On the contribution of the 6.7 keV line emission of Algol binary system 1 [619014]

1

On the contribution of the 6.7 keV line emission of Algol binary system 1
to the 6.7 keV line emission from the Galactic Ridge 2
*Ambrose C. EZE1, 2 & Romanus N.C. EZE2, 3 3
[anonimizat] ,Tel:+[anonimizat] ;[anonimizat] ,Tel:+[anonimizat] 4
1Department of Physical and Geosciences, Faculty of Natural and Applied Sciences, Godfrey 5
Okoye University, Ugwuomu -Nike, P.M.B. 01014, Enugu State. Nigeria. 6
2Department of Physics and Astronomy, Faculty of Physical Sciences, University of Nigeria, 7
Nsukka, 410001, Nigeria. 8
3Institute of Space and Astronomical Science, Japan Aerospace Exploration Agency, 3 -1-1 9
Yoshinodai, Chou -ku, Sagamihara, Kanagawa 252 – 0222, Japan. 10
*Correspondence: [anonimizat] 11
Abstract: We carried out spectroscopic analysis of the extracted stellar flare of the Algol binary 12
system and resolved a strong 6.7 keV line emission. The 6.7 keV li ne emission of the Algol binary 13
system is similar to the 6.7 keV line of the Galactic Ridge X -ray Emission ( GRXE ). The 6.7 keV 14
line emission of large equivalent width (EW) compared favorably with the 6.7 keV emission lines 15
obtained in the different Galactic Ridge regions . In the Galaxy, we have a reasonable number of 16
Algol binary systems as eclipsing strong coronal X -ray emitters and many other stars, which are 17
characterized by frequent quiescent and super flaring phases as observed by Suzaku, and th ese 18
systems, could contribute to the 6.7 keV emission line from the Galactic Ridge. 19
Keywords : Binaries, Algo l-stellar flares, X -ray, Galactic Ridge X-ray Emission . 20
21
1. INTRODUCTION 22
Flare stars are variable and intrinsically faint stars that exhibit violent and sporadic flare 23
activity. Flare stars have strong magnetic fields in their coronae. The eruption in the magnetic fie ld 24
generates stellar flares which are due to sudden, rapid and intense dramatic increase in the brightn ess 25
of the stars that last for a few minutes. The stellar flares rise to the peak brightness during rapid 26
rotation of these stars, but decay to normal brightness in an exponential curve. The energy emitted 27
by flare stars comes from the magnetic field. Flare stars exhibit coronal activitie s of about 3 orders 28
of magnitude more energetic than in the Sun [1]. The characteristic of the spectra of flare stars is the 29
presence of large areas of strong magnetic field in the coronae which give rise to strong emission 30

2

lines. The presence of emission lines requires the existence of dense chromospheres, and the heating 1
of the dense chromospheres is associated with magnetic regions in the coronae. The stellar flare 2
emission measure depends on the temperature in the flare [2]. High temperature in the flar e result to 3
large emission measure and, probably emission lines of abundant element in the coronae. In X -ray 4
band, the emission lines of the ionized elements fall in the 1.8 to 40Å when the temperature in the 5
flare is KT ≥ 1keV, and this provides measureme nts of fluxes of iron (Fe) emission lines [1]. Spots 6
are also known to exist on the surface of flare stars; therefore, the physical processes involved in the 7
atmosphere of flare stars are probably not distinct from those occurring in the Sun. Flare stars a re 8
expected to flare only during those parts of their evolution when rotation is “fast”. The faster the 9
flare star rotates, the stronger are the magnetic fields generated by the dynamo [3]. This applies to 10
the flare stars of higher mass, but in flare stars of low mass, rotation need not be excessively fast in 11
order to generate magnetic field since the convection zone can penetrate into the center of the star s. 12
There are numerous flare stars including T. Tau stars, RS CVn (RS Canum Venaticorum variables) 13
systems, Algols, W UMa and NU UMa systems [1, 3, 4, 5] that have been observed in the Milky 14
Way Galaxy. 15
Algol (Beta Persei) is an eclipsing binary system in the constellation Perseus at Right 16
Ascension 03h 08m 10.1315s and Declination +40ș57' 20.33". The Algol binary system is about 28.46 17
pc away from the Earth at an orbital inclination of 81.4ș, and located about 92.8 light years from t he 18
Sun with an apparent magnitude of about -2.5. Algol (Beta Persei) was first detect ed in X -ray energy 19
region by Small Astronomy Satellite (SAS) 3 in October 1975 [6]. It was confirmed that Algol’s 20
stellar flares, observed with Sounding rocket flights, are st rong coronal X -ray emitters, and the 21
Mass -transfer model; Roche Lobe overflow or stellar wind mechanisms explain the X -ray emission 22
from Algol [7]. The Algol binary system consists of a primary early -type main -sequence star (Algol 23
A; B -star, e.g. B8V) and a Roche Lobe filling secondary sub -giant star (Algol B; K -star, e.g. K2IV). 24
The X -ray emission from the Algol binary system arises mostly from the corona of the K -star since 25
B-star is X -ray dark [8]. The two stars (K – and B – stars) are tidally locked and rapidly rotating and 26
this causes the convection zone of the K -star to generate mag netic energy that is dissipated at the 27
stellar surface in the form of X -rays [9, 10] . The presence of elemental abundance (such as; S, Si, Al, 28
Mg, Ne, Fe, C, N, O) in the convection zone (chromospheres/coronal) during the quiescent and peak 29
flared phases o f the Algol binary system have been obtained and confirmed by GIGA (Japanese for 30
‘galaxy’ X -ray) and ASCA (Advanced Satellite for Cosmology and Astrophysics) satellites [11, 12] . 31

