Kilohertz QPOs, spectral state transitions and the distance to the neutron star X-ray transient IGR J17473-2721.
ATel #1651; D. Altamirano (UvA), D. Galloway (Monash University), J. Chenevez (DTU/NSI, Denmark), J. in 't Zand (SRON), E. Kuulkers (ESA/ESAC, Spain), N. Degenaar(UvA), E. del Monte (INAF/IASF, Roma), M. Feroci (INAF/IASF, Roma), E. Costa (INAF/IASF, Roma), Y. Evangelista (INAF/IASF, Roma), M. Falanga (CEA, Saclay), C. Markwardt (U. Md./CRESST/NASA GSFC), R. Wijnands (UvA) & M. van der Klis (UvA).
on 8 Aug 2008; 10:51 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Diego Altamirano (firstname.lastname@example.org)
Subjects: X-ray, Binary, Neutron Star, Transient
We report on RXTE monitoring observations of the transient X-ray
binary IGR J17473-2721 since the beginning of its latest outburst on
March 26th, 2008 (see ATEL #1445, #1459, #1460, #1461 and
IGR J17473-2721 reached a maximum unabsorbed flux of ~1.30E-8 ergs
cm-2 s-1 (2-10 keV, assuming nH=3.8e22cm-2, ATEL #1459) on June 22nd,
and has been steadily decreasing since. The X-ray spectral state
(based on the X-ray colors in the 2-16 keV band) has switched from
hard to soft and back to hard. These state changes are also
evident from the Swift/BAT Hard X-ray monitoring
During the soft state, 6 observations show a significant (between 3.5
and 10 sigma) kHz QPO at frequency up to ~900 Hz, that reach up to 8%
rms amplitudes (2-60 keV). The combination of energy spectral and
power spectral variations are typical of neutron star atoll sources.
RXTE has detected 16 type-I (thermonuclear) X-ray bursts so
far during this outburst. Two bursts observed on July 17 and 19
exhibited photospheric radius expansion, reaching identical peak
(bolometric) fluxes of 9.5e-8 erg/cm2/s. The corresponding distance is
likely between 4.9 kpc (using the theoretical Eddington limit for a
pure He atmosphere) and 5.7 kpc (using the empirical value for the
Eddington luminosity from Kuulkers et al. 2003, A&A, 399, 663). We
found no evidence for burst oscillations.
We thank Jean Swank and the RXTE team for scheduling the observations.