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2. Sample selection and data analysis

2.1. The Ginga sample

We first selected a sample consisting of the sources among the Nandra & Pounds (1994) Ginga sample classified as pure Seyfert 1 galaxies. Seyfert 1.5, 2 and Narrow Emission Line Galaxies are excluded: generally these sources are highly absorbed and are therefore very faint in the ROSAT energy range. We have also been forced to exclude the Seyfert 1 3C 382 because no ROSAT PSPC observation is available. This led to the selection of 17 low redshift (z <0.06) sources spanning a wide range of luminosities (from a few tex2html_wrap_inline1639 up to almost 1045 erg s-1). The main source characteristics, as well as the date of Ginga observation (or the dates of the first and last observations if more than one) are listed in Table  1 (click here). From the Nandra & Pounds analysis we have used the slope of the intrinsic power law derived by including in the model a reflection component and, when relevant, a warm absorber (Table 10 of their paper and last column of our Table  2 (click here)).

   

Obj. z       tex2html_wrap_inline1647 Ginga   ROSAT 
Obs. date        Obs. date     Exp. time2      cts CR3
Mkn 335 0.026 3.96 12/87-06/91 29-06-91 24586 65989       2.68tex2html_wrap_inline16530.01
Fairall-9 0.046 2.82 11/90 10-05-91 8173 31834 3.89tex2html_wrap_inline16530.02
NGC 3783 0.01 9.41 01/90 08-07-93 23344 38051 1.63tex2html_wrap_inline16530.01
NGC 4051 0.002        1.37 06/87-11/90 16-11-91 28727 46509 1.62tex2html_wrap_inline16530.01
NGC 4593 0.009 1.97 06/87-12/87 14-07-92 1261 1849 1.47tex2html_wrap_inline16530.03
MCG 6-30-15 0.008 4.06 09/87-02/90 29-01-92 8513 17017 2.00tex2html_wrap_inline16530.02
Mkn 841 0.036 2.24 07/90-01/91 20-01-92 17185 36656 2.13tex2html_wrap_inline16530.01
3C 390.3 0.056 4.12 11/88 17-03-91 11516 12184 1.06tex2html_wrap_inline16530.01
NGC 7469 0.017 4.82 06/88 28-05-92 18575 32933 1.77tex2html_wrap_inline16530.01
Akn 120 0.033 11.3 09/88 18-09-91 24493 36127 1.47tex2html_wrap_inline16530.01
NGC 5548 0.017 1.93 06/88-07/90 16-07-90 18861 34440 1.83tex2html_wrap_inline16530.01
Mkn 509 0.036 3.99 10/88-10/90 29-10-92 2294 12534 5.46tex2html_wrap_inline16530.05
NGC 3516 0.009 3.55 10/89-10/89 03-10-92 13081 61206 4.68tex2html_wrap_inline16530.02
IC 4329 A 0.014 4.55 07/89 04-01-93 8230 23307 2.83tex2html_wrap_inline16530.02
MCG 2-58-22        0.048 3.51 06/89-11/89 21-05-93 18767 17322 0.92tex2html_wrap_inline16530.01
NGC 7213 0.006 1.94 06/90-19/90 10-05-91 6688 36316 5.43tex2html_wrap_inline16530.03
3C 111 0.048 32.61 02/89 13-02-93 2322 1001 0.43tex2html_wrap_inline16530.01
Table 1: Log of Ginga and ROSAT observations

Note: (1) Galactic column density in units of tex2html_wrap_inline1687; (2) in s.; (3) in counts/s.

   

