Stripped-envelope supernova light curves argue for central engine activity.

The luminosity of stripped-envelope supernovae, a common type of stellar explosion, is believed to be mainly driven by the radioactive decay of the nickel synthesized in the explosion and carried in its ejecta. Additional possible energy sources have been previously suggested, in which the two most observationally based results have been from a comparison of the observed time-weighted luminosity with the inferred radioactive power and from a comparison of the light curves with particular theoretical models. However, the former result was not statistically significant, and the latter is highly dependent on the specific models assumed.

Spherical symmetry in the kilonova AT2017gfo/GW170817.

The mergers of neutron stars expel a heavy-element enriched fireball that can be observed as a kilonova. The kilonova's geometry is a key diagnostic of the merger and is dictated by the properties of ultra-dense matter and the energetics of the collapse to a black hole. Current hydrodynamical merger models typically show aspherical ejecta.

Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star.

Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining.

The long, the short and the weak: the origin of gamma-ray bursts.

The origin of gamma-ray bursts (GRBs) is one of the most interesting puzzles in recent astronomy. During the last decade a consensus has formed that long GRBs (LGRBs) arise from the collapse of massive stars, and that short GRBs (SGRBs) have a different origin, most likely neutron star mergers. A key ingredient of the collapsar model that explains how the collapse of massive stars produces a GRB is the emergence of a relativistic jet that penetrates the stellar envelope.

Detectable radio flares following gravitational waves from mergers of binary neutron stars.

Mergers of neutron-star/neutron-star binaries are strong sources of gravitational waves. They can also launch subrelativistic and mildly relativistic outflows and are often assumed to be the sources of short γ-ray bursts. An electromagnetic signature that persisted for weeks to months after the event would strengthen any future claim of a detection of gravitational waves.

Inhomogeneity in cosmic ray sources as the origin of the electron spectrum and the PAMELA anomaly.

We show that inhomogeneity of cosmic ray (CR) sources, due to the concentration of supernova remnants (SNRs) towards the galactic spiral arms, can naturally explain the anomalous increase in the positron/electron ratio observed by PAMELA. We consistently recover the observed positron fraction between 1 and 100 GeV using SNRs as the sole source of CRs. The contribution of a few known nearby SNRs dominates the CR electron spectrum above approximately 100 GeV, leading to the relatively flat spectrum observed by Fermi and to the sharp cutoff observed by H.

Survival probabilities in time-dependent random walks.

We analyze the dynamics of random walks in which the jumping probabilities are periodic time-dependent functions. In particular, we determine the survival probability of biased walkers who are drifted towards an absorbing boundary. The typical lifetime of the walkers is found to decrease with an increment in the oscillation amplitude of the jumping probabilities.

Evolutionary minority game: the roles of response time and mutation threshold.

In the evolutionary minority game, agents are allowed to evolve their strategies ("mutate") based on past experience. We explore the dependence of the system's global behavior on the response time and the mutation threshold of the agents. We find that the precise values of these parameters determine if the strategy distribution of the population has a U shape, inverse U shape, or W shape.

Strategy updating rules and strategy distributions in dynamical multiagent systems.

In the evolutionary version of the minority game, agents update their strategies (gene value p) in order to improve their performance. Motivated by the recent intriguing results obtained for prize-to-fine ratios, which are smaller than unity, we explore the system's dynamics with a strategy updating rule of the form p-->p+/-delta(p) (0 View Article and Find Full Text PDF

Temporal oscillations and phase transitions in the evolutionary minority game.

The study of societies of adaptive agents seeking minority status is an active area of research. Recently, it has been demonstrated that such systems display an intriguing phase transition: agents tend to self-segregate or to cluster according to the value of the prize-to-fine ratio R. We show that such systems do not establish a true stationary distribution.

Self-segregation versus clustering in the evolutionary minority game.

Complex adaptive systems have been the subject of much recent attention. It is by now well established that members ("agents") tend to self-segregate into opposing groups characterized by extreme behavior. However, the study of such adaptive systems has mostly been restricted to simple situations in which the prize-to-fine ratio R equals unity.