IRCC seminar 2012/12/04

Flaring up of the Compact
Cloud G2 during
the Close Encounter withSgr A* in 2013 Summer
Takayuki Saitoh
Tokyo Institute of Technology

Collaborators：Junichiro Makino(Titech), Yoshiharu Asaki(JAXA), JunichiBaba(Titech), Shinya Komugi(NAOJ), Makoto Miyoshi(NAOJ), TohruNagao(Kyoto)l, Masaaki Takahashi(Aichi-Edu.), Takaaki Takeda(NAOJ),
Masato Tsuboi(JAXA), Ken-ichi Wakamatsu(Gifu)

arXiv:1212.0349  Today!!
http://v1.jmlab.jp/~saitoh/G2/

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Contents
1. Introduction

1. Gillessen et al. 2012 Nature
2. 2D Numerical simulation by Schartmann
et al. 2012 ApJ

2. Results of our 3D simulation

1. Saitoh et al. 2012 arXiv:1212.0349

3. Discussion & Summary

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5/Jan/2012 Nature• 3 Earth mass cloud
was found in theGalactic center• Rperi~270 au/Tperi~
2013 Summer• Giant radiation flare
would be observed
due to the massaccretion onto the SgrA*

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IR bandimagesby VLTObs

Reconstructed
orbit

Gillessen et al. 2012

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P-V diagrams• Elongated structure has been observed

Gillessen et al. 2012

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Cloudʼs and orbital properties• Mass：~3 earth mass
• Effective Radius:~15mas ~125 AU

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Summary of Obs• Three earth mass cloud, G2, was found in
the Galactic center, which is approaching
the Sgr A* and will be pass the pericenter(~270 au) in 2013 summer.
• Interaction with the ambient hot gas may
induce the destruction of G2 by KH/RT
instabilities, resulting in the enhancementof the activity in the Sgr A*.
– 35 citations (4 Dec 2012)

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ESO animation

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Simulation• 2D, PLUTO(AMR)• 2 scenarios

1. Compact cloud scenario
2. Spherical shell cloud scenario• EOS : Isothermal• Hot ambient gas surrounding the Sgr A*– Radiatively Inefficient Accretion Flow (RIAF)• Density/Temperature profile:~1/r (Yuan+2003)– Profiles are (almost) fixed.

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Compact CloudSpherical shell• Spherical shell model can explain thep-v diagram much well.

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If ~0.1 Mearth falls into the Sgr A* and it releases 10 % of its grav.
energy, the released energy is ~1048erg~1039erg/s: if we assume 10 years as the duration time.
However, if we adopt the typical the eff. of RIAF ~ 10-6, ~1033 erg/s.

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Q• Is 2D approximation good for thissystem?

– Tidal force in the vertical direction to theorbital plan was excluded.
– Since the Vperi~5000km/s, the compression
energy will be enormous even if onlyseveral % of Vperi can be used.

• Here, we investigate the effects of threedimensionality.
– We adopt the compact cloud scenario, anddo not care details in the formation processof cloud.

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3D Simulation Setup• N-body/SPH simulations of the system with thecloud, hot ambient and Sgr A*.

– Gravity, hydrodynamics and radiative cooling w/Optically thin

• 3D uniform density cloud– 3MEarth, Radius 125AU• Orbital parameter：Gillessen+2012– Pericenter passage: A.D. 2013.5• Since A.D. 1995 to A.D. 2033

• hot ambient profile

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Run parameters

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Parallel N-body/SPH code：ASURA• C (C99) + MPI• Domain decomp.:Orthogonal RecursiveBisection• Gravity: Parallel Tree+GRAPE– Hardware accelerators : GRAPE-5/GRAPE-6A/GRAPE7/GRAPE-DR– Software accelerator : Phantom-GRAPE• Assembler tuned software library!!

– Symmetrized Plummer Potential (Saitoh&Makino 2012a)• Hydro：Density Independent SPH(Saitoh&Makino 2012b)• Time integrator: Leap-frog+Individual time steps+Time-step limiter (Saitoh&Makino 2009)+FAST (Saitoh&Makino 2010)

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Stereograms

The cross-eyed view method is used.

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Stereograms

The cross-eyed view method is used.

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Mass accretion rate
Haloorigin

Cloudorigin

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Luminosity Evolution

2006.26

2012.022012.74

2013.102013.46

2013.82

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Analytic Evaluation of Luminosity• Assume that…

1. All elements have elliptical orbits and share thesame ascending node.
2. Cloudʼs radius is 125 au at the point where thesemi-minor axis and orbits intersection.
3. All energy released at the pericenter.

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The effects of Ram pressure• Ram pressure：• Energy/sec with a conversion factor C• Substituting the hot ambient profile andorbit info. (r-vc; Burkert+2012):
1. A.D.2000,r2000=6x1016cm、σ=π(125AU)2、dE/dt =2. A.D.2013.5,r2013.5=4x1015cm,σ<1AUx40
AU=40AU2、dE/dt

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New observations of the gas cloud G2 in theGalactic Center:Gillessen+2012(arXiv:1209.2272)

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Summary• We performed 3D N-body/SPH simulationsof the 3 Mearth gas cloud G2 approaching theSgr A*.
• Due to the strong compression in thevertical direction by the tidal force, thecloud releases ~1035 erg/s during 2013.
– Main source is the recombination line from the
hot gas heated to ~104K.
– In particular, Paschen and Brackett series(infrared-bands), which do not suffer from thedust extinction effects signiﬁcantly, are good toobserve.