| 1. |
- Kasliwal, M. M., et al.
(författare)
-
Illuminating gravitational waves : A concordant picture of photons from a neutron star merger
- 2017
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 358:6370, s. 1559-
-
Tidskriftsartikel (refereegranskat)abstract
- Merging neutron stars offer an excellent laboratory for simultaneously studying strong-field gravity and matter in extreme environments. We establish the physical association of an electromagnetic counterpart (EM170817) with gravitational waves (GW170817) detected from merging neutron stars. By synthesizing a panchromatic data set, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. The weak gamma rays seen in EM170817 are dissimilar to classical short gamma-ray bursts with ultrarelativistic jets. Instead, we suggest that breakout of a wide-angle, mildly relativistic cocoon engulfing the jet explains the low-luminosity gamma rays, the high-luminosity ultraviolet-optical-infrared, and the delayed radio and x-ray emission. We posit that all neutron star mergers may lead to a wide-angle cocoon breakout, sometimes accompanied by a successful jet and sometimes by a choked jet.
|
|
| 2. |
- Kann, D. A., et al.
(författare)
-
THE AFTERGLOWS OF SWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFT AND SWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS
- 2010
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 720:2, s. 1513-1558
-
Tidskriftsartikel (refereegranskat)abstract
- We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
|
|
| 3. |
- Evans, P. A., et al.
(författare)
-
Swift and NuSTAR observations of GW170817 : Detection of a blue kilonova
- 2017
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 358:6370, s. 1565-1569
-
Tidskriftsartikel (refereegranskat)abstract
- With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counter part of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (approximate to 0.03 solar masses) wind-driven outflow with moderate electron fraction (Y-e approximate to 0.27). Combined with the x-ray limits, we favor an observer viewing angle of approximate to 30 degrees away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a gamma-ray burst afterglow).
|
|
| 4. |
- Soderberg, A. M., et al.
(författare)
-
PANCHROMATIC OBSERVATIONS OF SN 2011dh POINT TO A COMPACT PROGENITOR STAR
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 752:2, s. 78-
-
Tidskriftsartikel (refereegranskat)abstract
- We report the discovery and detailed monitoring of X-ray emission associated with the Type IIb SN 2011dh using data from the Swift and Chandra satellites, placing it among the best-studied X-ray supernovae (SNe) to date. We further present millimeter and radio data obtained with the Submillimeter Array, the Combined Array for Research in Millimeter-wave Astronomy, and the Expanded Very Large Array during the first three weeks after explosion. Combining these observations with early optical photometry, we show that the panchromatic data set is well described by non-thermal synchrotron emission (radio/mm) with inverse Compton scattering (X-ray) of a thermal population of optical photons. In this scenario, the shock partition fractions deviate from equipartition by a factor, (epsilon(e)/epsilon(B)) similar to 30. We derive the properties of the shock wave and the circumstellar environment and find a time-averaged shock velocity of (v) over bar approximate to 0.1c and a progenitor mass-loss rate of (M) over dot approximate to 6x10(-5) M-circle dot yr(-1) (for an assumed wind velocity, v(w) = 1000 km s(-1)). We show that these properties are consistent with the sub-class of Type IIb SNe characterized by compact progenitors (Type cIIb) and dissimilar from those with extended progenitors (Type eIIb). Furthermore, we consider the early optical emission in the context of a cooling envelope model to estimate a progenitor radius of R-* approximate to 10(11) cm, in line with the expectations for a Type cIIb SN. Together, these diagnostics are difficult to reconcile with the extended radius of the putative yellow supergiant progenitor star identified in archival Hubble Space Telescope observations, unless the stellar density profile is unusual. Finally, we searched for the high-energy shock breakout pulse using X-ray and gamma-ray observations obtained during the purported explosion date range. Based on the compact radius of the progenitor, we estimate that the shock breakout pulse was detectable with current instruments but likely missed due to their limited temporal/spatial coverage. Future all-sky missions will regularly detect shock breakout emission from compact SN progenitors enabling prompt follow-up observations with sensitive multi-wavelength facilities.
|
|
| 5. |
- Andreoni, Igor, et al.
(författare)
-
GROWTH on S190814bv : Deep Synoptic Limits on the Optical/Near-infrared Counterpart to a Neutron Star-Black Hole Merger
- 2020
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 890:2
-
Tidskriftsartikel (refereegranskat)abstract
- On 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star-black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg(2) at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering >98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be M-ej < 0.04 M-circle dot at polar viewing angles, or M-ej < 0.03 M-circle dot if the opacity is kappa < 2 cm(2)g(-1). Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be chi < 0.7 for mass ratios Q < 6, with weaker constraints for more compact NSs.
|
|
| 6. |
- Mooley, K., et al.
