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2. Variations of the TeV energy spectrum at different flux levels of Mkn 421 observed with the HEGRA system of Cherenkov telescopes

Author

Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J., Cortina, J., Costamante, L., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lopez, M., Lorenz, E., Fabrizio Lucarelli, Mang, O., Meyer, H., Mirzoyan, R., Milite, M., Moralejo, A., Ona, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Rauterberg, G., Reyes, R., Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., Wittek, W., and Remillard, R. A.

Subjects
Physics, Photon, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Mid infrared, FOS: Physical sciences, HEGRA, Astronomy and Astrophysics, Astrophysics, Power law, Spectral line, Space and Planetary Science, Energy spectrum, Cherenkov radiation, Background radiation
Abstract

The nearby BL Lacertae (BL Lac) object Markarian~421 (Mkn~421) at a red shift z=0.031 was observed to undergo strong TeV Gamma-ray outbursts in the observational periods from December 1999 until May 2001. The time averaged energy spectrum is well described by a power law with an exponential cut-off energy at 3.6(+0.4-0.3)_{stat}(+0.9-0.8)_{sys} TeV. The energy spectra derived for different average flux levels ranging from 0.5 to 10 * 10^{-11}ph/cm**2/s follow a clear correlation of photon index and flux level. Generally, the energy spectra are harder for high flux levels. From January to April 2001 Mkn~421 showed rapid variability (doubling time as short as 20 minutes), accompanied with a spectral hardening with increasing flux level within individual nights. For two successive nights (MJD 51989-51991, March 21-23,2001), this correlation of spectral hardness and change in flux has been observed within a few hours. The cut-off energy for the Mkn~421 TeV spectrum remains within the errors constant for the different flux levels and differs by 2.6+/-0.6_stat+/-0.6_sys TeV from the value determined for Mkn~501. This indicates that the observed exponential cut-off in the energy spectrum of Mkn~421 is not solely caused by absorption of multi-TeV photons by pair-production processes with photons of the extragalactic near/mid infrared background radiation., Comment: 12 pages, 9 figures, submitted to Astronomy&Astrophysics

Published
2002
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3. Observations of H1426+428 with HEGRA -- Observations in 2002 and reanalysis of 1999&2000 data

Author

Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H. -G, Bojahr, H., Bolz, O., Coarasa, T., Contreras, J. L., Juan Cortina, Costamante, L., Denninghoff, S., Fonseca, M. V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Mazine, D., Meyer, H., Mirzoyan, R., Moralejo, A., Ona-Wilhelmi, E., Panter, M., Plyasheshnikov, A., Prahl, J., Pühlhofer, G., Los Reyes, R., Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Vitale, V., Völk, H. J., Wiedner, C. A., and Wittek, W.

Subjects
Physics, Astrophysics::High Energy Astrophysical Phenomena, Flux, HEGRA, Astronomy and Astrophysics, Astrophysics, Spectral line, Wavelength, Extragalactic background light, Space and Planetary Science, Absorption (electromagnetic radiation), Cherenkov radiation, BL Lac object
Abstract

The HEGRA system of imaging air Cherenkov telescopes has been used to observe the BL Lac object H1426+428 ($z=0.129$) for 217.5 hours in 2002. In this data set alone, the source is detected at a confidence level of $5.3~\sigma$, confirming this object as a TeV source. The overall flux level during the observations in 2002 is found to be a factor of $\approx 2.5$ lower than during the previous observations by HEGRA in 1999&2000. A new spectral analysis has been carried out, improving the signal-to-noise ratio at the expense of a slightly increased systematic uncertainty and reducing the relative energy resolution to $\Delta E/E\le 12 %$ over a wide range of energies. The new method has also been applied to the previously published data set taken in 1999 and 2000, confirming the earlier claim of a flattening of the energy spectrum between 1 and 5 TeV. The data set taken in 2002 shows again a signal at energies above 1 TeV. We combine the energy spectra as determined by the CAT and VERITAS groups with our reanalyzed result of the 1999&2000 data set and apply a correction to account for effects of absorption of high energy photons on extragalactic background light in the optical to mid infrared band. The shape of the inferred source spectrum is mostly sensitive to the characteristics of the extragalactic background light between wavelengths of 1 and 15~$\mu$m, Comment: 12 pages, 4 Figures, submitted to A&A

Published
2003

4. An unidentified TeV source in the vicinity of Cygnus OB2

Author

Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlohr, K., Borst, H., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Gotting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Magnussen, N., Mang, O., Meyer, H., Milite, M., Mirzoyan, R., Moralejo, A., Ona, E., Panter, M., Plyasheshnikov, A., Prahl, J., Puhlhofer, G., Rauterberg, G., Reyes, R., Rhode, W., Ripken, J., Rohring, A., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Schroder, F., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Volk, H. J., Wiedner, C. A., Wittek, W. (HEGRA Collaboration), Uchiyama, Yasunobu, and Takahashi, Tadayuki

Subjects
Physics, Astrophysics (astro-ph), Flux, HEGRA, FOS: Physical sciences, Astronomy and Astrophysics, Radius, Astrophysics, Particle acceleration, Stars, Pulsar, Space and Planetary Science, Cygnus OB2, Heliosphere
Abstract

著者人数：62名, Accepted: 2002-08-09, 資料番号: SA1002274000

Published
2002
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5. Measurement of the radial distribution of Cherenkov light generated by TeV gamma-ray air showers

Author

Aharonian, F. A., Akhperjanian, A. G., Barrio, J. A., Bernlöhr, K., Bojahr, H., Contreras, J. L., Juan Cortina, Daum, A., Deckers, T., Fonseca, V., Fraß, A., Gonzalez, J. C., Heinzelmann, G., Hemberger, M., Hermann, G., Heß, M., Heusler, A., Hofmann, W., Hohl, H., Holl, I., Horns, D., Ibarra, I., Kankanyan, R., Kestel, M., Kirstein, O., Köhler, C., Konopelko, A., Kornmayer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lindner, A., Lorenz, E., Magnussen, N., Meyer, H., Mirzoyan, R., Moralejo, A., Padilla, L., Panter, M., Petry, D., Plaga, R., Prahl, J., Prosch, C., Pühlhofer, G., Rauterberg, G., Rhode, W., Röhring, A., Samorski, M., Schmele, D., Schröder, F., Stamm, W., Ulrich, M., Völk, H. J., Wiebel-Sooth, B., Wiedner, C. A., Willmer, M., and Wirth, H.

Subjects
Physics, Physics::Instrumentation and Detectors, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Gamma ray, Astrophysics::Instrumentation and Methods for Astrophysics, HEGRA, FOS: Physical sciences, Astronomy and Astrophysics, IACT, Radial distribution, Astrophysics, Shower, Air shower, High Energy Physics::Experiment, Cherenkov radiation, Zenith
Abstract

Using air showers induced by TeV gamma-rays from Mrk 501, the radial distribution of Cherenkov light is investigated. The shower geometry is reconstructed from the stereoscopic shower images obtained with the telescopes of the HEGRA IACT system. We observe a change in the shape of the light pool with shower energy, and with zenith angle. Data are well reproduced by Monte-Carlo air shower simulations., Comment: 15 Pages, 8 figures, Latex

Published
1998
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6. The time structure of Cherenkov images generated by TeV gamma-rays and by cosmic rays

Author

Heß, M., Bernlöhra, K., Daum, A., Hemberger, M., Hermann, G., Hofmann, W., Lampeitl, H., Aharonian, F. A., Akhperjanian, A. G., Barrio, J. A., Beteta, J. J. G., Contreras, J. L., Juan Cortina, Deckers, T., Fernandez, J., Fonseca, V., Gonzalez, J. C., Heinzelmann, G., Heusler, A., Hohl, H., Holl, I., Horns, D., Kankanyan, R., Kestel, M., Kirstein, O., Köhler, C., Konopelko, A., Kornmayer, H., Kranich, D., Krawczynski, H., Lindner, A., Lorenz, E., Magnussen, N., Meyer, H., Mirzoyan, R., Moralejo, A., Padilla, L., Panter, M., Petry, D., Plaga, R., Prahl, J., Prosch, C., Pühlhofer, G., Rauterberg, G., Rhode, W., Röhring, A., Samorski, M., Sanchez, J. A., Schmele, D., Schröder, F., Stamm, W., Völk, H. J., Wiebel-Sooth, B., Wiedner, C. A., and Willmer, M.

