Deep radio observations of the radio halo of the bullet cluster 1E 0657-55.8

We present deep 1.1-3.1 GHz Australia Telescope Compact Array observations of the radio halo of the bullet cluster, 1E 0657-55.8. In comparison to existing images of this radio halo the detection in our images is at higher significance. The radio halo is as extended as the X-ray emission in the direction of cluster merger but is significantly less extended than the X-ray emission in the perpendicular direction. At low significance we detect a faint second peak in the radio halo close to the X-ray centroid of the smaller sub-cluster (the bullet) suggesting that, similarly to the X-ray emission, the radio halo may consist of two components. Finally, we find that the distinctive shape of the western edge of the radio halo traces out the X-ray detected bow shock. The radio halo morphology and the lack of strong point-to-point correlations between radio, X-ray and weak-lensing properties suggests that the radio halo is still being formed. The colocation of the X-ray shock with a distinctive radio brightness edge illustrates that the shock is influencing the structure of the radio halo. These observations support the theory that shocks and turbulence influence the formation and evolution of radio halo synchrotron emission.Comment: 15 pages, 16 figures, 3 tables. Accepted by MNRA

Another shock for the Bullet cluster, and the source of seed electrons for radio relics

With Australia Telescope Compact Array observations, we detect a highly elongated Mpc-scale diffuse radio source on the eastern periphery of the Bullet cluster 1E0657-55.8, which we argue has the positional, spectral and polarimetric characteristics of a radio relic. This powerful relic (2.3+/-0.1 x 10^25 W Hz^-1) consists of a bright northern bulb and a faint linear tail. The bulb emits 94% of the observed radio flux and has the highest surface brightness of any known relic. Exactly coincident with the linear tail we find a sharp X-ray surface brightness edge in the deep Chandra image of the cluster -- a signature of a shock front in the hot intracluster medium (ICM), located on the opposite side of the cluster to the famous bow shock. This new example of an X-ray shock coincident with a relic further supports the hypothesis that shocks in the outer regions of clusters can form relics via diffusive shock (re-)acceleration. Intriguingly, our new relic suggests that seed electrons for reacceleration are coming from a local remnant of a radio galaxy, which we are lucky to catch before its complete disruption. If this scenario, in which a relic forms when a shock crosses a well-defined region of the ICM polluted with aged relativistic plasma -- as opposed to the usual assumption that seeds are uniformly mixed in the ICM -- is also the case for other relics, this may explain a number of peculiar properties of peripheral relics.Comment: 10 pages, 9 figures, 1 table, accepted for publication in MNRA

Fringing Analysis and Simulation for the Vera C. Rubin Observatory's Legacy Survey of Space and Time

The presence of fringing in astronomical CCD images will impact photometric quality and measurements. Yet its impact on the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) has not been fully studied. We present a detailed study on fringing for Charge-Coupled Devices (CCDs) already implemented on the Rubin Observatory LSST Camera's focal plane. After making physical measurements and knowing the compositions, we have developed a model for the e2v CCDs. We present a method to fit for the internal height variation of the epoxy layer within the sensors based on fringing measurements in a laboratory setting. This method is generic enough that it can be easily modified to work for other CCDs. Using the derived fringing model, we successfully reproduce comparable fringing amplitudes that match the observed levels in images taken by existing telescopes with different optical designs. This model is then used to forecast the expected level of fringing in a single LSST y-band sky background exposure with Rubin telescope optics in the presence of a realistic time varying sky spectrum. The predicted fringing amplitude in LSST images ranges from $0.04\%$ to $0.2\%$ depending on the location of a CCD on the focal plane. We find that the predicted variation in surface brightness caused by fringing in LSST y-band skybackground images is about $0.6\ \mu\rm{Jy}\ \rm{arcsec}^{-2}$, which is 40 times larger than the current measurement error. We conclude that it is necessary to include fringing correction in the Rubin's LSST image processing pipeline.Comment: 17 pages, 16 figures, submitted to PAS