Joel B. Coley

GX 301–2 is an accreting x-ray pulsar with a massive hypergiant companion WRAY 977, embedded within a dense circumstellar environment. We report on detected redshifted hydrogen- and helium-like iron lines, together with transitions from lower ionization states, observed with XRISM/Resolve during an x-ray flare. Notably, these spectral features evolve from absorption lines at the beginning of the observation to emission lines at the end, with intervening phases exhibiting a mixture of both absorption and emission features. This behavior constitutes direct evidence of inflowing material accreting onto the neutron star. The results suggest a dynamic accretion geometry, evolving from predominantly radial inflow to a transverse, potentially disk-like configuration during the x-ray flare. Observations of inflowing matter thus constitute a direct test of accretion hypotheses and highlight the complex interplay between stellar wind and transient accretion disks in wind-accreting systems.

The gamma-ray-emitting binary stellar system LS I +61° 303 was observed with the Imaging X-ray Polarimetry Explorer on two successive orbits over orbital phases of 0.74–1.05. Polarization is detected at a significance of 4.2 σ with an average polarization degree of 13.1% ± 3.0% in the 2–8 keV band after background subtraction. This is the second detection of polarization of the X-ray synchrotron emission from a gamma-ray binary and, again, suggests that the magnetic field in the particle acceleration region has a significant ordered component. The orbital motion on the sky of LS I +61° 303 is not well determined, which leads to ambiguity in interpretation of the X-ray electric vector position angle (EVPA) measurement. Use of orbital elements determined via radial velocity measurements combined with radio imaging of variable nebular emission suggests an offset between the X-ray EVPA and the compact object-massive star axis on the order of ∼30°. Such an offset could be produced by Coriolis forces due to binary motion. Use of two different sets orbital elements determined via optical polarimetry suggest either no offset or a perpendicular orientation but require an unexpectedly high inclination, while another set based on the same data but modeled assuming a moderate inclination suggests an offset of 15°. Use of orbital elements derived from modeling of the keV/TeV light curves suggests good alignment between the X-ray EVPA and the compact object-massive star axis. Such alignment was found for the gamma-ray binary PSR B1259-63. If the same physical situation holds for LS I +61° 303, that would favor the orbital elements derived from the keV/TeV light curves.

We present a comprehensive analysis of the X-ray spectrum of the highly obscured high-mass X-ray binary IGR J16318−4848 based on ∼250 ks Chandra/HETGS observations covering different orbital phases. We detected a strong narrow Fe K α emission line and interpret our finding as the iron line originating in the stellar wind close to the compact object. We tentatively identify a Compton shoulder associated with the Fe K α line. The ratio of the Compton-shoulder flux to that of the Fe K α core exhibits orbital-phase variability, reaching a maximum of ∼10% around orbital phase ϕ _orb ≃ 0.33. In addition, we do not detect ionized lines, implying that the plasma in the system is predominantly cold. We preliminarily report that the Fe K α line centroid exhibits an orbital modulation with an amplitude of 167 ± 32 km s ⁻¹ , adopting the best-known circular orbit in the source. This study presents the first detailed view of the high-resolution X-ray spectra of IGR J16318−4848 across different orbital phases, providing timely context for the newly taken XRISM observations of the source.

Superorbital modulations have been detected in the supergiant high-mass X-ray binary 4U 1538-52 using long-term monitoring with the Neil Gehrels Swift Observatory Burst Alert Telescope (BAT). The source also exhibits a long-term pulse-period evolution as seen with Rossi X-ray Timing Explorer, INTEGRAL, and Fermi Gamma-Ray Burst Monitor that appears uncorrelated with changes in its X-ray flux. To investigate the mechanisms causing these superorbital modulations and its possible dependence on pulse-period changes, we analyzed long-term monitoring with Swift-BAT and Monitor of All Sky X-ray Image Gas Slit Camera (MAXI-GSC) to construct dynamic power spectra and superorbital intensity profiles. In addition, we used pointed X-ray observations from Nuclear Spectroscopic Telescope Array and Neutron Star Interior Composition Explorer mission to investigate the pulsation and spectral properties across different superorbital and orbital phase intervals. We find the presence of superorbital modulations in the MAXI-GSC 2–20 keV lightcurves, consistent with the periodicity observed with the Swift-BAT lightcurves. However, no significant changes are detected in the pulse profiles or spectral parameters across different superorbital, orbital, or pulse-change intervals. This lack of spectral or timing variations with orbital and superorbital phases suggests that the mechanisms driving the observed superorbital modulation and pulse-period changes are likely associated with large-scale stellar wind structures, such as corotating interaction regions, within the stellar wind of the supergiant companion.

