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Effects on Power-Law Slope and Absorbing Column Density


The Seyfert 1 galaxy Fairall 9 (z=0.046) has a fairly small Galactic column (3.1e20 cm-2) and is a featureless power law below 4 keV. It is thus well suited for studying the effects of changes in the calibration on the power-law continuum slope and absorbing column density. 0.5-10 keV spectral fitting results are shown in Table 2. A Gaussian is included to model the Fe-K line in this source (but effects on the Fe-K line using data with better high-energy statistics will be discussed below; note the Fe-K line parameters refer to the galaxy frame, except EW).

The results show that both the absorbing column and power-law slope are entirely consistent, within the errors, when measured with the OLD or CURRENT calibration. Moreover, the absolute column density is close to the Galactic value in both SIS0 and SIS1, but 90% 1-parameter just barley enclose it. These fits also show that the GIS cannot measure column densities this small.

Note also that these are early ASCA data, from AO3 (December 1994), so the low-energy efficiency degradation of the SIS had not yet set in. The degradation, which increased with time, considerably affects column density measurements and will be discussed further in future documentation.

Table 2

0.5-10 keV Power-Law Plus Gaussian Spectral Fits to Fairall 9 (AO3)

(0.8-10 keV for GIS)

Error ranges are for 90% confidence, 1 parameter

    Parameter

    OLD

    CURRENT

    SIS0:

    -

    -

    NH (1e20 cm^-2)

    3.6 [3.0-4.2]

    3.9 [3.1-4.8]

    Gamma

    2.00 [1.98-2.02]

    2.03 [1.99-2.07]

    Center-Energy [keV]

    6.50 [6.35-6.64]

    6.68 [6.41-7.04]

    Width (sigma) [keV]

    0.58 [0.43-0.79]

    1.32 [0.78-2.1]

    Intensity [1.e-4 photons /cm^2/s ]

    1.0 [0.8-1.3]

    2.3 [1.4-3.6]

    EW [eV]

    437 [350-568]

    1050 [639-1643]

    0.5-2 keV flux [1e-12 ergs/cm/cm/s]

    40.0

    41.5

    2-10 keV flux [1e-12 ergs/cm/cm/s]

    23.0

    24.1

    Chi-Square (d.o.f.)

    373.4 (251)

    293.3 (251)

    SIS1:

    -

    -

    NH (1e20 cm^-2)

    4.3 [3.7-4.9]

    4.2 [3.6-4.7]

    Gamma

    2.01 [1.99-2.02]

    2.00 [1.98-2.02]

    Center-Energy [keV]

    6.48 [6.40-6.55]

    6.52 [6.44-6.60]

    Width (sigma) [keV]

    0.24 [0.16-0.33]

    0.25 [0.17-0.36]

    Intensity [1.e-4 photons /cm^2/s ]

    0.7 [0.5-0.8]

    0.8 [0.6-1.0]

    EW [eV]

    284 [203-324]

    332 [249-415]

    0.5-2 keV flux [1e-12 ergs/cm/cm/s]

    38.6

    40.8

    2-10 keV flux [1e-12 ergs/cm/cm/s]

    22.2

    23.6

    Chi-Square (d.o.f.)

    304.5 (241)

    262.3 (242)

    GIS2:

    -

    -

    NH (1e20 cm^-2)

    0.0 [0.0-0.8]

    0.0 [0.0-3.9]

    Gamma

    2.02 [2.01-2.04]

    1.99 [1.97-2.01]

    Center-Energy [keV]

    6.50 [6.38-6.61]

    6.55 [<6.68]

    Width (sigma) [keV]

    0.38 [0.22-0.59]

    0.36 [0.18-0.63]

    Intensity [1.e-4 photons /cm^2/s ]

    0.6 [0.4-0.8]

    0.7 [0.5-0.9]

    EW [eV]

    301 [201-401]

    215 [154-276]

    0.5-2 keV flux [1e-12 ergs/cm/cm/s]

    34.3

    41.7

    2-10 keV flux [1e-12 ergs/cm/cm/s]

    18.4

    22.8

    Chi-Square (d.o.f.)

    506.7 (564)

    519.8 (564)

    GIS3:

    -

    -

    NH (1e20 cm^-2)

    0.0 [0.0-0.8]

    0.0 [0.0-0.2]

    Gamma

    2.03 [2.02-2.05]

    2.04 [2.02-2.06]

    Center-Energy [keV]

    6.45 [6.34-6.58]

    6.51 [6.39-6.64]

    Width (sigma) [keV]

    0.58 [0.45-0.72]

    0.70 [0.56-0.90]

    Intensity [1.e-4 photons /cm^2/s ]

    0.9 [0.7-1.15]

    1.5 [1.2-1.8]

    EW [eV]

    485 [377-620]

    658 [526-790]

    0.5-2 keV flux [1e-12 ergs/cm/cm/s]

    36.4

    44.1

    2-10 keV flux [1e-12 ergs/cm/cm/s]

    19.5

    23.7

    Chi-Square (d.o.f.)

    612.3 (585)

    645.5 (585)


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This file was last modified on Monday, 30-Jul-2001 18:17:25 EDT
Curator: Michael Arida (SP Sys); arida@milkyway.gsfc.nasa.gov
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This file was last modified on Monday, 30-Jul-2001 18:17:25 EDT

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