Browsing by Author "Kreikenbohm, A."
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Item Ernie and Bert in the radio TANAMI blazars in the IceCube neutrino fields(European Space Agency) Krauß, Felicia; Kadler, M.; Mannheim, K.; Wilms, J.; Ojha, R.; Kreikenbohm, A.; Langejahn, M.; Müller, C.; Schulz, R.; Trüstedt, J.Item Extended X-ray emission in PKS 1718−649(EDP sciences, 2018-04-30) Beuchert, T.; Rodríguez-Ardila, A.; Moss, V. A.; Schulz, R.; Kadler, M.; Wilms, J.; Angioni, R.; Callingham, J. R.; Gräfe, C.; Krauß, F.; Kreikenbohm, A.; Langejahn, M.; Leiter, K.; Maccagni, F. M.; Müller, C.; Ojha, R.; Ros, E.; Tingay, S. J.PKS 1718−649 is one of the closest and most comprehensively studied candidates of a young active galactic nucleus (AGN) that is still embedded in its optical host galaxy. The compact radio structure, with a maximal extent of a few parsecs, makes it a member of the group of compact symmetric objects (CSO). Its environment imposes a turnover of the radio synchrotron spectrum towards lower frequencies, also classifying PKS 1718−649 as gigahertz-peaked radio spectrum (GPS) source. Its close proximity has allowed the first detection of extended X-ray emission in a GPS/CSO source with Chandra that is for the most part unrelated to nuclear feedback. However, not much is known about the nature of this emission. By co-adding all archival Chandra data and complementing these datasets with the large effective area of XMM-Newton, we are able to study the detailed physics of the environment of PKS 1718−649. Not only can we confirm that the bulk of the ≲kiloparsec-scale environment emits in the soft X-rays, but we also identify the emitting gas to form a hot, collisionally ionized medium. While the feedback of the central AGN still seems to be constrained to the inner few parsecs, we argue that supernovae are capable of producing the observed large-scale X-ray emission at a rate inferred from its estimated star formation rate.Item The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447(EDP sciences, 2015-12-23) Kreikenbohm, A.; Schulz, R.; Kadler, M.; Wilms, J.; Markowitz, A.; Chang, C. S.; Carpenter, B.; Elsässer, D.; Gehrels, N.; Mannheim, K.; Müller, C.; Ojha, R.; Ros, E.; Trüstedt, J.As part of the TANAMI multiwavelength progam, we discuss new X-ray observations of the γ-ray and radio-loud narrow line Seyfert 1 galaxy (γ-NLS1) PKS 2004−447. The active galaxy is a member of a small sample of radio-loud NLS1s detected in γ-rays by the Fermi Large Area Telescope. It stands out for being the radio-loudest and the only southern-hemisphere source in this sample. We present results from our X-ray monitoring program comprised of Swift snapshot observations from 2012 through 2014 and two new X-ray observations with XMM-Newton in 2012. Supplemented by archival data from 2004 and 2011, our data set allows for a careful analysis of the X-ray spectrum and variability of this peculiar source. The (0.5–10) keV spectrum is described well by a power law (Γ ~ 1.6), which can be interpreted as non-thermal emission from a relativistic jet. The source exhibits moderate flux variability on timescales of both months and years. Correlated brightness variations in the (0.5–2) keV and (2–10) keV bands are explained by a single variable spectral component, such as the one from the jet. A possible soft excess seen in the data from 2004 cannot be confirmed by the new XMM-Newton observations taken during low-flux states. Any contribution to the total flux in 2004 is less than 20% of the power-law component. The (0.5–10) keV luminosities of PKS 2004−447 are in the range of (0.5−2.7) × 10⁴⁴ erg s⁻¹. A comparison of the X-ray properties among the known γ-NLS1 galaxies shows that in four out of five cases the X-ray spectrum is dominated by a flat power law without intrinsic absorption. These objects are moderately variable in their brightness, while spectral variability is observed in at least two sources. The major difference across the X-ray spectra of γ-NLS1s is the luminosity, which spans a range of almost two orders of magnitude from 10⁴⁴ erg s⁻¹ to 10⁴⁶ erg s⁻¹ in the (0.5–10) keV band.Item The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447(EDP