Browsing by Author "Dutka, M. S."
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Item Gamma-ray emission in radio galaxies under the VLBI scope(EDP Sciences, 2019-06-19) Angioni, R.; Ros, E.; Kadler, M.; Ojha, R.; Müller, C.; Edwards, P. G.; Burd, P. R.; Carpenter, B.; Dutka, M. S.; Gulyaev, S.; Hase, H.; Horiuchi, S.; Krauß, F.; Lovell, J. E. J.; Natusch, T.; Phillips, C.; Plötz, C.; Quick, J. F. H.; Rösch, F.; Schulz, R.; Stevens, J.; Tzioumis, A. K.; Weston, S.; Wilms, J; Zensus, J. A.Aims. In the framework of the multi-wavelength and very long baseline interferometry (VLBI) monitoring program TANAMI (Tracking Active Nuclei with Austral Milliarcsecond Interferometry), we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the γ-ray properties of the sources. Our study investigates systematically, for the first time, the relationship between the two energy regimes in radio galaxies. In this first paper, we focus on Fermi-LAT-detected sources. Methods. The TANAMI program monitors a large sample of radio-loud AGN at 8.4 GHz and 22.3 GHz with the Australian long baseline array (LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa. We performed a kinematic analysis for five γ-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters such as speed and viewing angle. We analyzed 103 months of Fermi-LAT data in order to study possible connections between the γ-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey, with a total of fifteen sources. Results. We find that the first γ-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core, which appears to be a defining feature of high-energy emitting Fanaroff-Riley type II radio galaxies. We detect subluminal parsec-scale jet motions in the peculiar AGN PKS 0521−36, and we confirm the presence of fast γ-ray variability in the source down to timescales of six hours, which is not accompanied by variations in the VLBI jet. We robustly confirm the presence of significant superluminal motion, up to βapp ∼ 3, in the jet of the TeV radio galaxy PKS 0625−35. Our VLBI results constrain the jet viewing angle to be θ < 53◦ , allowing for the possibility of a closely aligned jet. Finally, by analyzing the first pc-scale multi-epoch images of the prototypical compact symmetric object (CSO) PKS 1718−649, we place an upper limit on the separation speed between the two mini-lobes. This in turn allows us to derive a lower limit on the age of the source. Conclusions. We can draw some preliminary conclusions on the relationship between pc-scale jets and γ-ray emission in radio galaxies, based on Fermi-LAT-detected sources with available multi-epoch VLBI measurements. We find that the VLBI core flux density correlates with the γ-ray flux, as seen in blazars. On the other hand, the γ-ray luminosity does not show any dependence on the core brightness temperature and core dominance, which are two common indicators of jet Doppler boosting. This seems to indicate that γ-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, in accordance with the unified model of jetted AGN.Item Gamma-ray emission in radio galaxies under the VLBI scope I. Parsec-scale jet kinematics and high-energy properties of γ-ray-detected TANAMI radio galaxies(EDP sciences, 2019-07-15) Angioni, R.; Ros, E.; Kadler, M.; Ojha, R.; Müller, C.; Edwards, P. G.; Burd, P. R.; Carpenter, B.; Dutka, M. S.; Gulyaev, S.; Hase, H.; Horiuchi, S.; Krauß, F.; Lovell, J. E. J.; Natusch, T.; Phillips, C.; Plötz, C.; Quick, J. F. H.; Rösch, F.; Schulz, R.; Stevens, J.; Tzioumis, A. K.; Weston, S.; Wilms, J.; Zensus, J. A.Aims. In the framework of the multi-wavelength and very long baseline interferometry (VLBI) monitoring program TANAMI (Tracking Active Nuclei with Austral Milliarcsecond Interferometry), we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the γ-ray properties of the sources. Our study investigates systematically, for the first time, the relationship between the two energy regimes in radio galaxies. In this first paper, we focus on Fermi-LAT-detected