About Chandra

Chandra at a Glance

Last modified: 01/08/21

Optics	Wolter Type-I
Mirror coatings	Iridium
Mirror outer diameters (1, 3, 4, 6)	1.23, 0.99, 0.87, 0.65 m
Mirror lengths	84 cm
Unobscured clear aperture	1145 cm²
Focal length	10.066 m
Plate scale	48.8 µm/arcsec
PSF FWHM (with detector)	0.5 arcsec
Ghost-free field of view	30 arcmin diameter
Effective Area:
@ 0.25 keV	800 cm²
@ 5.0 keV	400 cm²
@ 8.0 keV	100 cm²
Read more in the HRMA chapter of the Proposer's Observatory Guide

Focal plane arrays:
I-array (ACIS-I)	4 CCDs placed to lie tangent to the focal surface, used for imaging
S-array (ACIS-S)	6 CCDs in a linear array tangent to the grating Rowland circle, used for either imaging or as a grating readout
CCD format	1024 by 1024 pixels
Pixel size	24.0 µm (0.492 ± 0.0001 arcsec)
ACIS-I array size	16.9 by 16.9 arcmin
ACIS-S array size	8.3 by 50.6 arcmin
On-axis effective area of frontside illuminated (FI) chips (integrated over the PSF to >99% encircled energy):
@ 0.5 keV	110 cm²
@ 1.5 keV	600 cm²
@ 8.0 keV	40 cm²
Quantum efficiency for FI chips:
3.0 - 5.0 keV	> 80%
0.8 - 8.0 keV	> 30%
Quantum efficiency for backside illuminated (BI) chips:
0.8 - 6.5 keV	> 80%
0.3 - 8.0 keV	> 30%
Maximum readout rate per channel	~ 100 kpix/sec
Minimum row readout time	2.8 ms
Nominal frame time	3.2 sec (full frame)
Allowable frame times	0.2 to 10.0 sec
Frame transfer time	41 µs (per row)
Point-source sensitivity	4 X 10^-15 ergs/cm²/s in 10⁴ s (0.4 to 6.0 keV)
Read more in the ACIS chapter of the Proposer's Observatory Guide

Focal plane arrays:
HRC-I:	CsI-coated microchannel plate pairs, 90 X 90 mm
HRC-S:	CsI-coated microchannel plate pairs, 3-100 X 20 mm
Field of view:
HRC-I	~ 30 X 30 arcmin
HRC-S	6 X 90 arcmin
Spatial resolution, FWHM:	~ 20 µm, ~ 0.4 arcsec
Energy range:	0.08 - 10.0 keV
Spectral resolution (E/dE):	~ 1 @ 1 keV
Quantum efficiency:
@ 1.0 keV	30%
@ 8.0 keV	30%
On-axis effective area:
HRC-I @ 0.277 keV	133 cm²
HRC-I @ 1 keV	227 cm²
Time resolution	16 µs
Limiting sensitivity (point source, 3 sigma detection in 3 X 10⁵ s)	9 X 10^-16erg/cm²/s
On-orbit quiescent background (before ground processing):
HRC-I	9 X 10^-6cts/s/arcsec²
HRC-S	1.8 X 10^-4cts/s/(res. elm.)
Read more in the HRC chapter of the Proposer's Observatory Guide

HETGS range:	0.4 - 10.0 keV (31 - 1.2 Å)
High Energy Grating (HEG) range:	0.8 - 10.0 keV (15 - 1.2 Å)
Medium Energy Grating (MEG) range:	0.4 - 5.0 keV (31 - 2.5 Å)
Effective area (MEG+HEG first orders, with ACIS-S):
@ 0.5 keV	7 cm²
@ 1.0 keV	59 cm²
@ 1.5 keV	200 cm²
@ 6.5 keV	28 cm²
Resolving power (E/dE):
HEG:	65 - 1070 (1000 @ 1 keV, 12.4 Å)
MEG:	80 - 970 (660 @ 0.826 keV, 15 Å)
Resolution:
d lambda, HEG:	0.012 Å FWHM
d lambda, MEG:	0.023 Å FWHM
Absolute wavelength accuracy:
HEG:	± 0.006 Å
MEG:	± 0.011 Å
Wavelength scale:
HEG:	0.0055595 Å / ACIS pixel
MEG:	0.0111185 Å / ACIS pixel
Read more in the HETG chapter of the Proposer's Observatory Guide

Wavelength range:
HRC-S	1.7 - 170 Å
ACIS-S	1.4 - 63 Å
Energy range:
HRC-S	0.07 - 7.29 keV
ACIS-S	0.20 - 8.86 keV
Resolution: (d lambda, FWHM)	0.05 Å
Resolving power: (E/dE)
50 - 160 Å	>= 1000
3 - 50 Å	~ 20 ⨉ λ
Dispersion	1.148 Å/mm
Plate scale	48.80 µm/arcsec
Effective area (with HRC-S):
125 - 170 Å	1 - 2 cm²
60 - 120 Å	3 - 7 cm²
44 - 60 Å	7 - 12 cm²
19 - 40 Å	4 - 8 cm²
6 - 18 Å	10 - 25 cm²
2 - 5 Å	3 - 5 cm²
Background (quiescent)
HRC-S, on-orbit	0.12 counts/pixel/100-ksec
HRC-S, after filtering	~ 0.04 counts/pixel/100-ksec
ACIS-S, on-orbit	« 0.01 counts/pixel/100-ksec
Read more in the LETG chapter of the Proposer's Observatory Guide