J. Blanchard

TANAMI Blazars in the IceCube PeV Neutrino Fields

ABSTRACT The IceCube Collaboration has announced the discovery of a neutrino flux in excess of the atmospheric background. Due to thesteeply falling atmospheric background spectrum, events at PeV energies are most likely of extraterrestrial origin. We present themultiwavelength properties of the six radio brightest blazars positionally coincident with these events using contemporaneous data ofthe TANAMI blazar sample, including high-resolution images and spectral energy distributions. Assuming the X-ray to -ray emissionoriginates in the photoproduction of pions by accelerated protons, the integrated predicted neutrino luminosity of these sources is largeenough to explain the two detected PeV events. Key words. neutrinos – galaxies: active – quasars: general 1. Introduction The detection of neutrinos at PeV energies in excess of the at-mospheric background reported by the IceCube Collaboration(Aartsen et al. 2013; IceCube Collaboration 2013) has prompteda quest to identify their extraterrestrial sources. The two eventswith PeV energies (event 20, dubbed ‘Ernie’ and event 14,‘Bert’, hereafter E20 and E14), detected between May 2010 andMay 2012

TANAMI monitoring of Centaurus A: The complex dynamics in the inner parsec of an extragalactic jet

Context. Centaurus A (Cen A) is the closest radio-loud active galactic nucleus. Very Long Baseline Interferometry (VLBI) enables us to study the spectral and kinematic behavior of the radio jet-counterjet system on milliarcsecond scales, providing essential information for jet emission and propagation models. Aims. In the framework of the TANAMI monitoring, we investigate the kinematics and complex structure of Cen A on subparsec scales. We have been studying the evolution of the central parsec jet structure of Cen A for over 3.5 years. The proper motion analysis of individual jet components allows us to constrain jet formation and propagation and to test the proposed correlation of increased high-energy flux with jet ejection events. Cen A is an exceptional laboratory for such a detailed study because its proximity translates to unrivaled linear resolution, where one milliarcsecond corresponds to 0.018 pc. Methods. As a target of the southern-hemisphere VLBI monitoring program TANAMI, observations of Cen A are done approximately every six months at 8.4 GHz with the Australian Long Baseline Array (LBA) and associated telescopes in Antarctica, Chile, New Zealand, and South Africa, complemented by quasi-simultaneous 22.3 GHz observations. Results. The first seven epochs of high-resolution TANAMI VLBI observations at 8.4 GHz of Cen A are presented, resolving the jet on (sub-)milliarcsecond scales. They show a di erential motion of the subparsec scale jet with significantly higher component speeds farther downstream where the jet becomes optically thin. We determined apparent component speeds within a range of 0:1c to 0:3c and identified long-term stable features. In combination with the jet-to-counterjet ratio, we can constrain the angle to the line of sight to 12 45 . Conclusions. The high-resolution kinematics are best explained by a spine-sheath structure supported by the downstream acceleration occurring where the jet becomes optically thin. On top of the underlying, continuous flow, TANAMI observations clearly resolve individual jet features. The flow appears to be interrupted by an obstacle causing a local decrease in surface brightness and circumfluent jet behavior. We propose a jet-star interaction scenario to explain this appearance. The comparison of jet ejection times to high X-ray flux phases yields a partial overlap of the onset of the X-ray emission and increasing jet activity, but the limited data do not support a robust correlation.

HUNTING FOR TREASURES AMONG THE FERMI UNASSOCIATED SOURCES: A MULTIWAVELENGTH APPROACH

The Fermi Gamma-Ray Space Telescope has been detecting a wealth of sources where the multiwavelength counterpart is either inconclusive or missing altogether. We present a combination of factors that can be used to identify multiwavelength counterparts to these Fermi unassociated sources. This approach was used to select and investigate seven bright, high-latitude unassociated sources with radio, UV, X-ray, and γ-ray observations. As a result, four of these sources are candidates to be active galactic nuclei, and one to be a pulsar, while two do not fit easily into these known categories of sources. The latter pair of extraordinary sources might reveal a new category subclass or a new type of γ-ray emitter. These results altogether demonstrate the power of a multiwavelength approach to illuminate the nature of unassociated Fermi sources.

