Fe XXV Research Articles

Unveiling the rebrightening mechanism of GRS 1915+105: Insights from a change in the quasi-periodic oscillations and from a wind analysis

We report a significant rebrightening event in the microquasar GRS 1915+105 that was observed in July 2021 with NICER and NuSTAR. This event was characterized by quasi-periodic oscillations (QPOs) in the soft state, but is typically free of these oscillations. It was also marked by an increase in the disk wind ionization degree. By employing the Hilbert-Huang transform (HHT), we decomposed the stable low-frequency QPO from the light curves using data from NICER and NuSTAR. Our spectral analysis shows a weak change in the Fe XXV absorption lines and a strong change in the Fe XXV absorption edge with QPO phase. Other spectral parameters, including the photon index and the seed photon temperature, correlate positively with the QPO phase, but the electron temperature is inversely correlated. Based on our findings we propose that the observed QPOs were caused by magnetic activity and not by precession. The magnetic field drove a failed disk wind of high-ionization low-velocity material. These results support the accretion ejection instability model and provide deeper insights into the dynamics of accretion-ejection processes that are magnetized by a black hole.

Revealing the state transition of Cen X-3 at high spectral resolution with Chandra

Cen X-3 is a compact, high-mass X-ray binary (HMXRB), likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of a target of opportunity Chandra observation made during a low-flux to high-flux transition. The high-resolution spectra allow us to delve into the events that occurred during this episode. The spectrum is described by a single black body absorbed by a local column density of the order of 1023 − 24 cm−2, which is one to two orders of magnitude higher than found for previous analyses of data taken at similar orbital phases. Such a large column produces a Compton shoulder in the Fe Kα line. The transition appears to be caused by the onset of efficient cooling, which cools the plasma by 10 million degrees in just 10 ks, allowing matter to enter the magnetosphere. This happens after a major disturbance, probably the arrival of a train of wind clumps with individual masses in the range 1019 − 20 g. This train moves ballistically in an eccentric orbit around the NS, producing a distinctive Doppler modulation in the Fe XXV line.

EWOCS-II: X-ray properties of the Wolf–Rayet stars in the young Galactic super star cluster Westerlund 1

Context. Wolf–Rayet (WR) stars are massive evolved stars that exhibit particularly fast and dense stellar winds. Although they constitute a very short phase near the end of a massive star’s life, they play a crucial role in the evolution of massive stars and have a substantial impact on their surrounding environment. Aims. We present the most comprehensive and deepest X-ray study to date of the properties of the richest Wolf–Rayet population observed in a single stellar cluster, Westerlund 1 (Wd1). By examining the X-ray signatures of WR stars, we aim to shed light on the hottest plasma in their stellar winds and gain insights into whether they exist as single stars or within binary systems. Methods. This work is based on 36 Chandra observations obtained from the “Extended Westerlund 1 and 2 Open Clusters Survey” (EWOCS) project, plus 8 archival Chandra observations. The overall exposure depth Ms) and baseline of the EWOCS observations extending over more than one year enable us to perform a detailed photometric, colour, and spectral analysis, as well as to search for short- and long-term periodicity. Results. In X-rays, we detect 20 out of the 24 known Wolf–Rayet stars in Wd1 down to an observed luminosity of ~7 × 1029 erg s−1 (assuming a distance of 4.23 kpc to Wd1), with 8 WR stars being detected in X-rays for the first time. Nine stars show clear evidence of variability over the year-long baseline, with clear signs of periodicity. The X-ray colours and spectral analysis reveal that the vast majority of the WR stars are hard X-ray sources (kT≥2.0 keV). The Fe XXV emission line at ~6.7 keV, which commonly originates from the wind–wind collision zone in binary systems, is detected for the first time in the spectra of 17 WR stars in Wd1. In addition the ~6.4 keV fluorescent line is observed in the spectra of three stars, which are among the very few massive stars exhibiting this line, indicating that dense cold material coexists with the hot gas in these systems. Overall, our X-ray results alone suggest a very high binary fraction (≥80%) for the WR star population in Wd1. When combining our results with properties of the WR population from other wavelengths, we estimate a binary fraction of ≥92%, which could even reach unity. This suggests that either all the most massive stars are found in binary systems within Wd1, or that binarity is essential for the formation of such a rich population of WR stars.