Subjects
Physics, Photon, Physics::Instrumentation and Detectors, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Gamma ray, Astrophysics::Instrumentation and Methods for Astrophysics, HEGRA, FOS: Physical sciences, Astronomy and Astrophysics, Cosmic ray, Astrophysics, law.invention, Core (optical fiber), Telescope, Shower, law, Cherenkov radiation
Abstract

The time profiles of Cherenkov images of cosmic-ray showers and of gamma-ray showers are investigated, using data gathered with the HEGRA system of imaging atmospheric Cherenkov telescopes during the 1997 outbursts of Mrk 501. Photon arrival times are shown to vary across the shower images. The dominant feature is a time gradient along the major axis of the images. The gradient varies with the distance between the telescope and the shower core, and is maximal for large distances. The time profiles of cosmic-ray showers and of gamma-ray showers differ in a characteristic fashion. The main features of the time profiles can be understood in terms of simple geometrical models. Use of the timing information towards improved shower reconstruction and cosmic-ray suppression is discussed., Comment: 25 Pages, 16 figures, Latex

Published
1998
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10. Environmental factors on Microcystin levels in waterbodies

Author

Chorus, I., Lindenschmidt, K.E., Niesel, V., Fastner, J., Wiedner, C., Nixdorf, B., Chorus, I., Lindenschmidt, K.E., Niesel, V., Fastner, J., Wiedner, C., and Nixdorf, B.

Abstract

As discussed in the introduction to Chapter 3, understanding how environmental factors influence cyanotoxin concentrations in waterbodies requires differentiation between two potential mechanisms: a direct impact on cellular toxin content, and/or an impact on competition between genotypes which would lead to dominance of strains or species with or without microcystin. The field results reported in Chapter 2 reinforce published observations that some taxa produce microcystins, others contain certain neurotoxins, and some may contain both or neither. However, further differentiation is possible: Chapter 4.1 shows that Microcystis spp., Planktothrix agardhii and Planktothrix rubescens each typically contain specific microcystin variants, though relative shares of variants as well as total microcystin content of the field populations may vary. Section 4.2 also addresses the level below that of species — i.e. the level of strains or genotypes — by investigating microcystin content in different strains of Microcystis aeruginosa isolated from two lakes. This results demonstrate a substantial variability of of microcystin content between different strains of M. aeruginosa. In conjunction with culture study results reoported in Chapter 3 (which showed little impact of environmental factors on cellular toxin content), this result suggests competition between strain of a species to be a decisive determinant of microcystin concentration in natural populations.

Published
2001

11. Observations of 14 young open star clusters with the HEGRA system of Cherenkov telescopes

Author

Aharonian, F., primary, Akhperjanian, A., additional, Beilicke, M., additional, Bernlöhr, K., additional, Börst, H.-G., additional, Bojahr, H., additional, Bolz, O., additional, Coarasa, T., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, M. V., additional, Girma, M., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Lampeitl, H., additional, Lopez, M., additional, Lorenz, E., additional, Lucarelli, F., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Ona-Wilhelmi, E., additional, Panter, M., additional, Plyasheshnikov, A., additional, Pühlhofer, G., additional, de los Reyes, R., additional, Rhode, W., additional, Ripken, J., additional, Rowell, G., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Siems, M., additional, Sobzynska, D., additional, Stamm, W., additional, Tluczykont, M., additional, Vitale, V., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2006
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13. The Crab Nebula and Pulsar between 500 GeV and 80 TeV: Observations with the HEGRA Stereoscopic Air Cerenkov Telescopes

Author

Aharonian, F., primary, Akhperjanian, A., additional, Beilicke, M., additional, Bernlohr, K., additional, Borst, H.‐G., additional, Bojahr, H., additional, Bolz, O., additional, Coarasa, T., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, M. V., additional, Girma, M., additional, Gotting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kohnle, A., additional, Konopelko, A., additional, Kranich, D., additional, Lampeitl, H., additional, Lopez, M., additional, Lorenz, E., additional, Lucarelli, F., additional, Mang, O., additional, Mazin, D., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Ona‐Wilhelmi, E., additional, Panter, M., additional, Plyasheshnikov, A., additional, Puhlhofer, G., additional, de los Reyes, R., additional, Rhode, W., additional, Ripken, J., additional, Rowell, G., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Siems, M., additional, Sobzynska, D., additional, Stamm, W., additional, Tluczykont, M., additional, Vitale, V., additional, Volk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2004
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14. Search for TeV gamma ray emission from the Andromeda galaxy

Author

Aharonian, F. A., primary, Akhperjanian, A. G., additional, Beilicke, M., additional, Bernlöhr, K., additional, Bojahr, H., additional, Bolz, O., additional, Börst, H., additional, Coarasa, T., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Girma, M., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lopez, M., additional, Lorenz, E., additional, Lucarelli, F., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Ona, E., additional, Panter, M., additional, Plyasheshnikov, A., additional, Pühlhofer, G., additional, Rauterberg, G., additional, Reyes, R., additional, Rhode, W., additional, Ripken, J., additional, Röhring, A., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Siems, M., additional, Sobzynska, D., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2003
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15. A search for TeV gamma-ray emission from SNRs, pulsars and unidentified GeV sources in the Galactic plane in the longitude range between $-2^\circ$ and $85^\circ$

Author

Aharonian, F. A., primary, Akhperjanian, A. G., additional, Beilicke, M., additional, Bernlöhr, K., additional, Bojahr, H., additional, Bolz, O., additional, Börst, H., additional, Coarasa, T., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Girma, M., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lopez, M., additional, Lorenz, E., additional, Lucarelli, F., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Ona, E., additional, Panter, M., additional, Plyasheshnikov, A., additional, Pühlhofer, G., additional, Rauterberg, G., additional, Reyes, R., additional, Rhode, W., additional, Ripken, J., additional, Röhring, A., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Siems, M., additional, Sobzynska, D., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2002
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16. Search for point sources of gamma radiation above 15 TeV with the HEGRA AIROBICC array

Author

Aharonian, F., primary, Akhperjanian, A., additional, Barrio, J. A., additional, Bernlöhr, K., additional, Börst, H., additional, Bojahr, H., additional, Bolz, O., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gebauer, H. J., additional, González, J., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmayer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, López, M., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Oña, E., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Pühlhofer, G., additional, Rauterberg, G., additional, Röhring, A., additional, Rhode, W., additional, Rowell, G., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schmele, D., additional, Schröder, F., additional, Sevilla, I., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2002
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17. TeV gamma rays from the blazar H 1426+428 and the diffuse extragalactic background radiation

Author

Aharonian, F., primary, Akhperjanian, A., additional, Barrio, J., additional, Beilicke, M., additional, Bernlöhr, K., additional, Börst, H., additional, Bojahr, H., additional, Bolz, O., additional, Contreras, J., additional, Cornils, R., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Girma, M., additional, Gonzalez, J., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lopez, M., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Ona, E., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Pühlhofer, G., additional, Rauterberg, G., additional, Röhring, A., additional, Rhode, W., additional, Robrade, J., additional, Rowell, G., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schröder, F., additional, Sevilla, I., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2002
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18. TeV gamma-ray observations of SS-433 and a survey of the surrounding field with the HEGRA IACT-System

Author

Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H.-G., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kohnle, A., Konopelko, A., Kranich, D., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Mazin, D., Meyer, H., Mirzoyan, R., Moralejo, A., Oña-Wilhelmi, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Vitale, V., Völk, H. J., Wiedner, C. A., Wittek, W., Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H.-G., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kohnle, A., Konopelko, A., Kranich, D., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Mazin, D., Meyer, H., Mirzoyan, R., Moralejo, A., Oña-Wilhelmi, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Vitale, V., Völk, H. J., Wiedner, C. A., and Wittek, W.

