What follows is a tabulation of the various properties of X-ray instruments past, present, and future. The table is followed by a glossary, notes on the table entries, and some additional general information. At the end is a tabulation of information regarding the flux limits of some X-ray detectors. This last section has sparse information, because it is still in its infancy...

The folks at HEASARC have provided a similar comparison chart which provides more detail about a limited number of recent and current observatories. They also provide bar graphs that compare the lifetimes and energy coverage of all high-energy astronomical satellites launched through 2005.

SatelliteInstrument E band
[keV]
Spatial Spectral resolution1 [eV] at: Time resol.2 Effective area3 [cm2] at: Notes
Field of viewResol. (FWHM) .1 keV.5 keV1 keV6 keV .1 keV.5 keV1 keV6 keV20 keV
Uhuru   1970-75
1st dedicated satel.
2-20 1°×10° -- -- -- 840 840 PC, collimated; survey
HEAO-1
1977-79

1st large satellite
LASS (A-1) 1-20 few° -- -- -- -- 10000 10000 10000 PC; large area sky survey
CXE
(A-2)
0.2-60 few° -- -- 4000 4000 4000 4000 PC; cosmic X-ray background exp.
MC (A-3) 1-20 few° ~1' -- -- -- -- -- -- scanning MC
(A-4) 15-104 1°×20° -- -- -- -- -- -- -- -- 200 collimated
Einstein
(HEAO-2)
1978-81

1st imaging telescope
IPC 0.3-3.5 75' 1' -- -- -- ~100 -- -- PC
HRI 0.2-3.0 25' 4" -- -- -- -- -- 5-20 -- -- MCP; Optional grating yields 2% E resol.
SSS 0.5-4.5 6' -- -- E/dE=3-25 -- -- ~200 -- -- solid state spec
FPCS 0.4-2.6 6' -- -- 3 -- -- 0.1-1.0 -- -- Bragg crystal spec
MPC 2-15 1.5° -- -- -- 1200 -- -- -- 700 -- PC w/o telescope
Tenma (Astro-B) 1983-85 PCs 2-60 ~3° -- 550 FWHM -- -- -- 640 10 GSPCs; varied fov
telesc. 0.1-2.0 0.2×5° -- ~14 -- -- 2 non-imag telescopes
EXOSAT
1983-86
ME 1-50 0.75° -- -- -- -- -- ~1600 PC
LE+CMA .05-2.0 18" -- -- -- telescopic; gratings avail.
LE+PSD telescopic
GS 2-20 -- -- -- -- -- -- -- ~100 GSPC
Ginga (Astro-C) 1987-91 LAC 1.5-37 0.8×1.7° -- -- -- -- ~1200 0.98ms -- -- -- ~4000 Columnated PC
ASM 1-20 1×180° -- -- -- -- -- ~70 All-sky monitor
GBD 1.5-500 4π sr -- -- -- -- -- -- -- ~60 GRB detector
BBXRT
2-11 Dec 1990
0.3-12 17.4' 4' diam. pixel -- 85 90 150 -- ~40 (A0+B0) ~200 (A0+B0) ~190 (A0+B0) -- 5 pixel ccd; ×2 (A&B); shuttle (Astro-1)
ROSAT
1990-99
HRI 0.1-2.4 20'×20' 5" -- -- -- -- ~10 80 -- -- MCP
PSPC 0.1-2.4 114' 15" -- ~380 500 -- ~40 210 -- -- Imaging PC, ×2
ASCA
(Astro-D)
1993-00
SIS 0.4-10 22'×22' 1' -- 50-100 70-140 120-320 4s4 -- 80 260 210 -- 2×2 ccd array; ×2
GIS 0.7-10 50' 3' -- -- 190 460 60us -- -- 100 250 -- GSPC; ×2
BeppoSAX
1996-02
LECS 0.1-2 37' 2-3' -- 125 190 530 16us -- 4 25 35 -- GSPC, 14" pixels
MECS 1.3-10 28' (r) 2-3' -- -- -- 480 15us -- -- -- 100 -- ×2; GSPC; 20" pixels
HPGSPC 3-120 1.1° -- -- -- -- 600 -- -- -- 150 260 GSPC
PDS 15-300 1.4° -- -- -- -- -- 16us -- -- -- -- 500 scinillator shields are 60-600keV GRB mntr
WFC 1.8-28 20°×20° 5' -- -- -- 1200 -- -- -- 100 ~70 ×2; CM PCs
Astro-E
10 Feb 2000
R.I.P.
XRS 0.4-10 4'×2' 1.5' -- 12 12 12 -- 150 130 -- Microcalorimeter; cryogenic (2yr)
XIS 0.4-10 19'×19' 1.5' -- ~35 ~50 130 -- 300 250 -- 1 ccd/mirror (×4)
HXD 10-700 4 Pi -- 30% (10keV); 9% (662keV) -- -- -- -- 230 16 columnated
SatelliteInstrument E band
[keV]
Spatial Spectral resolution1 [eV] at: Time resol.2 Effective area3 [cm2] at: Notes
Field of viewResol. (FWHM) .1 keV.5 keV1 keV6 keV .1 keV.5 keV1 keV6 keV20 keV
RossiXTE
1995-  
PCA 2-60 -- -- -- -- 1125 1us -- -- -- 5000
HEXTE 15-250 -- -- -- -- 8us -- -- -- -- ~1600 4 SC cluster (×2)
ASM 2-10 -- -- -- -- -- -- --
Chandra
(AXAF)
1999-  
HRC-I .08-10 31'×31' <0.4" 80 16us 10 65 225 40 -- 90×90mm MCP
HRC-S .08-6 7'×97' 0.1 1.3 5 180 8 10+11 20+10 5 -- 20×300mm MCP; uses LETG
ACIS-I 0.2-10 16'×16' 1-2"

