G54.1+0.3 - Discovery of VHE gamma-ray emission from a young PWN PDF Print
Smoothed excess map from G54.1+0.3, as measured by VERITAS. The gray scale indicates the number of excess gamma-ray events. See Figure 1 below for more details.



G54.1+0.3 - Discovery of VHE gamma-ray emission from a young PWN



Reference:  V. A. Acciari et al. (The VERITAS Collaboration), Astrophysical Journal Letters, 719:L69, 2010

Full text version

ArXiv version: ArXiV:1005.0032

Contact person: Ester Aliu & Scott Wakely


At the center of the SNR G54.1+0.3 lies one of the youngest and most energetic pulsars in the Galaxy: PSR J1930+1852. The confinement of the pulsar winds in the surroundings creates a pulsar wind nebula (PWN) seen in radio (Reich et al. 1985, Velusamy & Becker 1988) and X-rays (Lu et al. 2001). The first pointed observations of G54.1+0.3 with VERITAS took place during a survey of northern-hemisphere Galactic pulsars between September 2007 and October 2008. The analysis of these data revealed evidence of a VHE gamma-ray signal at the position of PSR J1930+1852 and this triggered further observations in 2009 which confirmed the signal.

VERITAS observations show a VHE gamma-ray source consistent with the pulsar position with a significance of 6.8 sigma and point-like given the resolution of the instrument. The integral flux above 1 TeV is ~ 2.5% of the Crab Nebula flux and significant emission is measured between 250 GeV and 4 TeV, well described by a power-law energy spectrum with a photon index 2.39 ± 0.23 (stat) ± 0.30 (sys). Based on the source location, morphology, measured spectrum, lack of variability and a comparison with similar systems previously detected in the TeV band, the most likely counterpart of this new VHE gamma-ray source is the PWN in the SNR G54.+0.3.

The measured X-ray to VHE gamma-ray luminosity ratio is the lowest among all the nebulae supposedly driven by young rotation-powered pulsars,  which could indicate a particle-dominated PWN. However, the recent finding of a partial IR shell, suggested to be composed of freshly-formed ejecta dust that appears to be heated by the expanding PWN (Temim et al., 2010), could also explain the low ratio, as it could be an additional source of seed photons from the local dust which are then up-scattered to TeV energies and contribute to the observed emission. Given the association by Leahy et al. (2008) of the PWN with a molecular CO cloud, an alternative interpretation of the TeV emission from G54.1+0.3 would be radiation from the decay of neutral pions produced in the hadronic interactions between the dense target and the SNR.


Figures from paper (click to get full size image):




Last Updated on Tuesday, 21 June 2011 08:25

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