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101 results on '"Hillas, A. M."'

1. The Effects of the Galactic Magnetic Field on UHECR From Local Sources

Author

Taylor, Andrew M., Hillas, A. M., Taylor, Andrew M., and Hillas, A. M.

Abstract

We summarise the results found following a study of the effects that Galactic magnetic fields can have on the propagation of cosmic rays from local extragalactic sources. This study focuses on the coherent structures in the Jansson-Farrar Galactic magnetic field model, namely the: disk field, a toroidal field, and an x-field components. The phenomena of Galactic magnetic field shadowing, source deflection, and Galactic magnetic field tunnel vision are all noted. Attention throughout this study is placed on particles with rigidity around $10^{18.5}$ EV, believed to dominate the cosmic ray spectrum above the ankle. The Galactic magnetic field component predominantly responsible for giving rise to each of these different effects was determined., Comment: 6 pages, 3 figures, ICRC 2019 proceedings

Published
2019

2. The Effects of the Galactic Magnetic Field on UHECR From Local Sources

Author

Taylor, Andrew M., Hillas, A. M., Taylor, Andrew M., and Hillas, A. M.

Abstract

We summarise the results found following a study of the effects that Galactic magnetic fields can have on the propagation of cosmic rays from local extragalactic sources. This study focuses on the coherent structures in the Jansson-Farrar Galactic magnetic field model, namely the: disk field, a toroidal field, and an x-field components. The phenomena of Galactic magnetic field shadowing, source deflection, and Galactic magnetic field tunnel vision are all noted. Attention throughout this study is placed on particles with rigidity around $10^{18.5}$ EV, believed to dominate the cosmic ray spectrum above the ankle. The Galactic magnetic field component predominantly responsible for giving rise to each of these different effects was determined., Comment: 6 pages, 3 figures, ICRC 2019 proceedings

Published
2019

3. Multiwavelength Observations of Markarian 421 During a TeV/X-Ray Flare

Author

Macomb, D. J., Akerlof, C. W., Aller, H. D., Aller, M. F., Bertsch, D. L., Bruhweiler, F., Buckley, J. H., Carter-Lewis, D. A., Cawley, M. F., Cheng, K. -P., Dermer, C., Fegan, D. J., Gaidos, J. A., Gear, W. K., Hall, C. R., Hartman, R. C., Hillas, A. M., Kafatos, M., Kerrick, A. D., Kniffen, D. A., Kondo, Y., 窪, 秀利, Lamb, R. C., 槙野, 文命, 牧島, 一夫, Marscher, A., McEnery, J., McHardy, I. M., Meyer, D. I., Moore, E. M., Ramos, E., Robson, E. I., Rose, H. J., Schubnell, M. S., Sembroski, G., Stevens, J. A., 高橋, 忠幸, 田代, 信, Weekes, T. C., Wilson, C., Zweerink, J., Kubo, H., Makino, Fumiyoshi, Makishima, K., Takahashi, Tadayuki, Tashiro, M., Macomb, D. J., Akerlof, C. W., Aller, H. D., Aller, M. F., Bertsch, D. L., Bruhweiler, F., Buckley, J. H., Carter-Lewis, D. A., Cawley, M. F., Cheng, K. -P., Dermer, C., Fegan, D. J., Gaidos, J. A., Gear, W. K., Hall, C. R., Hartman, R. C., Hillas, A. M., Kafatos, M., Kerrick, A. D., Kniffen, D. A., Kondo, Y., 窪, 秀利, Lamb, R. C., 槙野, 文命, 牧島, 一夫, Marscher, A., McEnery, J., McHardy, I. M., Meyer, D. I., Moore, E. M., Ramos, E., Robson, E. I., Rose, H. J., Schubnell, M. S., Sembroski, G., Stevens, J. A., 高橋, 忠幸, 田代, 信, Weekes, T. C., Wilson, C., Zweerink, J., Kubo, H., Makino, Fumiyoshi, Makishima, K., Takahashi, Tadayuki, and Tashiro, M.

Abstract

著者人数：41名, Accepted: 1995-06-09

Published
2015

4. Simultaneous X-Ray and TeV Observations of a Rapid Flare from Markarian 421

Author

Maraschi, L., Fossati, G., Tavecchio, F., Chiappetti, L., Celotti, A., Ghisellini, G., Grandi, P., Pian, E., Tagliaferri, G., Treves, A., Breslin, A. C., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Fegan, D. J., Fegan, S., Finley, J., Gaidos, J., Hall, T., Hillas, A. M., Krennrich, F., Lessard, R. W., Masterson, C., Moriarty, P., Quinn, J., Rose, J., Samuelson, F., Weekes, T. C., Urry, C. M., 高橋, 忠幸, Takahashi, Tadayuki, Maraschi, L., Fossati, G., Tavecchio, F., Chiappetti, L., Celotti, A., Ghisellini, G., Grandi, P., Pian, E., Tagliaferri, G., Treves, A., Breslin, A. C., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Fegan, D. J., Fegan, S., Finley, J., Gaidos, J., Hall, T., Hillas, A. M., Krennrich, F., Lessard, R. W., Masterson, C., Moriarty, P., Quinn, J., Rose, J., Samuelson, F., Weekes, T. C., Urry, C. M., 高橋, 忠幸, and Takahashi, Tadayuki

Abstract

著者人数：31名, Accepted: 1999-09-29

Published
2015

5. TEV gamma ray emission from the active galactic nucleus Markarian 421

Author

University of Michigan, Ann Arbor, Michigan 48109 USA, St. Patrick???s College, Maynooth, Co. Kildare, Ireland, Whipple Observatory, Harvard???Smithsonian CfA, Amado, Arizona 85645 USA, University College Dublin, Belfield, Dublin 4, Ireland, Whipple Observatory, Harvard???Smithsonian CfA, Amado, Arizona 86545 USA, Purdue University, West Lafayette, Indiana 47907 USA, University of Leeds, Leeds LS2 9JT, United Kingdom, Iowa State University, Ames, Iowa 50011 USA, University of Leeds, Leeds LS2 9JT, UK, Schubnell, M., Akerlof, C. W., Cawley, M. F., Chantell, M., Connaughton, V., Fegan, D. J., Fennell, S., Gaidos, J. A., Hillas, A. M., Kerrick, A. D., Kwok, P., Lamb, R. C., Lewis, D. A., Meyer, D. I., Mohanty, G., Rose, J., Rovero, A. C., Sembroski, G., Weekes, T. C., West, M., Whitaker, T., Wilson, C., University of Michigan, Ann Arbor, Michigan 48109 USA, St. Patrick???s College, Maynooth, Co. Kildare, Ireland, Whipple Observatory, Harvard???Smithsonian CfA, Amado, Arizona 85645 USA, University College Dublin, Belfield, Dublin 4, Ireland, Whipple Observatory, Harvard???Smithsonian CfA, Amado, Arizona 86545 USA, Purdue University, West Lafayette, Indiana 47907 USA, University of Leeds, Leeds LS2 9JT, United Kingdom, Iowa State University, Ames, Iowa 50011 USA, University of Leeds, Leeds LS2 9JT, UK, Schubnell, M., Akerlof, C. W., Cawley, M. F., Chantell, M., Connaughton, V., Fegan, D. J., Fennell, S., Gaidos, J. A., Hillas, A. M., Kerrick, A. D., Kwok, P., Lamb, R. C., Lewis, D. A., Meyer, D. I., Mohanty, G., Rose, J., Rovero, A. C., Sembroski, G., Weekes, T. C., West, M., Whitaker, T., and Wilson, C.

Abstract

TeV energy gamma ray emission from the blazar Markarian 421 was detected with the Whipple 10 meter imaging Cherenkov telescope initially during the observation period March???June 1992 at an average photon flux of 1.5??10???11 cm2 s???1. The photon spectrum in the TeV range lies on the extrapolation of the data points observed by EGRET during viewing phase I and indicates that the emission follows an unchanged power law between 100 MeV and 10 TeV with no significant intergalactic absorption. More recent observations from the spring of 1993 confirm the 1992 measurements. Here we give an update on the status of the observations, the analysis for time variability, and the results from the analysis to determine the spectral index for Markarian 421 at TeV energies.The search for TeV emission from other extragalactic sources detected by the EGRET instrument on the Compton Gamma Ray Observatory at GeV energies have so far been negative.

Published
2011

6. Observations of the Crab nebula at TeV energies

Author

University of Michigan, Whipple Observatory, S.A.O., St. Patrick???s College, Maynooth, Ireland, University College, Dublin, Ireland, Purdue University, University of Leeds, Iowa State University, University of Leeds, United Kingdom, Weekes, T. C., Akerlof, C. W., Chantell, M., Colombo, E., Cawley, M. F., Connaughton, V., Fegan, D. J., Fennell, S., Gaidos, J., Hillas, A. M., Kerrick, A. D., Kwok, P., Lewis, D. A., Lamb, R. C., Meyer, D. I., Mohanty, G., Rose, J., Rovero, A., Sembroski, G., Schubnell, M. S., Punch, M., West, M., Whitaker, T., Wilson, C., University of Michigan, Whipple Observatory, S.A.O., St. Patrick???s College, Maynooth, Ireland, University College, Dublin, Ireland, Purdue University, University of Leeds, Iowa State University, University of Leeds, United Kingdom, Weekes, T. C., Akerlof, C. W., Chantell, M., Colombo, E., Cawley, M. F., Connaughton, V., Fegan, D. J., Fennell, S., Gaidos, J., Hillas, A. M., Kerrick, A. D., Kwok, P., Lewis, D. A., Lamb, R. C., Meyer, D. I., Mohanty, G., Rose, J., Rovero, A., Sembroski, G., Schubnell, M. S., Punch, M., West, M., Whitaker, T., and Wilson, C.

