• The database of Upper Limits from Pointed and Slew observations has been built for regions free of pointed and slew PPS sources. If there is a source detected by the Pipeline or in the catalogues, no upper limit is provided, it is recommended to click on the appropriate boxes such that sources are found and displayed in the results tabs.


• The 4XMM-DR13 SED plots show the spectral energy density (ergs/s/cm2/micron) times the wavelength (in microns) computed at the central wavelength of the bands, so as to be consistent with what is plotted at other (longer) wavelength bands. This may be slightly different from the integral flux computed in the energy (frequency) band, displayed for the 4XMM-DR11 catalogue. Converting integral fluxes to flux densities at central wavelengths was done assuming that f(E) is constant in the band. Note that fluxes for the unique sources across all observations, SC_EP_flux, were used, instead of the per observation source fluxes EP_flux.


• The observations performed in mosaic mode have a global Observation Data File (ODF) which is also split into 'pseudo ODFs' (see Chapter 2 of the Data Files Handbook).
  The ObsID of all 'pseudo ODFs' belonging to a mosaic have the first 8 digits in common (e.g. 06730001). Split 'pseudo ODFs' can be recognised because the last two digits of their ObsIDs are not 01 but 31, 32, 33, etc. (e.g. 0673000131, 0673000132 etc). Note that the data (i.e. the X-ray events) of the 'pseudo ODF' subsets has been extracted from the global ODF (i.e. the same data for the sky area covered in the pseudo ODF). Pseudo ODF subsets should therefore never be combined or merged with the global ODF.


• JS9 display functionalities can be used for on-the-fly visualization of the PPS files in the list "Open FITS file with JS9". For "EPIC Events" it is convenient to bin the image by selecting View -> Bin/Filter/Section and typing for example bin=32 in the pop-up window. Then click "Run", and "Load full image" to view the entire "EPIC Events" image.   


• To overlay (blend) or blink more than one image loaded in JS9, say an EPIC combined image and an OM image, you can first sync the display commands using:
        File -> sync ... -> sync images ... -> all images
  and then re-project the OM image to the EPIC image using:
        WCS -> wcs reproject -> all images in this display.
  Then, for example, blink the EPIC and OM images with:
        View -> Blinking

  Note: if you zoom or pan any of the images, you need to deselect and select again the images in the Blinking form, for the commands to apply to all loaded images.  

Older (valid) watchouts can be found here.