Table Of ContentPASJ:Publ.Astron.Soc.Japan,1–??,
(cid:13)c 2010.AstronomicalSocietyofJapan.
Suzaku and Optical Spectroscopic Observations of SS 433 in the 2006
April Multiwavelength Campaign
Kaori Kubota,1 Yoshihiro Ueda,1 Nobuyuki Kawai,2 Taro Kotani,3 Masaki Namiki,4 Kenzo Kinugasa,5
Shinobu Ozaki,6 Takashi Iijima,7 Sergei Fabrika,8 Takayuki Yuasa,9 Shin’ya Yamada,9 Kazuo Makishima,9
1Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502
[email protected]
2Tokyo Institute of Technology
0 3Aoyama Gakuin University
1
4Osaka University
0
2 5Gunma Astronomical Observatory
6Okayama Astrophysical Observatory, National Astronomical Observatory of Japan
n 7Astronomical Observatory of Padova
a
J 8Special Astrophysical Observatory
9Department of Physics, University of Tokyo
8
1
(Received 2009 November11; accepted 2010 January 15)
]
E Abstract
H
We report results of the 2006 April multi-wavelengths campaign of SS 433, focusing on X-ray data
. observedwithSuzakuattwoorbitalphases(in-andout-of-eclipse)andsimultaneousopticalspectroscopic
h
p observations. By analyzing the FeXXV Kα lines originating from the jets, we detect rapid variability of
- the Doppler shifts, dz/dt≈0.019/0.33 day−1, which is larger than those expected from the precession
o
and/or nodding motion. This phenomenon probably corresponding to “jitter” motions observed for the
r
t first time in X-rays, for which significant variability both in the jet angle and intrinsic speed is required.
s
From the time lag of optical Doppler curves from those of X-rays, we estimate the distance of the optical
a
[ jets from the base to be ≈(3−4)×1014 cm. Based on the radiatively cooling jet model, we determine
1 the innermost temperature of the jets to be T0 = 13±2 keV and 16±3 keV (the average of the blue and
red jets) for the out-of-eclipse and in-eclipse phase, respectively,from the line intensity ratio of Fe Kα
v XXV
and Fe Kα. While the broad band continuum spectra over the 5–40 keV band in eclipse is consistent
9 XXVI
8 with a multi-temperature bremsstrahlung emission expected from the jets, and its reflection component
9 from cold matter, the out-of-eclipse spectrum is harder than the jet emission with the base temperature
2 determined above, implying the presence of an additional hard component.
1. Key words: stars: individual (SS433) — binaries — accretion discs — ISM: jets and outflows —
0 X-rays: individual (SS433)
0
1
: 1. Introduction & Anderson 1989) and P=13.082 days (Goranskii et al.
v
1998), respectively.
i
X SS433isaunique Galacticbinarysystemthatexhibits Soon after the discovery of SS 433, many efforts were
r continuous relativistic jets, and hence is an ideal tar- done to determine the kinematic model and parameters
a get to study fundamental problems of astrophysical jets, of the jets, by tracing the Doppler shifts of emission lines
including the acceleration/collimation mechanism, struc- in the optical spectra. Margon et al. (1979) for the first
ture, and influence on the environment (for a review, re- time proposed a kinetic model, where the jets of about
fer to e.g., Margon 1984; Fabrika 2004). The intrinsic 1/4 the light speed make precession, with a period of
speed of the jets is 0.26c (c is the light speed), and the 162.15 days, according to the latest value obtained by
jet axis precesses with a period of 162 days. The optical Gies et al. (2002). In superposition to the “precession”
and X-ray spectra show several pairs of Doppler shifted motion, another regular periodicity of the Doppler shifts
linesfromthebipolarjets. Thestrongemissionlines,such is observed as a “nodding” motions with an amplitude of
as Hα and lines from ionized heavy elements, give direct ∆z∼0.01 and a period of 6.28 days. They are caused by
evidence that the jets mainly contain baryonic plasmas. the tidal torques from the companion star. Furthermore,
Most recently, Kubota et al. (2010) constrains the mass faster random variability of Doppler shifts were some-
of the compact object to be 1.9–4.9 M , indicating that times reported (see e.g., Ciatti et al. 1981; Katz & Piran
⊙
the supercritical accretion star is most likely a low mass 1982; Iijima 1993; Collins & Garasi 1994). These phe-
blackhole,althoughapossibilityofamassiveneutronstar nomena are called as “jitter”, which contains an impor-
cannot be ruled out. The inclination angle and orbital tant clue to understandthe collimationmechanismofthe
period are accurately measured to be i=78.8◦ (Margon jets. The origins of “jitter” have not been understood,
2 Kubota et al. [Vol. ,
in particular whether they are caused by the change of ergy resolution, and high sensitivity above 10 keV, pro-
the speed or orientation due to insufficient observational vides usthe best opportunitytoinvestigatetime variabil-
quality (Collins & Garasi 1994). ityofthewidebandspectrumofSS433. §2describesthe
SS 433 is also a target of great interest in high energy observationsanddatareduction. Theresultsbasedonthe
astrophysics, and has been observed by many satellites Suzaku data of out-of-eclipse are summarized in § 3, and
from early on (e.g., with EXOSAT, Watson et al. 1986; thoseofin-eclipsearein§4. Wediscussourresultsin§5,
Tenma, Matsuoka et al. 1986; Ginga, Kawai et al. 1989). including the comparison of the X-ray and optical data.
