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Last modified: December 2013

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AHELP for CIAO 4.9


Context: proposaltools


PIMMS (Portable, Interactive Multi-Mission Simulator) converts source fluxes and count rates between missions.


PIMMS can be run over the web using a browser or run locally using the command-line interface (CLI). Note that as of Chandra Cycle 13 (December 2010), PIMMS is not part of the CIAO Proposal toolkit and users wishing to use the CLI version need to download PIMMS from HEASARC at

PIMMS is a tool for estimating the source flux or count rate for a specific mission from either a count rate estimated by a previous mission or flux in some energy bound. It is very useful for simple source spectra, but not for complicated spectral or spatial structures. PIMMS also estimates the amount of Chandra ACIS pile-up assuming a point source on-axis, and accounts for this when estimating count rates. The tool was developed at NASA-GSFC, and the CXC implemented its own version for use as a Chandra proposal planning tool. Detailed information concerning PIMMS is available at:

Latest Effective Areas

The latest Chandra effective area curves are always included in the CXC web version of PIMMS as well as in the CLI version downloadable from HEASARC. The CXC web version of PIMMS also includes Chandra effective area curves for past proposing cycles going back to cycle 3. Users wishing to install older versions of Chandra effective area curves on top of the HEASARC CLI version of PIMMS should contact the Chandra Helpdesk.

ACIS Pile-up

As mentioned above, PIMMS estimates the effect of pile-up on ACIS counting rates. However, if a grating is inserted, the impacts of pile up are only estimated for the counting rate of the zeroth order image.The pile-up fraction in PIMMS software is defined as the ratio of the number of frames with two or more spurious pile-up events to the number of frames with a single, unpiled event. Note that the command-line version of PIMMS assumes that the entire ACIS bandpass is used.

Raymond-Smith Models

(1) The calculation only extends to 8 keV regardless of output AND input energy ranges. Any input model will be truncated at 8 keV, no attempt will be made to "convert" counts above 8 keV. Similarly, the output gives flux/counts up to 8 keV. (2) The available temperatures are listed in a pop-up menu from which the user selects that closest to the desired temperature.

Running PIMMS Over the Web

PIMMS can be accessed via the URL:

A general help file for the Proposal Planning Toolkit is available by clicking the 'HELP' button. Descriptions for each parameter may be found by clicking the appropriate parameter name. The web version of PIMMS has some features not found in the command-line version, such as background count rates for Chandra mission, the ACIS frame time option, and the truncation of energy at 8 keV in Raymond-Smith Models.

Background Count Rates

The web version of PIMMS provides background in a 1.5" radius circle for imaging (ACIS or HRC) observations. Extended source size specification affects only background determination. PIMMS also estimates the background per resolution element for HRC-S/LETG spectra.

ACIS Frame Time

In the web version of PIMMS, the user can either enter the ACIS frame time or choose to have PIMMS calculate the most efficient frame time for a given number of CCDs and sub-array. In the latter case, PIMMS will calculate the frame time that results in the least amount of pile-up and will present the corresponding results. The actual frame time used in performing these calculations can be examined using the "View Output" button.

Running PIMMS from the Command Line

The command-line version of PIMMS can be downloaded from

The HEASARC web site also includes a PIMMS user guide, and there is a 'HELP' command in PIMMS. Contact the CXC Helpdesk for any problems related to running the CLI version of PIMMS with Chandra data.

See Also

colden, dates, obsvis, precess, prop-coords, prop-time, prop-tools

Last modified: December 2013
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