Free Access
Erratum
This article is an erratum for:
[https://doi.org/10.1051/0004-6361/202038166]


Issue
A&A
Volume 649, May 2021
Article Number C1
Number of page(s) 1
Section Astrophysical processes
DOI https://doi.org/10.1051/0004-6361/202038166e
Published online 30 April 2021

This is a corrigendum to the original article Yeung (2020) and is mostly adapted from Appendix C.4 of the author’s Ph.D. Thesis (Yeung 2021).

In Sect. 3.4 of the original article, we deduced from the power law with a scaling factor (PLSF) fitting result that Γ for P2M is lower than that for P1M. Nevertheless, the previous calculation of the significance of this difference did not consider the covariance of the Γ values for P1M and P2M (it should be noted that the spectral data for P1M and P2M are fit simultaneously such that their solutions share the same scaling factor ϵ). After taking this covariance into account, which is computed to be 0.010, we now determine that Γ for P2M is lower than that for P1M by 0.35 ± 0.08, which corresponds to ∼​4.2σ (much higher than the ∼2.1σ reported in the original paper). Additionally, Fig. 1 demonstrates that the 4σ confidence region of Γ values for P1M and P2M excludes all equal-value combinations.

thumbnail Fig. 1.

Confidence regions of Γ values for P1M and P2M. The plotted covariance contours respectively correspond to the significance levels of 1σ, 2σ, 3σ, and 4σ (from innermost to outermost). The reference line (which is black, dashed, and straight) indicates the combinations of equal Γ values.

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The revised significance strengthens the argument that the flux ratio of P1 to P2 still decreases with photon energy even above 10 GeV. This, in turn, strengthens the interpretation that there are anisotropic pulsar winds that could lead to the observed harder spectrum at P2M relative to P1M (as put forward by Aharonian et al. 2012).

Moreover, taking the statistical errors into account, the ϵ values obtained for MAGIC and VERITAS (both ∼1.22) are basically consistent with the estimated systematic errors of around 15% on energy scales of IACT telescopes under excellent atmospheric conditions (e.g., Aharonian et al. 2006; Aleksić et al. 2016). This provides further confirmation for the physical reasonableness of those fitting results.

References

  1. Aharonian, F., Akhperjanian, A. G., Bazer-Bachi, A. R., et al. 2006, A&A, 457, 899 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  2. Aharonian, F. A., Bogovalov, S. V., & Khangulyan, D. 2012, Nature, 482, 507 [Google Scholar]
  3. Aleksić, J., Ansoldi, S., Antonelli, L. A., et al. 2016, Astroparticle Physics, 72, 76 [Google Scholar]
  4. Yeung, K. H. 2021, PhD thesis, Staats-und Universitätsbibliothek Hamburg Carl von Ossietzky [Google Scholar]
  5. Yeung, P. K. H. 2020, A&A, 640, A43 [EDP Sciences] [Google Scholar]

© ESO 2021

All Figures

thumbnail Fig. 1.

Confidence regions of Γ values for P1M and P2M. The plotted covariance contours respectively correspond to the significance levels of 1σ, 2σ, 3σ, and 4σ (from innermost to outermost). The reference line (which is black, dashed, and straight) indicates the combinations of equal Γ values.

Open with DEXTER
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