In August 17, 2017, the LIGO-Virgo scientific collaboration, for the first time, detected a gravitational wave (GW) signal from a binary neutron star (NS) merger event. Multi-wavelength electro-magnetic (EM) counterparts to GW170817 have also been detected. This has opened up a new era of GW astronomy, whereby comprehensive analyses of multi-messenger signals will shed light on both GW and EM studies. For NS-NS mergers, many associated EM counterparts have already been proposed in the literature, and their relative brightness is essentially determined by the properties of the merger remnant. Depending on the total mass of the NS-NS system and the NS EoS, NS-NS mergers could result in four different types of final products: (1) immediate collapse into a black hole (BH); (2) a temporal hypermassive NS (supported by differential rotation) which survives 10–100 ms before collapsing into a BH; (3) a supramassive NS temporarily supported by rigid rotation, which collapses to a BH at a later time after the NS spins down; and (4) a stable NS.
In this talk, I will briefly review the possible EM signatures for different merger remnants. Moreover, under the assumptions that Short GRBs are produced by double neutron star mergers and that the X-ray plateau followed by a steep decay as observed in SGRB X-ray light curves marks the collapse of a supramassive NS to a BH, I will show that current observations already impose interesting constraints on the properties of NS-NS merger products. Finally, I will talk about some constraints on the merger product of GW170817.

BIO
He Gao got his Ph.D. in Department of Physics and Astronomy, University of Nevada Las Vegas (UNLV). Then he became a Postdoctoral fellow in Pennsylvania State University for one year. After that he came back to China and became an associate professor in Department of Astronomy, Beijing Normal University. His research interest is on high energy astrophysics, including theory of Gamma-Ray Bursts and Afterglows, Fast Radio Bursts, Electromagnetic Counterpart of GW events.