the morphology and spectral properties of such an extended diffuse emission are subject to a number of potentially critical uncertainties, related to the high density of cosmic rays, gas, magnetic fields and abundance of point sources. We will present a thorough study of the systematic uncertainties related to the modelling of diffuse background and to the propa…
The excess of $γ$ rays in the data measured by Fermi-LAT from the Galactic center region is one of the most intriguing mysteries in Astroparticle Physics. This Galactic center excess (GCE), has been measured with respect to different interstellar emission models (IEMs), source catalogs, data selections and techniques. Although several proposed interpretations have appeared in the literature, there are not firm conclusions as to its origin. The main difficulty in solving this puzzle lies in modeling a region of such complexity and thus precisely measuring the characteristics of the GCE. In this…
Fermi-LAT observations of the Galactic Center (GC) have revealed a spherically- symmetric excess of GeV gamma rays extending to at least 10 deg from the dynamical center of the Galaxy. A critical uncertainty in extracting the intensity, spectrum, and morphology of this excess concerns the accuracy of astrophysical diffuse gamma-ray emission models near the GC. Recently, it has been noted that many diffuse emission models utilize a cosmic-ray injection rate far below that predicted based on the observed star formation rate in the Central Molecular Zone. In this study, we add a cosmic-ray inject…
Studies of Fermi data indicate an excess of GeV gamma rays around the Galactic center (GC), possibly due to dark matter. We show that young gamma-ray pulsars can yield a similar signal. First, a high concentration of GC supernovae naturally leads to a population of kicked pulsars symmetric about the GC. Second, while very-young pulsars with soft spectra reside near the Galactic plane, pulsars with spectra that have hardened with age accumulate at larger angles. This combination, including unresolved foreground pulsars, traces the morphology and spectrum of the Excess.
The so-called "GeV-excess" of the diffuse Galactic gamma-ray emission is studied with a spectral template fit based on energy spectra. The spectral templates can be obtained in a data-driven way from the gamma-ray data, which avoids the use of emissivity models to subtract the standardbackground processes from the data. Instead, one can determine these backgrounds simultaneously with any "signals" in any sky direction, including the Galactic disk and the Galactic center. Using the spectral template fit two hypothesis of the "GeV-excess" were tested: the dark matter (DM) hypothesis assuming the…
Several groups have identified an extended excess of gamma rays over the modeled foreground and background emissions towards the Galactic center (GC) based on observations with the Fermi Large Area Telescope. This excess emission is compatible in morphology and spectrum with a telltale sign from dark matter (DM) annihilation. Here, we present a critical reassessment of DM interpretations of the GC signal in light of the foreground and background uncertainties that some of us recently outlaid in Calore et al. 2014. We find that a much larger number of DM models fits the gamma-ray data than prev…
We present the effective $J$-factors for the Milky Way for scenarios in which dark matter annihilation is p-wave or d-wave suppressed. We find that the velocity suppression of dark matter annihilation can have a sizable effect on the morphology of a potential dark matter annihilation signal in the Galactic Center. The gamma-ray flux from the innermost region of the Galactic Center is in particular suppressed. We find that for dark matter density profiles with steep inner slopes, the morphology of the Inner Galaxy gamma-ray emission in p-wave models can be made similar to the morphology in stan…
It has been proposed that a recent outburst of cosmic-ray electrons could account for the excess of GeV-scale gamma rays observed from the region surrounding the Galactic Center. After studying this possibility in some detail, we identify scenarios in which a series of leptonic cosmic-ray outbursts could plausibly generate the observed excess. The morphology of the emission observed outside of $\sim1^{\circ}-2^{\circ}$ from the Galactic Center can be accommodated with two outbursts, one which took place approximately $\sim10^6$ years ago, and another (injecting only about 10\% as much energy a…
The H.E.S.S. collaboration has reported a high-energy spherically symmetric diffuse gamma-ray emission in the inner 50 pc of the Milky Way, up to ~ 50 TeV. Here we propose a leptonic model which provides an alternative to the hadronic scenario presented by the H.E.S.S. collaboration, and connects the newly reported TeV emission to the Fermi-LAT Galactic center GeV excess. Our model relies on a combination of inverse Compton emission from a population of millisecond pulsars---which can account for the GeV excess---and a supermassive black hole-induced spike of heavy (~ 60 TeV) dark matter parti…
Misaligned blazars have been the subject of some of the most successful radio and gamma-ray multiwavelength campaigns. These campaigns have included many of the major ground and space based gamma-ray telescopes and span decades of energy. Even though misaligned blazars account for only a small number of the total AGN detected at VHE, they provide a unique view on the AGN population. By viewing blazars at larger angles to our line of sight, they become a unique laboratory for the study of AGN jet substructure and the morphology of non-thermal emission processes. This contribution will discuss o…
