GW170817 was the first gravitational-wave detection of a binary neutron-star merger. It was accompanied by radiation across the electromagnetic spectrum and localized to the galaxy NGC 4993 at a ...distance of 40 megaparsecs. It has been proposed that the observed γ-ray, X-ray and radio emission is due to an ultra-relativistic jet being launched during the merger (and successfully breaking out of the surrounding material), directed away from our line of sight (off-axis). The presence of such a jet is predicted from models that posit neutron-star mergers as the drivers of short hard-γ-ray bursts. Here we report that the radio light curve of GW170817 has no direct signature of the afterglow of an off-axis jet. Although we cannot completely rule out the existence of a jet directed away from the line of sight, the observed γ-ray emission could not have originated from such a jet. Instead, the radio data require the existence of a mildly relativistic wide-angle outflow moving towards us. This outflow could be the high-velocity tail of the neutron-rich material that was ejected dynamically during the merger, or a cocoon of material that breaks out when a jet launched during the merger transfers its energy to the dynamical ejecta. Because the cocoon model explains the radio light curve of GW170817, as well as the γ-ray and X-ray emission (and possibly also the ultraviolet and optical emission), it is the model that is most consistent with the observational data. Cocoons may be a ubiquitous phenomenon produced in neutron-star mergers, giving rise to a hitherto unidentified population of radio, ultraviolet, X-ray and γ-ray transients in the local Universe.
Context. The astrophysical r-process site where about half of the elements, heavier than iron are produced, has been a puzzle for several decades. Here we discuss the role of one of the leading ideas ...– neutron star mergers (NSMs) – in the light of the first direct detection of such an event in both gravitational (GW) and electromagnetic (EM) waves. Aims. Our aim is to understand the implications of the first GW/EM observations of a NSM for cosmic nucleosynthesis. Methods. We analyse bolometric and NIR lightcurves of the first detected double NSM and compare them to nuclear reaction network-based macronova models. Results. The slope of the bolometric lightcurve is consistent with the radioactive decay of neutron star ejecta with Ye ≲ 0.3 (but not larger), which provides strong evidence for an r-process origin of the electromagnetic emission. This rules out in particular “nickel winds” as major source of the emission. We find that the NIR lightcurves can be well fitted either with or without lanthanide-rich ejecta. Our limits on the ejecta mass together with estimated rates directly confirm earlier purely theoretical or indirect observational conclusions that double neutron star mergers are indeed a major site of cosmic nucleosynthesis. If the ejecta mass was typical, NSMs can easily produce all of the estimated Galactic r-process matter, and – depending on the real rate – potentially even more. This could be a hint that the event ejected a particularly large amount of mass, maybe due to a substantial difference between the component masses. This would be compatible with the mass limits obtained from the GW-observation. Conclusions. The recent observations suggests that NSMs are responsible for a broad range of r-process nuclei and that they are at least a major, but likely the dominant r-process site in the Universe.
The gravitational waves from the first binary neutron star merger, GW170817, were accompanied by a multiwavelength electromagnetic counterpart, from γ-rays to radio. The accompanying γ-rays seem at ...first to confirm the association of mergers with short gamma-ray bursts (sGRBs). The common interpretation was that we see an emission from an sGRB jet seen off-axis. However, a closer examination of the subluminous γ-rays and the peculiar radio afterglow was inconsistent with this simple interpretation. Here we present results of 3D and 2D numerical simulations that follow the hydrodynamics and emission of the outflow from a neutron star merger, form its ejection and up to its deceleration by the circum-merger medium. Our results show that the current set of γ-rays, X-rays, and radio observations can be explained by the emission from a mildly relativistic cocoon material (Lorentz factor ∼2-5) that was formed while a jet propagated through the material ejected during the merger. The γ-rays are generated when the cocoon breaks out from the engulfing ejecta, while the afterglow is produced by interaction of the cocoon matter with the interstellar medium. The strong early UV/optical signal may be a Lorentz-boosted macronova/kilonova. The fate of the jet itself is currently unknown, but our full-electromagnetic (EM) models define a path to resolving between successful and choked jet scenarios, outputting coupled predictions for the image size, morphology, observed time-dependent polarization, and light-curve behavior from radio to X-ray. The predictive power of these models will prove key in interpreting the ongoing multifaceted observations of this unprecedented event.
