Observation and spectral measurements of the crab nebula with Milagro

A. A. Abdo, B. T. Allen, R. Atkins, T. Aune, W. Benbow, D. Berley, E. Blaufuss, E. Bonamente, J. Bussons, C. Chen, G. E. Christopher, D. G. Coyne, T. Deyoung, B. L. Dingus, D. E. Dorfan, R. W. Ellsworth, A. Falcone, L. Fleysher, R. Fleysher, J. Galbraith-FrewM. M. Gonzalez, J. A. Goodman, T. J. Haines, E. Hays, C. M. Hoffman, P. H. Hüntemeyer, L. A. Kelley, B. E. Kolterman, C. P. Lansdell, J. T. Linnemann, J. McCullough, J. E. McEnery, T. Morgan, A. I. Mincer, M. F. Morales, P. Nemethy, D. Noyes, J. Pretz, J. M. Ryan, F. W. Samuelson, P. M. Saz Parkinson, A. Shoup, G. Sinnis, A. J. Smith, G. W. Sullivan, V. Vasileiou, G. P. Walker, M. Wascko, D. A. Williams, S. Westerhoff, G. B. Yodh

    Research output: Contribution to journalArticle

    Abstract

    The Crab Nebula was detected with the Milagro experiment at a statistical significance of 17 standard deviations over the lifetime of the experiment. The experiment was sensitive to approximately 100GeV-100TeV gamma-ray air showers by observing the particle footprint reaching the ground. The fraction of detectors recording signals from photons at the ground is a suitable proxy for the energy of the primary particle and has been used to measure the photon energy spectrum of the Crab Nebula between ∼1 and ∼100TeV. The TeV emission is believed to be caused by inverse-Compton upscattering of ambient photons by an energetic electron population. The location of a TeV steepening or cutoff in the energy spectrum reveals important details about the underlying electron population. We describe the experiment and the technique for distinguishing gamma-ray events from the much more-abundant hadronic events. We describe the calculation of the significance of the excess from the Crab and how the energy spectrum is fitted. The differential photon energy spectrum, including the statistical errors from the fit, obtained using a simple power-law hypothesis for data between 2005 September and 2008 March is (6.5 ± 0.4) × 10-14(E/10 TeV)-3.1±0.1(cm2 s TeV )-1 between ∼1TeV and 100TeV. Allowing for a possible exponential cutoff, the photon energy spectrum is fitted as (2.5+0.7 - 0.4) × 10-12(E/3 TeV)-2.5 ± 0.4exp (- E/32+39 - 18 TeV) (cm2 s TeV)-1. The results are subject to an 30% systematic uncertainty in the overall flux and an ∼0.1 systematic uncertainty in the power-law indices quoted. Uncertainty in the overall energy scale has been absorbed into these errors. Fixing the spectral index to values that have been measured below 1TeV by IACT experiments (2.4-2.6), the fit to the Milagro data suggests that Crab exhibits a spectral steepening or cutoff between about 20-40TeV.

    Original languageEnglish (US)
    Article number63
    JournalAstrophysical Journal
    Volume750
    Issue number1
    DOIs
    StatePublished - May 1 2012

    Fingerprint

    Crab nebula
    crab
    energy spectra
    photons
    crabs
    cut-off
    energy
    gamma rays
    experiment
    power law
    cosmic ray showers
    footprints
    fixing
    electron
    standard deviation
    electrons
    recording
    footprint
    life (durability)
    energetics

    Keywords

    • acceleration of particles
    • astroparticle physics
    • gamma rays: general
    • pulsars: individual (Crab Pulsar)

    ASJC Scopus subject areas

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

    Abdo, A. A., Allen, B. T., Atkins, R., Aune, T., Benbow, W., Berley, D., ... Yodh, G. B. (2012). Observation and spectral measurements of the crab nebula with Milagro. Astrophysical Journal, 750(1), [63]. https://doi.org/10.1088/0004-637X/750/1/63

    Observation and spectral measurements of the crab nebula with Milagro. / Abdo, A. A.; Allen, B. T.; Atkins, R.; Aune, T.; Benbow, W.; Berley, D.; Blaufuss, E.; Bonamente, E.; Bussons, J.; Chen, C.; Christopher, G. E.; Coyne, D. G.; Deyoung, T.; Dingus, B. L.; Dorfan, D. E.; Ellsworth, R. W.; Falcone, A.; Fleysher, L.; Fleysher, R.; Galbraith-Frew, J.; Gonzalez, M. M.; Goodman, J. A.; Haines, T. J.; Hays, E.; Hoffman, C. M.; Hüntemeyer, P. H.; Kelley, L. A.; Kolterman, B. E.; Lansdell, C. P.; Linnemann, J. T.; McCullough, J.; McEnery, J. E.; Morgan, T.; Mincer, A. I.; Morales, M. F.; Nemethy, P.; Noyes, D.; Pretz, J.; Ryan, J. M.; Samuelson, F. W.; Saz Parkinson, P. M.; Shoup, A.; Sinnis, G.; Smith, A. J.; Sullivan, G. W.; Vasileiou, V.; Walker, G. P.; Wascko, M.; Williams, D. A.; Westerhoff, S.; Yodh, G. B.

