keV Line Emission Research Articles

XMM‐Newton Observations of the Peculiar Be X‐Ray Binary A0538‐66

ABSTRACTA0538‐66 is a neutron star/Be x‐ray binary located in the Large Magellanic Cloud and, since its discovery in the 70s, it showed a peculiar behavior that makes it a unique object in the high‐mass x‐ray binaries scene: the extremely eccentric orbit (), the short spin period of the neutron star ( ms), the episodes of super‐Eddington accretion. These characteristics contribute to a remarkable bursting activity that lasts from minutes to hours and increases the flux by a factor . In 2018, A0538‐66 was observed by XMM‐Newton in a particularly active state, characterized by a forest of short bursts lasting s each. In this contribution, we present a reanalysis of these observations. The timing analysis allowed us to distinguish between the epochs of direct accretion and propeller state that do not correlate with the orbital position of the neutron star. The spectral analysis revealed that during the accretion regime, three components (a soft one, a hard one, and a ‐keV emission line) equally contribute to the overall emission, while the propeller regime is characterized by a single soft component. We discuss these findings in the context of spherical and disk accretion regimes, highlighting the similarities and differences with other x‐ray binary systems.

Discovery of a Long Thermonuclear X-Ray Burst from the Ultracompact Binary 4U 1850–087

We report the detection of a long X-ray burst from the ultracompact binary 4U 1850–087. The type I X-ray burst was observed on MJD 60171.65 by the Monitor of All-sky X-ray Image and Neutron Star Interior Composition Explorer (NICER). We analyze the NICER data between MJD 60095.19 and 60177.43, which includes the observation covering parts of the long X-ray burst decay phase, i.e., 0.15–3.8 hr after the trigger. The persistent spectra are well described by a multicolor disk blackbody, with an inner temperature of ∼0.5 keV, a thermally Comptonized continuum, an asymptotic power-law photon index of Γ ∼ 2.2, and an electron temperature of kT e ∼ 20–30 keV. The mean persistent flux was around 3.8 × 10−10 erg cm−2 s−1, corresponding to a local mass accretion rate of ∼1%ṁEdd . Part of the time-resolved burst spectra show a clear deviation from the blackbody model, which can be improved by considering the enhanced persistent emission due to the Poynting–Robertson drag or the reflected disk emission illuminated by the burst. From the burst flux during the cooling phase, we estimate the burst duration, τ ≈ 0.78 hr, the burst fluence, E b ≈ 4.1 × 1041 erg, and the ignition column depth, y ign ≈ 3.5 × 1010 g cm−2. These long X-ray burst parameters from 4U 1850–087 suggest a regime of unstable burning of a thick, pure helium layer slowly accreted from a helium donor star. Moreover, we identify 7σ significant ∼1 keV emission lines in the burst spectra, which may originate from the surrounding accretion disk.

Dark matter search in the Perseus cluster with simultaneous analysis of Hitomi and Suzaku data

Abstract The reported detection of a 3.5 keV emission line in the Perseus cluster, possibly originating from dark matter decay, is still under scrutiny. Despite extensive observations, the detection has not yet been confirmed, and its origin remains a topic of active debate. Most of the previous searches relied on spectroscopy with X-ray charge-coupled devices, such as the X-ray Imaging Spectrometer on Suzaku. Although this provided a large amount of observational data, it only offered moderate spectral resolution. The X-ray astronomy satellite Hitomi offers new results using its high-resolution X-ray spectrometer (Soft X-ray Spectrometer). However, the data gathered were somewhat limited in terms of statistics. In this work, we present the results of a new spectral analysis of the Perseus cluster that combines the spectra from the XIS and SXS, along with the Soft X-ray Imager on Hitomi, thereby complementing each other’s capability. Our search was conducted for a line emission or absorption in the energy range of 2.6–5.9 keV assuming the Navarro–Frenk–White mass distribution with a concentration parameter of 5.0 and virial radius, r200, of 1.79 Mpc. We also considered the instrumental systematic uncertainty caused by the effective area calibration, which we empirically evaluated using the Crab Nebula spectra. On combining these results, we found no significant line features above the baryonic thermal emission from the intra-cluster medium. The upper limit at 3.5 keV, at a 3σ confidence level, is tightly constrained to 4.2 × 10−5 photons cm−2 s−1 for the $15^{\prime }$ circular sky region, which encloses a dark matter mass of $1.67\times 10^{14}\, M_{\odot }$, assuming a line velocity dispersion of 180 km s−1. This constraint is three times tighter than the previous one, which only used the SXS. On the basis of these findings, we provide the upper limit of the dark matter decay rate and the mixing angle for the sterile neutrino origin.