The ASCA satellite, which carried X-ray CCD cameras
for the first time, detected many pairs of Doppler shifted 2. Observations and Data Reduction
emissionlinesfromionizedmetalssuchasSi,S,Ar,Ca,Fe
2.1. Suzaku
andNioriginatingfromthetwinjets(Kotanietal.1994).
By detailed analysis of the line intensities of Fe Kα We observed SS 433 with Suzaku on two occasions, on
XXVI
to Fe Kα, Kotani et al. (1996) estimated the length 2006 April 4–5 and April 8–9 for a net exposure of ≈40
XXV
of the X-ray jets and temperature of the jet base to be ks each. Suzaku (Mitsuda et al. 2007) carries the four
∼ 1013 cm and ∼20 keV, respectively. The emission lines X-ray Imaging Spectrometers (XIS-0, 1, 2 and 3) coupled
are resolved with the Chandra HETGS, which are found with the X-ray Telescopes (XRTs) and the Hard X-ray
to have Doppler widths of ≈1000–5000km s−1 (Marshall Detector (HXD), which covers the 0.2–10 keV and 10–
et al. 2002; Namiki et al. 2003; Lopez et al. 2006). The 600 keV bands, respectively. The XIS-0, 2, and 3 are
broad band continuum (up to 100 keV) is approximated front-side illuminated CCDs (XIS-FI), while the XIS-1 is
by a thermal bremsstrahlung spectrum with a temper- a back-side illuminated one (XIS-BI). The energy reso-
ature of ∼10–30 keV, depending whether in- or out-of- lution of the XISs is ≈130 eV (FWHM) at 6 keV. The
eclipse (Kawai et al. 1989; Cherepashchuk et al. 2005). first observation was performed at the orbital phase of
Basically, hydrodynamical radiative plasma flow models φ=0.97 (as calculated from the ephemeris by Goranskii
are found to successfully apply to the data (Brinkmann etal.1998),duringthemidstofaneclipsebythecompan-
et al. 1991; Kotani et al. 1996). Additional complex fea- ionstar,while the secondwasatφ=0.26after the source
turesaredetectedfromtheXMMspectra,however,which recoveredfromtheeclipse. Fromouropticalobservations,
could be Compton scattered emission from the jet base the precessionphase is found to be ψ≃0.6 (as calculated
(Brinkmannetal.2005)oraniron-Kabsorptionedgedue from the ephemeris by Gies et al. 2002), when we see the
to partial covering (Kubota et al. 2007). From the width accretion disk in almost an edge-on view. At this preces-
of an eclipse in the 25–50 keV band with INTEGRAL, sion phase, the directions of the twin jets with respect to
Cherepashchuketal.(2007)andKrivosheyevetal.(2009) the line-of-sightare invertedfrom those observedat most
propose that a hot extended corona around the accretion of the precessionphases, and both show redshifts. In this
disk is responsible for the hard X-ray emission via ther- paper,wecallthejetwithalargerredshiftas“red”jetand
malComptonizationwithatemperatureof∼20keV.High the otheras“blue”jet. The XISwasoperatedinthe nor-
qualityX-rayspectracoveringthe broadbandarecritical mal clock/editing mode without an window option. The
to establish the interpretation of the high energy spectra targetwasobservedatthe XIS nominalposition. Table 1
of SS 433. gives the log of the X-ray observations.
Simultaneous, multi-wavelength observations of this 2.1.1. XIS data
sourceareparticularlyimportanttorevealthestructureof WeanalyzetheXISdatainastandardmannerwiththe
thejets. PreviousstudiesrevealedthatX-raysareemitted HEAsoft1 version 6.6.2 software package. Photon events
from a region close to the base of the jets (∼1010−13 cm; areextractedfromacircularregioncenteredatthetarget
Kotani et al. 1996), while the optical emission originates with a radius of 6 mm (4′.35). The background is taken
far away from the jet base at a distance of ∼1014−15 cm from the surrounding annulus region. For spectral anal-
(Fabrika 2004). Radio synchrotron emission is observed ysis, we make the response matrix file (RMF) and ancil-
on a larger scale (≥1015 cm). Comparison of (quasi) si- laryresponsefile(ARF)usingxisrmfgenandxissimarfgen
multaneous data enables us to trace the evolution of the (Ishisaki et al. 2007), respectively. The spectra of all the
same matter traveling along the jets on a spatial scale of XIS sensors are combined to improve the statistics, to-
many orders of magnitudes. gether with the corresponding responses. We screen out
For this purpose, we organized a multi-wavelength ob- events suffering from telemetry saturation, using GTI fil-
servation campaign in the period from 2006 March 29 to ters provided by the Suzaku team2.
