Fifth set of INTEGRAL observations of GX339-4: preliminary spectral fit results
ATel #1050; 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 5 Apr 2007; 22:06 UT
Credential Certification: Erik Kuulkers (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Binary, Black Hole, Transient, Variables
Referred to by ATel #: 1074
We present the results of preliminary spectral fits to the fifth period of 150 ksec
public INTEGRAL ToO observations of GX 339-4 (see ATels #980, #986, #1000, #1012,
#1029, #1032, #1048), obtained between UT 2007, Mar 29, 04:40 and Mar 31, 01:42. We made joint
spectral fits to spectra obtained with the JEM-X (5-20 keV) and IBIS/ISGRI (23-100 keV)
instruments. The spectrum continued to soften, as observed in the previous
observation (ATel #1032), with a contribution of the disk compared to the power-law
emission (see below) of about 74%.
A phenomenological model consisting of an absorbed multi-color disk with
T_in = 0.98 Â± 0.08 keV plus a power-law with a photon index of 2.6 Â± 0.2 fits the
spectrum fairly (chi-square per degrees of freedom, d.o.f., of 48/25). 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 51/23), and we do not find any break energy between 20 and 100 keV compatible
with the data. We note that a fit with a compTT model gives slightly worse results
(chi-square per d.o.f. of 54/24). The situation resembles that of our second and
fourth INTEGRAL observations (ATels #1012 and #1032): approximately same
photon index and no evidence for a break at high energies,
with characteristics typical of a high state.
The unabsorbed total luminosity in the 5-100 keV range, assuming a distance of
8.5 kpc, is about 1 E+37 erg/s. This corresponds to a decrease of about 50% in luminosity
with respect to that observed in our fourth observation (ATel #1032).
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