sources. Methods. The TANAMI program monitors a large sample of radio-loud AGN at 8.4 GHz and 22.3 GHz with the Australian long baseline array (LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa. We performed a kinematic analysis for five γ-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters such as speed and viewing angle. We analyzed 103 months of Fermi-LAT data in order to study possible connections between the γ-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey, with a total of fifteen sources. Results. We find that the first γ-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core, which appears to be a defining feature of high-energy emitting Fanaroff-Riley type II radio galaxies. We detect subluminal parsec-scale jet motions in the peculiar AGN PKS 0521−36, and we confirm the presence of fast γ-ray variability in the source down to timescales of six hours, which is not accompanied by variations in the VLBI jet. We robustly confirm the presence of significant superluminal motion, up to βₐₚₚ ∼ 3, in the jet of the TeV radio galaxy PKS 0625−35. Our VLBI results constrain the jet viewing angle to be θ < 53°, allowing for the possibility of a closely aligned jet. Finally, by analyzing the first pc-scale multi-epoch images of the prototypical compact symmetric object (CSO) PKS 1718−649, we place an upper limit on the separation speed between the two mini-lobes. This in turn allows us to derive a lower limit on the age of the source. Conclusions. We can draw some preliminary conclusions on the relationship between pc-scale jets and γ-ray emission in radio galaxies, based on Fermi-LAT-detected sources with available multi-epoch VLBI measurements. We find that the VLBI core flux density correlates with the γ-ray flux, as seen in blazars. On the other hand, the γ-ray luminosity does not show any dependence on the core brightness temperature and core dominance, which are two common indicators of jet Doppler boosting. This seems to indicate that γ-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, in accordance with the unified model of jetted AGN.Item Gamma-ray emission in radio galaxies under the VLBI scope II. The relationship between gamma-ray emission and parsec-scale jets in radio galaxies(EDP sciences, 2020-07-20) Angioni, R.; Ros, E.; Kadler, M.; Ojha, R.; Mueller, C.; Edwards, P.G.; Burd, P.R.; Carpenter, B.; Dutka, M. S.; Gulyaev, S.; Hase, H.; Horiuchi, S.; Krauss, F.; Lovell, J.E.J.; Natusch, T.; Phillips, C.; Ploetz, C.; Quick, J. F. H.; Roesch, F.; Schulz, R.; Stevens, J.; Tzioumis, A. K.; Weston, S.; Wilms, J.; Zensus, J. A.Aims. This is the second paper in our series studying the evolution of parsec-scale radio emission in radio galaxies in the Southern Hemisphere. Following our study of the radio and high-energy properties of γ-ray-emitting sources, here we investigate the kinematic and spectral properties of the parsec-scale jets of radio galaxies that have not yet been detected by the Fermi Large Area Telescope (Fermi-LAT) instrument on board NASA’s Fermi Gamma-ray Space Telescope. For many sources, these results represent the first milliarcsecond resolution information in the literature. These studies were conducted within the framework of the Tracking Active Nuclei with Austral Milliarcsecond Interferometry (TANAMI) monitoring program and in the context of high-energy γ-ray observations from Fermi-LAT. Methods. We took advantage of the regular 8.4 GHz and 22.3 GHz Very Long Baseline Interferometry (VLBI) observations provided by the TANAMI monitoring program, and explored the kinematic properties of six γ-ray-faint radio galaxies. We complemented this with ∼ 8.5 years of Fermi-LAT data, deriving updated upper limits on the γ-ray emission from this subsample of TANAMI radio galaxies. We included publicly available VLBI kinematics of γ-ray-quiet radio galaxies monitored by the MOJAVE program and performed a consistent Fermi-LAT analysis. We combined these results with those from our previous paper to construct the