2 X-ray observations

The Lockman Hole field, centered on the sky position RA 10:52:43, DEC +57:28:48 (2000) was observed with XMM in five separate revolutions (70, 71, 73, 74 and 81) during the period April 27-May 19, 2000 for a total exposure time of 190 ksec. The pointing direction was changed slightly (by about 10 $\hbox{$^{\prime\prime}$ }$ in RA and DEC in order to bridge the gaps between the CCD detectors between exposures) and the roll angle varied in the range 48.66 to 54.25 degrees between the different revolutions. The EPIC cameras were operated in the standard full-frame mode. The thin filter was used for the PN camera, while the thin and the thick filter were alternated for the MOS1 and MOS2 cameras in order to obtain diagnostics about the soft proton particle background. Table 1 gives a summary of the observations.

The PN and MOS data were preprocessed by the XMM Survey Scientist Consortium (SSC; Watson et al. 2001) using the XMM Standard Analysis System (SAS) routines. The attitude and deadtime information was not available for the datasets but can be regarded stable enough to be assumed constant for each revolution. The preprocessed FITS events files were analysed using FTOOLS routines.

A substantial fraction of the observations was affected by high and flaring background fluxes with count rates up to several hundred per second, compared to a quiet count rate of several counts per second per detector. The data were screened for low background intervals, rejecting times with a 0.5-10 keV count rate higher than 8 cts/s for the PN and 3 cts/s for each of the two MOS cameras. The remaining good time intervals added up to about 100 ksec (see Table 1). The actual exposure time for the three different detectors, pn-CCD, MOS1 and MOS2 were slightly different due to the varying start and end times of individual observations. A number of hot pixels and hot columns were removed interactively from the events lists by identifying them in images accumulated in detector coordinates and then spatially filtering them out of the datasets. An Al-K$_\alpha$ line at 1.5 keV is present in both detector types. The PN background spectrum shows in addition a strong Cu-K$_\alpha$ line at 8.1 keV, which is not present in the MOS background. PN photons in the energy range 7.9-8.3 keV have therefore been neglected in the further analysis.

 

 

Table 1: Observing Log

Date	Start	End	Dur.	Exp.	Filter	Filter
2000	[UT]	[UT]	[s]	[s]	MOS1	MOS2
27.04	02:45	22:08	69761	31216	thin	thick
29.04	02:37	22:00	69761	28608	thick	thin
02.05	17:50	00:21	23512	12944	thin	thick
05.05	08:48	21:01	43961	4999	thin	thick
19.05	04:28	22:17	64109	21744	thin	thick