Third set of INTEGRAL observations of GX339-4: preliminary spectral fit results
ATel #1029; 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 14 Mar 2007; 16:45 UT
Credential Certification: Erik Kuulkers (firstname.lastname@example.org)
Subjects: Binary, Black Hole, Transient, Variables
We present the results of preliminary spectral fits to the third period
of 145.6 ksec public INTEGRAL ToO observations of GX 339-4 (see ATels #980,
#986, #1000, #1012), obtained between UT 2007, Mar 4, 15:51 and Mar 6, 13:04.
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 hardened with
respect to the second period of observations (ATel #1012), with a ratio of
the soft (disk) to hard (power-law) X-ray emission being 26%
(in contrast to the 50% and 90% of the first and second period observations,
An absorbed multi-color disk black-body, with T_in = 0.95 (+0.05, -0.04 keV),
plus a cut-off power-law fits better (chi-square per degrees of freedom, dof,
of 75/58) than adding a single power-law (chi-square per dof of 95/60).
The obtained values for the photon index, cut-off and
un-folded energies are 2.45 (+0.10, -0.13), 21 (+10, -6) keV and
157 (+60, -40) keV, respectively. A model containing a multi-color black-body plus a
compTT model also fits the spectrum quite well (chi-square per dof of 79/59),
implying a temperature of the electrons and an opacity of the corona of
53 (+80, -27) keV and 0.94 +/- 0.5, respectively. We do not see evidence for
any iron-like emission feature in the residuals at 6-8 keV greater than 10% of the flux.
The implied unabsorbed luminosity of the source in the 5-300 keV band is
L= 5.25 +/- 1.7 E+37 erg/s, assuming a distance to the source of 8.5 kpc.
So, the unabsorbed luminosity increased by 70% with respect the second INTEGRAL
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. The luminosity was slightly decreasing in the 20-60 keV energy
PostScript figures of the preliminary spectral fit results, as well as
the JEM-X and IBIS/ISGRI light curves, can be found at