CRAB NEBULA: FIVE-YEAR OBSERVATION WITH ARGO-YBJ
- Autori: B. Bartoli; BERNARDINI, Paolo; 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; D'AMONE, ANTONIO; Danzengluobu; DE MITRI, Ivan; 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; MANCARELLA, Giovanni; S. M. Mari; MARSELLA, GIOVANNI; MARTELLO, Daniele; S. Mastroianni; P. Montini; C. C. Ning; PANAREO, Marco; PERRONE, Lorenzo; 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
- Anno di pubblicazione: 2015
- Tipologia: Articolo in rivista
- OA Link: http://hdl.handle.net/10447/612153
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.