largest sample of radio galaxies with combined VLBI and γ-ray measurements to date. The connection between parsec-scale jet emission and high-energy properties in the misaligned jets of radio galaxies was explored. Results. For the first time, we report evidence of superluminal motion up to βapp = 3.6 in the jet of the γ-ray-faint radio galaxy PKS 2153−69. We find a clear trend of higher apparent speed as a function of distance from the jet core, which indicates that the jet is still being accelerated on scales of tens of parsecs, or ∼ 105 Rs, corresponding to the end of the collimation and cceleration zone in nearby radio galaxies. We find evidence of subluminal apparent motion in the jets of PKS 1258−321 and IC 4296, and no measurable apparent motion for PKS 1549−79, PKS 1733−565, and PKS 2027−308. For all these sources, TANAMI provides the first multi-epoch kinematic analysis on parsec scales. We then compare the VLBI properties of γ-ray-detected and undetected radio galaxies, and find that the two populations show a significantly different distribution of median core flux density, and, possibly, of median core brightness temperature. In terms of correlation between VLBI and γ-ray properties, we find a significant correlation between median core flux density and γ-ray flux, but no correlation with typical Doppler boosting indicators such as median core brightness temperature and core dominance. Conclusions. Our study suggests that high-energy emission from radio galaxies is related to parsec-scale radio emission from the inner jet, but is not driven by Doppler boosting effects, in contrast to the situation in their blazar counterparts. This implies that γ-ray loudness does not necessarily reflect a higher prevalence of boosting effectsItem RAPID GAMMA-RAY FLUX VARIABILITY DURING THE 2013 MARCH CRAB NEBULA FLARE(IOP, 2013-09-11) Mayer, M.; Buehler, R.; Hays, E.; Cheung, C. C.; Dutka, M. S.; Grove, J. E.; Kerr, M.; Ojha, R.We report on a bright flare in the Crab Nebula detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The period of significantly increased luminosity occurred in 2013 March and lasted for approximately two weeks. During this period, we observed flux variability on timescales of approximately 5 hr. The combined photon flux above 100 MeV from the pulsar and its nebula reached a peak value of (12.5 ± 0.8) centerdot 10⁻⁶ cm⁻² s⁻¹ on 2013 March 6. This value exceeds the average flux by almost a factor of six and implies a ~20 times higher flux for the synchrotron component of the nebula alone. This is the second brightest flare observed from this source. Spectral and temporal analysis of the LAT data collected during the outburst reveal a rapidly varying synchrotron component of the Crab Nebula while the pulsar emission remains constant in time.Item TANAMI - Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry(2010-01-18) Muller, Cornelia; Kadler, Matthias; Ojha, Roopesh; Bock, M.; Booth, R.; Dutka, M. S.; Edwards, P. G.; Fey, A. L.; Fuhrmann, L.; Hase, H.; Horiuchi, S.; Hungwe, F.; Ros, E.; Taylor, G. B.; Thompson, D. J.; Tingay, S. J.; Tosti, G.; Tzioumis, A. K.; Wilms, J.; Zensus, J. A.We present a summary of the observation strategy of TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry), a monitoring program to study the parsec-scale structure and dynamics of relativistic jets in active galactic nuclei (AGN) of the Southern Hemisphere with the Australian Long Baseline Array (LBA) and the trans-oceanic antennas Hartebeesthoek, TIGO, and O'Higgins. TANAMI is focusing on extragalactic sources south of -30 degrees declination with observations at 8.4 GHz and 22 GHz every ~2 months at milliarcsecond resolution. The initial TANAMI sample of 43 sources has been defined before the launch of the Fermi Gamma Ray Space Telescope to include the most promising candidates for bright gamma-ray emission to be detected with its Large Area Telescope (LAT). Since November 2008, we have been adding new sources to the sample, which now includes