(0.49" pix)
-- 50(FI)/ 115(BI) 55(FI)/ 125(BI) 130(FI)/ 190(BI) 3.3s -- 110/FI, 400/BI 410/FI, 800/BI 200/FI, 160/BI -- 4 (2×2) FI chips
ACIS-S 0.5-10 8'×48' -- -- -- 4 FI & 2 BI chips;
HETG & METG used simultaneously
  +HEG 0.9-10 -- -- 1 FWHM 45 FWHM -- -- 11+1 23+0 --
  +MEG 0.4-5 -- 0.5 FWHM 2 FWHM 75 FWHM -- 6+11 50+3 20+0 --
  +LETG 0.2-9 -- 1.5 5 300 -- 10+? 50+? 25+? --
XMM- Newton5
2000-
MOS6 0.2-12 30' 6" -- ~50 57 130 3s(1.5ms) -- 420 850 768 -- ×2; 7 FI chips; 1.1" pix
PN 0.1-12 30' 6" ~60 67 125 73ms(7us) 100 1000 1227 900 -- 6×2 BI chips; 4.1" pix
RGS6 0.33-2.5 ~5' -- -- 0.8 HEW, 1.5 FWHM 4.0 HEW, 4.5 FWHM -- .6s(16ms) per chip -- 120+60 135+75 -- -- ×2; 1×9 FI chips; splits beam w/MOS
HETE-2
2000-
SXC 0.5-10 0.91 sr <30" 46 129 1.2 s 14 2 perpendicular 1-D CMs with CCDs
WXM 2-25 1.6 sr 10' -- -- -- ~1200 1 ms -- -- -- ~350 2 perpendicular 1-D CMs with PSPCs
FREGATE 6-400 3 sr -- -- -- 10 us -- -- -- 120 NaI detector
HETE-2 is a GRB survey instrument, which always points in the anti-solar direction; it also has an optical camera.
Integral
2002-
JEM-X 3-35 4.8° 3' -- -- -- 1000 122 us -- -- -- 500 500 coded mask
Primarily a gamma ray mission; payload includes SPI spectrometer (20keV-8MeV, E/dE ~ 500 @ 1 MeV), IBIS imager (15keV-10MeV, 12' resolution), and OMC optical camera (500-850nm, 5°×5° fov).
Swift
2004-
XRT 0.2-10 23.6' diameter 18" HPD @1.5 keV -- 50 FWHM 100
FWHM (in 2005)
260
FWHM (in 2005)
2.2 ms
(timing mode)
-- 30 100 60 -- 600x602 pix CCD; 2.36"/pix; F >~ 2×10-14 erg/cm2/s in 10ks
A GRB hunting satellite with rapid autonomous slewing. Payload also includes BAT X-ray coded mask imager (15-150keV, 5240 cm2, 1.4 sr fov, 4' positioning) and UVOT (170-650 nm, 17'×17' fov, 0.3" positioning, 7 filters & 2 grisms).
Suzaku
(Astro-E2)
2005-
XRS
R.I.P.
0.3-12 2.9'×2.9' 2.0' -- 7 7 7 100 us -- 25 150 130 -- Microcalorimeter; lost cryogen before 1st obs
XIS 0.4-12
(0.2-12 FI)
18'×18' 2.0' -- ~35 ~50 130 8 s -- 3×60 FI
150 BI
3×200 FI
250 BI
3×220 FI
200 BI
-- 4 co-aligned XRTs; 3 w/ FI, 1 w/ BI CCDs
HXD PIN 10-60 34'×34' non- imaging ~3000 61 us -- -- -- -- 230 16 columnated units
HXD GSO 30-600 4.5°×4.5° ~10% (sqrt(7.6/EMeV)% FWHM) 315 cm2 at 100 keV
Fermi
(GLAST)
2008-
LAT ≥20,000 >2 sr -- -- -- -- -- -- -- -- -- 20 MeV - 300 GeV
GBM (<)10- (>)25,000 4π sr -- -- -- -- -- -- -- -- <~10% E resol.
SatelliteInstrument E band
[keV]
Spatial Spectral resolution1 [eV] at: Time resol.2 Effective area3 [cm2] at: Notes
Field of viewResol. (FWHM) .1 keV.5 keV1 keV6 keV .1 keV.5 keV1 keV6 keV20 keV
NeXT

