Mon.Not.R.Astron.Soc.000,1-??(YYYY) Printed27January2012 (MNLATEXstylefilev2.2) Very fast photometric and X-ray observations of the intermediate polar V2069 Cygni (RX J2123.7+4217) 2 I. Nasiroglu,1,2⋆ A. S lowikowska,3⋆ G. Kanbach,1⋆ and F. Haberl1⋆ 1 1Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, 85748 Garching, Germany 0 2Universityof Cukurova, Department of Physics, 01330 Adana, Turkey 2 3Institute of Astronomy, University of Zielona G´ora, Lubuska 2, 65-265 Zielona G´ora, Poland n a J Accepted 2011November 24.Received2011November23;inoriginalform2011September 16 6 2 ABSTRACT ] We present fast timing photometric observations of the intermediate polar V2069 R Cygni (RX J2123.7+4217)using the Optical Timing Analyzer (OPTIMA) at the 1.3 S m telescope of Skinakas Observatory. The optical (450-950 nm) light curve of V2069 . h Cygni was measured with sub-second resolution for the first time during July 2009 p and revealed a double-peaked pulsation with a period of 743.38± 0.25. A similar - double-peakedmodulationwasfoundin the simultaneous Swift satellite observations. o Wesuggestthatthisperiodrepresentsthespinofthewhitedwarfaccretor.Moreover, r t we present the results from a detailed analysis of the XMM–Newton observationthat as alsoshowsadouble-peakedmodulation,howevershiftedinphase,with742.35±0.23s [ period.The X-rayspectraobtainedfromthe XMM–Newton EPIC(EuropeanPhoton Imaging Camera) instruments were modelled by a plasma emission and a soft black 1 bodycomponentwithapartialcoveringphoto-electricabsorptionmodelwithcovering v fractionof0.65.AnadditionalGaussianemissionlineat6.385keVwithanequivalent 9 width of243eV is requiredto accountfor fluorescentemissionfromneutral iron.The 2 6 ironfluorescence(∼6.4keV)andFeXXVIlines(∼6.95keV)areclearlyresolvedinthe 5 EPICspectra.In the Porb–Pspin diagramof IPs,V2069Cyg showsa low spinto orbit . ratio of ∼0.0276 in comparison with ∼0.1 for other intermediate polars. 1 0 Key words: stars:binaries - stars:novae, cataclysmic variables - X-rays: binaries - 2 stars:magnetic field - stars:individual: V2069 Cyg (RX J2123.7+4217) 1 : v i X 1 INTRODUCTION V2069 Cyg (RX J2123.7+4217) was discovered as a r a hardX-raysourcebyMotch et al.(1996)andidentifiedasa Magnetic cataclysmic variables (CVs) are interacting CV.Thorstensen & Taylor(2001)reportedamostprobable close binary systems in which material transferred from orbital period of 0.311683 days (7.48 h) from their spec- a Roche-lobe filling low mass companion is accreted by a troscopic observations. de Martino et al. (2009) performed magnetic white dwarf (WD).Magnetic CVs are subdivided a preliminary analysis of XMM–Newton observations that in two groups: polars (or AM Her type) and intermediate showedastrongpeakatthefundamentalfrequencyof116.3 polars (IPs; or DQ Herculis type).In polars, theWD has a cyclesd−1 andharmonicsuptothethirdinthepowerspec- sufficiently strong magnetic field (B ∼ 107−108 G) which trum.Additionally,thesinusoidalfittotheprofilefromboth locks the system into synchronous rotation (Pspin = Porb) EPIC-pn and EPIC-MOS data revealed a fundamental pe- and prevents the accretion disk to form around the WD. riod of 743.2±0.4 s and 55 per cent pulsed fraction. They In IPs, the field of the WD is one order of magnitude alsoreportedaspectralfitconsisting ofa56eVblackbody weaker (B ∼ 106−107 G), and therefore insufficient to (bbody) component plus 16 keV thermal plasma emission force the WD to spin with the same period as the binary and a Gaussian at 6.4 keVemission line with an equivalent system orbits (Pspin < Porb). Theaccretion in IPs happens width (EW) of 159 eV, being absorbed by a partial (69 per throughadiskwithadisruptedinnerregion(Cropper1990; cent)coveringmodelwithNH =1.1×1023 cm−2andatotal Patterson 1994; Warner1995; Hellier 2001). absorber with NH = 5×1021 cm−2. Their spectral analy- sis confirmed that V2069 Cyg is a hard X-ray emitting IP with a soft X-ray component. Butters et al. (2011) carried out an analysis of RXTE data in the 2.0−10.0 keV energy ⋆ E-mail: [email protected] (IN); [email protected] range and found the spin period of the V2069 Cyg WD to (AS);[email protected](GK);[email protected](FH) 2 Nasiroglu et al. be 743.2±0.9 s with a double-peak modulation. They also Table 1. Log of the photometric (OPTIMA) and X- reported thespectral results with a 6.4 keV iron line which ray (Swift/XRT and XMM–Newton/EPIC) observations of is typical of IPs. V2069Cyg. No. Date Detector ObsBeg Expo. 2 OBSERVATIONS 2009 (MJD) (h) 2.1 