3

ROSAT (Röntgensatellit) observation revealed that the X -ray luminosity of the Algol binary system 1
during the flared and quiescent phases are 32102 ergs-1 and 31107.0 ergs-1 [13, 14] . The B -star has 2
a mass of 3.7 M ʘ and a radius of 2.9 R ʘ, whereas the mass of the K -star is 0.81 M ʘ with a radius of 3
3.5 R ʘ, and the binary separation between the two stars is about 14.14 R ʘ (Mʘ = 1.988 × 1030 kg, R ʘ 4
= 6.957×105 m; [15]). The massive B -star is in the main sequence phase, whereas the less massive 5
sub-giant K -star is still on the evolutionary stage and this can give rise to an Algol Paradox. In the 6
stellar evolution model, as the K -star fills its Roche Lobe, most of its mass is transferred onto the B – 7
star in the main sequence phase as both stars ar e tidally locked with an orbital period of 2.87 days. 8
During Algol binary eclipsing, the B -star occults major fractions of the X -ray emission from the K – 9
star. Tidal forces synchronize rotational and orbital periods of this close binary system. Stellar 10
flaring activities in the Algol binary system occur as a result of chromospheric and coronal activities; 11
chromospheric evaporation. This generates magnetic activities and the charged particles produced, 12
during magnetic activities, transport the released magnet ic energy into the corona [13] which 13
manifest as stellar flares. The light -curve of the Algol binary system shows a definite and significant 14
stellar flare activity as K -star comes out of the eclipse contributing 85% of X -ray emission whereas 15
B-star contrib utes 15% of the X -ray emission [16]. The observed X -ray stellar flares from Algol 16
begin with a magnetic instability that eventually leads to magnetic reconnection in tangled magnetic 17
fields in the corona. In the reconnection region, heating, particle accel eration, and some bulk mass 18
acceleration take place and the energized particle travels along closed magnetic fields toward the 19
stellar surface (of B -star) where accretions are formed. As the material/particles reach denser layers 20
in the chromospheres, the y deposit their energy by collisions, heating the ambient plasma 21
explosively to millions of temperature [17]. The ensuing over pressure drives the hot plasma into 22
coronal loops, at which point the “X -ray stellar flares” manifests with extreme luminosities and 23
radiative energies with often time scales in excess of one hour. This suggests that stellar flares f rom 24
Algol belong to a class of “2 -ribbons”or arcade stellar flares which exhibit long rise time with large 25
magnetic field structure and complex loop arc ades [18]. 26
In early 80s, GRXE was unresolved X -rays emission along the galactic plane [19, 20] , with 27
hard energy spectra (2 -10 keV) as basic properties. These spectra are characterized by many intense 28
emission lines from highly ionized ions of the abundant elements (C, N, O, Ne, Mg, Si, Sr, Ar, Ca, 29
and Fe). Two hypotheses; “Diffuse source” and “Po int source” scenarios were posited for the origin 30
of GRXE. The “Diffuse source” scenario proposed that GRXE is diffuse in nature, suggesting that 31

