Fe Emission Line Research Articles

Indication of a fast ejecta fragment in the atomic cloud interacting with the southwestern limb of SN 1006

Context. Supernova remnants interacting with molecular and atomic clouds are interesting X-ray sources for studies of broadband nonthermal emission. X-ray line emission in these systems can be produced by different processes, such as low-energy cosmic rays (LECRs) interacting with the cloud and fast ejecta fragments moving in the cloud. Aims. This paper is aimed at studying the origin of the non-thermal X-ray emission of the southwestern limb of SN 1006 beyond the main shock to determine whether the emission is due to LECRs diffusing in the cloud or to ejecta knots moving into the cloud. Methods. We analyzed the X-ray emission of the southwestern limb of SN 1006, where the remnant interacts with an atomic cloud, using three different X-ray telescopes: NuSTAR, Chandra, and XMM-Newton. We also performed a combined spectro-imaging analysis of this region. Results. Our analysis of the nonthermal X-ray emission of the southwestern limb of SN 1006 interacting with an atomic cloud has led to the detection of an extended X-ray source in the atomic cloud, approximately 2 pc upstream of the shock front. The source is characterized by a hard continuum (described by a power law with photon index Γ ∼ 1.4) and by Ne, Si, and Fe emission lines. The observed flux suggests that the origin of the X-ray emission is not associated with LECRs interacting with the cloud. On the other hand, the spectral properties of the source, together with the detection of an IR counterpart visible with Spitzer-MIPS at 24 μm, are in good agreement with the general expectations for a fast ejecta fragment moving within the atomic cloud. Conclusions. We detected X-ray and IR emission from a possible ejecta fragment, with an approximate radius of 1 × 1017 cm and approximate mass of 10−3 M⊙ at about 2 pc out of the shell of SN 1006, in the interaction region between the southwestern limb of the remnant and the atomic cloud.

Magneto-electrical fusion enhancement of LIBS signal: A case of Al and Fe emission lines’ characteristic analysis in soil

Soil is a vital resource for human survival. In particular, aluminum (Al) and iron (Fe) metal elements in soil play significant roles in stabilizing soil organic matter. Therefore, the rapid...

X-ray plasma flow and turbulence in the colliding winds of WR140

ABSTRACT We analyse the XMM–Newton RGS spectra of Wolf–Rayet (WR) 140, an archetype long-period eccentric WR+O colliding wind binary. We evaluate the spectra of O and Fe emission lines and find that the plasmas emitting these lines have the largest approaching velocities with the largest velocity dispersions between phases 0.935 and 0.968 where the inferior conjunction of the O star occurs. This behaviour is the same as that of the Ne line-emission plasma presented in our previous paper. We perform a diagnosis of the electron number density ne using the He-like triplet lines of O and Ne-like Fe–L lines. The former results in a conservative upper limit of ne ≲ 1010–1012 cm−3 on the O line-emission site, while the latter cannot impose any constraint on the Fe line-emission site because of statistical limitations. We calculate the line-of-sight velocity and its dispersion separately along the shock cone. By comparing the observed and calculated line-of-sight velocities, we update the distance of the Ne line-emission site from the stagnation point. By assuming radiative cooling of the Ne line-emission plasma using the observed temperature and the local stellar wind density, we estimate that the line-emission site extends along the shock cone by at most ±58 per cent (phase 0.816) of the distance from the stagnation point. In this framework, the excess of the observed velocity dispersion over that calculated is ascribed to turbulence in the hot-shocked plasma at earlier orbital phases of 0.816, 0.912, and 0.935, with the largest velocity dispersion of 340-630 km s−1 at phase 0.912.