Abstract

The results of four years of observation of the Crab Nebula at TeV energies by the Whipple group are discussed and the status of the Crab Nebula as a standard candle for TeV astronomy is reviewed.

Published
2011

7. Detection of TeV photons from the active galaxy Markarian 421

Author

Physics Dept., University of Michigan, Ann Arbor, MI 48109, Whipple Observatory, Harvard???Smithsonian CfA, Box 97, Amado, Arizona 85645, Physics Dept., University College Dublin, Belfield, Dublin 4, Ireland, Physics Dept., St. Patrick???s College, Maynooth, Co. Kildare, Ireland, Physics Dept., Purdue University, West Lafayette, IN 47907, Physics Dept., University of Leeds, Leeds LS2 9JT, UK, Physics and Astronomy Dept., Iowa State University, Ames, Iowa 50011, Akerlof, C. W., Meyer, D. I., Shubnell, M. S., Punch, M., Chantell, M., Fennell, S., Jiang, Y., Lawrence, M. A., Rovero, A. C., Weekes, T. C., Whitaker, T., Fegan, D. J., Hagan, J., O???Flaherty, K. S., Cawley, M. F., Gaidos, J. A., Sembroski, G., Wilson, C., Hillas, A. M., Kerrick, A. D., Lamb, R. C., Lewis, D. A., Mohanty, G., Reynolds, P. T., Physics Dept., University of Michigan, Ann Arbor, MI 48109, Whipple Observatory, Harvard???Smithsonian CfA, Box 97, Amado, Arizona 85645, Physics Dept., University College Dublin, Belfield, Dublin 4, Ireland, Physics Dept., St. Patrick???s College, Maynooth, Co. Kildare, Ireland, Physics Dept., Purdue University, West Lafayette, IN 47907, Physics Dept., University of Leeds, Leeds LS2 9JT, UK, Physics and Astronomy Dept., Iowa State University, Ames, Iowa 50011, Akerlof, C. W., Meyer, D. I., Shubnell, M. S., Punch, M., Chantell, M., Fennell, S., Jiang, Y., Lawrence, M. A., Rovero, A. C., Weekes, T. C., Whitaker, T., Fegan, D. J., Hagan, J., O???Flaherty, K. S., Cawley, M. F., Gaidos, J. A., Sembroski, G., Wilson, C., Hillas, A. M., Kerrick, A. D., Lamb, R. C., Lewis, D. A., Mohanty, G., and Reynolds, P. T.

Published
2011

8. Observations of TeV photons at the Whipple Observatory

Author

University of Michigan, Ann Arbor, Michigan 48109, Iowa State University, Ames, Iowa 50011, St. Patrick???s College, Maynooth, Co. Kildare, Ireland, Harvard???Smithsonian Center for Astrophysics, P.O. Box 97, Amado, Arizona 85645, University College, Dublin, Ireland, University of Leeds, Leeds, United Kingdom, Lamb, R. C., Akerlof, C. W., Cawley, M. F., Colombo, E., Fegan, D. J., Hillas, A. M., Kwok, P. W., Lang, M. J., Lewis, D. A., Macomb, D. J., Meyer, D. I., O???Flaherty, K. S., Reynolds, P. T., Vacanti, G., Weekes, T. C., University of Michigan, Ann Arbor, Michigan 48109, Iowa State University, Ames, Iowa 50011, St. Patrick???s College, Maynooth, Co. Kildare, Ireland, Harvard???Smithsonian Center for Astrophysics, P.O. Box 97, Amado, Arizona 85645, University College, Dublin, Ireland, University of Leeds, Leeds, United Kingdom, Lamb, R. C., Akerlof, C. W., Cawley, M. F., Colombo, E., Fegan, D. J., Hillas, A. M., Kwok, P. W., Lang, M. J., Lewis, D. A., Macomb, D. J., Meyer, D. I., O???Flaherty, K. S., Reynolds, P. T., Vacanti, G., and Weekes, T. C.

Abstract

The Whipple Observatory 10 m gamma???ray telescope has been used to search for TeV gamma???ray emission from a number of objects. This paper reports observations of six galactic and three extragalactic objects using the Cherenkov image technique. With the introduction of a high???resolution camera (1/4?? pixel) in 1988, the Crab Nebula was detected at a significance level of 20 ?? in 30 hours of on???source observation. Upper limits at a fraction of the Crab flux are set for most of the other objects, based on the absence of any significant dc excess or periodic effect when an a priori Monte Carlo determined imaging selection criterion (the ??????azwidth cut??????) is employed. There are weak indications that one source, Hercules X???1, may be an episodic emitter. The Whipple detection system will be improved shortly with the addition of a second reflector 11 m in diameter (GRANITE) for stereoscopic viewing of showers. The combination of the two???reflector system should have a signal???to???noise advantage of 103 over a simple nonimaging Cherenkov receiver.

Published
2011

9. Detection of TeV gamma rays from the AGN Markarian 421

Author

University of Michigan, Ann Arbor, Michigan 48109, St. Patrick???s College, Maynooth, Co., Kildare, Ireland, Whipple Observatory, Harvard???Smithsonian CfA, Amado, Arizona 85645, University College Dublin, Belfield, Dublin 4, Ireland, Purdue University, West Lafayette, Indiana 47907, University of Leeds, Leeds LS2 9JT, United Kingdom, Iowa State University, Ames, Iowa 50011, Schubnell, M., Akerlof, C. W., Cawley, M. F., Chantell, M., Fegan, D. J., Fennell, S., O???Flaherty, K. S., Gaidos, J. A., Hagan, J., Hillas, A. M., Jiang, Y., Kerrick, A. D., Lamb, R. C., Lawrence, M. A., Lewis, D. A., Meyer, D. I., Mohanty, G., Punch, M., Reynolds, P. T., Rovero, A. C., Sembroski, G., Weekes, T. C., Whitaker, T., Wilson, C., University of Michigan, Ann Arbor, Michigan 48109, St. Patrick???s College, Maynooth, Co., Kildare, Ireland, Whipple Observatory, Harvard???Smithsonian CfA, Amado, Arizona 85645, University College Dublin, Belfield, Dublin 4, Ireland, Purdue University, West Lafayette, Indiana 47907, University of Leeds, Leeds LS2 9JT, United Kingdom, Iowa State University, Ames, Iowa 50011, Schubnell, M., Akerlof, C. W., Cawley, M. F., Chantell, M., Fegan, D. J., Fennell, S., O???Flaherty, K. S., Gaidos, J. A., Hagan, J., Hillas, A. M., Jiang, Y., Kerrick, A. D., Lamb, R. C., Lawrence, M. A., Lewis, D. A., Meyer, D. I., Mohanty, G., Punch, M., Reynolds, P. T., Rovero, A. C., Sembroski, G., Weekes, T. C., Whitaker, T., and Wilson, C.

Abstract

We present here the detection of TeV gamma rays from the extragalactic source Markarian 421. Observations obtained with the Whipple 10 m imaging Cherenkov telescope in March???June 1992 give a gamma ray signal with statistical significance of 6.3?? above background. The excess corresponds to an average flux of 1.5??10???11 cm???2 s???1 above 0.5 TeV, equivalent to 0.3 of that from the Crab Nebula. The estimated location of the source agrees with the position of Mrk 421 to the angular uncertainty of the Whipple instrument (6 arc minutes).

Published
2011

10. Searches for TeV counterparts to classical gamma-ray bursts

Author

University of Michigan, United States of America, Whipple Observatory, Harvard-Smithsonian CfA, United States of America, University of Leeds, United Kingdom, Iowa State University, United States of America, St. Patrick???s College, Maynooth, Ireland, University College, Dublin, Ireland, Purdue University, United States of America, Goddard Space Flight Center, Marshall Space Flight Center, Connaughton, V., Akerlof, C. W., Biller, S., Buckley, J., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Fegan, D. J., Finley, J., Gaidos, J., Hillas, A. M., Lamb, R. C., Lessard, R., McEnery, J., Mohanty, G., Porter, N. A., Quinn, J., Rose, H. J., Samuelson, F., Schubnell, M. S., Sembroski, G., Srinivasan, R., Weekes, T. C., Wilson, C., Zweerink, J., Barthelmy, S., Cline, T., Gehrels, N., Fishman, G. J., Kouveliotou, C., Meegan, C., University of Michigan, United States of America, Whipple Observatory, Harvard-Smithsonian CfA, United States of America, University of Leeds, United Kingdom, Iowa State University, United States of America, St. Patrick???s College, Maynooth, Ireland, University College, Dublin, Ireland, Purdue University, United States of America, Goddard Space Flight Center, Marshall Space Flight Center, Connaughton, V., Akerlof, C. W., Biller, S., Buckley, J., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Fegan, D. J., Finley, J., Gaidos, J., Hillas, A. M., Lamb, R. C., Lessard, R., McEnery, J., Mohanty, G., Porter, N. A., Quinn, J., Rose, H. J., Samuelson, F., Schubnell, M. S., Sembroski, G., Srinivasan, R., Weekes, T. C., Wilson, C., Zweerink, J., Barthelmy, S., Cline, T., Gehrels, N., Fishman, G. J., Kouveliotou, C., and Meegan, C.

