The first direct detection of gravitational waves (GW) by the ground-based interferometers is expected to occur within the next few years. These interferometers will detect the mergers of compact object binaries composed of neutron stars and/or black
holes to a fiducial distance of ~200 Mpc and a localization region of ~100 sq. deg. To maximize the science gains from such GW detections it is essential to identify electromagnetic (EM) counterparts. The most promising such counterpart is optical/IR emission powered by the radioactive decay of r-process elements synthesized in the neutron-rich merger ejecta - a kilonova. Here we present detailed simulated observations that encompass a range of strategies for kilonova searches during GW follow-up. We assess both the detectability of kilonovae and our ability to distinguish them from a wide range of contaminating transients. We find that if pre-existing template images for the localization region are available, then nightly observations to a depth of i=24 mag and z=23 mag are required to achieve a 95% detection rate; observations that commence within 12 hours of trigger will also capture the kilonova peak and provide stronger constraints on the ejecta properties. We also find that kilonovae can be robustly separated from other types of transients utilizing cuts on color (i-z > 0 mag) and rise time (< 4 days). In the absence of a pre-existing template the observations must reach ~1 mag deeper to achieve the same kilonova detection rate, but robust rejection of contaminants can still be achieved. Motivated by the results of our simulations we discuss the expected performance of current and future wide-field telescopes in achieving these observational goals, and find that prior to LSST the Dark Energy Camera on the Blanco 4-m telescope and Hyper Suprime-Cam on the Subaru 8-m telescope offer the best kilonova discovery potential.
We present a non-linear numerical model for a geometrically thin accretion disk with the addition of stochastic non-linear fluctuations in the viscous parameter. These numerical realizations attempt to study the stochastic effects on the disk angular
momentum transport. We show that this simple model is capable of reproducing several observed phenomenologies of accretion driven systems. The most notable of these is the observed linear rms-flux relationship in the disk luminosity. This feature is not formally captured by the linearized disk equations used in previous work. A Fourier analysis of the dissipation and mass accretion rates across disk radii show coherence for frequencies below the local viscous frequency. This is consistent with the coherence behavior observed in astrophysical sources such as Cygnus X-1.
The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160 ks of Suzaku data taken in 2006, previously examined by Kataoka et al. (2007). Spectral fi
ts to the XIS and HXD/PIN data over a range of 0.7-45 keV reveal a well-defined iron K line complex with a narrow Ka core and relativistically broadened features consistent with emission from the inner regions of the accretion disk. Furthermore, the inner region of the disk appears to be truncated with an inner radius of r_in = 11.7^{+3.5}_{-5.2} r_g. If we assume that fluorescent iron line features terminate at the inner-most stable circular orbit (ISCO), we measure a black hole spin of a < -0.1 at a 90% confidence level. A rapidly spinning prograde black hole (a > 0.8) can be ruled out at the 99% confidence level. Alternatively, the disk may be truncated well outside of the ISCO of a rapid prograde hole. The most compelling scenario is the possibility that the inner regions of the disk were destroyed/ejected by catastrophic instabilities just prior to the time these observations were made.
