Bright broad-band afterglows of gravitational wave bursts from mergers of binary neutron stars Xuefeng Wu Purple Mountain Observatory Chinese Center for Antarctic Astronomy Chinese Academy of Sciences Collaborators: He Gao, Xuan Ding, Bing Zhang, Zi-Gao Dai, Yizhong Fan, & Daming Wei Beijing Gravitational Waves Workshop Tsinghua University; July 1 - 2, 2013

NS-NS coalescence Electromagnetic (EM) emission signal accompany with a GWB is essential for GW identification. The brand new channel of GW signals combining with old channel of EM emission would lead us better understand our universe. Remnant ? EOS Normal Stiff BH NS Introduction: see Bing Zhang’s talk

Metzger & Berger, 2012 SGRB Multi-band transient ~hours, days, weeks, or even years Li-Paczyński Nova Opical flare ~ 1 day Ejecta-ISM shock Radio ~years Li & Paczyński, 1998 Nakar& Piran, 2011 EM signals for a BH post-merger product

Short GRBs γ-ray Light curve

Li-Paczynski Nova / Kilonova Metzger et al. (2010)

Radio Afterglows Rosswog, Piran & Nakar (2012)

What if the central product is magnetar rather than a black hole?

Why Magnetar ? Theoretical reason Stiff EoS

Why Magnetar ? Theoretical reason Stiff EoS Lattimer (2012) Stiff equation-of-state: maximum NS mass close to 2.5 M 

Why Magnetar ? Theoretical reason Stiff EoS Observational reason Zhang, 2013 (Ref therein) Lattimer & Prakash (2010) NS with mass > 2 Msun has been discovered (e.g., PSR J , M=2.01+/-0.04 Msun) NS-NS systems: total mass can be ~ 2.6 Msun

Why Magnetar ? Theoretical reason Stiff EoS Observational reason Zhang, 2013 (Ref therein) Based on the observations of the SGRB X-ray afterglows. Rowlinson et al Rowlinson et al GRB NS with mass > 2 Msun has been discovered (e.g., PSR J , M=2.01+/-0.04 Msun) NS-NS systems: total mass can be ~ 2.6 Msun

Why Magnetar ? Theoretical reason Stiff EoS Observational reason Zhang, 2013 (Ref therein) Based on the observations of the SGRB X-ray afterglows. Rowlinson et al Rowlinson et al GRB A postmerger magnetar would be initially rotating near the Keplerian velocity P~1ms. NS with mass > 2 Msun has been discovered (e.g., PSR J , M=2.01+/-0.04 Msun) NS-NS systems: total mass can be ~ 2.6 Msun

Inferred physical parameters of magnetar Some inferred initial rotation periods are as long as ~10 ms!

(Fan, Wu & Wei 2013) Initial period of NS from merger - theoretical expectation The expected rotation period is ~1 ms!

(Fan, Wu & Wei 2013) Signature of gravitational wave? The total energy radiated in wide energy band during the X- ray plateau phase is much smaller than that expected for a merger-formed magnetar (E_k ~ P -2 ). Two possible solutions: (a)The radiation efficiency of the outflow is very low. But this possibility is disfavored by the extremely dim forward shock emission of some events. (b) Strong gravitational wave radiation (?)

(Fan, Wu & Wei 2013) The observed “too-short” duration of the X-ray plateau can be accounted for!

(Fan, Wu & Wei 2013) Is it possible to have an ellipticity ~ 0.01? (a)The super-strong interior magnetic field (~10 17 G) may be able to deform the magnetar significantly (Dall’Osso et al. 2009). (b) Ellipticity up to 0.1 is possible for a quark star (Lin 2007; Johnson-McDaniel & Owen 2013)

Hotokezaka,et al., arXiv: Mass Ejection during NS-NS Merger Initial velocity: 0.1 – 0.3 c Ejected mass: – 0.01 Msun

Jet-ISM shock (Afterglow) Shocked ISM Ejecta SGRB Radio Optical X-ray Poynting flux MNS Magnetar as the central product SGRB Late central engine activity ~Plateau & X-ray flare Magnetic Dissipation X-ray Afterglow 1000 ~10000 s Ejecta-ISM shock with Energy Injection (EI) Multi-band transient ~hours, days, weeks, or even years Gao, Ding, Wu, Zhang & Dai, 2013 Zhang, 2013

