The INTEGRAL/IBIS source AXJ1838.0-0655: a soft X-ray to TeV gamma-ray broad band emitter

Abstract

We report on INTEGRAL observations of AX J1838.0-0655, one of the unidentified objects listed in the first IBIS/ISGRI survey catalogue and located in the Scutum arm region. This object, detected in the 20-300 keV band at a confidence level of 15.3 sigma (9 x 10^-11 erg cm-2 s-1) is the likely counterpart of the still unidentified TeV source HESS J1837-069. It has been detected in the past by various X-ray telescopes, including ASCA, implying that it is a persistent rather than a transient source; the ASCA image is compatible with the source not being resolved. The broad 1-300 keV spectrum is characterized by an absorbed (NH = 6.7+/-1.3 x 10^22 cm-2) and hard (Gamma =1.5 +/- 0.2) power law continuum. Possible counterparts (radio and infrared) present within the X-ray error box are discussed, even if no clear association can be identified. The broad band spectrum together with the TeV detection suggests that AX J1838.0-0655 maybe a supernova remnant or a pulsar wind nebula, which has so far eluded detection in the radio band. This is the second unidentified HESS source that shows a substantial soft gamma-ray emission.