The unusual multiwavelength properties of the gamma-ray source PMN J1603−4904

Context: We investigate the nature and classification of PMN J1603−4904, a bright radio source close to the Galactic plane, which is associated with one of the brightest hard-spectrum γ-ray sources detected by Fermi/LAT. It has previously been classified as a low-peaked BL Lac object based on its broadband emission and the absence of optical emission lines. Optical measurements, however, suffer strongly from extinction and the absence of pronounced short-time γ-ray variability over years of monitoring is unusual for a blazar. Aims: In this paper, we are combining new and archival multiwavelength data of PMN J1603−4904 in order to reconsider the classification and nature of this unusual γ-ray source. Methods. For the first time, we study the radio morphology of PMN J1603−4904 at 8.4 GHz and 22.3 GHz, and its spectral properties on milliarcsecond scales, based on VLBI observations from the TANAMI program. We combine the resulting images with multiwavelength data in the radio, IR, optical/UV, X-ray, and γ-ray regimes. Results: PMN J1603−4904 shows a symmetric brightness distribution at 8.4 GHz on milliarcsecond scales, with the brightest, and most compact component in the center of the emission region. The morphology is reminiscent of a compact symmetric object (CSO). Such objects, thought to be young radio galaxies, have been predicted to produce γ-ray emission but have not been detected as a class by the Fermi γ-ray telescope so far. Sparse (u,v)-coverage at 22.3 GHz prevents an unambiguous modeling of the source morphology at this higher frequency. Moreover, infrared measurements reveal an excess in the spectral energy distribution (SED), which can be modeled with a blackbody with a temperature of about 1600 K, and which is usually not present in blazar SEDs. Conclusions: The TANAMI VLBI data and the shape of the broadband SED challenge the current blazar classification of one of the brightest γ-ray sources in the sky. PMN J1603−4904 seems to be either a highly peculiar BL Lac object or a misaligned jet source. In the latter case, the intriguing VLBI structure opens room for a possible classification of PMN J1603−4904 as a γ-ray bright CSO.

MULTI-WAVELENGTH OBSERVATIONS OF PKS 2142–75 DURING ACTIVE AND QUIESCENT GAMMA-RAY STATES

PKS 2142–75 (a.k.a. 2FGL J2147.4–7534) is a flat-spectrum radio quasar that was observed quasi-simultaneously by a suite of instruments across the electromagnetic spectrum during two flaring states in 2010 April and 2011 August as well as a quiescent state from 2011 December through 2012 January. The results of these campaigns and model spectral energy distributions (SEDs) from the active and quiescent states are presented. The SED model parameters of PKS 2142–75 indicate that the two flares of the source are created by unique physical conditions. SED studies of flat-spectrum radio quasars are beginning to indicate that there might be two types of flares, those that can be described purely by changes in the electron distribution and those that require changes in other parameters, such as the magnetic field strength or the size of the emitting region.

EVOLUTION OF THE PARSEC-SCALE STRUCTURE OF PKS 1934-638 REVISITED: FIRST SCIENCE WITH THE ASKAP AND NEW ZEALAND TELESCOPES

We have studied the archetypal Gigahertz Peaked Spectrum radio galaxy, PKS 1934−638, using the Australian Long Baseline Array augmented with two new telescopes that greatly improve the angular resolution of the array. These very long baseline interferometry observations represent the first scientific results from a new antenna in New Zealand and the first antenna of the Australian SKA Pathfinder. A compact double radio source, PKS 1934−638 has been monitored over a period of 40 years and the observation described here provides the latest datum, eight years after the previous observation, to aid in the study of the long-term evolution of the source structure. We take advantage of these new long baselines to probe PKS 1934−638 at the relatively low frequency of 1.4 GHz in order to examine the effects of optical depth on the structure of the radio source. Optical depth effects, resulting in the observation of frequency-dependent structure, may have previously been interpreted in terms of an expansion of the source as a function of time. Expansion and frequency-dependent effects are important to disentangle in order to estimate the age of PKS 1934−638. We show that frequency-dependent structure effects are likely to be important in PKS 1934−638 and present a simple two-dimensional synchrotron source model in which opacity effects due to synchrotron self-absorption are taken into account. Evidence for expansion of the radio source over 40 years is therefore weak with consequences for the estimated age of the radio source.

BL LAC OBJECT PKS B1144−379: An extreme scintillator

Rapid variability in the radio flux density of the BL Lac object PKS B1144-379 has been observed at four frequencies, ranging from 1.5 to 15 GHz, with the Very Large Array and the University of Tasmanias Ceduna antenna. Intrinsic and line-of-sight effects were examined as possible causes of this variability, with interstellar scintillation best explaining the frequency dependence of the variability timescales and modulation indices. This scintillation is consistent with a compact source 20-40 {mu}as or 0.15-0.3 pc in size. The inferred brightness temperature for PKS B1144-379 (assuming that the observed variations are due to scintillation) is 6.2 Multiplication-Sign 10{sup 12} K at 4.9 GHz, with approximately 10% of the total flux in the scintillating component. We show that scintillation surveys aimed at identifying variability timescales of days to weeks are an effective way to identify the active galactic nuclei with the highest brightness temperatures.

