Narrow Results

The Antarctic Muon and Neutrino Detector Array (AMANDA) is a high-energy neutrino telescope operating at the geographic South Pole. It is a lattice of photo-multiplier tubes buried deep in the polar ice. The primary goal of this detector is to discover astrophysical sources of high energy neutrinos. We describe the detector methods of operation and present results from the AMANDA-B10 prototype. We demonstrate the improved sensitivity of the current AMANDA-II detector. We conclude with an outlook to the envisioned sensitivity of the future IceCube detector.

The author reviews a model for the emission of high energy cosmic rays, gamma-rays and neutrinos from AGN (Active Galactic Nuclei) that he has proposed since 1985. Further discussion of the knee energy phenomenon of the cosmic ray energy spectrum requires the existence of a heavy particle with mass in the knee energy range. A possible method of detecting such a particle in the Pierre Auger Project is suggested. Also presented is a relation between the spectra of neutrinos and gamma-rays emitted from AGN. This relation can be tested by high energy neutrino detectors such as ICECUBE, the Mediterranean Sea Detector and possibly by the Pierre Auger Project.

The new distant metagalactic γ-sources 1739+522 (z = 1.375) and 3c454.3 (z = 0.857) are detected at energies E > 0.8 TeV with the fluxes (0.53 ± 0.10) × 10^-12cm^-2s^-1 and (0.43 ± 0.13) × 10^-12cm^-2s^-1, respectively. The γ-ray spectra and fluxes of known blazars Mkn 421, Mkn 501 and distant flat-spectrum radio quasars 1739+522 and 3c454.3 are presented.

It is shown that the DAMA data indicate two dark matter components, one that circulates around the galactic center (GC) and another that is emitted from the GC. From the location of the maximum yearly variation, one can compute the ratio of the two components.

The continua of highly active radio-loud AGN are dominated by synchrotron radiation over virtually the entire spectrum. Despite this fact, it has often been thought that no correlation between optical and radio polarization should be observed, based on the idea that the synchrotron radiation at very different wavelengths is emitted at very different regions in the jet. However, a clear correlation between the Faraday-rotation-corrected VLBI core radio polarization angle and the nearly simultaneously measured optical polarization angle was found by Gabuzda et al., suggesting that the optical and compact radio polarizations are more closely related than had been thought. We have obtained new data in order to investigate this question. Our preliminary results show that, although the optical and radio core polarizations of BL Lac objects are usually aligned, the behavior displayed by quasars is more complex, and some may involve additional phenomenology, such as internal or very high core Faraday rotation.

Adopting the smoothed particle hydrodynamics (SPH) numerical method, we performed a grid of evolving models of a 3D, axially symmetric, physically viscous accretion disc around a black hole (BH) in an AGN. In such disc models, the role of the specific angular momentum λ and of the physical turbulent viscosity parameter α, according to the Shakura and Sunyaev prescription, are examined. One or two shock fronts develop in the radial inviscid flow, according to the assigned initial kinematic and thermodynamic conditions. Couples of (α, λ) values determine radial periodical oscillations in the shock front. An outflow can develop from the subsonic post shock region, close to the black hole, in some cases. This provides evidence for a link between the accretion disc and the fueling of a jet, through the presence of shock fronts in an accretion disc close to the centrifugal barrier.

Flaring activity of Active Galactic Nuclei (AGN) in VHE γ-ray astronomy is observed on timescales from minutes to years and can be explained either by the interaction of relativistic jets with the surrounding material or by imprints of the central engine, like temporal modulation caused by binary systems of supermassive black holes. The key to answer those questions lies in combining 24/7 monitoring with short high sensitivity exposures as provided by the third generation γ-ray astronomy instruments like MAGIC, VERITAS and H.E.S.S. The long-term observations can be provided by a global network of small robotic Cherenkov telescopes.¹ As a first step, we are currently setting up a dedicated Cherenkov telescope, which will carry out joint observations with the Whipple 10 m telescope for AGN monitoring. The new telescope will be designed for low costs but high performance by upgrading one of the former HEGRA telescopes, still located at the MAGIC site on the Canary Island of La Palma (Spain). The main novelties will be its robotic operation and a novel camera type, resulting in a greatly improved sensitivity and a lower energy threshold.