We report on a pair of X-ray Multi-Mirror Mission (XMM-Newton) observations of the Supergiant X-ray binary 4U 1909+07, which were performed on 2021 October 3 and 8, respectively. We measure the neutron star rotation period in each observation to be ∼602.62 s. This continues a long spin-up trend that has persisted since 2001 where the neutron star spin period was found to be ∼604.66 s. In our timing analysis, we observe strong variations in the amplitude of the 1–10 keV pulse profile as a function of time, and for the first time, we find a low flux interval extending for a single pulse period in which pulsations are no longer detected. We interpret this low flux interval as a pulse dropout similar to those observed in Vela X-1 and GX 301-2, which were each explained by a low-density cavity in the wind driving the propeller effect. In our time-resolved spectral analysis, we observed the spectral continuum, which can be described as an absorbed power law modified by a high-energy cutoff, to significantly soften during the pulse-dropout phase. No evidence of an increasing absorption column density was found. The observed softening in 4U 1909+07 also supports an interpretation that the observed pulse dropout may be driven by the propeller effect, but the quasi-spherical settling accretion regime cannot be ruled out.

Context. X-ray spectra of accretion-powered X-ray pulsars can often be described using a power-law continuum with a high-energy cutoff, which might be further modified by additional spectral components. The Be X-ray binary system 4U 0115+63 is well known for having one of the highest numbers of detected harmonics of its cyclotron resonant scattering features (CRSFs), a pronounced spectral component known as the “10 keV feature”, and quasiperiodic oscillations (QPOs) with a period of about 500 s during outbursts. Aims. The changes in count rate by a factor of two during the ∼500 s QPOs allow us to probe the variation in the spectral components with flux. We study the “10 keV feature” in emission, aiming to disentangle it from the broadband continuum and CRSFs and investigate its origin. Methods. We focus on the flux-dependent behavior of the CRSF and its harmonics, and particularly the contribution of the “10 keV feature”, as seen in the flux-resolved analysis of two NuSTAR observations of the 2015 outburst. Results. Comparing the flux-resolved spectra of a given observation with the respective total dataset revealed a distinct change in overall spectral shape at the position of the “10 keV feature” but no comparable deviation at the energies of the harmonic CRSFs. The change associated with the “10 keV feature” does not seem to involve its centroid energy, which remains constant within a given observation. We find indications for an anticorrelation between the continuum flux and the ratio of the “10 keV feature” flux to the continuum flux within each observation. Conclusions. The analysis strengthens previous claims that the “10 keV feature” shows some independence from the remaining features. This result supports the interpretation that the “10 keV feature” has a different formation mechanism than the continuum emission, although its origin lies within the same physical environment.

