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Spectral Fits

Simultaneity: Although it is known that the slope of the X-ray spectrum of 3C 273 changes with time, examination of the softness ratio against time (see lightcurve plots below) shows that there was no detectable spectral variability in either of the two campaigns. Therefore we do not enforce exactly identical time intervals (GTI) for spectral extraction, in favor of improving signal-to-noise.

NOTE also that in the July 1996 campaign the BeppoSAX observation is only quasi-simultaneous with ASCA and RXTE.

The Model is a power-law with Galactic absorption only (1.79e20 cm-2). Therefore there is only 1 free parameter (the power-law slope) in all cases (apart from the independent normalizations).

Energy Range: To ensure fair, direct comparison we must use identical energy ranges. Note that the ranges for ASCA/PCA and ASCA/BeppoSAX comparisons are different.

Iron K Line: The iron line is strong in the July 1996 campaign and affects the slope measurements. Therefore we REMOVE data in the iron K band in BOTH sets of observations.

Statiscal Errors quoted are for 90% confidence, 1 interesting parameter.

JULY 1996: 3-10 keV fits, excluding 4.5-6.5 keV Fe-K region

    DETECTOR

    Photon Index

    4-10 keV flux (1)

    CHI-SQUARE/D.O.F.

    PCA

    1.648 (1.640-1.657)

    5.5

    16.3/10

    SIS0

    1.675 (1.612-1.741)

    4.3

    131.1/103

    SIS1

    1.588 (1.515-1.663)

    4.4

    90.0/95

    GIS2

    1.657 (1.603-1.712)

    4.4

    230.7/216

    GIS3

    1.667 (1.620-1.715)

    4.6

    253.5/241

    SIS+GIS (2)

    1.654 (1.626-1.683)

    4.4

    707.8/658

    SIS+GIS (MECS comp) (2,3)

    1.667 (1.653-1.682)

    4.4

    768.3/688

    MECS (3)

    1.61 (1.60-1.62)

    4.4

    44/52

JUNE 1998: 3-10 keV fits, excluding 4.5-6.5 keV Fe-K region

    DETECTOR

    Photon Index

    4-10 keV flux (1)

    CHI-SQUARE/D.O.F.

    PCA

    1.676 (1.666-1.687)

    8.7

    5.6/9

    SIS0

    1.694 (1.656-1.733)

    6.3

    129.4/133

    SIS1

    1.635 (1.592-1.678)

    6.6

    126.3/124

    GIS2

    1.670 (1.636-1.704)

    6.6

    291.4/315

    GIS3

    1.652 (1.624-1.681)

    7.2

    341.5/347

    SIS+GIS (2)

    1.656 (1.634-1.674)

    6.7

    816.2/843

    SIS+GIS (MECS comp) (2,3)

    1.646 (1.637-1.655)

    6.7

    784.3/753

    MECS (3)

    1.63 (1.61-1.64)

    6.8

    44/52

(1) Flux in units of 10-11 erg cm-2 s-1.

(2) Simultaneous fit with SIS0,SIS1,GIS2, and GIS3 with the relative normalizations free. The flux is averaged over four instruments.

(3) The energy range of the data for comparison of ASCA with BeppoSax is 1.5-4 keV and 8-10 keV (i.e. excluding 4-8 keV for the iron line). The BeppoSAX results are taken from report by Grandi and Guainazzi.


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This file was last modified on Monday, 30-Jul-2001 18:17:24 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 18:17:24 EDT

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