Constraining blazar distances with combined Fermi and TeV data: an empirical approach

We discuss a method to constrain the distance of blazars with unknown redshift using combined observations in the GeV and TeV regimes. We assume that the VHE spectrum corrected for the absorption through the interaction with the Extragalactic Background Light can not be harder than the spectrum in the Fermi/LAT band. Starting from the observed VHE spectral data we derive the EBL-corrected spectra as a function of the redshift z and fit them with power laws to be compared with power law fits to the LAT data. We apply the method to all TeV blazars detected by LAT with known distance and derive an empirical law describing the relation between the upper limits and the true redshifts that can be used to estimate the distance of unknown redshift blazars. Using different EBL models leads to systematic changes in the derived upper limits. Finally, we use this relation to infer the distance of the unknown redshift blazar PKS 1424+240.Comment: 5 pages, 4 figures, accepted for publication in MNRAS, minor revisio

VHE Gamma-Ray Induced Pair Cascades in Blazars and Radio Galaxies: Application to NGC 1275

Recent blazar detections by HESS, MAGIC, and VERITAS suggest that very-high-energy (VHE, E > 100 GeV) gamma-rays may be produced in most, if not all, types of blazars, including those that possess intense circumnuclear radiation fields. In this paper, we investigate the interaction of nuclear VHE gamma-rays with the circumnuclear radiation fields through gamma-gamma absorption and pair production, and the subsequent Compton-supported pair cascades. We have developed a Monte-Carlo code to follow the spatial development of the cascade in full 3-dimensional geometry, and calculate the radiative output due to the cascade as a function of viewing angle with respect to the primary VHE gamma-ray beam (presumably the jet axis of the blazar). We show that even for relatively weak magnetic fields, the cascades can be efficiently isotropized, leading to substantial off-axis cascade emission peaking in the Fermi energy range at detectable levels for nearby radio galaxies. We demonstrate that this scenario can explain the Fermi flux and spectrum of the radio galaxy NGC 1275.Comment: Accepted for publication in The Astrophysical Journa

EGMF Constraints from Simultaneous GeV-TeV Observations of Blazars

Attenuation of the TeV gamma-ray flux from distant blazars through pair production with extragalactic background light leads to the development of electromagnetic cascades and subsequent, lower energy, GeV secondary gamma-ray emission. Due to the deflection of VHE cascade electrons by extragalactic magnetic fields (EGMF), the spectral shape of this arriving cascade gamma-ray emission is dependent on the strength of the EGMF. Thus, the spectral shape of the GeV-TeV emission from blazars has the potential to probe the EGMF strength along the line of sight to the object. We investigate constraints on the EGMF derived from observations of blazars for which TeV observations simultaneous with those by the Fermi telescope were reported. We study the dependence of the EGMF bound on the hidden assumptions it rests upon. We select blazar objects for which simultaneous Fermi/LAT GeV and Veritas, MAGIC or HESS TeV emission have been published. We model the development of electromagnetic cascades along the gamma-ray beams from these sources using Monte Carlo simulations, including the calculation of the temporal delay incurred by cascade photons, relative to the light propagation time of direct gamma-rays from the source. Constraints on EGMF could be derived from the simultaneous GeV-TeV data on the blazars RGB J0710+591, 1ES 0229+200, and 1ES 1218+304. The measured source flux level in the GeV band is lower than the expected cascade component calculated under the assumption of zero EGMF. Assuming that the reason for the suppression of the cascade component is the extended nature of the cascade emission, we find that B>10^{-15} G (assuming EGMF correlation length of ~1 Mpc) is consistent with the data. Alternatively, the assumption that the suppression of the cascade emission is caused by the time delay of the cascade photons the data are consistent with B>10^{-17} G for the same correlation length.Comment: 9 pages, 9 figure

Baseband Predistortion Lineariser Using Direct Spline Computation

A baseband predistorter is presented. Key features of the predistorter resides in the use of cubic splines interpolation to generate predistorted input data to the power amplifier, resulting in a reduction of computational effort with respect to traditional polynomial interpolators. Simulated behaviour of the proposed scheme is presented, demonstrating the effectiveness of the approach

Signatures of the anomalous ZγZ\gamma and ZZ production at the lepton and hadron Colliders

The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. Experimental limits obtained or expected on each coupling are collected. A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure.Comment: 17 pages and 9 figures, version to appear in Phys. ReV. e-mail: [email protected]

