Session M04: Multimessenger Astrophysics and Cataclysmic Events II

Multimessenger astrophysics with neutrinos and gamma rays in the coming decade

The study of the gamma-ray sky has revealed a large population of extreme astrophysical objects capable of emitting electromagnetic radiation up to the highest observable energies, in the PeV range. The discovery of TeV-PeV astrophysical neutrinos by IceCube provides a complementary view of the high-energy sky that, in combination with gamma-ray observations, can address many pressing questions in astrophysics. Some of these include the origin of cosmic rays, the nature of transient sources, and the properties of extreme astrophysical environments. In this talk I will present a summary of recent results is neutrino and gamma-ray astrophysics and discuss what new advances may be enabled by next-generation observatories over the coming decade.   

Detecting gravitational waves from unexpected sources.

The detection of gravitational waves (GWs) from merging binary black holes in 2015 was a pivotal point that gave birth to GW Astronomy. Since then, LIGO and Virgo have observed many binaries, primarily black hole mergers, but also binary neutron stars and neutron star-black hole coalescences. These detections provide new insight into our Universe, and some of these events question our understanding of the Universe. For example, the discovery of an intermediate-mass black hole was unexpected and challenged the current astrophysical models. While we regularly observe binaries, some sources are yet waiting to be discovered. One of them is a core-collapse supernova that is an explosion of a massive star. Astronomers observe them regularly with optical telescopes, but we have not yet observed GWs from them. The searches for such unexpected, unknown, or poorly-modeled sources benefit from methods that use minimal assumptions on the signal morphology, typically referred to as burst methods. In my talk, I will discuss some of the recent discoveries of LIGO and Virgo in the context of burst searches. I will also talk about the prospects for the detection of GWs from a core-collapse supernova.   

Multiresolution Gabor regression of transient gravitational-wave signals.

The analysis of the gravitational-wave transient signals embedded into a non-stationary detector noise requires the identification of time-dependent spectral components in the resulting time series. This talk presents a Gabor regression method where a stack of wavelets with different windows spanning a wide range of resolutions, is used to scan power at each time-frequency location. Such a wavelet scan (or ``wavescan'') extends the conventional multi-resolution analysis to capture the local variations of power due to the temporal and spectral leakage. To achieve the high-resolution localization, a wavelet, least affected by the leakage, is selected from the stack at each time-frequency location. The presented method is used to obtain the high-resolution time-frequency distribution of the signal power, extract signals from noise in the wavelet domain, and reconstruct the corresponding time-domain waveforms. To demonstrate the performance of the method for detection of GW signals, the multiresolution Gabor regression is applied to the analysis of the gravitational wave data from the LIGO detectors.   

A Force Explosion Condition for Spherically Symmetric Core-collapse Supernovae

Understanding which stars explode leaving behind neutron stars and which stars collapse forming black holes remains a fundamental astrophysical problem. We derive an analytic explosion condition for spherically symmetric core-collapse supernovae. The derivation starts with the exact governing equations, considers the balance of integral forces, includes the important dimensionless parameters, and includes an explicit set of self-consistent approximations. The force explosion condition is $\tilde{L}_\nu\tau_g - 0.06 \tilde{\kappa} > 0.38$, and only depends upon two dimensionless parameters. The first compares the neutrino power deposited in the gain region with the accretion power, $\tilde{L}_\nu \tau_g = L_{\nu} \tau_g R_{\rm NS}/ ( G \dot{M} M_{\rm NS})$. The second, $\tilde{\kappa} = \kappa \dot{M} / \sqrt{G M_{\rm NS} R_{\rm NS}}$, parameterizes the neutrino optical depth in the accreted matter near the neutron-star surface.Using numerical, steady-state and fully hydrodynamic solutions, we test the explosion condition. The success of these tests is promising in two ways. One, the force explosion condition helps to illuminate the underlying physics of explosions.Two, this condition may be a useful explosion diagnostic for 3D radiation hydrodynamic core-collapse simulations.   

CSP-II: Near-infrared Spectroscopy of Stripped-Envelope Supernovae

We present 76 NIR spectra of 35 stripped-envelope supernovae obtained by the Carnegie Supernova Project-II, encompassing optical spectroscopic Types IIb, Ib, Ic, and Ic-BL. The spectra range in phase from pre-maximum to 80 days past maximum. This unique data set constitutes the largest NIR spectroscopic sample of SESNe to date. NIR spectroscopy provides observables with additional information compared to observations in the optical. The NIR contains the resonance lines of He I and allows a more detailed look at whether Type Ic supernovae are completely stripped of their outer He layer. The NIR spectra of SESNe have many similarities, but closer examination through statistical means reveals a strong dichotomy between NIR He-rich and He-poor SNe. These NIR subgroups correspond to the optical IIb/Ib and Ic/Ic-BL types, respectively. The largest difference between the two groups is observed in the 2 $\mu$m region, near the He I $\lambda$2.0581 $\mu$m line. The division between the two is not an arbitrary one along a continuous sequence. Early spectra of He-rich SNe show stronger He I $\lambda$2.0581 $\mu$m absorption compared to the He-poor SNe, but with a wide range of profile shapes. This line also provides evidence for trace amounts of He in half of our He-poor SNe.