The SWIFT BAT Software Guide Version 6.3 30 ... - HEASARC - Nasa

5.8. MAKING BAT SKY IMAGES 47
Figure 5.5: Schematic diagram of making sky images using batfftimage.
5.7.11 Making Multiple Spectra
By default, batbinevt makes a single (type I) pulse height spectrum. You can choose other energy
binning strategies. Please see then time-selection section of the Light Curve thread for more ideas
on how to do this.
5.8 Making BAT Sky Images
This thread describes how to make a sky image from BAT event data using the ‘batbinevt’ and
‘batfftimage’ tasks.
Figure 5.5 shows schematically how sky images are created using the batfftimage from detector
images. Note that the sky image on the right hand side covers a significant portion of the sky (∼2
steradians).
5.8.1 Introduction
While the BAT does not have focussing optics, it is possible to create sky images using the task
batfftimage. This task combines a detector plane image and information about the coded aperture
pattern to reconstruct the sky flux at each point in the field of view. Sky images have the same
flux units as all other mask weighted counts values.
The steps of this procedure are: (1) make a source detector plane image using batbinevt; (2)
optionally make a background detector plane image; and finally (3) to make a sky image using
batfftimage.
5.8.2 Prerequisites
• BAT event data
– for example, (in obsid/bat/event/swNNNNNNNNNNNbevshsp uf.evt.gz);
BAT quality map,