X-Ray Spectral Variations of Circinus X-1 Observed with NICER throughout an Entire Orbital Cycle

Circinus X-1 (Cir X-1) is a neutron star binary with an elliptical orbit of 16.6 days. The source is unique for its extreme youth, providing a key to understanding early binary evolution. However, its X-ray variability is too complex to reach a clear interpretation. We conducted the first high-cadence (every 4 hr, on average) observations covering one entire orbit using the NICER X-ray telescope. The X-ray flux behavior can be divided into stable, dip, and flaring phases. The X-ray spectra in all phases can be described by a common model consisting of a partially covered disk blackbody emission and the line features from a highly ionized photoionized plasma. The spectral change over the orbit is attributable to rapid changes of the partial covering medium in the line of sight and gradual changes of the disk blackbody emission. Emission lines of H- and He-like Mg, Si, S, and Fe are detected, most prominently in the dip phase. The Fe emission lines change to absorption in the course of the transition from the dip phase to the flaring phase. The estimated ionization degree indicates no significant changes, suggesting that the photoionized plasma is stable over the orbit. We propose a simple model in which the disk blackbody emission is partially blocked by a local medium in the line of sight that has spatial structures depending on the azimuth of the accretion disk. Emission lines upon the continuum emission are from the photoionized plasma located outside of the blocking material.

High-resolution emission spectroscopy retrievals of MASCARA-1b with CRIRES+: strong detections of CO, H2O, and Fe emission lines and a C/O consistent with solar

ABSTRACT The characterization of exoplanet atmospheres has proven to be successful using high-resolution spectroscopy. Phase curve observations of hot/ultra-hot Jupiters can reveal their compositions and thermal structures, thereby allowing the detection of molecules and atoms in the planetary atmosphere using the cross-correlation technique. We present pre-eclipse observations of the ultra-hot Jupiter, MASCARA-1b, observed with the recently upgraded CRIRES+ high-resolution infrared spectrograph at the VLT. We report a detection of Fe (≈ 8.3σ) in the K-band and confirm previous detections of CO (>15σ) and H2O (>10σ) in the day-side atmosphere of MASCARA-1b. Using a Bayesian inference framework, we retrieve the abundances of the detected species and constrain planetary orbital velocities, T–P profiles, and the carbon-to-oxygen ratio (C/O). A free retrieval results in an elevated CO abundance ($\log _{10}(\chi _{\rm {{}^{12}CO}}) = -2.85^{+0.57}_{-0.69}$), leading to a supersolar C/O ratio. More realistically, allowing for vertically-varying chemistry in the atmosphere by incorporating a chemical-equilibrium model results in a C/O of $0.68^{+0.12}_{-0.22}$ and a metallicity of $[\rm M/H] = 0.62^{+0.28}_{-0.55}$, both consistent with solar values. Finally, we also report a slight offset of the Fe feature in both Kp and vsys that could be a signature of atmospheric dynamics. Due to the 3D structure of exoplanet atmospheres and the exclusion of time/phase dependence in our 1D forward models, further follow-up observations and analysis are required to confirm or refute this result.

Peering into the central region of a nano-quasar: XMM–Newton and Chandra views of the CH Cyg symbiotic system

ABSTRACT We present the analysis of archival XMM–Newton and Chandra observations of CH Cyg, one of the most studied symbiotic stars (SySts). The combination of the high-resolution XMM–Newton RGS and Chandra HETG X-ray spectra allowed us to obtain reliable estimates of the chemical abundances and to corroborate the presence of multitemperature X-ray-emitting gas. Spectral fitting of the medium-resolution XMM–Newton MOS (MOS1+MOS2) spectrum required the use of an additional component not seen in previous studies in order to fit the 2.0–4.0 keV energy range. Detailed spectral modelling of the XMM–Newton MOS data suggests the presence of a reflection component, very similar to that found in active galactic nuclei. The reflection component is very likely produced by an ionized disc (the accretion disc around the white dwarf) and naturally explains the presence of the fluorescent Fe emission line at 6.4 keV while also contributing to the soft and medium energy ranges. The variability of the global X-ray properties of CH Cyg are discussed as well as the variation of the three Fe lines around the 6–7 keV energy range. We conclude that reflection components are needed to model the hard X-ray emission and may be present in most β/δ-type SySt.

Spectral study of the Galactic ridge X-ray emission with Suzaku: Comparison of the spectral shape with point sources

Abstract The Galactic ridge X-ray emission (GRXE) is unresolved X-ray emission located on the Galactic plane, and whether the GRXE comes from truly diffuse plasma or unresolved point sources is still debatable. We present results of spectral analysis of the GRXE with Suzaku. In order to examine the point source origin, we fitted the GRXE spectra in the 1.2–10 keV energy band with a point source model, which is a mixture of active binary stars (ABs) and non-magnetic cataclysmic variables (non-mCVs), and found that the model cannot represent the GRXE spectral shape as long as the standard metal abundances of these species are assumed. In particular, the standard abundance model cannot account for the observed intensities of Si, S, and Ar lines as well as the previously reported Fe line. Assuming spatial densities in the solar neighborhood, integration of the ABs and non-mCVs accounts for only 30% of the observed GRXE flux. Other species of the point sources or diffuse emission with stronger Si, S, Ar, and Fe emission lines shall explain the rest.

