INTEGRAL observations of PSR J 1811 − 1925 and its associated

We present spectral measurements made in the soft (20–100 keV) gamma-ray band of the region containing the composite supernova remnant G11.2-0.3 and its associated pulsar PSR J1811−1925. Analysis of INTEGRAL/IBIS data allows characterisation of the system above 10 keV. The IBIS spectrum is best fitted by a power law having photon index Γ = 1.8 +0.4 −0.3 and a 20–100 keV flux of 1.5 ×10 −11 erg cm s. Analysis of archival Chandra data over different energy bands rules out the supernova shell as the site of the soft gammaray emission while broad band (1–200 keV) spectral analysis strongly indicates that the INTEGRAL/IBIS photons originate in the central zone of the system which contains both the pulsar and its nebula. The composite X-ray and soft gamma-ray spectrum indicates that the pulsar provides around half of the emission seen in the soft gamma-ray domain; its spectrum is hard with no sign of a cut off up to at least 80 keV. The other half of the emission above 10 keV comes from the PWN; with a Γ=1.7 its spectrum is softer than that of the pulsar. From the IBIS/ISGRI mosaics we are able to derive 2σ upper limits for the 20–100 keV flux from the location of the nearby TeV source HESS J1809−193 to be 4.8 ×10 erg cm s. We have also examined the likelihood of an association between PSR J1811−1925 and HESS J1809−193. Although PSR J1811−1925 is the most energetic pulsar in the region, the only one detected above 10 keV and thus a possible source of energy to fuel the TeV fluxes, there is no morphological evidence to support this pairing, making it an unlikely counterpart.