A DISPLACED SUPERMASSIVE BLACK HOLE IN M87

Isophotal analysis of M87, using data from the Advanced Camera for Surveys, reveals a projected displacement of 6.8 +/- 0.8 pc (similar to 0 ''.1) between the nuclear point source (presumed to be the location of the supermassive black hole, SMBH) and the photo-center of the galaxy. The displacement is along a position angle of 307 degrees +/- 17 degrees and is consistent with the jet axis. This suggests the active SMBH in M87 does not currently reside at the galaxy center of mass, but is displaced in the counter-jet direction. Possible explanations for the displacement include orbital motion of an SMBH binary, gravitational perturbations due to massive objects ( e. g., globular clusters), acceleration by an asymmetric or intrinsically one-sided jet, and gravitational recoil resulting from the coalescence of an SMBIIbinary. The displacement direction favors the latter two mechanisms. However, jet asymmetry is only viable, at the observed accretion rate, for a jet age of >0.1 Gyr and if the galaxy restoring force is negligible. This could be the case in the low-density core of M87. A moderate recoil similar to 1Myr ago might explain the disturbed nature of the nuclear gas disk, could be aligned with the jet axis, and can produce the observed offset. Alternatively, the displacement could be due to residual oscillations resulting from a large recoil that occurred in the aftermath of a major merger <= 1 Gyr ago

The SKA and "High-Resolution" Science

"High-resolution", or "long-baseline", science with the SKA and its precursors covers a broad range of topics in astrophysics. In several research areas, the coupling between improved brightness sensitivity of the SKA and a sub-arcsecond resolution would uncover truly unique avenues and opportunities for studying extreme states of matter, vicinity of compact relativistic objects, and complex processes in astrophysical plasmas. At the same time, long baselines would secure excellent positional and astrometric measurements with the SKA and critically enhance SKA image fidelity at all scales. The latter aspect may also have a substantial impact on the survey speed of the SKA, thus affecting several key science projects of the instrument.Comment: JENAM-2010: Invited talk at JENAM session S7: The Square Kilometre Array: Paving the way for the new 21st century radio astronomy paradigm; 9 page

Large orders in strong-field QED

We address the issue of large-order expansions in strong-field QED. Our approach is based on the one-loop effective action encoded in the associated photon polarisation tensor. We concentrate on the simple case of crossed fields aiming at possible applications of high-power lasers to measure vacuum birefringence. A simple next-to-leading order derivative expansion reveals that the indices of refraction increase with frequency. This signals normal dispersion in the small-frequency regime where the derivative expansion makes sense. To gain information beyond that regime we determine the factorial growth of the derivative expansion coefficients evaluating the first 80 orders by means of computer algebra. From this we can infer a nonperturbative imaginary part for the indices of refraction indicating absorption (pair production) as soon as energy and intensity become (super)critical. These results compare favourably with an analytic evaluation of the polarisation tensor asymptotics. Kramers-Kronig relations finally allow for a nonperturbative definition of the real parts as well and show that absorption goes hand in hand with anomalous dispersion for sufficiently large frequencies and fields.Comment: 26 pages, 6 figure

Active Galactic Nuclei at the Crossroads of Astrophysics

Over the last five decades, AGN studies have produced a number of spectacular examples of synergies and multifaceted approaches in astrophysics. The field of AGN research now spans the entire spectral range and covers more than twelve orders of magnitude in the spatial and temporal domains. The next generation of astrophysical facilities will open up new possibilities for AGN studies, especially in the areas of high-resolution and high-fidelity imaging and spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These studies will address in detail a number of critical issues in AGN research such as processes in the immediate vicinity of supermassive black holes, physical conditions of broad-line and narrow-line regions, formation and evolution of accretion disks and relativistic outflows, and the connection between nuclear activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical Symposia Serie

A search for AGN in the most extreme UV-selected starbursts using the European VLBI Network

