SCIENCE WITH THE NEW GENERATION OF HIGH ENERGY GAMMA‐RAY EXPERIMENTS: Proceedings of the 7th Workshop on Gamma‐Ray Physics in the LHC Era
1223(2010); http://dx.doi.org/10.1063/1.3395986View Description Hide Description
Since its launch from Cape Canaveral on June 11, 2008, the Large Area Telescope (LAT) onboard the Fermi Gamma‐ray Space Telescope has been performing a survey of the high‐energy astrophysical phenomena, including pulsars, black holes and active galactic nuclei; gamma‐ray bursts; the origin of cosmic rays and supernova remnants and searches for new phenomena such as supersymmetric dark‐matter annihilation. In this contribution I report on the performance of the LAT and on the highlight results achieved in its first year of observations.
1223(2010); http://dx.doi.org/10.1063/1.3395978View Description Hide Description
H.E.S.S. is an array of four imaging atmospheric Cherenkov telescopes situated in the Khomas highlands in Namibia. Due to its large field of view, good angular resolution and excellent sensitivity it is ideally suited to detect VHE γ‐ray sources. The Galactic plane survey and dedicated observations in pointing mode have led to the discovery of many previously unknown VHE γ‐ray sources—galactic and extragalactic alike, including new classes of sources such as starburst galaxies. Beside the discovery potential, H.E.S.S. excels at morphological studies as well as the measurement of (spatially resolved) spectra and lightcurves down to a few minute timescales, thereby fostering the investigation of the underlying processes and emission mechanisms in the observed objects.
1223(2010); http://dx.doi.org/10.1063/1.3395992View Description Hide Description
We summarize here the main highlights of the AGILE astrophysics mission. The satellite, launched in April 2007, is devoted to γ‐ray observations in the 30 MeV–30 GeV energy range, with simultaneous hard X‐ray imaging in the 18–60 keV band, and optimal timing capabilities for the study of transient phenomena. The very large field of view (2.5 sr) of the gamma‐ray imager coupled with the hard X‐ray monitoring capability makes AGILE well suited to study Galactic and extragalactic sources, as well as GRBs and other fast transients. AGILE reaches its optimal performance near 100 MeV with good imaging and sensitivity. Gamma‐ray and hard X‐ray sources can be monitored 14 times a day, and an extensive database has been obtained for a variety of sources. We summarize here the breakthroughs and most important results obtained for several sources including microquasars and other Galactic compact objects (most notably, the discovery of gamma‐ray emission above 100 MeV from Cygnus X‐3), Supernova Remnants and pulsar wind nebulae, gamma‐ray pulsars, a bright class of blazars (3C 454.3, TXS HB Mrk 421), short and long GRBs (including the remarkable short burst GRB 090510), and terrestrial gamma‐ray flashes (TGFs).
1223(2010); http://dx.doi.org/10.1063/1.3395994View Description Hide Description
On the 15th of June 2006, the PAMELA satellite‐borne experiment was launched from the Baikonur cosmodrome and it has been collecting data since July 2006. The instrument allows precision studies of the charged cosmic radiation to be conducted over a wide energy range (100 MeV–100’s GeV) with high statistics. The primary scientific goal is the measurement of the antiproton and positron energy spectrum in order to search for exotic sources, such as dark matter particle annihilations. PAMELA is also searching for primordial antinuclei (anti‐helium), and testing cosmic‐ray propagation models through precise measurements of the antiparticle energy spectrum and precision studies of light nuclei and their isotopes. Moreover, PAMELA is investigating phenomena connected with solar and earth physics. Results of the antiproton and positron data will be presented.
1223(2010); http://dx.doi.org/10.1063/1.3395995View Description Hide Description
AMS02 (Alpha Magnetic Spectrometer) is the second version of a typical particle physics detector which will be installed, starting from summer 2010, on the International Space Station (ISS) to measure the spectrum of charged cosmic rays in the region 1 GeV–1 TeV, with a high capability of identifying and measuring energy and direction of photons. Thanks to the large acceptance, to the long flight duration (at least 3 years) and to the state of the art of the techniques for particle identification, AMS has the possibility of achieving the highest sensitivity in the search of WIMP Dark Matter in this energy domain, through the contemporary measuremnt of the absolute and relative spectra of electrons and positrons, protons and antiprotons, photons and, eventually, antideuterons.