April 15. The campaign includes two Suzaku observa- 2.1.2. HXD/PIN data
tions performed in- and out-of eclipse phase and a large TheHXDisanon-imagingcollimatedX-raysensorcon-
setofopticalspectroscopy,optical/IRphotometryandra- sisting of two main detection parts; silicon p-intrinsic-n
dio observations. As for details of this campaign, refer to diodes (hereafter PIN) and gadolinium silicate crystals
the papers by Kotani et al. (2006, 2008). In this paper, (Ce-doped Gd SiO ; GSO). They cover the energy range
2 5
we present the results from the Suzaku observations and of 10−70 keV (PIN) and 40−600 keV (GSO) with low
thosefromopticalspectroscopy. Suzaku,the5thJapanese
1 http://heasrc.nasa.gov/lheasoft
X-raysatellite, coversthe wide energy bandfrom0.2–600
2 http://www-cr.scphys.kyoto-u.ac.jp/menber/hiroya/xis/gtifile.html
keV. The large effective area below 10 keV with good en-
No. ] Suzaku and Optical Spectroscopic Observations of SS 433 3
background levels (Takahashi et al. 2007). In the present around the epochs of the Suzaku observations, aiming
study, we concentrate on the PIN data, since the signals to trace the evolution of the jet structure from the
from SS 433 above 40 keV is below the sensitivity of the X-ray and optical data. From 2006 April 2 to 12,
GSO. Since the observations were performed in the nor- four observatories participated in this campaign: the
malmodeoftheHXD,wesimplyextractthespectrafrom Special Astrophysical Observatory (SAO), the Gunma
the PIN event data, following the standard analysis pro- Astronomical Observatory (GAO), the Nishi-Harima
cedure3. We subtract the non X-ray background (NXB) Astronomical Observatory (NHAO), and the Asiago
from the data, utilizing the modeled NXB distributed by Observatory of the University Padova. Table 2 gives the
the Suzaku team 4. The version keyword of the NXB logsofthe opticalobservations. We observedSS433with
files is METHOD=LCFITDT (i.e., so-called the “tuned back- the 6-m Russian telescope5 with the Multi Pupil Fiber
ground”), which gives the best reproductivity of the PIN Spectrograph 6 at the SAO (PI: Fabrika). At the GAO,
NXB (0.34% systematic error in the 15–40 keV for a 40 the 150 cm telescope equipped with GLOWS7 (Gunma
ksec exposure; Fukazawa et al. 2009). LOW Resolution spectrograph and imager, R=400–500)
In addition to the NXB, two kinds of diffuse/extended was used (PI: Kinugasa). At the NHAO, having the 2-
background should be subtracted before the spectral m Nayuta telescope8, we employed the optical spectro-
analysis; the cosmic X-ray background (CXB) and the graph (Ozaki & Tokimasa 2005) with a low dispersion
Galactic X-ray background (GXB). The GXB is partic- mode (R ∼1000) for our observations (PI: Ozaki). The
ularly important because a target source is close to the Galileo 122-cm telescope was used at the Padova-Asiago
Galactic plane. Since the surface brightness of the GXB Observatory(PI:Iijima,R=800). Wealsotookadditional
varies field to field, we estimate its spectrum using the spectral data of SS 433 at the GAO about 1-month be-
PINdatainanear-byfield, (l,b)∼(28◦.5,−0◦.2)(OBSID fore and 1 and 2-months after the Suzaku observations.
500009020), located ≈11◦.5 away from SS 433. This From these data, we determine the Doppler shift of both
region is free from bright X-ray sources and has been recedingandapproachingjetsusingtheHαemissionlines.
well studied with Chandra, from which hundreds of faint Note that we werenotable to detect Hα originatingfrom
point sources are detected below 10 keV (Ebisawa et al. thejetsonApril2(atGAO)andApril12(atNHAO)due
2005; Revnivtsev & Sazonov 2007). They cannot be re- to the limited signal-to-noise ratio.
solved with the PIN, and hence contribute to the PIN
signal as a part of the GXB emission. To estimate the 3. Suzaku Results I. (out of Eclipse)
summed GXB+CXB flux, we analyze the PIN spectra in
this region by subtracting the NXB in the same man- In this section, we present the results obtained from
ner as above. We find the GXB+CXB spectrum can the Suzaku data on 2006April 8–9(out of eclipse phase).
be well fit with a single power-law model in the 12–40 For spectral fitting, we use the XSPEC package9 version
keV band and obtain the best-fit Γ = 2.1 and flux of 11.3.2ag (Arnaud et al. 2006).
2.1×10−11 erg cm−2 s−1. Thus, assuming that the GXB
3.1. Light Curves
(and the CXB) is the same between this region and that
aroundSS433,wesubtractthemodeledGXB+CXBspec- Figure3showsthesummedXISlightcurvesofthefour
trumfromthePINdataofSS433,inadditiontotheNXB. sensorsinthethreeenergybands,0.5–2keV,2–5keV,and
Figure 1 shows the total and source spectra of SS 433 af- 5–10keVfortheXIS-FI(0.3–2keV,2–5keV,and5–8keV
ter the backgroundsubtractionforthe eclipseandout-of- fortheXIS-BI).Asnoticed,significantvariabilityisfound
eclipse phase. The contributionofthe NXB, andthe sum especially in the hard band above the 5 keV. We confirm
ofthe GXB andthe CXB areseparatelyplotted. We find that this tendency also appear in hard X-ray band light
thatthefluxleveloftheGXB+CXBisonly0.3timesthat curveinthe12–40keVbandobtainedwiththeHXD/PIN
of the NXB. To evaluate the possible uncertainties in the (see Figure2). Forthe subsequentanalysis,wedivide the
estimated GXB flux, we refer to the spatial distribution time region into two, epoch A (the first half), when the
of the GXB obtained from the Galactic ridge survey with intensity and spectrum was almost stable, and epoch B,
theINTEGRAL/IBIS(Krivonosetal.2007),whichcovers when the spectrum exhibited a drastic change. Figure 4
almost the same energy band as the HXD/PIN. We con- shows the XIS spectra in epoch A and B. It is seen that
firmthatthe systematic errorsbyusing the differentfield the average spectrum, in particular the iron-K emission
separated by 10 degrees are smaller than the statistical line profiles, is very different in the two epochs.
