We report measurements of the mass density, Omega_M, and
cosmological-constant energy density, Omega_Lambda, of the universe based on
the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology
Project. The magnitude-redshift data for these SNe, at redshifts between 0.18
and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova
Survey, at redshifts below 0.1, to yield values for the cosmological
parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve
width-luminosity relation. The measurement yields a joint probability
distribution of the cosmological parameters that is approximated by the
relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of
interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we
find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04}
(identified systematics). The data are strongly inconsistent with a Lambda = 0
flat cosmology, the simplest inflationary universe model. An open, Lambda = 0
cosmology also does not fit the data well: the data indicate that the
cosmological constant is non-zero and positive, with a confidence of P(Lambda >
0) = 99%, including the identified systematic uncertainties. The best-fit age
of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h)
Gyr for a flat cosmology. The size of our sample allows us to perform a variety
of statistical tests to check for possible systematic errors and biases. We
find no significant differences in either the host reddening distribution or
Malmquist bias between the low-redshift Calan/Tololo sample and our
high-redshift sample. The conclusions are robust whether or not a
width-luminosity relation is used to standardize the SN peak magnitudes.

/pdf/measurements-of-omega-and-lambda-from-42-high-redshift-z1htxv5kgf.pdf

Measurements of Omega and Lambda from 42 High-Redshift Supernovae

The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous high-resolution full-disk images of the corona and transition region up to 0.5 R ⊙ above the solar limb with 1.5-arcsec spatial resolution and 12-second temporal resolution. The AIA consists of four telescopes that employ normal-incidence, multilayer-coated optics to provide narrow-band imaging of seven extreme ultraviolet (EUV) band passes centered on specific lines: Fe xviii (94 A), Fe viii, xxi (131 A), Fe ix (171 A), Fe xii, xxiv (193 A), Fe xiv (211 A), He ii (304 A), and Fe xvi (335 A). One telescope observes C iv (near 1600 A) and the nearby continuum (1700 A) and has a filter that observes in the visible to enable coalignment with images from other telescopes. The temperature diagnostics of the EUV emissions cover the range from 6×104 K to 2×107 K. The AIA was launched as a part of NASA’s Solar Dynamics Observatory (SDO) mission on 11 February 2010. AIA will advance our understanding of the mechanisms of solar variability and of how the Sun’s energy is stored and released into the heliosphere and geospace.

/pdf/the-atmospheric-imaging-assembly-aia-on-the-solar-dynamics-22pv2dupqt.pdf

The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO)

Many physically motivated extensions to general relativity (GR) predict significant deviations at energies present in massive neutron stars. We report the measurement of a 2.01 $\pm $ 0.04 solar mass (M$_\odot $) pulsar in a 2.46-h orbit around a 0.172 $\pm $ 0.003 M$_\odot $ white dwarf. The high pulsar mass and the compact orbit make this system a sensitive laboratory of a previously untested strong-field gravity regime. Thus far, the observed orbital decay agrees with GR, supporting its validity even for the extreme conditions present in the system. The resulting constraints on deviations support the use of GR-based templates for ground-based gravitational wave detection experiments. Additionally, the system strengthens recent constraints on the properties of dense matter and provides novel insight to binary stellar astrophysics and pulsar recycling.

/pdf/a-massive-pulsar-in-a-compact-relativistic-binary-4fslj44n2n.pdf

A massive pulsar in a compact relativistic binary

On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is $5.0\times {10}^{-8}$. We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of $(+1.74\pm 0.05)\,{\rm{s}}$ between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between $-3\times {10}^{-15}$ and $+7\times {10}^{-16}$ times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1–1.4 per year during the 2018–2019 observing run and 0.3–1.7 per year at design sensitivity.

/pdf/gravitational-waves-and-gamma-rays-from-a-binary-neutron-pp53mlzg1t.pdf

Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A

The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy. LIGO will support studies concerning the nature and nonlinear dynamics of gravity, the structures of black holes, and the equation of state of nuclear matter. It will also measure the masses, birth rates, collisions, and distributions of black holes and neutron stars in the universe and probe the cores of supernovae and the very early universe. The technology for LIGO has been developed during the past 20 years. Construction will begin in 1992, and under the present schedule, LIGO's gravitational-wave searches will begin in 1998.

/pdf/ligo-the-laser-interferometer-gravitational-wave-observatory-1ru47xyhtr.pdf

LIGO: The Laser Interferometer Gravitational-Wave Observatory.

