We present the results of our 600 ks RGS observation as part of the multiwavelength campaign on Mrk 509. The very high quality of the spectrum allows us to investigate the ionized outflow with an unprecedented accuracy due to the long exposure and the use of the RGS multipointing mode. We detect multiple absorption lines from the interstellar medium and from the ionized absorber in Mrk 509. A number of emission components are also detected, including broad emission lines consistent with an origin in the broad line region, the narrow O vii forbidden emission line and also (narrow) radiative recombination continua. The ionized absorber consists of two velocity components (v = −13 ± 11 km s −1 and v = −319 ± 14 km s −1 ), which both are consistent with earlier results, including UV data. There is another tentative component outflowing at high velocity, −770 ± 109 km s −1 , which is only seen in a few highly ionized absorption lines. The outflow shows discrete ionization components, spanning four orders of magnitude in ionization parameter. Due to the excellent statistics of our spectrum, we demonstrate for the first time that the outflow in Mrk 509 in the important range of log ξ between 1−3 cannot be described by a smooth, continuous absorption measure distribution, but instead shows two strong, discrete peaks. At the highest and lowest ionization parameters we cannot differentiate smooth and discrete components.

We report on the long term X-ray monitoring of the outburst decay of the low magnetic field magnetar SGR 0418+5729 , using all the available X-ray data obtained with RXTE, Swift, Chandra, and XMM-Newton observations, from the discovery of the source in June 2009, up to August 2012. The timing analysis allowed us to obtain the first measurement of the period derivative of SGR 0418+5729: P = 4(1) × 10 −15 s s −1 , significant at ∼ 3.5σ confidence level. This leads to a surface dipolar magnetic field of B dip 6 × 10 12 Gauss. This measurement confirms SGR 0418+5729 as the lowest magnetic field magnetar. Following the flux and spectral evolution from the beginning of the outburst up to ∼1200 days, we observe a gradual cooling of the tiny hot spot responsible for the X-ray emission, from a temperature of ∼ 0.9 to 0.3 keV. Simultaneously, the X-ray flux decreased by about 3 orders of magnitude: from about 1.4 × 10 −11 to 1.2 × 10 −14 erg s −1 cm −2 . Deep radio, millimeter, optical and gamma-ray observations did not detect the source counterpart, implying stringent limits on its multiband emission, as well as constraints on the presence of a fossil disk. By modeling the magneto-thermal secular evolution of SGR 0418+5729 , we infer a realistic age of ∼550 kyr, and a dipolar magnetic field at birth of ∼ 10 14 G. The outburst characteristics suggest the presence of a thin twisted bundle with a small heated spot at its base. The bundle untwisted in the first few months following the outburst, while the hot spot decreases in temperature and size. We estimate the outburst rate of low magnetic field magnetars to be about one per year per galaxy, and we briefly discuss the consequences of such result in several other astrophysical contexts.

We introduce the Galactic Bulge Survey (GBS) and we provide the Chandra source list for the region that has been observed to date. Among the goals of the GBS are constraining the neutron star equation of state and the black hole mass distribution via the identification of eclipsing neutron star and black hole low-mass X-ray binaries. The latter goal will, in addition, be obtained by significantly enlarging the number of black hole systems for which a black hole mass can be derived. Further goals include constraining X-ray binary formation scenarios, in particular the common envelope phase and the occurrence of kicks, via source-type number counts and an investigation of the spatial distribution of X-ray binaries, respectively. The GBS targets two strips of 6 • × 1 • (12 square degrees in total), one above (1 • < b < 2 • ) and one below (−2 • < b < −1 • ) the Galactic plane in the direction of the Galactic Center at both X-ray and optical wavelengths. By avoiding the Galactic plane (−1 • < b < 1 • ) we limit the influence of extinction on the X-ray and optical emission but still sample relatively large number densities of sources. The survey is designed such that a large fraction of the X-ray sources can be identified from their optical spectra. The X-ray survey, by design, covers a large area on the sky while the depth is shallow using 2 ks per Chandra pointing. In this way we maximize the predicted number ratio of (quiescent) low-mass X-ray binaries to Cataclysmic Variables. The survey is approximately homogeneous in depth to an 0.5-10 keV flux of 7.7×10 −14 erg cm −2 s −1 . So far, we have covered about two-thirds (8.3 square degrees) of the projected survey area with Chandra providing over 1200 unique X-ray sources. We discuss the characteristics and the variability of the brightest of these sources.

We have monitored the atoll‐type neutron star low‐mass X‐ray binary 4U 1636−53 with the Rossi X‐ray Timing Explorer (RXTE) for more than 1.5 yr. Our campaign consisted of short (∼2 ks) pointings separated by 2 d, regularly monitoring the spectral and timing properties of the source. During the campaign we observed a clear long‐term oscillation with a period of ∼30–40 d, already seen in the light curves from the RXTE All‐Sky Monitor, which corresponded to regular transitions between the hard (island) and soft (banana) states. We detected kilohertz (kHz) quasi‐periodic oscillations (QPOs) in about a third of the observations, most of which were in the soft (banana) state. The distribution of the frequencies of the peak identified as the lower kHz QPO is found to be different from that previously observed in an independent data set. This suggests that the kHz QPOs in the system shows no intrinsically preferred frequency.

