Abstract for Proposal 085320
Probing the Interstellar Medium in the Direction of the Galactic Centre
X-ray Dust scattering halos can be used to probe the dust grains in
the interstellar medium (ISM). Recent studies show that this
scattering effect is prominent in the direction of the Galactic center
(GC), and so it can be used to explore the distribution and properties
of the complex ISM towards the GC. The dust scattering halo and
opacity can also systematically bias the spectral shape and
variability of all the X-ray sources in the GC, and so it is important
to quantify this bias. However, so far there are only three transients
observed within 10 arcmin of Sgr A* whose halo is clearly
observed. Therefore, we propose 40 ks joint Chandra and XMM-Newton TOO
program to observe the dust scattering halo of a future X-ray
transient in this GC region.
Details on Observing Strategy and Trigger Criteria
We will trigger this TOO if: a new X-ray transient within 10 arcmin of
Sgr A*, and the source 4-6 keV flux stays above 2.e-11 erg/cm2/s for
at least 3 days, and the nearby transient AX J1745.6-2901 is in
quiescence or does not blend with the halo of the new transient.