The optical and optical/near-infrared pseudo-bolometric light curves of 85 stripped-envelope supernovae (SNe) are constructed using a consistent method and a standard cosmology. The light curves are ...analysed to derive temporal characteristics and peak luminosity L
p, enabling the construction of a luminosity function. Subsequently, the mass of 56Ni synthesized in the explosion, along with the ratio of ejecta mass to ejecta kinetic energy, are found. Analysis shows that host-galaxy extinction is an important factor in accurately determining luminosity values as it is significantly greater than Galactic extinction in most cases. It is found that broad-lined SNe Ic (SNe Ic-BL) and gamma-ray burst SNe are the most luminous subtypes with a combined median L
p, in erg s−1, of log(L
p) = 43.00 compared to 42.51 for SNe Ic, 42.50 for SNe Ib, and 42.36 for SNe IIb. It is also found that SNe Ic-BL synthesize approximately twice the amount of 56Ni compared with SNe Ic, Ib, and IIb, with median M
Ni = 0.34, 0.16, 0.14, and 0.11 M⊙, respectively. SNe Ic-BL, and to a lesser extent SNe Ic, typically rise from L
p/2 to L
p more quickly than SNe Ib/IIb; consequently, their light curves are not as broad.
We describe a dynamic science portal called the GROWTH Marshal that allows time-domain astronomers to define science programs; program filters to save sources from different discovery streams; ...coordinate follow-up with various robotic or classical telescopes; analyze the panchromatic follow-up data; and generate summary tables for publication. The GROWTH marshal currently serves 137 scientists, 38 science programs, and 67 telescopes. Every night, in real time, several science programs apply various customized filters to the 105 nightly alerts from the Zwicky Transient Facility. Here, we describe the schematic and explain the functionality of the various components of this international collaborative platform.
A radio counterpart to a neutron star merger Hallinan, G.; Corsi, A.; Mooley, K. P. ...
Science (American Association for the Advancement of Science),
12/2017, Letnik:
358, Številka:
6370
Journal Article
Recenzirano
Odprti dostop
Gravitational waves have been detected from a binary neutron star merger event, GW170817. The detection of electromagnetic radiation from the same source has shown that the merger occurred in the ...outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from Earth. We report the detection of a counterpart radio source that appears 16 days after the event, allowing us to diagnose the energetics and environment of the merger. The observed radio emission can be explained by either a collimated ultrarelativistic jet, viewed off-axis, or a cocoon of mildly relativistic ejecta. Within 100 days of the merger, the radio light curves will enable observers to distinguish between these models, and the angular velocity and geometry of the debris will be directly measurable by very long baseline interferometry.
We report the first plausible optical electromagnetic counterpart to a (candidate) binary black hole merger. Detected by the Zwicky Transient Facility, the electromagnetic flare is consistent with ...expectations for a kicked binary black hole merger in the accretion disk of an active galactic nucleus B. McKernan, K. E. S. Ford, I. Bartoset al., Astrophys. J. Lett.884, L50 (2019) and is unlikely <O(0.01%)) due to intrinsic variability of this source. The lack of color evolution implies that it is not a supernova and instead is strongly suggestive of a constant temperature shock. Other false-positive events, such as microlensing ora tidal disruption event, are ruled out or constrained to be <O(0.1%). If the flare is associated withS190521g, we find plausible values of total mass M(BBH) ∼ 100 Mꙩ, kick velocity v(k) ∼ 200 km/s at θ ∼ 60° in a disk with aspect ratio H/a ∼ 0.01(i.e., disk height H at radius a) and gas density ρ ∼ 10^(−10)g/cu.cm. The merger could have occurred at a disk migration trap (a ∼ 700 r(g); r(g) ≡ GM(SMBH)/sq.c, where M(SMBH) is the mass of the active galactic nucleus supermassive black hole). The combination of parameters implies a significant spin for at least one of the black holes in S190521g. The timing of our spectroscopy prevents useful constraints on broad-line asymmetry due to an off-center flare. We predict a repeat flare in this source due to a reencountering with the disk in ∼ 1.6 yr(M(SMBH)/10^(8) Mꙩ)(a/10^(3)r(g))^(3/2).
