The very small accretion disks in ultracompact X-ray binaries are special laboratories in which to study disk accretion and outflows. We report on three sets of new (250 ks total) and archival (50 ...ks) Chandra/HETG observations of the "dipping" neutron star X-ray binary 4U 1916-053, which has an orbital period of P 50 minutes. We find that the bulk of the absorption in all three spectra originates in a disk atmosphere that is redshifted by v 220-290 km s−1, corresponding to the gravitational redshift at a radius of R ∼ 1200 GM/c2. This shift is present in the strongest, most highly ionized lines (Si xiv and Fe xxvi), with a significance of 5 . Absorption lines observed during dipping events (typically associated with the outermost disk) instead display no velocity shifts and serve as a local standard of rest, suggesting that the redshift is intrinsic to an inner disk atmosphere and not due to radial motion in the galaxy or a kick. In two spectra, there is also evidence of a more strongly redshifted component that would correspond to a disk atmosphere at R ∼ 70 GM/c2; this component is significant at the 3 level. Finally, in one spectrum, we find evidence of a disk wind with a blueshift of . If real, this wind would require magnetic driving.
Understanding how black holes accrete and supply feedback to their environment is one of the outstanding challenges of modern astrophysics. Swift J1910.2-0546 is a candidate black hole low-mass X-ray ...binary that was discovered in 2012 when it entered an accretion outburst. To investigate the binary configuration and the accretion morphology, we monitored the evolution of the outburst for Asymptotically = to3 months at X-ray, UV, optical (B, V, R, I), and near-infrared (J, H, K) wavelengths using Swift and SMARTS. The source evolved from a hard to a soft X-ray spectral state with a relatively cold accretion disk that peaked at Asymptotically = to0.5 keV. A Chandra/HETG spectrum obtained during this soft state did not reveal signatures of an ionized disk wind. Both the low disk temperature and the absence of a detectable wind could indicate that the system is viewed at relatively low inclination. The multi-wavelength light curves revealed two notable features that appear to be related to X-ray state changes. First, a prominent flux decrease was observed in all wavebands Asymptotically = to1-2 weeks before the source entered the soft state. This dip occurred in (0.6-10 keV) X-rays Asymptotically = to6 days later than at longer wavelengths, which could possibly reflect the viscous timescale of the disk. Second, about two weeks after the source transitioned back into the hard state, the UV emission significantly increased while the X-rays steadily decayed. We discuss how these observations may reflect changes in the accretion morphology, perhaps related to the quenching/launch of a jet or the collapse/recovery of a hot flow.
Abstract
The neutron star (NS) low-mass X-ray binary (LMXB) the Rapid Burster (RB; MXB 1730-335) uniquely shows both Type I and Type II X-ray bursts. The origin of the latter is ill-understood but ...has been linked to magnetospheric gating of the accretion flow. We present a spectral analysis of simultaneous Swift, NuSTAR and XMM–Newton observations of the RB during its 2015 outburst. Although a broad Fe K line has been observed before, the high quality of our observations allows us to model this line using relativistic reflection models for the first time. We find that the disc is strongly truncated at
$41.8^{+6.7}_{-5.3}$
gravitational radii (∼87 km), which supports magnetospheric Type II burst models and strongly disfavours models involving instabilities at the innermost stable circular orbit. Assuming that the RB magnetic field indeed truncates the disc, we find B = (6.2 ± 1.5) × 108 G, larger than typically inferred for NS LMXBs. In addition, we find a low inclination (
$i = 29^{\circ } \pm 2^{\circ }$
). Finally, we comment on the origin of the Comptonized and thermal components in the RB spectrum.