Quark structure of hadrons and high energy collisions

There exists a large field for phenomenological models in which the knowledge of the structure of hadrons in terms of QCD constituents obtained from deep inelastic scatterings is related to their behaviour in soft processes. One of the simplest and oldest models is the additive quark model, with the rules of quark statistics following from it. Originally, the relations of quark combinatorics for hadron yields were based on the qualitative description of a multiparticle production process as a process of the production of non-correlated quarks and antiquarks followed by their subsequent fusion into hadrons [20],[21]. As a large amount of new precision measurements appear, and, on the other hand, our understanding of QCD becomes deeper, a new level of understanding of quark-gluon physics in the region of soft interactions forces us to review the relations of quark combinatorics. To do so, an especially good possibility is provided by the experimental data for hadronic Z^0 decays which allow us to check the relations of quark combinatorics for a new type of processes: quark jets in the decays Z^0 -> q\bar{q} -> hadrons [32].Comment: 55 pages, 23 figure

Probing the central black hole in M87 with gamma-rays

Recent high-sensitivity observation of the nearby radio galaxy M87 have provided important insights into the central engine that drives the large-scale outflows seen in radio, optical and X-rays. This review summarizes the observational status achieved in the high energy (HE;<100 GeV) and very high energy (VHE; >100 GeV) gamma-ray domains, and discusses the theoretical progress in understanding the physical origin of this emission and its relation to the activity of the central black hole.Comment: Invited compact review to be published in Modern Physics Letters A; 19 pages, 4 figure

Piezoelectric Rainfall Energy Harvester Performance by Advanced Arduino based Measuring System

This paper presents the performances of rainfall energy harvesting through the use of a piezoelectric transducer and an Arduino-based measuring system. Different studies agree on the possibility of generating electricity from rainfall, but to date, a study on measuring the quantity of energy produced during rainfall is still missing. The present study begins with results obtained from laboratory researchers using piezoelectric transducers and oscilloscopes, finalized to measure the energy produced from a single raindrop, and concludes with an ad hoc Arduino-based measuring system, aimed to measure the actual amount of electrical energy produced by a piezoelectric transducer that is exposed to rainfall of variable durations

X-ray spectral curvature of High Frequency Peaked BL Lacs: a predictor for the TeV flux

Most of the extragalactic sources detected at TeV energies are BL Lac objects. They belong to the subclass of "high frequency peaked BL Lacs" (HBLs) exhibiting spectral energy distributions with a lower energy peak in the X-ray band; this is widely interpreted as synchrotron emission from relativistic electrons. The X-ray spectra are generally curved, and well described in terms of a log-parabolic shape. In a previous investigation of TeV HBLs (TBLs) we found two correlations between their spectral parameters. (1) The synchrotron peak luminosity L_p increases with its peak energy E_p; (2) the curvature parameter b decreases as E_p increases. The first is consistent with the synchrotron scenario, while the second is expected from statistical/stochastic acceleration mechanisms for the emitting electrons. Here we present an extensive X-ray analysis of a sample of HBLs observed with XMM-Newton and SWIFT but undetected at TeV energies (UBLs), to compare their spectral behavior with that of TBLs. Investigating the distributions of their spectral parameters and comparing the TBL X-ray spectra with that of UBLs, we develop a criterion to select the best HBLs candidates for future TeV observations.Comment: 25 pages, 6 figures, Astrophysical Journal publishe

Radio Spectral Index Analysis and Classes of Ejection in LS I +61 303

LS I +61303 is a gamma-ray binary with periodic radio outbursts coincident with the orbital period of P=26.5 d. The origin of the radio emission is unclear,it could be due either to a jet, as in microquasars, or to the shock boundary between the Be star and a possible pulsar wind. We here analyze the radio spectral index over 6.7 yr from Green Bank Interferometer data at 2.2 GHz and 8.3 GHz. We find two new characteristics in the radio emission. The first characteristic is that the periodic outbursts indeed consist of two consecutive outbursts; the first outburst is optically thick, whereas the second outburst is optically thin. The spectrum of LS I +61 303 is well reproduced by the shock-in-jet model commonly used in the context of microquasars and AGNs: the optically thin spectrum is due to shocks caused by relativistic plasma ("transient jet") traveling through a pre-existing much slower steady flow ("steady jet"). This steady flow is responsible for the preceding optically thick spectrum. The second characteristic we find is that the observed spectral evolution, from optically thick to optically thin emission, occurs twice during the orbital period. We observed this occurrence at the orbital phase of the main 26.5 d outburst and also at an earlier phase, shifted by $\Delta \Phi \sim$ 0.3 (i.e almost 8 days before). We show that this result qualitatively and quantitatively agrees with the two-peak accretion/ejection model proposed in the past for LS I +61303. We conclude that the radio emission in LS I +61303 originates from a jet and suggest that the variable TeV emission comes from the usual Compton losses expected as an important by-product in the shock-in-jet theory.Comment: 27 pages, 7 figures, accepted for publication in Ap