The High-Energy Stereoscopic System (HESS) has detected intense diffuse TeV emission correlated with the distribution of molecular gas along the galactic ridge at the centre of our Galaxy. Earlier HESS observations of this region had already revealed the presence of several point sources at these energies, one of them (HESS J1745-290) coincident with the supermassive black hole Sagittarius A*. It is still not entirely clear what the origin of the TeV emission is, nor even whether it is due to hadronic or leptonic interactions. It is reasonable to suppose, however, that at least for the diffuse emission, the tight correlation of the intensity distribution with the molecular gas indicates a pionic-decay process involving relativistic protons. In this paper, we explore the possible source(s) of energetic hadrons at the galactic centre, and their propagation through a turbulent medium. We conclude that though Sagittarius A* itself may be the source of cosmic rays producing the emission in HESS J1745-290, it cannot be responsible for the diffuse emission farther out. A distribution of point sources, such as pulsar wind nebulae dispersed along the galactic plane, similarly do not produce a TeV emission profile consistent with the HESS map. We conclude that only a relativistic proton distribution accelerated throughout the inter-cloud medium can account for the TeV emission profile measured with HESS.
The detection by the HESS atmospheric Cerenkov telescope of fourteen new sources from the Galactic plane makes it possible to estimate the contribution of unresolved sources like those detected by HESS to the diffuse Galactic emission measured by the Milagro Collaboration. The number-intensity relation and the luminosity function for the HESS source population are investigated. By evaluating the contribution of such a source population to the diffuse emission we conclude that a significant fraction of the TeV energy emission measured by the Milagro experiment could be due to unresolved sources…
The Whipple 10 meter atmospheric Cherenkov telescope has made observations of the region known as the Cygnus arm. This region has been recently reported by the Milagro experiment to contain a diffuse TeV gamma-ray source centered at RA=308 and Dec=42. We report upper limits (using the Whipple 10 m telescope) obtained during the Fall 2004 observing season centered on RA=310 and Dec=42.65.
We obtained new upper limits on the diffuse gamma rays from the inner Galactic (IG) and outer Galactic (OG) planes in 3.10 TeV region, using the Tibet air shower data and new Monte Carlo simulation results. A difference of the effective area of the air-shower array for observing gamma rays and cosmic rays was carefully taken into account in this analysis, resulting in that the flux upper limits of the diffuse TeV gamma rays were reduced by factors of 4.0.3.7 for 3.10 TeV than those in our previous results (Amenomori, M., Ayabe, S., Cui, S.W., et al. Observation of multi-TeV diffuse gamma rays …
The detection of TeV gamma-rays from the blazar H 1426+428 at an integral flux level of (4 +- 2(stat) +- 1(syst)) 10^(-12) erg cm^(-2) s^(-1) above 1 TeV with the HEGRA imaging atmospheric Cherenkov telescope system is reported. H 1426+428 is located at a redshift of z=0.129, which makes it the most distant source detected in TeV gamma-rays so far. The TeV radiation is expected to be strongly absorbed by the diffuse extragalactic background radiation (DEBRA). The observed energy spectrum of TeV photons is in good agreement with an intrinsic power law spectrum of the source ~E^(-1.9) corrected …
The intense Compton cooling of ultra-relativistic electrons in the Klein-Nishina regime in radiation dominated environments, such as that found in the Galactic Centre, may result in radically different electron spectra than those produced by Synchrotron cooling. We explore these effects and their impact on the X-ray and gamma-ray spectra produced in electron accelerators in this region in comparison to elsewhere in our galaxy. We discuss the broad-band emission expected from the newly discovered pulsar wind nebula G 359.95-0.04 and the possible relationship of this X-ray source to the central …
