First detection of a VHE gamma-ray spectral maximum from a cosmic source: HESS discovery of the Vela X nebula

Abstract

The Vela supernova remnant (SNR) is a complex region containing a number of sources of non-thermal radiation. The inner section of this SNR, within 2 degrees of the pulsar PSR B0833-45, has been observed by the HESS γ-ray atmospheric Cherenkov detector in 2004 and 2005. A strong signal is seen from an extended region to the south of the pulsar, within an integration region of radius 0.8° around the position (α = 08h 35m 00s, δ = –45° 36′ J2000.0). The excess coincides with a region of hard X-ray emission seen by the ROSAT and ASCA satellites. The observed energy spectrum of the source between 550 GeV and 65 TeV is well fit by a power law function with photon index Γ = 1.45 ± 0.09 stat ± 0.2sys and an exponential cutoff at an energy of 13.8 ± 2.3stat ± 4.1sys TeV. The integral flux above 1 TeV is (1.28 ± 0.17stat ± 0.38sys) × 10-11cm-2 s-1. This result is the first clear measurement of a peak in the spectral energy distribution from a VHE γ-ray source, likely related to inverse Compton emission. A fit of an Inverse Compton model to the HESS spectral energy distribution gives a total energy in non-thermal electrons of ~2 × 1045 erg between 5 TeV and 100 TeV, assuming a distance of 290 parsec to the pulsar. The best fit electron power law index is 2.0, with a spectral break at 67 TeV.

Astronomy & Astrophysics 448, L43-L47 (2006)
ArXiv pre-print

Auxiliary informations

Figure 1

Fits file for Fig. 1

H.E.S.S. data points for Figure 3

Mean energy     Flux      Flux Error
  [TeV]    [/TeV cm^2 s] [/TeV cm^2 s]
   0.727   1.86e-11       3.93e-12
   1.06    8.09e-12       1.44e-12
   1.56    4.5e-12        5.74e-13
   2.28    2.9e-12        2.6e-13
   3.34    1.31e-12       1.31e-13
   4.9     6.97e-13       6.92e-14
   7.18    3.34e-13       3.56e-14
   10.5    1.78e-13       1.89e-14
   15.4    7.49e-14       8.97e-15
   22.4    2.17e-14       4.26e-15
   32.9    4.12e-15       1.64e-15
   48.1    3.03e-15       1.12e-15

Remarks: Statistical errors only. Systematic error on energy scale estimated to 20%. See paper for details.

Table of Contents