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XMM-Newton observation of XTE J1817-300

ATel #791; G. Sala, J. Greiner (MPE Garching)
on 7 Apr 2006; 15:33 UT
Credential Certification: J. Greiner (jcg@mpe.mpg.de)

Subjects: X-ray, Black Hole

The black hole candidate XTE J1817-300 was observed for 20 ks with XMM-Newton on 13 March 2006, 45 days after the X-ray maximum as seen with RXTE/ASM. The EPIC-pn camera was used in the Burst mode and a simultaneous high resolution spectra was obtained by RGS1.
Spectral fits have been performed using XSPEC. The EPIC-pn spectrum is dominated in the 1-6 keV range by a thermal disk with kT=0.74 keV, and a power law with photon index 3.3±0.1 at higher energies. We find NH=(2.6-2.8)x1021cm-2 and a flux of 8.6x10-9 erg/cm/s (0.4-10 keV). This corresponds to a luminosity of 1.0x1036 (d/1 kpc)2 erg/s.
In the RGS spectrum, we detect the OI K-alpha interstellar absorption line at 527 eV, with equivalent width 1.36(+0.02/-0.01) eV. This value and the detected NH fits well in the OI K-alpha line vs NH correlation reported in Sala et al.(2006, submitted to A&A) using GRO J1655-40 XMM-Newton observations together with several sources found in the literature.
The observed NH value is marginally larger than the average value in the source direction (Dickey & Lockman, 1990, ARAA, 28, 215). This locates XTE J1817-330 behind the galactic slab of ISM (adopted to be 150 pc), and provides a lower limit for the distance of 1.0 kpc. Recalling that the maximum flux detected during high/soft state by RXTE/ASM was ~2 Crab, and assuming the source was at 10% of the Eddington luminosity (as many other BH transients at maximum) at that time, we derive an upper limit of 4 kpc. Thus we estimate the distance to be in the range 1-4 kpc.