ASTROSAT is an astronomy satellite designed for simultaneous multi-wavelength studies in the Optical/UV and a broad X-ray energy range. With four X-ray instruments and a pair of UV-Optical telescopes, ASTROSAT will provide unprecedented opportunity for simultaneous multi-wavelength observations, which is of immense value in study of highly variable sources, especially X-ray binaries and active galactic nuclei. The Large Area X-ray Proportional Counters (LAXPC) of ASTROSAT, which has the largest effective area in the hard X-ray band compared to all previous X-ray missions, will enable high time resolution X-ray measurements in the 2–80 keV band with moderate energy resolution. Here we give a brief summary of the payload characteristics of ASTROSAT and discuss some of the main science topics that will be addressed with the LAXPC, and with simultaneous observations with the UVIT telescopes, with particular emphasis on X-ray binaries and compact objects. The possibility of aiding gravitational wave experiments is also briefly mentioned.

The hard X-ray modulation telescope (HXMT) is a slat-collimated instrument sensitive in the 1–250 keV energy band. It will use the direct demodulation technique to conduct an all sky imaging survey with both high sensitivity and high spatial resolution. The moderate field of view also allows for sensitive spectroscopic and timing observations of bright sources in the pointed mode. The wide energy coverage and large collecting area in the hard X-ray band (nearly 5000 cm² effective area at 30–100 keV) make HXMT a unique instrument for some scientific goals. Here we give brief discussion about scientific objectives that can be addressed with HXMT, involving black holes at a variety of scales and equations of states of matter at extreme conditions.

In the framework of AGN unification, BL Lacs and their parent population would share the same intrinsic characteristics, the observational differences being due to the orientation of the jet compared to our line of sight. BL Lacs would be those objects whose jet is oriented towards us, Doppler boosting the emission. The growing number of BL Lacs detected at HE (> 100 MeV) and VHE (> 100 GeV) is a challenge for this scheme, since the high values of Doppler factors needed to explain the emission of these sources imply a large density for the parent population.

We studied the BL Lac source sample detected by Fermi after 11 months of observation. Using the data presented in Fermi's first AGN catalog, we put constraints on the intrinsic characteristics of this BL Lac population, such as the intrinsic luminosity and Lorentz factor distributions. Based on these results, we used Monte Carlo simulations to constrain the space density of the parent population and the jet opening angle.

In the framework of Active Galactic Nuclei (AGN) unification, BL Lacs and their parent population would share the same intrinsic characteristics, the observational differences being due to the orientation of the relativistic jet compared to the line of sight. BL Lacs would be the objects whose jet is oriented towards us, their emission being amplified by the relativistic Doppler boosting. Constraints arising from fast variability and/or large optical depth to pair production commonly imply large Lorentz factors. The growing number of BL Lacs detected at HE (> 100 MeV) and VHE (> 100 GeV) is a challenge for this unification scheme. Indeed, the high values of Doppler factor needed in the simplest radiative model to explain the emission of these sources imply a large density for the parent population. A possible solution to this Doppler factor crisis lies in considering different geometries for the jet. In this study, we use the BL Lacs detected at HE and VHE to investigate the intrinsic properties of the associated parent population. Using the results presented in Fermi's second AGN catalog and performing MC simulations of the parent population, we constrain the jet parameters: its intrinsic luminosity, Lorentz factor and geometric opening angle. The simulated density of parent population and Doppler factors of the objects detectable at HE within this population are presented according to the jet parameters.

The majority of blazars detected at very high energies (VHE; E > 100 GeV) are high-frequency-peaked BL Lac objects (HBLs). Low- and intermediate-frequency-peaked BL Lacs (LBLs/IBLs with synchrotron-peak frequencies in the infrared and optical regime) are generally more powerful, more luminous, and have a richer jet environment than HBLs. However, only a handful of these IBL and LBLs have been detected by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array has been monitoring five known VHE LBLs/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with typical exposures of 5-10 hours per year. The results of these long-term observations are presented, including a bright, subhour-scale VHE flare of BL Lacertae in June 2011, the first low-state detections of 3C 66A and W Comae, and the detection and characterization of the IBL B2 1215+30.

I report about the unification of relativistic jets from compact objects. The mass range is between 1.4 and 10 billion solar masses (i.e. from neutron stars to supermassive black holes in galaxies).

Suzaku is the fifth in the series of Japanese astronomy satellites devoted to observations of celestial X-ray sources launched on a Japanese M-V rocket on July 10, 2005. Suzaku features the excellent X-ray sensitivity, with high throughput over a broad-band energy range of 0.2 to 600 keV. Suzaku's broad bandpass, low background, and good CCD resolution makes it a unique tool capable of addressing a variety of outstanding problems in astrophysics.

