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Observations of X-Ray Pulsars from the Kvant Module M. GILFANOV, R. SUNYAEV, E. CHURAZOV, V. LOZNIKOV, V. EFREMOV, A. KANIOVSK1Y, A. KUZNETSOV, N. YAMBURENKO, A. MELIORANSKrY, G.K. SKINNER, O. AL-EMAM, T.G. PATTERSON, A.P. WILLMORE, A.C. BRINKMAN, J. HEISE, J.J.M. IN'T ZAND, R. JAGER, W. PIETSCH, S. DOEBEREINER, J. ENGEHAUSER, C. REPPIN, J. TRUEMPER, W. VOGES, E. KENDZIORRA, M. MAISACK, B. MONY, R. STAUBERT, A.N. PARMAR, AND A. SMITH.* INTRODUCTION The Roentgen international X-ray obsenatory on the Kvant module of the Mir space station has been operating successfully since the beginning of June 1987. Many X-ray sources were obsened in 1987-1989 and among them were several X-ray pulsars. Four telescopes mounted on board the Kvant module cover a wide energy range with good t~ng resolution: Coded Mask hnaging Spectrometer 11M (2-30 keV; timing resolution 1 s), GSPC (2-100 keV; 1.25 . 2.5 ms); Phoswich type detectors HEXE (20-200 keV; 0.3 . 25ms), and Pulsar X-1 (5~1300 keV; 5-10 s). Timing analysis of the Kvant module data suffers from the presence of only short continuous ~ntenals of source obseIvations (10-25 mitl), separated by 90 minute gaps (90 min. is the orbital period of the Mir space station around the Earth). On average there are appro2nmatel~r four sessions per day. The presence of 90 min. gaps leads to the appearance of beat frequences v=vO+n/90 n~in (n = 1, 2, 3..~. Special analysis was applied to avoid this difficult~r. Presented below are the results of the pulsation period measurements of the X-ray pulsars Her X-1, Cen X-3, SMC X-1, Vela X-1, A0535 ~ 26 by the instruments on board ~e Kvant module in 1987-1989 ~ble 1 and Figures 1,2,3,5,7,8~. The values of the periods are reduced to the solar * Space Research Institute, Academy of Sciences, Moscow, USSR; Space Research Laboratory, Utrecht, Ihe Netherlands; Department of Space R=earch, University of Birmingham, Edg- baston, Birmingham; Max Planck f~r Physik and Astrophysik, Institute f~r Extraterrestrische Physik, Astronomisches Institute der Unive~sitat ~bingen, Garshing, Germany; Noordwijk Ihe Netherlands. 134

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HIGH-ENERGY ASTROPHYSICS 135 TABLE 1 Pulse periods of X-ray pulsars measured with KVANT module in 1987-1989. Errors are 1 a values. Source nameDate JD. Period, s Error , ~ Her X-1VI I I .1987 702. 1.2377728 2.5 10 ~ 7 VII.1988 7368 1.237767 1.8 10-6 X.1988 7441 1.2377643 6. 0-10-7 SMC X-1X.1988 7452 0.7100972 2.2 10~. I I I .1989 7591 0.7099830 S.0 - 10 ~ ~ Cen X-3II.1989 7S63 4.822S83 1.4 10-6 Vela X-1X1.1988 7490 283.1676 5.3-10-3 II .1989 7561 283.1466 3 0 - 10-2 L A0535+26 1 IV.1989 1 76C ~ 1 103.267** 1 3. .~10-' * Julian date of observation JD - 2440000 ** Without reduction to binary system barycenter system baTycenter and to the binary system batycenter (excluding A0535 + 26~. CRAB NEBULA PULSAR OBSERVATIONS More than 100 among 2000 sessions performed until now by the Roentgen observatory were shared with the Crab Nebula Observations in order to calibrate all instruments. The reduction of time series from the Kvant module to UT (Universal Time) was performed using the data of an onboard timer with the accuracy ~ S 10-8s~s-i (Gavrilova et al. 1988~. Observation of the Crab Nebula pulsar NP0532 allows us to confirm the validity of the reduction procedure. Usually the data combined over one day (3-4 sessions) were used for timing analysis via the epoch folding method (Leahy e! al. 19g3~. The results of pulsation penod measurements In September-October 1987 are presented on Figure 1. The values of periods are reduced to the so- lar system ba~ycenter. The predicted values of the periods arising from radioobse~vations are shown by a solid curve (the reference is given in Hanger 1984~: P(t) = P ~ P (t-to) ~ P-(t-to)2/2, where P(t)-is the pe- nod at the time of observations, P-0.033235335646 s, P = 4.219036~10-~3 s/s, P = -2.8110710-24s/s2, to = ID 2444128.5 (12.9.79~. The deviations

