Energy injection into the external shock system that generates the afterglow to a gamma-ray burst (GRB) can result in a rebrightening of the emission. Here we investigate the off-axis view of a ...rebrightened refreshed shock afterglow. We find that the afterglow light curve, when viewed from outside of the jet opening angle, could be characterized by a slow rise, or long plateau, with a maximum flux determined by the total system energy. Using the broadband afterglow data for GRB 170817A, associated with the gravitational-wave-detected binary neutron star merger GW170817, we show that a refreshed shock model with a simple top-hat jet can reproduce the observed afterglow features. We consider two refreshed shock models: a single episode of energy injection, and an episode of continuous energy injection. The best-fit model parameters give a jet opening angle for our first and second models, respectively, of θj = 5 and 6 , an inclination to the line of sight = 16 and 17 , an initial on-axis isotropic equivalent kinetic energy and erg, and a total/final, on-axis isotropic equivalent refreshed shock energy and erg. The first model fitting prefers an initial bulk Lorentz factor Γ0,1 < 60, with a comparatively low central value of Γ0,1 = 19.5, indicating that, in this case, the on-axis jet could have been a "failed GRB." Alternatively, our second model is consistent with a bright GRB for an on-axis observer, with . Due to the low Lorentz factor and/or the jet opening angles at θj ∼ /3, both models are unable to reproduce the γ-ray emission observed in GRB 170817A, which would therefore require an alternative explanation such as cocoon shock breakout.
The historic detection of gravitational waves from a binary neutron star merger (GW170817) and its electromagnetic counterpart led to the first accurate (sub-arcsecond) localization of a ...gravitational-wave event. The transient was found to be ∼10″ from the nucleus of the S0 galaxy NGC 4993. We report here the luminosity distance to this galaxy using two independent methods. (1) Based on our MUSE/VLT measurement of the heliocentric redshift (zhelio = 0.009783 0.000023), we infer the systemic recession velocity of the NGC 4993 group of galaxies in the cosmic microwave background (CMB) frame to be vCMB = 3231 53 km s−1. Using constrained cosmological simulations we estimate the line-of-sight peculiar velocity to be vpec = 307 230 km s−1, resulting in a cosmic velocity of vcosmic = 2924 236 km s−1 (zcosmic = 0.00980 0.00079) and a distance of Dz = 40.4 3.4 Mpc assuming a local Hubble constant of H0 = 73.24 1.74 km s−1 Mpc−1. (2) Using Hubble Space Telescope measurements of the effective radius (15 5 1 5) and contained intensity and MUSE/VLT measurements of the velocity dispersion, we place NGC 4993 on the Fundamental Plane (FP) of E and S0 galaxies. Comparing to a frame of 10 clusters containing 226 galaxies, this yields a distance estimate of DFP = 44.0 7.5 Mpc. The combined redshift and FP distance is DNGC 4993 = 41.0 3.1 Mpc. This "electromagnetic" distance estimate is consistent with the independent measurement of the distance to GW170817 as obtained from the gravitational-wave signal ( D GW = 43.8 − 6.9 + 2.9 Mpc) and confirms that GW170817 occurred in NGC 4993.
The unprecedented optical and near-infrared lightcurves of the first electromagnetic counterpart to a gravitational-wave source, GW170817, a binary neutron star merger, exhibited a strong evolution ...from blue to near-infrared (a so-called "kilonova" or "macronova"). The emerging near-infrared component is widely attributed to the formation of r-process elements that provide the opacity to shift the blue light into the near-infrared. An alternative scenario is that the light from the blue component gets extinguished by dust formed by the kilonova and subsequently is re-emitted at near-infrared wavelengths. We test here this hypothesis using the lightcurves of AT 2017gfo, the kilonova accompanying GW170817. We find that of the order of of carbon is required to reproduce the optical/near-infrared lightcurves as the kilonova fades. This putative dust cools from ∼2000 K at ∼4 days after the event to ∼1500 K over the course of the following week, thus requiring dust with a high condensation temperature, such as carbon. We contrast this with the nucleosynthetic yields predicted by a range of kilonova wind models. These suggest that at most of carbon is formed. Moreover, the decay in the inferred dust temperature is slower than that expected in kilonova models. We therefore conclude that in current models of the blue component of the kilonova, the near-infrared component in the kilonova accompanying GW170817 is unlikely to be due to dust.