2013
HXI 5-80 9'×9' <1.7' HPD -- -- -- <0.1 ms -- -- -- ~700 ~400 telescope w/ multi- layers; <1.5 keV resol (FWHM) @ 60 keV
SXT-S 0.3-10 3'×3' <1.7' HPD -- <7 <7 <7 <0.1 ms -- ~40 160 210 -- microcalorimeter
SXT-I 0.3-12 35'×35' <1.7' HPD <150 4 s ~250 ~400 360 -- soft X-ray telescope; CCD camera
SGD 10-600 0.55°×0.55° (<150 keV)
<10°×10° (>150 keV)
-- -- -- -- -- <0.1 ms -- -- -- -- ~200 non-imaging; 2 keV resol (FWHM) @ 40 keV; >30 cm2 area @ 100 keV
XEUS
Constellation X

2008?
2013?
???
RGS 0.25-2 >2.5' 5"-15" HPD -- 1 4 -- -- ~1400 ~1500 -- -- grating
XMS 0.25-10 5"-15" HPD -- ~2 ~2 ~4 -- ~8000 ~15000 ~6000 -- calorimeter
HXT 6-≥40 >8' 30"-1' HPD -- -- -- <600 -- -- -- >~1500 >~1500 HXT: multilayer XRT; CdTe or CdZnTe ccd


Glossary and further notes:

Abbreviations:

BI
Back-Illuminated ccd chips
CM
Coded Mask detector
FI
Front-Illuminated ccd chips
GSPC
Gas Scintillation PC detector
MC
Modulation Collimator
MCP
MicroChannel Plate detector
PC
Proportional Counter detector
SC
Scintillation Counter
spec
spectrometer
XRT
X-Ray Telescope

