Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session Y8: Supernovae and Gamma Ray Bursts II |
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Sponsoring Units: DAP Chair: Shunsaku Joriuchi, University of California, Irvine Room: 202 |
Tuesday, April 8, 2014 1:30PM - 1:42PM |
Y8.00001: Computational Study of White Dwarf Stars Jose Pacheco, Ajit Hira, Danelle Jaramillo We begin our interest in the computational simulation of the astrophysical phenomena with a study of white dwarf stars. Of particular interest to astrophysicists are the conditions inside a white dwarf star in the time frame leading up to its explosive end as a Type Ia supernova, for an understanding of the massive stellar explosions. In addition, the studies of the evolution of white dwarfs could serve as promising probes of theories of gravitation. First, we set up the equations of equilibrium for the star of interest. Then we derived the appropriate equation of state. Next, a FORTRAN computer program was developed to implement our model for white dwarfs. This code allows for different sizes and masses of stars. Simulations were done in the mass interval from 0.4 to 0.8 solar masses. Our goal was to obtain both atmospheric and orbital parameters. The computational results thus obtained are compared with relevant observational data. The data are further analyzed to identify trends in terms of sizes and masses of stars. We hope to extend our computational studies to red giant stars in the future. [Preview Abstract] |
Tuesday, April 8, 2014 1:42PM - 1:54PM |
Y8.00002: Nuclear Mixing Meters for Classical Novae K.J. Kelly, C. Iliadis, L.N. Downen, A.E. Champagne, J. Jos\'{e} Mass transfer from a main sequence star onto a white dwarf partner can lead to a thermonuclear runaway (TNR) followed by a violent mass expulsion episode known as a classical nova. Characteristics of novae depend upon evolutionary parameters such as the composition of matter undergoing the TNR and observations suggest mixing between accreted material (presumed to be of solar composition) and the underlying white dwarf prior to the TNR. Using results of models of oxygen-neon novae, the elemental abundance \emph{ratios} $\Sigma$CNO/H, Ne/H, Mg/H, Al/H, and Si/H are found to be indicators of this mixing. The impact of nuclear physics uncertainties on these results was investigated through Monte Carlo post-processing calculations using T-$\rho$ profiles for all mass zones as computed by the hydrodynamic models. Although $^{30}$P($p$,$\gamma$)$^{31}$S significantly affects the Si/H abundance ratio, overall the mixing meters are found to be robust against nuclear physics uncertainties. A comparison of our results with observations provides strong constraints for nova models. [Preview Abstract] |
Tuesday, April 8, 2014 1:54PM - 2:06PM |
Y8.00003: Visible and Near-infrared Light Curves of SN 2009nr Jonathan Heath, Ginger Bryngelson This study explores the behavior of SN 2009nr, an apparently normal type Ia supernova (SN Ia). A plot of this object's brightness over time is known as a light curve. Because of the uniformity of their light curves, SNe Ia are valuable markers for determining the expansion of the universe and other cosmological parameters. Understanding the properties of these supernovae is vital in order to build our confidence in their use as standard candles. A small, but increasing number of SN Ia late-time observations have been made in the near-infrared (NIR). Most exhibit a flattening of the NIR power even as the visible light declines at a steady rate. It is still unclear as to why they exhibit this behavior and how typical this is. In order to characterize the late behavior of SNe Ia, images of SN 2009nr were analyzed using the Image Reduction and Analysis Facility (IRAF). NIR (J, H, K) images were taken with the 4m Mayall Telescope at Kitt Peak National-Observatory using the FLAMINGOS IR Imaging Spectrometer while visible (B, V, R, I) images used the Mosaic 1 imager. The supernova's apparent magnitude for each night of observation (by filter) was found by using reference stars. We present preliminary light curves of SN 2009nr and a comparison to another SN observed at similar epochs. [Preview Abstract] |
Tuesday, April 8, 2014 2:06PM - 2:18PM |
Y8.00004: The Power of Thermonuclear Supernovae at Late Epochs Ginger Bryngelson, Peter Milne, Mark Leising Type Ia supernovae (SNe Ia) shape our understanding of the expansion of the universe in their use as distance indicators. Thought to be the runaway thermonuclear explosion of a white dwarf star in a binary system, SNe Ia are bright enough to be seen in far-way galaxies. Their brightness fades slowly over hundreds of days, powered by radioactive isotopes synthesized in the explosion. At some point after 200 days, the continually expanding ejecta is diffuse enough to allow gamma-rays to escape, and soon the brightness of the SN is only powered by positrons trapped by the SN's magnetic field. Only a handful of SNe Ia have been observed during epochs later than 200 days after explosion in both visible and near-infrared light. We discuss our observations of multiple SNe Ia which exploded in nearby galaxies. These were bright enough to be observed out to late epochs (about 525 days post peak). Their brightness was monitored over time in visible light (B,V,R,I bands) and near-infrared (J,H,K) bands, and light curves were constructed. We convert these observations to luminosity and compare them to a simple positron deposition model to estimate the feasibility of positron escape. [Preview Abstract] |
Tuesday, April 8, 2014 2:18PM - 2:30PM |