Abstract

Intense effort has gone into the observation of optical, radio and X-ray GRB counterparts, either simultaneous to the burst or as quasi-steady remnants. Here we report on a similar study at higher energies of 250 GeV and above using ground-based telescopes. Imaging atmospheric Cherenkov telescopes have achieved great sensitivity and now complement observations by orbiting telescopes such as CGRO. Previous studies of bursts by the Whipple Collaboration (4) combined with recent improvements to the telescope, indicate that sensitivity to a fluence of 6??10???9???erg-cm???26??10???9erg-cm???2 can be achieved. Observations by the Whipple Collaboration of nine BATSE positions, one within 2 minutes of the BATSE burst, using coordinates distributed through BACODINE will be reported. Analysis techniques will be described and an upper limit to the high-energy delayed or extended emission of observed candidates will be calculated. ?? 1996 American Institute of Physics.

Published
2011

11. Mapping the most energetic cosmic rays

Author

Hillas, A. M. and Hillas, A. M.

Abstract

The correlation between the directions of optically-detected AGNs within 75 Mpc and the arrival directions of cosmic rays above 57 EeV detected by the Auger collaboration up to August 2007 is examined using uniform-exposure plots and a form of right ascension resonance which does not require choice of an association window radius. Using the latter, the chance of accidental correlation is found to be well below 1 in 10^5 even without using 3.2 degree windows; the correlation with FRI-like radio galaxies within 75 Mpc, listed by Nagar & Matulich (which are in AGN clusters), is separately just as significant; and a correlation can also be found in other data at a lower energy. Cen A is currently inactive at this energy, as more distant radio galaxies are so prominent. The efficacy of a 57 EeV cut to select this revelatory (proton) sample of the Auger data may be almost accidental and not robust. The cosmic rays in the Auger sample seem to be scattered by ~3-4 degrees en route, from about 50 Mpc, and in one relatively well probed sky region there may be a 4 degree systematic deflection in a Bz component of the magnetic field in the galactic halo. The sources appear to be mostly within 120 Mpc. This is compatible with a GZK survival horizon, but only if (a) the Auger energies are underestimated by ~25% and (b) the sudden fall in the energy spectrum is not simply a GZK effect but essentially reflects an energy cut-off in the sources., Comment: Submitted to Astroparticle Physics; 27 pages, 13 figures (20 panels)

Published
2009
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12. Mapping the most energetic cosmic rays

Author

Hillas, A. M. and Hillas, A. M.

Abstract

The correlation between the directions of optically-detected AGNs within 75 Mpc and the arrival directions of cosmic rays above 57 EeV detected by the Auger collaboration up to August 2007 is examined using uniform-exposure plots and a form of right ascension resonance which does not require choice of an association window radius. Using the latter, the chance of accidental correlation is found to be well below 1 in 10^5 even without using 3.2 degree windows; the correlation with FRI-like radio galaxies within 75 Mpc, listed by Nagar & Matulich (which are in AGN clusters), is separately just as significant; and a correlation can also be found in other data at a lower energy. Cen A is currently inactive at this energy, as more distant radio galaxies are so prominent. The efficacy of a 57 EeV cut to select this revelatory (proton) sample of the Auger data may be almost accidental and not robust. The cosmic rays in the Auger sample seem to be scattered by ~3-4 degrees en route, from about 50 Mpc, and in one relatively well probed sky region there may be a 4 degree systematic deflection in a Bz component of the magnetic field in the galactic halo. The sources appear to be mostly within 120 Mpc. This is compatible with a GZK survival horizon, but only if (a) the Auger energies are underestimated by ~25% and (b) the sudden fall in the energy spectrum is not simply a GZK effect but essentially reflects an energy cut-off in the sources., Comment: Submitted to Astroparticle Physics; 27 pages, 13 figures (20 panels)

Published
2009
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13. Cosmic Rays: Recent Progress and some Current Questions

Author

Hillas, A. M. and Hillas, A. M.

Abstract

Recent progress suggests we are moving towards a quantitative understanding of the whole cosmic ray spectrum, and that many bumps due to different components and processes hide beneath a relatively smooth total flux between knee and ankle. The knee is much better understood: the KASCADE observations support a rather sharp rigidity cut-off; while theoretical developments (strong magnetic field generation) indicate that supernova remnants (SNR) of different types should indeed accelerate to a very similar rigidity. X-ray and TeV observations of shell-type SNR produce evidence in favour of acceleration at their outer boundaries. There is some still-disputed evidence that the transition to extragalactic cosmic rays has already occurred just above 10**17 eV, unmarked by an "ankle", in which case the whole spectrum can be well described by adding a single power-law source spectrum from many extragalactic sources (but modified by energy losses) to the SNR pre-knee component, if the sources photodisintegrate all nuclei. At the highest energy, the experiments using fluorscence light to calibrate energy do not yet show any conflict with an expected GZK "termination". GRBs seem not to make a significant contribution., Comment: 12 pages, 8 figures, Based on invited talk in "Cosmology, Galaxy Formation and Astroparticle Physics on the pathway to the SKA", Oxford, April 2006 Version 2: section 6 (relevance of GRBs) added in response to questions; $ minor clarifications

Published
2006

14. Cosmic Rays: Recent Progress and some Current Questions

Author

Hillas, A. M. and Hillas, A. M.

Abstract

Recent progress suggests we are moving towards a quantitative understanding of the whole cosmic ray spectrum, and that many bumps due to different components and processes hide beneath a relatively smooth total flux between knee and ankle. The knee is much better understood: the KASCADE observations support a rather sharp rigidity cut-off; while theoretical developments (strong magnetic field generation) indicate that supernova remnants (SNR) of different types should indeed accelerate to a very similar rigidity. X-ray and TeV observations of shell-type SNR produce evidence in favour of acceleration at their outer boundaries. There is some still-disputed evidence that the transition to extragalactic cosmic rays has already occurred just above 10**17 eV, unmarked by an "ankle", in which case the whole spectrum can be well described by adding a single power-law source spectrum from many extragalactic sources (but modified by energy losses) to the SNR pre-knee component, if the sources photodisintegrate all nuclei. At the highest energy, the experiments using fluorscence light to calibrate energy do not yet show any conflict with an expected GZK "termination". GRBs seem not to make a significant contribution., Comment: 12 pages, 8 figures, Based on invited talk in "Cosmology, Galaxy Formation and Astroparticle Physics on the pathway to the SKA", Oxford, April 2006 Version 2: section 6 (relevance of GRBs) added in response to questions; $ minor clarifications

Published
2006

15. Spectrum of very high energy gamma-rays from the blazar 1ES 1959+650 during flaring activity in 2002

Author

Daniel, M. K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cogan, P., Cui, W., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Humensky, T. B., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Daniel, M. K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cogan, P., Cui, W., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Humensky, T. B., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

The blazar 1ES 1959+650 was observed in a flaring state with the Whipple 10 m Imaging Atmospheric Cerenkov Telescope in 2002 May. A spectral analysis has been carried out on the data from that time period, and the resulting very high energy gamma-ray spectrum (E greater than or equal to 316 GeV) can be well fitted by a power law of differential spectral index alpha = 2.78 +/- 0.12(stat) +/- 0.21(sys). On 2002 June 4, the source flared dramatically in the gamma-ray range without any coincident increase in the X-ray emission, providing the first unambiguous example of an "orphan'' gamma-ray flare from a blazar. The gamma-ray spectrum for these data can also be described by a simple power-law fit with alpha = 2.82 +/- 0.15(stat) +/- 0.30(sys). There is no compelling evidence for spectral variability or for any cutoff to the spectrum.

Published
2005

16. Spectrum of very high energy gamma-rays from the blazar 1ES 1959+650 during flaring activity in 2002

Author

Daniel, M. K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cogan, P., Cui, W., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Humensky, T. B., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Daniel, M. K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cogan, P., Cui, W., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Humensky, T. B., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

The blazar 1ES 1959+650 was observed in a flaring state with the Whipple 10 m Imaging Atmospheric Cerenkov Telescope in 2002 May. A spectral analysis has been carried out on the data from that time period, and the resulting very high energy gamma-ray spectrum (E greater than or equal to 316 GeV) can be well fitted by a power law of differential spectral index alpha = 2.78 +/- 0.12(stat) +/- 0.21(sys). On 2002 June 4, the source flared dramatically in the gamma-ray range without any coincident increase in the X-ray emission, providing the first unambiguous example of an "orphan'' gamma-ray flare from a blazar. The gamma-ray spectrum for these data can also be described by a simple power-law fit with alpha = 2.82 +/- 0.15(stat) +/- 0.30(sys). There is no compelling evidence for spectral variability or for any cutoff to the spectrum.

