540 research outputs found
A new population of very high energy gamma-ray sources in the Milky Way
No full textVery high energy γ-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (HESS) reveals a population of eight previously unknown firmly detected sources of very high energy γ-rays. At least two have no known radio or x-ray counterpart and may be representative of a new class of “dark” nucleonic cosmic ray sources.F. Aharonian, A. G. Akhperjanian, K. M. Aye, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr, C. Boisson, O. Bolz, C. Borgmeier, I. Braun, F. Breitling, A. M. Brown, J. Bussons Gordo, P. M. Chadwick, L. M. Chounet, R. Cornils, L. Costamante, B. Degrange, A. Djannati-Ataï, L. O'C. Drury, G. Dubus, T. Ergin, P. Espigat, F. Feinstein, P. Fleury, G. Fontaine, S. Funk, Y. A. Gallant, B. Giebels, S. Gillessen, P. Goret, C. Hadjichristidis, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, O. C. de Jager, I. Jung, B. Khélifi, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, A. Lemière, M. Lemoine, N. Leroy, T. Lohse, A. Marcowith, C. Masterson, T. J. L. McComb, M. de Naurois, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, G. Pühlhofer, M. Punch, B. C. Raubenheimer, M. Raue, J. Raux, S. M. Rayner, I. Redondo, A. Reimer, O. Reimer, J. Ripken, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Saugé, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, R. Steenkamp, C. Stegmann, J.-P. Tavernet, R. Terrier, C. G. Théoret, M. Tluczykont, D. J. van der Walt, G. Vasileiadis, C. Venter, P. Vincent, B. Visser, H. J. Völk, S. J. Wagne
Discovery of very-high-energy gamma-rays from the Galactic Centre ridge
No full textThe source of Galactic cosmic rays (with energies up to 1015 eV) remains unclear, although it is widely believed that they originate in the shock waves of expanding supernova remnants. At present the best way to investigate their acceleration and propagation is by observing the γ-rays produced when cosmic rays interact with interstellar gas. Here we report observations of an extended region of very-high-energy (> 1011 eV) γ-ray emission correlated spatially with a complex of giant molecular clouds in the central 200 parsecs of the Milky Way. The hardness of the γ-ray spectrum and the conditions in those molecular clouds indicate that the cosmic rays giving rise to the γ-rays are likely to be protons and nuclei rather than electrons. The energy associated with the cosmic rays could have come from a single supernova explosion around 104 years ago.F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, K. Bernlohr, C. Boisson, O. Bolz, V. Borrel, I. Braun, F. Breitling, A. M. Brown, P. M. Chadwick, L.-M. Chounet, R. Cornils, L. Costamante, B. Degrange, H. J. Dickinson, A. Djannati-Ataı, L. O’C. Drury, G. Dubus, D. Emmanoulopoulos, P. Espigat, F. Feinstein, G. Fontaine, Y. Fuchs, S. Funk, Y. A. Gallant, B. Giebels, S. Gillessen, J. F. Glicenstein, P. Goret, C. Hadjichristidis, D. Hauser, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, A. Jacholkowska, O. C. de Jager, B. Khelifi, S. Klages, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, A. Lemiere, M. Lemoine-Goumard, N. Leroy, T. Lohse, A. Marcowith, J. M. Martin, O. Martineau-Huynh, C. Masterson, T. J. L. McComb, M. de Naurois, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, G. Puhlhofer, M. Punch, B. C. Raubenheimer, M. Raue, J. Raux, S. M. Rayner, A., O. Reimer, J. Ripken, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Sauge, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, D. Spangler, R. Steenkamp, C. Stegmann, J.-P. Tavernet, R. Terrier, C. G. The´oret, M. Tluczykont, C. van Eldik, C. Vasileiadis, C. Venter, P. Vincent, H. J. Volk and S. J. Wagne
Discovery of Very High Energy Gamma Rays Associated with an X-ray Binary
