1. Intraday Variability and Images of Microquasar Cygnus X-3 † Jeong-Sook Kim 1,2 & Soon-Wook Kim 1 1.Astrophysics Research Group, KASI 2.Kyunghee University † Collaboration with Kurayama, Tomoharu (KVN/KASI) Honma, Mareki (VERA 觀測所 /NAOJ) & Sasao, Tetsuo ( 前 KVN/KASI & VERA/NAOJ)

2. Microquasars: introduction Microquasars: Jet-ejecting X- ray binaires Basic components of a microquasar are a spinning BH/NS, an accretion disk around it, and a collimated relativistic (or superluminal) jets, together with normal companion star. Over fifty BH/NS transients are known Most of jets have been usually observed with flares, presumably associated with instabilities in accretion disk.

3. Cyg X-3: Restless, Frequently Flaring Microquasar (Jet-emitting XRB) Cygnus X-3 GRS 1915+105 200 days 500 days Difficulty for catching the radio jets (“microquasar phenomena”) in BH/NS X- ray binaries is due to their unpredictable, transient nature with the recurrence time-scale of a few to hundred years, while they are undetectable in quiescence. Two radio-bright, frequently flaring microquasars: GRS 1915+105 & Cyg X-3. Numerous VLBI/array studies for GRS 1915+105. X-rays radio Cyg X-3, the radio-brightest, has been poorly studied (only 2 VLBI for small flares & 3 for giant flares) before our VERA observations, in spite of long-term monitoring for two decades ⇒ motivation Goal: catching Variability (Flares) & Imaging (Jets) to study related physics of accretion and radiation processes.

4. YearsProposal titlePIaffiliationTotal observing time VERA NRO+NiCT VERA only 2004Rapid Variability in Microquasar Cyg X －３ with Water Maser W75 N as a Calibrator Makoto Inoue NAOJ8h 2006 – 2007 Monitering Flares and Imaging Jets in Microquasar Cygnus X-3 Soon-Wook Kim KASI40 h 2007 – 2008 Astrometry of Flaring Microquasar Cygnus X-3 Soon-Wook Kim KASI48h 2008 – 2009 Astrometry of Flaring Microquasar Cygnus X-3: II. Follow-up Observations Soon-Wook Kim KASI68h List of accepted proposal of VERA for Cygnus X-3

5. VERA: Japanese VLBI Facility - VLBI Exploration of Radio Astrometry (Japan) Ishigaji- jima 20m Iriki 20m Mizusawa 20m (& 10m) Ogasawara 20m Correlation Center at Mitaka/NAO J Ishigaki Iriki Mizusawa Ogasawara Seoul Jeju Ulsan KVN VERA

6. Examples of VERA observation for Cyg X-3 Time variability Imaging

7. Time variability: one baseline detection NRO45m-NiCT34m, 2004 Top figure: ~30 min. flux variability in relatively low flux state with NRO45m- NiCT34m baseline in 2004. Lower figure: recent observation at the MIZ-IRI baseline. Variability time scale is apparently close to an hour in the flares with a peak of ~350 mJy., 2008

8. Upper panel is the X-ray monitoring with RXTE all sky monitor in space. We carried out VERA observation in January on the rise phase before the peak of a small, precursor flare, prior to the giant flare of 5.5 Jy. Light curve with red color is monitoring data of RATAN. Unlike the case of January observation, no other radio observation so far has been reported before our May observation; hard to tell what was going on. RXTE and RATAN monitoring in 2007 January May

9. MIZ- OGA ISH-OGA Long baseline Short baseline ISH- MIZ IRI-OGA IRI-ISH MIZ-IRI 2007 January Cyg X-3 flared up to ~ 1Jy; plausibly at least 2 or 3 flares, although flux variation is different in each baseline. Structure due to jets is plausible. Imaging in 2007

10. 2007 May Baseline: Long-> short In the later half of our observation, Cyg X-3 flared up to ~ a few hundred mJy, lasting 2-3 hours, consistent for all baselines. Possible flaring activity in the earlier epochs. Jet-like structure is more evident than that in 2007 January. ISH-MIZ ISH-OGA MIZ-OGA MIZ-IRI IRI-OGA IRI-ISH

11. Summary of VERA Observations for Cyg X-3 Time variabilities of ~30 min. & ~ hour were detected for low (tens of mJy) and higher (a few hundred mJy) flux states, consistent with other observations of Cyg X-3 and GRS 1915+105. Plausible jet-like features for small flares peaked at ~ Jy could be obtained with VERA. However, for more detailed structure associated with jet activity, VERA- only observation with 6 baselines is not enough; collaboration with the East Asia VLBI facilities is required. The shorter baseline than VERA’s is necessary to study a detailed jet structure. Radio monitoring like RATAN is important to describe what was going on before and after a detailed VBLI observation.

12. Future Plan Observations in 2007 & 2008 are under analysis. Multi-wavelength study together with our VERA results is under investigation, focusing on the physics of accretion and radiation processes, and proper motion. We will carry out 8 observations of Cyg X-3 for the 2008-2009 VERA open user observation.

13. Thank you