The AMS02 experiment is also able to verify the existence of antimatter in the universe through the measurement of the ratio antihelium/helium at the level.
AMS02 will measure also with high precision the nuclei spectra up to iron, providing relevant informations on the theories of transport and diffusion of cosmic rays.
1223(2010); http://dx.doi.org/10.1063/1.3395996View Description Hide Description
The DAMA/LIBRA set‐up (about 250 kg highly radiopure NaI(Tl) sensitive mass) is running at the Gran Sasso National Laboratory of the I.N.F.N.. The first DAMA/LIBRA results confirm the evidence for the presence of a Dark Matter particle component in the galactic halo, as pointed out by the former DAMA/NaI set‐up; cumulatively the data support such evidence at 8.2 σ C.L. and satisfy all the many peculiarities of the Dark Matter annual modulation signature. The main aspects and prospects of this model independent experimental approach will be outlined.
1223(2010); http://dx.doi.org/10.1063/1.3395997View Description Hide Description
Motivated by the PAMELA anomaly in the fluxes of cosmic‐ray and we study the cosmic γ‐ray induced by the inverse Compton (IC) scattering process in unstable dark matter scenario assuming that the anomaly is due to the emission by the decay of dark matter. We calculate the fluxes of IC‐induced γ‐ray produced in our Galaxy and that from cosmological distance, and show that both of them are significant. We discuss a possibility that large dark matter mass over TeV scale might be constrained by the γ‐ray observation by Fermi Gamma‐ray Space Telescope.
1223(2010); http://dx.doi.org/10.1063/1.3395998View Description Hide Description
The Fermi Gamma‐ray Space Telescope was successfully launched on June 11, 2008 and has already opened a new era for gamma‐ray astronomy. The Large Area Telescope (LAT), the main instrument on board Fermi, with its large field of view and effective area, combined with its excellent timing capabilities, presents a significant improvement in sensitivity over its predecessor EGRET. The preliminary results of the Spectral Energy Distribution Analysis performed on a sample of bright blazars are presented. We have studied the quasi‐simultaneous Spectral Energy Distributions (SED) of 48 blazars, detected within the three months of the Fermi LAT Bright AGN Sample (LBAS) data taking period, combining Fermi and Swift data with radio NIR‐Optical and hard‐X/gamma‐ray data. We have used these SEDs to characterize the peak position and intensity of both the low and the high‐energy features of blazar spectra. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broad‐band colors, i.e. the radio to optical and optical to X‐ray spectral slopes, and from the gamma‐ray spectral index. Our data show that the synchrotron peak frequency is positioned between and in FSRQs and between and in BL Lacertae objects. We find that the gamma‐ray spectral slope is strongly correlated with the synchrotron peak energy, as expected at first order in synchrotron—inverse Compton scenarios. However, simple homogeneous, one‐zone, Synchrotron Self Compton (SSC) models cannot explain most of our SEDs, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving External Compton Radiation or multiple SSC components are required to reproduce the overall SEDs and the observed spectral variability.
1223(2010); http://dx.doi.org/10.1063/1.3395999View Description Hide Description
We have studied the quasi‐simultaneous Spectral Energy Distributions (SED) of 48 LBAS blazars, detected within the three months of the LAT Bright AGN Sample (LBAS) data taking period, combining Fermi and Swift data with radio NIR‐Optical and hard‐ X/gamma‐ray data.
Using these quasi‐simultaneous SEDs, sampling both the low and the high energy peak of the blazars broad band emission, we were able to apply a diagnostic tool based on the estimate of the peak frequencies of the synchrotron (S) and Inverse Compton (IC) components.