Abstract

We present results of a search for TeV γ-ray emission from the microquasar SS-433 and the surrounding region covering a ~$8^\circ$$\times$$8^\circ$field of view. Analysis of data taken with the HEGRA stereoscopic system of imaging atmospheric Čerenkov imaging telescopes reveals no evidence of steady or variable emission from any position. Observation times of over 100 h have been achieved in central parts of the field of view. We set 99% confidence level upper limits to a number of a-priori-chosen objects of interest, including SS-443 and its interaction regions, 32 pulsars, 3 supernova remnants and the GeV source GeV J1907+0537. Our upper limit of 3.2% Crab flux (for energies $E>0.8$TeV) for the eastern-lobe region e3of SS-433 permits, after comparison with X-ray fluxes, a lower limit of $B\geq19~\mu$G on the post-shocked magnetic field in this region. An ensemble upper limit at 0.3% Crab flux ($E>0.7$TeV) from a subset (11) of the 32 pulsars implies a maximum of 4.5% of the spin-down pulsar power is available for TeV γ-ray production. For one of the SNR in our FoV, 3C 396, recent Chandra observations suggest that a central pulsar-driven wind nebula may be the source of X-ray emission. Our upper limit implies that a maximum of 0.1% of the spin-down power from the central source of 3C 396 would be available for TeV γ-rays.

Published
2005
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19. Simultaneous X‐Ray and TeV Gamma‐Ray Observation of the TeV Blazar Markarian 421 during 2000 February and May

Author

Krawczynski, H., primary, Sambruna, R., additional, Kohnle, A., additional, Coppi, P. S., additional, Aharonian, F., additional, Akhperjanian, A., additional, Barrio, J., additional, Bernlohr, K., additional, Borst, H., additional, Bojahr, H., additional, Bolz, O., additional, Contreras, J., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J., additional, Gotting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Lampeitl, H., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Puhlhofer, G., additional, Rauterberg, G., additional, Rohring, A., additional, Rhode, W., additional, Rowell, G., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schroder, F., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Volk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2001
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20. A search for gamma-ray emission from the Galactic plane in the longitude range between $\mathsf{37}^\circ$ and $\mathsf{43}^\circ$

Author

Aharonian, F. A., primary, Akhperjanian, A. G., additional, Barrio, J. A., additional, Bernlöhr, K., additional, Bolz, O., additional, Börst, H., additional, Bojahr, H., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J. C., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Iserlohe, C., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Pühlhofer, G., additional, Rhode, W., additional, Röhring, A., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schröder, F., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

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2001
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21. A study of Tycho's SNR at TeV energies with the HEGRA CT-System

Author

Aharonian, F. A., primary, Akhperjanian, A. G., additional, Barrio, J. A., additional, Bernlöhr, K., additional, Börst, H., additional, Bojahr, H., additional, Bolz, O., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J. C., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Pühlhofer, G., additional, Rauterberg, G., additional, Röhring, A., additional, Rhode, W., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schröder, F., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C., additional, and Wittek, W., additional

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2001
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22. Evidence for TeV gamma ray emission from Cassiopeia A

Author

Aharonian, F., primary, Akhperjanian, A., additional, Barrio, J., additional, Bernlöhr, K., additional, Börst, H., additional, Bojahr, H., additional, Bolz, O., additional, Contreras, J., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Iserlohe, C., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lopez, M., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Ona, E., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Pühlhofer, G., additional, Rauterberg, G., additional, Röhring, A., additional, Rhode, W., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schröder, F., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

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2001
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23. Search for a TeV gamma-ray halo of Mkn 501

Author

Aharonian, F. A., primary, Akhperjanian, A. G., additional, Barrio, J. A., additional, Bernlöhr, K., additional, Bolz, O., additional, Börst, H., additional, Bojahr, H., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J. C., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Iserlohe, C., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Pühlhofer, G., additional, Rhode, W., additional, Röhring, A., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schröder, F., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C., additional, and Wittek, W., additional

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2001
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24. The TeV Energy Spectrum of Markarian 501 Measured with the Stereoscopic Telescope System of HEGRA during 1998 and 1999

Author

Aharonian, F., primary, Akhperjanian, A., additional, Barrio, J., additional, Bernlohr, K., additional, Borst, H., additional, Bojahr, H., additional, Bolz, O., additional, Contreras, J., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J., additional, Gotting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Iserlohe, C., additional, Ibarra, A., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Puhlhofer, G., additional, Rohring, A., additional, Rhode, W., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schroder, F., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Volk, H., additional, Wiedner, C., additional, and Wittek, W., additional

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2001
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25. Reanalysis of the high energy cutoff of the 1997 Mkn 501 TeV energy spectrum

Author

Aharonian, F. A., primary, Akhperjanian, A. G., additional, Barrio, J. A., additional, Bernlöhr, K., additional, Bolz, O., additional, Börst, H., additional, Bojahr, H., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J. C., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Iserlohe, C., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Pühlhofer, G., additional, Rhode, W., additional, Röhring, A., additional, Rowell, G. P., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schröder, F., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C., additional, and Wittek, W., additional

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2001
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26. Observation of the Monoceros Loop SNRregion with the HEGRA system of IACTs

Author

Aharonian, F. A., Akhperjanian, A. G., Beilicke, M., Bernlöhr, K., Börst, H.-G., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, M. V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona-Wilhelmi, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Vitale, V., Völk, H. J., Wiedner, C. A., Wittek, W., Aharonian, F. A., Akhperjanian, A. G., Beilicke, M., Bernlöhr, K., Börst, H.-G., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, M. V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona-Wilhelmi, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Vitale, V., Völk, H. J., Wiedner, C. A., and Wittek, W.

Abstract

The array of 5 imaging atmospheric Čerenkov telescopes (IACTs) deployed at La Palma (Canary Islands), and operated by the HEGRA (High Energy Gamma Ray Astronomy) collaboration, was used for observations of the Monoceros Loop SNRregion for a total of about 120 hrs and 20 hrs in ON-source and OFF-source mode, respectively. The giant molecular cloud Rosette Nebula appears in the sky region, close to the south-east part of the SNRrim. Using the HEGRA system of IACTs of rather large field of view (4.3 degree in diameter), we have mapped the extended sky region of $3^\circ \times 3^\circ$associated with the Monoceros SNR/Rosette Nebula, which is centered towards the hard spectrum X-ray point source SAX J0635+533. The EGRET unidentified source of diffuse γ-ray emission (3EG J0634+0521) observed in the energy range between 100 MeV–10 GeV, was effectively in the field of view of our present observations. Also, the GeV source GeV J0633+0645 was within the available field of view. The performance of the IACTs array reveals an energy threshold of 500 GeV and an angular resolution of $0.1^\circ$for γ-rays. In what follows, we present the result of the data analysis and its physical interpretation.

