A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

X-ray observations have revealed that many microquasars and low-mass X-ray binaries (LMXBs) exhibit narrow absorption features identified with resonant absorption from Fe xxv and Fe xxvi and other abundant ions. In many well studied systems there is evidence for blue-shifts, indicating outflowing plasmas. We succesfully model the changes in both the X-ray continuum and the Fe absorption features during dips from all the bright dipping LMXBs observed by XMM-Newton (EXO 0748−676, XB 1254−690, X 1624−490, MXB 1659−298, 4U 1746−371 and XB 1916−053) as resulting primarily from an increase in column density and a decrease in the ionization state of a highly-ionized absorber in a similar way as was done for XB 1323−619. This implies that the complex spectral changes in the X-ray continua observed from the dip sources as a class can be most simply explained primarily by changes in the highly ionized absorbers present in these systems. There is no need to invoke unusual abundances or partial covering of extended emission regions. Outside of the dips, the absorption line properties do not vary strongly with orbital phase. This implies that the ionized plasma has a cylindrical geometry with a maximum column density close to the plane of the accretion disk. Since dipping sources are simply normal LMXBs viewed from close to the orbital plane this implies that ionized plasmas are a common feature of LMXBs.

Abstract.We report the detection of narrow Fe  and Fe  X-ray absorption lines at 6.68 ± 0.04 keV and 6.97 ± 0.05 keV in the persistent emission of the dipping low-mass X-ray binary 4U 1323−62 during a 2003 January XMM-Newton observation. These features are superposed on a broad emission feature centered on 6.6 +0.1 −0.2 keV. During dipping intervals the equivalent width of the Fe  feature increases while that of the Fe  feature decreases, consistent with the presence of less strongly ionized material in the line-of-sight. As observed previously, the changes in the 1.0-10 keV spectrum during dips are inconsistent with a simple increase in absorption by cool material. However, the changes in both the absorption features and the continuum can be modeled by variations in the properties of an ionized absorber. No partial covering of any component of the spectrum, and hence no extended corona, are required. From persistent to deep dipping, the photo-ionization parameter, ξ, expressed in erg cm s −1 , decreases from log(ξ) of 3.9 ± 0.1 to log(ξ) of 3.13 ± 0.07, while the equivalent hydrogen column density of the ionized absorber increases from (3.8 ± 0.4) × 10 22 atoms cm −2 to (37 ± 2) × 10 22 atoms cm −2 . Since highly-ionized absorption features are seen from many other dip sources, this mechanism may also explain the overall changes in X-ray spectrum observed during dipping intervals from these systems.

We analysed the XMM-Newton archival observations of 16 neutron star (NS), low-mass X-ray binaries (LMXBs) to study the Fe K emission in these objects. The sample includes all the observations of NS LMXBs performed in EPIC pn timing mode with XMM-Newton publicly available until September 30, 2009. We performed a detailed data analysis considering pile-up and background effects. The properties of the Fe lines differed from previous published analyses because of either incorrect pile-up corrections or different continuum parameterisation. Eighty percent of the observations for which a spectrum can be extracted showed significant Fe line emission. We found an average line centroid of 6.67 ± 0.02 keV and a finite width, σ, of 0.33 ± 0.02 keV. The equivalent width of the lines varied between 17 and 189 eV, with an average weighted value of 42 ± 3 eV. For sources where several observations were available, the Fe line parameters changed between observations whenever the continuum changed significantly. The line parameters did not show any correlation with luminosity. Most important, we could fit the Fe line with a simple Gaussian component for all the sources. The lines did not show the asymmetric profiles that were interpreted as indicating relativistic effects in previous analyses of these LMXBs.

MAXI J1659−152 is a bright X-ray transient black-hole candidate binary system discovered in September 2010. We report here on MAXI, RXTE, Swift, and XMM-Newton observations during its 2010/2011 outburst. We find that during the first one and a half week of the outburst the X-ray light curves display drops in intensity at regular intervals, which we interpret as absorption dips. About three weeks into the outbursts, again drops in intensity are seen. These dips have, however, a spectral behaviour opposite to that of the absorption dips, and are related to fast spectral state changes (hence referred to as transition dips). The absorption dips recur with a period of 2.414 ± 0.005 h, which we interpret as the orbital period of the system. This implies that MAXI J1659−152 is the shortest period black-hole candidate binary known to date. The inclination of the accretion disk with respect to the line of sight is estimated to be 65-80• . We propose the companion to the black-hole candidate to be close to an M5 dwarf star, with a mass and radius of about 0.15-0.25 M and 0.2-0.25 R , respectively. We derive that the companion had an initial mass of about 1.5 M , which evolved to its current mass in about 5-6 billion years. The system is rather compact (orbital separation of 1.33 R ), and is located at a distance of 8.6 ± 3.7 kpc, with a height above the Galactic plane of 2.4 ± 1.0 kpc. The characteristics of short orbital period and high Galactic scale height are shared with two other transient black-hole candidate X-ray binaries, i.e., XTE J1118+480 and Swift J1735.5−0127. We suggest that all three are kicked out of the Galactic plane into the halo, rather than being formed in a globular cluster.