PoS(MQW7)111 http://pos.sissa.it/ ce. s that followed the main outburst J 54, L79 (2002). The pre-outburst sion of the accretion disk. We inter- urst gives rise to a jet radiating also asar V4641 Sgr using the visual and he orbital phase. In addition, a larger (the narrow outbursts separated by a ed from the level of brightness higher stem. It displays low-amplitude fluc- . We argue that the luminosity of four ) as the thermal instability of the accre- C public, 25165 Czech Ondˇrejov, T is 377 days, with a trend of a decrease. We interpret the C T ive Commons Attribution-NonCommercial-ShareAlike Licen [email protected] [email protected] We present an analysis of the optical activity of the microqu photographic data. We analyze four smaller (echo) outburst (1999). Their mean recurrence time long quiescence, a clear trend in the evolution of their characteristic features of the recent activity of V4641 Sgr in the optical. This supports theobservations finding (1964–1967) by Uemura reveal et ongoing al., activity PAS oftuations the on sy the timescale of several weeks,brightening independent which on lasted t for several tens ofthan days in and other occurr years can be resolved. tion disk operating in dwarf novae andecho soft outbursts X-ray is transients too high to bepret explained them by the as thermal due emis to the thermal instability, in which the outb ˇ ech Šimon Copyright owned by the author(s) under the terms of the Creat c Long-term optical activity of theV4641 microquasar Sgr Vojt Astronomical Institute, Academy of Sciences ofRepublic the Czech Re E-mail: Arne Henden AAVSO, 49 Bay State Road, Cambridge,E-mail: MA 02138, USA VII Microquasar Workshop: Microquasars and Beyond September 1 - 5, 2008 Foca, Izmir, Turkey PoS(MQW7)111 ows . It was found that the E etor and a B9III donor at the e the 1999 main outburst was th that of soft X-ray transients from [10]. Three values of the ssband was investigated using 81728 . mber 1999 was observed in X- 2 t can be seen that the O–C values des are displayed with respect to mberg Observatory. These plates + rst was detected on a photographic um brightened during these events lightcurve contained the 1999 main time evolution, with the superposed f them is defined by multiple obser- ar Observers (AAVSO) International oints are connected by line in densely accretion onto the black hole. During February 1999 (e.g. [7]). The major e brightness is displayed in Figure 1g. of SXTs at the outburst maximum vs. 298 ion. Rapid optical fluctuations indicate m activity with large-amplitude events, nd accumulation of the points near the minal jet ejection [5]. This event was ly contributes to the optical flux. It was s. The data were folded with the orbital . s variations (Figure 1h). en formed [9]. Several smaller outbursts V h magnetic flares [14]. 81728 d [2]. It is the optical counterpart maller amplitude. In the case of one miss- . M 2 filter. The exposure time was 60 min. These = B 2451764 orb 2 P = of the outbursts was investigated using the method of C T Min I 2 (falling into the seasonal gap) also the main outburst foll − = E The evolution of the recurrence time The recent photometric history of V4641 Sgr in the optical pa Photometric history of V4641 Sgr in the epoch long time befor In order to compare the peak magnitude of the echo outburst wi V4641 Sgr is a binary system consisting of the black hole accr was investigated (Figure 1e). The parameters of 10 SXTs come orb orbital modulation is precluded by the long-term brightnes of the X-ray transient SAXplate J1819.3–2525 [13]. in The 1978 first [1]. outbu rays, optical, The and major radio. outburstpreceded which by Radio occurred an structures increased in suggest X-rayoutburst Septe superlu was activity associated starting with already an in episodeoutburst, of extended super-Eddington optically thick envelope/outflow has be the visual data from thedatabase American [4]. Association Since of our Variable analysis St wasthe focused on accuracy the of long-ter these dataoutburst proved and