Published
2004
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27. TeV γ-ray light curve and energy spectrum of Mkn 421during its 2001 flare as measured with HEGRA CT1*

Author

Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H. G., Bojahr, H., Bolz, O., Coarasa, J. A., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Goebel, F., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kranich, D., Krawczynski, H., Lampeitl, H., López, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Oña-Wilhelmi, E., Paneque, D., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Schweizer, T., Sevilla, I., Siems, M., Sobczyńska, D., Stamm, W., Tluczykont, M., Tonello, N., Vitale, V., Völk, H. J., Wagner, R. M., Wiedner, C. A., Wittek, W., Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H. G., Bojahr, H., Bolz, O., Coarasa, J. A., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Goebel, F., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kranich, D., Krawczynski, H., Lampeitl, H., López, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Oña-Wilhelmi, E., Paneque, D., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Schweizer, T., Sevilla, I., Siems, M., Sobczyńska, D., Stamm, W., Tluczykont, M., Tonello, N., Vitale, V., Völk, H. J., Wagner, R. M., Wiedner, C. A., and Wittek, W.

Abstract

In the first months of 2001 the AGN Mkn 421showed highly variable, strong TeV activity at flux levels frequently exceeding 1 Crab. Here we present the light curve and energy spectrum of Mkn 421as measured with the HEGRA stand alone telescope CT1. Around 30% of the data were taken under moonlight conditions. The spectrum shows a significant exponential energy cutoff at around 3.4 TeV. The results from the dark night- and the moon data are in excellent agreement with each other. A significant spectral shape variation depending on the flux level has been found. The TeV light curve is also found to be highly correlated with the X-ray light curve of the RXTE / ASM satellite, showing no significant time lag larger than 0.2 d. The derived correlation coefficient of 0.83 corresponds to a $5.2~\sigma$significance.

Published
2003
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28. Detection of TeV gamma-rays from the BL Lac 1ES 1959+650 in its low states and during a major outburst in 2002 *

Author

Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H.-G., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, M. V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona-Wilhelmi, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Robrade, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Vitale, V., Völk, H. J., Wiedner, C. A., Wittek, W., Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H.-G., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, M. V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona-Wilhelmi, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Reyes, R. de los, Rhode, W., Ripken, J., Robrade, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Vitale, V., Völk, H. J., Wiedner, C. A., and Wittek, W.

Abstract

TeV γ-rays from the BL Lac object 1ES 1959+650  have been measured during the years 2000 and 2001 with a significance of 5.2 σat a value of 5.3% of the Crab flux and in May 2002 during strong outbursts with >$23\,\sigma$at a flux level of up to 2.2 Crab, making 1ES 1959+650  the TeV Blazar with the third best event statistics. The deep observation of 197.4 h has been performed with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes (IACT system). 1ES 1959+650  is located at a redshift of $z = 0.047$, providing an intermediate distance between the nearby Blazars Mkn 421 and Mkn 501, and the much more distant object H1426+428. This makes 1ES 1959+650  an important member of the class of TeV Blazars in view of the absorption of TeV photons by the diffuse extragalactic background radiation (DEBRA). The differential energy spectrum of 1ES 1959+650  during the flares can be fitted by a power law with a spectral index of $2.83 \pm 0.14_{\mbox{\tiny stat}} \pm 0.08_{\mbox{\tiny sys}}$or by a power law with an exponential cut-off at $(4.2^{+0.8}_{-0.6~{\mbox{\tiny stat}}} \pm 0.9_{\mbox{\tiny sys}})$TeV and a spectral index of $1.83 \pm 0.15_{\mbox{\tiny stat}} \pm 0.08_{\mbox{\tiny sys}}$. The low state differential energy spectrum obtained with lower statistics can be described by a pure power law with a spectral index of $3.18 \pm 0.17_{\mbox{\tiny stat}} \pm 0.08_{\mbox{\tiny sys}}$.

Published
2003
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29. A search for TeV gamma-ray emission from SNRs, pulsars and unidentified GeV sources in the Galactic plane in the longitude range between $-2^\circ$and $85^\circ$

Author

Aharonian, F. A., Akhperjanian, A. G., Beilicke, M., Bernlöhr, K., Bojahr, H., Bolz, O., Börst, H., Coarasa, T., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Rauterberg, G., Reyes, R., Rhode, W., Ripken, J., Röhring, A., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., Wittek, W., Aharonian, F. A., Akhperjanian, A. G., Beilicke, M., Bernlöhr, K., Bojahr, H., Bolz, O., Börst, H., Coarasa, T., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Rauterberg, G., Reyes, R., Rhode, W., Ripken, J., Röhring, A., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., and Wittek, W.

Abstract

Using the HEGRA system of imaging atmospheric Cherenkov telescopes, one quarter of the Galactic plane ($-2^\circ < l < 85^\circ$) was surveyed for TeV gamma-ray emission from point sources and moderately extended sources (Ø$\;\le0.8^\circ$). The region covered includes 86 known pulsars (PSR), 63 known supernova remnants (SNR) and nine GeV sources, representing a significant fraction of the known populations. No evidence for emission of TeV gamma radiation was detected, and upper limits range from 0.15 Crab units up to several Crab units, depending on the observation time and zenith angles covered. The ensemble sums over selected SNR and pulsar subsamples and over the GeV-sources yield no indication of emission from these potential sources. The upper limit for the SNR population is 6.7% of the Crab flux and for the pulsar ensemble is 3.6% of the Crab flux.

Published
2002
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30. Variations of the TeV energy spectrum at different flux levels of Mkn 421observed with the HEGRA system of Cherenkov telescopes

Author

Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J., Cortina, J., Costamante, L., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Milite, M., Moralejo, A., Ona, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Rauterberg, G., Reyes, R., Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., Wittek, W., Remillard, R. A., Aharonian, F., Akhperjanian, A., Beilicke, M., Bernlöhr, K., Börst, H., Bojahr, H., Bolz, O., Coarasa, T., Contreras, J., Cortina, J., Costamante, L., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Milite, M., Moralejo, A., Ona, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Rauterberg, G., Reyes, R., Rhode, W., Ripken, J., Rowell, G., Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., Wittek, W., and Remillard, R. A.

Abstract

The nearby BL Lacertae (BL Lac) object Markarian 421 (Mkn 421) at a red shift $z=0.031$was observed to undergo strong TeV γ-ray outbursts in the observational periods from December 1999 until May 2001. The time averaged flux level $F(E>1{\rm \,TeV})$in the 1999/2000 season was $(1.43\pm0.04)$$\times$10-11ph cm-2s-1, whereas in the 2000/2001 season the average integral flux increased to $(4.19\pm0.04)$$\times$10-11ph cm-2s-1. Both energy spectra are curved and well fit by a power law with an exponential cut-off energy at $3.6(+0.4-0.3)_{\rm stat}(+0.9-0.8)_{\rm sys}$TeV. The respective energy spectra averaged over each of the two time periods indicate a spectral hardening for the 2000/2001 spectrum. The photon index changes from $2.39\pm0.09_{\rm stat}$for 1999/2000 to $2.19\pm0.02_{\rm stat}$in 2000/2001. The energy spectra derived for different average flux levels ranging from 0.5 to 10 $\times$10-11ph cm-2s-1follow a clear correlation of photon index and flux level. Generally, the energy spectra are harder for high flux levels. From January to April 2001 Mkn 421showed rapid variability (doubling time as short as 20 min), accompanied with a spectral hardening with increasing flux level within individual nights. For two successive nights (MJD 51989-51991, March 21-23, 2001), this correlation of spectral hardness and change in flux has been observed within a few hours. The cut-off energy for the Mkn 421TeV spectrum remains within the errors constant for the different flux levels and differs by $\Delta E=2.6\pm0.6_{\rm stat}\pm0.6_{\rm sys}$TeV  from the value determined for Mkn 501. This indicates that the observed exponential cut-off in the energy spectrum of Mkn 421is not solely caused by absorption of multi-TeV photons by pair-production processes with photons of the extragalactic near/mid infrared background radiation.