A novel approach to detect line emission under high background in high-resolution X-ray spectra

ABSTRACT We develop a novel statistical approach to identify emission features or set upper limits in high-resolution spectra in the presence of high background. The method relies on detecting differences from the background using smooth tests and using classical likelihood ratio tests to characterize known shapes like emission lines. We perform signal detection or place upper limits on line fluxes while accounting for the problem of multiple comparisons. We illustrate the method by applying it to a Chandra LETGS + HRC-S observation of symbiotic star RT Cru, successfully detecting previously known features like the Fe line emission in the 6–7 keV range and the Iridium-edge due to the mirror coating on Chandra. We search for thermal emission lines from Ne x, Fe xvii, O viii, and O vii, but do not detect them, and place upper limits on their intensities consistent with a ≈1 keV plasma. We serendipitously detect a line at 16.93 Å (0.732 keV) that we attribute to photoionization or a reflection component.

The Temperature Dependence of Hot Prograde Flows in Solar Active Regions

Using simultaneous observations from the EUV Variability Experiment (EVE) and imaging from the Atmospheric Imaging Assembly (AIA), we characterise the temperature dependence of apparent hot flows in solar active regions. The EVE instrument performs Sun-as-a-star spectroscopy and is composed of two spectrographs: MEGS-A and MEGS-B (Multiple EUV Grating Spectrograph-A, -B). It is known that EVE can measure wavelength shifts and thus can observe relative Doppler velocities in solar atmospheric plasmas over an extended temperature range. However, MEGS-A is affected by a known astigmatism effect (Chamberlin: Solar Phys.291, 1665, 2016); inhomogeneities in EUV brightness on the solar surface result in purely instrumental wavelength errors. We validate our methods by independently quantifying this effect and comparing to Chamberlin’s results, and we explore the wavelength dependence as an extension of his formula as derived for He ii 304 Å. MEGS-B is unaffected by this instrumental effect in any case, and this has allowed us to find evidence of hot prograde flows in active regions. Using our image-based models for the astigmatism and flows, we independently confirm our original MEGS-B result. We now extend our knowledge of the temperature dependence of these flows via the additional Fe emission lines available in MEGS-A. We find a monotonic increase of apparent flow speed with temperature up through lines of Fe xvi, nominally formed at about 6.4 MK.

Timing and spectral studies of Cen X-3 in multiple luminosity states using AstroSat

ABSTRACT We present the results of timing and spectral analysis of the high-mass X-ray binary pulsar, Cen X-3, with the help of observations carried out using the Large Area X-ray Proportional Counter onboard AstroSat. As part of our analysis, we sampled the source properties during four different observation epochs covering two widely different intensity states. We obtain a timing solution and report precise measurements of the spin and orbital parameters corresponding to these observational epochs. The pulse profiles during the two intensity states reveal dramatically varying shapes within a time span of 1 month. We report the detection of one of the lowest measured frequencies of quasi-periodic oscillations at 0.026 ± 0.001 Hz for Cen X-3 during its low-intensity state. We also find correlated periodic and aperiodic noise components in the power density spectra. We further carried out a phase-averaged and a pulse phase-resolved spectral study, where we find that the best-fitting continuum spectrum is well described by an absorbed Comptonization model along with a blackbody. Cen X-3 exhibited the presence of the ∼28 keV cyclotron resonant scattering feature absorption line and a ∼6.6 keV Fe emission line in both the intensity states. Significant variations in the line-forming regions and mode of accretion for Cen X-3 within time spans of a month make Cen X-3 a highly dynamic persistent binary.