Recently the Milagro experiment observed diffuse multi-TeV gamma-ray emission in the Cygnus region, which is significantly stronger than what predicted by the Galactic cosmic ray model. However, the sub-GeV observation by EGRET shows no excess to the prediction based on the same model. This TeV excess implies possible high energy cosmic rays populated in the region with harder spectrum than that observed on the Earth. In the work we studied this theoretical speculation in detail. We find that, a diffuse proton source with power index $α_p\lesssim 2.3$, or a diffuse electron source with power i…
Using data from the HEGRA air shower array, taken in the period from April 1998 to March 2000, upper limits on the ratio I_gamma /I_CR of the diffuse photon flux I_gamma to the hadronic cosmic ray flux I_CR are determined for the energy region 20 TeV to 100 TeV. The analysis uses a gamma-hadron discrimination which is based on differences in the development of photon- and hadron-induced air showers after the shower maximum. A method which is sensitive only to the non-isotropic component of the diffuse photon flux yields an upper limit of I_gamma /I_CR (at 54 TeV) < 2.0*10^-3 (at the 90% confid…
We report the TeV gamma-ray observations of the nearby normal spiral galaxy NGC 253. At a distance of $\sim$2.5 Mpc, NGC 253 is one of the nearest starburst galaxies. This relative closeness, coupled with the high star formation rate in the galaxy, make it a good candidate TeV gamma-ray source. Observations were carried out in 2000 and 2001 with the CANGAROO-II 10 m imaging atmospheric Cerenkov telescope. TeV gamma-ray emission is detected at the $\sim 11σ$ level with a flux of $(7.8 \pm 2.5)\times 10^{-12} {\rm cm}^{-2} {\rm sec}^{-1}$ at energies $>$0.5 TeV. The data indicate that the emissi…
Data from the Tibet-III air shower array (with energies around 3 TeV) and from the Tibet-II array (with energies around 10 TeV) have been searched for diffuse gamma rays from the Galactic plane. These arrays have an angular resolution of about 0.9 degrees. The sky regions searched are the inner Galaxy, 20 degrees <= l <= 55 degrees, and outer Galaxy, 140 degrees <= l <= 225 degrees, and |b| <= 2 degrees or <= 5 degrees. No significant Galactic plane gamma-ray excess was observed. The 99% confidence level upper limits for gamma-ray intensity obtained are (for |b| <= 2 degrees) 1.1 times 10^{-15…
The detection of non-baryonic dark matter through its gamma-ray annihilation in the centre of our galaxy has been studied. The gamma fluxes according to different models have been simulated and compared to those expected to be observed with the Alpha Magnetic Spectrometer (AMS), during a long-term mission on board of the International Space Station. Under the assumption that the dark matter halo is composed of the lightest, stable supersymmetric particle, the neutralino, the results of the simulations in the framework of mSUGRA models, show that with a cuspy dark matter halo or a clumpy halo, …
Recent progress in pushing the sensitivity of the Imaging Atmospheric Cherenkov Technique into the 10 mCrab regime has enabled first sensitive observations of the innermost few 100 pc of the Milky Way in Very High Energy (VHE; >100 GeV) gamma rays. These observations are a valuable tool to understand the acceleration and propagation of energetic particles near the Galactic Centre. Remarkably, besides two compact gamma-ray sources, faint diffuse gamma-ray emission has been discovered with high significance. The current VHE gamma-ray view of the Galactic Centre region is reviewed, and possible c…
Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. We show that such cascades can contribute between ~1% and ~50% of the GeV-TeV diffuse photon flux measured by the EGRET experiment. The GLAST satellite should have a good chance to discover this flux.
