Applications for edge detection techniques usingChandraandXMM–Newtondata: galaxy clusters and beyond

Abstract

The unrivalled spatial resolution of the Chandra X-ray observatory has allowed many breakthroughs to be made in high energy astrophysics. Here we explore applications of Gaussian Gradient Magnitude (GGM) filtering to X-ray data, which dramatically improves the clarity of surface brightness edges in X-ray observations, and maps gradients in X-ray surface brightness over a range of spatial scales. In galaxy clusters, we find that this method is able to reveal remarkable substructure behind the cold fronts in Abell 2142 and Abell 496, possibly the result of Kelvin Helmholtz instabilities. In Abell 2319 and Abell 3667, we demonstrate that the GGM filter can provide a straightforward way of mapping variations in the widths and jump ratios along the lengths of cold fronts. We present results from our ongoing programme of analysing the Chandra and XMM-Newton archives with the GGM filter. In the Perseus cluster we identify a previously unseen edge around 850 kpc from the core to the east, lying outside a known large scale cold front, which is possibly a bow shock. In MKW 3s we find an unusual 'V' shape surface brightness enhancement starting at the cluster core, which may be linked to the AGN jet. In the Crab nebula a new, moving feature in the outer part of the torus is identified which moves across the plane of the sky at a speed of ∼0.1c, and lies much further from the central pulsar than the previous motions seen by Chandra.

Is there a giant Kelvin–Helmholtz instability in the sloshing cold front of the Perseus cluster?

“…To determine the widths of the bays edges, we fit their surface brightness profiles with a broken powerlaw model, which is convolved with a Gaussian, as in and Walker et al (2016). In all three cases we obtain widths consistent with the known cold fronts in these clusters.…”

A Deep X-Ray Look at Abell 2142—Viscosity Constraints From Kelvin–Helmholtz Eddies, a Displaced Cool Peak That Makes a Warm Core, and A Possible Plasma Depletion Layer

“…Such a pattern is predicted by hydrodynamic simulations of gas sloshing for the recently formed fronts (see, e.g., A06 and their Figure 7 It is not clear whether the NW front and its more distant opposite (Rossetti et al 2013, outside this Chandra image) are part of the same slosing pattern as the inner two or they are caused by another disturbance. A closer look at Figure 1 and the unsharp-masked image in Figure 5(b), as well as the gradient image in Walker et al (2016) hints at subtle filamentary brightness enhancements that start at the NW front and go inward, as if they were extensions of the southern front. While Walker et al interpreted them as projected KH instability of the NW front, they may instead be the structures surviving from the stage when the cool gas currently in the core detached from the NW front and sank inward.…”

“…The latter three (153 ks total) were taken in 2014 (PI M. Markevitch) and centered the cluster in ACIS-S3. An image from these observations have been looked at by Walker et al (2016). We processed the data using CIAO (v4.9.1) and CALDB (v4.7.7), with standard event filtering procedure to mask bad pixels, filter by event grades, remove cosmic ray afterglows and streak events, and detector background events identified using the VFAINT mode data.…”

Gas Sloshing Regulates and Records the Evolution of the Fornax Cluster

“…The northeast front at r = 10.6 kpc (116 ), F3, is the most evident front (Figure 2-top-left). We apply a Gaussian Gradient Magnitude (GGM) filter to highlight sharp edges in the Chandra X-ray image, which determines the magnitude of surface brightness gradients using Gaussian derivatives (Sanders et al 2016b; Walker et al 2016). Brighter regions correspond to sharp features in surface brightness.…”