Broad-band spectral analysis of LMXB 2S 0921-63 with Suzaku

ABSTRACT We present the broad-band spectral analysis of the low-mass X-ray binary 2S 0921-63 by using the Suzaku archival data covering the orbital phase between 0.31 and 1.16 during four close observations. It is the first time that a broad-band spectral analysis of 2S 0921-63 has been done up to 25 keV. The 0.5–10 keV XIS count rate varied between ∼1 and ∼5 counts s−1 during the observations. A partial X-ray eclipse and broad post-eclipse intensity dip were observed during the observations. The X-ray emission hardened marginally during the intensity dip. We have modelled the source spectra by simultaneously fitting the XIS and HXD-PIN spectra for each of the four observations. The broad-band spectra of the source can be described by a model comprising a very hot blackbody having temperature, kTBB ≈ 1.66–2.13 keV, a high-energy cut-off power law, and an Fe emission line at Eline ∼ 6.7 keV. A second model, accounting for the Comptonization of the thermal emission from accretion disc along with an Fe emission line, describes the broad-band spectra of 2S 0921-63 equally well.

Insight-HXMT Study of the Inner Accretion Disk in the Black Hole Candidate EXO 1846–031

We study the spectral evolution of the black hole candidate EXO 1846−031 during its 2019 outburst, in the 1–150 keV band, with the Hard X-ray Modulation Telescope. The continuum spectrum is well modeled with an absorbed disk-blackbody plus cutoff power law, in the hard, intermediate, and soft states. In addition, we detect an ≈6.6 keV Fe emission line in the hard intermediate state. Throughout the soft intermediate and soft states, the fitted inner disk radius remains almost constant; we suggest that it has settled at the innermost stable circular orbit (ISCO). However, in the hard and hard intermediate states, the apparent inner radius was unphysically small (smaller than the ISCO), even after accounting for the Compton scattering of some of the disk photons by the corona in the fit. We argue that this is the result of a high hardening factor, f col ≈ 2.0–2.7, in the early phases of the outburst evolution, well above the canonical value of 1.7 suitable for a steady disk. We suggest that the inner disk radius was already close to the ISCO in the low/hard state. Furthermore, we propose that this high value of the hardening factor in the relatively hard state was probably caused by the additional illuminating of the coronal irradiation onto the disk. Additionally, we estimate the spin parameter using the continuum-fitting method, over a range of plausible black hole masses and distances. We compare our results with the spin measured using the reflection-fitting method and find that the inconsistency of the two results is partly caused by different choices of f col.

Multi-mission view of extragalactic black hole X-ray binaries LMC X-1 and LMC X-3: Evolution of broadband spectral features

Extragalactic black hole X-ray binaries LMC X-1 and LMC X-3 are the persistent sources, usually found in soft spectral state. We present the results from spectral and timing study of these sources using MAXI, NICER, NuSTAR and AstroSat observations carried out during 2014-2020. Study of long-term MAXI lightcurve shows that the fractional variability of flux in 2-10keV is moderate ($\sim$20%) in LMCX-1 and high ($\sim$50%) in LMCX-3. The energy spectra of both sources are characterized by a disc blackbody and a Comptonization component with LMCX-1 having an additional Fe-line emission feature. NICER (0.3-10keV), NuSTAR (3.0-40keV) and AstroSat (0.5-20keV) spectral analysis collectively show that LMC X-1 remained in the soft state (disc flux contribution $f_{disc}>80$%, photon index$\Gamma\sim2.06-4.08$) throughout 2014-2020. Mass accretion rate, $\dot{M}$ of LMC X-1 calculated from bolometric luminosity (0.1-50keV) is found to be within $0.07-0.24\dot{M}_{Edd}$ (Eddington mass accretion rate). Although LMC X-3 remained in the soft state ($f_{disc}>95\%,\Gamma\sim2.3$) during most of the time, it exhibits transition into intermediate ($f_{disc}=47-73\%,\Gamma\sim2.02-2.36$) and hard state ($f_{disc}\sim26\%,\Gamma\sim1.6$). $\dot{M}$ of LMC X-3 through different spectral states varies within $0.01-0.42\dot{M}_{Edd}$. Temporal study show that the Power Density Spectra (PDS) in 0.3-10keV follow a red-noise with rms of 2% for LMC X-1 and in case of LMC X-3, it is 0.08-2.35% during the soft state, but relatively high in the intermediate(3.05-4.91%) and hard state($\sim$17.06%). From continuum-fitting method we constrain spin of LMC X-1 and LMC X-3 to be within 0.85-0.94 and 0.16-0.33 respectively and from Fe-line fitting method, spin of LMC X-1 is found to be 0.93-0.94. Finally, we discuss the implication of our findings in the context of accretion disc dynamics around the vicinity of the BHs.