The High-resolution Fe K Spectrum of Cygnus X-3

We analyze features of the Fe K spectrum of the high-mass X-ray binary Cygnus X-3. The spectrum was obtained with the Chandra High Energy Transmission Grating Spectrometer in the third diffraction order. The increased energy resolution of the third order enables us to fully resolve the Fe xxv Heα complex and the Fe xxvi Lyα lines. The emission-line spectrum shows the expected features of photoionization equilibrium, excited in the dense stellar wind of the companion star. We detect discrete emission from inner-shell transitions, in addition to absorption likely due to multiple unresolved transitions in lower ionization states. The emission-line intensity ratios observed in the range of the spectrum occupied by the Fe xxv n = 1–2 forbidden and intercombination lines suggest that there is a substantial contribution from resonantly scattered inner-shell emission from the Li- and Be-like ionization states. The Fe xxv forbidden and intercombination lines arise in the ionization zone closest to the compact object, and since they are not subject to radiative-transfer effects, we can use them in principle to constrain the radial velocity amplitude of the compact object. We infer that the results indicate a compact object mass of the order of the mass of the Wolf–Rayet companion star, but we note that the presence of resonantly scattered radiation from Li-like ions may complicate the interpretation of the He-like emission spectrum, and specifically of the radial velocity curve of the Fe xxv forbidden line.

High-velocity Blue-shifted Fe xxv Heα Line during a Superflare of the RS Canum Venaticorum–type Star IM Peg

The Monitor of All-sky X-ray Image (MAXI) detected a superflare, releasing 5 × 1037 erg in 2−10 keV, of the RS CVn-type star IM Peg at 10:41 UT on 2023 July 23 with its Gas Slit Camera (2−30 keV). We conducted X-ray follow-up observations of the superflare with the Neutron Star Interior Composition Explorer (NICER; 0.2−12 keV) starting at 16:52 UT on July 23 until 06:00 UT on August 2. NICER X-ray spectra clearly showed emission lines of the Fe xxv Heα and Fe xxvi Lyα for ∼1.5 days since the MAXI detection. The Fe XXV Heα line was blueshifted with its maximum Doppler velocity reaching −2200 ± 600 km s−1, suggesting an upward-moving plasma during the flare, such as a coronal mass ejection (CME) and/or chromospheric evaporation. This is the first case that the Fe xxv Heα line is blueshifted during a stellar flare, and its velocity overwhelmingly exceeds the escape velocity of the star (−230 km s−1). One hour before the most pronounced blueshift detection, a signature of the reheating of the flare plasma was observed. We discuss the origin of the blueshift, a CME, or high-velocity chromospheric evaporation.

Influence of the Gravitational Darkening Effect on the Spectrum of a Hot, Rapidly Rotating Neutron Star. II. Iron Lines

Rapidly rotating neutron stars are similar to highly flattened ellipsoids. Observed spectra of flattened stars must exhibit effects of nonspherical shape and gravitational darkening. We examined in detail the influence of both effects on the observed central energies and profiles of lines of highly ionized iron, Fe xxv and Fe xxvi. We note that the gravitational darkening effect does not change the central energy of lines. Most importantly, spectra of neutron stars that rotate with different frequencies and are seen at various inclination angles differ significantly. The appearance and the depth of lines strongly depend on the parameters, like the inclination angle of the star or the frequency of the star rotation. In this paper we clearly show that the gravitational darkening effect should be included in realistic models of the atmospheres of the neutron stars.

