ALBERT

Description: INTEGRAL Gamma-Ray (IGR) J14091–6108 is a Galactic X-ray source known to have an iron emission line, a hard X-ray spectrum, and an optical counterpart. Here, we report on X-ray observations of the source with XMM–Newton and NuSTAR as well as optical spectroscopy with European Southern Obseratory/Very Large Telescope and National Optical Astronomy Observatory/Southern Astrophysical Research Telescope. In the X-rays, this provides data with much better statistical quality than the previous observations, and this is the first report of the optical spectrum. Timing analysis of the XMM data shows a very significant detection of 576.3 ± 0.6 s period. The signal has a pulsed fraction of 30 ± 3 per cent in the 0.3–12 keV range and shows a strong drop with energy. The optical spectra show strong emission lines with significant variability in the lines and continuum, indicating that they come from an irradiated accretion disc. Based on these measurements, we identify the source as a magnetic cataclysmic variable of intermediate polar (IP) type where the white dwarf spin period is 576.3 s. The X-ray spectrum is consistent with the continuum emission mechanism being due to thermal bremsstrahlung, but partial covering absorption and reflection are also required. In addition, we use the IP mass model, which suggests that the white dwarf in this system has a high mass, possibly approaching the Chandrasekhar limit.

Description: Studying the population of faint hard X-ray sources along the plane of the Galaxy is challenging because of high extinction and crowding, which make the identification of individual sources more difficult. IGR J18293–1213 is part of the population of persistent sources which have been discovered by the INTEGRAL satellite. We report on NuSTAR and Swift /XRT observations of this source, performed on 2015 September 11. We detected three eclipsing intervals in the NuSTAR light curve, allowing us to constrain the duration of these eclipses, $\Delta t= 30.8^{+6.3}_{-0.0}$  min, and the orbital period of the system, T = 6.92 ± 0.01 h. Even though we only report an upper limit on the amplitude of a putative spin modulation, the orbital period and the hard thermal bremsstrahlung spectrum of IGR J18293–1213 provide strong evidence that this source is a magnetic cataclysmic variable. Our NuSTAR and Swift /XRT joint spectral analysis places strong constraints on the white dwarf mass $M_{\rm wd} = 0.78^{+0.10}_{-0.09}$  M . Assuming that the mass to radius ratio of the companion star M * / R * = 1 (solar units) and using T , t , and M wd , we derived the mass of the companion star M * = 0.82 ± 0.01 M , the orbital separation of the binary system a = 2.14 ± 0.04 R , and its orbital inclination compared to the line of sight $i=(72 {^{\circ}_{.}} 2^{+2.4}_{-0.0})\pm 1 {^{\circ}_{.}} 0$ .

Description: Here, we report on observations of two hard X-ray sources that were originally discovered with the INTEGRAL satellite: IGR J04059+5416 and IGR J08297–4250. We use the Chandra X-ray Observatory to localize the sources and then archival near-IR images to identify the counterparts. Both sources have counterparts in the catalogue of extended 2 Micron All-Sky Survey sources, and the counterpart to IGR J04059+5416 has been previously identified as a galaxy. Thus, we place IGR J04059+5416 in the class of active galactic nuclei (AGN), and we suggest that IGR J08297–4250 is also an AGN. If this identification is correct, the near-IR images suggest that the host galaxy of IGR J08297–4250 may be merging with a smaller nearby galaxy. For IGR J04059+5416, the 0.3–86 keV spectrum from Chandra and INTEGRAL is consistent with an absorbed power-law with a column density of $N_{\rm H} = (3.1^{+2.0}_{-1.5})\times 10^{22}$  cm –2 and a photon index of  = 1.4 ± 0.7, and we suggest that it is a Seyfert galaxy. For IGR J08297–4250, the photon index is similar,  = 1.5 ± 0.8, but the source is highly absorbed ( $N_{\rm H} = (6.1^{+10.1}_{-4.3})\times 10^{23}$  cm –2 ).