High time resolved photometric observations 1 Jul02 OPTIMA 55014.922 2.5 2 Jul18 OPTIMA 55030.951 1.2 Weperformed photometricobservationsofV2069 Cygwith 3 Jul19 OPTIMA 55031.845 2.1 theOptical TimingAnalyzer(OPTIMA) instrumentat the 4 Jul21 OPTIMA 55033.820 4.1 1.3mtelescopeatSkinakasObservatory,Crete,Greece.The 5 Jul22 OPTIMA 55034.871 3.0 high-speedphotometerOPTIMAisasensitive,portablede- 6 Jul24 OPTIMA 55036.804 1.2 tector to observe extremely faint optical pulsars and other 7 Jul26 OPTIMA 55038.040 1.4 highly variable astrophysical sources. The detector con- 8 Jul26 OPTIMA 55038.827 1.7 tainseightfibre-fedsinglephotoncounters-avalanchephoto- 9 Jul28 OPTIMA 55040.897 1.5 diodes(APDs),andaGPS (GlobalPositioning System)for A Jul21 Swift 55033.786 0.8 B Jul22 Swift 55034.048 0.9 thetimecontrol.Singlephotonsarerecordedinallchannels withabsolutetimetaggingaccuracyof∼4µs.Thequantum C Apr30 XMM–Newton 54951.463 7.8 efficiencyoftheAPDsreachesamaximumof60%at750nm andliesabove20%intherange450–950nm(Kanbach et al. 2003). To observe V2069 Cyg OPTIMA was pointed at RA(J2000)=21h23m44s.82,Dec(J2000)=+42◦18′01′.′7,cor- respondingtothecentralapertureofahexagonalbundleof fibres (Fig. 1). A separate fibre is located at a distance of ∼ 1′ as a night sky background monitor. The log of the observations is given in Tab. 1. 2.2 Swift/XRT observations ThesimultaneoussoftX-rayobservationsofV2069Cygwere performed with the Swift’s X-ray telescope (XRT;Burrows etal. 2005) in theenergy range of 0.3−10 keV.The CCD of theSwift/XRTwasoperatedinthePhoton-Countingmode whichretainsfullimagingandspectroscopicresolutionwith a time resolution of 2.54 s. The Swift source position is: RA(J2000)=21h23m44s.69Dec.(J2000)=+42◦17′59′.′6with ′′ an error radius of 3.5. For the XRT data we applied the following types of filters: grade 0–4, and a circular region Figure 1. OPTIMA fibre bundle centred on V2069 Cyg. The filter centred at the position of the source with 10-pixels ring fibres (1–6) are used to monitor the background sky simul- radius (corresponding to ∼23′.′5). taneously. 2.3 XMM–Newton observations The XMM–Newton observation of V2069 Cyg was per- formedon2009April30(ObservationID:0601270101).The EPICinstrumentswereoperatedinfull-frameimagingmode with thin and medium optical blocking filters for EPIC-pn events (PATTERN=0) from EPIC-pn data and single- to (Stru¨deretal. 2001) and EPIC-MOS (Turner et al. 2001), quadruple-pixelevents (PATTERN 0–12) from EPIC-MOS respectively.Theexposuretimeswere26433 sforEPIC-pn, data. For the timing analysis we used single- and double- 28023 sforEPIC-MOS1,28029 sforEPIC-MOS2.Weused pixel events from the EPIC-pn data (PATTERN 0–4), and theXMM–Newton ScienceAnalysisSoftware(SAS)v.10.0.0 single-toquadruple-pixeleventsfromEPIC-MOSdata.We to process the event files. The source coordinates derived sorted out bad CCD pixels and columns (FLAG=0). After from a standard source detection analysis of the combined the standard pipeline processing of the EPIC photon event EPIC images are RA(J2000) = 21h23m44s.60, Dec(J2000) files,werejectedsomepartofthedatawhichwasaffectedby ◦ ′ ′′ = +42 1800.1. We identified the circular photon extrac- veryhighsoftprotonbackground.Wecreatedgoodtimein- tion regions (with radius of 36′′, 53′′ and 56′′ for EPIC- tervals(GTIs) from backgroundlight curves(7.0−15.0 keV pn,EPIC-MOS1 andEPIC-MOS2respectively) around the band) using count rates below 15 cts ks−1 arcmin−2 for sourcebyoptimisingthesignaltonoiseratio.Acircularre- EPIC-pndataand2.5ctsks−1arcmin−2forMOSdata.The gion was used for the background extraction from a nearby spectra of EPIC-pn,EPIC-MOS1and EPIC-MOS2 contain ′′ source-free area (with radius of 35 ) on the same CCD 10576, 5908, and 6000 background subtracted counts, re- as the source. To create spectra we selected single-pixel spectively. Fast photometric observations of V2069 Cyg 3 10000 Ch 00 Ch 05 Source Counts 0 0 5 5 8000 s) s/ nt ou6000 c N ( 4000 unts/s 000 o 5 C 2000 0 2000 4000 6000 8000 Time (s) Figure 2. OPTIMA light curves of V2069 Cyg from July 2nd, 00 5 4 2009 observation (no. 1 in Tab. 1), shown as raw, uncalibrated 2000 4000 6000 8000 countrates binned in 1 s intervals. Source count rates were ob- Time (s) tained from the central fibre (channel 0) after subtraction of the properly calibrated sky background trace (channel 5). The Figure3.LightcurveofV2069CygasderivedinFig.2,zoomed skybackgroundisdecreasinginbrightnessbecauseofthesetting inthecountratescaleforbettervisibility.Theopticalperiodicity Moon. isclearlyvisible.Thedataarebackgroundsubtractedandbinned into10sintervals.Time0correspondstoMJD=55014.92172. 