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INTEGRAL and RXTE monitoring of XTE J1817-330: evolving through a state change?

ATel #738; E. Kuulkers (ESA/ESAC, Spain), P. Goldoni (APC & CEA, Saclay), S. E. Shaw (Southampton, UK/ ISDC, Geneva), S. Brandt, J. Chenevez (DNSC, Denmark), T. J.-L. Courvoisier (ISDC, Geneva), K. Ebisawa (NASA/GSFC, USA), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (NASA/GSFC, USA), N. Mowlavi (ISDC, Geneva), T. Oosterbroek, A. Orr (ESA/ESTEC, Netherlands), A. Paizis (IASF, Milano), J. Rodriguez (CEA, Saclay), C. Sanchez-Fernandez (ESA/ESAC, Spain) & R. Wijnands (UvA, Netherlands)
on 16 Feb 2006; 19:07 UT
Credential Certification: Erik Kuulkers (ekuulker@rssd.esa.int)

Subjects: X-ray, Gamma Ray, Binary, Black Hole, Transient, Variables

Referred to by ATel #: 742, 752

INTEGRAL Galactic Bulge monitoring observations (ATel #438) indicate that the X-ray transient and black-hole candidate XTE J1817-330 (ATel #714) has increased in hard X-rays (20-60 keV) compared to the observations performed on Feb 9, 2006 (ATel #731). The 20-60 keV fluxes were 46+/-2 mCrab on Feb 11 and 79+/-2 mCrab on Feb 14. The 60-150 keV fluxes did not show a significant increase: they were 45+/-7 and 60+/-7 mCrab, respectively, on the above quoted days. Preliminary spectral analysis indicates that in the range 20-150 keV the spectrum of the source has indeed steepened: a power-law with photon index of 2.6+/-0.1 fits the INTEGRAL observations on Feb 14.

The RXTE/PCA Galactic Bulge scans, however, show a decrease of the source at lower energies (2-10 keV), from 840 mCrab on Feb 9 to 710 mCrab on Feb 12 to 670 mCrab on Feb 15 (all +/-4 mCrab). This is in contrast to the spectral behaviour described above.

These findings may indicate a state change, which could be accompanied by changes in the emission at other wavelengths. We again note that an INTEGRAL ToO observation of XTEJ1817-330 is presently ongoing and will last up to Feb 17, 11:20 UTC. Observations at other wavelengths are therefore encouraged.