SCIENCE WITH THE NEW GENERATION OF HIGH ENERGY GAMMA‐RAY EXPERIMENTS: Proceedings of the 6th Edition: Bridging the Gap Between GeV and TeV
1112(2009); http://dx.doi.org/10.1063/1.3125783View Description Hide Description
With AGILE and Fermi now in orbit and TeV telescopes continuing to improve their performance, a variety of multiwavelength opportunities is increasingly available. One goal of such programs is to take advantage of the complementary capabilities of the two types of telescopes: the wide field surveys of the satellite detectors and the high sensitivity and resolution of the ground‐based telescopes. Some aspects of these multiwavelength efforts will be carried out in near‐real‐time but must be anticipated with advance preparation. These include gamma‐ray burst follow‐ups and flare campaigns. Other projects such as long‐term variability studies and gamma‐ray source identification require deep observations and cooperative work with astrophysicists at longer wavelengths, along with the theoretical studies that tie the observations together.
1112(2009); http://dx.doi.org/10.1063/1.3125796View Description Hide Description
The Large Area Telescope (LAT) instrument on the Fermi mission is revealing the rich spectral and temporal gamma‐ray burst phenomena in the band. The synergy with Fermi’s GBM detectors links these observations to those in the well‐explored 10–1000 keV range; the addition of the band observations brings new hint and new information about burst emission in both the prompt and afterglow phases. In this contribution we describe the prospects for the Fermi Large Area Telescope (LAT) in observing Gamma‐Ray Bursts (GRBs), and some preliminary results. Here we focus our attention on the importance of multi frequencies approach to GRB science during the just began Fermi era.
1112(2009); http://dx.doi.org/10.1063/1.3125778View Description Hide Description
Over the past few years, very‐high‐energy gamma‐ray astronomy has emerged as a truly observational discipline, with many detected sources representing different galactic and extragalactic source populations ‐supernova remnants, pulsar wind nebulae, giant molecular clouds, star formation regions, compact binary systems and active galactic nuclei. The H.E.S.S. array of imaging atmospheric Cherenkov telescopes has revealed a sky full of sources of very high energy γ‐rays, challenging our knowledge of particle acceleration (either hadronic or leptonic) and propagation in environments with extreme conditions. We will review the latest results published and discus the most interesting cases.
1112(2009); http://dx.doi.org/10.1063/1.3125788View Description Hide Description
MAGIC is a single‐dish Cherenkov telescope located on La Palma (Spain), hence with an optimal view on the Northern sky. Sensitive in the 30 GeV–30 TeV energy band, it is nowadays the only ground‐based instrument being able to measure high‐energy γ‐rays below 100 GeV. We review the most recent experimental results obtained using MAGIC.
1112(2009); http://dx.doi.org/10.1063/1.3125789View Description Hide Description
The VERITAS collaboration operates an array of four imaging atmospheric Cherenkov telescopes in southern Arizona. The first season of observations (including all four telescopes) was performed in 2007/2008. New γ‐ray sources were discovered and a variety of other TeV sources were observed and detected, in many cases within coordinated multi‐wavelength campaigns. The status, observational performances and results of the first year of observations (galactic and extra‐galactic sources) with the full array are presented.
1112(2009); http://dx.doi.org/10.1063/1.3125790View Description Hide Description
Colliding winds of massive stars in binary systems are viable candidates for non‐thermal high‐energy photon emission. Long since, coincidences between massive star systems/associations and γ‐ray sources have been noted. Now, with the sensitivity of the Fermi Gamma Ray Observatory and current very‐high‐energy (VHE) Cherenkov instruments, will it be possible to sensibly probe these systems as high‐energy emitters.
We will summarize the characteristics and broadband predictions of generic optically thin emission models in the observables accessible at GeV and TeV energies. The ability to constrain orbital parameters of massive star‐star binaries through GeV‐to‐TeV observations is discussed. As an example we will present orbital parameter constraints for the nearby Wolf‐Rayet binary system WR 147 based on recently published VHE flux limits. Combining our broadband emission model with the cataloged binaries systems and their individual parameters allows us to conclude on the population of massive star‐star systems at high‐energy γ‐rays.