3 DATA ANALYSIS 3.1 Timing analysis of the OPTIMA and Swift/XRT data We analysed the data using the HEASOFT analysis pack- 00 2ω 0 6 age v.6.9. The X-ray and optical photon arrival times were converted to the solar system barycentre. OPTIMA count ω rates of the source were obtained from the central fibre (see Fig. 1). Raw data were binned with 1 s and, after 0 0 0 ’flat-fielding’ all fibre channels on a source free region of 4 er sky background, the corresponding calibrated background ow P countsweresubtracted.Wechosethefibrenumber5asthe best representative of the background, because its APD re- 0 0 0 sponsewasclosesttotheAPDresponseofchannel0(Fig.2). 2 inst. freq. The resulting photometric light curve shows a promi- nent periodic variability (Fig. 3). The power spectrum was computedwiththeFastFourierTransform(FFT)algorithm 0 and normalised such that the white noise level expected 10−3 0.01 0.1 Frequency (Hz) from the data uncertainties corresponds to a power of 2 (Fig. 4). The power spectrum shows peaks at the funda- mental spin frequency (first harmonic) 0.00134277 Hz and Figure4.PowerspectrumobtainedfromOPTIMAdata(Tab.1, its second harmonic 0.00268555 Hz (periods 744.73 s and allepochs).Itshowsprominentpeaksatthefundamentalspinfre- 372.35 s, respectively), as well as a known systematic fre- quency(firstharmonic)of0.00134277Hzanditssecondharmonic quency of 0.03718 Hz (26.9 s). A χ2 folding analysis which of0.00268555 Hz.Aninstrumental frequency at0.0371094 Hzis alsovisible. folds the data over a range of periods reveals the best spin period of theWD as 743.38±0.25 s, Fig. 5. The optical light curve folded with the 743.38 s spin WDspinperiodof743.38s(seeFig.7).However,theweaker period shows a double-peaked profile (see Fig. 6) with very high duty cycle (∼ 90 per cent), that is the percentage of peakisonlymarginallyvisibleandisseparatedbylessthan half thepulse cycle. the rotation phase where there is a pulsed emission. Since thepowerspectrumoftheopticaldataisdominatedbythe secondharmonicofthespinfrequencyitisclearlyseenthat 3.2 Timing analysis of the XMM–Newton data these two peaks are similar and separated by about half of the cycle in phase. Norton et al. (1999) reported the same For the timing analysis of the XMM–Newton data we cor- resultintheX-raydataofIPYYDra,wherethepowerspec- rected the event arrival times to the solar system barycen- trum is dominated by the second harmonic (i.e. 2/Pspin). tre. The background subtracted X-ray light curves in the On the other hand, due to low statistics, we could not de- 0.2−10.0keVenergybandobtainedfromEPIC-pnandcom- terminethespinperiodfromtheSwift-XRTdata,therefore bined MOS data with a time binning of 55 s are shown in the XRT data were folded according to the optical period. Fig. 8. The periodic variations around 745 s can be seen TheSwift/XRTalsoshowsadouble-peakmodulationatthe clearly in the X-ray light curves. To improve the statis- 4 Nasiroglu et al. 04 1 5× 1.4 04 1 4× 1.2 Chi squared 2×103×1044 X−ray Intensity 0.81 104 0.6 0 0.5 1 1.5 0−6 −4 −2 0 2 4 6 Phase Period (s) Figure 7. Pulse profile obtained from Swift-XRT data Figure 5.χ2 periodogramasafunctionoftheperiod,obtained (0.3−10.0 keV) folded at 743.38 s (16 bins/period) with an ar- from OPTIMA data. The central value (=0) corresponds to the bitrary zero point (MJD = 55014.0). The profile is background bestspinperiodof743.38s. subtractedandnormalisedtoanaveragecountrateof0.0918cts s−1. 1.02 5 1.01 22. Optical Intensity 0.991 Counts/s 0.511.5 6 0. 0.98 Counts/s 0.4 0 0.5 1 1.5 2 Phase (743.38 s) 0.2 0 5000 104 1.5×104 2×104 2.5×104 Figure6.PulseprofileobtainedfromallOPTIMAdata(Tab.1, Time (s) all epochs) folded with the 743.38 s spin cycle (32 bins/period). Theprofileisbackgroundsubtractedandnormalisedtotheaver- Figure 8. X-ray broad-band (0.2−10.0 keV) light curves of agecountrateof4621ctss−1.Epoch,MJD=54951.0. V2069CygobtainedfromtheEPIC-pn(top)andsummedMOS1 and MOS2 (bottom) data. The periodic variations can be seen clearly.Thedataarebackground subtractedandbinnedto55s. Time0correspondstoMJD=54951.46333. tics for timing analysis a combined EPIC-pn, EPIC-MOS1 and EPIC-MOS2 event list from the source extraction re- gionwascreated.TheFFTtiminganalysisofthecombined X-ray data revealed the presence of four harmonic frequen- certainty. We obtained the optical spin period a bit longer cies with a strong peak at the fundamental