The flux upper limits of the diffuse gamma rays, from the inner and outer Galactic planes, are revised by factors of 4.0$\sim$3.7 for mode energies 3$\sim$10 TeV, respectively, by using the simulation results of the effective area ratios for gamma-ray induced showers and cosmic-ray induced ones in the Tibet air shower array. In our previous work, (Amenomori et al., ApJ, 580, 887, 2002) the flux upper limits were deduced only from the flux ratio of air showers generated by gamma rays versus cosmic rays. The details of the simulation are given in the paper (Amenomori et al., Advances in Space Re…
Using the cosmic ray (CR) data available in the energy interval $(10 - 2 \times 10^{7})$ GeV/particle, we have calculated the profile of the primary $γ$-ray spectrum produced by the interaction of these CR with thermal nuclei of the ISM. Normalized to the EGRET measurements, this allows an estimate of the galactic diffuse $γ$-ray background due to intermediate and high energy CR at TeV energies. On the other hand, over the last few years, several particles with energies above $10^{20}$ eV (beyond the Greisen-Zatsepin-Kuzmin cut-off) have been detected. These particles are very likely extragala…
We simulate the neutrino and $γ$-ray emissions of the Galaxy which are originated from the hadronic scattering of cosmic rays (CR) with the interstellar medium (ISM). Rather than assuming a uniform CR density, we estimate the spatial distribution of CR nuclei by means of numerical simulations. We consider several models of the galactic magnetic field and of the ISM distribution finding only a weak dependence of our results on their choice. We found that by extrapolating the predicted $γ$-ray spectra down to few GeV we get a good agreement with EGRET measurements. Then, we can reliably compare …
We employ the Monte Carlo particle collision code DPMJET3.04 to determine the multiplicity spectra of various secondary particles (in addition to $π^0$'s) with $γ$'s as the final decay state, that are produced in cosmic-ray ($p$'s and $α$'s) interactions with the interstellar medium. We derive an easy-to-use $γ$-ray production matrix for cosmic rays with energies up to about 10 PeV. This $γ$-ray production matrix is applied to the GeV excess in diffuse Galactic $γ$-rays observed by EGRET, and we conclude the non-$π^0$ decay components are insufficient to explain the GeV excess, although they h…
The diffuse Galactic gamma-ray background, as observed with EGRET on CGRO, exceeds the model predictions significantly above 1 GeV. This is particularly true for the inner Galaxy. We shall discuss here the contribution of the Galactic Cosmic Ray (GCR) sources, considered as unresolved, and in addition the possibility that the transport of the GCRs out of the Galaxy is not uniform over the Galactic disk. In both cases the spectrum of the diffuse gamma-rays is harder than the GCR spectrum in the neighborhood of the Solar system, as observed in situ. The source contribution is a necessary and, as…
Diffuse $γ$-ray emission produced by the interaction of cosmic-ray particles with matter and radiation in the Galaxy can be used to probe the distribution of cosmic rays and their sources in different regions of the Galaxy. With its large field of view and long observation time, the Milagro Gamma Ray Observatory is an ideal instrument for surveying large regions of the Northern Hemisphere sky and for detecting diffuse $γ$-ray emission at very high energies. Here, the spatial distribution and the flux of the diffuse $γ$-ray emission in the TeV energy range with a median energy of 15 TeV for Gal…
Diffuse 511 keV line emission, from the annihilation of cold positrons, has been observed in the direction of the Galactic Centre for more than 30 years. The latest high-resolution maps of this emission produced by the SPI instrument on INTEGRAL suggest at least one component of the emission is spatially coincident with the distribution of ~70 luminous, low-mass X-ray binaries detected in the soft gamma-ray band. The X-ray band, however, is generally a more sensitive probe of X-ray binary populations. Recent X-ray surveys of the Galactic Centre have discovered a much larger population (>4000) …
The CANGAROO-II telescope observed sub-TeV gamma-ray emission from the nearby starburst galaxy NGC 253. The emission region was extended with a radial size of 0.3-0.6 degree. On the contrary, H.E.S.S could not confirm this emission and gave upper limits at the level of the CANGAROO-II flux. In order to resolve this discrepancy, we analyzed new observational results for NGC 253 by CANGAROO-III and also assessed the results by CANGAROO-II. Observation was made with three telescopes of the CANGAROO-III in October 2004. We analyzed three-fold coincidence data by the robust Fisher Discriminant meth…