X-Ray and Radio Monitoring of the Neutron Star Low-mass X-Ray Binary 1A 1744-361: Quasiperiodic Oscillations, Transient Ejections, and a Disk Atmosphere

We report on X-ray (NICER/NuSTAR/MAXI/Swift) and radio (MeerKAT) timing and spectroscopic analysis from a 3 month monitoring campaign in 2022 of a high-intensity outburst of the dipping neutron star low-mass X-ray binary 1A 1744−361. The 0.5–6.8 keV NICER X-ray hardness–intensity and color–color diagrams of the observations throughout the outburst suggest that 1A 1744−361 spent most of its outburst in an atoll-state, but we show that the source exhibited Z-state-like properties at the peak of the outburst, similar to a small sample of other atoll-state sources. A timing analysis with NICER data revealed several instances of an ≈8 Hz quasiperiodic oscillation (QPO; fractional rms amplitudes of ∼5%) around the peak of the outburst, the first from this source, which we connect to the normal branch QPOs seen in the Z-state. Our observations of 1A 1744−361 are fully consistent with the idea of the mass accretion rate being the main distinguishing parameter between atoll- and Z-states. Radio monitoring data by MeerKAT suggests that the source was at its radio-brightest during the outburst peak, and that the source transitioned from the “island” spectral state to the “banana” state within ∼3 days of the outburst onset, launching transient jet ejecta. The observations present the strongest evidence for radio flaring, including jet ejecta, during the island-to-banana spectral state transition at low accretion rates (atoll-state). The source also exhibited Fe xxv, Fe xxvi Kα, and Kβ X-ray absorption lines, whose origins likely lie in an accretion disk atmosphere.

Emission Line Intensity Ratios of Fe xxvi/ xxv/ xxiv in Solar Flares Observed by Hinotori

High-resolution spectra observed by the Solar X-ray spectrometer on board the Hinotori mission are revisited. Flat crystals slightly offset to the satellite spin axis produce automatic spectral scans for emission lines emerging from highly charged iron ions in solar flares every half-spin time period. All the downlinked data of the mission are converted to FITS format and major flare spectral data are revived as IDL save files in ISAS/DARTS. Based on these data sets, single-temperature fits are performed for the emission line complex of highly charged iron ions in the wavelength range of 1.75–1.95 Å and compared with theoretical predictions. Synthetic spectra with single electron temperatures estimated from j/w line-intensity ratios fit fairly well for Fe xxiv and Fe xxiii lines in the wavelength range of 1.85–1.88 Å, while intensity ratios of Fe xxv lines (x, y, z) and the inner-shell excitation line of Fe xxiv (q) to the Fe xxv resonance line (w) have systematic excesses. Empirical relations for the observed line ratios are derived. Ion fractions of Fe+25/Fe+24 estimated by intensity ratios of Lyα/w in the temperature range of log T e =7.25–7.45 are consistent with values in ionization equilibrium, and the remaining excesses of the Fe xxv line ratios may suggest problems with the atomic parameters or atomic modeling.

Electron and ion temperature measurement with a new x-ray imaging crystal spectrometer on WEST.

A new x-ray imaging crystal spectrometer (XICS) has been installed, aligned, and used during experimental campaigns on the WEST tokamak. It has three interchangeable crystals for measuring the Ar XVII, Ar XVIII, and Fe XXV spectra, respectively. A patented rotating table holding the crystals is used to monitor the crystal facing the plasma remotely and without changing the position of the camera. Here, the focus is made on the Ar XVII spectrum, between 3.93 and 4.00 Å. The design of the diagnostic is presented, and a synthetic diagnostic, implemented with the Python library ToFu, is used to show the instrument's operational performance and limits. The instrument function exhibits the following two main features: a distortion for the Ar XVII spectrum, presumably due to the crystal manufacturing in two parts, and the measurement of three W spectral lines on the Ar XVI spectrum. Line of sight-integrated profiles of the electron and ion temperatures are thus extracted from the Ar XVII spectrum from two distinct spectral line ratios and from the Doppler broadening, respectively. The bremsstrahlung emission and the W line measurements are the two main limitations to compute the electron temperature. Tomographic inversions are also implemented with the library ToFu and used in order to obtain the local electron and ion temperature profiles, which are compared to other measurements from the WEST ECE (electron cyclotron emission) diagnostic. It is shown that both the XICS line-integrated and ECE Te measurements are in better agreement. Systematic differences are shown between the electron temperature profiles calculated from the two available line ratios.

