New Results on Stellar Flares Monitored with MAXI/GSC

Yohko Tsuboi, Kyohei Yamazaki, Akiko Uzawa, Takanori Matsumura (Chuo Univ.), Satoshi Nakahira (Aoyama Gakuin Univ.), Motoki

Nakajima (Nihon Univ.), and the MAXI team

Stars detected with MAXI/GSC

Flare

theta Ori C

Eta Carinae

RS CVn stars

T Tauri star Massive stellar binary : 2

Low-mass star : 8 Single T Tauri star : 1 RS CVn binary : 7

T Tauri star TWA-7• fast rotator

• deep convection zoneTWA-7

V=19.2 km s-1

(cf. Vsun=0.6 km s-1)

X-ray variability of TWA-7Phase 0 Phase 1 Phase 2

td < 8 [ks]

Spectrum of TWA-7 flare

Lx = 1.2+0.3 ×1033

[erg s-1]

cf. Lx_sun

=1027[erg s-1]

-0.4

One of the brightest flare in those on T Tauri stars

RS CVn type stars

• close detached binaries• tidally locked• fast rotators

deep convection zone

Flares from RS CVn stars• 14 flares from 7 RS CVn binaries• 2 biggest flares in all the stellar flares

Lx = 5+4 ×1033 erg s-1-2

Lx = 4+1 ×1033 erg s-1-

II Peg GT Mus

Flare frequency

Flares come from specific stars

Then which component is special?

Interaction between each component is special?

Poisson distribution (the expectation value is the same as that of the data)

Spin velocity [km s-1] Spin velocity [km s-1]

Spin velocity vs flares

MAXI detectedMAXI non detected

Probability that two datasets differ significantly

69% (not weighted)97% (flare freq. weighted)

21%44%

Radius [solar radius] Radius [solar radius]

MAXI detectedMAXI non detected

Radius vs flares

96% (not weighted)99.8% (flare freq. weighted)

10%74%

Probability that two datasets differ significantly

Orbital period [day] Separation [solar radius]

MAXI detectedMAXI non detected

Binary parameters vs flares

51% (not weighted)86% (flare freq. weighted)

11%73%

Probability that two datasets differ significantly

Summary

Lx = 5+4 erg s-1 -2

• We increased the big flare samples (14 flares from 7 RS Cvns, 1 flare from 1 T Tauri star)

• 2 biggest flares : II Peg : GT Mus: Lx = 4+-1 erg s-1

• Hint for “Main big flare maker is subgiantcomponent”

2, 3 years are needed to conclude

TWA-7 RS CVn stars

V=19.2 km s-1 Vcool=10-100 km s-1

Only spin velocity and the depth of the convection zone are keys to originate big flares?