Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session M2: GRBs and Other Transients |
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Sponsoring Units: DAP Chair: Sylvia Zhu, University of Maryland Room: Holiday 1 |
Sunday, April 12, 2015 3:30PM - 3:42PM |
M2.00001: An Overview of Recent Fermi-LAT Observations of Gamma-ray Bursts Daniel Kocevski The Fermi Gamma-ray Burst Monitor (GBM) has detected over 1300 gamma-ray bursts (GRBs) in 6 years of operations, with over 80 of these bursts detected by the Fermi Large Area Telescope (LAT) above 40 MeV. These high-energy detections in the Fermi-era have revealed previously undetected features in GRB spectra, including additional power-law components and spectral cut-offs, as well as delayed and long-lived GeV emission. The interpretation of these new features has proven to be a source for vigorous debate within the GRB community. I will review recent Fermi-LAT observations of GRBs, ranging from the detection of the long-lived GRB 130427A, to the broad-band fits of simultanous X-ray and gamma-ray data, as well as the stacking analysis of non-detected bursts. I will discuss what these new observations reveal about the origin of the high-energy emission from GRBs. [Preview Abstract] |
Sunday, April 12, 2015 3:42PM - 3:54PM |
M2.00002: Precursors in gamma-ray bursts detected by the Fermi-LAT and GBM Sylvia Zhu Many aspects of gamma-ray bursts (GRBs) remain mysterious more than 40 years after their initial discovery. However, observations of GRBs by the Fermi Large Area Telescope (LAT) and Gamma-ray Burst Monitor (GBM) have uncovered new information about the observed properties and the underlying physics. In a small minority (roughly 5-20\%), a dim, temporally distinct precursor peak occurs before the brightest part of the prompt emission in the keV-MeV range. The origin of precursors is still unknown, and studies of precursors can probe the formation of the GRB central engine and/or the nature of the jets that produce the emission. We present a systematic search for precursor emission in LAT and GBM data, and the temporal and spectral properties and energetics of the population of GRBs with precursors. [Preview Abstract] |
Sunday, April 12, 2015 3:54PM - 4:06PM |
M2.00003: A Characteristic Value for the BAT / XRT- plateau Flux Ratio in GRB? Demosthenes Kazanas, Judith Racusin, Joseph Sultana, Apostolos Mastichiadis We present the statistics of the ratio, $R$, between the prompt and afterglow ``plateau" fluxes of GRB. This we define as the ratio between the mean prompt energy flux in {\em Swift} BAT and the {\em Swift} XRT one, immediately following the steep transition between these two states and the beginning of the afterglow stage referred to as the ``plateau.'' Like the distribution of many other GRB observables, the histogram of $R$ is log-normal with maximum at a value $R_m \simeq 2,000$, FWHM of about 2 decades and with the entire distribution spanning about 5 decades in the value of $R$. We note that the peak of the distribution is close to the proton-to-electron mass ratio $(R_m \simeq m_p/m_e = 1836)$, as proposed to be the case in an earlier publication, on the basis of a specific model of the GRB dissipation process. It therefore appears that, in addition to the values of the energy of peak luminosity $\mathbf{E_{p}\sim m_{e} c^2}$, GRB present us with one more quantity with an apparent characteristic value. The fact that the values of both these quantities ($E_p$ and $R$) are consistent with the same specific model invoked to account for the efficient conversion of their relativistic proton energies to electrons, argues favorably for its underlying assumptions. [Preview Abstract] |
Sunday, April 12, 2015 4:06PM - 4:18PM |
M2.00004: Constraints on the Source for Gamma-ray bursts from Observed X-Ray Afterglows Grant Mathews, Remo Ruffini X-ray afterglows from long-duration gamma ray bursts (GRBs) are associated with energetic type Ic supernovae and the late time behavior of the afterglow from all GRBs follows the same universal normalization and power-law behavior at late times ($\sim 10^4$ - $10^7$ sec) when plotted relative to the time of the initial GRB trigger. We describe constraints from this afterglow on the engine for GRBs in the context of simple model for X-ray emission from accelerated relativistic electrons within an outgoing relativistic shock. We show that this universal scaling imposes 3 constraints: 1) The shock breakout energy is the same ($\sim 10^{51}$ ergs) for all bursts independently of the observed GRB luminosity; 2) After breakout, the shock propagates through an optically thin low-density ($\sim 1-10$ g cm$^{-3}$ medium; 3) The energy radiated by the shock is a small fraction of the total shock energy. These suggest that the late-time power-law afterglow emission derives from the underlying energetic supernova with a similar total shock energy. The correlation of the of the observed GRB energy with the luminosity of the plateau suggests a GRB engine occurring at different radii within the expanding SN consistent with the induced gravitational collapse paradigm. [Preview Abstract] |
