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emanom (goflib-0.20.1) [xmmsas_20230412_1735-21.0.0]


Description

Emanom is a general tool for determining whether an EPIC MOS chip is likely to be in an anomalous state, that is, having an anomalously high quiescent particle background(QPB) below $\sim1.0$ keV. It is part of the goflib library of functions, subroutines, and tasks. It is generally used with Extended Source Analysis Software (ESAS) analyses. The algorithm is based on an updated version of Kuntz & Snowden (2008) which relies upon the 2.5-5.0 keV/0.4-0.8 keV hardness ratio to identify observations where the low energy band is anomalously high. The object of this routine is to identify the chips whose QPB spectrum, for this observation, is significantly different from their normal QPB spectrum. This routine uses rather restrictive criteria and may not be suitable for other uses. The work upon which this algorithm is based will be published shortly.

For each chip experiencing anomalous states (currently MOS1-4, MOS1-5, MOS2-2, and MOS2-5) this algorithm calculates the 2.5-5.0 keV/0.4-0.8 keV hardness ratio and compares that values to the noan_lim and anom_lim values for that chip. If the hardness ratio is $>$ noan_lim the chip is considered good (G), and the QPB background spectrum should be well characterised. If the hardness ratio is $<$anom_lim then the chip is considered bad (B), and the QPB background spectrum cannot be constructed for this chip. If the hardness ratio falls between noan_lim and anom_lim, then the chip is considered intermediate (I), and the standard method for constructing the QPB spectrum may be sufficient, but the user should exercise caution. If there are so few counts in the spectrum that the hardness ratio is not defined then the chip is considered to be in an unknown state (U), and if the chip is not active it is considered to be off (O).

The values for anom_lim and noam_lim are as follows:

MOS1, CCD4, anom_lim: 2.75 MOS1, CCD4, noam_lim: 3.00

MOS1, CCD5, anom_lim: 2.25 MOS1, CCD5, noam_lim: 3.60

MOS2, CCD2, anom_lim: 2.10 MOS2, CCD2, noam_lim: 2.50

MOS2, CCD5, anom_lim: 2.00 MOS2, CCD5, noam_lim: 4.00

The hardness ratios, the uncertainty in the hardness ratios, and the flag (B, G, I, O, or U) are recorded in the header keywords ANOMHRn, ANOMHEn, and ANOMFLn respectively if writekeys is true.

Note that chips that are in anomalous states still have useable spectra at energies greater than 1 keV.

XMM-Newton SOC -- 2023-04-16