errors, and hence do not affect our conclusions. Figure 2
3.2. Individual Spectral Analysis
shows the light curves of the HXD/PIN in the 12–40keV
from which the NXB is subtracted. In this subsection, we study the properties of emission
linesoriginatingfromtheblueandredjetsandtheirevolu-
2.2. Optical Spectroscopy
tionbasedononlythe XISdata. Toexaminethe spectral
We organized quasi-simultaneous optical spectroscopic
5 http://w0.sao.ru/Doc-en/Telescopes/bta/descrip.htm
observations of SS 433 using ground-based telescopes 6 http://w0.sao.ru/Doc-en/Telescopes/bta/instrum/
34 hhttttpp::////hwewawsa.racs.tgrsof.ci.snaass.aac.g.jopv//sduozcask/us/uaznaakluy/saisn/ahlxydsi/sp/ianbncx/b/ 897 hhhttttttppp::://////whwewwawwsa..rnacsh.tnaroao.snga.o.pg.rjoepvf/./gnduhonacmos//atx.eajlpne/sacidnouspt/erxsus/mpneaecny/tust/ad.hetvmicle bcldsi.html
4 Kubota et al. [Vol. ,
variability, we divide the one day data into eight parts respectively. It is beyond the scope of this paper to ap-
(data number 1 to 8) with an equalinterval, and perform plyafullyanalyticspectralmodelofthejetsthatincludes
spectral fitting to each spectrum. To focus on the iron-K bothcontinuumandlineemissionbyself-consistentcalcu-
band by making the best use of the energy resolution of lation. Instead,weonlyconsideracontinuummodel,over
the XIS, we only analyze the 5.0–10 keV band. whichthe11emissionlinesaresuperposedasindependent
The fitting model consists of a bremsstrahlung contin- parameters.
uum and 11 emission lines, modified by the interstellar We adopt a multi-temperature bremsstrahlung model
absorption. It is expressed as a function of energy E: for the continuum; assuming a power law dependence of
the temperature of the jet T on the distance from the jet
e−σ(E)NH×[Bremss(kT)+Fe Kα
I z=0 baser,wecancomputeamodelspectrumaccordingtothe
+(Fe Kα+Fe Kα+Ni Kα
XXV XXVI XXVII expected relation between the differential emission mea-
+Fe Kβ+Fe Kβ)
XXV XXVI z=zred sure and temperature. Here we consider a stationary jet
+(Fe Kα+Fe Kα+Ni Kα
XXV XXVI XXVII model consisting of radiatively cooling, expanding plas-
+Fe Kβ+Fe Kβ) ],
XXV XXVI z=zblue mas (e.g., Kotani et al. 1996). The jets are assumed to
where σ(E) is the photo-electric cross section and N is moveinatruncatedconewithaconstantvelocity. Hence,
H
the hydrogen column density toward the source. We fix thedensitychangesasn(r)∝r−2. Thismodelpredictsap-
N at 1.5×1022cm−2, which is converted with the for- proximately T ∝r−2(γ−1), where γ is the adiabatic index
H
mula by Predehl & Schmitt (1995) from A =8, a typical (5/3 for non relativistic particles). Since we cannot well
V
extinction for SS 433 (Fabrika 2004). In this study, for constrain the power law index from our data, we assume
simplicity, we adopt a single temperature bremsstrahlung T ∝r−4/3 according to this model. The free parameters
model for the continuum, considering the limited energy are the innermost temperature T0 and its normalization.
band; although a more complicated model is applied for Wealsoconsiderareflectioncomponentfromcoldmat-
the analysis of the broad band spectra in the next sub- ter, which is indicatedby the presence of the fluorescence
section, the results on the emission lines are little af- 6.4 keV iron K emission line, although it has been ne-
fected. The modelincludes 11narrowGaussianlines, five glectedinmostofpreviousstudies. Forthis we adoptthe
pairsofDoppler-shiftedlinesfromFe Kα,Fe Kα, reflection code by Magdziarz & Zdziarski (1995), avail-
XXV XXVI
Ni Kα,Fe Kβ andFe Kβ fromthetwojets, able as reflect model on XSPEC applicable for any inci-
XXVII XXV XXVI
and one stationary line of Fe Kα. The Doppler shifts of dent spectrum. The free parameter is the the reflection
I
the red and blue jets are free parameters that are linked strengthR≡Ω/2π,whereΩ isthe solidangleseenbythe
togetheramongallthelinesoriginatingfromthesamejet. X-ray emitter (i.e., the jets). We fix solar metal abun-
The velocity dispersion (1σ width) of the emission lines dances andaninclination angleof 79◦, assuming thatthe
is fixed at 1500 km s−1, which is found by Lopez et al. reflectionmainlytakesplaceinouterpartsoftheaccretion
(2006) when the precession phase is the closest to ours disk.
