Master thesis - UBC Physics & Astronomy

24 M. Alexandersen : Master thesis
Figure 9. The Swift observation of GRB050724, split into time intervals
to clearly show the expanding halo. From top left to bottom right: 345 −
1000 s after the burst, 1000 − 2322 s after burst, 6068 − 8120 s after burst
(entire second orbit), 11990 − 13881 s after burst (entire third orbit). All
the data has been filtered to the 0.8 − 2.2 keV energy range. The halo is
clearly visible in both parts of the first orbit, and is clearly expanding.
In the second orbit, the ring is visible at a larger radius, and in the third
orbit the halo is still faintly visible.
A dynamical image effectively reduces the original three-dimensional
image to a two dimensional one. The two spatial dimensions are combined
into one, the angle out from the GRB position, θ. Since the haloes are
circular on the ordinary image, all parts of a ring is at the same angle
from the GRB position, so at a given time, an entire ring in the ordinary
image is represented by a single point in the dynamical image, thereby
combining all the counts and making it significantly more visible relative
to the background.