Swift/XRT Deep Galactic Plane Survey Discovery of a New Intermediate Polar Cataclysmic Variable, Swift J183920.1-045350

Abstract We report on the Swift/XRT Deep Galactic Plane Survey discovery and multiwavelength follow-up observations of a new intermediate polar (IP) cataclysmic variable, Swift J183920.1-045350. A 449.7 s spin period is found in XMM-Newton and NuSTAR data, accompanied by a 459.9 s optical period that is most likely the synodic, or beat period, produced from a 5.6 hr orbital period. The orbital period is seen with moderate significance in independent long-baseline optical photometry observations taken with the ZTF and SAAO telescopes. We find that the X-ray pulse fraction of the source decreases with increasing energy. The X-ray spectra are consistent with the presence of an Fe emission line complex with both local and interstellar absorption. In the optical spectra, strong Hα, H i, He i, and He ii emission lines are observed, all common features in magnetic CVs. The source properties are thus typical of known IPs, with the exception of its estimated distance of 2.26 − 0.83 + 1.93 kpc, which is larger than typical, extending the reach of the CV population in our Galaxy.

Broad-band spectral study of LMXB black hole candidate 4U 1957+11 with NuSTAR

We present here the results of broadband spectral analysis of a low-mass X-ray binary and a black hole candidate 4U 1957+11. The source was observed nine times with the Nuclear Spectroscopic Telescope Array (NuSTAR) between September 2018 and November 2019. During these observations, the spectral state of 4U 1957+11 evolved marginally. The disc dominant spectra are described well with a hot, multicolor disc blackbody with disc temperature varying in the range kT in ∼ 1.35–1.86 keV and a non-thermal component having a steep slope (Γ = 2–3). A broad Fe emission line feature (5–8 keV) was observed in the spectra of all the observations. The relativistic disc model was used to study the effect of distance, inclination and the black hole mass on its spin. Simulations indicate a higher spin for smaller distances and lower black hole masses. At smaller distances and higher masses, spin is maximum and almost independent of the distance. An inverse correlation exists between the spin and the spectral hardening factor for all the cases. The system prefers a moderate spin of about 0.85 for black hole masses between 4–6 M ⊙ for a 7 kpc distance.

The X-Ray Binary Population in the Galactic Center Revealed through Multi-decade Observations

Abstract We present an investigation of the quiescent and transient X-ray binaries (XRBs) of the Galactic Center (GC). We extended our Chandra analysis of the non-thermal X-ray sources, located in the central parsec, from Hailey et al. (2018), using an additional 4.6 Msec of ACIS-S data obtained in 2012–2018. The individual Chandra spectra of the 12 sources fit to an absorbed power-law model with a mean photon index Γ ≈ 2 and show no Fe emission lines. Long-term variability was detected from nine of them, confirming that a majority are quiescent XRBs. Frequent X-ray monitoring of the GC revealed that the 12 non-thermal X-ray sources, as well as four X-ray transients have shown at most a single outburst over the last two decades. They are distinct from the six known neutron star LMXBs in the GC, which have all undergone multiple outbursts with ≲ 5 year recurrence time on average. Based on the outburst history data of the broader population of X-ray transients, we conclude that the 16 sources represent a population of ∼240–630 tightly bound BH-LMXBs with ∼4−12 hr orbital periods, consistent with the stellar/binary dynamics modeling in the vicinity of Sgr A*. The distribution of the 16 BH-LMXB candidates is disk-like (at 87% CL) and aligned with the nuclear star cluster. Our results have implications for XRB formation and the rate of gravitational wave events in other galactic nuclei.