Published
2005

17. Tev Gamma-ray observations of the galactic center

Author

Kosack, K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Connaughton, V., Cui, W., Daniel, M., D'Vall, M., Perez, I. D. L., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Gutierrez, K., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., McEnery, J., Moriarty, R., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Kosack, K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Connaughton, V., Cui, W., Daniel, M., D'Vall, M., Perez, I. D. L., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Gutierrez, K., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., McEnery, J., Moriarty, R., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

We report a possible detection of TeV gamma rays from the Galactic center by the Whipple 10 m gamma-ray telescope. Twenty-six hours of data were taken over an extended period from 1995 through 2003 resulting in a total significance of 3.7 sigma. The measured excess corresponds to an integral flux of 1.6 x 10(-8) +/- 0.5 x 10(-8) (stat) +/- 0.3 x 10(-8) (sys) photons m(-2) s(-1) above an energy of 2.8 TeV, roughly 40% of the flux from the Crab Nebula at this energy. The 95% confidence region has an angular extent of about 15' and includes the position of Sgr A*. The detection is consistent with a point source and shows no evidence of variability.

Published
2004

18. Constraints on the very high energy emission from BL Lacertae objects

Author

Horan, D., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Evans, J. L., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Horan, D., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Evans, J. L., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

We present results from observations of 29 BL Lacertae objects, taken with the Whipple Observatory 10 m gamma-ray telescope between 1995 and 2000. The observed objects are mostly at low redshift (z<0.2), but observations of objects of up to z=0.444 are also reported. Five of the objects are EGRET sources and two are unconfirmed TeV sources. Three of the confirmed sources of extragalactic TeV gamma rays were originally observed as part of this survey and have been reported elsewhere. No significant excesses are detected from any of the other objects observed, on timescales of days, months, or years. We report 99.9% confidence level flux upper limits for the objects for each observing season. The flux upper limits are typically 20% of the Crab flux, although for some sources, limits as sensitive as 6% of the Crab flux were derived. The results are consistent with the synchrotron self-Compton model predictions considered in this work.

Published
2004

19. A search for TeV gamma-ray emission from high-peaked flat-spectrum radio quasars using the Whipple air Cerenkov telescope

Author

Falcone, A. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R., Pallassini, R., Petry, D., Pizlo, F., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Tyler, K., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Falcone, A. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R., Pallassini, R., Petry, D., Pizlo, F., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Tyler, K., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

Blazars have traditionally been separated into two broad categories based on their optical emission characteristics. Blazars with faint or no emission lines are referred to as BL Lacertae objects ( BL Lacs), and blazars with prominent, broad emission lines are commonly referred to as flat-spectrum radio quasars (FSRQs). The spectral energy distribution of FSRQs has generally been thought of as being more akin to the low-peaked BL Lacs, which exhibit a peak in the infrared region of the spectrum, as opposed to high-peaked BL Lacs (HBLs), which exhibit a peak in UV/X-ray region of the spectrum. All blazars that are currently confirmed as sources of TeV emission fall into the HBL category. Recent surveys have found several FSRQs that exhibit spectral properties, particularly the synchrotron peak frequency, similar to HBLs. These objects are potential sources of TeV emission according to several models of blazar jet emission and the evolution of blazars. Measurements of TeV flux or flux upper limits could impact existing theories explaining the links between different blazar types and could have a significant impact on our understanding of the nature of objects that are capable of TeV emission. In particular, the presence ( or absence) of TeV emission from FSRQs could confirm ( or cast doubt on) recent evolutionary models that expect intermediate objects in a transitional state between FSRQ and BL Lac. The Whipple 10 m imaging air Cerenkov gamma-ray telescope is well suited for TeV gamma-ray observations. Using the Whipple telescope, we have taken data on a small selection of nearby (z < 0.1 in most cases) high-peaked FSRQs. Although one of the objects, B2 0321+33, showed marginal evidence of flaring, no significant emission was detected. The implications of this paucity of emission and the derived upper limits are discussed.

Published
2004

20. VERITAS: the Very Energetic Radiation Imaging Telescope Array System

Author

Krennrich, F., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Vassiliev, V. V., Walker, G., Wakely, S. P., Weekes, T. C., Zweerink, J., Krennrich, F., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Vassiliev, V. V., Walker, G., Wakely, S. P., Weekes, T. C., and Zweerink, J.

Abstract

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is the major next generation imaging atmospheric Cherenkov gamma-ray telescope in the western hemisphere and will be located in southern Arizona nearby Kitt Peak National Observatory. The VERITAS observatory will provide unprecedented sensitivity to photon energies between 50 GeV and 50 TeV. The first stage is an array of four telescopes to be fully operational in early 2006, with an expansion to seven telescopes envisioned for 2008. The construction of a prototype telescope is underway, for which first light is expected in Fall 2003. The technical concept is outlined and a progress report is given. (C) 2004 Published by Elsevier B.V.

Published
2004

21. Observation of M87 at 400 GeV with the Whipple 10 meter telescope

Author

Le Bohec, S., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Le Bohec, S., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

We present results from observations taken with the Whipple 10 m very high energy gamma-ray telescope with maximal sensitivity at 400 GeV during 39 hr between 2000 and 2003 in the direction of the giant radio galaxy M87. Using the entire data set, we derive a 99% confidence level upper limit on the flux of gamma-ray emission above 400 GeV from M87 to be less than or equal to 6: 9; 10(-1)2 cm(-2) s(-1). This suggests variability at the 90% confidence level when compared to the flux measured by the HEGRA collaboration in 1999 if the differential spectrum is steeper than a power law of index 3.75. Our search for a correlation between the Rossi X-Ray Timing Explorer all-sky monitor observation and a potential gamma-ray signal is inconclusive.

Published
2004

22. Evidence for TeV gamma ray emission from TeV J2032+4130 in Whipple archival data

Author

Lang, M. J., Carter-Lewis, D. A., Fegan, D. J., Fegan, S. J., Hillas, A. M., Lamb, R. C., Punch, M., Reynolds, P. T., Weekes, T. C., Lang, M. J., Carter-Lewis, D. A., Fegan, D. J., Fegan, S. J., Hillas, A. M., Lamb, R. C., Punch, M., Reynolds, P. T., and Weekes, T. C.

Abstract

A reanalysis of data taken on the Cygnus region in 1989-90 using the Whipple Observatory atmospheric Cherenkov imaging telescope confirms the existence of the TeV J2032+4130 source reported by the Crimean Astrophysical Observatory and published by the HEGRA Collaboration. The significance at the a priori HEGRA position is 3.3sigma. The peak signal was found at RA=20hr32min, Dec=+41deg33min. This is 0.6deg north of Cygnus X-3 which was the original target of the observations. The flux level (12% of the level of the Crab Nebula) is intermediate between the two later observations and suggests that the TeV source is variable., Comment: 5 pages, 2 figures, accepted for publication in Astronomy & Astrophysics

Published
2004
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23. Evidence for TeV gamma ray emission from TeV J2032+4130 in Whipple archival data

Author

Lang, M. J., Carter-Lewis, D. A., Fegan, D. J., Fegan, S. J., Hillas, A. M., Lamb, R. C., Punch, M., Reynolds, P. T., Weekes, T. C., Lang, M. J., Carter-Lewis, D. A., Fegan, D. J., Fegan, S. J., Hillas, A. M., Lamb, R. C., Punch, M., Reynolds, P. T., and Weekes, T. C.

Abstract

A reanalysis of data taken on the Cygnus region in 1989-90 using the Whipple Observatory atmospheric Cherenkov imaging telescope confirms the existence of the TeV J2032+4130 source reported by the Crimean Astrophysical Observatory and published by the HEGRA Collaboration. The significance at the a priori HEGRA position is 3.3sigma. The peak signal was found at RA=20hr32min, Dec=+41deg33min. This is 0.6deg north of Cygnus X-3 which was the original target of the observations. The flux level (12% of the level of the Crab Nebula) is intermediate between the two later observations and suggests that the TeV source is variable., Comment: 5 pages, 2 figures, accepted for publication in Astronomy & Astrophysics

Published
2004
Full Text
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24. Observation of M87 at 400 GeV with the Whipple 10 meter telescope

Author

Le Bohec, S., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Le Bohec, S., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

We present results from observations taken with the Whipple 10 m very high energy gamma-ray telescope with maximal sensitivity at 400 GeV during 39 hr between 2000 and 2003 in the direction of the giant radio galaxy M87. Using the entire data set, we derive a 99% confidence level upper limit on the flux of gamma-ray emission above 400 GeV from M87 to be less than or equal to 6: 9; 10(-1)2 cm(-2) s(-1). This suggests variability at the 90% confidence level when compared to the flux measured by the HEGRA collaboration in 1999 if the differential spectrum is steeper than a power law of index 3.75. Our search for a correlation between the Rossi X-Ray Timing Explorer all-sky monitor observation and a potential gamma-ray signal is inconclusive.