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136 Q' 33. 342BOO ~33. 342300 X - AMERICAN AND SOVIET PERSPECTIVES , / / / 3334~800L 7054 . . 7064 Date JO 2440000 7074 FIGURE 1 PuLsation period of the pulsar in Crab Nebula as measured by GSPC instrument on board the Kvant module in September-October 1987. The errors are 1~ values. The solid line shows the extrapolation of radio data. Of the measured values from the fit are within statistical errors PIP 1 10-7. These measurements of the NP0532 pulsation period and compar- isons with the radiodata confirmed the correctness of all timing analysis procedures, which were applied below for other pulsars. HERCULES X-1 Well-known X-ray pulsar Her X-1 was intensively monitored by the instruments on board the Kvant module (Figure 2 and Bible 1~. The measurements of the HEXE and GSPC instruments have shown (Voges et al. 1988; Sunyaev e! al. 1988) that the pulsar entered the stage of quasistabonaly acceleration analogous to ones observed in 1972-1978. The orbital parameters are from Deeter et al. (1981~. Average spin-up rate over the period of Kvant observation was PIP = ~-4.9~1.5) 10~8yr~~.

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HIGH-ENERGY ASTROPHYSICS 4972 ~974 19" 2978 f ~f~2 f~d l ~1~8 137 , , , , 1 1 1 t''''''''''' Her X-1 4,=7 8 `.237 810 2.Z37 d300 o ~o d.237 ~ - `.237 7 - _ 4.~7 770 `.~7 ].~7 ~ - UHURU m - oso ~ V 1 x t -HEAD. bd - EINSTEIN - ARrQ X - SAS 3 o - W~-AIT - LET~ - IT - ~, - NASA-SACLAY ~3 2 D 2 - ~ ~ - ~ ~m-~ _ , ~=_~A - EXOBAT - ,- - ASTF\ON O - KVANT $ - 6~ - A . I , I . I . I . I , I . I . , f ~- 00 - 00 4000 5000 " - 70~ - - O8tC ~ 2440000 ~ FIGURE 2 Pulsation period history for Her X-1. E~lurs are 1~ values. References on the previous experiments are presented in the papers of Sunyaev et al. (1988) and Nagase (1989~. SMC X-1 The results of ~XE observations were used for SMC X-1 period determination. l~wo successful sem of sessions were performed in 1988 1989, when the source was within the field of view of the telescope (Figure 3 and 1bble 1~. The observations of another telescope on board the module - Coded Mask Imaging Spectrometer TIM - detected an X-ray eclipse of source on Janua~y 8, 1989 (the pulsar was beyond the field of view of the HEXE instrument w~th the smaller field of view). The time of the sessions when there is no significant flux from the source coincides with the predicted time of the eclipse based on the orbital parameters of Gruber (1988~. The count rate measured by the 11M instrument dunug three sets of sessions of SMC X-1 obsenations (7-11 January 1989) is shown on Figure 4. Upper limits on the source intensity during the eclipse are shown by tnangles. Continuous spin-up of this puBar with the average rate P/P = (~.2:10.2~10~4yr-: (during Kvant module observations) agrees well with the simplest models of disk-accretion fed pulsars (Pringle and Rees 1972; Ghosh and Lamb 1979~.

