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ATEL # 1049; J. M. Miller (Univ. Michigan), E. Kuulkers (ESA/ESAC), M. D. Caballero-Garcia (LAEFF/INTA), M. Diaz Trigo (ESA/ESAC), on behalf of a larger team
on 5 Apr 2007; 19:00 UT
Password Certification: Jon Miller (firstname.lastname@example.org)
Subjects: Radio, Infra-Red, X-ray, Binaries, Black Holes, Neutron Stars, Transients
Swift observed the new Galactic X-ray source IGR J17394-4638 starting on 2007 April 03. We report on 1 ksec of data taken in photon counting mode, for the purpose of obtaining a refined source position for multi-wavelength follow-up.
There is no evidence for an X-ray source within 2 arcmin of 264.92, -46.64 (ATEL 1048); indeed, there is no clear evidence for any X-ray sources within the XRT field of view.
In order to set a conservative upper-limit on the source flux, we extracted counts from a 2 arcmin region centered on the INTEGRAL position. We made fits assuming a Gamma = 2.0 power-law as a fiducial spectrum, and the standard Galactic column density along this line of sight (2.3 E+21 atoms/cm^2).
Fits to the 0.5-2.0 keV band using this model give a 95% confidence upper limit on the flux of 4 E-13 cgs, extrapolated across the 0.5-10.0 keV band.
Fits to the 6.0-10.0 keV band give a 95% confidence upper limit on the flux of 3 E-11 cgs, extrapolating across the 0.5-10.0 keV band.
This limit is an order of magnitude below the flux measured with INTEGRAL (7.4 E-10 cgs, 5-20 keV).
Given the low column density expected along this line of sight, the INTEGRAL detection and tight Swift limits can be reconciled if the X-ray source suffers strong internal obscuration, or if the source faded significantly between 2007 March 29 and April 03. Observations in IR and radio bands, and further X-ray observations, may be able to test these possibilities.
We thank the Swift team for granting our TOO request and for their responsiveness.