among available Chandra HETGS observations. ThefittingresultsfortheepochAspectraareshownin
First, we fit the first four spectra (epoch A) simulta- Figures 6 and 7. The best-fit parameters are summarized
neously, which exhibit little variability. In this fit, the in Table 3. In the analysis, the relative normalization
intensities of the 6.4 keV Fe Kα lines are linked one an- between the XIS and HXD/PIN is fixed at 0.923, based
I
other among all the spectra. Then, we perform spec- on the calibration using the Crab Nebula (Ishida et al.
tral fitting to the last four spectra (epoch B) separately. 2007). We obtain the innermost jet temperature of T0=
For these spectra, we fix the intensity of the Fe Kα line 27±2 keV. To make the reflection parameter physically
I
at the best-fit value obtained from the epoch A data, meaningful,welimitR≤1inthefittingandfinallyobtain
6.9×10−5photons−1cm−2, since five emission lines (in- R=1.0+0 . Theequivalentwidthofthe6.4keVlinewith
−0.41
cluding four jet lines) are blended around 6.4 keV and it respect to the reflection component turns out to be 1.0
is difficult to separate its contribution in epoch B. keV at the best-fit value, well consistent with theoretical
Figure5plotsthetimevariabilityofthecenterenergies calculations (Matt et al. 1991) within a possible range of
of the Fe Kα lines emitted from the twin jets. As viewing angle and an iron abundance.
XXV
noticed, we detect rapid variability of the Doppler shifts
from data number 6 to 8, with a corresponding rate of 4. Suzaku Results II. (in Eclipse)
dz/dt≈0.019/0.33day−1. Below we analyze the summed
spectra only from data number 1–4 (epoch A), where the The same analysis as in the previous section is applied
change of the line energies is smaller than 20 eV. for the data of the first Suzaku observation (in-eclipse).
Figure 8 shows the X-ray light curves on 2006 April 4–
3.3. Broad Band Spectra
5 in the three energy bands. A long term variability is
We have obtained the simultaneous, broad band X-ray clearlyseen,asexpectedfromtheeclipseofthejetsbythe
spectrum of SS 433 covering up to 40 keV with the XIS companion star. Similarly to the out-of-eclipse data, we
and HXD/PIN . This gives us an ideal opportunity to in- make8time-slicedspectraandperformspectralfitting to
vestigate the origin of the continuum emission. In this each one, using the same spectral model described in § 3.
subsection, we perform a simultaneous fitting to the XIS In this period, since the spectra around 6.4 keV are very
and PIN spectrum in the 5–10 keV and 12–40 keV band, crowded and hence the intensity of the FeI Kα line can-
No. ] Suzaku and Optical Spectroscopic Observations of SS 433 5
notbedetermined,wefixitat3.7×10−5photons−1cm−2, day and 0.38±0.08 day, respectively. Assuming that the
a value that is estimated from the analysis of the broad- jets speed is constant at 0.26c, we estimate the distance
band spectra with a reflection component, as described of the optical jets measured from the X-ray jets to be
below. Figure 9 showsthe evolutionof the line center en- l =(4.3±0.6)×1014cm(red)andl =(2.6±0.6)×1014
opt opt
ergiesoftheFe Kαlines. Wedonotdetectsignificant cm (blue). Thus, the Hα emitting region may not be at
XXV
variability of the Doppler shifts which were observed in the symmetric location between the twin jets, depending
the out-of-eclipse phase (Figure 5). on the efficiency of the cooling determined by the plasma
We also make simultaneous fit to the XIS and density. The order of the jet size is well consistent with
HXD/PIN spectra to constrainthe continuummodel, us- previous estimates (Fabrika 2004).
ingthesamemulti-temperaturejetmodelwithareflection The jitter observedin X-rays on 2006 April 8–9 is con-
component as described in the previous subsection. We firmed in the optical spectra taken after this event. Since
limitR≤1andfixtheequivalentwidthofthefluorescence thelengthoftheopticaljetsis1000timeslargerthanthat
Fe Kα line with respect to the reflection component at of the X-ray jets, fast time variability observed in X-rays
I
1.0 keV, based on the result of the out-of-eclipse data, is significantly smeared out in the optical band. Thus,
sinceitisdifficulttoconstraintheabsoluteintensityfrom soon after a rapid change of Doppler shifts is observed in
the data. We obtain T =21±1 keV and R=1.0+0 . X-rays, the optical emission lines become broad (if un-
0 −0.13
Figures 10 and 11 show the data and best-fit model. The resolved),by including the contribution from jet material
best fit parameters are summarized in Table 3. ejectedatdifferentepochs. Thisiscalleda“projectionef-
fect”,previouslyobservedfromnoddingmotions(Borisov
5. Discussion & Fabrika 1987). Thus, we investigate the change of the
widthofHαlinesoriginatingfromthejetsbeforeandafter
5.1. X-ray and Optical Doppler Shift Curves
the second Suzaku observation(out-of-eclipse). The opti-
Figure 12 shows the Doppler shifts of the SS 433 jets calspectraobservedatthe GAOareplottedinFigure14.