We present optical, X‐ray and radio observations of the black hole transient (BHT) XTE J1752−223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752−223 is fainter than 24.4 mag in the i′ band. A comparison with measurements of the source during its 2009–2010 outburst shows that the outburst amplitude is more than 8 mag in the i′ band. Known X‐ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital‐period system (Porb≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲d≲ 8 kpc. Simultaneous X‐ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X‐ray and radio flux of XTE J1752−223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low‐luminosity end of the X‐ray–radio correlation for this source and compared it with other BHTs. We found that XTE J1752−223 adds to the number of outliers with respect to the ‘standard’ X‐ray–radio luminosity relation. Furthermore, XTE J1752−223 is the second source, after the BHT H1743−322, that shows a transition from the region of the outliers towards the ‘standard’ correlation at low luminosity. Finally, we report on a faint, variable X‐ray source we discovered with Chandra at an angular distance of ∼2.9 arcsec to XTE J1752−223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X‐ray emission associated with a jet from XTE J1752−223.

Using high‐precision astrometric optical observations from the Walter Baade Magellan Telescope in conjunction with high‐resolution very long baseline interferometric (VLBI) radio imaging with the Very Long Baseline Array (VLBA), we have located the core of the X‐ray binary system XTE J1752−223. Compact radio emission from the core was detected following the state transition from the soft to the hard X‐ray state. Its position to the south‐east of all previously detected jet components mandated a re‐analysis of the existing VLBI data. Our analysis suggests that the outburst comprised at least two ejection events prior to 2010 February 26. No radio‐emitting components were detected to the south‐east of the core at any epoch, suggesting that the receding jets were Doppler‐deboosted below our sensitivity limit. From the ratio of the brightness of the detected components to the measured upper limits for the receding ejecta, we constrain the jet speed β > 0.66 and the inclination angle to the line of sight θ < 49°. Assuming that the initial ejection event occurred at the transition from the hard intermediate state to the soft intermediate state, an initial period of ballistic motion followed by a Sedov phase (i.e. self‐similar adiabatic expansion) appears to fit the motion of the ejecta better than a uniform deceleration model. The accurate core location can provide a long time baseline for a future proper motion determination should the system show a second outburst, providing insights into the formation mechanism of the compact object.

We present phase‐resolved optical spectroscopy of the counterpart to the neutron star (NS) low‐mass X‐ray binary EXO 0748−676, almost one year after it turned into quiescence. The spectra display prominent Hβ and Hγ and weak Fe ii lines in emission. An average of all the spectra (corrected for the orbital motion) also exhibits a very weak line from Mg i. Tomographic reconstructions show that the accretion disc is not contributing to the optical line emission, which is instead dominated by the irradiated hemisphere of the companion star facing the NS. We could not detect absorption features from the mass donor star in the spectra. The emission lines appear broad, with an intrinsic full width at half‐maximum (FWHM) of 255 ± 22 km s−1. Under the assumption that the width of the Fe ii emission lines is dominated by rotational broadening, we obtain a lower limit on the compact object mass which is inconsistent with an NS accretor. We discuss this incongruity and conclude that either the lines are blends of unresolved features (although this requires some fine‐tuning) or they are broadened by additional effects such as bulk gas motion in an outflow. The fact that the Fe ii lines slightly lag in phase with respect to the companion star can be understood as outflowing gas consistent with a black‐widow‐like scenario. Nevertheless, we cannot rule out the possibility that blends of various emission lines cause the apparent phase lag of the Fe ii emission lines as well as their large width.

We report on Chandra observations of the bright ultra-luminous X-ray (ULX) source in NGC 3921. Previous XMM-Newton observations reported in the literature show the presence of a bright ULX at a 0.5-10 keV luminosity of 2×10 40 erg s −1 . Our Chandra observation finds the source at a lower luminosity of ≈ 8 × 10 39 erg s −1 , furthermore, we provide a Chandra position of the ULX accurate to 0.7 at 90% confidence. The X-ray variability makes it unlikely that the high luminosity is caused by several separate X-ray sources. In 3 epochs of archival Hubble Space Telescope (HST) observations we find a candidate counterpart to the ULX. There is direct evidence for variability between the two epochs of WFPC2 F814W observations with the observation obtained in 2000 showing a brighter source. Furthermore, converting the 1994 F336W and 2000 F300W WFPC2 and the 2010 F336W WFC3 observations to the Johnson U -band filter assuming a spectral type of O7 I we find evidence for a brightening of the U -band light in 2000. Using the higher resolution WFC3 observations the candidate counterpart is resolved into two sources of similar color. We discuss the nature of the ULX and the probable association with the optical counterpart(s). Finally, we investigate a potential new explanation for some (bright) ULXs as the decaying stages of flares caused by the tidal disruption of a star by a recoiled supermassive black hole. However, we find that there should be at most only 1 of such systems within z=0.08.