Long-term Study of the First Galactic Ultraluminous X-Ray Source Swift J0243.6+6124 Using NICER

We present the results obtained from detailed X-ray timing and spectral studies of X-ray pulsar Swift J0243.6+6124 during its giant and normal X-ray outbursts between 2017 and 2023 observed by the Neutron star Interior Composition Explorer (NICER). We focused on a timing analysis of the normal outbursts. A distinct break is found in the power density spectra of the source. The corresponding break frequency and slopes of the power laws around the break vary with luminosity, indicating a change in the accretion dynamics with the mass accretion rate. Interestingly, we detected quasiperiodic oscillations within a specific luminosity range, providing further insights into the underlying physical processes. We also studied the neutron star spin period evolution and a luminosity variation in the pulse profile during the recent 2023 outburst. The spectral analysis was conducted comprehensively for the giant and all other normal outbursts. We identified a double transition at luminosities of ≈7.5 × 1037 and 2.1 × 1038 erg s−1 in the evolution of continuum parameters like the photon index and cutoff energy with luminosity. This indicates three distinct accretion modes experienced by the source, mainly during the giant X-ray outburst. A soft blackbody component with a temperature of 0.08–0.7 keV is also detected in the spectra. The observed temperature undergoes a discontinuous transition when the pulsar evolves from a sub- to super-Eddington state. Notably, in addition to an evolving 6–7 keV iron line complex, a 1 keV emission line was observed during the super-Eddington state of the source, implying X-ray reflection from the accretion disk or outflow material.

Upper limits of 44Ti decay emission in four nearby thermonuclear supernova remnants

ABSTRACT To identify progenitors and investigate evidence of He burning, we searched for decay radiation of freshly synthesized 44Ti in four young nearby thermonuclear supernova remnants: Kepler, SN 1885, G1.9+0.3, and SN 1006, by analysing the up-to-date NuSTAR archival data. No apparent flux excess from the 68 and 78 keV line emissions accompanying decay was detected above the power-law continuum applied for the remnants and the absorbed stray light. By comparing the inferred upper limits of the line flux and the initial 44Ti masses with a wide variety of supernova nucleosynthesis models, we placed constraints on the supernova progenitors. We derived the first NuSTAR line flux upper limit for Kepler and ruled out most of the double-detonation scenarios with a thick He layer under low density. We estimated, for the first time, the upper limit for SN 1885, which is high because of the large distance, yet still remains consistent with the He shell detonation. The new flux and mass limit of G1.9+0.3 derived from a longer total exposure is lower than the results from previous studies and evidently excludes explosive burning of He-rich matter. The relatively advanced age and the large spatial extent of SN 1006 have prevented meaningful constraints.

Geocoronal Solar Wind Charge Exchange Process Associated With the 2006‐December‐13 Coronal Mass Ejection Event

AbstractWe report the discovery of a geocoronal solar wind charge exchange (SWCX) event corresponding to the well‐known 2006 December 13th coronal mass ejection (CME) event. Strong evidence for the charge exchange origin of this transient diffuse emission is provided by prominent non‐thermal emission lines at energies of O7+, Ne9+, Mg11+, Si12+, Si13+. Especially, a 0.53 keV emission line that most likely arises from the N5+ 1s15p1 → 1s2 transition is detected. Previously, the forecastability of SWCX occurrence with proton flares has been disputed. In this particular event, we found that the SWCX signal coincided with the arrival of the magnetic cloud inside CME, triggered with a time delay after the proton flux fluctuation as the CME shock front passed through the Earth. Moreover, a spacecraft orbital modulation in SWCX light curve suggests that the emission arises close to the Earth. The line of sight was found to always pass through the northern magnetospheric cusp. The SWCX intensity was high when the line of sight passed the dusk side of the cusp, suggesting an azimuthal anisotropy in the flow of solar‐wind ions inside the cusp. An axisymmetric SWCX emission model is found to underestimate the observed peak intensity by a factor of about 50. We suggest this discrepancy is related to the azimuthal anisotropy of the solar‐wind flow in the cusp.