No full text© 2005 American Association for the Advancement of ScienceX-ray binaries are composed of a normal star in orbit around a neutron star or stellar-mass black hole. Radio and x-ray observations have led to the presumption that some x-ray binaries called microquasars behave as scaled-down active galactic nuclei. Microquasars have resolved radio emission that is thought to arise from a relativistic outflow akin to active galactic nuclei jets, in which particles can be accelerated to large energies. Very high energy gamma-rays produced by the interactions of these particles have been observed from several active galactic nuclei. Using the High Energy Stereoscopic System, we find evidence for gamma-ray emission of >100 gigaelectron volts from a candidate microquasar, LS 5039, showing that particles are also accelerated to very high energies in these systems.F. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr, C. Boisson, O. Bolz, V. Borrel, I. Braun, F. Breitling, A. M. Brown, J. Bussons Gordo, P. M. Chadwick, L.-M. Chounet, R. Cornils, L. Costamante, B. Degrange, H. J. Dickinson, A. Djannati-Ataï, L. O'C. Drury, G. Dubus, D. Emmanoulopoulos, P. Espigat, F. Feinstein, P. Fleury, G. Fontaine, Y. Fuchs, S. Funk, Y. A. Gallant, B. Giebels, S. Gillessen, J. F. Glicenstein, P. Goret, C. Hadjichristidis, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, A. Jacholkowska, O. C. de Jager, B. Khélifi, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, A. Lemière, M. Lemoine-Goumard, N. Leroy, T. Lohse, A. Marcowith, J.-M. Martin, O. Martineau-Huynh, C. Masterson, T. J. L. McComb, M. de Naurois, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, G. Pühlhofer, M. Punch, B. C. Raubenheimer, M. Raue, J. Raux, S. M. Rayner, A. Reimer, O. Reimer, J. Ripken, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Saugé, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, D. Spangler, R. Steenkamp, C. Stegmann, J.-P. Tavernet, R. Terrier, C. G. Théoret, M. Tluczykont, G. Vasileiadis, C. Venter, P. Vincent, H. J. Völk, and S. J. Wagne
Observations of selected AGN with HESS
No full textA sample of selected active galactic nuclei (AGN) was observed in 2003 and 2004 with the High Energy Stereoscopic System (HESS), an array of imaging atmospheric-Cherenkov telescopes in Namibia. The redshifts of these candidate very-high-energy (VHE, >100 GeV) γ-ray emitters range from z = 0.00183 to z = 0.333. Significant detections were already reported for some of these objects, such as PKS 2155-304 and Markarian 421. Marginal evidence (3.1σ) for a signal is found from large-zenith-angle observations of Markarian 501, corresponding to an integral flux of I(>1.65 TeV) = (1.5±0.6 stat±0.3syst) × 10-12 cm -2 s-1 or ∼15% of the Crab Nebula flux. Integral flux upper limits for 19 other AGN, based on exposures of ∼1 to ∼8 h live time, and with average energy thresholds between 160 GeV and 610 GeV, range from 0.4% to 5.1% of the Crab Nebula flux. All the upper limits are the most constraining ever reported for these objects. © ESO 2005.F. Aharonian, A. G. Akhperjanian , A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson, O. Bolz, V. Borre, I. Braun, F. Breitling, A. M. Brown, P.M. Chadwick, L.-M. Chounet, R. Cornils, L. Costamante, B. Degrange, H. J. Dickinson, A. Djannati-Ataï, L. O’C. Drury, G. Dubus, D. Emmanoulopoulos, P. Espigat, F. Feinstein, G. Fontaine, Y. Fuchs, S. Funk, Y. A. Gallant, B. Giebels, S. Gillessen, J. F. Glicenstein, P. Goret, C. Hadjichristidis , M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, A. Jacholkowska, O. C. de Jager, B. Khélifi, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, A. Lemière, M. Lemoine-Goumard, N. Leroy, T. Lohse, J. M. Martin, O. Martineau-Huynh, A. Marcowith, C. Masterson, T. J. L.McComb, M. de Naurois, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, G. Pühlhofer, M. Punch, B. C. Raubenheimer, M. Raue, J. Raux, S. M. Rayner, A. Reimer, O. Reimer, J. Ripken, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Saugé, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, D. Spangler, R. Steenkamp, C. Stegmann, J.-P. Tavernet, R. Terrier, C. G. Théoret, M. Tluczykont, G. Vasileiadis, C. Venter, P. Vincent, H. J. Völk, and S. J. Wagne
Ground-based gamma-rays Detectors Status and needs for the future
No full textGround-based γ-ray astronomy has considerably developed during the last five years, which have attracted the attention of the wider scientific community.