1112(2009); http://dx.doi.org/10.1063/1.3125791View Description Hide Description
Very high energy γ‐ray emission has been recently detected by H.E.S.S. from the direction of associations between supernova remnants and molecular clouds. In such associations dense molecular clouds may reveal accelerated cosmic rays in the vicinity of supernova remnant forward shocks. Hadronic interactions could explain part or all of the observed γ‐ray fluxes. The discovery of a new VHE γ‐ray source, HESS coincident with the supernova remnant W51C, is reported. Amongst possible associations for this source is a shocked molecular cloud.
1112(2009); http://dx.doi.org/10.1063/1.3125792View Description Hide Description
We present a theoretical model that explains the high energy phenomenology of the neighborhood of SNR IC 443, as observed with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope and the Energetic Gamma‐Ray Experiment Telescope (EGRET). We also discuss how the model can be tested with observations by the Fermi Gamma‐ray Large Area Space Telescope. We interpret MAGIC as delayed TeV emission of cosmic‐rays diffusing from IC 443 and interacting with a known cloud located at a distance of about 20 pc in the foreground of the remnant. This scenario naturally explains the displacement between EGRET and MAGIC sources, their fluxes, and their spectra. Finally, we predict how this context can be observed by Fermi.
1112(2009); http://dx.doi.org/10.1063/1.3125793View Description Hide Description
The 17 m diameter Cherenkov telescope MAGIC, located on the Canary Island of La Palma, has the lowest trigger threshold among operating Cherenkov telescopes; this makes it a very promising tool for the detection of the pulsed gamma‐ray (γ‐ray) emission from ground. Recently, a new analog summation trigger concept, which allows reducing the threshold even further, has been designed and implemented. The analog signals of patches in the camera, comprising 18 pixels each, are summed up in the analog mode. In order to prevent triggers from photomultiplier (PMT) afterpulses, the individual pixel signals are clipped at a preset amplitude level and then added up. The average FWHM of the time duration of signals induced by cosmic rays is 2.6 ns. This allows one to keep the coincidence time window very small and thus to strongly suppress accidental triggers. In the usual digital trigger designs, the signal should be above a certain threshold from each individual pixel to contribute to the trigger. In the summation trigger all low amplitude signals in a given patch in the camera are summed up and fully contribute to the trigger.
The new trigger concept provides a low cost trigger for Cherenkov telescopes and it is very effective and stable. This trigger system for the MAGIC telescope was installed in October 2007 and was successfully used in the detection of the Crab Pulsar above 25 GeV.
1112(2009); http://dx.doi.org/10.1063/1.3125794View Description Hide Description
The Large Area Telescope on the recently launched Fermi Gamma‐ray Space Telescope (formerly GLAST), with its large field of view and effective area, combined with its excellent timing capabilities, is poised to revolutionize the field of gamma‐ray astrophysics. The large improvement in sensitivity over EGRET is expected to result in the discovery of many new gamma‐ray pulsars, which in turn should lead to fundamental advances in our understanding of pulsar physics and the role of neutron stars in the Galaxy. Almost immediately after launch, Fermi clearly detected all previously known gamma‐ray pulsars and is producing high precision results on these. An extensive radio and X‐ray timing campaign of known (primarily radio) pulsars is being carried out in order to facilitate the discovery of new gamma‐ray pulsars. In addition, a highly efficient time‐differencing technique is being used to conduct blind searches for radio‐quiet pulsars, which has already resulted in new discoveries. I present some recent results from searches for pulsars carried out on Fermi data, both blind searches, and using contemporaneous timing of known radio pulsars.