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.

Suzaku observations of Fe K-shell lines in the supernova remnant W 51 C and hard X-ray sources in the proximity

Abstract In this paper, we investigate the Fe K-shell lines in the supernova remnant W 51 C and hard X-ray sources in the proximity. We measure the intensities of the Fe i Kα and Fe xxv Heα lines at 6.40 and 6.68 keV, respectively, and find that the intensity of the 6.68 keV line is consistent with the background level expected from previous studies, while that of the 6.40 keV line is higher at the significance level of 2.0σ. Given the presence of gamma-ray emission and high ionization rate point spatially coincident with the remnant, we conclude that the enhanced 6.40 keV line most likely originates from the interaction between low-energy cosmic rays and molecular clouds. Also, we discover an enhanced 6.68 keV line emission from the compact H ii region G49.0−0.3 at a significance level of 3.4σ. Spectral analysis reveals that the temperature and abundance of the thermal plasma with the 6.68 keV line is $kT=3.0^{+0.8}_{-0.7}$ keV and Z = 0.5 ± 0.2 solar, respectively. These values are explained by the thermal plasma generated by the stellar winds of O stars.

The 6.7 keV thermal emission lines in the stellar flare spectra of two chromospherically active Binaries: Algol and GT Mus

Chromospherically active binaries’ (CABs) are late-type evolved stars with strong chromosphere/coronae and high flare activity levels. Starspot evolution in these CABs and binaries reveals strong stellar and chromospheric activities. In binaries, the tidal interaction via the internal dynamo motion, during rapid rotation of the component stars generates magnetic fields. The magnetic activity heats the tenuous coronal plasma, and the reconnection of energetic particles leads to stellar flare formation. Cyclic-variation signatures in brightness and emission lines are indicators of coronal/chromospheric activities. The spatial population densities of CABs are large, and their hard energy spectral characteristics are prominent in our galaxy. Photo-ionization/collisional excitation processes in the coronae of CABs generate a strong thermal emission line at 6.7 keV. In the present work, we re-analyzed stellar flare data of two CABs (Algol & GT Muscae) observed with Suzaku. We resolved the 6.7 keV emission spectrum and equivalent width (EW) in each source’s stellar flare data. The resolved energy spectra are remarkably similar to that of the hard energy spectra at 6.7 keV of X-ray point sources observed in different Galactic regions. The EW of the 6.7 keV emission line obtained in this work compares favorably with the EW range (260 eV – 980 eV) of the 6.7 keV energy spectra of Galactic point sources. Hence, cumulative X-ray emission lines of coronal plasma (and their EWs) emitted by numerous point sources in different Galactic plane positions give clues on the Galactic Ridge X-ray Emission (GRXE) mechanism. We are of the view that CABs could account for a large number of fast-transient X-ray sources that emit thermal emission line at 6.7 keV during their quiescent and flared phases, and these underlying population sources could contribute significantly to the total luminosity of 6.7 keV GRXE.

Improved imaging using Mn He-α x rays at OMEGA EP.

In this paper, we report on a crystal based x-ray imaging system fielded at the OMEGA EP laser facility. This new system has a pointing accuracy of +/100 μm, a temporal resolution down to 100ps (depending on backlighter characteristics), variable magnification, and a spatial resolution of 21.9 µm at the object plane at a magnification of 15×. The system is designed to use a crystal along the crystal plane that satisfies the Bragg condition for the x ray of interest. The thin crystal is then bent into a spherical geometry and attached to a glass backing substrate to hold it in the diagnostic, and the x rays are imaged onto a charge coupled device. We report on data acquired with the new Los Alamos National Laboratory supplied spherical quartz crystal to image the Mn He-α 6.15 keV line emission.