Investigation of Nonequilibrium Ionization Plasma during a Giant Flare of UX Arietis Triggered with MAXI and Observed with NICER

We detected a giant X-ray flare from the RS CVn–type binary star UX Ari using the Monitor of All-sky X-ray Image on 2020 August 17 and started a series of Neutron star Interior Composition Explorer observations 89 minutes later. For a week, the entire duration of the flare was covered with 32 snapshot observations including the rising phase. The X-ray luminosity reached 2 × 1033 erg s−1, and the entire energy release was ∼1038 erg in the 0.5–8.0 keV band. X-ray spectra characterized by continuum emission with lines of Fe xxv Heα and Fe xxvi Lyα were obtained. We found that the temperature peaks before the flux does, which suggests that the period of plasma formation in the magnetic flare loop was captured. Using the continuum information (temperature, flux, and their delay time), we estimated the flare loop size to be ∼3 × 1011 cm and the peak electron density to be ∼4 × 1010 cm−3. Furthermore, using the line ratio of Fe xxv and Fe xxvi, we investigated any potential indications of deviation from collisional ionization equilibrium (CIE). The X-ray spectra were consistent with CIE plasma throughout the flare, but the possibility of an ionizing plasma away from CIE was not rejected in the flux rising phase.

Discovery of Kiloparsec-scale Semirelativistic Fe Kα Complex Emission in NGC 5728

We present Chandra ACIS-S imaging spectroscopy results of the extended (1.″5–8″, 300–1600 pc) hard X-ray emission of NGC 5728, the host galaxy of a Compton-thick active galactic nucleus. We find spectrally and spatially resolved features in the Fe Kα complex (5.0–7.5 keV) redward and blueward of the neutral Fe line at 6.4 keV in the extended narrow-line region bicone. A simple phenomenological fit of a power law plus Gaussians gives a significance of 5.4σ and 3.7σ for the red and blue wings, respectively. Fits to a suite of physically consistent models confirm a significance of ≥3σ for the red wing. The significance of the blue wing may be diminished by the presence of rest-frame highly ionized Fe xxv and Fe xxvi lines (1.4σ–3.7σ range). A detailed investigation of the Chandra ACIS-S point-spread function and comparison with the observed morphology demonstrates that these red and blue wings are radially extended (∼5″, ∼1 kpc) along the optical bicone axis. If the wing emission is due solely to redshifted and blueshifted high-velocity neutral Fe Kα, then the implied line-of-sight velocities are +/− ∼0.1c, and their fluxes are consistent with being equal. A symmetric high-velocity outflow is then a viable explanation. This outflow has deprojected velocities ∼100 times larger than the outflows detected in optical spectroscopic studies, potentially dominating the kinetic feedback power.

Redshifted Iron Emission and Absorption Lines in the Chandra X-Ray Spectrum of Centaurus A

Cen A hosts the closest active galactic nucleus to the Milky Way, which makes it an ideal target for investigating the dynamical processes in the vicinity of accreting supermassive black holes. In this paper, we present 14 Chandra HETGS spectra of the nucleus of Cen A that were observed throughout 2022. We compared them with each other, and contrasted them against the two previous Chandra HETGS spectra from 2001. This enabled an investigation into the spectral changes occurring on timescales of months and 21 years. All Chandra spectra could be well fitted by an absorbed power law with a strong and narrow Fe Kα line, a leaked power-law feature at low energies, and Si and S Kα lines that could not be associated with the central engine. The flux of the continuum varied by a factor of 2.74 ± 0.05 over the course of the observations, whereas the Fe line only varied by 18.8% ± 8.8%. The photon index increased over 21 years, and the hydrogen column density varied significantly within a few months as well. The Fe Kα line was found at a lower energy than expected from the Cen A redshift, amounting to an excess velocity of 326−94+84kms−1 relative to Cen A. We investigated warped accretion disks, bulk motion, and outflows as possible explanations of this shift. The spectra also featured ionized absorption lines from Fe xxv and Fe xxvi, describing a variable inflow.