Multiwavelength (MW) observations are an essential diagnostic tool to study the physics of blazars. Blazars, the most extreme objects among the Active Galactic Nuclei (AGNs), are characterized by rapid variability at all wavelengths from radio through TeV γ-rays. Considerable progress has been made in recent years thanks to multiwavelength monitoring campaigns. In this contribution, I will give a brief overview of the MW campaigns carried out in the past by large collaboration and their impact on the knowledge of the most important source/jet parameters needed by the physical models used to fit the observed blazar spectral energy distribution (SED). Furthermore, I will discuss some of the perspectives for multiwavelength observations during the operation of the gamma-ray mission GLAST.

MAGIC is presently the imaging atmospheric Cherenkov telescope with the largest reflecting surface and the lowest energy threshold. MAGIC concluded its first year of regular observation in April 2006. During this period and the preceding commissioning phase, 25 Active Galactic Nuclei have been observed and VHE γ-ray emission has been confirmed by 4 of them. Two more AGNs have been detected as γ-ray sources with high statistical significance for the first time. We report in this paper the results obtained analyzing data of the detected sources. Temporal and spectral properties of detected signals are shown and discussed.

Selected scientific highlights are presented from the first 5 years of observations of the gamma-ray sky by ESA's INTEGRAL space telescope. Its unprecedented angular resolution and sensitivity at high energies (≳ 20 keV) has allowed INTEGRAL to detect around 500 objects, many of which are new. Sources that have been classified are predominantly represented by active galactic nuclei (AGN) and X-ray binaries (XRBs) whereby a compact object (a supermassive black hole in AGN, usually a neutron star in XRBs) accretes matter from a large disk (AGN) or from a stellar companion (XRBs, often mediated by a disk). Together with unclassified sources, they account for nearly all of the diffuse Galactic background emission. Furthermore, INTEGRAL has created an all-sky map of the 511 keV distribution helping to identify potential dark matter sites. The distribution of Al-26 follows massive star-forming regions and reflects the rotation of the Galaxy. Gamma-ray bursts (GRBs) are detected in the wide field of view (FOV) at a rate of 1 per month, but INTEGRAL's design also enables it to detect GRBs outside its FOV. Previously rare, XRBs with supergiant companions are an emerging class. This underscores INTEGRAL's ability to peer through the dust that enshrouds these sources and which made them invisible to previous X-ray surveys. Their increasing numbers (as well as those of other classes) offer larger samples on which to perform statistical analyses. A synthetic view of populations of γ-ray sources is instrumental for highlighting signatures of stellar and galactic evolution. In addition, it permits a speculation on the nature of the roughly 100 sources that remain unclassified.

The location of the main emitting region responsible for the bulk of the Blazar emission is a puzzling issue in our understanding of jetted Active Galactic Nuclei. Fast flares and a high Compton dominance are more easily explained if the gamma-ray zone is well inside the Broad Line Region (BLR), while the absence of γ-γ absorption features in the Fermi-LAT spectra as well as the detection at Very High Energies (VHE) of some FSRQ put the blazar zone at much larger distances along the jet, beyond the BLR. The latter seems now to be the most typical behavior in FSRQ, questioning SED models based on the external Compton process on BLR photons.

During the last year the Gamma-Ray sky has glowed of new light: the PAMELA experiment, the Pierre Auger Observatory, the AGILE satellite, and the Fermi Gamma-ray Space Telescope are contributing in an unprecedented way to the unveiling of the cosmic distribution of gamma-ray sources and their viable relation with cosmic rays. The Alpha Magnetic Spectrometer, to be launched next July 2010, will add, for the first time, a precious energetic window, up to a few TeV, to this exciting investigation. We analyze the perspectives of AMS results and the possibilities for the detection of Galactic and Extragalactic gamma-ray astrophysical sources like Pulsars, Microquasars, Gamma-Ray Bursts, and Active Galactic Nuclei.

The radio-loud active galactic nuclei having the radio emission arising from a core region rather than from lobes are often referred to as “blazars” and include Flat Spectrum Radio Quasars (FSRQ) and BL Lacertae (BL Lac) objects. We present results of long term observations of FSRQs as well as BL Lac type objects by SHALON Cherenkov telescopic system at energies > 800 GeV.