frequency of than the X-ray spin period, however both periods are com- 0.00134277 Hz that corresponds to a period of 744.73 s, as patible within theirerrors. shown in Fig. 9. We found that the fundamental frequency We folded the light curve to obtain the pulse pro- is much stronger than the second harmonic at energies files from the EPIC data (Fig. 10) with the spin period above 0.5 keV, while the second harmonic (with very weak in the different energy bands of 0.2−1.0 keV, 1.0−2.0 keV, power) is stronger than thefundamentalfrequency at ener- 2.0−4.5 keV and 4.5−10.0 keV and calculated hardness ra- gies below 0.5 keV. A similar behaviour was also reported tios(Fig.11)asafunctionofpulsephase.Thehardnessra- by Evans& Hellier (2004) for V405 Aur. To determine the tioswerederivedfromthepulseprofilesintwoneighbouring pulseperiodanditserrorweappliedtheBayesianformalism standard energy bands [HRi=(Ri+1−Ri)/(Ri+1+Ri), where as described in Gregory & Loredo (1996). Using the com- Ri denotesthebackgroundsubtracted countrateintheen- binedandmergedEPICdatainthe0.2−10keVenergyband ergybandi,withifrom1to4].TheXMM–Newtondataalso revealsthespinperiodoftheWDas742.35±0.23 s,1σ un- showadouble-peakedmodulationwith742.35speriodcon- Fast photometric observations of V2069 Cyg 5 2 ω V1. e 400 0.2−1 k81 0. 2 300 2 keV11. wer 1−0.8 Po 200 5 keV11.2 4. 2−0.8 100 2ω 3ω 4ω V1 10 ke11. − 010−4 10−3 0.01 0.1 4.50.9 0 0.5 1 1.5 Frequency (Hz) Phase (742.35 s) Figure 9. Power spectrum obtained from the combined and Figure10.PulseprofilesobtainedfromEPICbinneddatafolded merged event data of EPIC-pn and EPIC-MOS(0.2−10.0 keV). with 742.35 s spin cycle (20 bins/period) for different energy It shows a strong peak at the fundamental frequency of ranges:0.2−1.0keV,1.0−2.0keV,2.0−4.5keVand4.5−10.0keV 0.00134277 Hzwhichcorresponds tothe spinperiodof744.73 s, from top to bottom. The intensity profiles are background sub- andpeaksatthesecond(0.00268555 Hz),third(0.00402832 Hz) tracted and normalised to average count rates of 0.078, 0.167, and fourth (0.00537109 Hz) harmonic. The time binning of the 0.221, and 0.196 cts s−1 (from top to bottom). Epoch, MJD = inputlightcurveis1s. 54951.0. 1 0. R10 H sistentwiththevaluesobtainedfromOPTIMA,Swift/XRT 0.1 − and RXTE data. The double-peaked pulse profile is more prominent at lower energies (0.2−0.7 keV), while the sec- 05 ond peak is weaker at the higher energies (0.7−10.0 keV; R200. seeFig. 12).Herethesecondpeak isseparated byless than H05 0. half of the pulse cycle, and the power spectrum of the X- − ray data is dominated by the fundamental spin frequency r(ia.ye.d1a/tPasopfinI)P. AV7s0im9iClaarsbbeyhNavoirotuornwetasalo.b(s1e9r9v9e)d,winhetrheetXhe- HR300.05 powerspectrumisdominatedbythefundamentalharmonic. 5 0 The pulse profiles have highly asymmetrical rise and de- −0. 0 0.5 1 1.5 cay flanks. A dip feature is significant before the primary Phase (742.35 s) pulse maximum in the 0.2−1.0 keV band and centred on the primary maximum in the 1.0−2.0 keV band, while the Figure11.Hardnessratioasafunctionofphasederivedfromthe primary maximum is more symmetric at higher energies pulseprofiles(Fig.10)intwoneighbouringstandardenergybands (Fig. 10). A similar feature was also observed in V709 Cas (0.2−1.0keVand1.0−2.0keV,1.0−2.0keVand2.0−4.5keVand (deMartino et al. 2001), in NY Lup (Haberlet al. 2002) 2.0−4.5keV and4.5−10.0keV,fromtoptobottom). and in UU Col (deMartino et al. 2006b). The evolution of the pulse profiles with double-peaked structure from lower energies to higher, is causing the variations in thehardness 3.3 Orbital phase resolved timing analysis ratios. InFig. 11,thehardnessratiosshowahardening(in- crease) at spin minimum and a softening (decrease) at spin We investigated if the pulse shape of the rotating WD is maximumwhichismoreprominentinHR3.Thistypicalbe- changing with orbital phase of the binary system. The or- haviourisoftenobservedfromIPsandisgenerallyproduced bital phase was determined with the following ephemeris: by the larger photoelectric absorption when viewing along phase (BJD)= [T −2451066.7837(20)]/0.311683(2), where, the accretion curtain (deMartino et al. 2001; Haberl et al. T is the observation time (Thorstensen & Taylor 2001). 