attfilter (attfilter-1.4) [xmmsas_20211130_0941-20.0.0]

Description

Starting from an attitude data time series as created by atthkgen and a given exposure in the current ODF (pointed at by the environment variable SAS_ODF) attfilter carries out the following operations in sequential order:

- Inquire the start and end time of the exposure specified via the parameter instexpid
- Disregard the attitude data (specified via parameter attset) which lie outside the exposure time window
- Compute the
*median*spacecraft attitude within the exposure time window. In default of a mathematically rigorous definition of this quantity the median attitude is calculated as the composition of the individual medians of:- Right Ascension (J2000) of star tracker viewing direction
- Declination (J2000) of star tracker viewing direction
- Astronomical position angle of spacecraft

- Generate a GTI table with the task tabgtigen
under the control
of a filtering expression which involves the previously computed median
spacecraft attitude values and a user-specified set of tolerance angles
(see parameter tolangles)
.
There are two ways to choose the filtering expression: The user can
either give the full expression himself via the parameter
expression in conjunction with setting filtertype=user
or choose one of two predefined filters (in the following
designates the median and the actual spacecraft
pointing direction at time expressed as unit vectors in the
earth-centered J2000 sky reference system):
- cone (filtertype=cone):

(1)This equation describes a cone with symmetry axis and half-opening angle . - pyramid (filtertype=pyramid):

- cone (filtertype=cone):
- Add the median spacecraft attitude values to the new GTI table as attributes MEDI_RA, MEDI_DEC, and MEDI_APA.

The task's main output is a new GTI table in a new or previously existing data set suitable for direct event list filtering.

XMM-Newton SOC -- 2021-11-30