1112(2009); http://dx.doi.org/10.1063/1.3125795View Description Hide Description
The Fermi Gamma‐ray Space Telescope, launched in June 2008, is an international space mission entirely devoted to the study of the high‐energy gamma rays from the Universe. The main instrument aboard Fermi is the Large Area Telescope (LAT), a pair conversion telescope equipped with the state‐of‐the art in gamma‐ray detectors technology. Thanks to its large field of view and effective area, combined with its excellent timing capability, Fermi‐LAT is a perfect instrument for probing physics of gamma‐ray emission in pulsars. LAT is expected to discover tens of new pulsars, both radio‐loud and radio‐quiet (Geminga‐like). Moreover, LAT will observe with unprecedented statistics the brightest pulsars, investigating the details of magnetospheric emission. The first two months of the mission have been focused on the commissioning and first light, during which the LAT firmly detected the six previously known EGRET gamma‐ray pulsars. One of the main sources of interest during our first light observations has been the Vela pulsar, the brightest persistent source in the whole gamma‐ray sky. Thanks to its brightness, the Vela pulsar is an ideal candidate for calibrating the LAT and testing its performance. In addition, observations of Vela will help answer many questions related to the physics of pulsar emission processes. We present here some recent results obtained by the LAT on the Vela pulsar, using high‐quality timing solutions provided by radio observations carried out within the Fermi pulsar radio timing campaign.
1112(2009); http://dx.doi.org/10.1063/1.3125797View Description Hide Description
The study of Galactic diffuse γ radiation combined with the knowledge of the distribution of the molecular hydrogen in the Galaxy offers a unique tool to probe the cosmic ray flux in the Galaxy. A methodology to study the level of the cosmic ray “sea” and to unveil target‐accelerator systems in the Galaxy, which makes use of the data from the high resolution survey of the Galactic molecular clouds performed with the NANTEN telescope and of the data from γ‐ray instruments, has been developed. Some predictions concerning the level of the cosmic ray “sea” and the γ‐ray emission close to cosmic ray sources for instruments such as Fermi and Cherenkov Telescope Array are presented.
1112(2009); http://dx.doi.org/10.1063/1.3125770View Description Hide Description
To estimate the opacity of very high‐energy photons with the background light, we have modelled the extragalactic optical and infrared diffuse light using available information on cosmic sources in the universe from far‐UV to sub‐millimeter wavelengths over a wide range of cosmic epochs. To this end we have used number counts, redshift distributions, luminosity functions of extragalactic sources and direct measurements or upper limits to the extragalactic backgrounds by COBE. From the redshift‐dependent background spectrum, the photon‐photon opacities for sources of high‐energy emission at any redshifts were then computed. We have applied our photon‐photon opacity estimates to the analysis of spectral data at TeV energies on a few BLAZARs of particular interest (including a quasar detected by MAGIC, 3C279). We find no evidence in current data for any truly diffuse background components in addition to those from resolved sources. We have tested in particular the effects of a photon background originating at very high redshifts, as would be the emissions by a primeval population of Population III stars at We could not identify any opacity features in our studied BLAZAR spectra consistent with such an emission and place a stringent limit on such a diffuse photon intensity of between 1 and
Constraints on Extragalactic Background Light from Cherenkov telescopes: status and perspectives for the next 5 years1112(2009); http://dx.doi.org/10.1063/1.3125771View Description Hide Description
Very high energy (VHE, ) γ‐rays are absorbed via interaction with low‐energy photons from the extragalactic background light (EBL) if the involved photon energies are above the threshold for electron‐positron pair creation. The VHE γ‐ray absorption, which is energy dependent and increases strongly with redshift, distorts the VHE energy spectra observed from distant objects. The observed energy spectra of the AGNs carry therefore an imprint of the EBL. Recent detections of hard spectra of distant blazars by H.E.S.S. and MAGIC put strong constraints on the EBL density in the optical to near infrared waveband. It is, however, not yet possible to distinguish between an intrinsic softening of blazar spectra and a softening caused by the interaction with low energy EBL photons. In this paper, we give an overview of the EBL constraints, their limitations and perspectives for the joint efforts of the Fermi Gamma‐Ray Space telescope and imaging atmospheric Cherenkov telescopes.
