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INTEGRAL observations suggest IGR J17098-3628 is not the source of 10 mHz QPOs

ATel #3229; E. Kuulkers, C. Sanchez-Fernandez (ESA/ESAC, Spain) and J. Rodriguez (CEA Saclay, AIM-SAp, France)
on 22 Mar 2011; 20:26 UT
Credential Certification: Erik Kuulkers (ekuulker@rssd.esa.int)

Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient

Referred to by ATel #: 3230, 3913, 4773

~10 mHz quasi-periodic oscillations (QPOs) have been seen during part of RXTE/PCA observations aimed at IGR J17091-3624 on March 14. Since IGR J17098-3628 is only 9' away from IGR J17091-3624, it could not be excluded that IGR J17098-3628 was the source of the QPOs, due to source confusion by the PCA (ATel #3225).

We report on INTEGRAL observations obtained before and after the RXTE/PCA observations, between UT March 13 03:21 and 16:40 (INTEGRAL revolution 1027), and between UT March 15 09:23 and 22:43 (INTEGRAL revolution 1028). We find IGR J17091-3624 to be still active (see also ATels #3144, #3159, #3203), while we do not detect any significant high-energy emission from IGR J17098-3628 (see also ATel #3148). The JEM-X (3-25 keV) and IBIS/ISGRI (18-40 keV) fluxes for IGR J17091-3624 are 58+/-3 mCrab and 28+/-1 mCrab, respectively, for INTEGRAL revolution 1027, and 54+/-3 mCrab and 26+/-1 mCrab, respectively, for INTEGRAL revolution 1028. We derive 3 sigma upper limits on the 3-25 keV flux from IGR J17098-3628 of about 6 and 5 mCrab, for INTEGRAL revolutions 1027 and 1028, respectively (with effective exposure times of 4.0 and and 5.3 ksec, respectively). The source separation between the two sources is just below the angular resolution of ISGRI (12' FWHM); IGR J17098-3628 is not detected up to a level of about 10 mCrab (18-40 keV), in either of the two INTEGRAL revolutions (effective exposure times of 44 and 42 ksec, respectively).

These findings suggest that IGR J17098-3628 can be excluded as the source of ~10 mHz QPOs.