Summary
Dissimilatory sulphite reductase DsrAB occurs in sulphate/sulphite‐reducing prokaryotes, in sulphur disproportionators and also in sulphur oxidizers, where it functions in reverse. ...Predictions of physiological traits in metagenomic studies relying on the presence of dsrAB, other dsr genes or combinations thereof suffer from the lack of information on crucial Dsr proteins. The iron–sulphur flavoprotein DsrL is an example of this group. It has a documented essential function during sulphur oxidation and was recently also found in some metagenomes of probable sulphate and sulphite reducers. Here, we show that DsrL and reverse acting rDsrAB can form a complex and are copurified from the phototrophic sulphur oxidizer Allochromatium vinosum. Recombinant DsrL exhibits NAD(P)H:acceptor oxidoreductase activity with a strong preference for NADH over NADPH. In vitro, the rDsrABL complex effectively catalyses NADH‐dependent sulphite reduction, which is strongly enhanced by the sulphur‐binding protein DsrC. Our work reveals NAD+ as suitable in vivo electron acceptor for sulphur oxidation in organisms operating the rDsr pathway and points to reduced nicotinamide adenine dinucleotides as electron donors for sulphite reduction in sulphate/sulphite‐reducing prokaryotes that contain DsrL. In addition, dsrL cannot be used as a marker distinguishing sulphate/sulphite reducers and sulphur oxidizers in metagenomic studies without further analysis.
Abstract
A brief Chandra observation of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.326 showed it to be a relatively bright, soft X-ray source with a count rate of about ...1 count ks−1. In this article, we present results for the quasar from a 65-ks XMM–Newton observation, which constrains its spectral shape well. The quasar is clearly detected with a total of ∼460 net counts in the 0.2–10 keV band. The spectrum is characterized by a simple power-law model with a photon index of
$\Gamma = 2.30^{+0.10}_{-0.10}$
and the intrinsic 2–10 keV luminosity is 3.14 × 1045 erg s−1. The 1σ upper limit to any intrinsic absorption column density is N
H = 6.07 × 1022 cm−2. No significant iron emission lines were detected. We derive an X-ray-to-optical flux ratio αox of −1.74 ± 0.01, consistent with the values found in other quasars of comparable ultraviolet luminosity. We did not detect significant flux variations either in the XMM–Newton exposure or between XMM–Newton and Chandra observations, which are separated by ∼8 months. The X-ray observation enables the bolometric luminosity to be calculated after modelling the spectral energy distribution: the accretion rate is found to be sub-Eddington.
We report on Chandra observations of the bright ultraluminous 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 x 10 super(40) erg s super(-1). Our Chandra observation finds the source at a lower luminosity of approximate8 x 10 super(39) erg s super(-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 three epochs of archival Hubble Space Telescope 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 O7I, we find evidence for a brightening of the U-band light in 2000. Using the higher resolution WFC3 observations, we resolve the candidate counterpart 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 one of such systems within z = 0.08.
We report on the detection of a thermal disc component from the stellar-mass black hole binary XTE J1118+480 in the canonical low/hard state. The presence of a thermal component with a temperature of ...approximately 0.21 keV in the Chandra spectra of XTE J1118+480 is found at more than the 14σ confidence level. Based on this evidence, we argue that the accretion disc in XTE J1118+480 is not truncated far from the central black hole in contrast with previous claims.
We present new XMM–Newton data of the high-redshift (z= 1.883), Mpc-sized giant radio galaxy 6C 0905+39. The larger collecting area and longer observation time for our new data means that we can ...better characterize the extended X-ray emission, in particular its spectrum, which arises from cosmic microwave background photons scattered into the X-ray band by the energetic electrons in the spent synchrotron plasma of the (largely) radio-quiet lobes of 6C 0905+39. We calculate the energy that its jet-ejected plasma has dumped into its surroundings in the last 3 × 107yr and discuss the impact that similar, or even more extreme, examples of spent, radio-quiet lobes would have on their surroundings. Interestingly, there is an indication that the emission from the hotspots is softer than the rest of the extended emission and the core, implying it is due to synchrotron emission. We confirm our previous detection of the low-energy turnover in the eastern hotspot of 6C 0905+39.
Models of jet production in black hole systems suggest that the properties of the accretion disk-such as its mass accretion rate, inner radius, and emergent magnetic field-should drive and modulate ...the production of relativistic jets. Contemporaneous radio monitoring was done using the Arcminute MicroKelvin Array radio telescope. Two important and simple results are obtained: (1) the jet (as traced by radio flux) does not appear to be modulated by changes in the inner radius of the accretion disk and (2) the jet is sensitive to disk properties, including its flux, temperature, and ionization. Some more complex results may reveal aspects of a coupled disk-corona-jet system. The overall picture that emerges from this study is broadly consistent with some jet-focused models for black hole special energy distributions in which a relativistic plasma is accelerated at z = 10-100 GM/c super(2). We discuss these results in the context of disk-jet connections across the black hole mass scale.
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