1112(2009); http://dx.doi.org/10.1063/1.3125772View Description Hide Description
During the first year of observations, AGILE detected several blazars at high significance: 3 C 279, 3C 454.3, PKS 1510‐089, S5 3 C 273, MKN 421, and W Comae. We obtained long‐term coverage of the Crazy Diamond 3 C 454.3, for more than 100 days at energies above 100 MeV. 3 C 273 was the first blazar detected simultaneously by the AGILE gamma‐ray imaging detector and by its hard X‐ray monitor. S5 an intermediate BL Lac object, exhibited a very fast and intense gamma‐ray transient event during an optical high‐state phase, while MKN 421 and W Comae where detected during an AGILE target of opportunity (ToO) repointing. Thanks to the rapid dissemination of our alerts, we were able to obtain multi‐wavelength ToO data from other observatories such as Spitzer, Swift, INTEGRAL, RXTE, Suzaku, MAGIC, VERITAS, as well as optical coverage by means of the WEBT Consortium and REM.
1112(2009); http://dx.doi.org/10.1063/1.3125773View Description Hide Description
In the next years the FERMI gamma ray telescope and the Cherenkov telescopes will put very stringent constraints to models of gamma ray emission from galaxy clusters providing crucial information on relativistic particles in the inter‐galactic‐medium.
We derive the broad band non‐thermal spectrum of galaxy clusters in the context of general calculations in which relativistic particles (protons and secondary electrons due to proton‐proton collisions) interact with MHD turbulence generated in the cluster volume during cluster mergers, and discuss the importance of future gamma ray observations.
1112(2009); http://dx.doi.org/10.1063/1.3125774View Description Hide Description
IceCube is a cubic‐kilometer neutrino telescope under construction at the geographic South Pole. Once completed it will comprise 4800 optical sensors deployed on 80 vertical strings at depths in the ice between 1450 and 2450 meters. Part of the array is already operational and data was recorded in the configurations with 9 (year 2006/2007), 22 (year 2007/2008) and 40‐strings (year 2008/2009) respectively. Here we report preliminary results on the search for point‐like neutrino sources using data collected with the first 22 strings (IC‐22).
1112(2009); http://dx.doi.org/10.1063/1.3125775View Description Hide Description
The ARGO‐YBJ experiment has been put in stable data taking at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l.). In this paper we report a few selected results in Gamma‐Ray Astronomy (Crab Nebula and Mrk421 observations, search for high energy tails of Gamma Ray Bursts) and Cosmic Ray Physics (Moon and Sun shadow observations, proton‐air cross section measurement, preliminary measurement of the antiproton/proton ratio at TeV energies).
1112(2009); http://dx.doi.org/10.1063/1.3125776View Description Hide Description
The detection of γ‐rays, antiprotons and positrons due to pair annihilation of dark matter particles in the Milky Way halo is a viable indirect technique to search for signatures of supersymmetric dark matter where the major challenge is the discrimination of the signal from the background generated by standard production mechanisms. The new PAMELA antiproton data are consistent with the standard secondary production and this allows us to constrain exotic contribution to the spectrum due to neutralino annihilations. In particular, we show that in the framework of minimal supergravity (mSUGRA), in a clumpy halo scenario (with clumpiness factor ) and for large values of almost all the parameter space allowed by WMAP is excluded. Instead, the PAMELA positron fraction data exhibit an excess that cannot be explained by secondary production. PPB‐BETS and ATIC reported a feature in electron spectrum at a few hundred GeV. The excesses seem to be consistent and imply a source, conventional or exotic, of additional leptonic component. Here we discuss the status of indirect dark matter searches and a perspective for PAMELA and Fermi γ‐ray space telescope (Fermi) experiments.