Extract the Background Spectrum

To extract the background spectrum using the GUI:

1)

Follow steps 1 - 3 of §7.4.1 (GUI instructions).

2)

Make an annulus around the object whose background spectrum you wish to extract. This can be done using two circles, each defining the inner and outer edges of the annulus. The region in the inner circle can be excluded by selecting it, and then clicking the ``-'' sign in the Edit Region window, and ``Apply''.

3)

Adjust the sizes and positions of the circles until you are satisfied with the extraction region. In this case, we will center the annulus on the spectrum extraction region from §7.4.1 and let the background region extend from 20'' to 1' around the source.

4)

Click on ``2D Region'' in the heraXmmselect GUI.

5)

Confirm that the correct values were transferred to the ``Selection Expression'' box and that the operator is correct; in this case, it should show

((X,Y) in CIRCLE(25705.5,18820.5,1200))&&!((X,Y) in CIRCLE(25705.5,18820.5,400))

6)

Follow steps 6 - 10 of §7.4.1 (GUI instructions), giving the output files appropriate names. In this case, let the spectrum be mos1_bkg_pi.fits and the filtered file be mos1_filt_time_bkg.fits.

Once again, the counts per channel are displayed automatically in fv.

To extract the background spectrum using the Command Window:

1)

Follow steps 1 and 2 of §7.4.1 (Command Window instructions).

2)

Make an annulus around the object whose background spectrum you wish to extract. This can be done using two circles, each defining the inner and outer edges of the annulus. Select the inner circle. From ``Regions'' on the pulldown menu, select ``Properties'', then ``Exclude''.

3)

Adjust the sizes and positions of the circles until you are satisfied with the extraction region. In this case, we will center the annulus on the spectrum extraction region from §7.4.1 and let the background region extend from 20'' to 1' around the source. Double-clicking on the regions will bring up windows listing the center coordinates and the radius of each circle.

4)

Follow step 5 in §7.4.1 (Command Window instructions), remembering to change the output file names and the extraction expression:

spectrumset='mos1_bkg_pi.fits'
filteredset='mos1_filt_time_bkg.fits'
expression='((X,Y) in CIRCLE(25705.5,18820.5,1200))&&!((X,Y) in CIRCLE(25705.5,18820.5,400))'

The spectrum, in counts per channel, may be seen with fv.

As with the source spectrum, the background spectrum's area needs to be set.

To find the background spectrum's source area using the GUI:

1)

Call backscale in the Available Tools panel and enter the spectrum, mos1_bkg_pi.fits as the input data set.

2)

Directly beneath, enter the file containing the bad pixel extensions, i.e., the event file from which it was extracted, mos1_filt_time.fits. Verify that the option to correct for bad pixels in the source box is set to ``yes''.

3)

Click ``Run''.

To find the background spectrum's source area using the Command Window, type:

backscale spectrumset=mos1_bkg_pi.fits
$$ withbadpixcorr=yes badpixlocation=mos1_filt_time.fits