4

GRXE is generated when hot plasma fills the interstellar medium over the large scales [21, 22] , of 1
the Milky W ay Galaxy with Supernova explosions as a probable candidate sources of this hot 2
plasma. This hypothesis failed in explaining the origin of GRXE in that; energy injection (that is, 3
heating and replenishment of plasma) and confinement on the Galactic Plane [23] are not possible. 4
The “Point source scenario” proposed that GRXE is discrete or “point -like” in nature, suggesting 5
that GRXE is the integrated emission of faint galactic point sources [24, 25] . GRXE have a strong 6
iron emission lines in 6 – 7 keV energy range [26]. These emission lines were resolved into; 6.4 keV 7
(Neutral or low -ionized) line emission, 6.7 keV (He -like) line emission, and 7.0 keV (H -like) line 8
emission [27]. The 6.7 keV and 7.0 keV emission lines are thermal emissions with broadening 9
spectra while 6.4 keV line emission is a narrow non -thermal emission consistent with the 10
fluorescence of cool matter. The 6.4 keV is an indication of reflection of incident X -rays by cold gas 11
[28], whereas the 6.7 keV and 7.0 keV GRXE are as a result of cumul ative emission from numerous 12
discrete/faint coronally X -ray sources (discrete X -ray stars). 13
GRXE traces the stellar mass population distribution in the Galaxy. Numerous point sources, 14
including RS CVn system, dwarf novae, and magnetic cataclysmic variable s (mCVs) explain the 15
origin of GRXE [29], and each population source contributes to different X -ray energy regimes. The 16
point source hypothesis explain the origin of 6.7 keV line emission, but the uncertainty associated 17
with this hypothesis was if there are numerous number of faint galactic X -ray sources that can 18
explain the total luminosity of 6.7 keV line emission. X -ray emitting stellar coronae and accreting 19
white dwarf binaries like polars (Ps) and intermediate polars (IPs; Ps and IPs are examples of mCVs) 20
show soft and hard spectral indices [22], and these sources along with active binaries (ABs) and 21
coronally active stars and binaries (ASBs) are the plausible candidate of 6.7 keV GRXE origin. 22
Magnetic CVs are the most probable candidate sources due t o their spectral resemblance to the 23
GRXE and iron K -lines. The major contributor to the 6.7 keV GRXE are magnetic CVs ( mainly 24
intermediate polars; IPs) because these population sources exhibit low luminosities, high volume 25
densities, and hard spectr a shape [26, 28, 30] . The combination of IPs and active binaries (ABs) will 26
explain most of the 6.7 keV line emission in the Galactic Ridge [28, 31] . Is there an additional 27
galactic source whose spectral component could contribute to the total luminosity of 6.7 k eV 28
GRXE? Galactic sources reside very close to the galactic plane and these galactic sources might be 29
high mass X -ray binaries rather than CVs [26], and other yet to be identified galactic binary systems 30
that can contribute to the total luminosity of 6.7 k eV GRXE. Therefore, Algol could be among these 31

5

sources, and thus, the need for this present work though the space density of these unidentified 1
stellar point sources or binary systems required to provide the luminosity function of 6.7 keV GRXE 2
must be high . The luminosity function of CVs [32] and intermediate polars (IPs; [33]) have proven 3
that these stellar population point sources are the major contributors to the 6.7 keV line emission 4
though contributions from hard X -ray emitting symbiotic stars (hSSs) and other white dwarf 5
binaries or binary systems to the 6.7 keV line emission are possible. The observed Fe emission lines 6
emitted by hSSs are similar and contribute to the Fe emission lines of the GRXE [31]. 7
2. DATA ACQUISITION 8
We retrieved the observed Algol stellar flare data used in this research work from Suzaku 9
data Public Archive. The observation of Algol’s stellar flares was performed with X -ray Imaging 10
Spectrometer (XIS) at the focal planes of the X -ray Ray Telescope (XRT) on board the Suzaku 11
Satellite on March 8th – 10th, 2007 with a net exposure time of about 512 kilo seconds and 12
observation identification (Obs Id; 401093010). The XIS contains three functional sets of X -ray 13
Charge Coupled Device (CCD) camera systems (XIS 0, 1, and 3). XIS 0 and 3 have front – 14
illuminated ( FI) CCDs; while XIS 1 has a back -illuminated (BI) CCD. Details of Suzaku Satellite, 15
the XRT and XIS of Suzaku satellite are found in [34, 35, 36] respectively. 16
17
2.1 DATA ANALYSIS 18
The spectroscopic data analysis of the extracted Algol stellar flares’ was d one using version 19
2.0 of the off -line standard Suzaku pipeline products and the tools provided in HEASoft version 6.10 20
packages. We created work directory and other necessary files, and loaded the retrieved Algol data 21
(photon count/flux) into the work dire ctory and prepare for the analysis. We used “ds 9” command 22
to bring out the Algol’s flux, and z oom to fit frame. This is to minimize the effect of other observed 23
apparent source fluxes on the Algol. We choose scale; log, color, and save. We extracted the A lgol 24
flux and background spectra (photon count/flux) using XSELECT respectively. The Algol flux was 25
extracted from a circular region using 180 arc -seconds radius, and the extracted flux was saved. 26
During the extraction, we ensured that this arc -second radi us covered about 90% of the Algol’s flux. 27
The background spectra (flux) were extracted from a circular region center using 100 arc -seconds 28
radius with no apparent sources, and we save the extracted background flux. We subtracted the 29
background spectra from the source spectra, and generated the light -curve. We then extracted only 30