X-ray iron absorption line in Swift J1858.6−0814

Abstract We present the spectral analysis of bright steady states in an outburst of the transient neutron star low-mass X-ray binary Swift J1858.6−0814 observed with the Neutron star Interior Composition Explorer (NICER). We detected an ionized iron K absorption line (H-like Fe) at 6.97 keV in the spectrum. We estimate the photoionization parameter using the ratio of the equivalent widths of the Fe xxvi (H-like) (17 ± 5 eV) and Fe xxv (He-like) (<3 eV) and discuss the origin of the iron absorption line. The irradiated gas producing the absorption line would locate within (3–6) × 109 cm of the X-ray source. We suggest that the observed H-like Fe absorption line originates from the highly ionized gas in the inner accretion disk in Swift J1858.6−0814.

A spectral study of GRS 1915+105 during its March 2017 NuSTAR observations

ABSTRACT The Nuclear Spectroscopic Telescope Array Mission (NuSTAR) observed the enigmatic microquasar GRS 1915+105 twice, on 2017 March 26 and 28. Using these NuSTAR observations, we performed a time-resolved spectral analysis. We detected a type C quasi-periodic oscillation (QPO) along with the harmonic and the sub-harmonic in both epochs. From our spectral modelling, we found a dual reflection component, where one of the components comes from the hot inner flow and the second component originates from the exterior region of the accretion disc. Additionally, we found strong, highly ionized accretion disc winds as indicated by Fe xxv (on 2017 March 26) and Fe xxvi (on 2017 March 28) absorption lines, likely ultrafast outflows. Finally, at the end of the second observation, we detected variability class, which marked the onset of heartbeat oscillations in the X-ray light curve. We perform time-resolved spectral analysis to comprehend the physical conditions responsible for the onset of the heartbeat. We found that the accretion disc became highly ionized (log ξ > 4), and the high-energy cut-off showed some signs of increase, approaching >100 keV before the onset of the heartbeat class. We have not detected any signature of accretion disc instabilities thought to cause the heartbeat oscillations. We also found a strong positive correlation between the QPO frequency and the power-law index.

Spectral study of neutron star low-mass X-ray binary source 1A 1744−361

ABSTRACT We present X-ray observations of the recent outburst of 2022 from the neutron star low-mass X-ray binary source 1A 1744−361. Spectral properties of the source have been analysed using joint Nuclear Spectroscopic Telescope Array and Neutron Star Interior Composition Explorer observations. During our observations, the source happens to be in the banana state (soft state) of the hardness–intensity diagram. In addition to a power law with a high-energy cut-off, the spectrum is found to exhibit broad iron Kα emission along with distinct absorption features. A prominent absorption feature observed at 6.92 keV may be interpreted as Kα absorption line from hydrogen-like iron. The absorption feature observed at 7.98 keV may be interpreted as a blend of Fe xxv and Ni xxvii transitions. We have summarized the evidence of variability of the spectral features observed in the X-ray continuum by time-resolved spectroscopy.

