Probing the clumping structure of Giant Molecular Clouds through the spectrum, polarisation and morphology of X-ray Reflection Nebulae

Abstract

We suggest a 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-alpha line's shoulder. We consider the particular case of Sgr B2, one of the brightest and most massive XRN in our Galaxy. We parametrise the gas distribution inside the cloud using a simple clumping model, with the slope of the clump mass function (alpha), the minimum clump mass (m_{min}), the fraction of the cloud's mass contained in clumps (f_{DGMF}), 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-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. Finally, clumps in GMCs should be visible both as bright spots and regions of heavy absorption in high resolution X-ray observations. We therefore further 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.

15 pages, 15 figures, submitted to A&A

References in corpus (10)

• Theory of Star Formation
• A SCUBA survey of Orion, the low-mass end of the core mass function
• X-ray hiccups from SgrA* observed by XMM-Newton. The second brightest flare and three moderate flares caught in half a day
• Discovery of Variable Iron Fluorescence from Reflection Nebulae in the Galactic Center
• Anisotropic Formation of Magnetized Cores in Turbulent Clouds
• Hard X-ray Morphological and Spectral Studies of The Galactic Center Molecular Cloud Sgr B2: Constraining Past Sgr A* Flaring Activity
• The dense gas mass fraction in the W51 cloud and its protoclusters
• Prospects of 3D mapping of the Galactic Centre clouds with X-ray polarimetry
• Ionized gas at the edge of the Central Molecular Zone
• Reflection nebulae in the Galactic Center: the case for soft X-ray imaging polarimetry

Cited by in corpus (13)

• Not that long time ago in the nearest galaxy: 3D slice of molecular gas revealed by a 110 years old flare of Sgr A*
• Polarization and long-term variability of Sgr A* X-ray echo
• Non-Equilibrium Chemistry and Destruction of CO by X-ray Flares
• The Galactic LMXB Population and the Galactic Centre Region
• Can Sgr A* flares reveal the molecular gas density PDF?
• Examining molecular clouds in the Galactic Centre region using X-ray reflection spectra simulations
• SRG/eROSITA view of X-ray reflection in the Central Molecular Zone: a snapshot in September-October 2019
• Sgr B2 hard X-ray emission with INTEGRAL after 2009: still detectable?
• New Constraints on Cosmic Particle Populations at the Galactic Center using X-ray Observations of the Molecular Cloud Sagittarius B2
• X-raying molecular clouds with a short flare: probing statistics of gas density and velocity fields
• 25 years of XMM-Newton observations of the Sgr A complex: 3D distribution and internal structure of the clouds
• Impact of intrinsic polarisation of Sgr A* historical flares on (polarisation) properties of their X-ray echoes
• Tree-based solvers for adaptive mesh refinement code FLASH -- IV: An X-ray radiation scheme to couple discrete and diffuse X-ray emission sources to the thermochemistry of the interstellar medium