6

the portion (of the light -curve, see the purple broken lines in Fig. 1) where the Algol binary system 1
showed stellar flares. The Redistribution Matrix File (RMF), and Ancillary Resp onse File (ARF), 2
was created for the XIS sensors (XIS 0, XIS 1, XIS 3) using the Flexible Image Transport System 3
Tools (FTOOLS), X -ray imaging spectrometer response matrix file generator ( xisrmf -gene) and X – 4
ray imaging spectrometer Ancillary matrix respons e file generator ( xissamrf -gene) respectively. 5
We merged the spectral data of XIS 0, and 3, and referred it as XIS front illuminated (FI) spectrum. 6
We referred XIS1 spectrum as XIS back -illuminated (BI) spectrum. The spectral analysis was 7
performed using XSPEC version 12.8. We modeled the spectrum using thermal bremsstrahlung 8
model with a Gaussian line. Our spectral fitting covers 4.5 – 7.5 keV for both the XIS FI and XIS BI. 9
We were not able to measure the absorption (hydrogen column density, NH) in both full and partial 10
covering matters due to low photon counts in the Algol’s extracted stellar flares spectra and 11
primarily to the 4.5 keV lower limits to our fits. 12
13
3. RESULTS/ANALYSIS 14
The spectroscopic analysis of the extracted stellar flares of eclipsing Algol (Beta Persei) was 15
modeled with a thermal bremsstrahlung model and a Gaussian line for the 6.7 keV line emission 16
which was clearly resolved during th e flared phases. Table below shows the best -fit spectral 17
parameters and the error in each parameter ar e estimated at the 90% confidence ranges. Fig. 1 shows 18
the background subtracted light -curve of the Algol binary system. Fig. 2 shows the resolved 6.7 keV 19
emission line of stellar flares of Algol binary system. The 6.7 keV emission line corresponds to the 20
peak of the spectrum curve of both XIS FI and XIS BI. 21
3.1 THE EQUIVALENT WIDTHS (EW) OF THE 6.7 keV LINE EMISSION OF THE 22
ALGOL STELLAR FLARES AND THE GRXE 23
We compared the 6.7 keV line emission spectrum and equivalent width of Algol (Beta 24
Persei) with the 6.7 keV emission lines and equivalent widths obtained in the Galactic Ridge. The 25
work by [27] analyzed the spectral data of iron emission lines on the Galac tic Ridge observed at 26
eight different r egions with Suzaku satellite. They obtained ~ 6.67 keV emission line energy (on 27
each region) at equivalent widt h range; ~ 300 eV – 980 eV, and argued that the ~6.7 keV emission 28
line was clearly found in the Galactic R idge, indicating that thin thermal hot plasmas with equivalent 29

7

width range; ~ 300 eV – 980 eV are located along the Galactic Ridge. This observed center energies 1
of the ~6.7 keV emission line from [27] are consistent with the theoretical value of Fe line i n 2
Collision Ionization Equilibrium (CIE) plasma (6.680 keV ; [37]). In 2012, [30] carried out a 3
broadband spectral analysis of the GRXE at different twelve (12) Galactic bulge/ridge regions 4
observed with Suzaku satellite for total exposure of one mega seconds, and obtained a 5
composite/cumulative center energy spectrum at 6.68 keV with EW =14
17 322
 eV, and the stellar 6
population point sources; cataclysmic variables (CVs) and active binaries (ABs) are the major 7
contributors of the GRXE. Hence, the 6.7 keV line emission of large equivalent width (EW = 510.18 8
eV) from Algol’s stellar flar es compared favorably with the 6.7 keV emission lines and equivalent 9
widths obtained from the Galactic Ridge. 10
11
4. DISCUSSION OF RESULT S 12
The 6.7 keV emission line is produced as a result of collision/excitation ionization in the hot 13
plasma . The light -curve of the Algol binary system shows a typical signature of a stellar flare. The 14
6.7 keV line emission of stellar flares of Algol observed with Suzaku satellite fitted well with the 15
thermal bremstrahlung model and a Gaussian line. (The 6.7 keV emission line is thermal in nature 16
since it is only 6.7 keV emission line is observed in the thermal continuum temperature of the 17
Suzaku ). The continuum temperature of the 6.7 keV emission line from stellar flares of Algol is KT 18
= 3.613 keV. The 6.7 keV emission line, we obtained from stellar flares of Algol binary system is 19
similar to the 6.7 keV emission lines obtained from Galactic Ridge regions. In this present work, we 20
resolved prominent 6.7 keV emission line, with an equivalent width (EW= 510.18 eV), from stellar 21
flares of Algol binary system which compares favorably with the 6.7 keV emission lines and 22
equivalent widths obtained in the different Galactic Ridge regions. Therefore, the Algol binary 23
system might be among the probable galactic sources whose stellar flares contribute to the 6.7 keV 24
GRXE. 25
4.1 CONTRIBUTION OF STELLAR FLARES FROM ALGOL BINARY SYSTEM TO 26
THE 6.7 keV EMISSION LINE FROM THE GALACTIC RIDGE 27
28
Our Galaxy hosts luminous point sources such as low mass accreting White Dwarfs; 29
magnetic &non -magnet ic CVs, active binaries, and coronally active late -type stars with intrinsic X – 30
ray luminosity range; 1030-33 ergs-1 which are plausible candidates for the origin of the 6.7 keV 31

