Core-collapse supernova science is now entering an era in which engine models are beginning to make both qualitative and, in some cases, quantitative predictions. Although the evidence in support of ...the convective engine for core-collapse supernova continues to grow, it is difficult to place quantitative constraints on this engine. Some studies have made specific predictions for the remnant distribution from the convective engine, but the results differ between different groups. Here we use a broad parameterization for the supernova engine to understand the differences between distinct studies. With this broader set of models, we place error bars on the remnant mass and basic yields from the uncertainties in the explosive engine. We find that, even with only three progenitors and a narrow range of explosion energies, we can produce a wide range of remnant masses and nucleosynthetic yields.
Abstract
The Very Large Array Sky Survey (VLASS) is observing the entire sky north of −40° in the
S
band (2 GHz <
ν
< 4 GHz), with the highest angular resolution (2.″5) of any all-sky radio continuum ...survey to date. VLASS will cover its entire footprint over three distinct epochs, the first of which has now been observed in full. Based on
Quick Look
images from this first epoch, we have created a catalog of 1.9 × 10
6
reliably detected radio components. Due to the limitations of the
Quick Look
images, component flux densities are underestimated by ∼15% at
S
peak
> 3 mJy beam
−1
and are often unreliable for fainter components. We use this catalog to perform statistical analyses of the
ν
∼ 3 GHz radio sky. Comparisons with the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey show the typical 1.4–3 GHz spectral index,
α
, to be ∼−0.71. The radio color–color distribution of point and extended components is explored by matching with FIRST and the LOFAR Two-meter Sky Survey. We present the VLASS source counts,
dN
/
dS
, which are found to be consistent with previous observations at 1.4 and 3 GHz. Resolution improvements over FIRST result in excess power in the VLASS two-point correlation function at angular scales ≲7″, and in 18% of active galactic nuclei associated with a single FIRST component being split into multicomponent sources by VLASS.
Abstract
Type Ia supernovae (SNe) are believed to be caused by the thermonuclear explosion of a white dwarf (WD), but the nature of the progenitor system(s) is still unclear. Recent theoretical and ...observational developments have led to renewed interest in double-degenerate models, in particular the “helium-ignited violent merger” or “dynamically driven double-degenerate double-detonation” (D
6
). In this paper we take the output of an existing D
6
SN model and carry it into the supernova remnant (SNR) phase up to 4000 yr after the explosion, past the time when all the ejecta have been shocked. Assuming a uniform ambient medium, we reveal specific signatures of the explosion mechanism and spatial variations intrinsic to the ejecta. The first detonation produces an ejecta tail visible at early times, while the second detonation leaves a central density peak in the ejecta that is visible at late times. The SNR shell is off-center at all times, because of an initial velocity shift due to binary motion. The companion WD produces a large conical shadow in the ejecta, visible in projection as a dark patch surrounded by a bright ring. This is a clear and long-lasting feature that is localized, and its impact on the observed morphology is dependent on the viewing angle of the SNR. These results offer a new way to diagnose the explosion mechanism and progenitor system using observations of a Type Ia SNR.
We present a Chandra Director's Discretionary Time observation of PSR J1119-6127 and its compact X-ray pulsar wind nebula (PWN) obtained on 2016 October 27, three months after the Fermi and Swift ...detection of millisecond bursts in hard X-rays, accompanied by a 160 times increase in flux. This magnetar-like activity, the first observed from a rotation-powered radio pulsar, provides an important probe of the physical processes that differentiate radio pulsars from magnetars. The post-burst X-ray spectrum of the pulsar can be described by a single power-law model with a photon index of 2.0 0.2 and an unabsorbed flux of 10−12 erg cm−2 s−1 in the 0.5-7.0 keV energy range. At the time of Chandra observations, the pulsar was still brighter by a factor of ∼22 in comparison with its quiescence. The X-ray images reveal a nebula brighter than in the pre-burst Chandra observations (from 2002 and 2004), with an unabsorbed flux of 10−13 erg cm−2 s−1. This implies a current X-ray efficiency of at a distance of 8.4 kpc. In addition, a faint torus-like structure is visible along the southeast-northwest direction and a jet-like feature perpendicular to the torus toward the southwest. The PWN is best fitted by an absorbed power-law with a photon index of 2.2 0.5 (post-burst). While the pulsar can still be energetically powered by rotation, the observed changes in PSR J1119-6127 and its PWN following the magnetar-like bursts point to an additional source of energy powered by its high magnetic field.
The core of the dead star becomes a pulsar - a rapidly rotating, highly magnetized pulsating star the size of a city, which spews out a wind of fast-moving, electrically charged particles. In the ...past two decades, NASA's Chandra X-ray Observatory has enabled close-up views of their nebulae5, but direct imaging of the magnetic fields responsible for their high-energy radiation has not been possible. Astronomers had previously imaged magnetic fields in astronomical sources using radio and optical telescopes, but these types of radiation are subject to rotation effects and absorption by dust, respectively, both of which hinder observation. By contrast, X-ray polarization offers a direct probe of the geometry of the magnetic field in the acceleration zone, where the pulsar dumps its particle wind and emits high-energy radiation.