sciences, 2016-04-01) Schulz, R.; Kreikenbohm, A.; Kadler, M.; Ojha, R.; Ros, E.; Stevens, J.; Edwards, P. G.; Carpenter, B.; Elsässer, D.; Gehrels, N.; Grossberger, C.; Hase, H.; Horiuchi, S.; Lovell, J. E. J.; Mannheim, K.; Markowitz, A.; Müller, C.; Phillips, C.; Plötz, C.; Quick, J.; Trüstedt, J.; Tzioumis, A. K.; Wilms, J.Context. Γ-ray-detected radio-loud narrow-line Seyfert 1 (γ-NLS1) galaxies constitute a small but interesting sample of the γ-ray-loud AGN. The radio-loudest γ-NLS1 known, PKS 2004−447, is located in the southern hemisphere and is monitored in the radio regime by the multiwavelength monitoring programme TANAMI. Aims. We aim for the first detailed study of the radio morphology and long-term radio spectral evolution of PKS 2004−447, which are essential for understanding the diversity of the radio properties of γ-NLS1s. Methods. The TANAMI VLBI monitoring program uses the Australian Long Baseline Array (LBA) and telescopes in Antarctica, Chile, New Zealand, and South Africa to monitor the jets of radio-loud active galaxies in the southern hemisphere. Lower resolution radio flux density measurements at multiple radio frequencies over four years of observations were obtained with the Australia Telescope Compact Array (ATCA). Results. The TANAMI VLBI image at 8.4 GHz shows an extended one-sided jet with a dominant compact VLBI core. Its brightness temperature is consistent with equipartition, but it is an order of magnitude below other γ-NLS1s with the sample value varying over two orders of magnitude. We find a compact morphology with a projected large-scale size < 11 kpc and a persistent steep radio spectrum with moderate flux-density variability. Conclusions. PKS 2004−447 appears to be a unique member of the γ-NLS1 sample. It exhibits blazar-like features, such as a flat featureless X-ray spectrum and a core-dominated, one-sided parsec-scale jet with indications for relativistic beaming. However, the data also reveal properties atypical for blazars, such as a radio spectrum and large-scale size consistent with compact-steep-spectrum (CSS) objects, which are usually associated with young radio sources. These characteristics are unique among all γ-NLS1s and extremely rare among γ-ray-loud AGN.Item Investigating source confusion in PMN J1603–4904(EDP sciences, 2018-02-20) Krauß, F.; Kreter, M.; Müller, C.; Markowitz, A.; Böck, M.; Burnett, T.; Dauser, T.; Kadler, M.; Kreikenbohm, A.; Ojha, R.; Wilms, J.PMN J1603–4904 is a likely member of the rare class of γ-ray emitting young radio galaxies. Only one other source, PKS 1718–649, has been confirmed so far. These objects, which may transition into larger radio galaxies, are a stepping stone to understanding AGN evolution. It is not completely clear how these young galaxies, seen edge-on, can produce high-energy γ rays. PMN J1603–4904 has been detected by TANAMI Very Long Baseline Interferometry (VLBI) observations and has been followed-up with multiwavelength observations. A Fermi Gamma-ray Space Telescope Large Area Telescope (Fermi-LAT) γ-ray source has been associated with this young galaxy in the LAT catalogs. We have obtained Chandra observations of the source to consider the possibility of source confusion due to the relatively large positional uncertainty of Fermi-LAT. The goal was to investigate the possibility of other X-ray bright sources in the vicinity of PMN J1603–4904 that could be counterparts to the γ-ray emission. With Chandra/ACIS, we find no other sources in the uncertainty ellipse of Fermi-LAT data, which includes an improved localization analysis of eight years of data. We further study the X-ray fluxes and spectra. We conclude that PMN J1603–4904 is indeed the second confirmed γ-ray bright young radio galaxy.Item Rapid Variability of Mrk 421 During Extreme Flaring as Seen Through the Eyes of XMM-Newton(2024-02-29) Gokus, A.; Wilms, J.; Kadler, M.; Dorner, D.; Nowak, M. A.; Kreikenbohm, A.; Leiter, K.; Bretz, T.; Schleicher, B.; Markowitz, A. G.; Pottschmidt, Katja; Mannheim, K.; Kreykenbohm, I.; Langejahn, M.; McBride, F.; Beuchert, T.; Dauser, T.; Kreter, M.; Abhir, J.; Baack, D.; Balbo, M.; Biland, A.; Brand, K.; Buss, J.; Eisenberger, L.; Elsaesser, D.; Guenther, P.; Hildebrand, D.; Linhoff, M.; Paravac, A.; Rhode, W.; Sliusar, V.; Hasan, S.; Walter, R.By