2002MNRAS.337..869G

In 2000 August, we observed the black hole candidate 1E 1740.7-2942 , the brightest persistent hard X-ray source within a few degrees of the Galactic Centre, for 10 ks with Chandra (ACIS-I). Attempting to compensate for pile-up effects, we found that the spectra were well-fitted by an absorbed power law, with photon indices Γ= 1.54^+0.42_–0.37(readout streak) and Γ= 1.42^+0.14_–0.14(annulus), consistent with a black hole low/hard state. We have analysed a public observation performed by Chandra which utilized short frames in order to avoid severe pile-up effects. Subtracting the core point spread function from the whole image, we did not find evidence for any elongated feature perpendicular to the radio jet axis, as reported in a recent analysis of the same data. Moreover, comparing the radial profiles with those of an unscattered X-ray point source, we found an indication of an extended, previously undetected, X-ray scattering halo. The measured halo fractional intensity at 3 keV is between 30 and 40 per cent within 40 arcsec but drops below detectable levels at 5 keV. Finally, by placing a limit on the X-ray flux from the radio-emitting lobe, which has been identified as the hotspot at the end of the northern jet of 1E 1740.7-2942, we are able to constrain the magnetic energy density in that region.