Our analysis shows a Fermi blazar’s divide based on the peak frequencies of the SED. The robust result is that the Synchrotron Self Compton (SSC) region divides in two the plane. Objects within or below this region, radiating likely via the SSC process, are high‐frequency‐peaked BL Lac object (HBL), or low/intermediate‐frequency‐peaked BL Lac object (LBL/IBL). All of the IBLs/LBLs within or below the SSC region are not Compton dominated. The objects lying above the SSC region, radiating likely via the External radiation Compton (ERC) process, are Flat Spectrum Radio Quasars and IBLs/LBLs. All of the IBLs/LBLs in the ERC region show a significant Compton dominance.
1223(2010); http://dx.doi.org/10.1063/1.3396000View Description Hide Description
For more than one year the Fermi Large Area Telescope has been surveying the γ‐ray sky from 20 MeV to more than 300 GeV with unprecedented statistics and angular resolution. One of the key science targets of the Fermi mission is diffuse γ‐ray emission. Galactic interstellar γ‐ray emission is produced by interactions of high‐energy cosmic rays with the interstellar gas and radiation field. We review the most important results on the subject obtained so far: the non‐confirmation of the excess of diffuse GeV emission seen by EGRET, the measurement of the γ‐ray emissivity spectrum of local interstellar gas, the study of the gradient of cosmic‐ray densities and of the ratio in the outer Galaxy. We also catch a glimpse at diffuse γ‐ray emission in the Large Magellanic Cloud. These results allow the improvement of large‐scale models of Galactic diffuse γ‐ray emission and new measurements of the extragalactic γ‐ray background.
1223(2010); http://dx.doi.org/10.1063/1.3396001View Description Hide Description
The 17 m diameter MAGIC telescope, located on the Canary island of La Palma, is the largest single‐dish Cherenkov telescope for unveiling the gamma‐ray universe. It reaches the lowest energy threshold among ground‐based gamma‐ray observatories: 55 GeV for normal observations, and as low as 25 GeV using a dedicated trigger system developed for pulsar observations. MAGIC also features a unique fast follow‐up capability for tracking transients like gamma‐ray bursts. Since Fall 2004 MAGIC has been taking data routinely, successfully detecting different classes of VHE sources like pulsar wind nebulae, gamma‐ray binaries, pulsars, active galactic nuclei and radio galaxies. Here we review some of the most relevant results from recent observations, and report about the status of MAGIC‐II, a stereoscopic extension by a second 17‐m telescope already in operation.
1223(2010); http://dx.doi.org/10.1063/1.3395975View Description Hide Description
The ARGO‐YBJ experiment at YangBaJing in Tibet (4300 m a.s.l.) has been taking data with its full layout since October 2007. Here we present the first significant results obtained in gamma‐ray astronomy and cosmic‐ray physics. Emphasis is placed on the analysis of gamma‐ray emission from point‐like sources (Crab Nebula, MRK 421), on the preliminary limit on the antiproton/proton flux ratio, on the large‐scale cosmic‐ray anisotropy and on the proton‐air cross section. The performance of the detector is also discussed, and the perspectives of the experiment are outlined.
1223(2010); http://dx.doi.org/10.1063/1.3395976View Description Hide Description
N body numerical simulations of the Universe are a fundamental tool for the study of dark matter. Starting from a large scale simulation, we have performed two resimulations of a Local Group‐like region with a higher resolution. In one of them, baryons have been included. This allows us to qualitatively and quantitatively study the effect of baryons in the distribution of dark matter. In this work, we present some results of our analysis of these simulations, which is aimed in particular to determine the effect of baryons on dark matter detectability by the Fermi Gamma Ray Telescope (FGST).
1223(2010); http://dx.doi.org/10.1063/1.3395977View Description Hide Description
A generic prediction of several extensions of the Standard Model of elementary‐particle interactions is the existence of axion‐like particles (ALPs), namely very light spin‐zero bosons characterized by a two‐photon coupling. While elusive in laboratory experiments, ALPs can give rise to observable astrophysical effects for their relevant parameters in experimentally allowed ranges. We show that the unexpectedly low opacity of the Universe inferred by the Imaging Atmospheric Cherenkov Telescopes since 2006 from blazar observations above 100 GeV can be explained naturally within the De Angelis, Roncadelli & Mansutti—hereafter DARMA—scenario, namely in terms of photon‐ALP oscillations occurring in extragalactic magnetic fields. We work out the implications of the DARMA scenario for the VHE gamma‐ray spectra of blazars by contemplating all of them at once, so that the emitted and observed spectral indices can be correlated. We demonstrate that by assuming the same nominal value for all VHE blazars, the predicted observed spectral index actually fits all observations. Moreover, becomes independent of redshift for sufficiently far‐away sources. Our prediction can be tested with the satellite‐borne Fermi/LAT detector as well as with the ground‐based IACTs H.E.S.S., MAGIC, CANGAROO III, VERITAS and the Extensive Air Shower arrays ARGO‐YBJ and MILAGRO.