A Search for the 3.5 keV Line from the Milky Way’s Dark Matter Halo with HaloSat

Abstract Previous detections of an X-ray emission line near 3.5 keV in galaxy clusters and other dark-matter-dominated objects have been interpreted as observational evidence for the decay of sterile neutrino dark matter. Motivated by this, we report on a search for a 3.5 keV emission line from the Milky Way’s galactic dark matter halo with HaloSat. As a single pixel, collimated instrument, HaloSat observations are impervious to potential systematic effects due to grazing incidence reflection and CCD pixelization, and thus may offer a check on possible instrumental systematic errors in previous analyses. We report nondetections of a ∼3.5 keV emission line in four HaloSat observations near the Galactic center. In the context of the sterile neutrino decay interpretation of the putative line feature, we provide 90% confidence level upper limits on the 3.5 keV line flux for a field centered 18.6 degrees from the Galactic center and the corresponding 7.1 keV sterile neutrino mixing angle: F ≤ 0.077 ph cm−2 s−1 sr−1 and sin 2 ( 2 θ ) ≤ 4.25 × 10 − 11 . The HaloSat mixing angle upper limit was calculated using a modern parameterization of the Milky Way’s dark matter distribution, and in order to compare with previous limits, we also report the limit calculated using a common historical model. The HaloSat mixing angle upper limit places constraints on a number of previous mixing angle estimates derived from observations of the Milky Way’s dark matter halo and galaxy clusters, and excludes several previous detections of the line. The upper limits cannot, however, entirely rule out the sterile neutrino decay interpretation of the 3.5 keV line feature.

X-Ray Redshifts for Obscured AGN: A Case Study in the J1030 Deep Field

Abstract We present a procedure to constrain the redshifts of obscured ( ) active galactic nuclei (AGN) based on low count statistics X-ray spectra, which can be adopted when photometric and/or spectroscopic redshifts are unavailable or difficult to obtain. We selected a sample of 54 obscured AGN candidates on the basis of their X-ray hardness ratio, , in the Chandra deep field (∼479 ks, 335 arcmin2) around the z = 6.3 QSO SDSS J1030+0524. The sample has a median value of ≈80 net counts in the 0.5–7 keV energy band. We estimate reliable X-ray redshift solutions taking advantage of the main features in obscured AGN spectra, like the Fe 6.4 keV emission line, the 7.1 keV Fe absorption edge, and the photoelectric absorption cutoff. The significance of such features is investigated through spectral simulations, and the derived X-ray redshift solutions are then compared with photometric redshifts. Both photometric and X-ray redshifts are derived for 33 sources. When multiple solutions are derived by any method, we find that combining the redshift solutions of the two techniques improves the rms by a factor of 2. Using our redshift estimates ( ), we derived absorbing column densities in the range and absorption-corrected, 2–10 keV rest-frame luminosities between and 1045 erg s−1, with median values of and , respectively. Our results suggest that the adopted procedure can be applied to current and future X-ray surveys for sources detected only in X-rays or that have uncertain photometric or single-line spectroscopic redshifts.

Spatial distribution of the X-ray-emitting plasma of U Geminorum in quiescence and outburst

Abstract We present our analysis of the Suzaku data of U Geminorum (U Gem) from 2012 both in quiescence and outburst. Unlike SS Cygni (SS Cyg), the hard X-ray flux of U Gem is known to increase at times of optical outburst. A sophisticated spectral model and reliable distance estimate now reveal that this can be attributed to the fact that the mass accretion rate onto the white dwarf (WD) does not exceed the critical rate that causes the optically thin to thick transition of the boundary layer. From comparison of the X-ray and optical light curves, the X-ray outburst peak seems to be retarded by 2.1 ± 0.5 d, although there remains uncertainty in the X-ray peak identification, due to short data coverage. The larger delay than SS Cyg (0.9–1.4 d) also supports the lower accretion rate in U Gem. A fluorescent iron 6.4 keV emission line bears significant information about the geometry of the X-ray-emitting hot plasma and the accretion disk (AD) that reflects the hard X-ray emission. Our reflection simulation has shown that the optically thick AD is truncated at a distance of 1.20–1.25 times the white dwarf radius (RWD) in quiescence, and the accreting matter in the disk turns into the optically thin hard-X-ray-emitting plasma at this radius. In outburst, on the other hand, our spectral analysis favors the picture that the optically thick disk reaches the WD surface, although disk truncation can take place in the region of <1.012 RWD. From the profile of the 6.4 keV line, we have also discovered that the accreting matter is heated up close to the maximum temperature immediately after the matter enters the boundary layer at the disk truncation radius. This is consistent with the fact that the hard X-ray spectra of dwarf novae, in general, can be well represented with the cooling flow model.

