XMM-Newton Users Handbook OM filter band passes

The OM set of filters covers part of the UV and optical range. The filter throughput curves are displayed in Fig. 102.

Figure 102: Throughput curves for the OM filters, folded with the detector sensitivity.
\epsfig{width=1.0\hsize, file=figs/throughput_ao9.ps}
The plotted quantity is the OM effective area for a given filter including the entire telescope response based on inflight measurements. Aperture radius is 6" for the optical and 17".5 for the UV filters.

The OM effective area has been corrected for time dependent sensitivity degradation. The current throughput is lower due to time dependent sensitivity degradation $-$ it was about (16, 7, 8, 13, 19, 22) percent for (V, B, U, UVW1, UVM2, UVW2) filters, respectively, in 2020 and is currently declining by less than $1\%$ a year in all filters. The time dependent sensitivity degradation correction for any observing epoch can be found in the corresponding CCF (OM_PHOTTONAT_0008.CCF, see XMM-CCF-REL-378 and references therein).

The principal characteristics of the OM filters are listed in Table 17.

Zeropoints (by definition the magnitude of an object producing one count per second), have been derived by using, for each filter, the equation:

zeropoint = 2.5 log10(Countrate$_{Vega}$) + m$_{Vega}$.

OM zeropoints have been defined in such a way that Vega has:

B$_{Vega}$ = V$_{Vega}$ = 0.03 mag, U$_{Vega}$ = UVW1$_{Vega}$ = UVM2$_{Vega}$ = UVW2$_{Vega}$ = 0.025 mag.

Zeropoints are listed in Table 17. An AB magnitude system has been defined also for OM. Their zeropoints are given in Table 17 as well.

Table 17: OM filters: effective wavelengths, widths and Zeropoints
Filter Effective wavelength Width$^a$ Zeropoint AB zeropoint
  (nm) (nm) (magnitudes) (magnitudes)
V 543 70 17.9633 17.9230
B$^b$ 450 105 19.2661 19.0809
U 344 84 18.2593 19.1890
UVW1 291 83 17.2038 18.5662
UVM2 231 48 15.7724 17.4120
UVW2 212 50 14.8667 16.5719
White$^c$ 406 347 20.2555 20.6900
Notes to Table 17:
$^a$ The width of a filter with a constant transmission equal to the transmission at the effective wavelength, having the same effective area as the corresponding OM filter.
$^b$ The effective wavelength of the B filter has been arbitrarily set to 450 nm to avoid the core of the Balmer line H$\gamma$.
$^c$ White filter values based entirely on simulations.

European Space Agency - XMM-Newton Science Operations Centre