Fourth set of INTEGRAL observations of GX339-4: preliminary spectral fit results
ATel #1032; M. D. Caballero-Garcia (LAEFF/INTA), J. Miller (Univ. of Michigan), E. Kuulkers (ESA/ESAC), M. Diaz Trigo (ESA/ESAC), on behalf of a larger collaboration
on 23 Mar 2007; 15:52 UT
Credential Certification: Erik Kuulkers (email@example.com)
Subjects: X-ray, Gamma Ray, Binary, Black Hole, Transient, Variables
Referred to by ATel #: 1050
We present the results of preliminary spectral fits to the fourth period
of 130 ksec public INTEGRAL ToO observations of GX 339-4 (see ATels #980,
#986, #1000, #1012, #1029), obtained between UT 2007, Mar 16, 17:03 and
Mar 18, 07:17. We made joint spectral fits to spectra obtained with the
JEM-X (5-20 keV) and IBIS/ISGRI (23-200 keV) instruments. The spectrum has
slightly softened with respect to the previous observation (ATel #1029),
with a contribution of the disk compared to the power-law emission of 36%.
A phenomenological model consisting of an absorbed multi-color disk with
T_in = 0.80 Â± 0.05 keV plus a power-law with a photon index of 2.7 Â± 0.1 fits
the spectrum fairly (chi-square per d.o.f. of 70/38). We find that, when using
a cut-off power-law rather than a power-law it does not improve the fit
(chi-square per d.o.f of 69/35), and we can not constrain the high-energy cut-off
(values between 20 and 300 keV are compatible with the data).
We note that a fit with a compTT model gives slightly worse results
(chi-square per d.o.f. of 86/36). The situation resembles that of our second
INTEGRAL observation (ATel #1012): approximately same photon index, unabsorbed
luminosity and no evidence for a break up to about 300 keV, with characteristics
typical of a high state.
The unabsorbed total luminosity in the 5-300 keV range, assuming a distance of 8.5 kpc,
is 1.17-2.32 E+37 erg/s. This corresponds to a decrease of 67% in luminosity with
respect to that observed in our third observation (ATel #1029).
We also examined the JEM-X and ISGRI light curves with a time binning of
1000 sec, in the 3-6, 6-10, 10-15, 15-35, 20-40, 40-60, 60-100, 100-200 keV
energy ranges. No strong variability or trends were seen.
PostScript figures of the preliminary spectral fit results,
as well as the JEM-X and IBIS/ISGRI
light curves, can be found at