Imaging the 511 keV Positron Annihilation Sky with COSI

Abstract The balloon-borne Compton Spectrometer and Imager (COSI) had a successful 46-day flight in 2016. The instrument is sensitive to photons in the energy range 0.2–5 MeV. Compton telescopes have the advantage of a unique imaging response and provide the possibility of strong background suppression. With its high-purity germanium detectors, COSI can precisely map γ-ray line emission. The strongest persistent and diffuse γ-ray line signal is the 511 keV emission line from the annihilation of electrons with positrons from the direction of the Galactic center. While many sources have been proposed to explain the amount of positrons, , the true contributions remain unsolved. In this study, we aim at imaging the 511 keV sky with COSI and pursue a full-forward modeling approach, using a simulated and binned imaging response. For the strong instrumental background, we describe an empirical approach to take the balloon environment into account. We perform two alternative methods to describe the signal: Richardson–Lucy deconvolution, an iterative method toward the maximum likelihood solution, and model fitting with predefined emission templates. Consistently with both methods, we find a 511 keV bulge signal with a flux between 0.9 and , confirming earlier measurements, and also indications of more extended emission. The upper limit we find for the 511 keV disk, , is consistent with previous detections. For large-scale emission with weak gradients, coded aperture mask instruments suffer from their inability to distinguish isotropic emission from instrumental background, while Compton telescopes provide a clear imaging response, independent of the true emission.

Evidence for magnetic activity at starbirth: a powerful X-ray flare from the Class 0 protostar HOPS 383

Context.Class 0 protostars represent the earliest evolutionary stage of solar-type stars, during which the majority of the system mass resides in an infalling envelope of gas and dust and is not yet in the central, nascent star. Although X-rays are a key signature of magnetic activity in more evolved protostars and young stars, whether such magnetic activity is present at the Class 0 stage is still debated.Aims.We aim to detect a bona fide Class 0 protostar in X-rays.Methods.We observed HOPS 383 in 2017 December in X-rays with theChandraX-ray Observatory (∼84 ks) and in near-infrared imaging with the Southern Astrophysical Research telescope.Results.HOPS 383 was detected in X-rays during a powerful flare. This hard (E > 2 keV) X-ray counterpart was spatially coincident with the northwest 4 cm component of HOPS 383, which would be the base of the radio thermal jet launched by HOPS 383. The flare duration was ∼3.3 h; at the peak, the X-ray luminosity reached ∼4 × 1031erg s−1in the 2−8 keV energy band, a level at least an order of magnitude larger than that of the undetected quiescent emission from HOPS 383. The X-ray flare spectrum is highly absorbed (NH ∼ 7 × 1023cm−2), and it displays a 6.4 keV emission line with an equivalent width of ∼1.1 keV, arising from neutral or low-ionization iron.Conclusions.The detection of a powerful X-ray flare from HOPS 383 constitutes direct proof that magnetic activity can be present at the earliest formative stages of solar-type stars.

The Chandra High-resolution X-Ray Spectrum of Quiescent Emission from Sgr A*

Abstract In quiescence, Sgr A* is surprisingly dim, shining 100,000 times less than expected for its environment. This problem has motivated a host of theoretical models to explain radiatively inefficient accretion flows. The Chandra Galactic Center X-ray Visionary Program obtained approximately 3 Ms (1 month) of Chandra high-energy transmission grating (HETG) data, offering the only opportunity to examine the quiescent X-ray emission of Sgr A* with high-resolution spectroscopy. Utilizing custom background regions and filters for removing overlapping point sources, this work provides the first-ever look at stacked HETG spectra of Sgr A*. We model the background data sets with a cubic spline and fit the unbinned Sgr A* spectra with a simple parametric model of a power law plus Gaussian lines under the effects of interstellar extinction. We detect a strong 6.7 keV iron emission line in the HEG spectra and a 3.1 keV emission line in the MEG spectra. In all cases, the line centroids and equivalent widths are consistent with those measured from low-resolution CCD spectra. An examination of the unbinned, stacked HEG ± 1 spectrum reveals fine structure in the iron line complex. In addition to resolving the resonant and forbidden lines from He-like iron, there are apparent emission features arising with higher statistical significance at lower energy, potentially associated with Fe xx–xxiv ions in a ∼1 keV plasma arising near the Bondi radius of Sgr A*. With this work, we release the cleaned and stacked Sgr A* and background HETG spectra to the public as a special legacy data set.