Published
2004

25. Constraints on the very high energy emission from BL Lacertae objects

Author

Horan, D., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Evans, J. L., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Horan, D., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Evans, J. L., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

We present results from observations of 29 BL Lacertae objects, taken with the Whipple Observatory 10 m gamma-ray telescope between 1995 and 2000. The observed objects are mostly at low redshift (z<0.2), but observations of objects of up to z=0.444 are also reported. Five of the objects are EGRET sources and two are unconfirmed TeV sources. Three of the confirmed sources of extragalactic TeV gamma rays were originally observed as part of this survey and have been reported elsewhere. No significant excesses are detected from any of the other objects observed, on timescales of days, months, or years. We report 99.9% confidence level flux upper limits for the objects for each observing season. The flux upper limits are typically 20% of the Crab flux, although for some sources, limits as sensitive as 6% of the Crab flux were derived. The results are consistent with the synchrotron self-Compton model predictions considered in this work.

Published
2004

26. A search for TeV gamma-ray emission from high-peaked flat-spectrum radio quasars using the Whipple air Cerenkov telescope

Author

Falcone, A. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R., Pallassini, R., Petry, D., Pizlo, F., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Tyler, K., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Falcone, A. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D., Duke, C., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R., Pallassini, R., Petry, D., Pizlo, F., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Tyler, K., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

Blazars have traditionally been separated into two broad categories based on their optical emission characteristics. Blazars with faint or no emission lines are referred to as BL Lacertae objects ( BL Lacs), and blazars with prominent, broad emission lines are commonly referred to as flat-spectrum radio quasars (FSRQs). The spectral energy distribution of FSRQs has generally been thought of as being more akin to the low-peaked BL Lacs, which exhibit a peak in the infrared region of the spectrum, as opposed to high-peaked BL Lacs (HBLs), which exhibit a peak in UV/X-ray region of the spectrum. All blazars that are currently confirmed as sources of TeV emission fall into the HBL category. Recent surveys have found several FSRQs that exhibit spectral properties, particularly the synchrotron peak frequency, similar to HBLs. These objects are potential sources of TeV emission according to several models of blazar jet emission and the evolution of blazars. Measurements of TeV flux or flux upper limits could impact existing theories explaining the links between different blazar types and could have a significant impact on our understanding of the nature of objects that are capable of TeV emission. In particular, the presence ( or absence) of TeV emission from FSRQs could confirm ( or cast doubt on) recent evolutionary models that expect intermediate objects in a transitional state between FSRQ and BL Lac. The Whipple 10 m imaging air Cerenkov gamma-ray telescope is well suited for TeV gamma-ray observations. Using the Whipple telescope, we have taken data on a small selection of nearby (z < 0.1 in most cases) high-peaked FSRQs. Although one of the objects, B2 0321+33, showed marginal evidence of flaring, no significant emission was detected. The implications of this paucity of emission and the derived upper limits are discussed.

Published
2004

27. Tev Gamma-ray observations of the galactic center

Author

Kosack, K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Connaughton, V., Cui, W., Daniel, M., D'Vall, M., Perez, I. D. L., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Gutierrez, K., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., McEnery, J., Moriarty, R., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Zweerink, J., Kosack, K., Badran, H. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Connaughton, V., Cui, W., Daniel, M., D'Vall, M., Perez, I. D. L., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J. A., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Gutierrez, K., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Jordan, M., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krawczynski, H., Krennrich, F., Lang, M. J., Le Bohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., McEnery, J., Moriarty, R., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Syson, A., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., and Zweerink, J.

Abstract

We report a possible detection of TeV gamma rays from the Galactic center by the Whipple 10 m gamma-ray telescope. Twenty-six hours of data were taken over an extended period from 1995 through 2003 resulting in a total significance of 3.7 sigma. The measured excess corresponds to an integral flux of 1.6 x 10(-8) +/- 0.5 x 10(-8) (stat) +/- 0.3 x 10(-8) (sys) photons m(-2) s(-1) above an energy of 2.8 TeV, roughly 40% of the flux from the Crab Nebula at this energy. The 95% confidence region has an angular extent of about 15' and includes the position of Sgr A*. The detection is consistent with a point source and shows no evidence of variability.

Published
2004

28. VERITAS: the Very Energetic Radiation Imaging Telescope Array System

Author

Krennrich, F., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Vassiliev, V. V., Walker, G., Wakely, S. P., Weekes, T. C., Zweerink, J., Krennrich, F., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D., Celik, O., Cui, W., Daniel, M., D'Vali, M., Perez, I. D. C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L. F., Gaidos, J., Gammell, S., Gibbs, K., Gillanders, G. H., Grube, J., Hall, J., Hall, T. A., Hanna, D., Hillas, A. M., Holder, J., Horan, D., Jarvis, A., Kenny, G. E., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Lang, M. J., LeBohec, S., Linton, E., Lloyd-Evans, J., Milovanovic, A., Moriarty, P., Muller, D., Nagai, T., Nolan, S., Ong, R. A., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Quinn, M., Ragan, K., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G., Swordy, S. P., Syson, A., Vassiliev, V. V., Walker, G., Wakely, S. P., Weekes, T. C., and Zweerink, J.

Abstract

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is the major next generation imaging atmospheric Cherenkov gamma-ray telescope in the western hemisphere and will be located in southern Arizona nearby Kitt Peak National Observatory. The VERITAS observatory will provide unprecedented sensitivity to photon energies between 50 GeV and 50 TeV. The first stage is an array of four telescopes to be fully operational in early 2006, with an expansion to seven telescopes envisioned for 2008. The construction of a prototype telescope is underway, for which first light is expected in Fall 2003. The technical concept is outlined and a progress report is given. (C) 2004 Published by Elsevier B.V.

Published
2004

29. Search for high-energy gamma rays from an X-ray-selected blazar sample

Author

Perez, I. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Cui, W., Dowdall, C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R. A., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Perez, I. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Cui, W., Dowdall, C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R. A., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., and Weekes, T. C.

Abstract

Our understanding of blazars has been greatly increased in recent years by extensive multiwavelength observations, particularly in the radio, X-ray, and gamma-ray regions. Over the past decade the Whipple 10 m telescope has contributed to this with the detection of five BL Lacertae objects at very high gamma-ray energies. The combination of multiwavelength data has shown that blazars follow a well-defined sequence in terms of their broadband spectral properties. Together with providing constraints on emission models, this information has yielded a means by which potential sources of TeV emission may be identified and predictions made as to their possible gamma-ray flux. We have used the Whipple telescope to search for TeV gamma-ray emission from eight objects selected from a list of such candidates. No evidence has been found for very high energy emission from the objects in our sample, and upper limits have been derived for the mean gamma-ray flux above 390 GeV. These flux upper limits are compared with the model predictions, and the implications of our results for future observations are discussed.

Published
2003

30. A search for correlations of TeV gamma rays with ultra-high-energy cosmic rays

Author

Akerlof, C. W., Biller, S., Boyle, P., Buckley, J., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Connaughton, V., Fegan, D. J., Finley, J., Gaidos, J., Hillas, A. M., Krennrich, F., Lamb, R. C., Lessard, R., McEnery, J., Mohanty, G., Porter, N. A., Quinn, J., Rodgers, A., Rose, H. J., Samuelson, F., Schubnell, M. S., Sembroski, G., Srinivasan, R., Weekes, T. C., Zweerink, J., Akerlof, C. W., Biller, S., Boyle, P., Buckley, J., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Connaughton, V., Fegan, D. J., Finley, J., Gaidos, J., Hillas, A. M., Krennrich, F., Lamb, R. C., Lessard, R., McEnery, J., Mohanty, G., Porter, N. A., Quinn, J., Rodgers, A., Rose, H. J., Samuelson, F., Schubnell, M. S., Sembroski, G., Srinivasan, R., Weekes, T. C., and Zweerink, J.

Abstract

A search was conducted for TeV gamma-rays emitted from the direction of the ultra-high-energy cosmic ray detected by the Fly's Eye experiment with energy E similar to 3 x 10(20) eV. No enhancement was found at a level of 10(-10)gamma cm(-2) s(-1) for E > 350 GeV. A steady source of ultra-high-energy cosmic ray protons or photons would be expected to produce a gamma-ray flux above this level. An upper limit was also set for the flux of TeV gamma-rays from 3C 147, the most prominent active galactic nucleus in the error box.

Published
2003

31. Detection of TeV gamma rays from the BL Lacertae object 1ES 1959+650 with the Whipple 10 meter telescope

Author

Holder, J., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Dowdall, C., Duke, C., Perez, I. D., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Holder, J., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Dowdall, C., Duke, C., Perez, I. D., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., and Weekes, T. C.

Abstract

We present the first strong detection of very high energy gamma-rays from the close (z=0.048) X-ray-selected BL Lacertae object 1ES 1959+650. Observations were made with the Whipple 10 m telescope on Mount Hopkins, Arizona, using the atmospheric Cerenkov imaging technique. The flux between 2002 May and July was highly variable, with a mean of 0.64+/-0.03 times the steady flux from the Crab Nebula and reaching a maximum of 5 crab, with variability on timescales as short as 7 hr.

