Constraining the spacetime spin using time delay in stationary axisymmetric spacetimes
- PDF / 629,980 Bytes
- 11 Pages / 595.276 x 790.866 pts Page_size
- 32 Downloads / 151 Views
Regular Article - Theoretical Physics
Constraining the spacetime spin using time delay in stationary axisymmetric spacetimes Haotian Liu1, Junji Jia2,a 1 2
School of Physics and Technology, Wuhan University, Wuhan 430072, China MOE Key Laboratory of Artificial Micro- and Nano-structures, Center for Astrophysics, School of Physics and Technology, Wuhan University, Wuhan 430072, China
Received: 19 June 2020 / Accepted: 25 September 2020 © The Author(s) 2020
Abstract Total travel time t and time delay t between images of gravitational lensing (GL) in the equatorial plane of stationary axisymmetric (SAS) spacetimes for null and timelike signals with arbitrary velocity are studied. Using a perturbative method in the weak field limit, t in general SAS spacetimes is expressed as a quasi-series of the impact parameter b with coefficients involving the source-lens distance rs and lens-detector distancesrd , signal velocity v, and asymptotic expansion coefficients of the metric functions. The time delay t to the leading order(s) were shown to be determined by the spacetime mass M, spin angular momentum a and postNewtonian parameter γ , and kinematic variables √ rs , rd , v and source angular position β. When β a M/rs,d , t is dominated by the contribution linear to spin a. Modeling the Sgr A* supermassive black hole as a Kerr–Newman black hole, we show that as long as β 1.5 × 10−5 [ ], then t will be able to reach the O(1) second level, which is well within the time resolution of current GRB, gravitational wave and neutrino observatories. Therefore measuring t in GL of these signals will allow us to constrain the spin of the Sgr A*.
1 Introducing Nowadays time delay between gravitational lensing (GL) images has become a useful tool in astrophysics and cosmology. Time delay in GL of compact objects can be used to constrain their properties including mass, charge and distance to earth [1–4], distinguish black hole (BH) and naked singularity [1,5], and test theories of gravity [6–12]. For GLs by galaxies or galaxy clusters, time delay can determine the Hubble parameter, matter density, dark matter substructure and dark universe parameters [13–19]. a e-mail:
[email protected] (corresponding author)
0123456789().: V,-vol
The observed GL events are usually from light signals. However, with the observation of supernova neutrinos [20– 23] and gravitational waves (GWs) [24–28], the astronomical observation entered the multimessenger era. Consequently, the time delays of neutrino and GW signals can be viewed as important supplements to time delay of light signals. Compared with time delay of light signals alone, the difference between time delays of light and neutrinos or light and GW signals can provide stronger constraints on the cosmology parameters [29–31]. In addition, the time delay of these signals can determine the properties of test particles like mass ordering of neutrinos and velocity of GW [31–33]. Although it is known that neutrinos as well as GWs in some gravitational theories beyond General Relativi
Data Loading...