    In: Astrophysical Journal, Vol. 750, No. 1, 63, 01.05.2012.

    Research output: Contribution to journalArticle

    Abdo, AA, Allen, BT, Atkins, R, Aune, T, Benbow, W, Berley, D, Blaufuss, E, Bonamente, E, Bussons, J, Chen, C, Christopher, GE, Coyne, DG, Deyoung, T, Dingus, BL, Dorfan, DE, Ellsworth, RW, Falcone, A, Fleysher, L, Fleysher, R, Galbraith-Frew, J, Gonzalez, MM, Goodman, JA, Haines, TJ, Hays, E, Hoffman, CM, Hüntemeyer, PH, Kelley, LA, Kolterman, BE, Lansdell, CP, Linnemann, JT, McCullough, J, McEnery, JE, Morgan, T, Mincer, AI, Morales, MF, Nemethy, P, Noyes, D, Pretz, J, Ryan, JM, Samuelson, FW, Saz Parkinson, PM, Shoup, A, Sinnis, G, Smith, AJ, Sullivan, GW, Vasileiou, V, Walker, GP, Wascko, M, Williams, DA, Westerhoff, S & Yodh, GB 2012, 'Observation and spectral measurements of the crab nebula with Milagro', Astrophysical Journal, vol. 750, no. 1, 63. https://doi.org/10.1088/0004-637X/750/1/63
    Abdo AA, Allen BT, Atkins R, Aune T, Benbow W, Berley D et al. Observation and spectral measurements of the crab nebula with Milagro. Astrophysical Journal. 2012 May 1;750(1). 63. https://doi.org/10.1088/0004-637X/750/1/63
    Abdo, A. A. ; Allen, B. T. ; Atkins, R. ; Aune, T. ; Benbow, W. ; Berley, D. ; Blaufuss, E. ; Bonamente, E. ; Bussons, J. ; Chen, C. ; Christopher, G. E. ; Coyne, D. G. ; Deyoung, T. ; Dingus, B. L. ; Dorfan, D. E. ; Ellsworth, R. W. ; Falcone, A. ; Fleysher, L. ; Fleysher, R. ; Galbraith-Frew, J. ; Gonzalez, M. M. ; Goodman, J. A. ; Haines, T. J. ; Hays, E. ; Hoffman, C. M. ; Hüntemeyer, P. H. ; Kelley, L. A. ; Kolterman, B. E. ; Lansdell, C. P. ; Linnemann, J. T. ; McCullough, J. ; McEnery, J. E. ; Morgan, T. ; Mincer, A. I. ; Morales, M. F. ; Nemethy, P. ; Noyes, D. ; Pretz, J. ; Ryan, J. M. ; Samuelson, F. W. ; Saz Parkinson, P. M. ; Shoup, A. ; Sinnis, G. ; Smith, A. J. ; Sullivan, G. W. ; Vasileiou, V. ; Walker, G. P. ; Wascko, M. ; Williams, D. A. ; Westerhoff, S. ; Yodh, G. B. / Observation and spectral measurements of the crab nebula with Milagro. In: Astrophysical Journal. 2012 ; Vol. 750, No. 1.
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    abstract = "The Crab Nebula was detected with the Milagro experiment at a statistical significance of 17 standard deviations over the lifetime of the experiment. The experiment was sensitive to approximately 100GeV-100TeV gamma-ray air showers by observing the particle footprint reaching the ground. The fraction of detectors recording signals from photons at the ground is a suitable proxy for the energy of the primary particle and has been used to measure the photon energy spectrum of the Crab Nebula between ∼1 and ∼100TeV. The TeV emission is believed to be caused by inverse-Compton upscattering of ambient photons by an energetic electron population. The location of a TeV steepening or cutoff in the energy spectrum reveals important details about the underlying electron population. We describe the experiment and the technique for distinguishing gamma-ray events from the much more-abundant hadronic events. We describe the calculation of the significance of the excess from the Crab and how the energy spectrum is fitted. The differential photon energy spectrum, including the statistical errors from the fit, obtained using a simple power-law hypothesis for data between 2005 September and 2008 March is (6.5 ± 0.4) × 10-14(E/10 TeV)-3.1±0.1(cm2 s TeV )-1 between ∼1TeV and 100TeV. Allowing for a possible exponential cutoff, the photon energy spectrum is fitted as (2.5+0.7 - 0.4) × 10-12(E/3 TeV)-2.5 ± 0.4exp (- E/32+39 - 18 TeV) (cm2 s TeV)-1. The results are subject to an 30{\%} systematic uncertainty in the overall flux and an ∼0.1 systematic uncertainty in the power-law indices quoted. Uncertainty in the overall energy scale has been absorbed into these errors. Fixing the spectral index to values that have been measured below 1TeV by IACT experiments (2.4-2.6), the fit to the Milagro data suggests that Crab exhibits a spectral steepening or cutoff between about 20-40TeV.",
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    T1 - Observation and spectral measurements of the crab nebula with Milagro

