D. J. Fegan

Vanuatu Cultural Centre

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

T. C. Weekes

Center for Astrophysics Harvard & Smithsonian

183

A. M. Hillas

University of Leeds

166

M. F. Cawley

Emory University

164

R. C. Lamb

East Carolina University

132

J. A. Gaidos

University of New Hampshire

127

D. A. Carter‐Lewis

Iowa State University

113

J. Quinn

University College Dublin

110

H. J. Rose

University of Liverpool

105

F. Krennrich

Iowa State University

102

P. T. Reynolds

Munster Technological University

101

Cooperative Institutions

Center for Astrophysics Harvard & Smithsonian

University College Dublin

Universidad Veritas

Iowa State University

Goddard Space Flight Center

University of Leeds

Centre National de la Recherche Scientifique

Purdue University West Lafayette

University of Michigan–Ann Arbor

University of Delaware

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

A Search for Correlations of TeV Gamma Rays with Ultra–High‐Energy Cosmic Rays

The Astrophysical Journal (2003)

C. Akerlof S. D. Biller P. Boyle J. Buckley D. A. Carter‐Lewis

A search was conducted for TeV γ-rays emitted from the direction of the ultra-high-energy cosmic ray detected by the Fly's Eye experiment with energy E ~ 3 × 1020 eV. No enhancement was found at a level of 10-10γ 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 γ-ray flux above this level. An upper limit was also set for the flux of TeV γ-rays from 3C 147, the most prominent active galactic nucleus in the error box.

Photon flux

10.1086/367825

Cite

Citations (4)

Detection of TeV gamma rays from the AGN Markarian 421

AIP conference proceedings (1993)

M. Schubnell C. Akerlof M. F. Cawley M. Chantell D. J. Fegan

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation M. Schubnell, C. W. Akerlof, M. F. Cawley, M. Chantell, D. J. Fegan, S. Fennell, K. S. O'Flaherty, J. A. Gaidos, J. Hagan, A. M. Hillas, Y. Jiang, A. D. Kerrick, R. C. Lamb, M. A. Lawrence, D. A. Lewis, D. I. Meyer, G. Mohanty, M. Punch, P. T. Reynolds, A. C. Rovero, G. Sembroski, T. C. Weekes, T. Whitaker, C. Wilson, The Whipple Colloboration; Detection of TeV gamma rays from the AGN Markarian 421. AIP Conf. Proc. 15 June 1993; 276 (1): 185–189. https://doi.org/10.1063/1.43879 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

10.1063/1.43879

Cite

Citations (1)

Short timescale variability in the broadband emission of the blazars Mkn421 and Mkn501

Astroparticle Physics (2000)

Barry McKernan M. Carson T. Yaqoob D. J. Fegan

10.1016/s0927-6505(00)00107-9

Cite

Citations (0)

First Results from a Search for TeV Emission from BL Lacs Out to Z = 0.2.

ICRC (1997)