Jet-ISM shock (Afterglow) Shocked ISM Ejecta SGRB Radio Optical X-ray Poynting flux MNS Magnetar as the central product SGRB Late central engine activity ~Plateau & X-ray flare Magnetic Dissipation X-ray Afterglow 1000 ~10000 s Ejecta-ISM shock with Energy Injection (EI) Multi-band transient ~hours, days, weeks, or even years Zhang, 2013 Gao, Ding, Wu, Zhang & Dai, 2013

Jet-ISM shock (Afterglow) Shocked ISM Ejecta SGRB Radio Optical X-ray Poynting flux MNS Magnetar as the central product SGRB Late central engine activity ~Plateau & X-ray flare Magnetic Dissipation X-ray Afterglow 1000 ~10000 s Ejecta-ISM shock with Energy Injection (EI) Multi-band transient ~hours, days, weeks, or even years Gao et al, 2013 Zhang, 2013 Rowlinson et al. 2013

Jet-ISM shock (Afterglow) Shocked ISM Ejecta SGRB Radio Optical X-ray Poynting flux MNS Magnetar as the central product SGRB Late central engine activity ~Plateau & X-ray flare Magnetic Dissipation X-ray Afterglow 1000 ~10000 s Ejecta-ISM shock with Energy Injection (EI) Multi-band transient ~hours, days, weeks, or even years Gao et al, 2013 Zhang, 2013

Magnetic Dissipation X-ray Afterglow Flux (ergcm -2 s -1 ) t Zhang, B., 2013, ApJL, 763,22 With, one can roughly estimate that the optical flux could be as bright as 17th magnitude in R band. The proto-magnetar would eject a wide-beam wind, whose dissipation would power an X-ray afterglow as bright as~ (10 −8 –10 −7 ) erg cm −2 s −1. The duration is typically 10 3 –10 4 s.

Jet-ISM shock (Afterglow) Shocked ISM Ejecta SGRB Radio Optical X-ray Poynting flux MNS Magnetar as the central product SGRB Late central engine activity ~Plateau & X-ray flare Magnetic Dissipation X-ray Afterglow 1000 ~10000 s Ejecta-ISM shock with Energy Injection (EI) Multi-band transient ~hours, days, weeks, or even years Zhang, 2013 Gao, Ding, Wu, Zhang & Dai, 2013

ISM (n) Energy conservation equation Ejecta-ISM shock with Energy Injection Gao, Ding, Wu, Zhang & Dai, 2013, arXiv: when Dynamics depends on and, namely and

Ejecta-ISM shock with Energy Injection For given different leads to different Dynamic cases. Some of them could be even relativistic Non-relativistic If

Ejecta-ISM shock with Energy Injection X-ray: Opt: Radio:

Ejecta-ISM shock with Energy Injection X-ray: Opt: Radio:

Ejecta-ISM shock with Energy Injection X-ray: Opt: Radio:

Ejecta-ISM shock with Energy Injection X-ray: Opt: Radio:

Ejecta-ISM shock with Energy Injection X-ray: Opt: Radio:

Ejecta-ISM shock with Energy Injection X-ray: Opt: Radio:

Late Re-brightening in SGRB

--- Li-Paczynski Model Perley et al. 2009, ApJ, 696, 1871

Late Re-brightening in SGRB Refreshing Shock Model Hascoet et al. 2012, A&A, 541, A88 Ek,0 = 7x10 50 erg Ek,inj = 30 Ek,0 ~ 2x10 52 erg ε_e = (ε_B )^0.5 ε_B = 5x10 −2, p = 2.5 n = cm −3 z = 0.5

Late Re-brightening in SGRB Gao, Ding, Wu, Zhang & Dai (2013) Model Ding, Gao, Wu, Zhang & Dai 2013, in preparation

Relativistic PTF Transient PTF11agg --- Another GWB magnetar candidate? Cenko et al. (2013)

Event Rate by VLA Bright Radio Transient Survery Bower & Sauer. 2011, ApJL, 728, 14 Field of 3C year archival observation 1.4 GHz event rate (>350 mJy ) is < 6×10−4 degree−2 yr−1, or < 20 yr −1 Bright GWB afterglow rate uncertainties: (1)NS-NS merger (2)Fraction of forming a massive millisecond magnetar

Thank You