(författare)
-
A mildly relativistic wide-angle outflow in the neutron-star merger event GW170817
- 2018
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 554:7691, s. 207-210
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- Arcavi, Iair, et al.
(författare)
-
Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star
- 2017
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7679, s. 210-213
-
Tidskriftsartikel (refereegranskat)abstract
- Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining(1). Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability(2-5). That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.
|
|
| 8. |
- Mooley, K., et al.
(författare)
-
Superluminal motion of a relativistic jet in the neutron-star merger GW170817
- 2018
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 561:7723, s. 355-359
-
Tidskriftsartikel (refereegranskat)abstract
- The binary neutron-star merger GW1708171was accompanied by radiation across the electromagnetic spectrum2and localized2to the galaxy NGC 4993 at a distance3of about 41 megaparsecs from Earth. The radio and X-ray afterglows of GW170817 exhibited delayed onset4–7, a gradual increase8in the emission with time (proportional to t0.8) to a peak about 150 days after the merger event9, followed by a relatively rapid decline9,10. So far, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon4,8,11–13and a successful-jet cocoon4,8,11–18(also called a structured jet). However, the observational data have remained inconclusive10,15,19,20as to whether GW170817 launched a successful relativistic jet. Here we report radio observations using very long-baseline interferometry. We find that the compact radio source associated with GW170817 exhibits superluminal apparent motion between 75 days and 230 days after the merger event. This measurement breaks the degeneracy between the choked- and successful-jet cocoon models and indicates that, although the early-time radio emission was powered by a wide-angle outflow8(a cocoon), the late-time emission was most probably dominated by an energetic and narrowly collimated jet (with an opening angle of less than five degrees) and observed from a viewing angle of about 20 degrees. The imaging of a collimated relativistic outflow emerging from GW170817 adds substantial weight to the evidence linking binary neutron-star mergers and short γ-ray bursts.
|
|
| 9. |
- Rosswog, Stephan, et al.
(författare)
-
The multimessenger picture of compact object encounters : binary mergers versus dynamical collisions
- 2013
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 430:4, s. 2585-2604
-
Tidskriftsartikel (refereegranskat)abstract
- We explore the multimessenger signatures of encounters between two neutron stars (ns(2)) and between a neutron star and a stellar mass black hole (nsbh). We focus on the differences between gravitational-wave-driven binary mergers and dynamical collisions that occur, for example, in globular clusters. Our discussion is based on Newtonian hydrodynamics simulations that incorporate a nuclear equation of state and a multiflavour neutrino treatment. For both types of encounters we compare the gravitational wave and neutrino emission properties. We also calculate the rates at which nearly unbound mass is delivered back to the central remnant in a ballistic-fallback-plus-viscous-disc model and we analyse the properties of the dynamically ejected matter. Last but not least we address the electromagnetic transients that accompany each type of encounter. We find that dynamical collisions are at least as promising as binary mergers for producing (short) gamma-ray bursts, but they also share the same possible caveats in terms of baryonic pollution. All encounter remnants produce peak neutrino luminosities of at least similar to 10(53) erg s(-1), some of the collision cases exceed this value by more than an order of magnitude. The canonical ns(2) merger case ejects more than 1 per cent of a solar mass of extremely neutron-rich (Y-e similar to 0.03) material, an amount that is consistent with double neutron star mergers being a major source of r-process in the galaxy. nsbh collisions eject very large amounts of matter (similar to 0.15 M-circle dot) which seriously constrains their admissible occurrence rates. The compact object collision rate (sum of ns(2) and nsbh) must therefore be less, likely much less, than 10 per cent of the ns(2) merger rate. The radioactively decaying ejecta produce optical-ultraviolet 'macronova' which, for the canonical merger case, peak after similar to 0.4 d with a luminosity of similar to 5 x 10(41) erg s(-1). ns(2) (nsbh) collisions reach up to two (four) times larger peak luminosities. The dynamic ejecta deposit a kinetic energy comparable to a supernova in the ambient medium. The canonical merger case releases approximately 2 x 10(50) erg, the most extreme (but likely rare) cases deposit kinetic energies of up to 10(52) erg. The deceleration of this mildly relativistic material by the ambient medium produces long lasting radio flares. A canonical ns(2) merger at the detection horizon of advanced LIGO/Virgo produces a radio flare that peaks on a time-scale of 1 yr with a flux of similar to 0.1 mJy at 1.4 GHz. Collisions eject more material at higher velocities and therefore produce brighter and longer lasting flares.
|
|