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138 . 7f 7000 .716000 . 71~0 - o , 7~4000 ~. 7~3000 ID .712000 . 711000 . 7f OOOO . 79000 AMERICAN AND SOVIET PERSPECTIVES Ig72 `974 1976 1978 ~SMC X-1 t be 2980 ]~2 1 ~` ~`~8 . . , . . . . . - GURU m - Rocket ~ - APO~SOYUS b4 - ~;A9~9 ~ - A.a=L ~_ x - e~sTEz~ id,, _ VIA to - tCVAN r X i.1.1.~.1.1,1,-1. , `0~ 2000 3000 4000 5000 6000 7000 8000 Oate ~ 2440000 + FIGURE 3 Pulsation period history for SMC X-1. References on previous ~penments are given in Darbro et al. (1981) and Nagase (1989~. CENTAURUS X-3 Roentgen observatory performed four sets of Cen X-3 observations at the beginning of 1989. On February 5, 1989, the source was in eclipse with the upper limit on its intensity in the 2-30 keV energy band 4 mCrab (3~ upper limit). The 1~ data were used for timing analysis. The value of the period based on all observations is presented in Figure 5 and in Bible 1. Figure 6a shows the pulsation period, measured in single sessions without reduction to the binary system bancenter. The solid line shows the predicted Doppler shift of period due to the neutron star motion in the binary system according to parameters from Nagase et al. (1983~; Nagase et al. (1984~; and KeLly et al. (1983~. Unfortunately this set of obsenabons was too short to allow us to measure the orbital parameters accurately. The best fit orbital parameters are within 1~ with that in the references above. VELA X-1 This X-ray pulsar was observed by TOM, HEXE, and Pulsar X-1 in- s~uments in November-December 1988 and lanuary-Februa~y 1989 (Figure

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HIGH-ENERGY ASTROPHYSICS .os .os .06 ~3 .05 .04 '03: .02 .01 o 139 it eel 108e . . . 533 534 535 536 537 538 Oate JED 2447000 + FIGURE 4 The count rate of SMC X-1. triangles mark upper limits during eclipse. 7 and Able 1~. The measured value of the pulsation period is the highest over the whole history of Vela X-1 observations since 1972. Companson of the periodic values measured in single sessions with the predicted Doppler shifts due to orbital motion confirmed the stabilibr of the binary system parameters since the last measurements of Mama in 1983 (Nagase et al. 1984b). Average spin-down rate since Tenma up to Kvant measurements is PIP = 1.410~4yr~~. Note that the spinning-up of the pulsar in 1975-1979 was of the same absolute value (Nagase 1984a). A0535+26 Observations of this pulsar were performed during the giant outburst of the transient, the beginning of which was detected by the Ginga satellite on March 31, 1989 (Making 1989~. For timing analysis the data of 17M were mainly used. There are both A0535+26 and Crab Nebula in the field of view of AM (7.5 x 7.5~. This allows us to express the intensity of the source in Crab units via direct comparison of corresponding count rates: 0.6 Crab in 2-6 keV energy band and 1.5 Crab in 6-10 keV (Sunyaev et al. 1989~. The high count rate of the sources within the field of view of the telescope leads to the overflow of its telemetry channels approximately two times. Therefore on the whole, energy band (2-30 keV), which is

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140 - lo - a, AMERICAN AWD SOV7ET PERSPECTIVES f 972 1974 1976 197e ~g80 1982 1984 1986 198e Cen X-3 4.~4 L 4. B3 ~ I, ~3 82 4. 2000 2000 3000 - Lit - ARSCL ] - COB 8 - ~s _ ED ~ _ Co Tic - TENS& O - VIA lo - KVANT 1 ~ .1. , 4000 5000 6000 7000 soon Date pro 2440000 + FIGURE 5 Pulsation period history for Cen X-3. References on previous "penments are given in Keller et al. (1983~; Murakami et al. (1983~; Howe et al. (19833; Nagase er al. (1984b); and Nagase (1989~. transmitted every 8 seconds, was used for the determination of period. The value of the period measured on April 9-10, 1989, and published by Sunyaev et al. (1989) is presented in Table 1 and Figure 8. Since the parameters of the binary system are not yet known, the value of the period was just reduced to the binary system barycenter. Further measurements are to show whether the acceleration of this pulsar does exist during the hares when the rate of accretion is large. The authors are pleased to thank E. Gavrilova for her assistance with reduction of all timing data to UT, V. Blagov, G. Kondrashina, ~ Prukoglyad, ~ Rodin, the teams headed by the corresponding member of the Academy of Sciences of the USSR Yin P. Semyonov, and the Space Flight Center team for control of the observatory operations and cosmonauts Yu. Romanenko, ~ Alemudrov, ~ Laveykin, M. Manarov, V. Titov, ~ VoLkov, and S. Krikalev for help with the work of the observatory.

