Missions

BBXRT is flown on the Shuttle with the ASTRO payload in December 1990. The effective area curve is that for pixel A0.

The Chandra X-ray Observatory was formerly known as AXAF; starting with v2.7, PIMMS has switched to Chandra.

Observations of bright sources with ACIS are limited by photon pile-ups (see Proposers Guide). This version of PIMMS includes a beta-test release of pile-up estimate (based on the separate pileup tool written at ASC). This feature, when turned on (by uncompressing the special files in the data directory), will provide you with an estimate of the degree of pile-up for ACIS imaging mode observations (ACIS-I, ACIS-S-BI, LETG-ACIS-S ORDER0, and HETG-ACIS-S ORDER0).

Note that this is valid only for point source observations on-axis.

Pile-up effect can be mitigated by placing the source off-axis --- the inferior PSF will spread the photons over many pixels. Quantitative analysis of this is not yet available in PIMMS. The other principal method of altering the frame time can be evaluated by PIMMS. For this purpose, the 'go' command of PIMMS for ACIS-I and ACIS-S-BI allows an optional numerical parameter. If given, it will be taken as the frame time (allowed range: 0.2-3.3 s), and gives the pile-up fraction accordingly. If absent, PIMMS will attempt to estimate the frame time at which the pile-up fraction is 10% (which is the rule-of-thumb number above which you will have a severe problem). For the two 0th order images, the default frame time of 3.3 s is assumed.

Currently PIMMS only have IPC and MPC effective area curves.

PIMMS currently has the effective area curves for the three channels of the spectrometer, which is used by GOs for pointed observations. Detectors are SW (70-190A), MW (140-480A) and LW (280-750A).

EXOSAT

For the Low Energy telescopes, only the LE1/CMA effective area data are kept within PIMMS. Specify filter OPEN, LX3, LX4, ALP, or BRN. The ME effective area is for a half-array; GSPC area is also available.

Ginga is the 3rd Japanese X-ray astronomy satellite, which carried the LAC (Large Area Counter) array with an effective area of ~4000 cm^2. Count rate can be calculated for TOP layer of the detector only or BOTH.

Currently, only the A4 LED is supported.

The PIMMS set-up for this instrument is meant to make it straightforward to use the Levine et al (1984, ApJS 54, 281) catalog for XTE proposals. As an input, use the A+B+C combined count rate; as an output, A+B+C rate as well as the individual rate in the four bands (A through D) are given. One suggested use is to specify HEAO1 A4 as both input and output instrument: by an iterative process, the user can find a spectral model that reproduces the distribution of counts in different bands. Then switch to a different output instrument (in terms of energy range, LED matches the higher end of XTE PCA and the lower end of XTE HEXTE) keeping that model.

For the German XRT, effective area curve with PSPC (filter OPEN or BRN) and HRI are available. Also, beginning with v2.3, the Snowden R bands (see Snowden et al 1994, ApJ 424, 714) are available as software filters (R1, R1R2, R4, R4R5, R4TOR7, R5, R6, R6R7, and R7). For the British WFC, filters S1, S2, P1 and P2 effective area curves are available; these are appropriate for the time of launch. Note the S1 and S2 sensitivity dropped to ~75% of initial value by the end of the survey, followed by a steeper decline to 15-20% of the original value after The Tumble. Non-survey (P1 and P2) filters have suffered much smaller degradation.