In this contribution we will discuss recent results concerning the intensity and the angular distribution of the gamma-ray and neutrino emissions as should be originated from the hadronic scattering of cosmic rays (CR) with the interstellar medium (ISM). We assumed that CR sources are supernova remnants (SNR) and estimated the spatial distribution of primary nuclei by solving numerically the diffusion equation. For the ISM, we considered recent models for the 3D spatial distributions of molecular hydrogen. Respect to previous results, we find the secondary gamma-ray and neutrino emissions to b…
We report Australia Telescope Compact Array (ATCA) radio-continuum and ROSAT PSPC X-ray observations of the region surrounding the peculiar galaxy pair ESO 295-IG022, lying at the centre of the poor cluster Abell S0102. We identify a radio galaxy coincident with the galaxy pair, with bipolar, bent radio jets appearing centred on the southern galaxy, and extending both to the south, for about 95 arcseconds (approximately 100 kpc at the distance of ESO 295-IG022), and to the north, for approximately 80 arcseconds, encompassing the northern galaxy. We discuss also the idea of an additional single…
TeV gamma rays emitted by GRBs are converted into electron-positron pairs via interactions with the extragalactic infrared radiation fields. In turn the pairs produced, whose trajectories are randomized by magnetic fields, will inverse Compton scatter off the cosmic microwave background photons. The beamed TeV gamma ray flux from GRBs is thus transformed into a GeV isotropic gamma ray flux, which contributes to the total extragalactic gamma-ray background emission. Assuming a model for the extragalactic radiation fields, for the GRB redshift distribution and for the GRB luminosity function, we…
The HEGRA-IACT-system with a FoV of ~1.5 deg radius has been used for surveying one quater of the Galactic disc in respect to point sources, moderately extended sources and for diffuse emission in the energy range above 1 TeV. In total 140 h of good observation time were accumulated. No new source has been discoverd. Limits on the level of 20% or lower of the Crab flux on about 87 potential sources like SNR, Pulsars and EGRET sources are derived. A limit on the diffuse emission is given on the level of dPhi/dE(E=1 TeV) = 6.1 10^-15 ph cm-2 s-1 sr-1 Mev-1 resulting in a lower limit of 2.5 on th…
We show that inverse Compton scattering of cosmic-microwave-background and starlight photons by cosmic-ray electrons in the interstellar and intergalactic space explains well the spectrum and intensity of the diffuse gamma-ray background radiation (GBR), which was measured by EGRET aboard the Compton Gamma Ray Observatory (CGRO) in directions away from the Galactic disk and centre. The Gamma Ray Large Area Space Telescope (GLAST) will be able to separate the Galactic foreground from the extragalactic gamma-rays, and to provide stringent tests of the theory.
In X-rays, the Galactic Centre (GC) Region appears as a complex of diffuse thermal and non-thermal X-ray emission intermixed with a population of luminous discrete sources. Here we present some new findings from the XMM-Newton GC survey, focusing particularly on Sgr A*, Sgr A East, the Radio Arc region, and a newly discovered X-ray non-thermal filament.
A search for TeV - PeV muon neutrinos from unresolved sources was performed on AMANDA-II data collected between 2000 and 2003 with an equivalent livetime of 807 days. This diffuse analysis sought to find an extraterrestrial neutrino flux from sources with non-thermal components. The signal is expected to have a harder spectrum than the atmospheric muon and neutrino backgrounds. Since no excess of events was seen in the data over the expected background, an upper limit of E^{2}Φ_{90% C.L.} < 7.4 x 10^{-8} GeV cm^{-2} s^{-1} sr^{-1} is placed on the diffuse flux of muon neutrinos with a Φ\propto…
Pion decay gamma rays have long been recognized as a unique signature of hadronic cosmic rays and their interactions with the interstellar medium. We present a model-independent way of constraining this signal with observations of the Galactic Plane in diffuse gamma rays. We combine detections by the EGRET instrument at GeV energies and the Milagro Cherenkov detector at TeV energies with upper limits from KASCADE and CASA-MIA ground arrays at PeV energies. Such a long "lever arm", spanning at least six orders of magnitude in energy, reveals a "TeV excess" in the diffuse Galactic Plane gamma-ra…
INTEGRAL Spectrometer SPI data from the first year of the Galactic Centre Deep Exposure has been analysed for the diffuse continuum from the Galactic ridge. A new catalogue of sources from the INTEGRAL Imager IBIS has been used to account for their contribution to the celestial signal. Apparently diffuse emission is detected at a level ~10% of the total source flux. A comparison of the spectrum of diffuse emission with that from an analysis of IBIS data alone shows that they are consistent. The question of the contribution of unresolved sources to this ridge emission is still open.