Published
2003

32. Search for TeV emissions from pulsars in binary systems

Author

Hall, T. A., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carson, M. J., Carter-Lewis, D. A., Catanese, M., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hillas, A. M., Horan, D., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krennrich, F., Lang, M. J., LeBohec, S., Lessard, R., Lloyd-Evans, J., McKernan, B., Moriarty, P., Muller, D., Ong, R., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Weekes, T. C., Hall, T. A., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carson, M. J., Carter-Lewis, D. A., Catanese, M., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hillas, A. M., Horan, D., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krennrich, F., Lang, M. J., LeBohec, S., Lessard, R., Lloyd-Evans, J., McKernan, B., Moriarty, P., Muller, D., Ong, R., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., and Weekes, T. C.

Abstract

A survey of binary systems containing pulsars was conducted, with the intention of detecting Galactic sources of very high energy gamma-ray emission. Observations were carried out with the Whipple 10 m imaging atmospheric Cerenkov telescope. Standard analysis techniques were applied to these sources to search for steady, unpulsed emission. Periodic tests were also performed to search for emission correlated with both the orbital and spin phases, where appropriate. Analyses indicate that the binaries in this study do not emit detectable levels of very high energy photons within the sensitivity of our instrument. The flux upper limits presented here fail to seriously constrain emission models.

Published
2003

33. A search for correlations of TeV gamma rays with ultra-high-energy cosmic rays

Author

Akerlof, C. W., Biller, S., Boyle, P., Buckley, J., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Connaughton, V., Fegan, D. J., Finley, J., Gaidos, J., Hillas, A. M., Krennrich, F., Lamb, R. C., Lessard, R., McEnery, J., Mohanty, G., Porter, N. A., Quinn, J., Rodgers, A., Rose, H. J., Samuelson, F., Schubnell, M. S., Sembroski, G., Srinivasan, R., Weekes, T. C., Zweerink, J., Akerlof, C. W., Biller, S., Boyle, P., Buckley, J., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Connaughton, V., Fegan, D. J., Finley, J., Gaidos, J., Hillas, A. M., Krennrich, F., Lamb, R. C., Lessard, R., McEnery, J., Mohanty, G., Porter, N. A., Quinn, J., Rodgers, A., Rose, H. J., Samuelson, F., Schubnell, M. S., Sembroski, G., Srinivasan, R., Weekes, T. C., and Zweerink, J.

Abstract

A search was conducted for TeV gamma-rays emitted from the direction of the ultra-high-energy cosmic ray detected by the Fly's Eye experiment with energy E similar to 3 x 10(20) eV. No enhancement was found at a level of 10(-10)gamma cm(-2) s(-1) for E > 350 GeV. A steady source of ultra-high-energy cosmic ray protons or photons would be expected to produce a gamma-ray flux above this level. An upper limit was also set for the flux of TeV gamma-rays from 3C 147, the most prominent active galactic nucleus in the error box.

Published
2003

34. Search for TeV emissions from pulsars in binary systems

Author

Hall, T. A., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carson, M. J., Carter-Lewis, D. A., Catanese, M., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hillas, A. M., Horan, D., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krennrich, F., Lang, M. J., LeBohec, S., Lessard, R., Lloyd-Evans, J., McKernan, B., Moriarty, P., Muller, D., Ong, R., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Weekes, T. C., Hall, T. A., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carson, M. J., Carter-Lewis, D. A., Catanese, M., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hillas, A. M., Horan, D., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Krennrich, F., Lang, M. J., LeBohec, S., Lessard, R., Lloyd-Evans, J., McKernan, B., Moriarty, P., Muller, D., Ong, R., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., and Weekes, T. C.

Abstract

A survey of binary systems containing pulsars was conducted, with the intention of detecting Galactic sources of very high energy gamma-ray emission. Observations were carried out with the Whipple 10 m imaging atmospheric Cerenkov telescope. Standard analysis techniques were applied to these sources to search for steady, unpulsed emission. Periodic tests were also performed to search for emission correlated with both the orbital and spin phases, where appropriate. Analyses indicate that the binaries in this study do not emit detectable levels of very high energy photons within the sensitivity of our instrument. The flux upper limits presented here fail to seriously constrain emission models.

Published
2003

35. Search for high-energy gamma rays from an X-ray-selected blazar sample

Author

Perez, I. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Cui, W., Dowdall, C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R. A., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Perez, I. D., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Celik, O., Cui, W., Dowdall, C., Duke, C., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R. A., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., and Weekes, T. C.

Abstract

Our understanding of blazars has been greatly increased in recent years by extensive multiwavelength observations, particularly in the radio, X-ray, and gamma-ray regions. Over the past decade the Whipple 10 m telescope has contributed to this with the detection of five BL Lacertae objects at very high gamma-ray energies. The combination of multiwavelength data has shown that blazars follow a well-defined sequence in terms of their broadband spectral properties. Together with providing constraints on emission models, this information has yielded a means by which potential sources of TeV emission may be identified and predictions made as to their possible gamma-ray flux. We have used the Whipple telescope to search for TeV gamma-ray emission from eight objects selected from a list of such candidates. No evidence has been found for very high energy emission from the objects in our sample, and upper limits have been derived for the mean gamma-ray flux above 390 GeV. These flux upper limits are compared with the model predictions, and the implications of our results for future observations are discussed.

Published
2003

36. Detection of TeV gamma rays from the BL Lacertae object 1ES 1959+650 with the Whipple 10 meter telescope

Author

Holder, J., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Dowdall, C., Duke, C., Perez, I. D., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Holder, J., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Dowdall, C., Duke, C., Perez, I. D., Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Fortson, L., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krawczynski, H., Krennrich, F., LeBohec, S., Linton, E. T., Lloyd-Evans, J., Moriarty, P., Muller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Petry, D., Power-Mooney, B., Quinn, J., Rebillot, P., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., and Weekes, T. C.

Abstract

We present the first strong detection of very high energy gamma-rays from the close (z=0.048) X-ray-selected BL Lacertae object 1ES 1959+650. Observations were made with the Whipple 10 m telescope on Mount Hopkins, Arizona, using the atmospheric Cerenkov imaging technique. The flux between 2002 May and July was highly variable, with a mean of 0.64+/-0.03 times the steady flux from the Crab Nebula and reaching a maximum of 5 crab, with variability on timescales as short as 7 hr.

Published
2003

37. Recent Results from the VERITAS Collaboration

Author

Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Muller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Weekes, T. C., Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Muller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., and Weekes, T. C.

Abstract

A decade after the discovery of TeV gamma-rays from the blazar Mrk 421 (Punch et al. 1992), the list of TeV blazars has increased to five BL Lac objects: Mrk 421 (Punch et al. 1992; Petry et al. 1996; Piron et al. 2001), Mrk 501 (Quinn et al. 1996; Aharonian et al. 1999; Djannati-Atai et al. 1999), 1ES2344+514 (Catanese et al. 1998), H1426+428 (Horan et al. 2000, 2002; Aharonian et al. 2002; Djannati-Atai et al. 2002) and 1ES1959+650 (Nishiyama et al. 1999; Konopelko et al. 2002; Holder et al. 2002). In this paper we report results from recent observations of Mrk 421, H1426+428 and 1ES1959+650 using the Whipple Observatory 10 m telescope., Comment: The Universe Viewed in Gamma-Rays proceedings

Published
2002

38. The TeV spectrum of H1426+428

Author

Petry, D., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Duke, C., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krennrich, F., LeBohec, S., Moriarty, P., Müller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Power-Mooney, B., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Petry, D., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Duke, C., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krennrich, F., LeBohec, S., Moriarty, P., Müller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Power-Mooney, B., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., and Weekes, T. C.

Abstract

The BL Lac object H1426+428 was recently detected as a high energy gamma-ray source by the VERITAS collaboration (Horan et al. 2002). We have reanalyzed the 2001 portion of the data used in the detection in order to examine the spectrum of H1426+428 above 250 GeV. We find that the time-averaged spectrum agrees with a power law of the shape dF/dE = 10^(-7.31 +- 0.15(stat) +- 0.16(syst)) x E^(-3.50 +- 0.35(stat) +- 0.05(syst)) m^(-2)s^(-1)TeV^(-1) The statistical evidence from our data for emission above 2.5 TeV is 2.6 sigma. With 95% c.l., the integral flux of H1426+428 above 2.5 TeV is larger than 3% of the corresponding flux from the Crab Nebula. The spectrum is consistent with the (non-contemporaneous) measurement by Aharonian et al. (2002) both in shape and in normalization. Below 800 GeV, the data clearly favours a spectrum steeper than that of any other TeV Blazar observed so far indicating a difference in the processes involved either at the source or in the intervening space., Comment: LaTeX, 8 pages, 4 figures, accepted for publication in ApJ

Published
2002
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39. Discovery of Spectral Variability of Markarian 421 at TeV Energies

Author

Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Müller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Weekes, T. C., Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Müller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., and Weekes, T. C.