Additional notes:

1 In grating spectrometers, the HEW resolution is appropriate for separating a weak line from the continuum, while FWHM is useful in resolving two separate emission lines. The resolution tabulated is for the grating order with the largest effective area (typically the first); higher grating orders will provide better spectral resolution if there is sufficient signal.
2 Time resolution for reading full field in standard operating mode (imaging, spectroscopy, etc.). Highest time resulution is noted parenthetically if a specialized mode (eg: timing or burst mode, partial frame readouts, etc.) is available.
3 For instruments with multiple redundant coaligned detectors, the effective areas are multiplied by the number of detectors to give the total effective area.
 
For grating spectrometers, effective areas are expressed as (first order area) + (next strongest order area). For Chandra, the next strongest order is the third for ACIS-S and second for HRC-S; for XMM-Newton's RGS, it's the second.
4 In non-imaging mode, the time resolution of the SIS detectors is 16ms.
5 XMM also has an optical/UV (160-600 nm) telescope.
6 The two MOS imagers and the two spectrometers on XMM-Newton share two XRTs, with the MOS arrays receiving ~42% of the incident light in each, and the RGSs getting ~40% (the rest is absorbed by the grating support structures). The effective areas tabulated are already doubled to account for the presence of a pair of detectors used simultaneously.


Some more general information:

Comparing FI and BI ccd chips. Generally speaking, FI chips offer higher spectral resolution than BI chips, but BI chips offer higher sensitivity, especially at low energies or above ~6 keV. In the case of the XMM-Newton Observatory, the high end of the detector passband is limited by a rapidly declining quantum efficiency (QE) above ~6 keV in the FI chips of XMM-Newton's MOS cameras, whereas the QE of the BI chips in the pn camera is nearly 100% through 10 keV, and has only rolled off to ~70% by 15 keV.

Converting between keV and Angstroms. Remember that wavelength (in Angstroms) times energy (in keV) is 12.3984.

Converting to/from "Crabs". A convenient unit of flux density often used in X-ray astronomy is the "Crab". The Crab nebula has a spectrum equal to:

I(E) = 9.7(±1) E-1.10(±.03) keV / s / cm2 / keV
If we integrate this from 2-10 keV, we find that the 2-10 keV flux of the Crab is 13.5 keV / s / cm2 = 2.16 × 10-8 erg / s / cm2.
If you ever need to convert flux density into Janskys (who on earth would use such an arcane unit?), a few of useful reference points are:
1 crab ~ 2.744 mJy at 2.0 keV
1 crab ~ 1.088 mJy at 5.0 keV
1 crab ~ 0.237 mJy at 20. keV

Information on limiting flux:

An instrument generally will only be sensitive to sources of a certain flux or brighter. This is the flux limit. The flux limit can be due to instrument noise, background glow, source confusion, . . . Of course, the flux limit is a function of the integration time of the observation, because the longer you integrate, the more you'll beat down the noise. Only hitting a limit when either there are so many faint sources that you hit the confusion limit, or if there is a truely diffuse background (as opposed to unresolved point sources) then you'll eventually hit a background limit.

In the following table, the dominant limiting factor is listed in bold. Specifically, this is the factor which dominates within a reasonable long look for the given instrument. Sure, you could push these limits down by an order of magnitude or so if you stared with the instrument for it's full lifetime, but who'd let you monopolize a satellite like that?

Satellite & Instrument Detection confidence Integration time Energy interval Background limit Confusion limit
ASCA SIS 5 sigma 100 ks 0.5-10 keV 1.0e-3 cps
ASCA GIS 5 sigma 100 ks 2-10 keV ~10 uCrab ~2.2E-13 ergs/cm2/s ~0.4 uCrab ~8.6E-15 ergs/cm2/s


Jonathan Gelbord / Eureka Scientific, Inc. / jonathan [AT] eurekasci [DOT] com