1223(2010); http://dx.doi.org/10.1063/1.3395979View Description Hide Description
Astrophysical observations require the existence of non‐baryonic dark matter (DM). If the dark matter particle has a mass in the TeV range and decays or annihilates via the weak interaction, very high energy (VHE) γ‐ray telescopes like H.E.S.S., MAGIC and VERITAS are well‐suited to search for dark matter signals, as photons produced in dark matter annihilations allow directional back‐tracking to their source. Dark matter searches and related observations performed by the H.E.S.S. collaboration are summarized here.
1223(2010); http://dx.doi.org/10.1063/1.3395980View Description Hide Description
The rise of nucleon UHECR above GZK astronomy made by protons (AUGER November 2007) is puzzled by three main mysteries: an unexpected nearby Virgo UHECR suppression (or absence), a rich crowded clustering frozen vertically along Cen A, a composition suggesting nuclei (not much directional) and not nucleons. The UHECR map, initially consistent with GZK volumes, to day seem to be not much correlated with expected Super Galactic Plane. Moreover slant depth data of UHECR from AUGER airshower shape do not favor the proton but points to a nuclei, while HIRES, on the contrary favors mostly nucleons. We tried (at least partially) to solve the contradictions assuming UHECR as light nuclei (mostly ) spread by planar galactic fields, randomly at vertical axis. The fragility and its mass and charge explains the Virgo absence (due to opacity above few Mpc) and the Cen A spread clustering (a quarter of the whole sample). However more events and rare doublets and clustering elsewhere are waiting for an answer. Here we foresee hint of new UHECR component: galactic ones. Moreover a careful updated views of UHECR sky over different (Radio, IR, Optics, X, gamma, TeV) background (also Fermi gamma very last records) are also favoring forgotten revolutionary Z‐shower model. Both Z‐Shower, proton GZK and Lightest nuclei UHECR models have dramatic influence on expected UHE neutrino Astronomy: to be soon revealed by UHE τ neutrino induced air‐showers in different ways.
1223(2010); http://dx.doi.org/10.1063/1.3395982View Description Hide Description
After 15 months of science operation, the Fermi Gamma‐ray Burst Monitor has triggered on more than 300 GRBs, including 12 detections above 100 MeV by the Large Area Telescope (LAT). With the Fermi/LAT high‐energy photons up to ∼30 GeV (the highest energy ever for GRBs) during the prompt emission were detected as well as long lasting high‐energy emission of several kilo‐seconds after the trigger time. Here, we present the common properties of the LAT detected bursts and their implications in terms of GRB jet astrophysics. Beyond a better understanding of GRB emission mechanisms, these observations also help to address more fundamental physics issues and constrain some theoretical scenarios for the UHECRs sources.
1223(2010); http://dx.doi.org/10.1063/1.3395983View Description Hide Description
On 2009 May 10, 00:22:59 UT the Fermi Gamma‐ray Burst Monitor (GBM) triggered and located the short and very bright GRB090510. For the first time, this hard GRB, with an Epeak of few MeV, also triggered independently the Fermi Large Area Telescope (LAT). Swift detected this GRB and the accurate position provided by the Swift/UVOT made possible a spectroscopic redshift measurement of with VLT/FORS2. This short GRB exhibits new features for this kind of events such an extra component (power‐law) at high energies and a long lasting (few minutes) emission observed by the LAT. These observations allow the derivation of very important physical parameters such as the minimum value of the bulk Lorentz factor and they put some unprecedent limits on the dependence of the speed of photons on their energy.