studying the variability of blazars across the electromagnetic spectrum, it is possible to resolve the underlying processes responsible for rapid flux increases, so-called flares. We report on an extremely bright X-ray flare in the high-peaked BL Lacertae object Mrk 421 that occurred simultaneously with enhanced 𝜸-ray activity detected at very high energies (VHE) by FACT on 2019 June 9. We triggered an observation with XMM-Newton, which observed the source quasi-continuously for 25 hours. We find that the source was in the brightest state ever observed using XMM-Newton, reaching a flux of 2.8 x 10 ⁻⁹ erg cm ⁻² s ⁻¹ over an energy range of 0.3 - 10 keV. We perform a spectral and timing analysis to reveal the mechanisms of particle acceleration and to search for the shortest source-intrinsic time scales. Mrk 421 exhibits the typical harder-when-brighter behaviour throughout the observation and shows a clock-wise hysteresis pattern, which indicates that the cooling dominates over the acceleration process. While the X-ray emission in different sub-bands is highly correlated, we can exclude large time lags as the computed zDCFs are consistent with a zero lag. We find rapid variability on time scales of 1 ks for the 0.3 - 10 keV band and down to 300s in the hard X-ray band (4 - 10 keV). Taking these time scales into account, we discuss different models to explain the observed X-ray flare, and find that a plasmoid-dominated magnetic reconnection process is able to describe our observation best.Item Redshifted Fe Kα line from the unusual γ-ray source PMN J1603–4904(EDP Sciences, 2015-02-04) Müller, C.; Krauß, F.; Dauser, T.; Kreikenbohm, A.; Beuchert, T.; Kadler, M.; Ojha, R.; Wilms, J.; Böck, M.; Carpenter, B.; Dutka, M.; Markowitz, A.; McConville, W.; Pottschmidt, Katja; Stawarz, Ł.; Taylor, G. B.Context. Multiwavelength observations have revealed the highly unusual properties of the γ-ray source PMN J1603–4904, which are difficult to reconcile with any other well-established γ-ray source class. The object is either a very atypical blazar or a compact jet source seen at a larger angle to the line of sight. Aims. To determine the physical origin of the high-energy emission processes in PMN J1603–4904, we study the X-ray spectrum in detail. Methods. We performed quasi-simultaneous X-ray observations with XMM-Newton and Suzaku in 2013 September. This resulted in the first high signal-to-noise X-ray spectrum of this source. Results. The 2–10 keV X-ray spectrum can be well described by an absorbed power law with an emission line at 5.44 ± 0.05 keV (observed frame). We interpret this feature as a Kα line from neutral iron and accordingly determine the redshift of PMN J1603–4904 to be z = 0.18 ± 0.01, which corresponds to a luminosity distance of 872 ± 54 Mpc. Conclusions. The detection of a redshifted X-ray emission line further challenges the original BL Lac classification of PMN J1603–4904. This result suggests that the source is observed at a larger angle to the line of sight than expected for blazars, and thus the source would add to the elusive class of γ-ray loud misaligned-jet objects, possibly a γ-ray bright young radio galaxy.Item Redshifted Kα Line from the Peculiar Gamma-ray Source PMN J1603–4904Müller, Cornelia; Krauß, F.; Dauser, T.; Kreikenbohm, A.; Beuchert, T.; Kadler, M.; Ojha, R.; Wilms, J.; Böck, M.; Carpenter, B.; Dutka, M.; Markowitz, A.; McConville, W.; Pottschmidt, Katja; Stawarz, L.; Taylor, G.B.The Southern Hemisphere AGN monitoring program TANAMI∗ provides regular VLBI monitoring (at 8 and 22 GHz) and multiwavelength coverage of extragalactic jets south of −30◦ declination. Here we focus on our latest results on the bright, hard-spectrum γ-ray source PMN J1603–4904. Our VLBI observations reveal a symmetric brightness distribution with the brightest, most compact component at the center of the emission region. No significant apparent motion is detected. Long-term monitoring with ATCA in the radio (5-40 GHz) and in the γ-rays by Fermi/LAT shows only mild variability and no major outbursts. Its broadband spectral energy distribution and other