Although the official name for this Italian-Dutch satellite is now BeppoSAX, the mission name within PIMMS remains SAX. It was launched in Apr 1996 by an Atlas G-Centaur directly into a 600 km orbit at 3 degrees inclination. SAX carries 4 narrow field instruments (1 LECS, 2 MECS, 1 HPGSPC, 1 PDS), covering the energy band from 0.1 to 200 keV, and two Wide Field Cameras (WFC, 2-30 keV) which view the sky through a coded mask perpendicularly to the axis of the narrow field instruments. The LECS (0.1-10 keV) is an imaging gas scintillation proportional counter similar to the MECS but extends the energy range down to 0.1 keV. The MECS (1-10 keV) is an imaging gas scintillation proportional counter similar to the LECS. There are 2 working MECS on board SAX(a third unit developed a fault in May 1997). The count rate estimate is for the 2 MECS, starting with version 2.4b (previous versions estimated for 3 MECS). The HPGSPC is an high pressure gas scintillation proportional counter sensitive in the energy range 3-120 keV with a FOV of 1 deg. The PSD, phoswich detector system, consists in four phoswich units. The observations are carried out with two halves of the experiment alternatively pointing source and background region, providing a continuous monitoring of the background. The PSD is sensitive in the 15-300 keV energy bandwidth and has a FOV of 1.5 deg. The Wide field Cameras is position sensitive proportional counter sensitive in the 2-30 keV band. There are 2 WFC on board SAX. The FOV per unit is 20 deg X 20 deg with an angular resolution of a few arcmin.

XTE, which was launched in Dec 1995, carries the All-Sky Monitor (ASM), large area proportional counter array (PCA) and the high energy X-ray Timing Experiment (HEXTE).

PCA is a mechanically-collimated array of five xenon proportional counter units (PCUs) with a total effective area of ~7000 cm²; however, different observations are taken with difeerent numbers of PCUs on. Therefore, starting with PIMMS v2.7, user must supply the count rate per PCU when this is used as the input mission (from xte pca). When used as the output mission (inst xte pca), the first output is count rate per PCU summed over all energies and over all 3 xenon layers. Additional outputs (the rates in the 6 canonical PCA channels required on the proposal form and used in RECOMMD) are given for 3 and 2 PCU combinations, which are becoming more frequent (and the proposal form requires numbers for 3 PCUs). The effective area curves, channel boundaries and the extimated background rates are all appropriate for "Epoch 4" gain setting.

HEXTE consists of two clusters of detectors, with 4 scintillation detectors in each cluster. Count rates are given per cluster. Values are given for the total count rate, and the count rates in the 4 canonical HEXTE channels required on the proposal form and used in HEXTEmporize.

The quoted detection times assume two-cluster 16-s source/background beamswitching, i.e., one cluster measures background while the other is on-source. In this case, the "detection time" applies to the combined HEXTE instrument. For those bright source observations (source rate >> background rate) where a HEXTE cluster is selected to be in STARE mode, this detection time can be also interpreted as appropriate for a single HEXTE cluster. For the combined HEXTE detection time, divide by sqrt(2).

PIMMS can also calculate conversion to/from flux values not folded through any instrument responses can also be used. To use flux, the unit must be specified: ERGS for ergs/cm/cm/s or PHOTONS for photons/cm/cm/s. Also necessary is the energy range of interest, to be specified in the form 2.5-10 (for 2.5 to 10 keV), or 2.0-40 A (for a wavelength range of 2.0 to 40 A, or roughly 0.03-6 keV). Optional keyword UNABSORBED following the range will make PIMMS calculate flux with Nh set to 0.0; this is useful in relating the flux to the total bolometric luminosity of the X-ray source before interstellar absorption.

PIMMS can also calculate conversion to/from flux densities at a specific energy, rather than flux integrated over a range of energies. To use density, the unit must be specified: ERGS for ergs/cm/cm/s/keV or PHOTONS for photons/cm/cm/s/kev. Also necessary is the energy of interest (in keV). Alternatively, this can be specified as the wavelength in Angstroms, with the optional argument Angstrom, in which case flux density is in (ergs or photons)/cm/cm/s/A. Flux density can be UNABSORBED as in flux.

PIMMS now supports the use of 'model normalization'; for the power law model, for example, normalization is the flux at 1 keV. For models imported from XSPEC, a normalization of 1.0 is the flux level as simulated within XSPEC.