Context. Accreting X-ray pulsars (XRPs) undergo different physical regimes depending on different mass accretion rates, with related changes in the emitted X-ray spectral properties. Recent observations have shown a dramatic change in the emission properties of this class of sources observed at low luminosity. Aims. We explore the timing and spectral properties of the XRP MAXI J0655-013 observed in the low-luminosity regime (about 5 × 10 ³³ erg s ⁻¹ ) to witness the corresponding spectral shape and pulse profiles. Methods. We employed recent XMM-Newton and NuSTAR pointed observations of the MAXI J0655-013 X-ray activity during the low-luminosity stage. We explored several spectral models to fit the data and test theoretical expectations of the dramatic transition of the spectral shape compared to the higher luminosity regime. We studied the pulsating nature of the source and found a precise timing solution. We explored the energy-resolved pulse profiles and the derived energy dependence of different pulsed fraction estimators (PF _minmax and PF _rms ). We also obtained NuSTAR pulsed fraction spectra (PFS) at different luminosity regimes. Results. The MAXI J0655-013 spectrum is well fit by a double Comptonization model, in agreement with recent observational results and theoretical expectations that explain the observed spectrum as being composed of two distinct bumps, each dominated by different polarization modes. We measured a spin period of 1081.86 ± 0.02 s, consistent with the source spinning up compared to previous observations, yielding an upper limit for the magnetic field strength of B ≲ 9 × 10 ¹³ G. The pulse profiles show a single broad peak interrupted by a sharp dip that coincides with an increase in the hardness ratio, and thus likely due to absorption. For the low-luminosity observation, the PF _minmax increases with energy up to ∼100% in the 10–30 keV band, while the PF _rms remains steady at ∼60%. The PFS obtained at high luminosity shows evidence of an iron K α emission line but no indications of a cyclotron line.

IGR J17091−3624 is the only black hole X-ray binary candidate—aside from the well-studied black hole system GRS 1915+105—observed to exhibit a wide range of structured variability patterns in its light curves. In 2025, the source underwent a “failed” outburst: it brightened in the hard state but did not transition to the soft state before returning to quiescence within a few weeks. During this period, IGR J17091−3624 was observed by multiple ground- and space-based facilities. Here, we present results from six pointed NuSTAR observations obtained during the outburst. None of the NuSTAR light curves showed the exotic variability classes typical of the soft state in this source; however, we detected, for the first time, strong dips in the count rate during one epoch, with a total duration of ∼4 ks as seen by NuSTAR. Through spectral and timing analysis of all six epochs, we investigate the hard-state spectral evolution and the nature of the dips. A clear evolution of the coronal properties with luminosity is observed over all six epochs, with clear signatures of relativistic disk reflection that remain largely unchanged across the first five epochs. The first five epochs also show a strong and stable quasiperiodic oscillation feature in the power spectra. The dips observed in Epoch 5 are consistent with partial obscuration by ionized material with a column density N _H ≈ 2.0 × 10 ²³ cm ⁻² . We discuss possible origins for this material and place constraints on the orbital parameters and distance of the system.

Context. IGR J17511−3057 is an accreting millisecond X-ray pulsar and a known type-I burster. The source was observed in outburst for the first time in 2009 and again in 2015, followed by a decade-long quiescence phase. Aims. The source was observed in a new outburst phase starting in February 2025 and lasting at least nine days. We investigated the spectral and temporal properties of IGR J17511−3057, aiming to characterize its current status and highlight possible long-term evolution of its properties. Methods. We analyzed the available NICER and NuSTAR observations performed during the latest outburst of the source. We updated the ephemerides of the neutron star and compared them to previous outbursts to investigate its long-term evolution. We also performed a spectral analysis of the broadband energy spectrum in different outburst phases and investigated the time-resolved spectrum of the type-I X-ray burst event observed with NuSTAR. Results. We detected X-ray pulsations at the frequency of ∼245 Hz. The long-term evolution of the neutron star ephemerides suggests a spin-down derivative of ∼ − 2.3 × 10 ⁻¹⁵ Hz/s, compatible with a rotation-powered phase while in quiescence. Moreover, the evolution of the orbital period and the time of the ascending node suggests a fast orbital shrinkage, which challenges the standard evolution scenario for this class of pulsars involving angular momentum loss via gravitational wave emission. The spectral analysis revealed a dominant power law-like Comptonization component, along with a thermal blackbody component, consistent with a hard state. Weak broad emission residuals around 6.6 keV suggest the presence of a K α transition of neutral or He-like Fe originating from the inner region of the accretion disk. A set of self-consistent reflection models confirmed the moderate ionization of the disk truncated at around (82–370) km from the neutron star. Finally, the study of the type-I X-ray burst revealed no signature of photospheric radius expansion. We found marginally significant burst oscillations during the rise and decay of the event, consistent with the neutron star spin frequency.