Proposal change classes
There are basically two different classes of modification that an XMM-Newton proposal can undergo:
- changes concerning the instruments safety or functionality
- changes to optimize the scientific return of the proposal
Changes concerning the instruments safety or functionality
The problems listed below require by mandate a modification of the proposal, either to properly operate the instruments or to avoid potentially harmful situations;- OM filters must be changed to prevent damages to the camera. This is due to the presence of a bright source in the OM field of view. The SOC will suggest alternative filters (if any), which can be safely used. Under no circumstances will the original filter be maintained. The Ground Segment software could in a few case impose unnecessarily restrictive constraints. In this case, a PI can ask the SOC to put the enhancement of the whole proposal on-hold and to trigger a further investigation. Although we welcome such feedback, they may dictate an unpredictabe delay in the scheduling of an XMM-Newton observation. We therefore suggest that this procedure is used only if the proposed OM filter change would seriously affect the scientific goal(s) of the proposal.
- OM memory/science windows too big. The memory limitations of the on-board computer correspond to limits in the size of the memory/science windows that can be defined in OM SCI USER DEFINED mode. If the limits are exceeded, the PI will be asked to provide new window definitions consistent with the requirement reported in the XMM-Newton Users' Handbook. Under no circumstances will the original window definition be maintained. The OM platescale is 0.476513 arcsecs/pixels.
- OM memory/science window overlapping. The boundaries of the memory/science OM windows in SCI USER DEFINED mode cannot overlap. The PI will be asked to provide a new window definition. Under no circumstances will the original window definition be maintained. Please note, however, that it is possible to define a window which is fully contained within another as these are not considered as overlapping.
Changes to optimize the scientific return of the proposal
The enhancement process aims also at maximizing the potential scientific outcome of each XMM-Newton observation. The SOC will suggest possible modifications to the proposals to achieve this goal. It is the ultimate responsibility of the PI to accept or reject these suggestions depending on the scientific goal of her/his proposal. The PI is strongly encouraged to check the impact of the changes suggested by the SOC and to compare them with her/his original goals.- Bit Rate Allocation Table (BRAT) does not support the expected count rate. The expected count rate can saturate the available telemetry. In this case, the PI can choose between one of the following options:
- Switch off one or more instruments, such that those remaining have sufficient telemetry bandwidth to support the expected source count rate, or
- Keep all the instruments active, with significant dead time in one/more of them
- EPIC cameras optical loading. Optical photons detected from sources within 2 arcmins of the target can pass through the EPIC camera filters, and distort the spectral response accuracy. In this case it is advisable to use a thicker filter. The SOC will provide the XMM-Newton PIs with all the necessary information to select the most appropriate filter.
As specified above, the PIs are encouraged to carefully verify the impact of the proposed changes.
- X-ray bright source in the EPIC cameras. The SOC has cross-correlated all the approved AO2 fields with the ROSAT All Sky Survey (RASS) catalogue. The goal of this check is two-fold;
- A bright source at a distance from the nominal target larger than 1 arcminute, may affect the background at the target location, as well as the telemetry downlink requirements. In these cases, the use of an EPIC windowed mode may be useful to reduce this contamination
- A bright source at a distance between 20 and 60 arcseconds from the nominal boresight position - and therefore presumably coincident with the nominal target - may fall outside the field of view of EPIC windowed modes are used. In these cases, the coordinates of the pointed targets should be verified
The PI is invited to cross-check the expected X-ray flux from the target source (and from any other potentially bright source in the target field of view), or to provide the SOC with her/his own estimate, if not originally specified in the proposal. It is the ultimate responsibility of the PI to change the EPIC modes to account for such an effect, depending on the scientific goal of her/his proposal. The correctness of the pointed target coordinates is also the ultimate responsibility of the PI.
- EPIC cameras pile-up. Photon pile-up is defined as the arrival of two or more photons in the same camera pixel before read-out. Such photons are interpreted as a single one, with energy equal to the sum of the energies of all the incoming photons. This affects both the spectral response and the point spread function of EPIC.
In cases where expected pile-up is higher than 5%, the SOC will suggest an instrumental mode with a reduced on-target field of view, and consequently a faster read-out.