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Intraday Variability and Images of Microquasar Cygnus X-3 †

Intraday Variability and Images of Microquasar Cygnus X-3 †. Jeong-Sook Kim 1,2 & Soon-Wook Kim 1 Astrophysics Research Group, KASI Kyunghee University

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Intraday Variability and Images of Microquasar Cygnus X-3 †

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  1. Intraday Variability and Images of Microquasar Cygnus X-3† • Jeong-Sook Kim1,2 & Soon-Wook Kim1 • Astrophysics Research Group, KASI • 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) • 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. X-rays GRS 1915+105 Cygnus X-3 radio 500 days • Two radio-bright, frequently flaring microquasars: GRS 1915+105 & Cyg X-3. • Numerous VLBI/array studies for GRS 1915+105. 200 days • 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. List of accepted proposal of VERA for Cygnus X-3

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

  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. January May RXTE and RATAN monitoring in 2007 • 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.

  9. ISH-MIZ Long baseline ISH-OGA MIZ-OGA MIZ-IRI IRI-OGA IRI-ISH Short baseline Imaging in 2007 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.

  10. ISH-MIZ ISH-OGA MIZ-OGA MIZ-IRI IRI-OGA IRI-ISH 2007 May • 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. Baseline: Long-> short

  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

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