We present a wide-field optical imaging search for electromagnetic counterparts to the likely neutron star-black hole (NS-BH) merger GW190814/S190814bv. This compact binary merger was detected ...through gravitational waves by the LIGO/Virgo interferometers, with masses suggestive of an NS-BH merger. We imaged the LIGO/Virgo localization region using the MegaCam instrument on the Canada-France-Hawaii Telescope (CFHT). We describe our hybrid observing strategy of both tiling and galaxy-targeted observations, as well as our image differencing and transient detection pipeline. Our observing campaign produced some of the deepest multiband images of the region between 1.7 and 8.7 days post-merger, reaching a 5 depth of g > 22.8 (AB mag) at 1.7 days and i > 23.1 and i > 23.9 at 3.7 and 8.7 days, respectively. These observations cover a mean total integrated probability of 67.0% of the localization region. We find no compelling candidate transient counterparts to this merger in our images, which suggests that the lighter object was tidally disrupted inside of the BH's innermost stable circular orbit, the transient lies outside of the observed sky footprint, or the lighter object is a low-mass BH. We use 5 source detection upper limits from our images in the NS-BH interpretation of this merger to constrain the mass of the kilonova ejecta to be Mej 0. 015M for a "blue" ( ) kilonova and Mej 0. 04M for a "red" ( ) kilonova. Our observations emphasize the key role of large-aperture telescopes and wide-field imagers such as CFHT MegaCam in enabling deep searches for electromagnetic counterparts to gravitational-wave events.
Abstract
We present a detailed analysis of broadband X-ray observations of the pulsar PSR J1420−6048 and its wind nebula (PWN) in the Kookaburra region with Chandra, XMM-Newton, and NuSTAR. Using the ...archival XMM-Newton and new NuSTAR data, we detected 68 ms pulsations of the pulsar and characterized its X-ray pulse profile, which exhibits a sharp spike and a broad bump separated by ∼0.5 in phase. A high-resolution Chandra image revealed a complex morphology of the PWN: a torus-jet structure, a few knots around the torus, one long (∼7′) and two short tails extending in the northwest direction, and a bright diffuse emission region to the south. Spatially integrated Chandra and NuSTAR spectra of the PWN out to 2.′5 are well-described by a power-law model with a photon index Γ ≈ 2. A spatially resolved spectroscopic study, as well as NuSTAR radial profiles of the 3–7 keV and 7–20 keV brightness, showed a hint of spectral softening with increasing distance from the pulsar. A multiwavelength spectral energy distribution (SED) of the source was then obtained by supplementing our X-ray measurements with published radio, Fermi-LAT, and H.E.S.S. data. The SED and radial variations of the X-ray spectrum were fit with a leptonic multizone emission model. Our detailed study of the PWN may be suggestive of (1) particle transport dominated by advection, (2) a low magnetic-field strength (
B
∼ 5
μ
G), and (3) electron acceleration to ∼PeV energies.
Abstract HESS J1641−463 is an unidentified gamma-ray source with a hard TeV gamma-ray spectrum, and thus it has been proposed to be a possible candidate for a cosmic-ray (CR) accelerator up to PeV ...energies (a PeVatron candidate). The source spatially coincides with the radio supernova remnant G338.5+0.1 but has not yet been fully explored in the X-ray band. We analyzed newly taken NuSTAR data, pointing at HESS J1641−463, with 82 ks effective exposure time. There is no apparent X-ray counterpart of HESS J1641−463, while nearby stellar cluster, Mercer 81, and stray-light X-rays are detected. Combined with the archival Chandra data, partially covering the source, we derived an upper limit of ∼6 × 10 −13 erg cm −2 s −1 in 2–10 keV (∼3 × 10 −13 erg cm −2 s −1 in 10–20 keV). If the gamma-ray emission is originated from the decay of π 0 mesons produced in interactions between CR protons and ambient materials, secondary electrons in the proton–proton interactions can potentially emit synchrotron photons in the X-ray band, which can be tested by our X-ray observations. Although the obtained X-ray upper limits cannot place a constraint on the primary proton spectrum, it will be possible with a future hard X-ray mission.
We present the first public database of high-energy observations of all known Galactic supernova remnants (SNRs). In Section 1 we introduce the rationale for this work motivated primarily by studying ...particle acceleration in SNRs, and which aims at bridging the already existing census of Galactic SNRs (primarily made at radio wavelengths) with the ever-growing but diverse observations of these objects at high-energies (in the X-ray and γ-ray regimes). In Section 2 we show how users can browse the database using a dedicated web front–end (http://www.physics.umanitoba.ca/snr/SNRcat). In Section 3 we give some basic statistics about the records we have collected so far, which provides a summary of our current view of Galactic SNRs. Finally, in Section 4, we discuss some possible extensions of this work. We believe that this catalogue will be useful to both observers and theorists, and timely with the synergy in radio/high-energy SNR studies as well as the upcoming new high-energy missions. A feedback form provided on the website will allow users to provide comments or input, thus helping us keep the database up-to-date with the latest observations.
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