Published
2002
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31. A search for gamma-ray emission from the Galactic plane in the longitude range between $\mathsf{37}^\circ$and $\mathsf{43}^\circ$

Author

Aharonian, F. A., Akhperjanian, A. G., Barrio, J. A., Bernlöhr, K., Bolz, O., Börst, H., Bojahr, H., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Gonzalez, J. C., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Ibarra, A., Iserlohe, C., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lorenz, E., Lucarelli, F., Magnussen, N., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Padilla, L., Panter, M., Plaga, R., Plyasheshnikov, A., Prahl, J., Pühlhofer, G., Rhode, W., Röhring, A., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Schröder, F., Siems, M., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., Wittek, W., Aharonian, F. A., Akhperjanian, A. G., Barrio, J. A., Bernlöhr, K., Bolz, O., Börst, H., Bojahr, H., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Gonzalez, J. C., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Ibarra, A., Iserlohe, C., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lorenz, E., Lucarelli, F., Magnussen, N., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Padilla, L., Panter, M., Plaga, R., Plyasheshnikov, A., Prahl, J., Pühlhofer, G., Rhode, W., Röhring, A., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Schröder, F., Siems, M., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., and Wittek, W.

Abstract

Using the HEGRA system of imaging atmospheric Cherenkov telescopes, a region of the Galactic plane ($-10^\circ < b < 5^\circ$, $38^\circ < l < 43^\circ$) was surveyed for TeV gamma-ray emission, both from point sources and of diffuse nature. The region covered includes 15 known pulsars, 6 known supernova remnants (SNR) and one unidentified EGRET source. No evidence for emission from point sources was detected; upper limits are typically below 0.1 Crab units for the flux above 1 TeV. For the diffuse gamma-ray flux from the Galactic plane, an upper limit of $6.1\times10^{-15}$ph cm-2s-1sr-1MeV-1was derived under the assumption that the spatial distribution measured by the EGRET instrument extends to the TeV regime. This upper flux limit is a factor of about 1.5 larger than the flux expected from the ensemble of gamma-ray unresolved Galactic cosmic ray sources.

Published
2001
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32. Rejection of the Hypothesis That Markarian 501 T[CLC]e[/CLC]V Photons Are Pure Bose-Einstein Condensates

Author

Aharonian, F., primary, Akhperjanian, A., additional, Barrio, J., additional, Bernlöhr, K., additional, Börst, H., additional, Bojahr, H., additional, Bolz, O., additional, Contreras, J., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J., additional, Götting, N., additional, Heinzelmann, G., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Iserlohe, C., additional, Jung, I., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Pühlhofer, G., additional, Röhring, A., additional, Rhode, W., additional, Rowell, G., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schröder, F., additional, Siems, M., additional, Stamm, W., additional, Tluczykont, M., additional, Völk, H. J., additional, Wiedner, C. A., additional, and Wittek, W., additional

Published
2000
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33. The Energy Spectrum of TeV Gamma Rays from the Crab Nebula as Measured by the HEGRA System of Imaging Air Cerenkov Telescopes

Author

Aharonian, F. A., primary, Akhperjanian, A. G., additional, Barrio, J. A., additional, Bernlohr, K., additional, Bojahr, H., additional, Calle, I., additional, Contreras, J. L., additional, Cortina, J., additional, Denninghoff, S., additional, Fonseca, V., additional, Gonzalez, J. C., additional, Gotting, N., additional, Heinzelmann, G., additional, Hemberger, M., additional, Hermann, G., additional, Heusler, A., additional, Hofmann, W., additional, Horns, D., additional, Ibarra, A., additional, Kankanyan, R., additional, Kestel, M., additional, Kettler, J., additional, Kohler, C., additional, Kohnle, A., additional, Konopelko, A., additional, Kornmeyer, H., additional, Kranich, D., additional, Krawczynski, H., additional, Lampeitl, H., additional, Lindner, A., additional, Lorenz, E., additional, Lucarelli, F., additional, Magnussen, N., additional, Mang, O., additional, Meyer, H., additional, Mirzoyan, R., additional, Moralejo, A., additional, Padilla, L., additional, Panter, M., additional, Plaga, R., additional, Plyasheshnikov, A., additional, Prahl, J., additional, Puhlhofer, G., additional, Rauterberg, G., additional, Rohring, A., additional, Sahakian, V., additional, Samorski, M., additional, Schilling, M., additional, Schmele, D., additional, Schroder, F., additional, Stamm, W., additional, Tluczykont, M., additional, Volk, H. J., additional, Wiebel‐Sooth, B., additional, Wiedner, C., additional, Willmer, M., additional, and Wittek, W., additional

Published
2000
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35. Correlated Intense X-Ray and TeV Activity of Markarian 501 in 1998 June

Author

Sambruna, R. M., Aharonian, F. A., Krawczynski, H., Akhperjanian, A. G., Barrio, J. A., Bernlöhr, K., Bojahr, H., Calle, I., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Gonzalez, J. C., Götting, N., Heinzelmann, G., Hemberger, M., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Ibarra, A., Kankanyan, R., Kestel, M., Kettler, J., Köhler, C., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Lampeitl, H., Lindner, A., Lorenz, E., Magnussen, N., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Padilla, L., Panter, M., Plaga, R., Plyasheshnikov, A., Prahl, J., Pühlhofer, G., Rauterberg, G., Röhring, A., Sahakian, V., Samorski, M., Schilling, M., Schmele, D., Schröder, F., Stamm, W., Tluczykont, M., Völk, H. J., Wiebel-Sooth, B., Wiedner, C., Willmer, M., Wittek, W., Chou, L., Coppi, P. S., Rothschild, R., and Urry, C. M.

Abstract

We present exactly simultaneous X-ray and TeV monitoring with RXTEand HEGRA of the TeV blazar Mrk 501 during 15 days in 1998 June. After an initial period of very low flux at both wavelengths, the source underwent a remarkable flare in the TeV and X-ray energy bands, lasting for about 6 days and with a larger amplitude at TeV energies than in the X-ray band. At the peak of the TeV flare, rapid TeV flux variability on subhour timescales is found. Large spectral variations are observed at X-rays, with the 3-20 keV photon index of a pure power-law continuum flattening from ? = 2.3 to ? = 1.8 on a timescale of 2-3 days. This implies that during the maximum of the TeV activity the synchrotron peak shifted to energies 50 keV, a behavior similar to that observed during the longer lasting, more intense flare in 1997 April. The TeV spectrum during the flare is described by a power law with photon index ? = 1.9 and an exponential cutoff at ~4 TeV; an indication for spectral softening during the flare decay is observed in the TeV hardness ratios. Our results generally support a scenario in which the TeV photons are emitted via inverse Compton scattering of ambient seed photons by the same electron population responsible for the synchrotron X-rays. The simultaneous spectral energy distributions can be fit with a one-zone synchrotron self-Compton model assuming a substantial increase of the magnetic field and the electron energy by factors of 3 and 10, respectively.

