Explore the vast range of titles available.

X-ray polarization is a powerful tool to investigate the geometry of accreting material around black holes, allowing independent measurements of the black hole spin and orientation of the innermost parts of the accretion disk. We perform X-ray spectropolarimetric analysis of an X-ray binary system in the Large Magellanic Cloud, LMC X-3, that hosts a stellar-mass black hole, known to be persistently accreting since its discovery. We report the first detection of the X-ray polarization in LMC X-3 with the Imaging X-ray Polarimetry Explorer, and find the average polarization degree (PD) of 3.2% ± 0.6% and a constant polarization angle of −42° ± 6° over the 2–8 keV range. Using accompanying spectroscopic observations by NICER, NuSTAR, and the Neil Gehrels Swift observatories, we confirm previous measurements of the black hole spin via the X-ray continuum method, a ≈ 0.2. From polarization analysis only, we found consistent results with low black hole spin, with an upper limit of a < 0.7 at a 90% confidence level. A slight increase in the PD with energy, similar to other black hole X-ray binaries in the soft state, is suggested from the data but with a low statistical significance.

I measure and collect timings of phase markers (like eclipse times) for the orbits of 25 X-ray binaries (XRBs) so as to calculate the steady evolutionary period change ( Ṗ ). I combine these with my observed Ṗ measures from 52 cataclysmic variables (CVs). Further, I subtract out the contributions from gravitational radiation ( ṖGR ) and mass transfer ( Ṗmt ), deriving the period change from the residual unknown angular momentum loss ( ṖAML = Ṗ – ṖGR – Ṗmt ). I have ṖAML measures for 77 XRBs and CVs, with these being direct measures of the driver of binary evolution. The venerable magnetic braking model of binary evolution has its most fundamental predictions tested, with most systems having predictions wrong by over 1 order of magnitude. Other proposed mechanisms to explain the angular momentum loss (AML) also fail, so we are left with no known mechanism that dominates the AML. An alternative path to the AML law is empirical, where my ṖAML measures are fitted to a power law involving the fundamental binary properties. With this, the dominant AML law for systems with orbital periods (P) from 0.13–1.0 day is ṖAML=−1500×10−12P1.29Mprim2.75Mcomp−1.00Ṁ−80.43 , in appropriate units. Similar AML laws for binaries below the period gap and for binaries with P > 1.0 day are derived. These three AML laws are of good accuracy and are the best representations of the actual evolution for all 77 XRBs and CVs of all classes, so the three taken together can be called “universal.”

The spin of a black hole (BH) encodes information about its formation and evolution history. Yet the understanding of the distribution of BH spins in X-ray binaries (XBs), of the models used to measure spin, and of their impact on systematic uncertainties remains incomplete. In this work, we expand on previous analyses of the entire NuSTAR archive of accreting BH XBs. Prior work compiled a sample of 245 spectral fits using the relativistic reflection method for NuSTAR observations of 36 BH systems. Here, we aim to probe two aspects: the connection between BH spin and binary system properties, and the relationships between parameters in the spectral fits. We identify moderate negative correlations between spin uncertainty and both BH mass and system inclination, and a moderate positive correlation with distance. We also point out tentative multidimensional degeneracies between inclination, disk density, Fe abundance, ionization, and the presence or absence of absorption features from ionized outflows linked to disk winds. Lastly, we provide a comprehensive view of the observed distribution of BH spins in XBs, in comparison to spins inferred from gravitational waves. We find that the distribution of BH spins in XBs can be described by a beta distribution with α = 5.66 and β = 1.09. This data set is highly complex, and the analysis presented here does not fully explore all potential parameter correlations. We make the full data set available in Zenodo to the community to encourage further exploration.

We present the results obtained from timing and spectral studies of 15 thermonuclear X-ray bursts from 4U 1820–30 observed with the Neutron Star Interior Composition Explorer (NICER) during its 5 yr of observations between 2017 and 2022. All bursts showed clear signs of photospheric radius expansion (PRE), where the neutron star (NS) photosphere expanded more than 50 km above the surface. One of the bursts produced a superexpansion with a blackbody emission radius of 902 km for the first time with NICER. We searched for burst oscillations in all 15 bursts and found evidence of a coherent oscillation at 716 Hz in a burst, with a 2.9σ detection level based on Monte Carlo simulations. If confirmed with future observations, 4U 1820–30 would become the fastest-spinning NS known in X-ray binary systems. The fractional rms amplitude of the candidate burst oscillation was found to be 5.8% in the energy range of 3–10 keV. Following the variable persistent model from burst time-resolved spectroscopy, an anticorrelation is seen between the maximum scaling factor value and the (preburst) persistent flux. We detected a low value of ionization at the peak of each burst based on reflection modeling of burst spectra. A partially interacting inner accretion disk or a weakly ionized outer disk may cause the observed ionization dip during the PRE phase.

The rapid variability of X-ray binaries (XRBs) produces a wide range of X-ray states that are linked to activity across the electromagnetic spectrum. It is particularly challenging to study a sample of sources large enough to include all types in their various states, and to cover the full range of frequencies that show flux density variations. Simultaneous observations with many telescopes are necessary. In this project, we monitor 48 XRBs with seven telescopes across the electromagnetic spectrum from 5 × 109 to 1019 Hz, including ground-based radio, IR, and optical observatories, and five instruments on two spacecraft over a 1 week period. We construct spectral energy distributions and matching X-ray color–intensity diagrams for 20 sources that have the most extensive detections. Our observations are consistent with several models of expected behavior proposed for the different classes: we detect no significant radio emission from pulsars or atoll sources, but we do detect radio emission from Z sources in the normal or horizontal branch, and from black holes in the high/soft, low/hard, and quiescent states. The survey data provide useful constraints for more detailed models predicting behavior from the different classes of sources.

