IGR J17454-2919 is a hard X-ray transient discovered by INTEGRAL on 2014 September 27. We report on our 20ks Chandra observation of the source, performed about five weeks after the discovery, as well as on INTEGRAL and Swift monitoring long-term obse
rvations. X-ray broad-band spectra of the source are compatible with an absorbed power-law, $Gammasim$1.6-1.8, ${rm N_H}sim$(10-12)$times 10^{22},{rm cm}^{-2}$, with no trace of a cut-off in the data up to about 100keV, and with an average absorbed 0.5-100keV flux of about (7.1-9.7)${times 10^{-10}~erg~cm^{-2}~s^{-1}}$. With Chandra, we determine the most accurate X-ray position of IGR J17454-2919, $alpha_{J2000}$=17$^{h}$ 45$^{m}$ 27$^{s}$.69, $delta_{J2000}$= $-$29$^{circ}$ 19$^{prime}$ 53$^{prime prime}$.8 (90% uncertainty of 0$^{primeprime}$.6), consistent with the NIR source 2MASS J17452768-2919534. We also include NIR investigations from our observations of the source field on 2014 October 6 with GROND. With the multi-wavelength information at hand, we discuss the possible nature of IGR J17454-2919.
We report the first broad-band (0.5-150 keV) simultaneous X-ray observations of the very faint X-ray transient IGRJ17285-2922/XTEJ1728-295 performed with XMM-Newton and INTEGRAL satellites during its last outburst, started on 2010, August 28. XMM-New
ton observed the source on 2010 September 9-10, for 22ks. INTEGRAL observations were part of the publicly available Galactic Bulge program, and overlapped with the times covered by XMM-Newton. The broad-band spectroscopy resulted in a best-fit with an absorbed power law displaying a photon index of 1.61+/-0.01, an absorbing column density of (5.10+/-0.05)E21 cm-2, and a flux of 2.4E-10 erg/cm2/s (1-100 keV), corrected for the absorption. The data did not require either a spectral cut-off (E>50 keV) or an additional soft component. The slopes of the XMM-Newton and INTEGRAL separate spectra were compatible, within the uncertainties. The timing analysis does not show evidence either for X-ray pulsations or for type I X-ray bursts. The broad band X-ray spectrum as well as the power density spectrum are indicative of a low hard state in a low mass X-ray binary, although nothing conclusive can be said about the nature of the compact object (neutron star or black hole). The results we are reporting here allow us to conclude that IGRJ17285-2922 is a low mass X-ray binary, located at a distance greater than 4 kpc.
GS 1826-238 is a well-studied X-ray bursting neutron star in a low mass binary system. Thermal Comptonisation by a hot electron cloud is a widely accepted mechanism accounting for its high energy emission, while the nature of most of its soft X-ray o
utput is not completely understood. A further low energy component is typically needed to model the observed spectra: pure blackbody and Comptonisation-modified blackbody radiation by a lower temperature (a few keV) electron plasma were suggested to explain the low energy data. We studied the steady emission of GS 1826-238 by means of broad band (X to soft Gamma-rays) measurements obtained by the INTEGRAL observatory in 2003 and 2006. The newly developed, up-to-date Comptonisation model CompTB is applied for the first time to study effectively the low-hard state variability of a low-luminosity neutron star in a low-mass X-ray binary system. We confirm that the 3-200 keV emission of GS is characterised by Comptonisation of soft seed photons by a hot electron plasma. A single spectral component is sufficient to model the observed spectra. At lower energies, no direct blackbody emission is observed and there is no need to postulate a low temperature Compton region. Compared to the 2003 measurements, the plasma temperature decreased from 20 to 14 keV in 2006, together with the seed photons temperature. The source intensity was also found to be 30% lower in 2006, whilst the average recurrence frequency of the X-ray bursts significantly increased. Possible explanations for this apparent deviation from the typical limit-cycle behaviour of this burster are discussed.
The broad-band 1-300 keV Suzaku spectrum of IGR J17497-2821, the X-ray transient discovered by INTEGRAL in September 2006, is presented. Suzaku observed IGR J17497-2821 on September 25, eight days after its discovery, for a net exposure of about 53 k
sec. During the Suzaku observation, IGR J17497-2821 is very bright, 2 x 10^37 erg/s at 8 kpc in the 1-300 keV range, and shows a hard spectrum, typical of black hole candidates in the low-hard state. Despite the multi-mission X-ray monitoring of the source, only with Suzaku is it possible to obtain a broad-band spectrum in the 1-300 keV range with a very high signal to noise ratio. A sum of a multi-color disc (DISKBB) and a thermal Comptonization component (COMPPS) with mild reflection is a good representation of our IGR J17497-2821 Suzaku spectrum. The spectral properties of the accretion disc as well as the cut-off energy in the spectrum at about 150 keV are clearly detected and constrained. We discuss the implications on the physical model used to interpret the data and the comparison with previous results.
