NIR and optical observations of the failed outbursts of black hole binary XTE J1550-564

A number of low mass X-ray binaries (LMXBs) undergo "failed outbursts" in which, instead of evolving through the canonical states, they remain in a hard state throughout the outburst. While the sources of X-ray and radio emission in the hard state are relatively well understood, the origin of the near infrared (NIR) and optical emission is more complex though it likely stems from an amalgam of different emission processes, occurring as it does, at the intersecting wavelengths of those processes. We aim to identify the NIR/optical emission region(s) during a number of failed outbursts of one such low mass X-ray binary and black hole candidate, XTE J1550-564, in order to confirm or refute their classification as hard-state, failed outbursts. We present unique NIR/optical images and spectra, obtained with the ESO-New Technology Telescope, during the failed outbursts of 2001 and 2000. We compare the NIR/optical photometric, timing, and spectral properties with those expected for the different emission mechanisms in the various LMXB states. The NIR/optical data are consistent with having come from reprocessing of X-rays in the accretion disk, with no evidence of direct thermal emission from the disk itself. However, the observed variability in high-cadence NIR light curves suggest that the radio jet extends and contributes to the NIR wavelengths. We find that these failed outbursts did not transition to an intermediate state but remained in a true, hard state where there was no sign of jet quenching or deviation from the observed hard state correlations.Comment: Accepted to Astronomy & Astrophysics (8 pages

Multi-wavelength observations revealing the most obscured high energy sources of our Galaxy

Contributed talk,19 pages, 2 figures, 1 tableInternational audienceA new type of high-energy binary system has been revealed by the INTEGRAL satellite. These sources are being unveiled by means of multi-wavelength optical, near- and mid-infrared observations. Among these sources, two distinct classes are appearing: the first one is constituted of intrinsically obscured high-energy sources, of which IGR J16318-4848 seems to be the most extreme example. The second one is populated by the so-called supergiant fast X-ray transients, with IGR J17544-2619 being the archetype. We first give here a general introduction on INTEGRAL sources, before reporting on multi-wavelength optical to mid-infrared observations of a sample constituted of 21 INTEGRAL sources. We show that in the case of obscured sources our observations suggest the presence of absorbing material (dust and/or cold gas) enshrouding the whole binary system. We finally discuss the nature of these two different types of sources, in the context of high energy binary systems, and give a scenario of unification of all these different types of high energy sources, based on their high energy properties

A closer look at the X-ray transient XTE J1908+094: identification of two new near-infrared candidate counterparts

We had reported in Chaty, Mignani, Israel (2002) on the near-infrared (NIR) identification of a possible counterpart to the black hole candidate XTE J1908+094 obtained with the ESO/NTT. Here, we present new, follow-up, CFHT adaptive optics observations of the XTE J1908+094 field, which resolved the previously proposed counterpart in two objects separated by about 0.8". Assuming that both objects are potential candidate counterparts, we derive that the binary system is a low-mass system with a companion star which could be either an intermediate/late type (A-K) main sequence star at a distance of 3-10 kpc, or a late-type ($>$K) main sequence star at a distance of 1-3 kpc. However, we show that the brighter of the two objects (J ~ 20.1, H ~ 18.7, K' ~ 17.8) is more likely to be the real counterpart of the X-ray source. Its position is more compatible with our astrometric solution, and colours and magnitudes of the other object are not consistent with the lower limit of 3 kpc derived independently from the peak bolometric flux of XTE J1908+094. Further multi-wavelength observations of both candidate counterparts are crucial in order to solve the pending identification.Comment: accepted for publication in MNRAS, 5 pages, 3 figure

Search for interactions between ejections of GRS 1915+105 and its environment

To unravel the effect of likely interactions between the energetic ejections of the galactic superluminal source GRS 1915+105 and its surrounding interstellar medium, we observed its environment. Two IRAS sources are symmetrically placed with respect to GRS 1915+105, and are aligned with the sub-arcsec ejections of this source. We analyzed these two sources IRAS 19124+1106 and IRAS 19132+1035 through near-infrared, millimeter and centimeter wavelengths. The evidence for these regions being interaction zones seems inconclusive.Comment: 4 pages, 3 figures, to appear in Proceedings of X-ray Astronomy '999 - Stellar Endpoints, AGN and the Diffuse Background, 2000. G. Malaguti, G. Palumbo & N. White (eds), Gordon & Breach (Singapore

Optical/near-infrared observations of the black hole candidate XTE J1720-318: from high-soft to low-hard state

Aims: To gain a better understanding of high-energy Galactic sources, we observed the Galactic X-ray binary and black hole candidate XTE J1720-318 in the optical and near-infrared, just after the onset of its X-ray outburst in January, 2003. These observations were obtained with the ESO/NTT as the Target of Opportunity, in February and April 2003. Methods: We performed an accurate astrometry and analysed photometrical and spectroscopic observations. We then produced a colour-magnitude diagram, looked at the overall evolution of the multi-wavelength light curve, and analysed the spectral energy distribution. Results: We discovered the optical counterpart in the R-band (R $\sim 21.5$) and confirmed the near-infrared counterpart. We show that, for an absorption between 6 and 8 magnitudes, XTE J1720-318 is likely to be an intermediate mass X-ray binary located at a distance between 3 and 10 kpc, hosting a main sequence star of spectral type between late B and early G. Our second set of observations took place simultaneously with the third secondary outburst present in X-ray and near-infrared light curves. The evolution of its spectral energy distribution shows that XTE J1720-318 entered a transition from a high-soft to a low-hard state in-between the two observations