Time-Resolved sub-Ångström Metrology by Temporal Phase Interferometry near X-Ray Resonances of Nuclei.

We introduce an analytical phase-reconstruction principle that retrieves atomic scale motion via time-domain interferometry. The approach is based on a resonant interaction with high-frequency light and does not require temporal resolution on the time scale of the resonance period. It is thus applicable to hard x rays and γ rays for measurements of extremely small spatial displacements or relative-frequency changes. Here, it is applied to retrieve the temporal phase of a 14.4keV emission line of an ^{57}Fe sample, which corresponds to a spatial translation of this sample. The small wavelength of this transition (λ=0.86 Å) allows for determining the motion of the emitter on sub-Ångström length and nanosecond timescales.

Measurement of Low-Energy Cosmic Rays via the Neutral Iron Line

There has been little information of Galactic low-energy cosmic rays (LECRs) so far because observations of LECRs in the solar system are affected by solar modulation and there is no effective way of indirect measurement. When LECRs in the MeV energy band collide with neutral iron atoms in the interstellar medium, uorescent X-rays at 6.4 keV are produced via inner-shell ionization of neutral iron atoms. We investigate the 6.4 keV line in supernova remnants (SNRs) as a prime candidate for the Galactic cosmic-ray origin. The line emission is discovered from 11 SNRs. The spectra and morphologies suggest that the 6.4 keV line is produced by LECRs interacting with cold gas. The proton energy density is estimated to be 10–100 eV cm−3. Furthermore, we measure the distribution of the 6.4 keV line emission near the Galactic center. The intensity profile is very similar to that of molecular clouds. The most plausible origin of the enhancement is the LECR proton bombardment. The energy density of MeV protons is estimated to be ∼ 80 eV cm−3. Since the diffusion length of MeV protons is short, they should be produced in situ. Surprisingly, there is no SNR in the vicinity, and thus another mechanism such as the stochastic acceleration would possibly work.

AstroSat SXT Observations of Her X-1

Abstract Two observations of the X-ray binary system Her X-1 by the AstroSat Soft X-ray Telescope were carried out in 2017. The first was during Low State and Turn-On, the second was during Main High State without and with dips. During Main High without dips, the power-law continuum, 1 keV emission line complex, and soft blackbody-like emission from Her X-1 are detected. Evidence is found in the spectrum for a highly ionized absorber, consistent with the recently detected corona in Her X-1. The X-ray spectra from different states are compared. The 6.4 keV fluorescent iron line is clearly detected in Low State. The different spectrum components are highly variable between states.

Contribution of GT-Mus to the 6.7 keV Emission Line from the Galactic Ridge

We performed the spectral analysis of Suzaku data on GT-Mus which was observed to emit 6.7 keV during its flaring period. GT-Mus was observed by the Suzaku team on December 12, 2007, with observation identity (402095010) for 96 kilo seconds. We downloaded GT-Mus data from the high energy astrophysics Suzaku archive. Our data reduction and analysis were done using XSELECT version 6.9 and XSPEC version 12.8. Errors reported in this work were done using the XPEC error command. We generated the spectrum and deduced a strong He-like (6.70 keV) emission from the source with Equivalent width of 282 ± 0.02 eV. This observed 6.7 keV emission line has an equivalent width which compares favorably with the equivalent width of 6.7 keV emission line from the galactic ridge (300-980 eV) depending on the Galactic position. From our analysis, we generated the light curve of the source which showed strong evidence of stellar flare. We therefore conclude that this observed stellar flare might be responsible for the observed 6.7 keV emission line. We however suggest that GT-Mus (HD101379) and other RS CVn stars that emit in 6.7 keV line could contribute to the 6.7 kev emission line from the galactic ridge during their flaring periods, since they exhibit the same level of chromospheric activities.