Description: As a complement to our optical and near-infrared study of the continuum properties of GX 339–4 in the two hard and one soft state observations made by the ESO/Very Large Telescope (VLT), FOcal Reducer and Spectrograph #2 (FORS2) and infrared spectrometer and array camera (ISAAC) in early 2010, we report here on the results of our spectral line analysis for the same observations. In the soft state, the presence of strong Balmer, Paschen and Brackett emission lines points to the optical and near-infrared spectra stemming from the irradiated chromosphere of the optically thick and geometrically thin accretion disc. Most of these H i features are still detected in emission in both hard states but are veiled by the compact jets continuum. We also confirm the presence of a broad Hβ absorption feature, prominent in the soft state and shallower in the first hard state, which we argue forms in the deep layers of the optically thick accretion disc. However, this trough is absent in the second hard state, a likely consequence of the formation of a geometrically thick extended envelope that arises above the disc plane and eventually enshrouds the region where the Hβ absorption feature forms. We detect this envelope through the presence of a broad Paβ emission line, which is constant during the first hard state but correlates with the underlying continuum during the second hard state, pointing to changing physical properties. We consider that this behaviour may be consistent with the launch of a thermally driven accretion disc wind during the second hard state.

Description: We present results from the spectral fitting of the candidate black hole X-ray binary Swift J1753.5-0127 in an accretion state previously unseen in this source. We fit the 0.7–78 keV spectrum with a number of models, however the preferred model is one of a multitemperature disc with an inner disc temperature k T in  = 0.252 ± 0.003 keV scattered into a steep power-law with photon index $\Gamma =6.39^{+0.08}_{-0.02}$ and an additional hard power-law tail ( = 1.79 ± 0.02). We report on the emergence of a strong disc-dominated component in the X-ray spectrum and we conclude that the source has entered the soft state for the first time in its ~10 yr prolonged outburst. Using reasonable estimates for the distance to the source (3 kpc) and black hole mass (5 M ), we find the unabsorbed luminosity (0.1–100 keV) to be 0.60 per cent of the Eddington luminosity, making this one of the lowest luminosity soft states recorded in X-ray binaries. We also find that the accretion disc extended towards the compact object during its transition from hard to soft, with the inner radius estimated to be $R_{\mathrm{in}}=28.0^{+0.7}_{-0.4} R_g$ or ~12 R g , dependent on the boundary condition chosen, assuming the above distance and mass, a spectral hardening factor f  = 1.7 and a binary inclination i  = 55°.

Description: We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights show steep power spectra dominated by slow variations on ~100–1000 s time-scales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ~ few  x  10 36  erg s –1 . Some are unresolved down to a time resolution of 24 ms. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power and characteristic time-scales of the fast flares can be explained as optically thin synchrotron emission from a compact jet arising on size scales ~140–500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong Hα emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e. red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in time-scale during the outburst.

Description: We report on FORS2 (FOcal Reducer/low dispersion Spectrograph 2) spectroscopy aiming at the identification of four Galactic plane sources discovered by INTEGRAL , IGR J18088–2741, IGR J18381–0924, IGR J17164–3803, and IGR J19173+0747, complemented by XMM–Newton spectroscopy for IGR J18381–0924. The presence of broad H i and He i emission lines and a flat Balmer decrement Hα/Hβ show that IGR J18088–2741 is a cataclysmic variable located beyond 8 kpc. For IGR J18381–0924, the detection of redshifted Hα and O i emission signatures and the absence of narrow forbidden emission lines point towards a low-luminosity Seyfert 1.9 nature at z = 0.031 ± 0.002. Its XMM–Newton spectrum, best fitted by an absorbed = 1.19 ± 0.07 power law combined with a $z=0.026_{-0.008}^{+0.016}$ redshifted iron emission feature, is in agreement with this classification. The likely IGR J17164–3803 optical counterpart is an M2 III star at 3–4 kpc which, based on the X-ray spectrum of the source, is the companion of a white dwarf in an X-ray faint symbiotic system. Finally, we challenge the accepted identification of IGR J19173+0747 as a high-mass X-ray binary. Indeed, the USNO optical counterpart is actually a blend of two objects located at the most likely 3 kpc distance, both lying within the error circle of the Swift position. The first is a cataclysmic variable, which we argue is the real nature of IGR J19173+0747. However, we cannot rule out the second one which we identify as an F3 V star which, if associated with IGR J19173+0747, likely belongs to a quiescent X-ray binary.

