Intraday Variability and Images of Microquasar

Cygnus X-3† Jeong-Sook Kim1,2 & Soon-Wook Kim1

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)

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.

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

rad

io

• 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.

Years

Proposal title PI affiliation

Total observing timeVERANRO+NiCT

VERA only

2004 Rapid Variability in Microquasar Cyg X －３　 with Water Maser W75 N as a Calibrator

Makoto

Inoue NAOJ 8h

2006 –

2007

Monitering Flares and Imaging Jets in Microquasar Cygnus X-3

Soon-Wook Kim

KASI 40 h

2007 –

2008

Astrometry of Flaring Microquasar Cygnus X-3

Soon-Wook Kim

KASI 48h

2008 –

2009

Astrometry of Flaring Microquasar Cygnus X-3: II. Follow-up Observations

Soon-Wook Kim

KASI 68h

List of accepted proposal of VERA for Cygnus X-3

VERA: Japanese VLBI Facility- VLBI Exploration of Radio Astrometry (Japan)

Ishigaji-jima 20m

Iriki 20m

Mizusawa 20m (& 10m)

Ogasawara 20m

Correlation Center at Mitaka/NAOJ

Ishigaki

Iriki

Mizusawa

Ogasawara

Seoul

Jeju

Ulsan

KVN

VERA

Examples of VERA observation for Cyg X-3

• Time variability

• Imaging

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

•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

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

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

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.

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.

Thank you