Off axis counterparts of SGRBs tagged by gravitational waves

Kazumi Kashiyama (Penn State)with K.Ioka, T.Nakamura and P. Meszaros

Why?The era of gravitational wave astronomy will come soon!

The “promising target” : compact binary mergers

Multi-messenger approach

since 2015 〜 20172nd generation network

Distance detectable : 〜 200Mpc, Event rate : 〜 40yr-1 for NS-NS merger

• GW detectors have bad eyesight! Angular resolution of 2nd generation 〜 10deg2

Off-axis X-ray, optical, radio counterpart searches

• SGRBs are the most reliable counterpart, but low-frequent. if θj 〜 0.1, the GW-SGRB simultaneous detection rate 〜 0.1yr-1

Point : “Pre-jet” envelope formation

Mildly relativistic! Optically thick! Neutron-rich!

Hyper-massive neutron star

Pre-jet envelope( Magnetically or Neutrino driven wind )

Tidal mass ejection

Rotational plane of binary

e.g. Lee et al. (2010) , Dessart et al. (2009), Shibata et al. (2011)

Possible off axis emissions from pre-jet envelope

Optical (kilonova) Radio active heating in the envelope (β-decay, fission, 56Ni→56Co→56Fe)

Interaction between the envelope and interstellar medium

Radio (afterglow)

〜 days

〜 years Nakar & Piran (2011)

Li & Paczynski (1998)Metzger et al. (2010)

UV-X-ray Interaction between the envelope and relativistic jets

≤ minutes???

relativistic jet cocoonBlack hole (magnetar) + accretion disk

Jet penetration problem in SGRBs

VS

Jet penetration problem in SGRBs

Faile

d Pen

etra

tion

Non-re

lativis

tic p

enet

ratio

n

Relati

vistic

pen

etra

tion

No coc

oon

( Fail → jet induced supernovae like? )Succeed penetration → jet+cocoon

Two possible off axis emissions from jet-envelope interaction

relativistic jetcocoon

Black hole (magnetar) + accretion disk

1. Hard X-rays from cocoon breakout2. Soft X-ray quasi-thermal emission from cocoon itself

X-rays from cocoon breakout

Too dim to be detected because of the small rcbo

cocoonjet

Energy budget of breakout photons:

@

Timescale of the emission:

Jet-cocoon dynamics →

UV-Soft X-rays from cocoon itself

cocoon

@

Adiabatic expansion:

Jet-cocoon dynamics →

Marginally detectable by future facilities?

for ~ minute @ soft X-ray or UV (down scattered)

Summary

• Off axis X-ray counterpart of compact binary mergers could be a key for GW astronomy.

• Consider jet and pre-jet envelope interaction– Cocoon breakout emission → too dim– Emission from cocoon itself• could be soft X-ray transient ~minute• might be detected by future facilities? • need to be modeled more precisely.

– Failed penetration cases could be also interesting.