We report the first X-ray polarimetric results of the neutron star (NS) low-mass X-ray binary Z-source GX 349+2 using the Imaging X-ray Polarimetry Explorer (IXPE). We discovered that the X-ray source was polarized at a polarization degree of PD = 1.1% ± 0.3% (1σ errors) with a polarization angle of PA = 32° ± 6° (1σ errors). Simultaneous Nuclear Spectroscopic Telescope Array observations show that the source transitioned through the normal branch, flaring branch, and soft apex of the Z-track during our IXPE observations. The X-ray spectropolarimetry results suggest a source geometry comprising an accretion disk component, a blackbody representing the emission from the NS surface, and a Comptonized component. We discuss the accretion geometry of the Z-source in light of the spectropolarimetric results.

We report the first polarimetric results of the neutron star low-mass X-ray binary Z-source GX 17+2 using the Imaging X-ray Polarimetry Explorer (IXPE) and the Very Large Array (VLA). We find that the X-ray source was polarized at PD = 1.9% ± 0.3% (1σ errors) with a polarization angle of PA = 11° ± 4° (1σ errors). Simultaneous Nuclear Spectroscopic Telescope Array observations show that the source was in the normal branch during our IXPE observations. The X-ray spectropolarimetry results suggest a source geometry comprising an accretion disk component, a Comptonization component, and a reflection component. The VLA radio polarization study shows a PD = 2.2% ± 0.2% with a Faraday-corrected intrinsic polarization angle of 1° ± 5°, which is an indication of the jet axis. Thus, we find the estimated X-ray PA from the source is consistent with the radio PA. We discuss the accretion geometry of the Z-source in light of our X-ray spectropolarimetry and radio findings.

The transient black hole X-ray binary MAXI J1803−298 was discovered on 2021 May 1, as it went into outburst from a quiescent state. As the source rose in flux it showed periodic absorption dips and fit the timing and spectral characteristics of a hard-state accreting black hole. We report on the results of a Target-of-Opportunity observation with NuSTAR obtained near the peak outburst flux beginning on 2021 May 13, after the source had transitioned into an intermediate state. MAXI J1803−298 is variable across the observation, which we investigate by extracting spectral and timing products separately for different levels of flux throughout the observation. Our timing analysis reveals two distinct potential quasiperiodic oscillations (QPOs) which are not harmonically related at 5.4 ± 0.2 Hz and 9.4 ± 0.3 Hz, present only during periods of lower flux. With clear relativistic reflection signatures detected in the source spectrum, we applied several different reflection models to the spectra of MAXI J1803−298. Here we report our results, utilizing high-density reflection models to constrain the disk geometry, and assess changes in the spectrum dependent on the source flux. With a standard broken power-law emissivity, we find a near-maximal spin for the black hole, and we are able to constrain the inclination of the accretion disk at 75° ± 2°, which is expected for a source that has shown periodic absorption dips. We also significantly detect a narrow absorption feature at 6.91 ± 0.06 keV with an equivalent width between 4 and 9 eV, which we interpret as the signature of a disk wind.

We report the first X-ray and radio polarimetric results of the neutron star (NS) low-mass X-raydis binary atoll-source 4U 1728−34 using the Imaging X-ray Polarimetry Explorer (IXPE) and Australia Telescope Compact Array. We discovered that the X-ray source was polarized at PD = 1.9% ± 1.0% with a polarization angle of PA = −41° ± 16°. Simultaneous Neutron Star Interior Composition Explorer observations show that the source was in a relatively hard state, marking it as the first IXPE observation of an NS atoll source in the hard state. We do not detect any significant linear polarization in the radio band, with a 3σ upper limit of 2% at 5.5 GHz and 1.8% at 9 GHz. Combining the radio data sets provides the deepest upper limits on the radio polarization at <1.5% on the linear and circular polarization (measured at 7.25 GHz). The X-ray polarimetric results suggest a source geometry with a Comptonization component possibly attributed to a boundary layer emission or BL emission reflected off the disk , consistent with the other NS atoll sources.

Sco X-1 is the brightest observed extrasolar X-ray source, which is a neutron star (NS) low-mass X-ray binary (LMXB) and is thought to have a strong potential for continuous gravitational waves (CW) detection due to its high accretion rate and relative proximity. Here, we compute the long-term evolution of its parameters, particularly the NS spin frequency (ν) and the surface magnetic field (B), to probe its nature and its potential for CW detection. We find that Sco X-1 is an unusually young (∼7 × 106 yr) LMXB and constrain the current NS mass to ∼1.4–1.6 M⊙. Our computations reveal a rapid B decay, with the maximum current value of ∼1.8 × 108 G, which can be useful to constrain the decay models. Note that the maximum current ν value is ∼550 Hz, implying that, unlike what is generally believed, a CW emission is not required to explain the current source properties. However, ν will exceed an observed cutoff frequency of ∼730 Hz, and perhaps even the NS breakup frequency, in the future without a CW emission. The minimum NS mass quadrupole moment (Q) to avoid this is ∼(2–3) × 1037 g cm2, corresponding to a CW strain of ∼10−26. Our estimation of current ν values can improve the CW search sensitivity.