A brief review of ground-based γ-ray detectors is given. The basic observational techniques and constraints are discussed. The needs for future, the advantages of broadening the energy range are described
Serendipitous discovery of the unidentified extended TeV gamma-ray source HESS J1303-631
No full textThe serendipitous discovery of an unidentified extended TeV γ-ray source close to the galactic plane named HESS J1303-631 at a significance of 21 standard deviations is reported. The observations were performed between February and June 2004 with the HESS stereoscopic system of Cherenkov telescopes in Namibia. HESS J1303-631 was discovered roughly 0.6° north of the binary system PSR B1259-63/SS 2883, the target object of the initial observation campaign which was also detected at TeV energies in the same field of view. HESS J1303-631 is extended with a width of an assumed intrinsic Gaussian emission profile of σ = (0.16 ± 0.02)° and the integral flux above 380 GeV is compatible with constant emission over the entire observational period of (17 ± 3)% of the Crab Nebula flux. The measured energy spectrum can be described by a power-law dN/dE ˜ E-Γ with a photon index of Γ = 2.44 ± 0.05stat ± 0.2syst. Up to now, no counterpart at other wavelengths is identified. Various possible TeV production scenarios are discussed.Aharonian, F., Akhperjanian, A. G., Aye, K.-M., Bazer-Bachi, A. R., Beilicke, M., Benbow, W., Berge, D., Berghaus, P., Bernlöhr, K:, Bolz, O., Boisson, C., Glicenstein, J.F., Breitling, F., Brown, A. M., Bussons Gordo, J., Chadwick, P. M., Braun, I., Chounet, L.-M., Cornils, R., Costamante, L., Degrange, B., Djannati-Atai, A., Drury, L.O'C., Emmanoulopoulos, D.; Espigat, P.; Feinstein, F.; Fleury, P., Fontaine, G., Funk, S., Gallant, Y. A., Giebels, B., Gillessen, S., Goret, P., Dubus, G., Hadjichristidis, C., Hauser, M., Heinzelmann, G., Henri, G., Hermann, G.; Hinton, J. A., Hofmann, W., Holleran, M., Horns, D., de Jager, O. C., Khélifi, B., Komin, N., Konopelko, A., Latham, I. J., Le Gallou, R., Lemoine-Goumard, M., Lemière, A., Leroy, N., Lohse, T.; Marcowith, A.; Masterson, C.; McComb, T. J. L.; de Naurois, M.; Nolan, S. J.; Noutsos, A.; Orford, K. J.; Osborne, J. L.; Ouchrif, M.; Panter, M.; Pelletier, G.; Pita, S.; Fuchs, Y.; Pühlhofer, G.; Punch, M.; Raubenheimer, B. C.; Raue, M.; Raux, J.; Rayner, S. M.; Redondo, I.; Reimer, A.; Reimer, O.; Ripken, J.; Terrier, R.; Rob, L.; Rolland, L.; Rowell, G.; Sahakian, V.; Saugé, L.; Schlenker, S.; Schlickeiser, R.; Schuster, C.; Schwanke, U.; Siewert, M.; Sol, H.; Steenkamp, R.; Stegmann, C.; Tavernet, J.-P-; Théoret, C. G., Tluczykont, M., Venter, C., Vasileiadis, G., Vincent, P.; Völk, H. J., Wagner, S. J., Martineau-Huynh, O. and van der Walt, D.J
Observations of Mkn 421 in 2004 with HESS at large zenith angles
No full textMkn 421 was observed during a high flux state for nine nights in April and May 2004 with the fully operational High Energy Stereoscopic System (HESS) in Namibia. The observations were carried out at zenith angles of 60°-65°, which result in an average energy threshold of 1.5 TeV and a collection area reaching 2 km2 at 10 TeV. Roughly 7000 photons from Mkn 421 were accumulated with an average gamma-ray rate of 8 photons/min. The overall significance of the detection exceeds 100 standard deviations. The light-curve of integrated fluxes above 2 TeV shows changes of the diurnal flux up to a factor of 4.3. For nights of high flux, intra-night variability is detected with a decay time of less than 1 h. The time averaged energy spectrum is curved and is well described by a power-law with a photon index Γ = 2.1 ± 0.1stat ± 0.3sys and an exponential cutoff at Ec = 3.1(+0.5 - 0.4)stat ± 0.9sys TeV and an average integral flux above 2 TeV of 3 Crab flux units. Significant variations of the spectral shape are detected with a spectral hardening as the flux increases. Contemporaneous multi-wavelength observations at lower energies (X-rays and gamma-rays above ≈300 GeV) indicate smaller relative variability amplitudes than seen above 2 TeV during high flux state observed in April 2004. © ESO 2005.Aharonian, F., Akhperjanian, A. G., Aye, K.