Sunday, April 12, 2015 4:18PM - 4:30PM |
M2.00005: iPTF14yb: The First GRB Discovered Outside the Gamma-Ray Bandpass and the Rate of Orphan Afterglows Stephen Cenko We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, the first unambiguous detection of an afterglow-like transient identified outside the $\gamma$-ray bandpass. Subsequent to our discovery announcement, the ``parent'' $\gamma$-ray burst GRB\,140226A was identified by the InterPlanetary Network of high-energy detectors. We demonstrate an association between iPTF14yb and GRB\,140226A based both on probabilistic arguments and by comparing iPTF14yb with the known population of long GRB afterglows and host galaxies. We furthermore estimate the rate of iPTF14yb-like transients based on iPTF observations, and demonstrate it is consistent with the rate of on-axis long GRBs. Finally, we briefly discuss the implications of the non-detection to date of bona fide ``orphan'' afterglows (i.e., those lacking entirely in high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets. [Preview Abstract] |
Sunday, April 12, 2015 4:30PM - 4:42PM |
M2.00006: Parameter study of r-process lanthanide production and heating rates in kilonovae Jonas Lippuner, Luke F. Roberts \def\h{heating rate}\def\l{lanthanide}\def\u{luminosity}\def\t{the }Explosive r-process nucleosynthesis in material ejected during compact object mergers may lead to radioactively powered transients called kilonovae. The timescale and peak \u\ of these transients are sensitive to \t composition of \t material after nuclear burning ceases, as \t composition determines \t local \h\ from nuclear decays and \t opacity. The presence of \l{s} in \t ejecta can drastically increase \t opacity. We use \t new general-purpose nuclear reaction network SkyNet to run a parameter study of r-process nucleosynthesis for a range of initial electron fractions $Y_e$, initial entropies $s$, and density decay timescales $\tau$. We find that \t ejecta is \l-free for $Y_e\agt0.22-0.3$, depending on $s$ and $\tau$. The \h\ is insensitive to $s$ and $\tau$, but certain, larger values of $Y_e$ lead to reduced \h{s}, because single nuclides dominate \t heating. With a simple model we estimate \t\u, time, and effective temperature at \t peak of \t light curve. Since \t opacity is much lower in \t\l-free case, we find \t\u\ peaks much earlier at $\sim1$ day vs.\ $\sim15$ days in \t\l-rich cases. Although there is significant variation in \t\h\ with $Y_e$, changes in \t\h\ do not mitigate \t effect of \t\l{s}. [Preview Abstract] |
Sunday, April 12, 2015 4:42PM - 4:54PM |
M2.00007: On the search for VHE emission from Fermi LAT Gamma-Ray Bursts with the High Altitude Water Cherenkov Observatory Kathryne Sparks Woodle Gamma-Ray bursts (GRBs) are extremely powerful transient events that occur at cosmological distances. Observations of energy spectra of GRBs can constrain the extra-galactic background light and test Lorentz invariance at high energies as well as provide information about the source itself. The High Altitude Water Cherenkov Observatory (HAWC) is a second-generation extensive air shower detector built near the peak of Sierra Negra in Mexico at an altitude of 4100 m. With its wide field of view ($\sim$2 sr) and high duty cycle, HAWC is sensitive to gamma rays in the sub-TeV to TeV energy range and can constrain the shape and cutoff of high-energy GRB spectra, especially in conjunction with observations from other detectors such as the Fermi LAT satellite. We will present a likelihood-based search for VHE emission from the Fermi LAT GRBs that occurred in the field of view of HAWC from May 2013 to August 2014. [Preview Abstract] |
Sunday, April 12, 2015 4:54PM - 5:06PM |
M2.00008: Self-triggered Search for GRB Emission at $\sim$100 GeV with HAWC Joshua Wood The High Altitude Water Cherenkov (HAWC) Observatory is a ground-based, TeV gamma-ray observatory currently under construction in the state of Puebla, Mexico at an altitude of 4100m. Its 22,000 m$^2$ instrumented area, wide field of view ($\sim$2 sr), and $>$95\% uptime make it an ideal instrument for discovering GRB emission at $\sim$100 GeV energies. Such a discovery would provide key information about the origins of prompt GRB emission as well as constraints on EBL models and Lorentz invariance. We will present prospects for discovering GRB emission at $\sim$100 GeV energies using a simple, blind search algorithm on HAWC data. [Preview Abstract] |
Sunday, April 12, 2015 5:06PM - 5:18PM |
M2.00009: Offline flare searches with HAWC Colas Rivi\`ere Several Galactic and extra-Galactic TeV emitters are known to have time variability. Coincident studies of flaring objects by various instruments at different wavelengths is essential for understanding the involved phenomena. The high duty cycle ($>95\%$) and large instantaneous field-of-view (about two steradians) of the HAWC gamma-ray observatory allows to monitor a large number of sources on multiple time scales. The on-going offline search for flares in existing HAWC data and preliminary results will be presented. [Preview Abstract] |
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