multiwavelength properties point to either a very atypical blazar or can be explained as a source seen edge-on, possibly a young radio galaxy. The latter would make PMN J1603– 4904 the first young radio galaxy detected in γ-rays, so additional confirmation is sought. Our recent Suzaku and XMM observations detect a narrow iron line, which results in the first redshift measurement of the system (z = 0.18 ± 0.01). This result suggests that the source is observed at a larger angle to the line of sight than expected for blazars, and allows us to constrain the linear extent of the arcsec-scale structure to be smaller than ∼3 kpc, which in the two-sided jet scenario is in agreement with the small linear scales characteristic of young radio galaxies.Item TANAMI blazars in the IceCube PeV-neutrino fields(EDP sciences, 2014-06-24) Krauß, F.; Kadler, M.; Mannheim, K.; Schulz, R.; Trüstedt, J.; Wilms, J.; Ojha, R.; Ros, E.; Anton, G.; Baumgartner, W.; Beuchert, T.; Blanchard, J.; Bürkel, C.; Carpenter, B.; Eberl, T.; Edwards, P. G.; Eisenacher, D.; Elsässer, D.; Fehn, K.; Fritsch, U.; Gehrels, N.; Gräfe, C.; Grossberger, C.; Hase, H.; Horiuchi, S.; James, C.; Kappes, A.; Katz, U.; Kreikenbohm, A.; Kreykenbohm, I.; Langejahn, M.; Leiter, K.; Litzinger, E.; Lovell, J. E. J.; Müller, C.; Phillips, C.; Plötz, C.; Quick, J.; Steinbring, T.; Stevens, J.; Thompson, D. J.; Tzioumis, A. K.The IceCube Collaboration has announced the discovery of a neutrino flux in excess of the atmospheric background. Owing to the steeply falling atmospheric background spectrum, events at PeV energies most likely have an extraterrestrial origin. We present the multiwavelength properties of the six radio-brightest blazars that are positionally coincident with these events using contemporaneous data of the TANAMI blazar sample, including high-resolution images and spectral energy distributions. Assuming the X-ray to γ-ray emission originates in the photoproduction of pions by accelerated protons, the integrated predicted neutrino luminosity of these sources is high enough to explain the two detected PeV events.Item TANAMI monitoring of Centaurus A: The complex dynamics in the inner parsec of an extragalactic jet(EDP sciences, 2014-10-01) Müller, C.; Kadler, M.; Ojha, R.; Perucho, M.; Grossberger, C.; Ros, E.; Wilms, J.; Blanchard, J.; Böck, M.; Carpenter, B.; Dutka, M.; Edwards, P. G.; Hase, H.; Horiuchi, S.; Kreikenbohm, A.; Lovell, J. E. J.; Markowitz, A.; Phillips, C.; Plötz, C.; Pursimo, T.; Quick, J.; Rothschild, R.; Schulz, R.; Steinbring, T.; Stevens, J.; Trüstedt, J.; Tzioumis, A. K.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 differential 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 0.1 c to 0.3 c 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 θ ~ 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.Item The unusual multiwavelength properties of the gamma-ray source PMN J1603−4904(EDP sciences, 2014-01-30) Müller, Cornelia; Kadler, M.; Ojha, R.; Böck, M.; Krauß, F.; Taylor, G. B.; Wilms, J.; Blanchard, J.; Carpenter, B.; Dauser, T.; Dutka, M.; Edwards, P. G.; Gehrels, N.; Grossberger, C.; Hase, H.; Horiuchi, S.; Kreikenbohm, A.; Lovell, J. E. J.; McConville, W.; Phillips, C.; Plötz, C.; Pursimo, T.; Quick, J.; Ros, E.; Schulz, R.; Stevens, J.; Tingay, S. J.; Trüstedt, J.; Tzioumis, A. K.; Zensus, J. A.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.Item X-ray monitoring of the radio and γ-ray loud Narrow-Line Seyfert 1 Galaxy PKS2004–447(EDP sciences, 2013-12-09) Kreikenbohm, A.; Kadler, M.; Wilms, J.; Schulz, R.; Müller, C.; Ojha, R.; Ros, E.; Mannheim, K.; Elsässer, D.We present preliminary results of the X-ray analysis of XMM-Newton and Swift observations as part of a multi-wavelength monitoring campaign in 2012 of the radio-loud narrow line Seyfert 1 galaxy PKS 2004–447. The source was recently detected in γ-rays by Fermi/LAT among only four other galaxies of that type. The 0:5 – 10 keV X-ray spectrum is well-described by a simple absorbed powerlaw (Γ ∼ 1.6). The source brightness exhibits variability on timescales of months to years with indications for spectral variability, which follows a “bluer-when-brighter” behaviour, similar to blazars.