Obj. tex2html_wrap_inline1689             tex2html_wrap_inline1691              tex2html_wrap_inline1693         tex2html_wrap_inline1695          tex2html_wrap_inline1697         
Mkn 335 6.70tex2html_wrap_inline16530.10 3.88tex2html_wrap_inline16530.13 3.01tex2html_wrap_inline16530.05 1.52/176 2.39tex2html_wrap_inline16530.15
Fairall-9 11.4tex2html_wrap_inline16530.15 2.97tex2html_wrap_inline16530.13 2.46tex2html_wrap_inline16530.05 1.04/186 1.94tex2html_wrap_inline16530.09
NGC 3783 9.14tex2html_wrap_inline16530.12 10.0tex2html_wrap_inline16530.29 2.79tex2html_wrap_inline16530.07 17.5/111 2.11tex2html_wrap_inline16530.07
NGC 4051 2.24tex2html_wrap_inline16530.04 1.79tex2html_wrap_inline16530.10 2.84tex2html_wrap_inline16530.04 1.66/174 1.84tex2html_wrap_inline16530.09
MCG 6-30-15        8.73tex2html_wrap_inline16530.15 4.83tex2html_wrap_inline16530.24 2.23tex2html_wrap_inline16530.07 2.46/189 2.12tex2html_wrap_inline16530.04
Mkn 841 5.28tex2html_wrap_inline16530.08 2.28tex2html_wrap_inline16530.11 2.42tex2html_wrap_inline16530.04 1.25/187 2.30tex2html_wrap_inline16530.02
3C 390.3 5.63tex2html_wrap_inline16530.13 6.33tex2html_wrap_inline16530.35 1.89tex2html_wrap_inline16530.07 1.15/177 1.86tex2html_wrap_inline16530.03
NGC 7469 8.63tex2html_wrap_inline16530.11 5.82tex2html_wrap_inline16530.18 2.29tex2html_wrap_inline16530.05 1.03/199 1.97tex2html_wrap_inline16530.05
Akn 120 9.13tex2html_wrap_inline16530.14 10.2tex2html_wrap_inline16530.31 2.53tex2html_wrap_inline16530.05 0.93/199 1.93tex2html_wrap_inline16530.11
NGC 5548 4.56tex2html_wrap_inline16530.06 1.33tex2html_wrap_inline16530.09 1.94tex2html_wrap_inline16530.04 1.84/196 1.81tex2html_wrap_inline16530.02
Mkn 509 17.7tex2html_wrap_inline16530.38 3.93tex2html_wrap_inline16530.23 2.63tex2html_wrap_inline16530.08 0.96/158 1.86tex2html_wrap_inline16530.02
NGC 3516 15.6tex2html_wrap_inline16530.16 2.78tex2html_wrap_inline16530.10 2.15tex2html_wrap_inline16530.04 3.28/208 2.08tex2html_wrap_inline16530.09
IC 4329A 23.2tex2html_wrap_inline16532.10 23.5tex2html_wrap_inline16533.2 1.30tex2html_wrap_inline16530.15 0.92/197 2.03tex2html_wrap_inline16530.04
MCG 2-58-223.59tex2html_wrap_inline16530.06 3.51tex2html_wrap_inline16530.18 2.11tex2html_wrap_inline16530.06 0.96/183 1.67tex2html_wrap_inline16530.08
NGC 7213 15.8tex2html_wrap_inline16530.20 2.15tex2html_wrap_inline16530.10 2.14tex2html_wrap_inline16530.04 1.55/195 1.96tex2html_wrap_inline16530.08
Table 2: Fit with a simple power law

Note: (1) Power law flux at 1 keV in units of tex2html_wrap_inline1819 keV-1 (2) Neutral column density in units of tex2html_wrap_inline1687 (3) Best fit power law index with reflection and warm absorber included.

2.2. ROSAT data analysis and sample selection

Of all these 17 sources we have then analized the PSPC (Pfeffermann et al. 1987) observations in the ROSAT (Trümper 1983) public archive. In case of repeated pointings we have selected the longest observation, because we are primarily interested in the spectral properties. The log book of the ROSAT observations can also be found in Table  1 (click here).

Data of each observation were analyzed using the EXSAS package (Zimmermann et al. 1994). After examination of the image to exclude serendipitous sources that may contaminate source and background extraction regions, source spectra were extracted from a circular region of 3 arcmin radius. The background was computed in an annulus between 3.5 and 7 arcmin. The date of observation, exposure times, total source counts and count rates are listed in Table  1 (click here). For each source we produced a 256 channel pulse-invariant (PI) spectrum. We ignored PI channels 1-11 (E<0.1 keV) and above 235 (E>2.36 keV) and rebinned the remaining channels in order to have a signal to noise ratio in each bin of at least 7. We have added systematic errors of 2% to account for residual calibration uncertainties (ROSAT NEWS No. 10, Aug. 1992). The spectral analysis was performed using the PSPC response matrix released on Mar. 92 for the observations performed before 21 Nov. 1991, and the matrix released on Jan. 1993 for observations performed after that date.

In order to have adequate statistics for spectral analysis, particularly below 1 keV, we have further selected objects with ROSAT PSPC total counts greater than 2000 cts and absorption column density lower than 1021 cm-2. Two objects do not satisfy the first requirement (Table  1 (click here) ): NGC 4593 and 3C 111. As for the second selection criterion, we present in Table  2 (click here) the results of the simple power law fits to the 15 remaining objects. One object, IC 4329A, has an absorbing column in excess of 1021 cm-2: the final sample is therefore composed of 14 objects, with total counts comprised between 12.000 and 65.000 cts.

Hereinafter all the errors refer to a 90% confidence level for one interesting parameter.


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