2002).InHR2,theratioshowstwoasymmetricmaxima,sep- For this purpose we obtained the WD pulse profiles in arated byadipcentredontheprimaryspinmaximumseen fourorbitalphaseranges:0.0−0.25, 0.25−0.5, 0.5−0.75 and in the 1.0−2.0 keV band and a second one appearing with 0.75−1.0. Results are shown in the Fig. 13 and Fig. 14 for a toothed-shape produced by the secondary spin maximum OPTIMA and EPIC data, respectively. There is some in- (see Fig. 10). In HR1, an antiphase behaviour is observed dication of a profile change, especially in the orbital phase with respect to HR2. range 0.5−0.75, for both optical and X-ray light curves. 6 Nasiroglu et al. 1.2 0−0.25 11.2 0. 0.2−0.7 keV 0.81 Phs. Phs. 0.25−0.5 0.80.811.2 1.2 −0.75 1.1 0.7−10.0 keV 0.911.1 Phs. 0.50.75−1.0 0.9111.2 0.8 Phs. 0.8 0 0.5 1 1.5 0 0.5 1 1.5 Phase (743.2s) Phase (743.2 s) Figure 12. Pulse profiles folded with 742.35 s (20 bins/period) Figure14.Orbitalphaseresolved(0.0−0.25,0.25−0.5,0.5−0.75 obtained from combined EPIC data (pn, MOS1 and MOS2) in and0.75−1.0)pulseprofilesfoldedwith742.35s(16bins/period) theenergyrange0.2−0.7keVand0.7−10.0keV.Epoch,MJD= obtained from combined EPIC data (pn, MOS1 and MOS2). 54951.0. Epoch,MJD=54951.0. 2 tioncurtain/stream),respectively(Staudeet al.2008).The 0.25 1.0 MEKAL model produces an emission spectrum from hot Phs. 0.0− 0.981 dsiioffnussefrogmasvaabroiovuestehleemWenDt’ss.sIunrafacfiersatnfidtitnoctluhdeesspleicnterae,mtihse- 0.5 1.02 plasma temperature for the MEKAL component could not − 25 1 beconstrained.Therefore,wefixedtheplasmatemperature Phs. 0.−0.75 0.981.02 waotbitt2ha0in1ke0ed1V3a,dbaeegvsrateleufisetowtfyifptrhieceardelodfmourc)e.IdPTshχe2r(Ssotpfaeu1c.dt0re0a2eltp(aχalr2.a2om0fe01t80e)r1.s4W.f6o9er Phs. 0.50 0.981 tthheebfietsatrfietsummodmealriissesdhoiwnnTainb.F2iga.n1d5.the spectra including −1. We determined the hydrogen column density as NH = 0.75 1 3.84 ×1021 cm−2. This is higher than the total Galactic Phs. 0.98 0 0.5 1 1.5 2 lhaytdedrogveanluecoflruommnDdiecnkseiyty&(3L.o7c9k×ma1n02(019c9m0−)2t,haant winatsercpaol-- Phase (743.38 s) culated using the HEASARCNH web interface1) in the di- Figure13.Orbitalphaseresolved(0.0−0.25,0.25−0.5,0.5−0.75 rection of thesource. Ourresult is comparable to thevalue and0.75−1.0)pulseprofilesfoldedwith743.38s(25bins/period) (5×1021 cm−2) obtained by de Martino et al. (2009). For obtainedfromOPTIMAdata(Tab.1,allepoch).Epoch,MJD= thepartialabsorberwefind,NH =8.29×1022 cm−2 witha 54951.0. covering fraction of 0.65. Similar values of partial absorber were derived for V2069 Cyg (deMartino et al. 2009) and theothersoftIPsobservedwithXMM–Newton (seeTab.3). TheabsorbedfluxofV2069Cyginthe0.2−10.0keVenergy 3.4 Spectral analysis of the XMM–Newton data band (derived for EPIC-pn) is 7.93×10−12 ergs cm−2s−1 In order to estimate the basic parameters of the emitting whichcorrespondstoasourceintrinsicflux(withabsorption region, a spectral analysis of theX-raydata was performed set to 0) of 2.64×10−11 ergs cm−2s−1 (EPIC-MOS values with XSPEC v.12.5.0x (Arnaud1996). ThethreeEPICspec- are 2 per cent higher corresponding to the constant factors tra were fitted simultaneously with a model consisting of derivedfromthefit).ThespectraaroundtheFe-Kemission thermal plasma emission (MEKAL; Mewe et al. 1985) and a line complex are shown enlarged in Fig. 16. The iron fluo- soft bbody component (as suggested by deMartino et al. rescence and FeXXVI lines are clearly resolved in the EPIC 2009),absorbed byasimple photoelectric absorber (phabs) spectra. The FeXXVI line energy identified from the XSPEC andapartially-coveringphotoelectricabsorber(pcfabs).An possible lines list is ∼6.95 keVand thefluorescenceline en- additionalGaussianlineisrequiredwhichrepresentsironK ergy derivedfrom thefit is∼6.385 ±0.017 keV.TheEW of fluorescentemissionat6.4keVasisoftenseenfromclassical thefluorescent line is 243 eV. IPs.Toaccountforcross-calibrationuncertaintiesaconstant factor was introduced. The absorbers phabsand pcfabs de- scribe the absorptions of the interstellar (along the line of sight) and circumstellar (inside the system by the accre- 1 http://heasarc.nasa.gov/cgi-bin/Tools/w3nh/w3nh.pl Fast photometric observations of V2069 Cyg 7 Table 2.Spectral fitresultfortheXMM–Newton EPICdata. Model Parameter Unit Value error phabs NH 1021 cm−2 3.84 (-0.04,+0.05) pcfabs NH 1022 cm−2 8.29 (-1,+1.2) CvrFract 0.65 ±0.02 mekal kT keV 20.0 frozen nH cm−3 1.0 frozen Abundance 1.0 frozen norm 6.29×10−3 (-2.4,+2.6)×10−4 bbody kT keV 7.68×10−2 (-4.3,+4.2)×10−3 norm 2.18×10−4 (-0.75,+1.2)×10−4 gaussian LineE keV 6.385 ±0.017 Sigma eV 51 (-32,+27) norm 2.6×10−5 (-5.4,+3.9)×10−6 constantfactor pn 1.0 frozen MOS1 1.026 ±0.018 MOS2 1.028 ±0.018 0.1 0.1 V−1 Counts s ke−1 0.01 V−1 0.05 10−3 Counts s ke−1 0.02 2 χ 0 0.01 −2 0.5 1 2 5 10 Channel Energy (keV) 5.5 6 6.5 7 7.5 Channel Energy (keV) Figure 15. The composite model (phabs*pcfabs* (mekal + Figure16.EnlargedpartofFig.15showingtheFelinecomplex bbody+gaussian)*constant)fittedtothespectrumoftheEPIC- intheEPICspectra. pn (black) and MOS (green and red) data in the 0.2−10 keV energyband.Thebottompanel showstheresiduals. 