If it is important to ensure that any particular part of the extended
object does not fall on a CCD gap, users must choose the pointing
direction appropriately (see XMM-Newton Users Handbook sections on EPIC pn chip array
![[*]](../icons/crossref.png){kind=icon}
,
EPIC MOS chip array
and position angle constraints
).
For both MOS and pn, when using the ''Full Frame'' imaging mode, it
must be decided if any given part of the source is
bright enough to give rise to local photon pile-up that would degrade
the calibration and prevent the achievement of the scientific goals
(see XMM-Newton Users Handbook section on EPIC pile-up
). In the case of a
bright extended source, pile-up might be a concern, and if so, the user
must decide whether ''Full Frame'' imaging with pile-up in the brightest
parts should be performed, or to use partial frame imaging to avoid
pile-up at the loss of imaging data over part of the extended object.
Unless the target is extremely bright, it should be possible to leave
RGS in the normal ''Spectroscopy'' mode (see XMM-Newton Users Handbook section 3.4.5
on RGS modes
).
The OM observing mode will depend on its optical characteristics. Please refer to section § 5.2.4.5.
If the observation is long compared to 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
targets. 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
.
For standard ''Spectroscopy'' mode observations with RGS, a standard readout sequence is proposed which can be modified according to the needs of the user. In case of particularly strong emission lines, observers might want to read out individual CCDs more often than others (see § 5.2.4.4).
For OM, it must be decided if a specific filter coverage is necessary
to achieve the science, or if the recommended filter sequence is adequate (see
XMM-Newton Users Handbook section on OM modes
and OM optical elements
).
While no limits are expected on the exposure duration for the X-ray instruments observing bright extended sources (except for visibility constraints and the duration of the observation), OM exposures are further constrained by telemetry and memory capacity limits (§ 5.2.4.5).