8

emission line [38], but these point sources have not completely explained the t otal luminosity of 6.7 1
keV emission line. X-ray flaring stars and X -ray binaries (e.g. Algol) whose luminosity range; 1030-2
33 ergs-1 could also be probable candidate sources that can contribute to the total luminosity of 6.7 3
keV emission line. About ~10% of the Chandra’s observed Galactic Ridge X -ray fluxes were 4
accounted for by the accumulated point sources fluxes (CVs; [39]). In the energy range; 2 – 10 keV, 5
~ 15% of GRXE are contributed by the galactic point sources [22], whereas in the energy range; 1 – 6
7 keV, ~25% of the total flux of the GRXE was attributed to the galactic point source’s origin 7
presumably cataclysmic variables and coronally active stars [25]. In view of this, about ~40% of the 8
GRXE at energies below ~ 7 keV are contributed by discrete point sources; coronally active binaries 9
and cataclysmic variables. 10
In 2009, [29] resolved about 80% of the Galactic Ridge sources (4 73) detected by Chandra 11
Observatory in energy range; 0.5 -7 keV into point/discrete sources (accreting White dwarfs of 12
luminosity; L 2-10 keV ~1031-32 ergs-1, and binary stars with strong coronal activity; coronally active 13
stars, of luminosity; L 2-10 keV < 1031 ergs-1) of strong Fe emission line at 6.7 keV, but the study did 14
not consider if stellar flares from other flaring stars and X -ray binaries (e.g. Algol) with intrinsic X – 15
ray luminosity range; 1031-33 ergs-1 are capable of generating various Fe emission lines in the Galactic 16
Ridge. Stellar flares from RS Canum Venaticorum variables (RS CVn’s), Algols, young stellar 17
objects and other flare stars with luminosity range; 31106.1 ergs-1 to 33108.4 ergs-1 and 18
temperature distribution (KT= a few keV to ~ 10 keV) is capable of generating the various emission 19
lines required for the GRXE [40]. The research work by [41] analyzed the X -ray spectra of Algol, 20
observed with XMM (X-ray Multi -Mirror Mission) -Newton, in both the quie scent and the flaring 21
phases and resolved 6.7 keV emission line. The equivalent width of the 6.7 keV emission line was 22
not reported, though they argued that the hot temperature component [ K710)42( ] of the stellar 23
flares of Algol have higher Fe abundance at 6.7 keV when compared to the cool temperature 24
component ( K6104.6 ). The photometric and spectroscopic analysis of 2002 X -ray point sources 25
by [42] r eported that the thermal source group A (hard spectrum; White Dwarfs such as magnetic 26
and non -magnetic CVs, pre -CV, and Symbiotic stars) and group B (soft and broad spectrum; X -ray 27
active stars in flares) are the major contributors of the 6.7 keV emission line. The mean equivalent 28
width of 6.7 keV is; 268ିଽଽାଶସସ eV for A and 413ିଶଵ଺ାଶ଺ଷ eV for B, and their fractional contribution to the 29
6.7 keV emission line at the Ga lactic Ridge was estimated; 2:1, but [42] did not explain the 30
mechanism that generates the 6.7 keV emission line. [31, 43 ] resolved 6.7 keV emission line of 31