Abstract

The detection of spectral variability of the gamma-ray blazar Mrk 421 at TeV energies is reported. Observations with the Whipple Observatory 10m gamma-ray telescope taken in 2000/2001 revealed exceptionally strong and long-lasting flaring activity. Flaring levels of 0.4 to 13 times that of the Crab Nebula flux provided sufficient statistics for a detailed study of the energy spectrum between 380 GeV and 8.2 TeV as a function of flux level. These spectra are well described by a power law with an exponential cutoff. There is no evidence for variation in the cutoff energy with flux, and all spectra are consistent with an average value for the cutoff energy of 4.3 TeV. The spectral index varies between 1.89 in a high flux state and 2.72 in a low state. The correlation between spectral index and flux is tight when averaging over the total 2000/2001 data set. Spectral measurements of Mrk~421 from previous years (1995/96 and 1999) by the Whipple collaboration are consistent with this flux-spectral index correlation, which suggest that this may be a constant or a long-term property of the source. If a similar flux-spectral index correlation were found for other gamma-ray blazars, this universal property could help disentangle the intrinsic emission mechanism from external absorption effects., Comment: 24 pages, 3 figures, submitted May 20 2002, accepted for publication in the Astrophysical Journal Letters

Published
2002
Full Text
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40. Recent Results from the VERITAS Collaboration

Author

Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Muller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Weekes, T. C., Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Muller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., and Weekes, T. C.

Abstract

A decade after the discovery of TeV gamma-rays from the blazar Mrk 421 (Punch et al. 1992), the list of TeV blazars has increased to five BL Lac objects: Mrk 421 (Punch et al. 1992; Petry et al. 1996; Piron et al. 2001), Mrk 501 (Quinn et al. 1996; Aharonian et al. 1999; Djannati-Atai et al. 1999), 1ES2344+514 (Catanese et al. 1998), H1426+428 (Horan et al. 2000, 2002; Aharonian et al. 2002; Djannati-Atai et al. 2002) and 1ES1959+650 (Nishiyama et al. 1999; Konopelko et al. 2002; Holder et al. 2002). In this paper we report results from recent observations of Mrk 421, H1426+428 and 1ES1959+650 using the Whipple Observatory 10 m telescope., Comment: The Universe Viewed in Gamma-Rays proceedings

Published
2002

41. Discovery of Spectral Variability of Markarian 421 at TeV Energies

Author

Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Müller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Weekes, T. C., Krennrich, F., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., Moriarty, P., Müller, D., Ong, R. A., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., and Weekes, T. C.

Abstract

The detection of spectral variability of the gamma-ray blazar Mrk 421 at TeV energies is reported. Observations with the Whipple Observatory 10m gamma-ray telescope taken in 2000/2001 revealed exceptionally strong and long-lasting flaring activity. Flaring levels of 0.4 to 13 times that of the Crab Nebula flux provided sufficient statistics for a detailed study of the energy spectrum between 380 GeV and 8.2 TeV as a function of flux level. These spectra are well described by a power law with an exponential cutoff. There is no evidence for variation in the cutoff energy with flux, and all spectra are consistent with an average value for the cutoff energy of 4.3 TeV. The spectral index varies between 1.89 in a high flux state and 2.72 in a low state. The correlation between spectral index and flux is tight when averaging over the total 2000/2001 data set. Spectral measurements of Mrk~421 from previous years (1995/96 and 1999) by the Whipple collaboration are consistent with this flux-spectral index correlation, which suggest that this may be a constant or a long-term property of the source. If a similar flux-spectral index correlation were found for other gamma-ray blazars, this universal property could help disentangle the intrinsic emission mechanism from external absorption effects., Comment: 24 pages, 3 figures, submitted May 20 2002, accepted for publication in the Astrophysical Journal Letters

Published
2002
Full Text
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42. The TeV spectrum of H1426+428

Author

Petry, D., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Duke, C., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krennrich, F., LeBohec, S., Moriarty, P., Müller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Power-Mooney, B., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., Weekes, T. C., Petry, D., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Cui, W., Duke, C., Perez, I. de la Calle, Falcone, A., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gammell, S., Hall, J., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Krennrich, F., LeBohec, S., Moriarty, P., Müller, D., Nagai, T. N., Ong, R., Page, M., Pallassini, R., Power-Mooney, B., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Schroedter, M., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Walker, G., and Weekes, T. C.

Abstract

The BL Lac object H1426+428 was recently detected as a high energy gamma-ray source by the VERITAS collaboration (Horan et al. 2002). We have reanalyzed the 2001 portion of the data used in the detection in order to examine the spectrum of H1426+428 above 250 GeV. We find that the time-averaged spectrum agrees with a power law of the shape dF/dE = 10^(-7.31 +- 0.15(stat) +- 0.16(syst)) x E^(-3.50 +- 0.35(stat) +- 0.05(syst)) m^(-2)s^(-1)TeV^(-1) The statistical evidence from our data for emission above 2.5 TeV is 2.6 sigma. With 95% c.l., the integral flux of H1426+428 above 2.5 TeV is larger than 3% of the corresponding flux from the Crab Nebula. The spectrum is consistent with the (non-contemporaneous) measurement by Aharonian et al. (2002) both in shape and in normalization. Below 800 GeV, the data clearly favours a spectrum steeper than that of any other TeV Blazar observed so far indicating a difference in the processes involved either at the source or in the intervening space., Comment: LaTeX, 8 pages, 4 figures, accepted for publication in ApJ

Published
2002
Full Text
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43. Cutoff in the TeV Energy Spectrum of Markarian 421 During Strong Flares in 2001

Author

Krennrich, F., Badran, H. M., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cui, W., Dunlea, S., Das, D., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., McKernan, B., Moriarty, P., Müller, D., Ong, R., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Weekes, T. C., Krennrich, F., Badran, H. M., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cui, W., Dunlea, S., Das, D., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., McKernan, B., Moriarty, P., Müller, D., Ong, R., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., and Weekes, T. C.

Abstract

Exceptionally strong and long lasting flaring activity of the blazar Markarian 421 (Mrk 421) occurred between January and March 2001. Based on the excellent signal-to-noise ratio of the data we derive the energy spectrum between 260 GeV - 17 TeV with unprecedented statistical precision. The spectrum is not well described by a simple power law even with a curvature term. Instead the data can be described by a power law with exponential cutoff: $\rm {{dN}\over{dE}} \propto \rm E^{-2.14 \pm 0.03_{stat}} \times e^{-E/E_{0}} m^{-2} s^{-1} TeV^{-1}$ with $\rm E_{0} = 4.3 \pm 0.3_{stat} TeV$. Mrk 421 is the second $\gamma$-ray blazar that unambiguously exhibits an absorption-like feature in its spectral energy distribution at 3-6 TeV suggesting that this may be a universal phenomenon, possibly due to the extragalactic infra-red background radiation., Comment: 14 pages, 3 figures, submitted to ApJL

Published
2001
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44. Cutoff in the TeV Energy Spectrum of Markarian 421 During Strong Flares in 2001

Author

Krennrich, F., Badran, H. M., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cui, W., Dunlea, S., Das, D., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., McKernan, B., Moriarty, P., Müller, D., Ong, R., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., Weekes, T. C., Krennrich, F., Badran, H. M., Bond, I. H., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cui, W., Dunlea, S., Das, D., Perez, I. de la Calle, Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gibbs, K., Gillanders, G. H., Hall, T. A., Hillas, A. M., Holder, J., Horan, D., Jordan, M., Kertzman, M., Kieda, D., Kildea, J., Knapp, J., Kosack, K., Lang, M. J., LeBohec, S., McKernan, B., Moriarty, P., Müller, D., Ong, R., Pallassini, R., Petry, D., Quinn, J., Reay, N. W., Reynolds, P. T., Rose, H. J., Sembroski, G. H., Sidwell, R., Stanton, N., Swordy, S. P., Vassiliev, V. V., Wakely, S. P., and Weekes, T. C.

Abstract

Exceptionally strong and long lasting flaring activity of the blazar Markarian 421 (Mrk 421) occurred between January and March 2001. Based on the excellent signal-to-noise ratio of the data we derive the energy spectrum between 260 GeV - 17 TeV with unprecedented statistical precision. The spectrum is not well described by a simple power law even with a curvature term. Instead the data can be described by a power law with exponential cutoff: $\rm {{dN}\over{dE}} \propto \rm E^{-2.14 \pm 0.03_{stat}} \times e^{-E/E_{0}} m^{-2} s^{-1} TeV^{-1}$ with $\rm E_{0} = 4.3 \pm 0.3_{stat} TeV$. Mrk 421 is the second $\gamma$-ray blazar that unambiguously exhibits an absorption-like feature in its spectral energy distribution at 3-6 TeV suggesting that this may be a universal phenomenon, possibly due to the extragalactic infra-red background radiation., Comment: 14 pages, 3 figures, submitted to ApJL

Published
2001
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45. Gamma-ray Observations of the Galactic Plane at Energies E > 500 GeV

Author

LeBohec, S., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Hall, T. A., Hillas, A. M., Horan, D., Knapp, J., Krennrich, F., Lessard, R. W., Macomb, D., Masterson, C., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Vassiliev, V. V., Weekes, T. C., LeBohec, S., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Hall, T. A., Hillas, A. M., Horan, D., Knapp, J., Krennrich, F., Lessard, R. W., Macomb, D., Masterson, C., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Vassiliev, V. V., and Weekes, T. C.

