Evolution of the X‐Ray Jets from 4U 1755−33

We report on new X-ray observations of the large-scale jets recentlydiscovered in X-rays from the black hole candidate 4U 1755-33. Our observationsin 2004 show that the jets found in 2001 are still present in X-rays. However,sensitive radio observations in 2004 failed to detect the jets. We suggest thatsynchrotron radiation is a viable emission mechanism for the jets and thatthermal bremsstrahlung and inverse-Compton emission are unlikely on energeticgrounds. In the synchrotron interpretation, the production of X-rays requiresacceleration of electrons up to ~ 60 TeV, the jet power is ~ 4x10^35 erg s^-1,and the radio non-detection requires a spectral index alpha > -0.65 (S_\nu\propto \nu^\alpha) which is similar to the indexes found in lobes surroundingsome other compact objects. We find an upper limit on the flux of 4U 1755-33 inquiescence of 5x10^-16 erg cm^-2 s^-1 in the 0.3-8 keV band.Comment: accepted by ApJ, 11 pages, 2 color figure