4 DISCUSSION Table3.Theparametersofthepartialabsorberobtainedfor Wehavepresentedtheoptical(OPTIMA)andX-ray(Swift- V2069CygandsomesoftIPsobservedwithXMM–Newton. XRT and XMM–Newton EPIC) observations of the IP V2069 Cyg. The timing analysis of the optical and X-ray Source NH(cm−2) CvrFract Referencea data reveals pulsations at periods of 743.38 ±0.25 s and 742.35±0.23 s respectively, representing the spin period of V2069Cyg 11×1022 0.69 1 the WD. We have found that the second harmonic is much MUCam 7.9×1022 0.61 2 PQGem 11.1×1022 0.45 3 stronger than the fundamental in the power spectrum ob- UUCol 10×1022 0.51 4 tainedfromtheopticaldata.Furthermore,thefundamental V405Aur 6.1×1022 0.52 5 frequencyfromXMMdataisweakorevenabsentatenergies NYLup 9.7×1022 0.47 6 <0.5keV,whileitisstrongerat>0.5keV,comparedtothe second harmonic. IP V405 Aur has shown very similar be- haviour in the XMM–Newton data (Evans & Hellier 2004). a Thedouble-peakedpulsationsatthespin periodareclearly References: (1) deMartinoetal. (2009); (2) Staudeetal. (2008);(3)Evans etal.(2006);(4)deMartinoetal.(2006b); observed in the optical and X-ray data (0.2−10 keV). The (5)Evans&Hellier(2004);(6)Haberletal.(2002); folded light curves show a more prominent double-peaked pulseprofile when thepower spectrum is dominated by the second harmonic. When the second harmonic is weak the curve possesses a similar profile but with a weaker second 8 Nasiroglu et al. peak. Therefore, the power spectrum of the optical data is dominated bythesecond harmonic, while theX-raydatais thefundamental.The peak separation is around 0.5 for the 01 1. optical data, and less than 0.5 for the X-raydata. IPsystems(assumingequilibriumrotation)withashort TIMA) 1 ssppionndpienrgiotdowthilelhshaovretreerlaKteivpelelyriasmnaplelrmioadgsnientothspehinerneesr,accocrrree-- Int. (OP 80.99 9 tion disk.Insuch short period systemstheWDis therefore 0. 2 expectedtohaveaweakmagneticfield.Themagneticforces 1. of theWD pickupthematerial from theaccretion disk ap- C) 1.1 proximatelyattheco-rotationradius.Thematerialattaches EPI − 1 to the field lines and is channelled onto the WD magnetic MM poles,whereitundergoesastrongshock.Afterthatitisset- nt. (X 0.9 tling on the surface and cooling by the emissions of X-ray I 8 0. bremsstrahlungandoptical/infraredcyclotron(Rosen et al. 0 0.5 1 1.5 1988;Norton et al.2004a).AsproposedbyEvans& Hellier Phase (743.38s) (2004)mostlikelytheprominentdouble-peakedmodulation in the soft X-ray emission is due to the changing view- Figure 17. Pulse profiles folded with 743.38 s (20 bins/period) ing geometry onto the accreting polar caps. We view the obtained fromcombined XMMEPIC 0.2−10 keV data and OP- heated surface of the WD most favourably when one of the TIMAdata.Epoch, MJD=54951.0. poles points towards us. Nevertheless, due to the highly inclined dipole axis, the external regions of the accretion curtains will not quite cross the line of sight, therefore the profilesandmustthereforehaveweakmagneticfields.These hard X-rayemission exhibitsadouble-peakedpulseprofiles shortperiodsystemsdidnotexhibitX-raybeatperiods(AE with a weaker secondary peak. However, the intensity of Aqr, DQ Her, XY Ari, V709 Cas, GK Per, YY Dra and the pulse profiles could be also affected by the opacity re- V405 Aur). In the power spectrum of V2069 Cyg we have sulting in electron scattering and absorption in the highly not found any specific signal at the beat frequency. This ionized post-shock region, or an offset of the magnetic axis absence indicates that in these short period IPs and V2069 from the WD centre (Allan et al. 1996; Norton et al. 1999; Cygaccretiondoesnotoccurinastream-fedordisc-overflow Evans& Hellier 2004). scenario (Norton et al. 1999). The pulse profiles of the optical and X-ray data (each The X-ray spectra of V2069 Cyg can be described by folded with both 742.35 s and 743.38 s spin period and thermalplasmaemission(kTof∼20keV)plusasoftbbody with a same reference time) are out of phase. As an component with complex absorption and an additional flu- example we show these profiles folded with 743.38 s in orescent iron-K emission line, which originates on the WD Fig. 17. de