9

stellar flares of four (4) hard X -ray emitting Symbiotic Stars (hSSs; EW range: 52 -158 eV) and 1
nineteen (19) magnetic Cataclysmic variables (mCVs; polar and intermediate polar, EW range: 32 – 2
157 eV), observed with Suzaku. He attributed the mechanism of the 6.7 keV emission line to be as a 3
result of photo – and collisional -ionization/excitation in the hot plasma and reported that these 4
sources could contribute to the 6.7 keV emission line in the Galactic Ridge but he did not estimate 5
the contributions of these sources. The contribution of stellar flare from coronally -active star and 6
binaries (ASBs; EW = 800 eV) and cataclysmic variables (CVs; magnetic and non -magnetic, EW 7
=170 eV ) to the thermal GRXE have been estimated [44]. He reported that ASBs and CVs 8
contributes 78±12% and 16±4% of the thermal GRXE in energy range; 2 -10 keV whereas in energy 9
range; 6 -10 keV, ASBs and CVs contributes 62±10% and 21±5% of the thermal GRXE respec tively 10
while the contribution of bright X -ray binaries (XRBs) was negligible on the cause of the research. 11
The author concludes that ~80% of the 6.7 keV – and 7.0 keV emission lines are attributed to the X – 12
ray emission (from the stellar flares) of these two population sources in ratio; 3:1 split between 13
ASBs and CVs, but the author did not specifically quantify the contribution of these sources to the 14
6.7 keV emission line. Further argument by [44] suggested that cumulative X -ray emission from 15
bright Galacti c X-ray binaries (XRBs) together with X -ray emission from relatively young galactic 16
source population might contribute ~20% of the thermal GRXE, and in view of this, Algol is an X – 17
ray binary system. 18
[38] were of the view that we need point sources with lar ge equivalent widths to explain the 19
total luminosity of 6.7 keV Fe characteristic emission line from the Galactic Ridge. The equivalent 20
width of 6.7 keV emission line emitted in the Galactic Plane and Ridge are 540±200 eV and 350±40 21
eV [22, 45] . The equiva lent width of 6.7 keV emission line (EW 6.7) resolved from stellar flares of an 22
X-ray point source determines the contribution of such source to the luminosity of 6.7 keV emis sion 23
line in the Galactic Ridge ( The larger the EW 6.7 emitted by an X -ray point so urce, the greater the 24
probability of its contribution to the luminosity of 6.7 keV emissi on line) . This implies that those X – 25
ray point sources whose spectra component have large equivalent widths of 6.7 keV emission line 26
could contribute significantly to t he total luminosity of 6.7 keV emission line in the Galactic Ridge. 27
About ~80% of the 6.7 keV and 7.0 keV emission lines are contributed by the X -ray emission (from 28
the stellar flares) of Coronally -active stars and binaries (ASBs) and cataclysmic variables [44]. If 29
these X -ray point sources (CVs, hSSs, active binaries; ABs, and coronally active stars and binaries; 30
ASBs) are the sole contributors to the total luminosity of 6.7 keV emission line from the Galactic 31

10

Ridge. We compared the equivalent width (510.18 eV) of 6.7 keV emission line of the Algol binary 1
system with the equivalent widths of the 6.7 keV emission line obtained from different Galactic 2
Ridge regions. We discovered that t he equivalent width of the Algol (Beta Persei), 510.18 eV 3
compares f avorably with the equivalent width of the 6.7 keV GRXE in the range; 300 eV – 980 eV 4
depending on the galactic positions [27], and this implies that Algol binaries are also probable X -ray 5
sources that may explain the total luminosity of the 6.7 keV emissio n line of the GRXE. 6
In order to determine the actual contribution of the 6.7 keV line emission of stars that flares 7
to that of the GRXE, the procedure by [25, 31 -32, 44, 46] should be followed where the stellar 8
density in the galaxy is taken into consider ation in determining the total luminosity of the 6.7 keV 9
line of the stars to be compared with that of the GRXE. However, this is beyond the scope of this 10
present work, but Eze et al., in preparation will adequately address the issue. 11
5. CONCLUSION 12
13
We analyzed Algol’s (Beta Persei) stellar flare data observed with Suzaku. The light -curve of 14
the Algol binary system shows a typical signature of a stellar flare. We resolved 6.7 keV emission 15
line of stellar flares of Algol binary system. The 6.7 keV emis sion line of stellar flares of Algol is 16
similar to the 6.7 keV emission lines from the Galactic Ridge in different regions. 17
We conclude that the equivalent width (EW) of the 6.7 keV emission line of the Algol binary 18
system, 510 eV, compares favorably with the EW of the 6.7 keV emission lines from the Galactic 19
Ridge. We are of the view that collection of similar systems (short period Algols; U Cep, TW Dra, 20
RZ Cas, δ Lib, RW Ara, XZ Sgr, X Gru, V505, TV Cas, etc.) like the Algol (Beta Persei) and other 21
flare stars could, along with CVs, hSSs, ABs, and ASBs, account for some fractional contributions to 22
the to tal luminosity of 6.7 keV emission line from the Galactic Ridge. 23
24
ACKNOWLEDGEMENT 25
The authors acknowledge the Suzaku team for providing data and any relevant files used in the 26
analysis presented here. This research made use of data obtained from Data Archives and 27
Transmission System (DARTS), provided by Center for Science -satellite Operation and Data 28
Archives (C -SODA) at ISAS/JAXA. We are also very gra teful to the Nigerian TETFund for the 29
TETFund National Research Grant support which was used to provide the computer and relevant 30
softwares used in this research work. 31