-M., Bazer-Bachi, A. R., Beilicke, M., Benbow, W., Berge, D., Berghaus, P., Bernlöhr, K., Boisson, C., Bolz, O., Braun, I., Breitling, F., Brown, A. M., Bussons Gordo, J., Chadwick, P. M., Chounet, L.-M., Cornils, R., Costamante, L., Degrange, B., Djannati-Ataï, A., O'C. Drury, L., Dubus, G., Emmanoulopoulos, D., Espigat, P., Feinstein, F., Fleury, P., Fontaine, G., Fuchs, Y., Funk, S., Gallant, Y. A., Giebels, B., Gillessen, S., Glicenstein, J. F., Goret, P., Hadjichristidis, C., Hauser, M., Heinzelmann, G., Henri, G., Hermann, G., Hinton, J. A., Hofmann, W., Holleran, M., Horns, D., de Jager, O. C., Khélifi, B., Komin, Nu., Konopelko, A., Latham, I. J., Le Gallou, R., Lemière, A., Lemoine, M., Leroy, N., Lohse, T., Marcowith, A., Masterson, C., McComb, T. J. L., de Naurois, M., Nolan, S. J., Noutsos, A., Orford, K. J., Osborne, J. L., Ouchrif, M., Panter, M., Pelletier, G., Pita, S., Pühlhofer, G., Punch, M., Raubenheimer, B. C., Raue, M., Raux, J., Rayner, S. M., Redondo, I., Reimer, A., Reimer, O., Ripken, J., Rob, L., Rolland, L., Rowell, G., Sahakian, V., Saugé, L., Schlenker, S., Schlickeiser, R., Schuster, C., Schwanke, U., Siewert, M., Sol, H., Steenkamp, R., Stegmann, C., Tavernet, J.-P., Terrier, R., Théoret, C. G., Tluczykont, M., Vasileiadis, G., Venter, C., Vincent, P., Völk, H. J. and Wagner, S. J
H.E.S.S. observations of PKS 2155-304
No full textThe high-frequency peaked BL Lac PKS 2155-304 at redshift z = 0.117 has been detected with high significance (∼45σ) at energies greater than 160 GeV, using the H.E.S.S. stereoscopic array of imaging air-Cherenkov telescopes in Namibia. A strong signal is found in each of the data sets corresponding to the dark periods of July and October, 2002, and June-September, 2003. The observed flux of VHE gamma rays shows variability on time scales of months, days, and hours. The monthly-averaged integral flux above 300 GeV varies between 10% and 60% of the flux observed from the Crab Nebula. Energy spectra are measured for these individual periods of data taking and are characterized by a steep power law with a time-averaged photon index of Γ = 3.32 ± 0.06. An improved x2 per degree of freedom is found when either a power law with an exponential cutoff energy or a broken power law are fit to the time-averaged energy spectrum. However, the significance of the improvement is marginal (∼2σ). The suggested presence of features in the energy spectrum may be intrinsic to the emission from the blazar, or an indication of absorption of TeV gamma rays by the extragalactic infrared background light.F. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr, O. Bolz, C. Boisson, C. Borgmeier, F. Breitling, A. M. Brown, J. Bussons Gordo, P. M. Chadwick, V. R. Chitnis, L.-M. Chounet, R. Cornils, L. Costamante, B. Degrange, A. Djannati-Ataï, L.O'C. Drury, T. Ergin, P. Espigat, F. Feinstein, P. Fleury, G. Fontaine, S. Funk, Y. A. Gallant, B. Giebels, S. Gillessen, P. Goret, J. Guy, C. Hadjichristidis, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, O. C. de Jager, I. Jung, B. Khélifi, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, M. Lemoine, A. Lemière, N. Leroy, T. Lohse, A. Marcowith, C. Masterson, T. J. L. McComb, M. de Naurois, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, M. Pohl, G. Pühlhofer, M. Punch, B. C. Raubenheimer, M. Raue, J. Raux, S. M. Rayner, I. Redondo, A. Reimer, O. Reimer, J. Ripken, M. Rivoal, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Saugé, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, R. Steenkamp, C. Stegmann, J.-P. Tavernet, C. G. Théoret, M. Tluczykont, D. J. van der Walt, G. Vasileiadis, P. Vincent, B. Visser, H. J. Völk and S. J. Wagne
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