Recent gamma-ray observations show that middle aged supernova remnants (SNRs) interacting with molecular clouds (MCs) can be sources of both GeV and TeV emission. Based on the MC association, two scenarios have been proposed to explain the observed gamma-ray emission. In one, energetic cosmic ray (CR) particles escape from the SNR and then illuminate nearby MCs, producing gamma-ray emission, while the other involves direct interaction between the SNR and MC. In the direct interaction scenario, re-acceleration of pre-existing CRs in the ambient medium is investigated while particles injected from the thermal pool are neglected in view of the slow shock speeds in middle aged SNRs. However, standard diffusive shock acceleration (DSA) theory produces a steady state particle spectrum that is too flat compared to observations, which suggests that the high energy part of the observed spectrum has not yet reached a steady state. We derive a time dependent DSA solution in the test particle limit for re-acceleration of pre-existing CRs case and show that it is capable of reproducing the observed gamma-ray emission in SNRs like IC 443 and W44, in the context of a MC interaction model. We also provide a simple physical picture to understand the time dependent DSA spectrum. A spatially averaged diffusion coefficient around the SNR can be estimated through fitting the gamma-ray spectrum. The spatially averaged diffusion coefficient in middle aged SNRs like IC 443 and W44 is estimated to be ~ 10^25 cm^2/s at ~ 1GeV, which is between the Bohm limit and interstellar value.

Time dependent diffusive shock acceleration and its application to middle aged supernova remnants

The association of long gamma-ray bursts (GRBs) with Type Ib/c supernovae implies that they explode into the winds of their Wolf-Rayet progenitor stars. Although the evolution of some GRB afterglows is consistent with expansion into a free wind, there is also good evidence for expansion into a constant density medium. The evidence includes the evolution of X-ray afterglows (when X-rays are below the cooling frequency), the evolution of the pre-jet break optical and X-ray afterglow, and the sharp turn-on observed for some afterglows. Recent observations of short bursts, which are expected to be interacting with a constant density medium, provide a check on the standard afterglow model. Although radio observations do not support the constant density model for long bursts in some cases, the evidence for constant density interaction is strong. The most plausible way to produce such a medium around a massive star is to shock the progenitor wind. This requires a smaller termination shock than would be expected, possibly due to a high pressure surroundings, a high progenitor velocity, or the particular evolution leading to a GRB. However, the need for the termination shock near the deceleration radius cannot be plausibly accomodated and may indicate that some long bursts have compact binary progenitors and explode directly into the interstellar medium.

What Gamma-Ray Bursts Explode Into

Young supernova remnants that contain pulsar wind nebulae provide diagnostics for both the inner part of the supernova and the interaction with the surrounding medium, providing an opportunity to relate these objects to supernova types. Among observed young nebulae, there is evidence for a range of supernova types, including Type IIP (Crab Nebula and SN 1054) and Type IIb/IIn/IIL (G292.0+1.8).

Pulsar Wind Nebulae and Their Supernovae

A plausible model for the Crab Nebula is one in which a particle dominated, highly relativistic wind from the pulsar passes through a shock front in which the particles attain a power law energy distribution. The electrons and positrons lose energy radiating synchrotron emission. Here, a one zone version of the model is developed and applied to observations of X-ray pulsar nebulae. Efficient conversion of pulsar spin-down power to X-ray luminosity is expected if the observed electrons are in the synchrotron cooling regime and their energy spectrum is similar to that in the Crab Nebula. In this case, the relation between X-ray luminosity and pulsar spin-down power depends only weakly on the model parameters. The dependence is stronger for a steeper particle spectrum, as appears to be present in N157B, and the efficiency of X-ray production can be lower. If the electrons are not in the cooling regime, the X-ray luminosity can be low, as appears to be the case for the compact nebula around the Vela pulsar. Slow cooling is likely to be caused by a sub-equipartition magnetic field in the radiating region. Observations can place constraints on the uncertain physics of relativistic MHD shocks. The model is related to those developed for gamma-ray burst afterglows.

Implications of the X-Ray Properties of Pulsar Nebulae

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Papers

Time dependent diffusive shock acceleration and its application to middle aged supernova remnants

What Gamma-Ray Bursts Explode Into

Pulsar Wind Nebulae and Their Supernovae

Time dependent diffusive shock acceleration and its application to middle aged supernova remnants

Implications of the X-Ray Properties of Pulsar Nebulae