Published
2000
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39. Search for TeV gamma ray emission from the Andromeda galaxy

Author

Aharonian, F. A., Akhperjanian, A. G., Beilicke, M., Bernlöhr, K., Bojahr, H., Bolz, O., Börst, H., Coarasa, T., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Girma, M., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lopez, M., Lorenz, E., Lucarelli, F., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona, E., Panter, M., Plyasheshnikov, A., Pühlhofer, G., Rauterberg, G., Reyes, R., Rhode, W., Ripken, J., Röhring, A., Gavin Rowell, Sahakian, V., Samorski, M., Schilling, M., Siems, M., Sobzynska, D., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C. A., and Wittek, W.

Subjects
Physics, Range (particle radiation), Annihilation, Andromeda Galaxy, Astrophysics::High Energy Astrophysical Phenomena, Dark matter, Astrophysics (astro-ph), Gamma ray, Flux, HEGRA, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Space and Planetary Science, Cherenkov radiation, Astrophysics::Galaxy Astrophysics
Abstract

Using the HEGRA system of imaging atmospheric Cherenkov telescopes, the Andromeda galaxy (M31) was surveyed for TeV gamma ray emission. Given the large field of view of the HEGRA telescopes, three pointings were sufficient to cover all of M31, including also M32 and NGC205. No indications for point sources of TeV gamma rays were found. Upper limits are given at a level of a few percent of the Crab flux. A specific search for monoenergetic gamma-ray lines from annihilation of supersymmetric dark matter particles accumulating near the center of M31 resulted in flux limits in the 10^-13/cm^2s range, well above the predicted MSSM flux levels except for models with pronounced dark-matter spikes or strongly enhanced annihilation rates., Comment: Latex, 7 pages, 4 Figures, submitted to A&A

40. Evidence for TeV gamma ray emission from Cassiopeia A

Author

Aharonian, F., Akhperjanian, A., Barrio, J., Bernlohr, K., Borst, H., Bojahr, H., Bolz, O., Contreras, J., Cortina, J., Denninghoff, S., Fonseca, V., Gonzalez, J., Gotting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Ibarra, A., Iserlohe, C., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Marcos López Moya, Lorenz, E., Lucarelli, F., Magnussen, N., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Ona, E., Padilla, L., Panter, M., Plaga, R., Plyasheshnikov, A., Prahl, J., Puhlhofer, G., Rauterberg, G., Rohring, A., Rhode, W., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Schroder, F., Siems, M., Stamm, W., Tluczykont, M., Volk, H. J., Wiedner, C. A., and Wittek, W.

Subjects
Physics, Spectral index, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Gamma ray, FOS: Physical sciences, HEGRA, Astronomy and Astrophysics, Cosmic ray, Astrophysics, law.invention, Cassiopeia A, Telescope, Space and Planetary Science, law, High Energy Physics::Experiment, Supernova remnant, Cherenkov radiation, Astrophysics::Galaxy Astrophysics
Abstract

232 hours of data were accumulated from 1997 to 1999, using the HEGRA Stereoscopic Cherenkov Telescope System to observe the supernova remnant Cassiopeia A. TeV gamma ray emission was detected at the 5 sigma level, and a flux of (5.8 +- 1.2(stat) +- 1.2(syst)) 10^(-9) ph m^(-2) s^(-1) above 1 TeV was derived. The spectral distribution is consistent with a power law with a differential spectral index of -2.5 +- 0.4(stat) +- 0.1(syst) between 1 and 10 TeV. As this is the first report of the detection of a TeV gamma ray source on the "centi-Crab" scale, we present the analysis in some detail. Implications for the acceleration of cosmic rays depend on the details of the source modeling. We discuss some important aspects in this paper., 9 pages, 6 figures, accepted for publication in Astronomy & Astrophysics

41. A study of Tycho's SNR at TeV energies with the HEGRA CT-system

Author

Aharonian, F. A., Akhperjanian, A. G., Barrio, J. A., Bernlöhr, K., Börst, H., Bojahr, H., Bolz, O., Contreras, J. L., Cortina, J., Denninghoff, S., Fonseca, V., Gonzalez, J. C., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Ibarra, A., Jung, I., Kankanyan, R., Kestel, M., Kettler, J., Kohnle, A., Konopelko, A., Kornmeyer, H., Kranich, D., Krawczynski, H., Lampeitl, H., Lorenz, E., Fabrizio Lucarelli, Magnussen, N., Mang, O., Meyer, H., Mirzoyan, R., Moralejo, A., Padilla, L., Panter, M., Plaga, R., Plyasheshnikov, A., Prahl, J., Pühlhofer, G., Rauterberg, G., Röhring, A., Rhode, W., Rowell, G. P., Sahakian, V., Samorski, M., Schilling, M., Schröder, F., Stamm, W., Tluczykont, M., Völk, H. J., Wiedner, C., and Wittek, W.

Subjects
Physics, Photon, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Hadron, FOS: Physical sciences, HEGRA, Flux, Astronomy and Astrophysics, Astrophysics, law.invention, Telescope, Space and Planetary Science, law, Limit (mathematics), Supernova remnant, Astrophysics::Galaxy Astrophysics, Cherenkov radiation
Abstract

Tycho's supernova remnant (SNR) was observed during 1997 and 1998 with the HEGRA Cherenkov Telescope System in a search for gamma-ray emission at energies above ~1 TeV. An analysis of these data, ~65 hours in total, resulted in no evidence for TeV gamma-ray emission. The 3sigma upper limit to the gamma-ray flux (>1 TeV) from Tycho is estimated at 5.78x10^{-13} photons cm^{-2} s^{-1}, or 33 milli-Crab. We interpret our upper limit within the framework of the following scenarios: (1) that the observed hard X-ray tail is due to synchrotron emission. A lower limit on the magnetic field within Tycho may be estimated B>=22 microG, assuming that the RXTE-detected X-rays were due to synchrotron emission. However, using results from a detailed model of the ASCA emission, a more conservative lower limit B>=6 microG is derived. (2) the hadronic model of Drury, Aharonian & Voelk, and (3) the more recent time-dependent kinetic theory of Berezhko & Voelk. Our upper limit lies within the range of predicted values of both hadronic models, according to uncertainties in physical parameters of Tycho, and shock acceleration details. In the latter case, the model was scaled to suit the parameters of Tycho and re-normalised to account for a simplification of the original model. We find that we cannot rule out Tycho as a potential contributor at an average level to the Galactic cosmic-ray flux., 9 pages, 6 figures. Accepted for publication in Astronomy and Astrophysics

42. Factors controlling the dominance of Planktothrix agardhii and Limnothrix redekei in eutrophic shallow lakes

Author

Wiedner, C., Zippel, P., and Rucker, J.