11

1
REFERENCES 2
[1] Nordon, R. ; Behar, E. A&A 2007 , 464, 309 -321. 3
4
[2] Gudel, M. Astron & Astrophys Review 2004 , 12, 71–237. 5
[3] Mullan, D. F. Iris Astronomical J. 1976 , 12, 161 -182. 6
7
[4] Pettersen, B. R., Solar Physics 1989 , 121, 299 -312. 8
[6] Pye, J.P.; Rosen, S.; Fyfe, D.; Schröder, A.C. A&A 2015 , 581, A25 . 9
[7] Schnopper, H.; Delvaille, J.P.; Epstein, A.; Helmken, H.; Murray, S. ApJ 1976 , 210, 75-77. 10
[8] Harnden, F.; Fabricant, D.; Topka, K.; Flannery, B.; Tucker, W.; Gorenstein, P. ApJ 1977 , 214, 11
12
418-422. 13
14
[9] White, N. E.; Holt, S. S.; Becker, R. H.; Boldt, E. A.; Serlemitsos, P. J. ApJ 1980 , 239, L69-L71. 15
[10] Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G.; Ayres, T.; Linsky, J. ApJ 1981 , 248, 279 – 16
290. 17
[11] Simon, T.; Drake, S. ApJ 1989 , 346, 303 . 18
[12] Stern, R.; Uchida, Y.; Tsuneta, S.; Nagase, F. ApJ 1992 , 400, 321 -329. 19
[13] Antunes, A.; Nagase, F.; White, N. E. ApJ 1994 , 436, L83 -L86. 20
21
[14] Ottmann, R.; Schmitt, J.H.M.M. A&A 1996 , 307, 813 -823. 22
23
[14] Berghofer, T. W.; Schmitt, J. ; Cassinelli, J. P. Astron. Astrophys. Suppl. Ser. 1996 , 118, 481 – 24
25
496. 26
27
[15] Favata, F.; Schmitt, J.H.M.M. A&A 1999 , 350, 900 -916. 28
29
[16] Chung, S. M.; Drake, J. J.; Kashayap, V. L.; Lin, L.W.; Ratzlaff, P.W. ApJ 2004 , 606, 1184 . 30
31
[17] Favata, F.; Micela G. Space Science Reviews 2003 , 108, 577 -708. 32
33
[18] Van den Oord, G.; Mewe, R. A&A 1989 , 213, 245 -260. 34
35
[19] Koyama, K.; Makishima, K.; Tanaka, Y. Publ. Astron. Soc. Japan 1986 , 38, 121 -131. 36
[20] Kaneda, H.; Makishima, K.; Yamauchi, S.; Koyama, K.; Matsuzaki, K.; Yamasaki, N. ApJ 37
38