    AU - Abdo, A. A.

    AU - Allen, B. T.

    AU - Atkins, R.

    AU - Aune, T.

    AU - Benbow, W.

    AU - Berley, D.

    AU - Blaufuss, E.

    AU - Bonamente, E.

    AU - Bussons, J.

    AU - Chen, C.

    AU - Christopher, G. E.

    AU - Coyne, D. G.

    AU - Deyoung, T.

    AU - Dingus, B. L.

    AU - Dorfan, D. E.

    AU - Ellsworth, R. W.

    AU - Falcone, A.

    AU - Fleysher, L.

    AU - Fleysher, R.

    AU - Galbraith-Frew, J.

    AU - Gonzalez, M. M.

    AU - Goodman, J. A.

    AU - Haines, T. J.

    AU - Hays, E.

    AU - Hoffman, C. M.

    AU - Hüntemeyer, P. H.

    AU - Kelley, L. A.

    AU - Kolterman, B. E.

    AU - Lansdell, C. P.

    AU - Linnemann, J. T.

    AU - McCullough, J.

    AU - McEnery, J. E.

    AU - Morgan, T.

    AU - Mincer, A. I.

    AU - Morales, M. F.

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    AU - Noyes, D.

    AU - Pretz, J.

    AU - Ryan, J. M.

    AU - Samuelson, F. W.

    AU - Saz Parkinson, P. M.

    AU - Shoup, A.

    AU - Sinnis, G.

    AU - Smith, A. J.

    AU - Sullivan, G. W.

    AU - Vasileiou, V.

    AU - Walker, G. P.

    AU - Wascko, M.

    AU - Williams, D. A.

    AU - Westerhoff, S.

    AU - Yodh, G. B.

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    N2 - The Crab Nebula was detected with the Milagro experiment at a statistical significance of 17 standard deviations over the lifetime of the experiment. The experiment was sensitive to approximately 100GeV-100TeV gamma-ray air showers by observing the particle footprint reaching the ground. The fraction of detectors recording signals from photons at the ground is a suitable proxy for the energy of the primary particle and has been used to measure the photon energy spectrum of the Crab Nebula between ∼1 and ∼100TeV. The TeV emission is believed to be caused by inverse-Compton upscattering of ambient photons by an energetic electron population. The location of a TeV steepening or cutoff in the energy spectrum reveals important details about the underlying electron population. We describe the experiment and the technique for distinguishing gamma-ray events from the much more-abundant hadronic events. We describe the calculation of the significance of the excess from the Crab and how the energy spectrum is fitted. The differential photon energy spectrum, including the statistical errors from the fit, obtained using a simple power-law hypothesis for data between 2005 September and 2008 March is (6.5 ± 0.4) × 10-14(E/10 TeV)-3.1±0.1(cm2 s TeV )-1 between ∼1TeV and 100TeV. Allowing for a possible exponential cutoff, the photon energy spectrum is fitted as (2.5+0.7 - 0.4) × 10-12(E/3 TeV)-2.5 ± 0.4exp (- E/32+39 - 18 TeV) (cm2 s TeV)-1. The results are subject to an 30% systematic uncertainty in the overall flux and an ∼0.1 systematic uncertainty in the power-law indices quoted. Uncertainty in the overall energy scale has been absorbed into these errors. Fixing the spectral index to values that have been measured below 1TeV by IACT experiments (2.4-2.6), the fit to the Milagro data suggests that Crab exhibits a spectral steepening or cutoff between about 20-40TeV.

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