For EPIC, users must avoid contamination of the target data by checking that any neighbouring bright sources are not
in the same CCD row/column as the desired object by selecting an appropriate
position angle if necessary. The EPIC team recommends using MOS1 in
imaging mode and MOS2 in timing mode in those cases where one needs to observe using one MOS
in imaging and the other MOS in timing mode. Users are referred
to the XMM-EPIC Status of Calibration and Data Analysis document
XMM-SOC-CAL-TN-0018 (https://xmmweb.esac.esa.int/docs/documents/CAL-TN-0018.pdf)
for more details.
To collect time series of the central source with OM, the user can also consider
using the ''Science User Defined'' mode with ''Image'' and ''Fast'' windows
(see § 5.2.4.5).
If the observation is long compared with the visibility window (as reported by the online XMM-Newton Target Visibility Tool), the user must consider how best to split the observation, e.g., into multiple observations that fit into continuous visibility periods.
Users must check the visible magnitude of in-field or nearby optical
sources and the science target itself. If the soft X-ray response is
important, one should choose the thinnest filter compatible with the
brightest visible objects, as described in the XMM-Newton Users Handbook section on
EPIC filters
![[*]](../icons/crossref.png){kind=icon}
.
If high time resolution is needed for RGS observations, it must be
decided whether a reduced number of CCDs shall be read out (see XMM-Newton Users Handbook
section 3.4.5 on RGS modes
).
For OM, it must be decided if a specific filter coverage is necessary
for the science, or if the recommended filter sequence is adequate (see
XMM-Newton Users Handbook section on OM modes
and OM optical elements
).
Telemetry and onboard memory limits place upper and lower boundaries on the duration of single OM exposures as listed in § 5.2.4.5.