Multimission view of the low-luminosity ‘obscured’ phase of GRS 1915+105

ABSTRACT GRS 1915+105 has been observed in an ‘obscured’ phase since 2019 May, exhibiting steady and low X-ray luminosities with sporadic re-brightenings. In this paper, we perform a comprehensive and wide-band analysis of the spectral and timing properties of the source during the period 2019–2021 using observations from AstroSat (SXT: 0.5–8 keV; LAXPC: 3–60 keV), the Neutron star Interior Composition Explorer (NICER) (0.5–12 keV), and the Nuclear Spectroscopic Telescope Array (NuSTAR) (3–60 keV). Spectral analysis reveals the presence of a highly variable obscurer ($N_{\rm H_{\rm 1}}\sim$ 1022–1024 atoms cm−2) throughout the observation period. The source is detected in the low/hard state for most of the time, with the spectra being described by a Comptonized component (Γ ∼ 1.16–1.79, kTe ∼ 2–31 keV). The source spectra steepen (Γ ∼ 2.5), indicating a softening of the spectrum, during the rise of the re-brightenings. Various emission and absorption lines corresponding to the neutral Fe Kα, Fe xxv Kα, Fe xxvi Kα, and the Ni xxviii Kα were detected, with the equivalent widths varying in the range 70 eV–3.5 keV. The column density of the absorbing plasma varied in the range 1016–1018 atoms cm−2 at a distance ≤2 × 1010 cm. Interestingly, the source is also seen to exhibit various variability classes (ρ, λ, δ, χ) at relatively low luminosities (∼0.01 LEdd) during the re-brightening phases. Different variability classes show the signature of quasi-periodic oscillations (νQPO: 20–180 mHz, rmsQPO: 7.5 per cent–16 per cent). The source showed a maximum bolometric luminosity (Lbol) of ∼0.01 LEdd (re-brightening phases) and a minimum Lbol of 0.004 LEdd (quiet phase) during the period. We discuss the possible disc dynamics around the black hole during this low-luminosity ‘obscured’ phase.

A UFO Seen Edge-on? Resolving Ultrafast Outflow Emission on ∼200 pc Scales with Chandra in the Active Nucleus of Mrk 34

We present Chandra ACIS imaging spectroscopy of the nucleus of the Seyfert 2 Galaxy Mrk 34. We identify spatially and spectrally resolved features in the band that includes Fe Kα, Fe xxv, and Fe xxvi. These features suggest high-velocity (≳15,000 km s−1 line-of-sight) material spanning ∼0.″5, within ∼200 pc of the nucleus. This outflow could have deprojected velocities ∼12–28× greater than the [O iii]-emitting outflows, and could potentially dominate the kinetic power in the outflow. This emission may point to the origins of the optical and X-ray winds observed at larger radii, and could indicate a link between ultrafast outflows and AGN feedback on ≳kiloparsec scales.

Origin of the diffuse 4–8 keV emission in M 82

We present the first spatially resolved, X-ray spectroscopic study of the 4−8 keV diffuse emission found in the central part of the nearby starburst galaxy M 82 on a few arcsecond scales. The new details that we see allow a number of important conclusions to be drawn on the nature of the hot gas and its origin as well as feedback on the interstellar medium. We use archival data from the Chandra X-ray Observatory with an exposure time of 570 ks. The Fe XXV emission at 6.7 keV, expected from metal-enriched hot gas, is enhanced only in a limited area close to the starburst disc and is weak or almost absent over the rest of the diffuse emission, resulting in spatial variations in equivalent width from < 0.1 keV to 1.9 keV. This shows the presence of non-thermal emission due to inverse Compton scattering of the far-infrared photons by radio emitting cosmic ray electrons. The morphological resemblance between the diffuse X-ray, radio, and far-infrared emission maps support this concept. Our decomposition of the diffuse emission spectrum indicates that ∼70% of the 4−8 keV luminosity originates from the inverse Compton emission. The metal-rich hot gas with a temperature of ≃5 keV makes a minor contribution to the 4−8 keV continuum, but it accounts for the majority of the observed Fe XXV line. This hot gas appears to emerge from the circumnuclear starburst ring and fill the galactic chimneys identified as mid-infrared and radio emission voids. The energetics argument suggests that much of the supernova energy in the starburst site has gone into creating of the chimneys and is transported to the halo. We argue that a hot, rarefied environment produced by strong supernova feedback results in displacing the brightest X-ray and radio supernova remnants which are instead found to reside in giant molecular clouds. We find a faint X-ray source with a radio counterpart, close to the kinematic centre of the galaxy and we carefully examine the possibility that this source is a low-luminosity active galactic nucleus in an advection-dominated accretion flow phase.