The morphology and characteristics of the so-called GeV gamma-ray excess detected in the Milky Way lead us to speculate about a possible common origin with the 511 keV line mapped by the SPI experiment about ten years ago. In the previous version of our paper, we assumed 30 GeV dark matter particles annihilating into $b \bar{b}$ and obtained both a morphology and a 511 keV flux (ϕ_{511 keV} ~ 10^{-3} ph/cm^2/s) in agreement with SPI observation. However our estimates assumed a negligible number density of electrons in the bulge which lead to an artificial increase in the flux (mostly due to ne…
The first remnants detected by the Fermi Gamma-ray Space Telescope were of the type of mixed-morphology supernova remnants interacting with molecular clouds. In this paper we are presenting preliminary results of the gamma-ray analysis of 4 selected mixed morphology remnants, G359.1-0.5, G337.8-0.1, G001.0-0.1, and G346.6-0.2, as well as G349.7+0.2, in the 0.2 - 300 GeV energy range from the data collected by Fermi Gamma-ray Space Telescope for 3 years. G359.1-0.5, G337.8-0.1, and G349.7+0.2 were all detected with significances above 5 sigma. The excess distribution of G359.1-0.5 shows extende…
Developments in neutrino astronomy have been to a great extent motivated by the search for the sources of the cosmic rays, leading at a very early stage to the concept of a cubic kilometer neutrino detector. Almost four decades later such an instrument, IceCube, is taking data and has produced the first evidence for a flux of high-energy neutrinos of cosmic origin. After a brief review of the history of the field, we will introduce IceCube and describe the first analysis of data taken with the completed instrument. The atmospheric neutrino flux cannot accommodate an excess of 28 neutrinos obse…
An excess of gamma rays at GeV energies has been pointed out in the Fermi-LAT data. This signal comes from a narrow region centred around the Galactic center and has been interpreted as possible evidence for light dark matter particles annihilating either into a mixture of leptons-antileptons and b-bbar or into b-bbar only. Focusing on the prompt gamma-ray emission, previous works found that the best fit to the data corresponds to annihilations proceeding predominantly into b-bbar. However, here we show that omitting the photon emission originating from primary and secondary electrons produced…
The center of the Milky Way is offering one of the most striking mystery in Astroparticle Physics. An excess of gamma rays (GCE) has been measured by several groups in the data collected by the Fermi Large Area Telescope (LAT) towards the Galactic center region. The spectrum and spatial morphology of the GCE have been claimed by some groups to be compatible with a signal from the Galactic halo of dark matter (DM). Instead, other analyses have demonstrated that the GCE properties, e.g., its energy spectrum, highly depend on the choice of the Galactic interstellar emission (IEM) model source cat…
We present a new extended gamma ray excess detected with the Fermi Satellite Large Area Telescope toward the Galactic Center that traces the morphology of infrared starlight emission. Combined with its measured spectrum, this new extended source is approximately consistent with inverse Compton emission from a high-energy electron-positron population with energies up to about 10 GeV. Previously detected emissions tracing the 20 cm radio, interpreted as bremsstrahlung radiation, and the Galactic Center Extended emission tracing a spherical distribution and peaking at 2 GeV, are also detected. We…
A generic prediction in the paradigm of weakly interacting dark matter is the production of relativistic particles from dark matter pair-annihilation in regions of high dark matter density. Ultra-relativistic electrons and positrons produced in the center of the Galaxy by dark matter annihilation should produce a diffuse synchrotron emission. While the spectral shape of the synchrotron dark matter haze depends on the particle model (and secondarily on the galactic magnetic fields), the morphology of the haze depends primarily on (1) the dark matter density distribution, (2) the galactic magnet…
The region around the Galactic center (GC) is now well established to be brighter at energies of a few GeV than expected from conventional models of diffuse gamma-ray emission and catalogs of known gamma-ray sources. We study the GeV excess using 6.5 years of data from the Fermi Large Area Telescope. We characterize the uncertainty of the GC excess spectrum and morphology due to uncertainties in cosmic-ray source distributions and propagation, uncertainties in the distribution of interstellar gas in the Milky Way, and uncertainties due to a potential contribution from the Fermi bubbles. We als…
Since the discovery of an excess in gamma rays in the direction of M31, its cause has been unclear. Published interpretations focus on a dark matter or stellar related origin. Studies of a similar excess in the Milky Way center motivate a correlation of the spatial morphology of the signal with the distribution of stellar mass in M31. However, a robust determination of the best theory for the observed excess emission is very challenging due to large uncertainties in the astrophysical gamma-ray foreground model. Here we perform a spectro-morphological analysis of the M31 gamma-ray excess using …
