Volume 589, May 2016
|Number of page(s)||15|
|Section||Interstellar and circumstellar matter|
|Published online||18 April 2016|
Probing the clumping structure of giant molecular clouds through the spectrum, polarisation and morphology of X-ray reflection nebulae
Max Planck Institut für Astrophysik,
2 II Tata Institute of Fundamental Research, Homi Bhabha Road, 400005 Mumbai, India
3 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
Received: 16 November 2015
Accepted: 14 February 2016
We introduce a new method for probing global properties of clump populations in giant molecular clouds (GMCs) in the case where these act as X-ray reflection nebulae (XRNe), based on the study of the clumping’s overall effect on the reflected X-ray signal, in particular on the Fe K-α line’s shoulder. We consider the particular case of Sgr B2, one of the brightest and most massive XRN in the Galactic center (GC) region. We parametrise the gas distribution inside the cloud using a simple clumping model with theslope of the clump mass function (α), the minimum clump mass (mmin), the fraction of the cloud’s mass contained in clumps (fDGMF), and the mass-size relation of individual clumps as free parameters, and investigate how these affect the reflected X-ray spectrum. In the case of very dense clumps, similar to those presently observed in Sgr B2, these occupy a small volume of the cloud and present a small projected area to the incoming X-ray radiation. We find that these contribute negligibly to the scattered X-rays. Clump populations with volume-filling factors of >10-3 do leave observational signatures, that are sensitive to the clump model parameters, in the reflected spectrum and polarisation. Future high angular resolution X-ray observations could therefore complement the traditional optical and radio observations of these GMCs, and prove to be a powerful probe in the study of their internal structure. Clumps in GMCs should further be visible both as bright spots and regions of heavy absorption in high resolution X-ray observations. We therefore also study the time-evolution of the X-ray morphology, under illumination by a transient source, as a probe of the 3D distribution and column density of individual clumps by future X-ray observatories.
Key words: Galaxy: center / scattering / polarization / ISM: structure
© ESO, 2016
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