to four be smaller quite echo sufficient.vations. outbursts This (Figure The 1a). echo outbursts Each displaypeak o magnitude multi-peak (Figures structure 1c a and 1d). followed the 1999 event in the subsequent years. The continu 2. Data analysis [6]. P Cygni profiles indicated rapidthat changes the in emission matter from eject an innerinterpreted accretion as region cyclo-synchrotron significant emission associated wit observations covered the years 1964–1967 (Figure 1f). The p covered segments. Typical uncertaintythe star is GSC 0.05 0684802768. mag. TheNotice statistical the Magnitu prevailing distribution skewness of toward th the higherphase brightnes according to the ephemeris of [2]: distance to V4641 Sgr were considered. studied on the photographicwere plates blue-band from sensitive, the which archive is of similar the to the Ba the extrapolation of the O–C curve of the echo outbursts. (SXTs), the relation of the absolute visual magnitude P distance of 7–12 kpc [8]. Its orbital period is Long-term optical activity of the microquasar V4641 Sgr 1. Introduction the O–C residuals in aof similar the way echo as outbursts in display [15,outburst-to-outburst a 11] fluctuations having (Figure clearly a 1b). defined significantly trend s I in their ing echo outburst in the epoch PoS(MQW7)111 (e) The of the main C T 999 main outburst is near (filled diamonds). The parameters orb P s denote V4641 Sgr at the maximum of g plates (1964–1967) (relative mag). (g) own: (1) two missing echo outbursts; (2) . Three values of the distance are assumed. y arrows. (b) O–C curve for nt the length of the reference period of 377 d to ata. (h) The Bamberg data folded with the orbital 3 of the echo outbursts. (c, d) Examples of the echo outbursts. C T of SXTs at the outburst maximum vs. V M (a) The AVVSO visual light curve of V4641 Sgr. The peak of the 1 of 10 SXTs, exceptthe for echo V4641 outburst. Sgr, Open are circles from mark [10]. V4641 Sgr Closed inStatistical circle quiescence distribution of the brightness in the Bamberg d (f) The photographic light curve of V4641 Sgr fromperiod. the See text Bamber for details. absolute visual magnitude and echo outbursts.one Two missing positions echo of outburst. the Dashed main horizontal outburst lines represe are sh show the relatively small scatter of the left hand edge of the plot. The echo outbursts are marked b Figure 1: Long-term optical activity of the microquasar V4641 Sgr PoS(MQW7)111 days, with a trend 8 d, provided that the . 2 ) as the thermal instability . The very luminous donor e Czech Republic and the = C re its main outburst. In this T orb orb P f the echo outburst implies that the timescale of years. P explained by the thermal emis- mal instability gives rise to the 1 mag) on the typical timescale S 98058 Gaia is acknowledged. file is inconsistent with a single < ]. ith n outburst. The morphology of the ernational database (Massachusetts, bservations made this analysis pos- ntense optical emission of the echo rable donor. vity of V4641 Sgr (the narrow out- outburst. This scenario also explains nd preclude the modulation observed t resembles the radio flares observed eaks starting from the quiescent level ystem. The prevailing skewness of the e explained by a jet or a series of suc- tuations, including a larger brightening olution of otron emission [14]. The thermal emis- 2 was missed due to a seasonal gap, the ery steeply, faster than what corresponds tions ( − ghtness indicates faint outbursts. he optical is launched during this outburst, = E 4 of the echo outbursts. C T is analogous to that in outbursts of dwarf novae (e.g. [11]) C T of four echo outbursts that followed the main outburst is 377 C T The support by the grant 205/08/1207 of the Grant Agency of th V4641 Sgr was active also in 1964–1967, that is long time befo We interpret the characteristic features of the recent acti The optical luminosity of the echo outbursts is too high to be The accumulation of the data points near the peak magnitude o We present an analysis of the