Gamma-ray data from the Fermi-Large Area Telescope reveal an unexplained, apparently diffuse, signal from the Galactic bulge that peaks near 2 GeV with an approximately spherical intensity profile $\propto r^{-2.4}$ that extends to angular radial scales of at least 10 degrees, possibly to 20 degrees. The origin of this "Galactic Centre Excess" (GCE) has been debated with proposed sources prominently including self-annihilating dark matter and a hitherto undetected population of millisecond pulsars (MSPs). However, the conventional channel for the generation of MSPs has been found to predict to…
We compare the full-sky morphology of the 511 keV gamma ray excess measured by the INTEGRAL/SPI experiment to predictions of models based on dark matter (DM) scatterings that produce low-energy positrons: either MeV-scale DM that annihilates directly into e+e- pairs, or heavy DM that inelastically scatters into an excited state (XDM) followed by decay into e+e- and the ground state.By direct comparison to the data, we find that such explanations are consistent with dark matter halo profiles predicted by numerical many-body simulations for a Milky Way-like galaxy. Our results favor an Einasto p…
A new measurement of a spatially extended gamma-ray signal from the center of the Andromeda galaxy (M31) has been recently published by the Fermi-LAT collaboration, reporting that the emission broadly resembles the so-called Galactic center excess (GCE) of the Milky Way (MW). At the same time, evidence is accumulating on a millisecond pulsar (MSPs) origin for the GCE. These elements prompt us to compare the mentioned observations with what is, perhaps, the simplest model for an MSP population, solely obtained by rescaling of the MSP luminosity function determined in the local MW disk via the r…
The Fermi-LAT γ-ray data have been used to study the morphological and spectral features of the so-called GeV excess - a diffuse radiation component recently discovered towards the Galactic centre. We used the likelihood method to analyze Fermi-LAT data. Our study does confirm the existence of such an extra component in the diffuse γ-ray emission at GeV energies. Based on a detailed morphological analysis, a spatial template that fits the data best was generated and adopted. Using this template, the energy distribution of γ-rays was derived in the 0.3-30 GeV energy interval. The spectrum appea…
The WMAP haze is an excess in the 22 to 93 GHz frequency bands of WMAP extending about 10 degrees from the galactic center. We show that synchrotron emission from electron-positron pairs injected into the interstellar medium by the galactic population of pulsars with energies in the 1 to 100 GeV range can explain the frequency spectrum of the WMAP haze and the drop in the average haze power with latitude. The same spectrum of high energy electron-positron pairs from pulsars, which gives rise to the haze, may also generate the observed excesses in AMS, HEAT and PAMELA. We discuss the spatial mo…
Recent claims of a gamma-ray excess in the diffuse galactic emission detected by the Fermi Large Area Telescope with a morphology similar to the WMAP haze were based on the assumption that spatial templates of the interstellar medium (ISM) column density and the 408 Mhz sky are good proxies for neutral pion and inverse Compton (IC) gamma-ray emission, respectively. We identify significant systematic effects in this procedure that can artificially induce an additional diffuse component with a morphology strikingly similar to the claimed gamma-ray haze. To quantitatively illustrate this point we…
The Fermi Large Area Telescope data appear to have an excess of gamma rays from the inner 150 pc of the Galactic Center (GC). The main explanations proposed for this are: an unresolved population of millisecond pulsars (MSPs), dark matter (DM) annihilation, and cosmic rays interacting with molecular clouds at the GC. In this conference proceeding article we highlight some of the cosmic-ray results of [1]. The MSPs and DM explanations were modeled with spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope $γ=1.2$. The cosmic-ray option w…
We analyze the distribution of arrival directions of ultra-high energy cosmic rays recorded at the Pierre Auger Observatory in 10 years of operation. The data set, about three times larger than that used in earlier studies, includes arrival directions with zenith angles up to $80^\circ$, thus covering from $-90^\circ$ to $+45^\circ$ in declination. After updating the fraction of events correlating with the active galactic nuclei (AGNs) in the Véron-Cetty and Véron catalog, we subject the arrival directions of the data with energies in excess of 40 EeV to different tests for anisotropy. We sear…
The TeV gamma-ray source MGRO J1908+06 is one of the highest-energy sources known, with observed emission by the High Altitude Water Cherenkov (HAWC) Observatory extending well past 100 TeV. The source exhibits both energy-dependent morphology and a spatially-dependent spectral index. The emission is likely to be dominantly leptonic, and associated with the radio-quiet PSR J1907+0602. However, one-population models do not describe the data well; a second particle population is needed to explain the shape of the spectral energy distribution at the highest energies. This component can be well-de…
If a component of dark matter has dissipative interactions, it can cool to form compact astrophysical objects with higher density than that of conventional cold dark matter (sub)haloes. Dark matter annihilations might then appear as point sources, leading to novel morphology for indirect detection. We explore dissipative models where interaction with the Standard Model might provide visible signals, and show how such objects might give rise to the observed excess in gamma rays arising from the galactic center.
