XMM-Newton Science Analysis System


emevents (emevents-8.8) [xmmsas_20230412_1735-21.0.0]

Patterns

Figure 1: List of EPIC-MOS patterns (IMAGING mode)

Figure 1 for Imaging mode should be interpreted as follows:

• each pattern is included in a 5x5 matrix used for proximity analysis.
• a pattern is centered by definition on the pixel with highest charge.
• this central pixel is colored in red (its charge is E$_1$).
• the other pixels above threshold in the pattern are colored in green (the sum of their charges is E$_2$).
• all pixels colored in white must be below threshold.
• the crossed pixels are indifferent (they can be above threshold).
• the patterns are recognized in increasing order (this is important only for pattern 30, which comprises patterns 0 and 26-29).

The philosophy for patterns 0-25 is that a good X-ray pattern must be compact, with the highest charge at the center, and isolated (all pixels around are below threshold).

Patterns 26-29 are the so-called diagonal patterns, not expected from a genuine X-ray, but which can arise in case of Si fluorescence or of pileup of two monopixel events.

The E$_3$ and E$_4$ data in the ODF event lists have nothing to do with the "white" and "crossed" pixels.

• E$_3$ is the sum of charges of pixels below threshold in the 8 pixels of the 3x3 corona (their number is known from the pattern number).
• E$_4$ is the sum of charges of pixels below threshold in the 16 pixels of the 5x5 corona. Their number N4 is known from the PERIPIX column in the event list, which stores the number of pixels above threshold in the 5x5 corona. Thus N4 = 16 - PERIPIX.

Figure 2: List of EPIC-MOS patterns (TIMING mode)

Figure 2 for Timing mode should be interpreted in the same way as in Imaging mode, with the difference that the place where maximum charge occurs is ignored. There are only crosses in the rows above and below that of the event. This means that the Timing pattern analysis is purely 1-D (it is insensitive to other rows), because each Timing 'row' is actually the sum of 100 true rows, so the rows are not physically related. Because there is no test for maximum charge, all doubles appear as PATTERN=1, whether leading or trailing.

Patterns 2 and 3 are not bounded. They are mostly not due to true X-rays, but to cosmic-ray tracks. After binning by 100 rows, cosmic-ray tracks appear as an horizontal string of pixels above threshold. Their beginning will be recorded by an event with PATTERN=2 and their end by an event with PATTERN=3. In other words, patterns 2 and 3 normally occur in pairs and define a horizontal string of pixels above threshold.