measuredwith the SuzakuXIS (circles) and optical spec- We find that while the Hα line width of the blue and red
troscopy (crosses). The two dot lines correspond to the jets was 40 ˚A (FWHM) and 58 ˚A on April 7, the lines
162.15 days period sinusoidal curves for the blue and became significantlybroaderwitha FWHM of188˚A and
red jets expected from the precession motion (Gies et al. 315˚A,respectively,onApril9. ThischangeoftheHαline
2002),whichisshiftedby–5.5daystofittheobservational width corresponds to ∆z=0.023 (blue jet) and ∆z=0.039
points. From this figure, it is confirmed that the Suzaku (red jet), which is larger only by ∆z=0.005 than the to-
observations were performed at a precession phase when tal observed change of the Doppler shifts of X-ray lines.
the jets axis are almostperpendicular to the line of sight. Thus, the broadening of the Hα lines seen in the April 9
Figure 13 is a blow-up of Figure 12 around the Suzaku spectrumismainlyattributabletotherapidchangeofthe
observation epoch. It is clearly seen that the observed Doppler shifts occurring close to the jet base.
DopplershiftcurvesbothfromtheX-rayandopticaldata
5.2. Origin of the X-ray Jitter
show strong deviation from the precession curve with a
162.15daysperiod. Exceptforthedataaround2006April We have detected the fastest variability of Doppler
8(MJD53834),bothamplitudeandperiodicityofthisde- shifts of X-ray emission lines ever observed from SS 433,
viationareconsistentwiththenoddingmotionofthejets, which can be interpreted as jitter motions of the jets, not
expressedasasinusoidalcurvewitha6.28daysperiodand the nodding motions where much slower change of red-
a semi-amplitude of ∆z ≈ 0.012 at our precession phase shifts isexpected. Assumingthatthe twinjets arealways
(Fabrika 2004). symmetric, we can estimate the orientation and intrinsic
As mentioned above, in the Suzaku XIS data on 2006 speed of the jets from the observedDoppler shifts of blue
April 8, we detect rapid variability of the Doppler shifts, andredcomponents. TheresultsareplottedinFigure15.
dz/dt≈ 0.019/0.33 day−1. This is larger than those ex- As noticed from the figure,we detect a significantchange
pected from the precessionand/or nodding motion of the inbothangleandspeedofthejetsduringthelatterinter-
jets; the maximum variability from the nodding motion val. From the former half toward the end of the observa-
is dz/dt ≈0.004/0.33 day−1 (Fabrika 2004). Hence, we tion,thejetspeedincreasedbyafactorof(8±2)%. Recall
interpret that our Suzaku result corresponds to a jitter that in the same epoch, the X-ray spectra became softer
whichwaspreviouslyreportedonlyfromtheopticalspec- andhencethetemperatureofthejetdecreased. Thisanti-
troscopy (e.g., Iijima 1993), observed for the first time in correlation between the jet speed and temperature must
X-rays. The origin of these phenomena will be discussed be explained in theoretical models of jets.
in the next subsection. Consideringthesmoothevolutionoffluxandlinecenter
UtilizingourquasisimultaneousX-rayandopticalspec- energy,weinferthattheX-rayjitteroriginatesfromacon-
troscopic data, we can determine a time lag between the tinuous change of the jet kinetic parameters, not reflect-
epochs when same jet material emits X-rays and opti- ing the production of discrete jets with largely different
cal lights, assuming that the Doppler shift remains con- Dopplershifts. SincethelengthoftheX-rayjetsis∼1012
stantintravelingalongthejet. Basedonthe opticaldata cm corresponding to a traveling time of only ∼100 sec,
points on MJD 53834.8 and previous X-ray curves, the we simply measure the flux-weighted average of Doppler
lag in the red and blue jet is estimated to be 0.64±0.08 shifts of jets emitted during the integration time (∼104
6 Kubota et al. [Vol. ,
sec) of each spectrum. If jets with very different Doppler blue and red jets). In the out-of-eclipse phase, however,
shifts are emitted within each exposure, we would expect T determined from the continuum (27±2 keV) is signifi-
0
broadeningoftheemissionlines. Wecheckthelinewidths cantly higher than that determined from the Fe line ratio
of the Fe Kα emission lines from the 8 time-sliced (13±2 keV). These facts suggest that the out-of-eclipse
XXV
spectra on 2006 April 8–9. The same fitting model as in spectrum may be contaminated by an additional hard X-
§ 3 is used, by making the width of Gaussian lines free. ray component that is hidden in eclipse. The spectrum
We find that the width is almostconstantover the obser- must be very hard and/or heavily absorbed since its con-
vation at 34±6 eV (the average from the blue jet) and tributionshouldnotbelargebelow∼7keV,wherethera-
36±7eV(redjet), whicharecomparableto the observed tio of the continuum intensity between the out-of-eclipse
line width resolvedwith Chandra/HETGS (Namiki et al. and in-eclipse phases is similar to that of the iron emis-
2003; Lopez et al. 2006). No significant line broadening sion lines originating from the jets. The presence of such
is observed in epoch B. Thus, we favor the continuously ahardcomponentnotdirectlyrelatedtothejetswassug-
changing jet model, although we cannot exclude the pos- gestedby the comparisonofin-andout-of-eclipsespectra
sibilityofmanydiscretejets withslightlydifferentkinetic observed with Ginga (Brinkmann et al. 1991; Yuan et al.
