The ARGO-YBJ air shower detector monitored the Crab Nebula gamma-ray emission from 2007 November to 2013 February. The integrated signal, consisting of similar to 3.3 x 10(5) events, reached the statistical significance of 21.1 standard deviations. The obtained energy spectrum in the energy range 0.3-20 TeV can be described by a power law function dN/dE = I-0 (E/2TeV)(-alpha), with a flux normalization I-0 = (5.2 +/- 0.2) x 10(-12) photons cm(-2) s(-1) TeV (1) and alpha = 2.63 +/- 0.05, corresponding to an integrated flux above 1 TeV of 1.97 x 10(-11) photons cm(-2) s(-1). The systematic error is estimated to be less than 30% for the flux normalization and 0.06 for the spectral index. Assuming a power law spectrum with an exponential cutoff dN/dE = I-0 (E/2 TeV)(-alpha) exp (-E/E-cut), the lower limit of the cutoff energy E-cut is 12 TeV, at 90% confidence level. Our extended data set allows the study of the TeV emission over long timescales. Over five years, the light curve of the Crab Nebula in 200-day bins is compatible with a steady emission with a probability of 7.3 x 10(-2). A correlated analysis with Fermi-LAT data over similar to 4.5 yr using the light curves of the two experiments gives a Pearson correlation coefficient r = 0.56 +/- 0.22. Concerning flux variations on timescales of days, a "blind" search for flares with a duration of 1-15 days gives no excess with a significance higher than four standard deviations. The average rate measured by ARGO-YBJ during the three most powerful flares detected by Fermi-LAT is 205 +/- 91 photons day(-1), consistent with the average value of 137 +/- 10 day(-1).

Bartoli, B., Bernardini, P., Bi, X.J., Branchini, P., Budano, A., Camarri, P., et al. (2015). CRAB NEBULA: FIVE-YEAR OBSERVATION WITH ARGO-YBJ. THE ASTROPHYSICAL JOURNAL, 798(2), 119 [10.1088/0004-637x/798/2/119].

CRAB NEBULA: FIVE-YEAR OBSERVATION WITH ARGO-YBJ

P. Branchini;A. Budano;S. M. Mari;P. Montini;P. Pistilli;F. Ruggieri;
2015-01-01

Abstract

The ARGO-YBJ air shower detector monitored the Crab Nebula gamma-ray emission from 2007 November to 2013 February. The integrated signal, consisting of similar to 3.3 x 10(5) events, reached the statistical significance of 21.1 standard deviations. The obtained energy spectrum in the energy range 0.3-20 TeV can be described by a power law function dN/dE = I-0 (E/2TeV)(-alpha), with a flux normalization I-0 = (5.2 +/- 0.2) x 10(-12) photons cm(-2) s(-1) TeV (1) and alpha = 2.63 +/- 0.05, corresponding to an integrated flux above 1 TeV of 1.97 x 10(-11) photons cm(-2) s(-1). The systematic error is estimated to be less than 30% for the flux normalization and 0.06 for the spectral index. Assuming a power law spectrum with an exponential cutoff dN/dE = I-0 (E/2 TeV)(-alpha) exp (-E/E-cut), the lower limit of the cutoff energy E-cut is 12 TeV, at 90% confidence level. Our extended data set allows the study of the TeV emission over long timescales. Over five years, the light curve of the Crab Nebula in 200-day bins is compatible with a steady emission with a probability of 7.3 x 10(-2). A correlated analysis with Fermi-LAT data over similar to 4.5 yr using the light curves of the two experiments gives a Pearson correlation coefficient r = 0.56 +/- 0.22. Concerning flux variations on timescales of days, a "blind" search for flares with a duration of 1-15 days gives no excess with a significance higher than four standard deviations. The average rate measured by ARGO-YBJ during the three most powerful flares detected by Fermi-LAT is 205 +/- 91 photons day(-1), consistent with the average value of 137 +/- 10 day(-1).
2015
Bartoli, B., Bernardini, P., Bi, X.J., Branchini, P., Budano, A., Camarri, P., et al. (2015). CRAB NEBULA: FIVE-YEAR OBSERVATION WITH ARGO-YBJ. THE ASTROPHYSICAL JOURNAL, 798(2), 119 [10.1088/0004-637x/798/2/119].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11590/440787
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