We have used the European VLBI Network (EVN) to observe a sample of Lyman Break Analogs (LBAs), nearby (z < 0.3) galaxies with properties similar to the more distant Lyman Break Galaxies (LBGs). The study of LBGs may help define the feed-back relationship between black holes (BHs) and their host galaxies. Previous VLA observations have shown that the kpc-scale radio emission from LBAs is dominated by starbursts. The main targets of this VLBI experiment were selected because they possessed emission-line properties between starbursts and Type 2 (obscured) AGN. Eight targets (three star-forming LBAs, four composite LBAs, and one Type 1 AGN) were observed at 5 GHz, four of which were also observed at 1.7 GHz. One star-forming LBA and one composite LBA were detected above 5 \sigma at 1.7 GHz (only), while the AGN was detected at 5 GHz. In both LBAs, the radio luminosity (LR) exceeds that expected from supernovae (remnants) based on a comparison with Arp220, Arp229A and Mrk273, by factors of 2 - 8. The composite LBA exhibits a compact core emitting around 10% of the VLA flux density. The high Tb of 3.5E7 K and excess core L_R with respect to the L_R/L_X relation of radio-quiet AGN indicate that this LBA possesses an obscured AGN (MBH ~ E5-E7 M_sun). While weak AGN may co-exist with the starbursts as shown in at least one of the LBAs, their contribution to the total radio flux is fairly minimal. Our results show that the detection of such weak AGN presents a challenge at radio, X-ray and optical emission-line wavelengths at z ~ 0.2, indicating the great difficulties that need to be overcome in order to study similar processes at high redshift when these types of galaxies were common.Comment: 10 pages, 4 figures, accepted for publication in MNRA

CSpritz: accurate prediction of protein disorder segments with annotation for homology, secondary structure and linear motifs

CSpritz is a web server for the prediction of intrinsic protein disorder. It is a combination of previous Spritz with two novel orthogonal systems developed by our group (Punch and ESpritz). Punch is based on sequence and structural templates trained with support vector machines. ESpritz is an efficient single sequence method based on bidirectional recursive neural networks. Spritz was extended to filter predictions based on structural homologues. After extensive testing, predictions are combined by averaging their probabilities. The CSpritz website can elaborate single or multiple predictions for either short or long disorder. The server provides a global output page, for download and simultaneous statistics of all predictions. Links are provided to each individual protein where the amino acid sequence and disorder prediction are displayed along with statistics for the individual protein. As a novel feature, CSpritz provides information about structural homologues as well as secondary structure and short functional linear motifs in each disordered segment. Benchmarking was performed on the very recent CASP9 data, where CSpritz would have ranked consistently well with a Sw measure of 49.27 and AUC of 0.828. The server, together with help and methods pages including examples, are freely available at URL: http://protein.bio.unipd.it/cspritz/

Feasibility studies of the time-like proton electromagnetic form factor measurements with PANDA at FAIR

The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the \PANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of $\bar p +p$ into a lepton pair as well as for the most important background channels have been performed. It is shown that precision measurements of the differential cross section of the reaction $\bar p +p \to e^++ e^-$ can be obtained in a wide angular and kinematical range. The individual determination of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of $q^2\simeq 14$ (GeV/c)$^2$. The total $\bar p +p\to e^++e^-$ cross section will be measured up to $q^2\simeq 28$ (GeV/c)$^2$. The results obtained from simulated events are compared to the existing data. Sensitivity to the two photons exchange mechanism is also investigated.Comment: 12 pages, 4 tables, 8 figures Revised, added details on simulations, 4 tables, 9 figure

Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR

Simulation results for future measurements of electromagnetic proton form factors at \PANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel $\bar p p \to e^+ e^-$ is studied on the basis of two different but consistent procedures. The suppression of the main background channel, $\textit{i.e.}$ $\bar p p \to \pi^+ \pi^-$, is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance

INTEGRAL observations of the blazar 3C454.3 in outburst

In Spring 2005, the blazar 3C454.3 underwent a dramatic outburst at all wavelengths from mm to X-rays. This prompted INTEGRAL observations, accomplished in 15-18 May 2005. The source was detected by the INTEGRAL instruments from 3 to 200 keV in a bright state (~5 x 10E-10 cgs), at least a factor of 2-3 higher than previously observed. This is one of the brightest blazar detections achieved by INTEGRAL. During the 2.5 days of INTEGRAL monitoring, we detected a ~20% decrease in the hard X-rays (20-40 keV), indicating that we have sampled the decaying part of the flare. The decrease is less apparent in the soft X-rays (5-15 keV). The simultaneous optical variations are weakly correlated with those at soft X-rays, and not clearly correlated with those at hard X-rays. The spectral energy distribution exhibits two components, as typically seen in blazars, which can be modeled with synchrotron radiation and inverse Compton scattering occurring in a region external to the broad line region.Comment: 5 pages, 3 eps figures, in press in A&A Letter

Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.Comment: 15 pages, 11 figures. Published in European Physical Journal