CRAB NEBULA: FIVE-YEAR OBSERVATION WITH ARGO-YBJ

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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 ∼3.3×10^5 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)^{−α}, with a flux normalization I_0 = (5.2±0.2)×10−12 photons cm−2 s−1 TeV−1 and α=2.63±0.05, corresponding to an integrated flux above 1 TeV of 1.97×10−11 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/2TeV)^{−α} 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 7.3×10−2. A correlated analysis with Fermi-LAT data over ∼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.

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  • B. Bartoli , P. Bernardini , X. J. Bi , P. Branchini , A. Budano , P. Camarri , Z. Cao , R. Cardarelli , S. Catalanotti , S. Z. Chen , T. L. Chen , P. Creti , S. W. Cui , B. Z. Dai , A. D'Amone , Danzengluobu , I. De Mitri , B. D'Ettorre Piazzoli , T. Di Girolamo , G. Di Sciascio , C. F. Feng , Zhaoyang Feng , Zhenyong Feng , Q. B. Gou , Y. Q. Guo , H. H. He , Haibing Hu , Hongbo Hu , M. Iacovacci , R. Iuppa , H. Y. Jia , Labaciren , H. J. Li , G. Liguori , C. Liu , J. Liu , M. Y. Liu , H. Lu , L. L. Ma , X. H. Ma , G. Mancarella , S. M. Mari , G. Marsella , D. Martello , S. Mastroianni , P. Montini , C. C. Ning , M. Panareo , L. Perrone , P. Pistilli , F. Ruggieri , P. Salvini , R. Santonico , P. R. Shen , X. D. Sheng , F. Shi , A. Surdo , Y. H. Tan , P. Vallania , S. Vernetto , C. Vigorito , H. Wang , C. Y. Wu , H. R. Wu , L. Xue , Q. Y. Yang , X. C. Yang , Z. G. Yao , A. F. Yuan , M. Zha , H. M. Zhang , L. Zhang , X. Y. Zhang , Y. Zhang , J. Zhao , Zhaxiciren , Zhaxisangzhu , X. X. Zhou , F. R. Zhu , Q. Q. Zhu , G. Zizzi , E. Striani

Titolo volume/Rivista

THE ASTROPHYSICAL JOURNAL

Anno di pubblicazione

2015

ISSN

1538-4357

ISBN

Non Disponibile

Numero di citazioni Wos

Nessuna citazione

Ultimo Aggiornamento Citazioni

Non Disponibile

Numero di citazioni Scopus

16

Ultimo Aggiornamento Citazioni

28/04/2018

Settori ERC

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Codici ASJC

Non Disponibile