Emission lines from X-ray illuminated accretion disc in black hole binaries

ABSTRACT X-ray flux from the inner hot region around central compact object in a binary system illuminates the upper surface of an accretion disc and it behaves like a corona. This region can be photoionized by the illuminating radiation, and thus can emit different emission lines. We study those line spectra in black hole X-ray binaries for different accretion flow parameters including its geometry. The varying range of model parameters captures maximum possible observational features. We also put light on the routinely observed Fe-line emission properties based on different model parameters, ionization rate, and Fe abundances. We find that the Fe-line equivalent width WE decreases with increasing disc accretion rate and increases with the column density of the illuminated gas. Our estimated line properties are in agreement with observational signatures.

An X-Ray Spectral Study of the Origin of Reflection Features in Bare Seyfert 1 Galaxy ESO 511–G030

Abstract The reprocessed X-ray emission from active galactic nuclei is an important diagnostic tool to study the dynamics and geometry of the matter surrounding supermassive black holes (SMBHs). We present a broadband (optical-UV to hard X-ray) spectral study of the bare Seyfert 1 galaxy, ESO 511–G030, using multi-epoch Suzaku and XMM-Newton data from 2012 and 2007, respectively. The broadband spectra of ESO 511–G030 exhibit a UV bump, a prominent soft excess below , a relatively broad ( ) Fe emission line at , and a weak Compton hump at . The soft X-ray excess in ESO 511–G030 can be described either as the thermal Comptonization of disk seed photons by a warm ( ), optically thick ( ), and compact ( ) corona or as the blurred reflection from an untruncated and moderate to highly ionized accretion disk. However, for the blurred reflection, the model requires some extreme configuration of the disk and corona. Both these models prefer a rapidly spinning black hole ( ) and a compact corona, indicating a relativistic origin of the broad Fe emission line. We found an inner disk temperature of that characterizes the UV bump and the SMBH accretes at a sub-Eddington rate ( ).

OUP accepted manuscript

We present results from timing and spectral analysis of the HMXB X-ray pulsar IGR J19294+1816 observed using \asr during its recent Type-I outburst in October, 2019. AstroSat observations sampled the outburst at the decline phase right after the outburst peak. We carried out timing analysis on the light curves obtained using the Large Area X-ray Proportional Counter (LAXPC) instrument on board AstroSat and measured a spin period of 12.485065$\pm$0.000015 s. The peak in the power density spectrum (PDS) corresponding to the spin period of 12.48 s also shows a broadened base. We also detected a Quasi Periodic Oscillation (QPO) feature at 0.032$\pm$0.002 Hz with an RMS fractional amplitude of $\sim$18% in the PDS. We further carried out a joint spectral analysis using both the Soft X-ray Telescope (SXT) and the LAXPC instruments and detected a Cyclotron Resonant Scattering Feature (CRSF) at 42.7$\pm$0.9 keV and an Fe emission line at 6.4$\pm$0.1 keV. IGR J19294+1816, being an intermediate spin pulsar, has exhibited a plethora of spectral and timing features during its most recent 2019 outburst, adding it to the list of transients that exhibit both a QPO as well as a CRSF.

X-ray variability of the HMXB Cen X−3: evidence for inhomogeneous accretion flows

ABSTRACT Cen X−3 is a compact high-mass X-ray binary likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of two pointed XMM–Newton observations. The first one took place during a normal state of the source, when it has a luminosity LX ∼ 1036 erg s−1. This observation covered orbital phases ϕ = 0.00–0.37, i.e. the egress from the eclipse. The egress light curve is highly structured, showing distinctive intervals. We argue that different intervals correspond to the emergence of different emitting structures. The light-curve analysis enables us to estimate the size of such structures around the compact star, the most conspicuous of which has a size ∼0.3R*, of the order of the Roche lobe radius. During the egress, the equivalent width of Fe emission lines, from highly ionized species, decreases as the X-ray continuum grows. On the other hand, the equivalent width of the Fe K α line, from near-neutral Fe, strengthens. This line is likely formed due to the X-ray illumination of the accretion stream. The second observation was taken when the source was 10 times X-ray brighter and covered the orbital phases ϕ = 0.36–0.80. The X-ray light curve in the high state shows dips. These dips are not caused by absorption but can be due to instabilities in the accretion stream. The typical dip duration, of about 1000 s, is much longer than the time-scale attributed to the accretion of the clumpy stellar wind of the massive donor star, but is similar to the viscous time-scale at the inner radius of the accretion disc.