parameters. Inthe opticaljets, by contrast,the evolution 1995). Thismayberelatedtotheextendedcoronaaround
of emission lines from discrete plasmoids were sometimes theaccretiondiskdiscussedinKrivosheyevetal.(2009)or
observed on a time scale of ∼0.1–0.3 days (Panferov & a reflectionfeature of the emissionfrom the inner disk by
Fabrika 1993). The relation of these phenomena to the the outer wall of the funnel (Medvedev & Fabrika 2009).
X-ray jitter is not clear. To constrain its origin, analysis of broad band data uti-
lizing a fully self-consistent model for the thermal jets
5.3. Broad Band X-ray Spectra
(including both continuum and emission lines) would be
We obtain for the first time simultaneous broad band required, which we leave for future studies.
spectra of SS433 coveringup to ∼40keVincluding those
observedwithCCDresolutionbelow10keVwithSuzaku. Acknowledgment
This gives us a unique opportunity to investigate the ori-
ginofthespectranotonlyfromtheemissionlinesbutalso This work was partly supported by the Grant-in-
from the continuum shape. We find that the spectrum in Aid for JSPS Fellows for young researchers (KK), the
eclipse is consistent with the emission from optically thin Grants-in-AidforScientific Research20540230(YU), and
plasmas in the twin jets as reported in previous works the Grant-in-Aid for the Global COE Program “The
(Brinkmannet al.1991;Kotanietal.1996),althoughthe Next Generation of Physics, Spun from Universality
out-of-eclipsespectrummayneedanadditionalhardcom- and Emergence” from from the Ministry of Education,
ponenttoself-consistentlyexplainbothemissionlinesand Culture, Sports, Science and Technology (MEXT) of
continuum. Japan.
Fromthelineintensities,wecanestimatetheinnermost
temperature of the jets based on the radiatively cooling References
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Fig. 1. ThePINspectraofSS433on2006April8–9(upper,
PASJ, 55, 281
out-of-eclipse)and April4–5 (lower, in-eclipse). From upper
Ozaki, S., & Tokimasa, N. 2005, Annual Report of the Nishi- to lower, the total spectrum, the NXB, the source spectrum
Harima Astronomical Observatory (ISSN 0917-6926), afterbackground subtraction,andtheGXB+CXB.
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Panferov, A. A., & Fabrika, S. N. 1993, Astronomy Letters,
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4
Predehl, P., & Schmitt,J. H. M. M. 1995, A&A,293, 889 0.
April 8−9 (Out of Eclipse)
Revnivtsev,M., & Sazonov, S. 2007, A&A,471, 159
3
Takahashi, T. et al. 2007, PASJ,59, 35 V 0.
WatWso.n1,9M86.,GM.,NSRtAewSa,r2t2,2G, 2.6C1., King, A. R., & Brinkmann, 40 ke 0.2
−
Yuan,W., Kawai, N., Brinkmann, W., & Matsuoka, M. 1995, 2
1 1
A&A,297, 451 0.
0
April 4−5 (in Eclipse)
3
V 0.
e
40 k 0.2
−
12 0.1
0
0 2×104 4×104 6×104 8×104 105
Second since MJD=53833.4, 53829.5
Fig. 2. The PIN light curves of SS 433 in the 12–40 keV
bandon2006April8–9(upper,out-of-eclipse)andApril4–5
(lower,in-eclipse). TheNXBissubtracted.
8 Kubota et al. [Vol. ,
Bin time: 180.0 s
5 1
2.
keV 52 eV
2.5 11. ec/k 0.1
− s
0.5 0.5 nts/
2.0−5.0 keV 0.511.52 1 2 3 4 5 6 7 8 normalized cou 0.014
2
V 2 A B χ 0
−10 ke 11.5 −4−2
5.0 0.5 5 10
0 channel energy (keV)
0 2×104 4×104 6×104 8×104 105
Seconds since MJD=53833.4
Fig. 6. The XIS spectrum in the 5–10 keV band on 2006
April8–9(datanumber1–4only;outofeclipse). Thebest-fit
Fig. 3. The XIS light curves of SS 433 on 2006 April 8–9
model is over-plotted with separate contribution of the re-
(out of eclipse) in three bands, 0.5–2 keV (upper), 2–5 keV
flectioncomponent(lowercurve,green)andGaussians(blue:
(middle),and5–10keV(lower). Thebinsizeis180sec. The
those from the blue jet, red: those from the red jet, green:
arrowsdefineepochs AandBforthespectralanalysis.
the fluorescence iron-K line at 6.4 keV). The fitting residu-
als in units of χ are plotted in the lower panel. The best fit
1
parametersaregiveninTable3.