M. Catanese P. J. Boyle A. M. Burdett J. Bussöns Gordo J. H. Buckley

Two active galactic nuclei have been detected at TeV energies using the atmospheric Cerenkov imaging technique. The Whipple Observatory γ-ray telescope has been used to observe all the BL Lacertae objects in the northern hemisphere out to a redshift of 0.1. We report the tentative detection of VHE emission from a third BL Lac object, 1ES 2344+514. Progress in extending this survey out to z=0.2 will also be reported. INTRODUCTION With the detection of very high energy (VHE, E > 250 GeV) emission from the two BL Lacertae objects (BL Lacs) , Markarian 421 (Mrk 421) (Punch et al. 1992) and Mrk 501 (Quinn et al. 1996), we began a survey of nearby BL Lacs to search for VHE emission. A collection of such sources could lead to constraintes on γ-ray emission models through investigation into the properties which are important for VHE emission and also an estimate of the density of extragalactic background IR light through its effect on the VHE γ-ray spectra (Gould and Schreder 1967; Stecker, de Jager, & Salamon 1993). BL Lacs are blazars, the only type of active galactic nucleus (AGN) detected above 100 MeV. The electromagnetic spectrum of blazars consists of synchrotron emission, which spans radio to UV or X-ray wavelengths, produced by electrons moving within jets oriented at small angles to our line of sight (Blandford & Konigl 1981), and a high energy part which can extend to γ-ray energies. Models of the high energy emission fall into three main categories: synchrotron self-Compton emission (e.g., Konigl 1981), inverse-Compton scattering of low energy photons arising outside the jet (e.g., Sikora, Begelman, and Rees 1994), and pair cascades initiated by protons (Mannheim 1993) or electrons. If protons produce the high energy emission, AGN could contribute significantly to the highest energy cosmic-ray flux (E > 1018eV) (Rachen, Stanev, and Biermann 1993). BL Lacs are particularly promising candidates for VHE emission because of two aspects of their low energy emission. First, BL Lacs may have less γ-ray absorbing material near the source because they have weak or no emission lines in their optical spectra (Dermer and Schlickeiser 1994). Second, in inverse Compton (IC) models of the high energy emission, the extension of the synchrotron emission of X-ray selected BL Lacs (e.g., Mrk 421 and Mrk 501) into the X-ray waveband implies a higher maximum γ-ray energy than for radio-loud BL Lacs (e.g., W Comae) and flat spectrum radio quasars (e.g., 3C 279) where the synchrotron emission ends in the optical to UV range. Table 1 lists the objects observed in our BL Lac survey so far. We have limited our search to BL Lacs with z 350 GeV) = 8.7× 10−11 photons cm−2 s−1 (Hillas et al. 1997). This procedure assumes that the Crab Nebula VHE γ-ray flux is constant, as 7 years of Whipple Observatory data indicate (Hillas et al. 1997), and that the object’s photon spectrum is identical to that of the Crab Nebula between 0.3 and 10 TeV, dN/dE ∝ E−2.4 (Hillas et al. 1997), which may not be the case. If no significant emission is seen from a candidate source, a 99.9% confidence upper limit is calculated using the method of Helene (1983). RESULTS In Table 1 we present the results of observations for which the analysis has been completed. With the exception of 1ES 2344+514, there is no evidence of emission from any of the objects in this survey. In particular, the EGRET sources W Comae (von Montigny et al. 1995) and BL Lacertae (Catanese et al. 1997a) are not detected despite long exposures. Also, only 1ES 2344+514 shows evidence of short term activity. Most of the excess from 1ES 2344+514 during 1995 comes from an apparent flare on 1995 December 20 (see Figure 1). We find a non-statistically significant excess from this object in 1996 which could simply mean that the average flux level dropped below the telescope sensitivity limit, as occasionally happens with Mrk 421 (Buckley et al. 1996). We currently consider the detection tentative because we see no evidence for a consistent signal nor is there independent confirmation of a high state for this object (e.g., from X-ray observations) during this period. Max. Observ. Exp. Daily Flux Object z Typea Epoch (hrs) Excess Exc. (Crab)b Fluxc 1ES 2344+514 0.044 X 1995/96 20.5 5.3σ 6.0σ 0.16±0.03 1.4±0.3 20-12-95 1.8 6.0σ 0.63±0.11 5.5±1.

BL Lac object

Extragalactic background light

Source

Cite

Citations (2)

VERITAS: Very LArge Energetic Radiation Imaging Telescope Array System

arXiv (Cornell University) (1997)

T. C. Weekes C. Akerlof S. D. Biller A. C. Breslin J. Buckley

A next generation atmospheric Cherenkov observatory is described based on the Whipple Observatory $\gamma$-ray telescope. A total of nine such imaging telescopes will be deployed in an array that will permit the maximum versatility and give high sensitivity in the 50 GeV - 50 TeV band (with maximum sensitivity from 100 GeV to 10 TeV).

Cherenkov Telescope Array

Source

Cite

Citations (1)

Results of a Three Year Search for Bursts of High Energy Gamma Rays Using Widely Spaced Cosmic Ray Stations

International Cosmic Ray Conference (1979)

D. J. Fegan B. McBreen Colm O’Sullivan

High energy

Source

Cite

Citations (0)

TeV Observations of Her X-l at the Whipple Observatory: 1984–1985