INTEGRAL observations of PSR J1811-1925 and its associated Pulsar Wind Nebula

Abstract

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 of 1.8^{+0.4}_{-0.3} and a 20-100 keV flux of 1.5E{-11} erg/cm^2/s. Analysis of archival Chandra data over different energy bands rules out the supernova shell as the site of the soft gamma-ray 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 power law slope of 1.7 its spectrum is softer than that of the pulsar. From the IBIS/ISGRI mosaics we are able to derive 2 sigma upper limits for the 20-100 keV flux from the location of the nearby TeV source HESS J1809-193 to be 4.8E{-12} erg/cm^2/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.