Study of the excess Fe XXV line emission in the central degrees of the Galactic centre usingXMM-Newtondata

The diffuse Fe XXV (6.7 keV) line emission observed in the Galactic ridge is widely accepted to be produced by a superposition of a large number of unresolved X-ray point sources. In the very central degrees of our Galaxy, however, the existence of an extremely hot (~7 keV) diffuse plasma is still under debate. In this work we measure the Fe XXV line emission using all availableXMM-Newtonobservations of the Galactic centre (GC) and inner disc (−10° <ℓ< 10°, −2° <b< 2°). We use recent stellar mass distribution models to estimate the amount of X-ray emission originating from unresolved point sources, and find that within a region ofℓ= ±1° andb= ±0.25° the 6.7keV emission is 1.3–1.5 times in excess of what is expected from unresolved point sources. The excess emission is enhanced towards regions where known supernova remnants are located, suggesting that at least a part of this emission is due to genuine diffuse very hot plasma. If the entire excess is due to very hot plasma, an energy injection rate of at least ~6 × 1040erg s−1is required, which cannot be provided by the measured supernova explosion rate or past Sgr A*activity alone. However, we find that almost the entire excess we observe can be explained by assuming GC stellar populations with iron abundances ~1.9 times higher than those in the bar/bulge, a value that can be reproduced by fitting diffuse X-ray spectra from the corresponding regions. Even in this case, a leftover X-ray excess is concentrated withinℓ= ±0.3° andb= ±0.15°, corresponding to a thermal energy of ~2 × 1052erg, which can be reproduced by the estimated supernova explosion rate in the GC. Finally we discuss a possible connection to the observed GCFermi-LAT excess.

Discovery of periodicities in two highly variable intermediate polars towards the Galactic centre

Aims. We performed a systematic analysis of X-ray point sources within 1.°5 of the Galactic centre using archival XMM-Newton data. While doing so, we discovered Fe Kα complex emission and pulsation in two highly variable sources, 4XMM J174917.7–283329 and 4XMM J174954.6–294336. In this work we report the findings of the X-ray spectral and timing studies. Methods. We performed detailed spectral modelling of the sources and searched for pulsation in the light curves using Fourier timing analysis. We also searched for multi-wavelength counterparts for the characterization of the sources. Results. The X-ray spectrum of 4XMM J174917.7–283329 shows the presence of complex Fe K emission in the 6–7 keV band. The equivalent widths of the 6.4 and 6.7 keV lines are 99−72+84 and 220−140+160 eV, respectively. The continuum is fitted by a partially absorbed apec model with a plasma temperature of kT = 13−2+10 keV. The inferred mass of the white dwarf (WD) is 0.9−0.2+0.3 M⊙. We detected pulsations with a period of 1212 ± 3 s and a pulsed fraction of 26 ± 6%. The light curves of 4XMM J174954.6–294336 display an asymmetric eclipse and dipping behaviour. To date, this is only the second known intermediate polar to show a total eclipse in X-rays. The spectrum of the sources is characterized by a power-law model with photon index Γ = 0.4 ± 0.2. The equivalent widths of the iron fluorescent (6.4 keV) and Fe XXV (6.7 keV) lines are 171−79+99 and 136−81+89 eV, respectively. The continuum is described by emission from optically thin plasma with a temperature of kT ∼ 35 keV. The inferred mass of the WD is 1.1−0.3+0.2 M⊙. We detect coherent pulsations from the source with a period of 1002 ± 2 s. The pulsed fraction is 66 ± 15%. Conclusions. The spectral modelling indicates the presence of intervening clouds with a high absorbing column density in front of both sources. The detected periodic modulations in the light curves are likely associated with the spin period of WDs in magnetic cataclysmic variables. The measured spin period, hard photon index, and equivalent width of the fluorescent Fe Kα line are consistent with the values found in intermediate polars. 4XMM J174954.6–294336 has already been classified as an intermediate polar, and we suggest that 4XMM J174917.7–283329 is a new intermediate polar. The X-ray eclipses in 4XMM J174954.6–294336 are most likely caused by a low-mass companion star obscuring the central X-ray source. The asymmetry in the eclipse is likely caused by a thick bulge that intercepts the line of sight during the ingress phase but not during the egress phase located behind the WD along the line of sight.