Martino et al. (2009) also reported that the X- surface (at 6.4 keV, with an EW of 243 eV). V2069 Cyg ray pulses(from EPIC-pn) areanti-phased with theoptical and V405 Aur show similar bbody parameters with kT of pulses (in the B-band from optical monitor on the XMM- ∼77 eV and ∼40 eV (Evans& Hellier 2004), respectively. Newton). X-ray and optical/infrared photons in some IPs Moreover, the two IPs have quite similar spin-orbit period originate from two different regions. The optical/infrared ratiosof0.0276forV2069Cyg(743.38s/26928 s)and0.036 photons are thought to originate in the X-ray heated mag- for V405 Aur(545.5 s/14986 s). netic polar caps, and possibly in the accretion stream Weadopted Mukai’s classification2 of IPs and updated (Eracleous et al. 1994; Israel et al. 2003; Revnivtsevet al. his Pspin–Porb diagram to include V2069 Cyg (see Fig. 18 2010).Norton et al.(2004b)suggestedthatoneofthemag- and Tab. 4). Several IPs are found close to Pspin/Porb = netic poles heated by the accretion flow will leave behind 0.1. There are28 systems in therange of 0.01 < Pspin/Porb a heated trail on the WD surface which will emit opti- 6 0.1 and Porb > 3 h, 5 systems with Pspin/Porb > 0.1 cal/infrared photons. During the emission some part of the and Porb < 2 h, and only one system with Pspin/Porb ∼ optical/infrared photonswill beabsorbed by theflow while 0.049 that lies in the ‘period gap’. Finally, there are 5 sys- the accretion flow is heating the second pole. At that time tems with Pspin/Porb < 0.01. Those are defined as fast ro- the rest of the optical/infrared modulations will be seen tating WDs. Only one of them, AE Aqr, shows propeller which is shifted with respect to theX-rays.The phaseshift behaviour.TheyalsoshowthesoftX-raybbodycomponent observed between the optical and X-ray pulse profiles in in their spectrum (Norton et al. 2004c; Parker et al. 2005; V2069 Cyg is most probably caused by this X-ray heated Evans& Hellier 2007; Norton & Mukai2007; Anzolin et al. mechanism. 2008). Ontheotherhand,Norton et al.(1999)suggestedthat IPs which show a single-peaked pulse profile resulting from stream-fed (or disc-overflow)accretion are an indicatorof a 5 CONCLUSIONS WD with a relatively strong magnetic field. These IPswith long WD spin periods (longer than 700 s) might show X- We conclude that V2069 Cyg is an example of an IP that raybeat periods(1/Pbeat=1/Pspin–1/Porb) atsome timein shows double-peaked emission profiles at the WD spin pe- their lives (FO Aqr, TX Col, BG CMi, AO Psc, V1223 Sgr andRXJ1712.6-2414). Conversely,IPswithshortWDspin periods(shorterthan550s)haveshowndouble-peakedpulse 2 http://asd.gsfc.nasa.gov/Koji.Mukai/iphome/iphome.html Fast photometric observations of V2069 Cyg 9 Table 4.39IPswithknownspinandorbitalperiods. a b Name Porb Pspin Pspin /Porb Properties PeriodReferences (h) (s) 0.01 < Pspin /Porb 6 0.1 and Porb > 3 h V709Cas 5.341 312.780 0.01627 DP 33,41 NYLup 9.870 693.010 0.01950 SXR 2,21,17,41 RXSJ213344.1+510725 7.193 570.800 0.02204 SXR 2,11,42 SwiftJ0732.5-1331 5.604 512.420 0.02540 - 5,41 V2069Cyg 7.480 743.384 0.02756 SXR,DP 18,41 RXSJ070407.9-262501 4.380 480.670 0.03205 SXR 2,22,44 ElUma 6.430 741.660 0.03204 - 3 V405Aur 4.160 545.456 0.03642 SXR,DP 2,20,23,41 YYDra 3.969 529.310 0.03705 DP 24,33 IGR J15094-6649 5.890 809.700 0.03819 - 12,41 IGR J00234+6141 4.033 563.500 0.03881 - 6 RXSJ165443.5-191620 3.700 546.000 0.04099 - 40 IGR J16500-3307 3.617 579.920 0.04454 - 36,41 PQGem 5.190 833.400 0.04461 SXR 2,19,21,27,41 V1223Sgr 3.366 745.630 0.06153 - 11,41 AOPsc 3.591 805.200 0.06229 - 11,41 UUCol 3.450 863.500 0.06952 SXR 2,9,21,43 MUCam 4.719 1187.250 0.06989 SXR 2,38,41 FOAqr 4.850 1254.400 0.07184 - 11,16,41 V2400Oph 3.430 927.660 0.07513 SXR,Diskless 2,8,21,26 WXPyx 5.540 1557.300 0.07808 SXR 2,21,39 BGCmi 3.230 913.000 0.07852 - 4,41 IGR J17195-4100 4.005 1139.500 0.07902 - 36,41 TXCol 5.718 1910.000 0.09284 - 41 V2306Cyg 4.350 1466.600 0.09365 - 11,34 RXSJ180340.0-401214 4.402 1520.510 0.09595 SXR 2,22 TVCol 5.486 1911.000 0.09676 - 41 V1062Tau 9.982 3726.000 0.10368 - 30,42 Pspin / Porb > 0.1 and Porb < 2 h HTCam 1.433 515.0592 0.09984 - 31 V1025Cen 1.410 2147.000 0.42297 - 29,37 DWCnc 1.435 2314.660 0.44806 - 35 SDSSJ233325.92+152222.1 1.385 2500.000 0.50127 - 25 EXHya 1.637 4021.000 0.68231 SXR 1,221,41 Period Gap (2 h < Porb < 3 h) XSSJ00564+4548 2.624 465.680 0.04929 - 7,10 Fast rotator (Pspin / Porb < 0.01) AEAqr 9.880 33.076 0.00093 DP,Propeller 11,13,26,33,41 GKPer 47.923 351.332 0.00204 SXR,DP 14,21,32,33 IGR J17303-0601 15.420 128.000 0.00231 SXR 2,11 DQHer 4.650 142.000 0.00848 DP 11,33,45 XYAri 6.065 206.300 0.00945 DP 28,33,41 a SXR:softX-raybbodycomponents; DP:double-peakedpulseprofiles. b REFERENCES: (1) (Allanetal. 