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 H.E.S.S. gamma-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 deg. around the position (RA = 08h 35m 00s, dec = -45 deg. 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 = 1.45 +/- 0.09(stat) +/- 0.2(sys) and an exponential cutoff at an energy of 13.8 +/- 2.3(stat) +/- 4.1(sys) TeV. The integral flux above 1 TeV is (1.28 +/- 0.17 (stat) +/- 0.38(sys)) x 10^{-11} cm^{-2} s^{-1}. This result is the first clear measurement of a peak in the spectral energy distribution from a VHE gamma-ray source, likely related to inverse Compton emission. A fit of an Inverse Compton model to the H.E.S.S. spectral energy distribution gives a total energy in non-thermal electrons of ~2 x 10^{45} 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.
Highlights
The region surrounding the Vela supernova remnant (SNR) is very well studied across the electromagnetic spectrum and contains a number of complex objects, including the SNR RX J0852.0−4622, which has been previously detected in the very high energy γ-ray (VHE) range (Katagiri et al 2005; Aharonian et al 2005b)
A region of extended γ-ray emission is detected, to the south of the pulsar position (previously reported by Khélifi et al (2005). This region was previously observed by the CANGAROO collaboration (Yoshikoshi et al 1997) and emission of VHE γ-rays was claimed from a source 0.13◦ to the southeast of the pulsar
As the distance to the pulsar is well measured, one can estimate the size of the emission region seen by HESS to be 5.1 parsec along the major axis by 3.8 parsec
Summary
The region surrounding the Vela supernova remnant (SNR) is very well studied across the electromagnetic spectrum and contains a number of complex objects, including the SNR RX J0852.0−4622, which has been previously detected in the very high energy γ-ray (VHE) range (Katagiri et al 2005; Aharonian et al 2005b). For offset PWN as a result of SNR expansion into an inhomogeneous medium (Blondin et al 2001), of which G18.0-0.7 served as a second example (Gaensler et al 2003) This second PWN was recently identified with VHE source −46.5. We discuss observations of the Vela pulsar and the centre of the Vela SNR with HESS, including the Vela X feature. A region of extended γ-ray emission is detected, to the south of the pulsar position (previously reported by Khélifi et al (2005). This region was previously observed by the CANGAROO collaboration (Yoshikoshi et al 1997) and emission of VHE γ-rays was claimed from a source 0.13◦ to the southeast of the pulsar.
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