Subjects
BACTERIA, EUTROPHICATION
Abstract

Lakes in the Scharmutzelsee-region (East-Brandenburg, Germany) were found to be dominated either by Limnothrix redekei or Planktothrix agardhii. These dominance regimes were stable over the whole investigation period from 1993 to 1995. Six lakes (maximum depth between 2 and 12 m) were compared in regard to physical and chemical conditions to find reasons for the superiority of the first or the second species. All investigated lakes are polymictic but show, nevertheless differences in their mixing-behaviour. In lakes dominated by Limnothrix redekei stratification events occur more often than in the lakes dominatedby Planktothrix agardhii. The latter are more wind-exposed due to their greater size and/or their surroundings. In combination with polymixis light and nutrient supply are discussed as the key factors for the species composition. A lower content of soluble reactive phosphorus and lower light supply are considered as possible advantages for Limnothrix redekei over Planktothrix agardhii in three lakes. A lower total nitrogen/total phosphorus ratio may be a reason for the dominance of Planktothrix agardhii in the other three investigated lakes. [ABSTRACT FROM AUTHOR]

Published
1997

44. Short Sleep Duration and Hypertension: A Double Hit for the Brain.

Author

Yiallourou S, Baril AA, Wiedner C, Song X, Bernal R, Himali D, Cavuoto MG, DeCarli C, Beiser A, Seshadri S, Himali JJ, and Pase MP

Subjects
Humans, Female, Middle Aged, Male, Aged, Time Factors, Executive Function, Blood Pressure physiology, Risk Factors, Cognitive Dysfunction physiopathology, Cognitive Dysfunction etiology, Sleep Duration, Hypertension physiopathology, Hypertension complications, Magnetic Resonance Imaging, Brain physiopathology, Brain diagnostic imaging, Sleep, Cognition, Polysomnography
Abstract

Background: Short sleep duration has been associated with an increased risk of cognitive impairment and dementia. Short sleep is associated with elevated blood pressure, yet the combined insult of short sleep and hypertension on brain health remains unclear. We assessed whether the association of sleep duration with cognition and vascular brain injury was moderated by hypertensive status., Methods and Results: A total of 682 dementia-free participants (mean age, 62±9 years; 53% women) from the Framingham Heart Study completed assessments of cognition, office blood pressure, and self-reported habitual and polysomnography-derived sleep duration; 637 underwent brain magnetic resonance imaging. Linear regressions were performed to assess effect modification by hypertensive status on total sleep time (coded in hours) and cognitive and magnetic resonance imaging outcomes. There was a significant interaction between sleep duration and hypertensive status when predicting executive function/processing speed (Trail Making B-A) and white matter hyperintensities. When results were stratified by hypertensive status, longer sleep duration was associated with better executive functioning/processing speed scores in the hypertensive group (meaning that shorter sleep duration was associated with poorer executive function/processing speed scores) (self-report sleep: β=0.041 [95% CI, 0.012-0.069], P =0.005; polysomnography sleep: β=0.045 [95% CI, 0.002-0.087], P =0.038), but no association was observed for the normotensive group. Similarly, shorter subjective sleep duration was associated with higher white matter hyperintensity burden in the hypertensive group (β=-0.115 [95% CI, -0.227 to -0.004], P =0.042), but not in the normotensive group., Conclusions: In individuals with hypertension, shorter sleep duration was associated with worse cognitive performance and greater brain injury.

Published
2024
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45. A population-based meta-analysis of circulating GFAP for cognition and dementia risk.

Author

Gonzales MM, Wiedner C, Wang CP, Liu Q, Bis JC, Li Z, Himali JJ, Ghosh S, Thomas EA, Parent DM, Kautz TF, Pase MP, Aparicio HJ, Djoussé L, Mukamal KJ, Psaty BM, Longstreth WT Jr, Mosley TH Jr, Gudnason V, Mbangdadji D, Lopez OL, Yaffe K, Sidney S, Bryan RN, Nasrallah IM, DeCarli CS, Beiser AS, Launer LJ, Fornage M, Tracy RP, Seshadri S, and Satizabal CL

Subjects
Antihypertensive Agents therapeutic use, Apolipoproteins, Cognition, Glial Fibrillary Acidic Protein, Humans, Alzheimer Disease, Dementia
Abstract

Objective: Expression of glial fibrillary acidic protein (GFAP), a marker of reactive astrocytosis, colocalizes with neuropathology in the brain. Blood levels of GFAP have been associated with cognitive decline and dementia status. However, further examinations at a population-based level are necessary to broaden generalizability to community settings., Methods: Circulating GFAP levels were assayed using a Simoa HD-1 analyzer in 4338 adults without prevalent dementia from four longitudinal community-based cohort studies. The associations between GFAP levels with general cognition, total brain volume, and hippocampal volume were evaluated with separate linear regression models in each cohort with adjustment for age, sex, education, race, diabetes, systolic blood pressure, antihypertensive medication, body mass index, apolipoprotein E ε4 status, site, and time between GFAP blood draw and the outcome. Associations with incident all-cause and Alzheimer's disease dementia were evaluated with adjusted Cox proportional hazard models. Meta-analysis was performed on the estimates derived from each cohort using random-effects models., Results: Meta-analyses indicated that higher circulating GFAP associated with lower general cognition (ß = -0.09, [95% confidence interval [CI]: -0.15 to -0.03], p = 0.005), but not with total brain or hippocampal volume (p &gt; 0.05). However, each standard deviation unit increase in log-transformed GFAP levels was significantly associated with a 2.5-fold higher risk of incident all-cause dementia (Hazard Ratio [HR]: 2.47 (95% CI: 1.52-4.01)) and Alzheimer's disease dementia (HR: 2.54 [95% CI: 1.42-4.53]) over up to 15-years of follow-up., Interpretation: Results support the potential role of circulating GFAP levels for aiding dementia risk prediction and improving clinical trial stratification in community settings., (© 2022 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association.)

Published
2022
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46. Genetic Identity and Herbivory Drive the Invasion of a Common Aquatic Microbial Invader.

Author

Bolius S, Morling K, Wiedner C, and Weithoff G

Abstract

Despite the increasing number of species invasions, the factors driving invasiveness are still under debate. This is particularly the case for "invisible" invasions by aquatic microbial species. Since in many cases only a few individuals or propagules enter a new habitat, their genetic variation is low and might limit their invasion success, known as the genetic bottleneck. Thus, a key question is, how genetic identity and diversity of invading species influences their invasion success and, subsequently, affect the resident community. We conducted invader-addition experiments using genetically different strains of the globally invasive, aquatic cyanobacterium Raphidiopsis raciborskii (formerly: Cylindrospermopsis raciborskii ) to determine the role of invader identity and genetic diversity (strain richness) at four levels of herbivory. We tested the invasion success of solitary single strain invasions against the invader genetic diversity, which was experimentally increased up to ten strains (multi-strain populations). By using amplicon sequencing we determined the strain-specific invasion success in the multi-strain treatments and compared those with the success of these strains in the single-strain treatments. Furthermore, we tested for the invasion success under different herbivore pressures. We showed that high grazing pressure by a generalist herbivore prevented invasion, whereas a specialist herbivore enabled coexistence of consumer and invader. We found a weak effect of diversity on invasion success only under highly competitive conditions. When invasions were successful, the magnitude of this success was strain-specific and consistent among invasions performed with single-strain or multi-strain populations. A strain-specific effect was also observed on the resident phytoplankton community composition, highlighting the strong role of invader genetic identity. Our results point to a strong effect of the genetic identity on the invasion success under low predation pressure. The genetic diversity of the invader population, however, had little effect on invasion success in our study, in contrast to most previous findings. Instead, it is the interaction between the consumer abundance and type together with the strain identity of the invader that defined invasion success. This study underlines the importance of strain choice in invasion research and in ecological studies in general., (Copyright © 2020 Bolius, Morling, Wiedner and Weithoff.)

Published
2020
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47. Low invasion success of an invasive cyanobacterium in a chlorophyte dominated lake.

