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???
Jet penetration problem in SGRBs
Faile
d Pe
netra
tion
Non-re
lativ
istic p
enet
ratio
n
Rela
tivisti
c pen
etra
tion
No co
coon
( 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
cocoon
jet
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.
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