XMM-Newton EPIC Background Components


Table summarizing the components within the XMM-Newton EPIC Background; temporal, spectral and spatial properties.
Count rate plots, giving an estimate of the to-be-expected EPIC background in 'low background' periods, both in-FOV (~photons+particles) and out-FOV (~particles), are available here.

PARTICLES PHOTONS
SOFT PROTONS INTERNAL
(cosmic-ray induced)
ELECTRONIC NOISE HARD X-RAYS SOFT X-RAYS
Source Few x 100 keV solar protons, accelerated by magnetospheric reconnection events. Dominate times of high-BG. Interaction of High Energy particles (cosmic rays) with detector - associated instrumental fluorescence.
Main MOS ref.
(1) Bright pixels & (parts of) columns.
(2) CAMEX readout noise (pn).
(3) (4) (5) (6) Artificial Low-E enhancements in outer MOS CCDs
(Also dark current - thought negligible).
X-ray background (AGN etc), Single Reflections from outside FOV, Out-of-time (OOT) events (pn) Local Bubble, Galactic Disk, Galactic Halo, Solar Wind Charge Exchange (SWCX) SWCX, Single Reflections from outside FOV, Out-of-time (OOT) events (pn)
Variable? (per Observation) Flares (up to >1000%). Unpredictable. Significant quiescent component (long flares) - survive GTI screening. (Also additional possible 'irreducable' component). +/-10%.
MOS , MOS : >2keV continuum unchanged, small changes in fluorescence lines. <1.5keV continuum varies - may be be due to Al redistribution.
pn: Difference between continuum and lines (some correlation).
(1) +/-10%.
(2) Very constant.
(3) (4) Believed constant.
Constant. Constant.
Long obs. may see effect of SWCX SWCX (e.g. variations at 0.5-1.2 keV [OVIII/MgXI], but not at 2-4 keV).
Variable? (Obs. to Obs.) Unpredictable. Affect 30%-40% of time. Flaring SP increasing? Quiescent SP not evolving. More SPs far from apogee. More SPs in winter than in summer. Low-E flares turn on before high-E. Majority @ +/-15%. Can be x10 higher in high radiation periods. No increase after solar flares.
Plus above 'per Observation' variations.
(1) >1000% (pixels come and go, also [micro-]meteorite damage).
(2) Mode-dependent (lowest eFF, then FF, LW, highest SW)
(3) effects 5-20+% of obs. (4) effects 20-50% of obs. (factor increases with high-BG rate). (5) (6) >50% of obs for later Revs (Rev.1300+)
Constant.
OOT events (pn) mode-dependent (LW:0.16%, FF:6.3%, eFF:2.3%)
Variation with RA/Dec (+/-35%).
SWCX SWCX may affect observations differently.
OOT events (pn) mode-dependent (LW:0.16%, FF:6.3%, eFF:2.3%)
Spectral Variable. Unpredictable. Continuum spectrum (no lines), fitted by unfolded xspec PL (double-exponential or broken power law [break energy stable ~3.2 keV]) model for E>0.5keV (E<0.5keV, less flux is seen). Variable in intensity + shape (higher the intensity, flatter the slope). Flat (MOS index~0.2) + fluorescence + detector noise.
MOS: 1.5keV Al-K, 1.7keV Si-K, 2.2keV Au. Det.noise <0.5keV. High-E lines (Cr 5.4, Mn 5.8, Fe-K 6.4, Au 9.1&11.4). (Here also)
PN: 1.5keV Al-K. No Si (self-absorbed). Cu-Ni-Zn-K (~8keV). MIP noise <0.3keV.

(1) low-E (<300eV), tail may reach higher-E.
(2) low-E (<300eV).
(3) (4) low-E (<500eV) (3) High-rate plus soft excess. (5) (6) Strong excess <1000eV.
1.4 power law. Below 5keV, dominates over internal component. Above 5keV, internal component component dominates (in times of low-BG). Thermal with ~<1keV emission lines.
Extragalactic @>0.8keV, index=1.4.
Galactic - emission/absorption varies.
SWCX SWCX very soft, with unusual OVIII/OVII line ratios (plus others) - Strong OVIII & MgXI
Spatial - Vignetted? Yes (scattered) - Vignetting is flatter than for photons - low-E SPs extremely flat, higher-E SPs steeper (MOS) - pn shows more constant vignetting with energy No - flat (see below). (1,2) Bright pixels and CAMEX - No.
MOS noise - (3) No/unclear (out-FOV) (see below) (4) Yes - evident in vignetting maps (in-FOV). (similar, smaller-magintude vignetting asymmetries seen in pn). (5) (6)
Yes. Yes.
Spatial - Structure? Perhaps, in MOS due to the RGA. No structure seen in pn. SP feature seen in MOS1-CCD2 at low-E. SPs observed only inside FOV. Yes. Detector + construction.
MOS: outer CCDs more Al, less Si. CCD edges more Si. Less Si out-FOV. Continuum diff. between out-FOV and in-FOV below Al line (redistribution?). More Au out-FOV. Changes in high-E lines. CCD-to-CCD: line intensity variations, energies/widths stable. (Here also)
PN: Line intensities show large spatial variations from electronic board. Central 'hole' in high-E lines (~8keV)., Residual MIP contribution near CAMEX readout (low-E, non-singles, parallel to readout).
Yes.
(1) Individual pixels & columns.
(Also [pn] sections of columns away from CAMEX, near to FOV centre)
(2) Near pn readout (CAMEX), perpendicular to readout.
(3) MOS1 CCDs 4 & 5, MOS2 CCDs 2 & 5 - unusual in- & out-FOV differences (esp. MOS1 CCD4) and spatial inhomogeneities. (4) MOS1 CCDs 2 & 5. (5) (6). Lower-level ~persistent low-E enhancement in MOS1 CCD2
No.
Single reflections: Diffuse flux from 0.4-1.4 deg (out-FOV) is ~7% of in-FOV signal. Effective area of 1 telescope ~3 sq.cm at 20-80 arcmintes off-axis.
OOT events (pn) smeared along readout from bright sources of X-rays.
(extra BG in pn LW mode due to frame store area).
No, apart from real astronomical objects.
Exgal.>0.8keV spatially uniform.
SWCX SWCX over whole FOV.
Single reflections: Diffuse flux from 0.4-1.4 deg (out-FOV) is ~7% of in-FOV signal. Effective area of 1 telescope ~3 sq.cm at 20-80 arcmintes off-axis.
OOT events (pn) smeared along readout from bright sources of X-rays.
(extra BG in pn LW mode due to frame store area).
Patterns Distribution similar to genuine X-rays. Distribution different from genuine X-rays. Distribution different from genuine X-rays. (5) MOS E1/E2 connection Genuine X-ray distribution. Genuine X-ray distribution.


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