opticalThe activity mean of V4641 Sgr on projects D-25-CZ4/08-09 DAAD, PECS 98023This Integral, research and has made PEC use of observations fromUSA). the We AAVSO Int thank the variable star observerssible. worldwide whose o of the accretion disk operating inoutbursts dwarf in novae V4641 and Sgr is SXTs. due The tosion i a of jet the radiating cyclo-synchr disk itself remainswhy outshined no by other the echo donor even outburstcyclically in was repeating observed outbursts, in but if V4641 no Sgr.the jet thermal The radiating emission in ther of t the hot disk remains outshined by the epoch, the activity usually displays low-amplitudeof fluctua several weeks. They are independentby on [2], the although orbital their phase amplitudes a are comparable.near These JD fluc 2 438 950, suggest persistentstatistical strong distribution activity in of Figure the 1g s toward the higher bri Acknowledgments bursts separated by a long quiescence, a clear trend in the ev mass exchange occurs via Rocheexpanding lobe bubble overflow. emitting synchrotron The radiation, flat-topcessive but pro bubbles. can b The very shortduring duration the of X-ray the outburst of echo the outburs microquasar GRO J1655–40 [3 of V4641 Sgr outshines the thermalecho emission outbursts shows of that the their disk optical even lightcurvesto i decay the v thermal timescale of the accretion disk in the system w these events do not consist ofof a brightness. long series of short, narrow p sion of the accretion disk analogous to that in SXTs of a compa and some SXTs (e.g. [12]). If one echo outburst in main outburst nicely fits the evolution of of a decrease. The evolution of their Long-term optical activity of the microquasar V4641 Sgr 3. Results PoS(MQW7)111 , , , A&A , A&A , L1 295 New clues on , 521 (2000). (1999). 540 (2001). , 66 (1980). , MNRAS 7253 88 , ApJ 5068 nova CH Ursae Majoris , IAUC , A&A ft X-ray transient 4U 1608–52 Light Curves and Radio Structure , IBVS n Episodes -Wilson, A. J. Mioduszewski, B. M. (1978). , et al., XTE J1819-254=SAX J1819.3-2525) f the black hole binary V4641 Sagittarii . Wu, D. J. McKay, D. P. Smits, R. J. Sault, onard, R. Stubbings, P. Nelson, T. , Sz. Mészáros, P. Székely, , M. R. Garcia, P. J. Callanan, Ch. D. communication 1024 Super-Eddington outburst of V4641 Sgr 5 XTE J1819–254, XTE J1743–363, XTE J1710–281, , Astr. Tsirk A Black Hole in the Superluminal Source SAX J1819.3-2525 Rapid Optical Fluctuations in the Black Hole Binary V4641 (1999). On the outburst amplitude of the soft X-ray transients 7120 , 489 (2001). , 617 (2004). , L79 (2002). 555 418 54 , IAUC The Orbital V-band Light Curve of V4641 Sagittarii Variable stars in Sagittarius GM Sagittarii and SAX J1819.3-2525 = XTE J1819-254 , 882 (2005). , ApJ The properties of outbursts and long-term activity of the so Outburst parameters and the long-term activity of the dwarf 363 , A&A , PASJ The SU UMa stars – an important sub-group of dwarf novae ,977 (2000). 544 , 1013 (2002). , 103 (2000). outburst mechanisms and improved spectroscopic elementsMNRAS o Bailyn, R. K. Jain, R. A.(V4641 Remillard, Sgr) 391 (QX Nor) Radio Emission from GRO J1655–40 during the 1994 Jet Ejectio XTE J1723–376 354 Richards, Ch. Bailyn, R. Santallo, Sagittarii Gaensler, D. A. Smith, R. J. Sault, R. P. Fender, R. E. Spencer (1998). of the 1999 September Transient EventApJ in V4641 Sagittarii (= [2]V. P. Goranskij, [1]V. P. Goranskij, [9]M. Revnivtsev, M. Gilfanov, E. Churazov, R. Sunyaev, [3]D. C. Hannikainen, R. W. Hunstead, D. Campbell-Wilson, K [7]C. B. Markwardt, J. H. Swank, F. E. Marshall, [4]A. Henden, 2008, AAVSO International database, private [5]) R. M. Hjellming, M. P. Rupen, R. W. Hunstead, D. Campbell [6]C. Lindstrom, J. Griffin, L. L. Kiss, M. Uemura, A. Derekas [8]J. A. Orosz, E. Kuulkers, M. van der Klis, J. E. McClintock Long-term optical activity of the microquasar V4641 Sgr References [15]N. Vogt, [10]T. Shahbaz, E. Kuulkers, [13]R. Stubbings, [12]V. Šimon, [14]M. Uemura, T. Kato, R. Ishioka, K. Tanabe, S. Kiyota, B. M [11]V. Šimon,