1998); (2) (Anzolinetal. 2008); (3) (Baskilletal. 2005); (4) (Kimetal. 2005); (5) (Butters etal. 2007); (6) (Bonnet-Bidaudetal. 2007); (7) (Bonnet-Bidaudetal. 2009); (8) (Buckleyetal. 1995); (9) (Burwitzetal. 1996); (10) (Butters etal. 2008); (11) (Butters etal. 2009a); (12) (Buttersetal. 2009b); (13) (Choietal. 1999); (14) (Cramptonetal. 1986); (15) (deMartinoetal. 2008); (16) (deMartinoetal. 1999); (17) (deMartinoetal. 2006a);(18) (deMartinoetal. 2009); (19) (Ducketal. 1994); (20) (Evans&Hellier 2004); (21) (Evans&Hellier 2007); (22)(G¨ansickeetal.2005);(23)(Harlaftis&Horne1999);(24)(Haswelletal.1997);(25)(Hiltonetal.2009);(26)(Hellier 2007); (27) (Hellieretal. 1994); (28) (Hellieretal. 1997); (29) (Hellieretal. 2002a); (30) (Hellieretal. 2002b); (31) (Kempetal.2002); (32) (Mauche 2004); (33) (Nortonetal.1999); (34) (Nortonetal.2002);(35) (Pattersonetal. 2004); (36) (Pretorius 2009); (37) (Hellier,Beardmore,&Buckley 1998); (38) (Staudeetal. 2003); (39) (Schlegel 2005); (40) (Scaringietal.2011);(41)(Scaringietal.2010);(42)(Thorstensen, Peters,&Skinner2010);(43)(deMartinoetal.2006b); (44)(Patterson etal.2011);(45)(Zhangetal.1995); 10 Nasiroglu et al. Pspin= Porb Pspin= 0.1 Porb Other DP DP, Propeller = 0.027 Porb DSXPR, SXR Pspin Diskless, SXR 10]00 V2069 Cyg s od [ = 0.01 Porb ri Pspin e P n pi S 100 = 0.001 Porb Pspin 1 10 Orbital Period [h] Figure 18. Porb–Pspin diagram of 39 IPs: DP, double-peak pulsation; SXR, soft X-ray component; disk-less, have no accretion disk. Theverticaldashedlinesshowtheapproximatelocationofthe‘periodgap’,andthediagonallinesareforPspin=Porb (solid)andPspin = 0.1/0.01/0.001 × Porb (dashed). V2069 Cyg (shown with astar) is located well withinthe population of double-peak IPs withsoft X-raycomponent buthasaratherlowspin-orbitperiodratioof0.0276. riod which are probably caused by a weak magnetic field, REFERENCES inaWDwithshortspinperiod.TheX-rayspectrumshows Allan A.,HorneK.,HellierC., MukaiK.,Barwig H.,Ben- a soft bbody component and thermal plasma emission and nieP. J., Hilditch R. W., 1996, MNRAS,279, 1345 its X-ray and optical emission have a double-peaked mod- Allan A., Hellier C., Beardmore A., 1998, MNRAS, 295, ulation. Weperformed simultaneousoptical/X-ray observa- 167 tions of V2069 Cyg to search for any delays between these Anzolin G., de Martino D., Bonnet-Bidaud J.-M., et al., twoenergybands.Howeverthelow countratesin theSwift 2008, A&A,489, 1243 data did not allow to constrain these delays. Arnaud K.A. 1996, ASPC, 101, 17 BaskillD.S.,WheatleyP.J.,OsborneJ.P.,2005,MNRAS, 357, 626 ACKNOWLEDGEMENTS BurrowsD.N.,HillJ.E.,NousekJ.A.,etal.2005a,Space Sci. Rev.,120, 165 Ilham Nasiroglu acknowledges support from the EU FP6 Bonnet-BidaudJ.M.,deMartinoD.,FalangaM.,Mouchet Transfer of Knowledge Project ”Astrophysics of Neu- M., Masetti N., 2007, A&A,473, 185 tronStars”(MKTD-CT-2006-042722).AgaS lowikowskaac- Bonnet-Bidaud J. M., de Martino D., Mouchet M., 2009, knowledgessupportfrom thegrantN203387737 ofthePol- ATel,1895, 1 ishMinistryofScienceandHigherEducation,aswellasthe Buckley D. A. H., Sekiguchi K., Motch C., et al., 1995, grant FNP HOM/2009/11B and the EU grant PERG05- MNRAS,275, 1028 GA-2009-249168. Gottfried Kanbach acknowledges support Burwitz V., Reinsch K., Beuermann K., Thomas H.-C., from the EU FP6 Transfer of Knowledge Project ASTRO- 1996, A&A,310, L25 CENTER(MTKD-CT-2006-039965) andthekindhospital- ity of the Skinakas team at UoC. We acknowledge the use ButtersO.W.,BarlowE.J.,NortonA.J.,MukaiK.,2007, ofpublicdatafromtheSwiftdataarchive.Wewouldliketo A&A,475, L29 thank Aysun Akyuz and Arne Rau for discussions on this ButtersO.W.,NortonA.J.,HakalaP.,MukaiK.,Barlow paper,aswellasAnnaZajczyk(CAMK)andAndrzejSzary E. J., 2008, A&A,487, 271 (UZG) for their help with observations. We thank the Ski- Butters O. W., Katajainen S., Norton A. J., Lehto H. J., nakas Observatory for their support and allocation of tele- Piirola V., 2009a, A&A,496, 891 scope time. SkinakasObservatory is a collaborative project Butters O. W., Norton A. J., Mukai K., Barlow E. J., oftheUniversityofCrete,theFoundationforResearchand 2009b, A&A,498, L17 Technology - Hellas, and the Max-Planck-Institute for Ex- Butters O. W., Norton A. J., Mukai K., Tomsick J. A., traterrestrial Physics. 2011, A&A,526, A77