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XMM-Newton observation of XTE J1856+053

ATEL # 1062; G. Sala, J. Greiner, F. Haberl (MPE Garching)
on 26 Apr 2007; 15:58 UT
Password Certification: Gloria Sala (gsala@mpe.mpg.de)

Subjects: X-ray, Binaries, Black Holes, Transients

The black hole transient XTE J1856+053 (ATel #1024, #1026, #1038, #1042) was observed by XMM-Newton on 14 March 2007. The observation was strongly affected by solar flares, resulting in a total integration time of 1.5 ks for EPIC-pn (in timing mode), and 5.3 and 4.2 ks for the RGS1 and RGS2.

The combined EPIC-pn plus RGS spectra can be fit with an absorbed thermal disk model (TBabs*diskbb) with kT=0.79-0.81 keV and NH=(4.3-4.5)x1022cm-2 (3-sigma error ranges). This model fits well the spectrum above 1 keV, but leaves large residuals below that energy, leading to a poor reduced chi^2 of 1.99. Adding a recombination emission edge, with the edge energy fixed at the O VIII K-shell energy (0.8714 keV) and with a plasma temperature kT=50(+/-3) eV, reduces substantially these excess residuals, leading to a chi^2=1.16 (898/774). If the recombination emission edge is a real feature of the source spectrum, the ratio of the plasma temperature to the edge energy (~0.06) points to a photoionized plasma as the origin site of the feature. We cannot exclude, however, that these residuals are caused by some calibration problem (more exactly, redistribution of higher energy photons to lower energies).

The observed 0.5-10.0 keV flux is 9.7x10-10 erg/cm/s. The absorption corrected 0.5-10.0 keV flux is (2.1-4.5)x10-8 erg/cm-2/s, corresponding to a luminosity of (2.5-5.4)x1038 erg/s (D/10 kpc)2.


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R. E. Rutledge , Editor
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