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HIGH-ENERGY ASTROPHYS CS 4.83 C:} - 4.82 o . 2 .2 .3 141 ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' AL t ~ \~ \~ 1 1 4.~5 . . . . . . . . . . . . . . . . . . .4 .5 .6 .7 .8 Orbi tal phase _ g / t\ - 283.2 q) ~ 1 d ~ / 283.] _ /1 \ Z82.9 :1 t- 282.6 _ ~_ 282. 7 . . . . . . . , . . . , . O .1 .2 .3 \1 eel Jose , I , ~, I . .4 .5 .6 .7 Orbi tal phase .8 .9 ~ FIGURE 6 Doppler shift of the periods due to orbital motion in binary system for Cen X-3 (a) and Vela X-1 (b). Circles mark the values measured in single sessions (a) and sets (b) of observations. Errors are la values. Solid curves show the predicted variation of periods

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142 AMERICAN AND SOVIET PERSPECTIVES Ig74 1976 497e 1980 2982 1984 ~gB6 1988 1 1 1 1 ~1 1 i 1 1 1 ' ~ 283. 2 _ 283. ~ _ 283 _ - ~282.9 2B2.8 _ Vela X-1 18 _ ll 1 t tt . ~ 1 .' ~ m - c~:Cus ~ - ARZe1~ V b4 - SAS- ~ - COS~ X - OSO ~ - FW~t - AST~ST - T~..A D - 6~A o ~ ICVANT Ea2.7 ~ ' ~ ~ ~ . . ~ . ~ . 2000 3000 4000 5000 6000 7000 8000 Date JO 2440000 ~ . FIGURE ~ Puls-penod history for Vela X-1. References on previous expenments are gIven in Nagase et al. (1984a) and Nagase (19893. 1974 1976 1978 2980 19B2 104.5 104 103.5 103 1984 ~gB6 1988 A 0535+26 + . m - AR~EL - SAS-3 m - B-1 loon - aelloon - HAKU~ * - G:NGA O - KVAt4T c: t a a.. m . I. I . I . , . I . I . I 2000 3000 4000 5000 6000 7000 8000 9000 $ ~ Oate JO 2440000 ~ FIGURE 8 Puls-period histoIy for A0535 ~ 26. References on previous exp~iments are given in Nagase et al. (1982), Nagase et al. (1984b) and Nagase (1989). See also Ricker et al 1976.

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HIGH-ENERGY ASTROPHYSICS 143 REFERENCES Darbro, W., P. Ghosh, RF. Elsner, et al. 1981. Astrophys. J. 246: 231. Deeter, J.E., et al. 1981. Astrophys. J. 247: 1003. Gavrilova, E., et al. 1988. Preprint IKI Pr-14Z. Gruber, D. 1988. Private communication. Ghosh, P., and Fed Lamb. 1979. Astophys. J. Z34: 296. Hasinger, H. 1984. Dissertation. Howe, S.K, FAN Pnmini, M.\U Bautz, et al. Astrophys J. 1983. Z72: 678. Kelly, R.L, S. Rappaport, G. Clark, et al. 1983. Astrophy~ J. 268: 790. Leahy, DA, W. Darbro, RF. Elsner, et al. 1983. Astrophys. J. 266: 160. Makino, F. 1989. IAU Circe No. 4768. Murakami, 1:, H. Inoue, N. Kawai, et al. 1983. Astrophys J. V. 264: 563. Nagase, F., S. Hayakawa, H. Kunieda, et al. 1982. Astrophys. J. 263: 814. Nagase, F., S. Hayakawa, H. Kuniedla, et al. 1984a. Astrophys J. 280: 259. Nagase, F., N. Sato, K Makishimi, et al. 19~. ISAS Preprint No. 234. Nagase, F. 1989. Publ. Astron. Soc. Japan. 41: 1. Pnagle, J.E., and MJ. Ree~ 197Z Astron. and Astrophys. 21: 1. Ricker, G.R, ~ Scheepmaker, J.E. Ballintine J.P. Dobr, G.A. Kriss, S.G. Ryckman, and W.H.G. Lewin. 1976. Astrophys. J (Lettj 204, L73. Sunyaev, R., et al. 1988. Sonet Astronomy Letters. 14: 979. Sunyaev, RN 1989. IAU Circ No. 4769. Voges, W., W. Pietsch, ~ Reppin, et al. 1982. Astrophys. J. 263: 803.