Multi-Component Dark Matter as a Solution to the Galactic Center GeV Excess
Universidade Federal do Rio Grande do Norte（北里奥格兰德联邦大学）；International Institute of Physics, Universidade Federal do Rio Grande do Norte（北里奥格兰德联邦大学国际物理研究所）；Millennium Institute for Subatomic Physics at the High-Energy Frontier (SAPHIR) of ANID（智利国家研究与发展局高能前沿亚原子物理千年研究所（SAPHIR））；Universidad de La Serena（拉塞雷纳大学）；Observatório Nacional（国家天文台）；Universidad Pedagógica y Tecnológica de Colombia（哥伦比亚教育技术大学）
A posteriori anisotropy study of ultra-high energy cosmic rays (UHECRs) with the Pierre Auger Observatory (PAO) has shown evidence of excess of cosmic ray particles above 55 EeV within $18^{\circ}$ of the direction of the radio galaxy Centaurus A. However, the origin of the excess remains elusive. We simulate the propagation of different species of particles coming from the direction of Centaurus A in the Galactic magnetic fields, and find that only particles of nuclear charge $Z\la 10$ can avoid being deflected outside of the $18^{\circ}$ window of Centaurus A. On the other hand, considering …
We compare the surface brightness profile and morphology of the Galactic Centre Excess (GCE) identified in wide-angle $γ$-ray maps from the Fermi-Large Area Telescope to dark matter annihilation predictions derived from high-resolution $Λ$CDM magnetohydrodynamic simulations of galaxy formation. These simulations produce isolated, disc-dominated galaxies with structure, stellar populations, gas content, and stellar and halo masses comparable to those of the Milky Way. For a specific choice of annihilation cross-section, they agree well with the Fermi-LAT data over the full observed angular rang…
We present the ionised gas outflow morphology in the Circinus galaxy using the Narrow Field Mode (NFM) of the MUSE instrument on board the Very Large Telescope (VLT). The NFM observations provide a spatial resolution of $\sim$0.1", corresponding to a physical scale of $\sim$2 pc, one of the highest spatial resolution achievable using ground-based AO-assisted observations in the optical wavelengths. The MUSE observations reveal a collimated clumpy outflow profile originating near the AGN location and extending up to 1.5" ($\sim$30 pc) in the NW direction. The collimated structure then fragments…
The Fermi-LAT data revealed giant bubbles of emission above and below the Galactic plane with an energy spectrum significantly harder than seen from other directions. How the bubbles connect to the Galactic plane is unclear. We find that bubble-like emission is not only found in the halo, but it is strongly present in the Galactic plane as well with a morphology close to the spatial distribution of the 1.8 MeV gamma-ray line from 26Al, a radioactive nucleus synthesized in SNRs. In addition, the spectral shape of this hard component coincides with the predicted spectrum from cosmic rays trapped…
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…
We present new X-ray (Chandra) and radio (ATCA) observations of the z=0.09 radio galaxy PKS B1416-493, a member of the southern equivalent of the 3CRR sample. We find the source to be embedded in a previously unrecognized bright kT=4.6 keV non cool-core cluster. The discovery of new clusters of such high temperature and luminosity within z=0.1 is rare. The radio source was chosen for observation based on its intermediate FRI/II morphology. We identify a cavity coincident with the northeast lobe, and excess counts associated with the southwest lobe that we interpret as inverse Compton X-ray emi…
Galaxy clusters can be sources of high-energy (HE) $γ$-ray radiation, due to the efficient acceleration of particles exceeding EeV energies. At present, though, the only candidate for emitting HE $γ$-rays is the Coma cluster, towards which an excess of $γ$-ray emission has been detected by the Fermi Large Area Telescope (LAT). Using $\mathrm{\sim12.3}$ years of \textit{Fermi}-LAT data, we explored the region of the Coma cluster between energies 100 MeV and 1 TeV by detailed spectral and morphological analysis. In the region of the Coma cluster, we detected diffuse gamma-ray emission of energie…