Author

Bolius S, Wiedner C, and Weithoff G

Subjects
Biomass, Ecosystem, Environment, Germany, Phytoplankton, Principal Component Analysis, Seasons, Temperature, Water, Water Microbiology, Chlorophyta growth & development, Cylindrospermopsis growth & development, Introduced Species, Lakes microbiology
Abstract

Biological invasions are a major threat to biodiversity and ecosystem functioning. Successful invasions depend on the interplay of multiple abiotic and biotic factors, however, the process of the invasion itself is often overlooked. The temporal variation of environmental factors suggests that a 'window of opportunity' for successful invasions exists. Especially aquatic habitats, like temperate lakes, undergo pronounced seasonal fluctuations and show temporally varying environmental conditions in e.g. nutrient availability, temperature and the composition of the resident community including competitors and consumers. We experimentally tested if an invasion window for the globally invasive cyanobacterium Cylindrospermopsis raciborskii exists. From May to September, we determined the invasion success of C. raciborskii in laboratory mesocosms with natural lake water. Although the invasion success was generally low, the invasiveness varied among months and differed in total invasive biomass, net development and final share of C. raciborskii in the community. During the first days, C. raciborskii strongly declined and this initial, short-term decline was independent of the ambient consumptive pressure. These results are in contrast to laboratory studies in which C. raciborskii successfully invaded, suggesting that a complex natural system develops a resistance to invasions.

Published
2019
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48. Seasonal patterns of nitrogen and phosphorus limitation in four German lakes and the predictability of limitation status from ambient nutrient concentrations.

Author

Kolzau S, Wiedner C, Rücker J, Köhler J, Köhler A, and Dolman AM

Subjects
Chlorophyll metabolism, Chlorophyll A, Cyanobacteria metabolism, Germany, Nitrogen metabolism, Phosphorus metabolism, Phytoplankton metabolism, Seasons, Lakes chemistry, Nitrogen chemistry, Phosphorus chemistry
Abstract

To identify the seasonal pattern of nitrogen (N) and phosphorus (P) limitation of phytoplankton in four different lakes, biweekly experiments were conducted from the end of March to September 2011. Lake water samples were enriched with N, P or both nutrients and incubated under two different light intensities. Chlorophyll a fluorescence (Chla) was measured and a model selection procedure was used to assign bioassay outcomes to different limitation categories. N and P were both limiting at some point. For the shallow lakes there was a trend from P limitation in spring to N or light limitation later in the year, while the deep lake remained predominantly P limited. To determine the ability of in-lake N:P ratios to predict the relative strength of N vs. P limitation, three separate regression models were fit with the log-transformed ratio of Chla of the P and N treatments (Response ratio = RR) as the response variable and those of ambient total phosphorus:total nitrogen (TN:TP), dissolved inorganic nitrogen:soluble reactive phosphorus (DIN:SRP), TN:SRP and DIN:TP mass ratios as predictors. All four N:P ratios had significant positive relationships with RR, such that high N:P ratios were associated with P limitation and low N:P ratios with N limitation. The TN:TP and DIN:TP ratios performed better than the DIN:SRP and TN:SRP in terms of misclassification rate and the DIN:TP ratio had the highest R₂ value. Nitrogen limitation was predictable, frequent and persistent, suggesting that nitrogen reduction could play a role in water quality management. However, there is still uncertainty about the efficacy of N restriction to control populations of N₂ fixing cyanobacteria.

Published
2014
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49. Phylogeography of cylindrospermopsin and paralytic shellfish toxin-producing nostocales cyanobacteria from mediterranean europe (Spain).

Author

Cirés S, Wörmer L, Ballot A, Agha R, Wiedner C, Velázquez D, Casero MC, and Quesada A

Subjects
Alkaloids, Bacterial Toxins, Cyanobacteria metabolism, Cyanobacteria Toxins, DNA, Bacterial classification, DNA, Bacterial genetics, Molecular Sequence Data, Sequence Analysis, DNA, Spain, Uracil metabolism, Cyanobacteria classification, Cyanobacteria genetics, Fresh Water microbiology, Marine Toxins metabolism, Phylogeography, Uracil analogs & derivatives
Abstract

Planktonic Nostocales cyanobacteria represent a challenge for microbiological research because of the wide range of cyanotoxins that they synthesize and their invasive behavior, which is presumably enhanced by global warming. To gain insight into the phylogeography of potentially toxic Nostocales from Mediterranean Europe, 31 strains of Anabaena (Anabaena crassa, A. lemmermannii, A. mendotae, and A. planctonica), Aphanizomenon (Aphanizomenon gracile, A. ovalisporum), and Cylindrospermopsis raciborskii were isolated from 14 freshwater bodies in Spain and polyphasically analyzed for their phylogeography, cyanotoxin production, and the presence of cyanotoxin biosynthesis genes. The potent cytotoxin cylindrospermopsin (CYN) was produced by all 6 Aphanizomenon ovalisporum strains at high levels (5.7 to 9.1 μg CYN mg(-1) [dry weight]) with low variation between strains (1.5 to 3.9-fold) and a marked extracellular release (19 to 41% dissolved CYN) during exponential growth. Paralytic shellfish poisoning (PSP) neurotoxins (saxitoxin, neosaxitoxin, and decarbamoylsaxitoxin) were detected in 2 Aphanizomenon gracile strains, both containing the sxtA gene. This gene was also amplified in non-PSP toxin-producing Aphanizomenon gracile and Aphanizomenon ovalisporum. Phylogenetic analyses supported the species identification and confirmed the high similarity of Spanish Anabaena and Aphanizomenon strains with other European strains. In contrast, Cylindrospermopsis raciborskii from Spain grouped together with American strains and was clearly separate from the rest of the European strains, raising questions about the current assumptions of the phylogeography and spreading routes of C. raciborskii. The present study confirms that the nostocalean genus Aphanizomenon is a major source of CYN and PSP toxins in Europe and demonstrates the presence of the sxtA gene in CYN-producing Aphanizomenon ovalisporum.

Published
2014
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50. Temperature-dependent dispersal strategies of Aphanizomenon ovalisporum (Nostocales, Cyanobacteria): implications for the annual life cycle.

Author

Cirés S, Wörmer L, Wiedner C, and Quesada A

Subjects
Aphanizomenon cytology, Aphanizomenon growth & development, Linear Models, Seasons, Aphanizomenon physiology, Ponds microbiology, Temperature
Abstract

Aphanizomenon ovalisporum is a planktonic nostocalean cyanobacterium with increasing research interest due to its ability to produce the potent cytotoxin cylindrospermopsin and its potential invasiveness under the global warming scenario. The present study provides novel data on the potential dispersal strategies of A. ovalisporum by analyzing the influence of temperature (10-40 °C) on akinete differentiation and cell morphometry in cultures of A. ovalisporum UAM 290 isolated from a Spanish pond. Our results confirmed a temperature-dependent akinete differentiation, with the maximum akinete production reached at 20 °C (15 % of the cells), a low basal production at 25-30 °C (<0.4 % of the cells) and no detectable production at 35 °C. Furthermore, we reported the fragmentation of A. ovalisporum filaments at temperatures of 25 °C and above. Additionally, we observed that the morphology of vegetative cells varied under different temperature scenarios. Indeed, a strong negative correlation was found between temperature and the width, length and biovolume of vegetative cells, whereas akinete dimensions remained stable along the temperature gradient. Therefore, linear regressions between temperature and the cell size parameters are herein presented aiming to facilitate the identification of A. ovalisporum in the field throughout the course of the year. This is the first study evidencing that akinete production is triggered by temperatures between 20 and 25 °C in A. ovalisporum and reporting the existence of filament fragmentation as a potential dispersal strategy of this species. The importance of these findings for understanding the annual life cycle and invasive potential of A. ovalisporum is further discussed herein.

Published
2013
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