| Abstract: | Using the High Energy Spectroscopic System (H.E.S.S.) telescopes we have
discovered a steady and extended very high-energy (VHE) $gamma$-ray source
towards the luminous blue variable candidate LBV1806$-$20, massive stellar
cluster Cl*1806$-$20, and magnetar SGR1806$-$20. The new VHE source,
HESSJ1808$-$204, was detected at a statistical significance of $>6sigma$
(post-trial) with a photon flux normalisation $(2.9 pm 0.4_{
m stat} pm
0.5_{
m sys}) imes 10^{-13}$,ph,cm$^{-2}$,s$^{-1}$,TeV$^{-1}$ at 1,TeV
and a power-law photon index of $2.3pm0.2_{
m stat}pm 0.3_{
m sys}$. The
luminosity of this source (0.2 to 10 TeV; scaled to distance $d$=8.7,kpc) is
$L_{
m VHE}sim1.6 imes 10^{34}(d/{
m 8.7, kpc})^2$,erg,s$^{-1}$. The
VHE $gamma$-ray emission is extended and is well fit by a single Gaussian with
statistical standard deviation of $0.095^circ pm 0.015^circ$. This extension
is similar to that of the synchrotron radio nebula G10.0$-$0.3, which is
thought to be powered by LBV1806$-$20. The VHE $gamma$-ray luminosity could be
provided by the stellar wind luminosity of LBV1806$-$20 by itself and/or the
massive star members of Cl*1806$-$20. Alternatively, magnetic dissipation (e.g.
via reconnection) from SGR1806$-$20 can potentially account for the VHE
luminosity. The origin and hadronic and/or leptonic nature of the accelerated
particles responsible for HESSJ1808$-$204 is not yet clear. If associated with
SGR1806$-$20, the potentially young age of the magnetar (650,yr) can be used
to infer the transport limits of these particles to match the VHE source size.
This discovery provides new interest in the potential for high-energy particle
acceleration from magnetars, massive stars, and/or stellar clusters. |
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