12

1997 , 491, 638 -652. 1
2
[21] Tanaka, Y. A&A 2002 , 382, 1052 -1060 . 3
4
[22] Ebisawa, K.; Tsujimoto, M.; Paizis, A.; Hamaguchi, K.; Bamba, A.; Cutri, R.; Kaneda, H.; 5
Maeda, Y.; Sato, G. ; Senda, A. et al . ApJ 2005 , 635, 214 -242. 6
7
[23]Tanaka Y.; Miyaji, T.; Hasinger, G. Astronomische Nachrichten 1999 , 320,181 . 8
9
[24] Revnivtsev, M.; Molkov, S.; Sazonov, S. MNRAS 2006 a, 373, L11 – L15. 10
11
[25] Revnivtsev, M.; Sazonov, S. A&A 2007 , 471, 159 -164. 12
13
[26] Revnivtsev, M.; Sazonov, S.; Gilfanov, M.; Churazov, E.; Sunyaev, R. A&A 2006b , 452, 169 – 14
178. 15
16
[27] Yamauchi, S.; Ebisawa, K.; Tanaka, Y.; Koyama, K.; Matsumoto, H.; Yamasaki, N.; Takahashi, 17
H.; Ezoe, Y. Publ. Astron. Soc. Japan 2009 , 61, 225 -232. 18
19
[28] Yuasa, T.; Nakazawa, K.; Makishima, K.; Saitou, K.; Ishida, M.; Ebisawa, K.; Mori, H.; 20
Yamada, S. A&A 2010 , 520, A25 . 21
22
[29] Revnivtsev, M.; Sazonov, S.; Churazov, E.; Forman, W.; Vikhlinin, A.; Sunyaev, R. Nature 23
2009 , 458, 1142 -1144. 24
25
[30] Yuasa, T.; Makishima, K.; Nakazawa, K. ApJ 2012 , 753, 129 . 26
27
[31] Eze, R.N.C. New Astronomy 2015 , 37, 35 -41 28
29
[32] Sazonov, S.; Revnivt sev, M.; Gilfanov, M.; Churazov, E.; Sunyaev, R. A&A 2006 , 450, 117 – 30
128. 31
[33] Revnivtsev, M.; Sazonov, S.; Krivonos, R.; Ritter, H.; Sunyaev, R. A&A 2008 , 490, 37 -43. 32
[34] Mitsuda, K.; Bautz, M.; Inoue, H.; Kelley, R.; Koyama, K.; Kunied, H.; Makishima, K.; 33
34
Ogarawa, Y.; Petre, P.; Takaha, T. et al., Publ. Astron. Soc. Japan 2007 , 59, 1 -7 35
36
[35] Serlemitsos, P.; Soong, Y.; Chan, K.; Okajima, T.; Lehan, J.; Maeda,Y.; Itoh, K.; Mori, H.; 37
38
Ilzuka, R.; Itoh, A. et al Publ. Astron. Soc. Japan 2007 , 59, 9 -21. 39
40
[36] Koyama, K.; Tsunemi, H.; Dotani,T.; Bautz, M.; Hayashida, K.; Tsuru, T.; Matsumoto, H.; 41
42
Ogawara, Y.; Ricker, G.; Doty, J. et al . Publ. Astron. Soc. Japan 2007a, 59,23 -33. 43
44
[37] Koyama, K.; Hyodo, Y.; Inui, T.; Nakaji ma, H.; Matsumoto, H.; Tsuru, T. Publ. Astron. Soc. 45
46

13

Japan 2007b , 59, 245 -255. 1
2
[38] Uchiyama, H.; Nobukawa, M.; Tsuru T.; Koyama, K. Publ. Astron. Soc. Japan 2013 , 65, 19 . 3
4
[39] Ebisawa, K.; Maeda, Y.; Kaneda, H.; Yamauchi, S. Science 2001 , 293, 1633 . 5
6
[40] Matsuoka, M.; Sugizaku, M.; Tsuboi, Y.; Yamazaki, K.; Matsumura, T.; Mihara, T.; Serino, M.; 7
8
Nakahira, S.; Yamamoto, T.; Ueno, S. et al. The 11th Asian -Pacific Regional IAU Meeting 2011 , 9
10
NARIT Conference Series , 2011 . 11
12
[41] Yang, X.; Lu, F.; Aschenbach, B.; Chen, L. Research in Astronomy and Astrophysics 2011 , 11, 13
457 – 470. 14
[42] Morihana, K.; Tsujimoto,M., T.; Yoshida, T.; Ebisawa, K. ApJ 2013 ,766, 14 . 15
16
[43] Eze, R.N.C. MNRAS 2014 , 437, 857 . 17
18
[44] Warwick, R. S. MNRAS 2014 , 445, 66 . 19
20
[45] Ebisawa, K.; Yamauchi, S.; Tanaka, Y.; Koyama , K.; Ezoe, Y.; Bamba, A.; Kokubun, M.; 21
22
Hyodo, Y.; Tsujimoto, M.; Takashi, H. Publ. Astron. Soc. Japan 2008 , 60, 223-229. 23
24
[46] Eze, R.; Saitou, K.; Ebisawa, K. Publ. Astron. Soc. Japan 2015 , arXiv:1511.09424v1[astro – 25
phy.HE]. 26
27
Table: Eclipsing Algol binary system Spectral parameters 28
Spectral Parameter Value Unit
KT 3.61 0.12 keV
Fcount 0.18±0.01 10-3 Photons s-1 cm-2
E6.7 6.660 0.003 keV
EW 6.7 510.18±0.50 eV
29
30
31 KT = Continuum temperature, F count = flux count, E 6.7 = Energy center of the 6.7 keV, EW 6.7 = equivalent width of
6.7 keV emission line.

14

1
2
3
4
Fig. 1 : Background subtracted light -curve of the eclipsing Algol’s stellar flares as a function of time
during observation .
Fig. 2 : The upper panel shows spectrum of the eclipsing Algol binary system, while the data and the best -fit model are
shown by crosses and solid lines respectively, and the peak of the spectrum is 6.7 keV line as represented wi th dotted
lines from the energy axis. The ratio of the data to the best -fit model is shown by crosses in the lower panel. 4.5 XIS FI
XIS BI
7 6 7.5