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