Using Target Visibility Checker

Input coordinates

RA & Dec coordinates of the desired target can be specified either in decimal degrees (DD.DD) or in "HH MM SS.S" and "DD MM SS.S" format. All internal operations are done in degrees. For RA, a floating point number indicates that you are giving your input in decimal degrees. An integer number will be taken as HH MM SS.S. For instance, 4 is taken as 4 hours but 4. is taken as 4 degrees.

When entering coordinates in the multiple targets section you must use sign (+/-) for the Declination.

The rest of parameters are optional, if you do not enter any of them the Visibility Checker will provide defaults, as indicated for each parameter below.

Target name

An optional Target Name can be entered which could be the name of the source or some other identifier. Default is "Target".

Revolution range

If you select this entry option you can provide the revolution range for which the visibility should be computed.
Enter the first and last revolutions for which you would like the visibility computed.
The default for these entries is the approximate revolution range covered by AO23 (revolution 4467 - 4650). The minimum and maximum values for which visibility information can be computed in this version are revolutions 4334 - 4765.
If you leave these fields untouched (default) or you use an out of range value, the tool will use the defaults.
Note: The tool internally uses revolutions for all computations.
The terms revolution and orbit are used interchangeable by the tool.

Date Range

Instead of a revolution range you may select a range of dates. If you select this option you may provide the date range for which the visibility should be computed. Enter the first and last dates for which you would like the visibility computed.
The format is 'free' for the dates but we recommend to use the forms YYYY-MM-DD or YYYY MM DD (or even DD Month YYYY).
The default for these entries is the approximate date range covered by the AO23: 2024-05-01 to 2025-04-30. The minimum and maximum values for which visibility information can be computed in this version are dates 2023-08-08 and 2025-12-14.
If you leave these fields untouched (default) or you use an out of range value, the tool will use the indicated defaults.

The following link contains the latest available revno file providing Perigee Passage crossing times.(R=Reconstructed data, P=Predicted data).

You can find out the equivalence between date and revolution number by using the orbit calculator.

Minimum and Maximum visibility

A time is specified for the minimum length that a target is required to be visible.
For example, if 10000 seconds are requested, the tool will return information about those revolutions in the specified range in which the target is visible for at least this time.
Default and minimum is 5000 secs. The maximum rounded visibility (see below) is set to 130 ks.
Any entered value outside the range (5 - 130 ks) is changed by the tool to the appropriate within range value, this is, if below 5 ks it will be changed to 5 ks or if above 130 ks it will be changed to 130 ks.

Note on visibility duration

The tool constrains the output visibility according to several factors:

• The XMM-Newton radiation model predicting when the radiation levels will allow XMM-Newton to execute scientific observations.
  This radiation model has been developed using the XMM-Newton Radiation Monitor data and predicts future behaviour taking into account the orbit evolution.
  To see more details about the model, refer to the Radiation Model TN page.
  To know more about the Radiation Monitor, you may visit the XMM-Newton Radiation Monitor Details page.
• The eclipse periods where special operations are required (thus giving less room for science).
• The nominal (altitude based) time when scientific observations may start or have to be finished.

A plot (pdf) with the factors that constrain the start of the scientific window is provided for AO23 (and as used in the visibility calculations).
For the end of the science window the factor that dominates is radiation and is the constraint that is taken into account.
The final combination of all these factors is represented for AO23 in the following PDF file.

Bin corners visible

This version of the Visibility Checker uses bin size of 2x2 degrees.
The visibility tool imposes that for a target to be visible, all corners of the corresponding bin must be visible.

Visibility checker output

The output of the tool is provided in the same Browser window in the form of tables.
It consists of the following components, depending on your selection criteria:

Summary of Visibility

If this option is selected the output will display the common information to all entered targets (XMM-Newton viewing constraints and the fixed parameters for this option that are the AO revolution range and a minimum visibility of 5000 secs), followed by the visibility summary for the requested targets. This information is provided in a results table, with one target per row with the following information:

• Target Name and target coordinates (in decimal degrees)
• Number of revolutions in the AO range when the target is visible more than the minimum.
• Minimum visibility duration in secs for the revolutions when the target is visible.
• Average duration in secs for the revolutions where the target is visible more that the default minimum.
• Maximum visibility duration in secs for the revolutions when the target is visible.
• A link to the detailed visibility results for the target (with the given AO parameters).
• In case no visible periods are found within the given constraints no results for duration are displayed, just a message indicating that the target is not visible.

Detailed Visibility

If this option is selected the output will display:

• one table containing default parameters related to the constraints used by the Visibility Checker (independent of the user input).
• one table containing parameters requested by user, common to all targets, providing minimum duration and the selected ranges (either in the form of orbits or dates).

    Then, for each target:

• one table containing the target name and coordinates
• followed by another table containing the results:
• the revolution number when the target is visible (for at least the minimum entered duration),
• the starting time and date when the target is visible,
• the total time that the target could be visible in this revolution,
• the time and date when the target becomes not visible,
• the phase in the revolution when the target becomes visible (0 = perigee, 0.5 = apogee),
• the phase in the revolution when the target becomes not visible,
• the rounded visibility: the total observation duration requested in the HRPS by potential proposers should not exceed the rounded visibility,
• the angle to the Sun,
• the mean astronomical position angle of the instruments during the visible period. The visibility checker uses a nominal roll angle of 0°.
  This position angle can be used in conjunction with SciSim to check the orientation of the source, especially for RGS observations.

Problems?

If the tool fails to yield a successful answer these are some of the common problems.

• The target may not be visible in the specified orbit range for the minimum requested duration. Try a shorter duration time or a different orbit range.
• The target might be visible in the specified orbit range (based on astronomical constraints -DBOB-) for the minimum requested duration but after further constraints are applied, e.g.: radiation model, the final duration is below the minimum or the requested minimum duration.
• Please note that with the option of multiple targets the output may take some time to be produced. Please be patient in these cases.