The evolution of a Type IIn supernova (SN IIn) is governed by the interaction between the SN ejecta and a hydrogen-rich circumstellar medium. The SNe IIn thus allow us to probe the late-time ...mass-loss history of their progenitor stars. We present a sample of SNe IIn from the untargeted, magnitude-limited surveys of the Palomar Transient Factory (PTF) and its successor, the intermediate PTF (iPTF). To date, statistics on SN IIn optical light-curve properties have generally been based on small (≲10 SNe) samples from targeted SN surveys. The SNe IIn found and followed by the PTF/iPTF were used to select a sample of 42 events with useful constraints on the rise times as well as with available post-peak photometry. The sample SNe were discovered in 2009−2016 and have at least one low-resolution classification spectrum, as well as photometry from the P48 and P60 telescopes at Palomar Observatory. We study the light-curve properties of these SNe IIn using spline fits (for the peak and the declining portion) and template matching (for the rising portion). We study the peak-magnitude distribution, rise times, decline rates, colour evolution, host galaxies, and K-corrections of the SNe in our sample. We find that the typical rise times are divided into fast and slow risers at 20 ± 6 d and 50 ± 11 d, respectively. The decline rates are possibly divided into two clusters (with slopes 0.013 ± 0.006 mag d
−1
and 0.040 ± 0.010 mag d
−1
), but this division has weak statistical significance. We find no significant correlation between the peak luminosity of SNe IIn and their rise times, but the more luminous SNe IIn are generally found to be more long-lasting. Slowly rising SNe IIn are generally found to decline slowly. The SNe in our sample were hosted by galaxies of absolute magnitude −22 ≲
M
g
≲ −13 mag. The K-corrections at light-curve peak of the SNe IIn in our sample are found to be within 0.2 mag for the observer’s frame
r
-band, for SNe at redshifts
z
< 0.25. By applying K-corrections and also including ostensibly “superluminous” SNe IIn, we find that the peak magnitudes are
M
r
peak
= −19.18 ± 1.32 mag. We conclude that the occurrence of conspicuous light-curve bumps in SNe IIn, such as in iPTF13z, are limited to 1.4
+14.6
−1.0
% of the SNe IIn. We also investigate a possible sub-type of SNe IIn with a fast rise to a ≳50 d plateau followed by a slow, linear decline.
Abstract
We report our Spitzer Space Telescope observations and detections of the binary neutron star merger GW170817. At 4.5 μm, GW170817 is detected at 21.9 mag AB at +43 days and 23.9 mag AB at ...+74 days after merger. At 3.6 μm, GW170817 is not detected to a limit of 23.2 mag AB at +43 days and 23.1 mag AB at +74 days. Our detections constitute the latest and reddest constraints on the kilonova/macronova emission and composition of heavy elements. The 4.5 μm luminosity at this late phase cannot be explained by elements exclusively from the first abundance peak of the r-process. Moreover, the steep decline in the Spitzer band, with a power-law index of 3.4 ± 0.2, can be explained by a few of the heaviest isotopes with half-life around 14 d dominating the luminosity (e.g. 140Ba, 143Pr, 147Nd, 156Eu, 191Os, 223Ra, 225Ra, 233Pa, 234Th) or a model with lower deposition efficiency. This data offers evidence that the heaviest elements in the second and third r-process abundance peak were indeed synthesized. Our conclusion is verified by both analytics and network simulations and robust despite intricacies and uncertainties in the nuclear physics. Future observations with Spitzer and James Webb Space Telescope will further illuminate the relative abundance of the synthesized heavy elements.
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