Abstract

In 1998 and 1999 the Whipple Observatory 10 m telescope was used to search for diffuse gamma ray emission from the Galactic Plane. No signifiant evidence of emission was found. Assuming the TeV emission profile matches EGRET observations above 1 GeV with a differential spectral index of 2.4, we derive an upper limit of {$\rm {3.0\cdot10^{-8}cm^{-2}s^{-1}sr^{-1}}$} for the average diffuse emission above {{$\rm500 GeV$}} in the galactic latitude range from {{$\rm-2^o$ to $\rm +2^o$}} at galactic longitude {{$\rm 40^o$}}. Comparisons with EGRET observations provide a lower limit of 2.31 for the differential spectral index of the diffuse emission, assuming there is no break in the spectrum between 30 GeV and 500 GeV. This constrains models for diffuse emission with a significant inverse Compton contribution., Comment: 18 pages, 9 figures, other comments

Published
2000
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46. Gamma-ray Observations of the Galactic Plane at Energies E > 500 GeV

Author

LeBohec, S., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Hall, T. A., Hillas, A. M., Horan, D., Knapp, J., Krennrich, F., Lessard, R. W., Macomb, D., Masterson, C., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Vassiliev, V. V., Weekes, T. C., LeBohec, S., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Dunlea, S., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Hall, T. A., Hillas, A. M., Horan, D., Knapp, J., Krennrich, F., Lessard, R. W., Macomb, D., Masterson, C., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Vassiliev, V. V., and Weekes, T. C.

Abstract

In 1998 and 1999 the Whipple Observatory 10 m telescope was used to search for diffuse gamma ray emission from the Galactic Plane. No signifiant evidence of emission was found. Assuming the TeV emission profile matches EGRET observations above 1 GeV with a differential spectral index of 2.4, we derive an upper limit of {$\rm {3.0\cdot10^{-8}cm^{-2}s^{-1}sr^{-1}}$} for the average diffuse emission above {{$\rm500 GeV$}} in the galactic latitude range from {{$\rm-2^o$ to $\rm +2^o$}} at galactic longitude {{$\rm 40^o$}}. Comparisons with EGRET observations provide a lower limit of 2.31 for the differential spectral index of the diffuse emission, assuming there is no break in the spectrum between 30 GeV and 500 GeV. This constrains models for diffuse emission with a significant inverse Compton contribution., Comment: 18 pages, 9 figures, other comments

Published
2000
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47. Search for Pulsed TeV Gamma-ray Emission from the Crab Pulsar

Author

Lessard, R. W., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., D'Vali, M., Fegan, D. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hall, T., Hillas, A. M., Krennrich, F., Lang, M. J., Masterson, C., Moriarty, P., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Srinivasan, R., Vassiliev, V. V., Weekes, T. C., Lessard, R. W., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., D'Vali, M., Fegan, D. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hall, T., Hillas, A. M., Krennrich, F., Lang, M. J., Masterson, C., Moriarty, P., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Srinivasan, R., Vassiliev, V. V., and Weekes, T. C.

Abstract

We present the results of a search for pulsed TeV emission from the Crab pulsar using the Whipple Observatory's 10 m gamma-ray telescope. The direction of the Crab pulsar was observed for a total of 73.4 hours between 1994 November and 1997 March. During this period the Whipple 10 m telescope was operated at its lowest energy threshold to date. Spectral analysis techniques were applied to search for the presence of a gamma-ray signal from the Crab pulsar over the energy band 250 GeV to 4 TeV. We do not see any evidence of the 33 ms pulsations present in other energy bands from the Crab pulsar. The 99.9% confidence level upper limit for pulsed emission above 250 GeV is derived to be 4.8x10^-12 cm^-2 s^-1 or <3% of the steady flux from the Crab Nebula. These results imply a sharp cut-off of the power-law spectrum seen by the EGRET instrument on the Compton Gamma-Ray Observatory. If the cut-off is exponential, it must begin at 60 GeV or lower to accommodate these upper limits., Comment: 20 pages including 6 figures, accepted for publication in the Astrophysical Journal

Published
1999
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48. A Search for Pulsed TeV Gamma Ray Emission from the Crab Pulsar

Author

Burdett, A. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hall, T. A., Hillas, A. M., Kildea, J., Knapp, J., Krennrich, F., Lang, M. J., LeBohec, S., Lessard, R. W., Masterson, C., Moriarty, P., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Srinivasan, R., Vassiliev, V. V., Weekes, T. C., Burdett, A. M., Bond, I. H., Boyle, P. J., Bradbury, S. M., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., D'Vali, M., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Gillanders, G. H., Hall, T. A., Hillas, A. M., Kildea, J., Knapp, J., Krennrich, F., Lang, M. J., LeBohec, S., Lessard, R. W., Masterson, C., Moriarty, P., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Srinivasan, R., Vassiliev, V. V., and Weekes, T. C.

Abstract

We present the results of a search for pulsed TeV emission from the Crab pulsar using the Whipple Observatory's 10m gamma-ray telescope. The direction of the Crab pulsar was observed for a total of 73.4 hours between 1994 November and 1997 March. Spectral analysis techniques were applied to search for the presence of a gamma-ray signal from the Crab pulsar over the energy band 250GeV to 4TeV. At these energies we do not see any evidence of the 33ms pulsations present at lower energies from the Crab pulsar. The 99.9% confidence level upper limit for pulsed emission above 250GeV is derived to be 4.8 10^-12 cm^-2 s^-1 or <3% of the steady flux from the Crab Nebula. These results imply a sharp cut-off of the power-law spectrum seen by the EGRET instrument on the Compton Gamma-Ray Observatory. If the cut-off is exponential, it must begin at 60GeV or lower to accommodate these upper limits., Comment: 4 pages, 2 figures, to be published in the proceedings of 26th International Cosmic Ray Conference (Salt Lake City, 1999)

Published
1999

49. VERITAS: Performance characteristics (baseline design)

Author

Vassiliev, V. V., Carter-Lewis, D. A., Hillas, A. M., Kertzman, M. P., Knapp, J., Krennrich, F., Lessard, R. W., Rose, H. J., Sembroski, G. H., Vassiliev, V. V., Carter-Lewis, D. A., Hillas, A. M., Kertzman, M. P., Knapp, J., Krennrich, F., Lessard, R. W., Rose, H. J., and Sembroski, G. H.

Abstract

VERITAS is a proposed major ground-based gamma-ray observatory to be built at the Whipple Observatory in southern Arizona, USA. It will consist of an array of seven 10m imaging Cherenkov telescopes designed to conduct gamma-ray observations in the energy range of 50 GeV - 50 TeV. A description of the baseline VERITAS design and optimization criteria are presented. We provide basic characteristics of the array performance for observations of point sources, such as angular resolution, energy threshold, energy resolution, and integral flux sensitivity. The limiting factors of the VERITAS performance are discussed., Comment: to be published in the proceedings of the 26th ICRC (Salt Lake City, 1999)

Published
1999

50. Whipple Observations of BL Lac Objects

Author

D'Vali, M., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Hall, T. A., Hillas, A. M., Knapp, J., Krennrich, F., Bohec, S. Le, Lessard, R. W., Masterson, C., Myles, S. D., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Vassiliev, V. V., Weekes, T. C., D'Vali, M., Bond, I. H., Bradbury, S. M., Buckley, J. H., Burdett, A. M., Carter-Lewis, D. A., Catanese, M., Cawley, M. F., Fegan, D. J., Fegan, S. J., Finley, J. P., Gaidos, J. A., Hall, T. A., Hillas, A. M., Knapp, J., Krennrich, F., Bohec, S. Le, Lessard, R. W., Masterson, C., Myles, S. D., Quinn, J., Rose, H. J., Samuelson, F. W., Sembroski, G. H., Vassiliev, V. V., and Weekes, T. C.

Abstract

Only BL Lac objects have been detected as extragalactic sources of very high energy (E > 300 GeV) gamma rays. Using the Whipple Observatory Gamma-ray Telescope, we have attempted to detect more BL Lacs using three approaches. First, we have conducted surveys of nearby BL Lacs, which led to the detections of Mrk 501 and 1ES 2344+514. Second, we have observed X-ray bright BL Lacs when the RXTE All-Sky Monitor identifies high state X-ray emission in an object, in order to efficiently detect extended high emission states. Third, we have conducted rapid observations of several BL Lacs and QSOs located close together in the sky to search for very high flux, short time-scale flare states such as have been seen from Mrk 421. We will present the results of a survey using the third observational technique., Comment: 4 pages, 2 figures, to be published in the proceedings of 26th International Cosmic Ray Conference (Salt Lake City, 1999)

Published
1999

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