We present an X-ray study of the field containing the extended TeV source HESS J1834-087 using data obtained with the XMM-Newton telescope. Previously, the coincidence of this source with both the shell-type supernova remnant (SNR) W41 and a giant molecular cloud (GMC) was interpreted as favoring pi^0-decay gamma-rays from interaction of the old SNR with the GMC. Alternatively, the TeV emission has been attributed to inverse Compton scattering from leptons deposited by PSR J1833-0827, a pulsar assumed to have been born in W41 but now located 24' from the center of the SNR (and the TeV source).…
We explore the possibility that the diffuse gamma-ray background radiation (GBR) at high galactic latitudes could be dominated by inverse Compton scattering of cosmic ray (CR) electrons on the cosmic microwave background radiation and on starlight from our own galaxy. Assuming that the mechanisms accelerating galactic CR hadrons and electrons are the same, we derive simple and successful relations between the spectral indices of the GBR above a few MeV, and of the CR electrons and CR nuclei above a few GeV. We reproduce the observed intensity and angular dependence of the GBR, in directions aw…
Diffuse VHE gamma radiation from the Galactic Centre ridge observed by the H.E.S.S. telescope has been convincingly linked with the propagation of recently accelerated cosmic rays that interact with molecular hydrogen clouds during their diffusion. Through a series of time-dependent simulations of that diffusion for different propagation parameters we have obtained the most probable values of the diffusion coefficient for the Galactic Centre region. Assuming that the diffusion coefficient is of the form kappa(E) = kappa_0*(E/E_0)^delta, then for different optimal combinations of kappa_0 and de…
We discover a faint shell-type radio and X-ray source, G353.6-0.7, associated with HESS J1731-347. G353.6-0.7 is likely an old supernova remnant (SNR), based on radio (0.8 GHz, 1.4 GHz and 5 GHz), infrared (8 $μ$m from the GLIMPSE Legacy Project and 21 $μ$m from the Midcourse Space Experiment), and X-ray (0.1 keV - 2.4 keV from the ROSAT survey and 5 - 20 keV from the INTEGRAL survey) data. The SNR, centered at ({\sl l}, {\sl b})=(353.55, -0.65) with a radius of $\sim$ 0.25$^{\circ}$, closely matches the outline of the recently discovered extended TeV source HESS J1731-347, which has no previo…
Diffuse Galactic gamma-ray emission is produced in interactions of cosmic rays with gas and ambient photon fields and thus provides us with an indirect measurement of cosmic rays in various locations in the Galaxy. The diffuse gamma-ray continuum is more intense than expected both at energies below 200 keV and above 1 GeV. The existing models for the high-energy excess are reviewed in the light of recent TeV gamma-ray measurements of both diffuse emission and of discrete Galactic sources such as supernova remnants. I specifically discuss whether particular classes of Galactic objects are obser…
In models with extra dimensions the fundamental scale of gravity M_D could be of order TeV. In that case the interaction cross section between a cosmic proton of energy E and a dark matter particle χwill grow fast with E for center of mass energies \sqrt{2m_χE} above M_D, and it could reach 1 mbarn at E\approx 10^9 GeV. We show that these gravity-mediated processes would break the proton and produce a diffuse flux of particles/antiparticles, while boosting χwith a fraction of the initial proton energy. We find that the expected cross sections and dark matter densities are not enough to produce…
Many astrophysical models predict a diffuse flux of high-energy neutrinos from active galactic nuclei and other extra-galactic sources. At muon energies above 1 TeV, the upward-going muon flux induced by neutrinos from active galactic nuclei is expected to exceed the flux due to atmospheric neutrinos. We have performed a search for this astrophysical neutrino flux by looking for upward-going muons in the highest energy data sample from the Super-Kamiokande detector using 1679.6 live days of data. We found one extremely high energy upward-going muon event, compared with an expected atmospheric …