all known radio- and gamma-ray bright AGN of the Southern Hemisphere. The combination of VLBI and gamma-ray observations is crucial to understand the broadband emission characteristics of AGN and the nature of relativistic jets.Item The TANAMI Program(AIP Publishing, 2010-07-22) Müller, Cornelia; Kadler, Matthias; Ojha, Roopesh; Böck, M.; Booth, R.; Dutka, M. S.; Edwards, P.; Fey, A. L.; Fuhrmann, L.; Hase, H.; Horiuchi, S.; Jauncey, D.L.; Johnston, K.J.; Katz, U.; Lister, M.; Lovell, J.E.J.; Plötz, C.; Quick, J.F.H.; Ros, E.; Taylor, G.B.; Thompson, D.J.; Tingay, S.J.; Tosti, G.; Tzioumis, A.K.; Wilms, J.; Zensus, J.A.TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) is a monitoring program to study the parsec-scale structures and dynamics of relativistic jets in active galactic nuclei (AGN) of the Southern Hemisphere with the Long Baseline Array and associated telescopes. Extragalactic jets south of -30 degrees declination are observed at 8.4 GHz and 22 GHz every two months at milliarcsecond resolution. The initial TANAMI sample is a hybrid radio and gamma-ray selected sample since the combination of VLBI and gamma-ray observations is crucial to understand the broadband emission characteristics of AGN.Item TANAMI: Milliarcsecond Resolution Observations of Extragalactic Gamma-ray Sources(arXiv, 2009-12-31) Ojha, Roopesh; Kadler, M.; Böck, M.; Booth, R.; Dutka, M. S.; Edwards, P. G.; Fey, A. L.; Fuhrmann, L.; Gaume, R. A.; Hase, H.; Horiuchi, S.; Jauncey, D.L.; Johnston, K. J.; Katz, U.; Lister, M.; Lovell, J. E. J.; Müller, C.; Plötz, C.; Quick, J. F. H.; Ros, E.; Taylor, G. B.; Thompson, D. J.; Tingay, S. J.; Tosti, G.; Tzioumis, A. K.; Wilms, J.; Zensus, J. A.The TANAMI (Tracking AGN with Austral Milliarcsecond Interferometry) and associated programs provide comprehensive radio monitoring of extragalactic gamma-ray sources south of declination -30 degrees. Joint quasi-simultaneous observations between the Fermi Gamma-ray Space Telescope and ground based observatories allow us to discriminate between competing theoretical blazar emission models. High resolution VLBI observations are the only way to spatially resolve the sub-parsec level emission regions where the high-energy radiation originates. The gap from radio to gamma-ray energies is spanned with near simultaneous data from the Swift satellite and ground based optical observatories. We present early results from the TANAMI program in the context of this panchromatic suite of observations.Item TANAMI: tracking active galactic nuclei with austral milliarcsecond interferometry(EDP sciences, 2010-09-10) Ojha, R.; Kadler, M.; Böck, M.; Booth, R.; Dutka, M. S.; Edwards, P. G.; Fey, A. L.; Fuhrmann, L.; Gaume, R. A.; Hase, H.; Horiuchi, S.; Jauncey, D. L.; Johnston, K. J.; Katz, U.; Lister, M.; Lovell, J. E. J.; Müller, C.; Plötz, C.; Quick, J. F. H.; Ros, E.; Taylor, G. B.; Thompson, D. J.; Tingay, S. J.; Tosti, G.; Tzioumis, A. K.; Wilms, J.; Zensus, J. A.Context. A number of theoretical models vie to explain the γ-ray emission from active galactic nuclei (AGN). This was a key discovery of EGRET. With its broader energy coverage, higher resolution, wider field of view and greater sensitivity, the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope is dramatically increasing our knowledge of AGN γ-ray emission. However, discriminating between competing theoretical models requires quasi-simultaneous observations across the electromagnetic spectrum. By resolving the powerful parsec-scale relativistic outflows in extragalactic jets and thereby allowing us to measure critical physical properties, Very Long Baseline Interferometry observations are crucial to understanding the physics of extragalactic γ-ray objects. Aims. We introduce the TANAMI program (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) which is monitoring an initial sample of 43 extragalactic jets located south of -30 degrees declination at 8.4 GHz and 22 GHz since 2007. All aspects of the program are discussed. First epoch