A
V
e
k
ec/ 0.1
s
s/
nt
u
o
c
1
B
d
e
maliz 0.1
nor 1
1 V
0.0 5 10 ke 0.1
channel energy (keV) ec/
unts/s 0.01
Fig. 4. The5.0–10keVspectraofSS433inepochA(upper) o
afonrdthBe(dbeofitntiotmio)n. oTfhtheefoeuprocXhIsS.s are summed. See Figure 3 alized c 10−3
m
6.7 nor 4
2
6.65 χ 0
2
6.6 −
4
−
6.55 5 10 20
V)
ergy (ke 6 6.4.55 channel energy (keV)
n
E Fig. 7. ThesimultaneousfittotheXISandHXD/PINspec-
6.4
tra of 2006 April 8–9 (out-of-eclipse), using a multi-temper-
6.35 ature jet model for the continuum (see text). The best-fit
models are over-plotted with separate contribution from the
6.3
reflection component and fluorescence iron-K line (green).
6.25 Residuals in units of χ are shown in the lower panel. See
1 2 3 4 5 6 7 8
Table3forthebest-fitparametersofthecontinuum.
Data number
Fig. 5. Time variability of the line center energy of
FeXXVKαdeterminedfromtheSuzakuspectraon2008April
8(out-of-eclipse). Thehorizontal linesshowthe averageval-
uesdeterminedfromthetimeaveragedspectra.
No. ] Suzaku and Optical Spectroscopic Observations of SS 433 9
Bin time: 180.0 s
5 1
2.
keV 52 eV
2.5 11. ec/k 0.1
− s
0.5 0.5 nts/
2.0−5.0 keV 0.511.52 normalized cou 0.014
2
V 2 1 2 3 4 5 6 7 8 χ 0
−10 ke 11.5 −4−2
5.0 0.5 5 10
0 channel energy (keV)
0 2×104 4×104 6×104 8×104 105
Seconds since MJD=53829.5
Fig. 10. The XIS spectrum in the 5–10 keV band on 2006
April 4–5 (in eclipse). The best-fit model is over-plotted
Fig. 8. TheXISlightcurvesofSS433on2006April4–5(in
withseparatecontributionofthereflectioncomponent(lower
eclipse)inthreebands,0.5–2keV(upper),2–5keV(middle),
curve, green) and Gaussians (blue: those from the blue jet,
and5–10keV(lower). Thebinsizeis180sec.
red: thosefromtheredjet,green: thefluorescenceiron-Kline
at6.4keV). Thefitting residualsinunits ofχareplotted in
thelowerpanel. ThebestfitparametersaregiveninTable3.
1
V
6.7 ke 0.1
c/
6.65 e
6.6 unts/s 0.01
o
Energy (keV) 66 6..45.555 normalized c 104−3
6.4 2
6.35 χ 0
2
−
6.3 4
−
6.25 5 10 20
1 2 3 4 5 6 7 8 channel energy (keV)
Data number
Fig. 11. The simultaneous fit to the XIS and HXD/PIN
Fig. 9. Time variability of the line center energy of
spectra of 2006 April4–5 (in eclipse), using a multi-temper-
FeXXVKαdeterminedfromtheSuzakuspectraon2008April
ature jet model for the continuum (see text). The best-fit
4–5(ineclipse). Thehorizontallinesshowtheaveragevalues
models are over-plotted with separate contribution from the
determinedfromthetimeaveragedspectra.
reflection component and fluorescence iron-K line (green).
Residuals in units of χ are shown in the lower panel. See
Table3forthebest-fitparametersofthecontinuum.
10 Kubota et al. [Vol. ,
0.15
0.15
0.1
oppler shift (z) 0.0 05 cos (theta) 0.1
D 0.05
-0.05
-0.1 0
53800 53820 53840 53860 53880 1 2 3 4 5 6 7 8
Time (MJD) Data number
0.29
Fig. 12. A summary of Doppler shifts of the jets observed
around the observation campaign epoch. The results deter-
minedfromtheoptical(Hα)andX-ray(FeXXVKα)areshown
by the crosses and circles, respectively. The doted lines cor- 0.28
rceesspsioonndmtoottiohnes.162.15-days sinusoidal curves due to the pre- ocity (v/c)
el
v
0.27
0.08
[1]
0.26
0.06 1 2 3 4 5 6 7 8
Data number
hift (z)
er s 0.04 [2] Fig. 15. Thechangeofthejetparametersobservedon2006
ppl April 8–9, in terms of the cosine of angle between the
o
D line-of-sightandjetaxis(upper)andintrinsicvelocity(lower).
0.02
0
53830 53835 53840
Time (MJD)
Fig. 13. A blow up of Figure 12 around the epoch of the
Suzakuobservations.
Blue Blue RedRed
April 7
April 9
3
nsity
e
nt
d I
alize 2
m
or
N
1
6600 6800 7000 7200
Wavelength (Angstrom)
Fig. 14. TheopticalspectraofSS433observedattheGAO
on 2006 April 7 (solid line) and April 9 (dashed line). The
vertical lines denote the line center positions of Hα origi-
nating from the red and blue jets. There are two HeI lines
(λ6678,λ7065) inthefigure.