Description: We report on FORS2 optical spectroscopy of the black hole X-ray binary V404 Cygni, performed at the very beginning of its 2015 outburst decay, complemented by quasi-simultaneous Swift X-ray and ultraviolet as well as Rapid Eye Mountain near-infrared observations. Its peculiar spectrum is dominated by a wealth of emission signatures of H i , He  i , and higher ionization species, in particular Fe  ii . The spectral features are divided between broad redshifted and narrow stationary varieties, the latter being emitted in the outer regions. Continuum and line variability at short time-scale is high, and we find Baldwin effect-like anticorrelations between the full widths at half-maximum and equivalent widths of the broad lines with their local continua. The Balmer decrement H α /H β is also abnormally large at 4.61 ± 0.62. We argue that these properties hint at the broad lines being optically thick and arising within a circumbinary component in which shocks between faster optically thick and slower optically thin regions may occur. We associate it to a nova-like nebula formed by the cooling remnant of strong accretion disc winds that turned off when the mass-accretion rate dropped following the last major flare. The Fe  ii lines likely arise from the overlap region between this nebula and the companion star winds, whereas we favour the shocks within the nebula as responsible for the optical continuum via self-absorbed optically thin bremsstrahlung. The presence of a near-infrared excess also points towards the contribution of a strongly variable compact jet or a dusty component.

Description: We present results from a multi-wavelength infrared (IR)-to-X-ray campaign of the infrared bright (but highly optical-ultraviolet extincted) quasi-stellar object (QSO) IRAS 13349+2438 obtained with the Chandra High Energy Transmission Grating Spectrometer (HETGS), the Hubble Space Telescope ( HST ) Space Telescope Imaging Spectrograph (STIS), the Hobby–Eberly Telescope (HET) 8 m and the Spitzer Infrared Spectrometer (IRS). Based on HET optical spectra of [O iii ], we refine the redshift of IRAS 13349 to be z  = 0.108 53. The weakness of the [O iii ] in combination with strong Fe ii in the HET spectra reveals extreme Eigenvector-1 characteristics in IRAS 13349, but the 2468 km s –1 width of the Hβ line argues against a narrow-line Seyfert 1 classification; on average, IR, optical and optical-ultraviolet (UV) spectra show IRAS 13349 to be a typical QSO. Independent estimates based on the Hβ line width and fits to the IRAS 13349 spectral energy distribution (SED) both give a black hole mass of M BH  = 10 9 M . The heavily reddened STIS UV spectra reveal for the first time blueshifted absorption from Ly α , N v and C iv , with components at systemic velocities of $-950 {{\rm km} {\rm s}^{-1}}$ and $-75 {\rm km} {\rm s}^{-1}\,$ . The higher velocity UV lines are coincident with the lower ionization ( ~ 1.6) WA-1 warm absorber lines seen in the X-rays with the HETGS. In addition, a  ~ 3.4 WA-2 is also required by the data, while a  ~ 3 WA-3 is predicted by theory and seen at less significance; all detected X-ray absorption lines are blueshifted by ~ 700-900 km s –1 . Theoretical models comparing different ionizing SEDs reveal that including the UV (i.e. the accretion disc) as part of the ionizing continuum has strong implications for the conclusions one would draw about the thermodynamic stability of the warm absorber. Specific to IRAS 13349, we find that an X-ray–UV ionizing SED favours a continuous distribution of ionization states in a smooth flow (this paper) versus discrete clouds in pressure equilibrium (previous work by other authors). Direct detections of dust are seen in both the IR and X-rays. We see weak polycyclic aromatic hydrocarbon (PAH) emission at 7.7 μm and 11.3 μm which may also be blended with forsterite, and 10 μm and 18 μm silicate emission, as well as an Fe L edge at 700 eV indicative of iron-based dust with a dust-to-gas ratio 〉90 per cent. We develop a geometrical model in which we view the nuclear regions of the QSO along a line of sight that passes through the upper atmosphere of an obscuring torus. This sight line is largely transparent in X-rays since the gas is ionized, but it is completely obscured by dust that blocks a direct view of the UV/optical emission region. In the context of our model, 20 per cent of the intrinsic UV/optical continuum is scattered into our sight line by the far wall of an obscuring torus. An additional 2.4 per cent of the direct light, which likely dominates the UV emission, is Thomson-scattered into our line of sight by another off-plane component of highly ionized gas.