1. Off axis counterparts of SGRBs tagged by gravitational waves Kazumi Kashiyama (Penn State) with K.Ioka, T.Nakamura and P. Meszaros

2. Why? The era of gravitational wave astronomy will come soon! The “promising target” : compact binary mergers Multi-messenger approach since 2015 〜 2017 2 nd generation network Distance detectable : 〜 200Mpc, Event rate : 〜 40yr -1 for NS-NS merger GW detectors have bad eyesight! Angular resolution of 2 nd generation 〜 10deg 2 Off-axis X-ray, optical, radio counterpart searches SGRBs are the most reliable counterpart, but low-frequent. if θ j 〜 0.1, the GW-SGRB simultaneous detection rate 〜 0.1yr -1

3. 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)

4. Possible off axis emissions from pre-jet envelope Optical (kilonova) Radio active heating in the envelope (β-decay, fission, 56 Ni→ 56 Co→ 56 Fe) 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???

5. relativistic jet cocoon Black hole (magnetar) + accretion disk Jet penetration problem in SGRBs VS

6. Jet penetration problem in SGRBs Failed Penetration Non-relativistic penetration Relativistic penetration No cocoon ( Fail → jet induced supernovae like? ) Succeed penetration → jet+cocoon

7. Two possible off axis emissions from jet-envelope interaction relativistic jet cocoon Black hole (magnetar) + accretion disk 1. Hard X-rays from cocoon breakout 2. Soft X-ray quasi-thermal emission from cocoon itself

8. X-rays from cocoon breakout Too dim to be detected because of the small r cbo cocoon jet Energy budget of breakout photons: @ Timescale of the emission: Jet-cocoon dynamics →

9. 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)

10. 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.