コンパクト連星合体の電磁波カウンターパート樫山和己（京大理）中村卓史（京大理）
井岡邦仁（KEK）
理論懇シンポジウム2011@国立天文台

重力波天文学の夜明け• ALIGO/VIRGO and LCGT within ～10yrs• The promising target : NS-NS, NS-BH, BH-BH– Probe the interior of NSs– “Standard sirens”– and more?
The determination of the red shift is crucial.
ground-based GW detectors→ angular resolution at most ～ deg.

Electromagnetic counterparts

EM counterparts of NS-NS/NS-BH mergers

・GRBs are the most reliable,
but may be low-frequent.

An anticipated GW event rate

・Other signals are dim.
→ Special follow-upstrategies are needed.
Metzger & Berger 2011

アイデア : “dirty” SGRBs
Matters can be also ejected to the axis.
If a jet launched after the wind …

→ jet - wind interaction→ cocoon formation→ off-axis X-ray
重力波との同時検出rateは ?

コンパクト連星合体に伴う質量放出•••（合体直前の潮汐破壊 Lee+2010）
合体直後の– ニュートリノ駆動風 Dessart+2009– 磁気駆動風 Shibata+2011
継続時間～0.1sec (?)

dense and thick !!

∝r -2

Dessart+2009

Initial pulse (IP) and extended emission (EE)

• IPs :
• EEs :
We assume that both IPs and EEs are jet originated.

•Perley + 2009

コクーン起源のoff-axis放射-その１•“cocoon breakout emissions”

Soderberg + 2008

– c.f. SN shock breakout– vsh > 0.03c→ radiation mediated : Pgas << Prad– hard X-ray > 60keV– cocoon size → opening angle Θc– energy budget and time scale

1/ΓcKatz + 2011

Rbcocoonjetコクーン起源のoff-axis放射-その２
jetPhotons escapewhen τ ～ 1.

cocoonΘfb•“emissions from cocoon fire balls”– Cocoons after breakout ～ dirty fire balls– Important parameters (Meszaros+93)• baryon load parameter• initial optical depth

・ dynamics of the fire ball・ observed typical energy and luminosity– Typically soft X-ray ～ keV– Opening angle Θfb～ 0.8

What to do• Parameters to be fixed– Cocoon energy– Cocoon volume– Cocoon mass
– Cocoon expansion velocity– Breakout radius• Input parameters– Jet luminosity– Jet opening angle– Envelope density– Envelope expansion velocity• Solve pressure balanceand conservation Eqs.
Matzner 2003, Bromberg + 2011

Liso [erg/sec]

Disc formation and wind1048

binary mergers

1051

On- and off-axis counterparts

1045

IPIP cocoon(soft X)

0.1 keV/cm2/s@100Mpc

EE cocoon(soft X)

off-axis

EE break out(hard X)

1042
1039

on-axisEE

IP break out(hard X)
10-5 keV/cm2/s@100Mpc

10-3

10-2

10-1

1

10

100t [sec]Summary and discussion• Off-axis X-ray counterparts compact binary mergers– cocoon formation by jet-ejecta interaction• Cocoon breakout → hard X-ray• Cocoon fire ball → soft X-ray– Too dim to be detected so far.
– All sky X-ray transient surveys are necessarily.
• Lobster and Janus?
• Cooperation with GW detectors– Other electromagnetic counterparts???

Appendix

“Cardinal Virtues”
Metzger & Berger 2011

1. Be detectable with present or upcoming telescope
facilities, provided a reasonable allocation ofresources.
2. Accompany a high fraction of GW events.
3. Be unambiguously identifiable (a “smoking gun”)
such that it can be distinguished from otherastrophysical transients.
4. Allow for a determination of ～arcsec sky positions.

Evolution of IP jet heads
Pressure balance at the jet head,IP jet head propagation velocity

Evolution of IP cocoon before breakout
Energy stored in a cocoon = injected jet energy

Pressure balance at the cocoon-envelope boundary

IP cocoon expansion velocity

Just before the breakout @IP cocoon breakout
jet and cocoon breakout
a “radiation mediated” shock breakout

Wider-angle ↑But dim ↓Evolution of IP cocoon after breakout 1
a polluted fire ballThe evolution is determined by
the baryon load

and the initial optical depth

The three critical radii
the Lorentz factor saturate @the fire ball begin to spread in the observer flame @the fire ball become optically thin @Evolution of IP cocoon after breakout 2
The temperature and radiation energy of the fire ball in the comoving flame
whereThe evolution of comoving volume( Rst < Rsp < Rph for the fiducial IP jet )The temperature and radiation energy @ r = Rph

Evolution of IP cocoon after breakout 3
Typical observed energy

The observed duration

whereThe mean luminosity

The energy spectrum is quasi-thermal ( ? )The opening angle

Detection threshold• 1mCrabs = 2.4×10−11 erg s−1 cm−2