XMM-Newton observation of XTE J1856+053
ATel #1062; G. Sala, J. Greiner, F. Haberl (MPE Garching)
on 26 Apr 2007; 15:58 UT
Credential Certification: Gloria Sala (gsala@mpe.mpg.de)
Subjects: X-ray, Binary, Black Hole, Transient
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.