results at 8.4 GHz are presented along with physical parameters derived therefrom. Methods. These observations were made during 2007/2008 using the telescopes of the Australian Long Baseline Array in conjunction with Hartebeesthoek in South Africa. These data were correlated at the Swinburne University correlator. Results. We present first epoch images for 43 sources, some observed for the first time at milliarcsecond resolution. Parameters of these images as well as physical parameters derived from them are also presented and discussed. These and subsequent images from the TANAMI survey are available at http://pulsar.sternwarte.uni-erlangen.de/tanami/. Conclusions. We obtain reliable, high dynamic range images of the southern hemisphere AGN. All the quasars and BL Lac objects in the sample have a single-sided radio morphology. Galaxies are either double-sided, single-sided or irregular. About 28% of the TANAMI sample has been detected by LAT during its first three months of operations. Initial analysis suggests that when galaxies are excluded, sources detected by LAT have larger opening angles than those not detected by LAT. Brightness temperatures of LAT detections and non-detections seem to have similar distributions. The redshift distributions of the TANAMI sample and sub-samples are similar to those seen for the bright γ-ray AGN seen by LAT and EGRET but none of the sources with a redshift above 1.8 have been detected by LAT.Item TANAMI: Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry⋆(EDP sciences, 2018-02-07) Müller, C.; Kadler, M.; Ojha, R.; Schulz, R.; Trüstedt, J.; Edwards, P. G.; Ros, E.; Carpenter, B.; Angioni, R.; Blanchard, J.; Böck, M.; Burd, P. R.; Dörr, M.; Dutka, M. S.; Eberl, T.; Gulyaev, S.; Hase, H.; Horiuchi, S.; Katz, U.; Krauß, F.; Lovell, J. E. J.; Natusch, T.; Nesci, R.; Phillips, C.; Plötz, C.; Pursimo, T.; Quick, J. F. H.; Stevens, J.; Thompson, D. J.; Tingay, S. J.; Tzioumis, A. K.; Weston, S.; Wilms, J.; Zensus, J. A.Context. TANAMI is a multiwavelength program monitoring active galactic nuclei (AGN) south of − 30° declination including high-resolution very long baseline interferometry (VLBI) imaging, radio, optical/UV, X-ray, and γ-ray studies. We have previously published first-epoch8.4 GHz VLBI images of the parsec-scale structure of the initial sample. In this paper, we present images of 39 additional sources. The full sample comprises most of the radio- and γ-ray brightest AGN in the southern quarter of the sky, overlapping with the region from which high-energy (> 100 TeV) neutrino events have been found. Aims. We characterize the parsec-scale radio properties of the jets and compare them with the quasi-simultaneous Fermi/LAT γ-ray data. Furthermore, we study the jet properties of sources which are in positional coincidence with high-energy neutrino events compared to the full sample. We test the positional agreement of high-energy neutrino events with various AGN samples. Methods. TANAMI VLBI observations at 8.4 GHz are made with southern hemisphere radio telescopes located in Australia, Antarctica, Chile, New Zealand, and South Africa. Results. Our observations yield the first images of many jets below − 30° declination at milliarcsecond resolution. We find that γ-ray loud TANAMI sources tend to be more compact on parsec-scales and have higher core brightness temperatures than γ-ray faint jets, indicating higher Doppler factors. No significant structural difference is found between sources in positional coincidence with high-energy neutrino events and other TANAMI jets. The 22 γ-ray brightest AGN in the TANAMI sky show only a weak positional agreement with high-energy neutrinos demonstrating that the > 100 TeV IceCube signal is not simply dominated by a small number of the γ-ray brightest blazars. Instead, a larger number of sources have to contribute to the signal with each individual source having only a small Poisson probability for producing an event in multi-year integrations of current neutrino detectors.