Y8.00005: On the similarities of the prompt gamma-ray emissions in Short and Long Gamma-Ray Busts Amir Shahmoradi Gamma-Ray Bursts (GRBs) are intense short pulses of low-energy (keV-MeV) gamma rays -- the so-called ``prompt emission'' -- followed by afterglow radiation in X-ray, optical, infrared or radio wavelengths. Extensive evidence has been accumulated over the past two decades pointing to at least two separate classes of Long and Short GRBs with different progenitors: death of supermassive stars and compact object binary mergers respectively. Despite having different progenitors, here I show that the prompt gamma-ray emissions from both classes of GRBs exhibit highly similar features and correlations, possibly indicating a unified mechanism for the generation of the observed correlations among the gamma-ray spectral and temporal parameters of both classes of GRBs. I highlight similar correlations that are also observed in Blazars' spectral energy distributions (SED) and discuss the potential effects of observational biases on these relations and their implications for the theoretical models of GRB prompt emission. [Preview Abstract] |
Tuesday, April 8, 2014 2:30PM - 2:42PM |
Y8.00006: Observing gamma-ray bursts with the scaler system of the HAWC Observatory Dirk Lennarz, Ignacio Taboada The origin and acceleration mechanisms of gamma-ray bursts (GRBs) are important questions in contemporary astrophysics. Several models are competing to explain the recent observations at higher energies (HE, above $\sim$ 20~MeV). The detection and temporal evolution of GRB emission at the highest energies ($\agt$ 10~GeV) would have important implications for the GRB physics. The High Altitude Water Cherenkov (HAWC) observatory is a new very-high-energy (VHE, $>100$~GeV) gamma-ray detector currently under construction at Sierra Negra in Mexico at an altitude of 4100 m above sea level. Unlike Imaging Atmospheric Cherenkov Telescopes, it has a large field of view and near 100\% duty cycle that will allow for observations of the prompt GRB phase. HAWC has two data acquisition (DAQ) systems - one reading out full air-shower events (TDC-DAQ) and the other one counting the hits in each photomultiplier tube (scaler DAQ). GRB~130427A was the most energetic GRB so far detected at a redshift $z<0.5$. It featured an unprecedented long high-energy emission and the most energetic photon so far detected from a GRB. In this contribution the results of the scaler analysis of GRB~130427A and other GRBs of interest are shown. [Preview Abstract] |
Tuesday, April 8, 2014 2:42PM - 2:54PM |
Y8.00007: A Search for VHE Emission from GRBs using the HAWC Observatory Air Shower Data Kathryne Sparks Woodle At an altitude of 4100 m near the peak of Sierra Negra in Mexico, the High Altitude Water Cherenkov Observatory (HAWC) is a second generation water Cherenkov detector that primarily looks for very high-energy gamma-rays from the galaxy and beyond. Due to its wide field of view ($\sim$2 sr) and high duty cycle, this extensive air shower detector can observe the beginning of the prompt phase of GRBs occurring overhead. HAWC is sensitive to showers in the sub-TeV to TeV energy range and will be able to help constrain the shape and cutoff of high-energy GRB spectra, especially in conjunction with observations from other detectors such as Fermi. With the design improvement and higher elevation than its predecessor Milagro, HAWC will be almost two orders of magnitude more sensitive to GRBs at 100 GeV when complete. Existing instruments identify about 5 GRBs within HAWC's field of view per month. The detector has been operated throughout construction, and we will present a search for high-energy emission from GRBs, triggered by existing instruments, using HAWC directional air shower data. [Preview Abstract] |
Tuesday, April 8, 2014 2:54PM - 3:06PM |
Y8.00008: Catching Fermi GBM Gamma-Ray Burst afterglows Adam Goldstein, Valerie Connaughton The Fermi Gamma-Ray Burst Monitor (GBM) detects over 240 Gamma-Ray Bursts (GRBs) per year and is the most prolific detector of short GRBs (lasting less than 2 s). Short GRBs are believed to originate from mergers of compact objects (neutron stars and black holes), which in turn are the most likely expected source of gravitational wave (GW) radiation detectable by the next-generation GW detectors, Advanced-LIGO and VIRGO. Observing the electromagnetic counterparts of GW candidates is very important in order to strengthen the significance of the GW detection and to establish the energetics of the merger event. Neither GBM nor the GW detectors can localize the merger to the sub-degree accuracy on the sky needed to measure the redshift of the event using optical telescopes. Follow-up observations of short GRBs with GBM require a knowledge of the GBM localization uncertainties and a strategy to tile the uncertainty region with the optical follow-up telescopes. The GBM team has recently characterized the systematic uncertainties on GRB localization and is starting to distribute probability maps that allow efficient covering of the uncertainty regions to any confidence level. The intermediate Palomar Transient Factory (iPTF) and other ground-based telescopes are using these new products to uncover the afterglows for GBM-detected GRBs in error boxes covering several tens of square degrees on the sky. This is encouraging for the development of strategies to observe the error boxes of short GRBs detected by GBM in the Advanced-LIGO/VIRGO era beginning in 2015-2016. [Preview Abstract] |
Tuesday, April 8, 2014 3:06PM - 3:18PM |
Y8.00009: Search For Correlation Between Known GRBs and Astrophysical Neutrinos As Observed By IceCube James Casey, Ignacio Taboada Gamma-Ray Bursts (GRBs) have long been proposed as the sources of UHE cosmic rays. In many GRB models, high-energy neutrinos are predicted to be generated during various phases of the burst. The IceCube collaboration has reported the observation of 28 high-energy neutrinos which includes an astrophysical component. The sources of these events, however, have yet to be determined. We examine the temporal and directional correlations between the 28 events and 568 GRBs reported from May 2010 to May 2012 and find that there is no correlation between the neutrino events and the GRBs. We set an upper limit on the fraction of the astrophysical signal reported by IceCube that can be attributed to known GRBs. For correlations times up to $\sim$20~hours, the 90\% C.L. upper limit on the fraction of the astrophysical neutrino flux that can be due to known GRBs is 14\%. For correlations times of up to 15 days, this upper limit is 36\%. [Preview Abstract] |
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