High resolution rapid response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)

Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including active galactic nuclei. A key tool of such studies is the ability to observe an object when it flares i.e. exhibits a rapid and significant increase in its flux density. Aims. We describe the specific observational procedures and the calibration techniques that have been developed and tested to create a single baseline radio interferometer that can rapidly observe a flaring object. This is the only facility that is dedicated to rapid high resolution radio observations of an object south of −30 degrees declination. An immediate application is to provide rapid contemporaneous radio coverage of AGN flaring at γ-ray frequencies detected by the Fermi Gamma-ray Space Telescope. Methods. A single baseline interferometer, the Ceduna Hobart Interferometer (CHI), was formed with radio telescopes in Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up at the University of Tasmania to correlate these data. Results. Measurements of the flux densities of flaring objects can be made using our observing strategy within half an hour of a triggering event. These observations can be calibrated with amplitude errors better than 15%. Lower limits to the brightness temperatures of the sources can also be calculated using CHI.

The TANAMI Multiwavelength Program: Dynamic spectral energy distributions of southern blazars

We thank the referee for helpful comments. We thank S. Cutini for her useful comments. We thank S. Markoff for helpful discussions. We thank J. Perkins, L. Baldini, and S. Digel for carefully reading the manuscript. We thank M. Buxton for her help with the SMARTS data. We acknowledge support and partial funding by the Deutsche Forschungsgemeinschaft grant WI 1860-10/1 (TANAMI) and GRK 1147, Deutsches Zentrum fur Luft- und Raumfahrt grants 50 OR 1311 and 50 OR 1103, and the Helmholtz Alliance for Astroparticle Physics (HAP). This research was funded in part by NASA through Fermi Guest Investigator grants NNH09ZDA001N, NH10ZDA001N, NNH12ZDA001N, and NNH13ZDA001N-FERMI. This research was supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. E.R. was partially supported by the Spanish MINECO project AYA2012-38491-C02-01 and by the Generalitat Valenciana project PROMETEO II/2014/057. We thank J. E. Davis for the development of the slxfig module that was used to prepare the figures in this work. We thank T. Johnson for the Fermi/LAT SED scripts, which were used to calculate the Fermi/LAT spectra. This research has made use of a collection of ISIS scripts provided by the Dr. Karl Remeis-Observatory, Bamberg, Germany at http://www.sternwarte.uni-erlangen.de/isis/. The Long Baseline Array and Australia Telescope Compact Array are part of the Australia Telescope National Facility, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. This paper has made use of up-to-date SMARTS optical/near-infrared light curves that are available at www.astro.yale.edu/smarts/glast/home.php. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat a l’Energie Atomique and the Centre National de la Recherche Scientifique / Institut National de Physique Nucleaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K.A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’Etudes Spatiales in France

Radio and gamma-ray properties of extragalactic jets from the TANAMI sample

The TANAMI program has been observing parsec-scale radio jets of southern (declination south of − 30°) γ -ray bright AGN, simultaneously with Fermi /LAT monitoring of their γ -ray emission, via high-resolution radio imaging with Very Long Baseline Interferometry techniques. We present the radio and γ -rayproperties of the TANAMI sources based on one year of contemporaneous TANAMI and Fermi /LAT data. A large fraction (72%) of the TANAMI sample can be associated with bright γ -ray sources for this time range. Association rates differ for different optical classes with all BL Lacs, 76% of quasars, and just 17% of galaxies detected by the LAT. Upper limits were established on the γ -ray flux from TANAMI sources not detected by LAT. This analysis led to the identification of three new Fermi sources whose detection was later confirmed. The γ -ray and radio luminosities are related by L γ ∝ L r 0.89±0.04 . The brightness temperatures of the radio cores increase with the average γ -ray luminosity and the presence of brightness temperatures above the inverse Compton limit implies strong Doppler boosting in those sources. The undetected sources have lower γ /radio luminosity ratios and lower contemporaneous brightness temperatures. Unless the Fermi /LAT-undetected blazars are much γ -ray-fainter than the Fermi /LAT-detected sources, their γ -ray luminosity should not be significantly lower than the upper limits calculated here.