Abstract We present rest-frame UV Hubble Space Telescope imaging of the largest and most complete sample of 23 long-duration gamma-ray burst (GRB) host galaxies between redshifts 4 and 6. Of these ...23, we present new WFC3/F110W imaging for 19 of the hosts, which we combine with archival WFC3/F110W and WFC3/F140W imaging for the remaining four. We use the photometry of the host galaxies from this sample to characterize both the rest-frame UV luminosity function (LF) and the size–luminosity relation of the sample. We find that when assuming the standard Schechter-function parameterization for the UV LF, the GRB host sample is best fit with α = − 1.30 − 0.25 + 0.30 and M * = − 20.33 − 0.54 + 0.44 mag, which are consistent with results based on z ∼ 5 Lyman-break galaxies. We find that ∼68% of our size–luminosity measurements fall within or below the same relation for Lyman-break galaxies at z ∼ 4. This study observationally confirms expectations that at z ∼ 5 Lyman-break and GRB host galaxies should trace the same population and demonstrates the utility of GRBs as probes of hidden star formation in the high-redshift Universe. Under the assumption that GRBs unbiasedly trace star formation at this redshift, our nondetection fraction of 7/23 is consistent at the 95% confidence level with 13%–53% of star formation at redshift z ∼ 5 occurring in galaxies fainter than our detection limit of M 1600Å ≈ −18.3 mag.
Long-duration gamma-ray bursts (GRBs) are powerful tracers of star-forming galaxies. We have defined a homogeneous sub-sample of 69 Swift GRB-selected galaxies spanning a very wide redshift range. ...Special attention has been devoted to making the sample optically unbiased through simple and well-defined selection criteria based on the high-energy properties of the bursts and their positions on the sky. In this paper, we present the survey design and summarize the results of our observing program conducted at the ESO Very Large Telescope (VLT) aimed at obtaining the most basic properties of galaxies in this sample, including a catalog of R and Ksubs magnitudes and redshifts. Seven hosts have detections of the Ly alpha emission line and we can exclude an early indication that Ly alpha emission is ubiquitous among GRB hosts, but confirm that Ly alpha is stronger in GRB-selected galaxies than in flux-limited samples of Lyman break galaxies.
ABSTRACT We report a multiwavelength (X-ray, ultraviolet/optical/infrared (UVOIR), radio) analysis of the relativistic tidal disruption event (TDE) candidate Sw J2058+05 from 3 months to 3 yr ...post-discovery in order to study its properties and compare its behavior with that of Sw J1644+57. Our main results are as follows: (1) The long-term X-ray light curve of Sw J2058+05 shows a remarkably similar trend to that of Sw J1644+57. After a prolonged power-law decay, the X-ray flux drops off rapidly by a factor of 160 within a span of Δt/ . Associating this sudden decline with the transition from super-Eddington to sub-Eddington accretion, we estimate the black hole mass to be in the range of 104-6 M . (2) We detect rapid ( 500 s) X-ray variability before the drop-off, suggesting that, even at late times, the X-rays originate from close to the black hole (ruling out a forward-shock origin). (3) We confirm using Hubble Space Telescope and Very Long Baseline Array astrometry that the location of the source coincides with the galaxy's center to within 400 pc (in projection). (4) We modeled Sw J2058+05's UVOIR spectral energy distribution with a single-temperature blackbody and find that while the radius remains more or less constant at a value of 63.4 4.5 AU ( cm) at all times during the outburst, the blackbody temperature drops significantly from ∼30,000 K at early times to a value of ∼15,000 K at late times (before the X-ray drop-off). Our results strengthen Sw J2058+05's interpretation as a TDE similar to Sw J1644+57.
GRB jet structure and the jet break Lamb, Gavin P; Kann, D Alexander; Fernández, Joseph John ...
Monthly notices of the Royal Astronomical Society,
09/2021, Letnik:
506, Številka:
3
Journal Article
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ABSTRACT
We investigate the shape of the jet break in within-beam gamma-ray burst (GRB) optical afterglows for various lateral jet structure profiles. We consider cases with and without lateral ...spreading and a range of inclinations within the jet core half-opening angle, θc. We fit model and observed afterglow light curves with a smoothly-broken power-law function with a free-parameter κ that describes the sharpness of the break. We find that the jet break is sharper (κ is greater) when lateral spreading is included than in the absence of lateral spreading. For profiles with a sharp-edged core, the sharpness parameter has a broad range of 0.1 ≲ κ ≲ 4.6, whereas profiles with a smooth-edged core have a narrower range of 0.1 ≲ κ ≲ 2.2 when models both with and without lateral spreading are included. For sharp-edged jets, the jet break sharpness depends strongly on the inclination of the system within θc, whereas for smooth-edged jets, κ is more strongly dependent on the size of θc. Using a sample of 20 GRBs, we find 9 candidate smooth-edged jet structures and 8 candidate sharp-edged jet structures, while the remaining 3 are consistent with either. The shape of the jet break, as measured by the sharpness parameter κ, can be used as an initial check for the presence of lateral structure in within-beam GRBs where the afterglow is well-sampled at and around the jet-break time.
While wide-field surveys of M31 have revealed much substructure at large radii, understanding the nature and origin of this material is not straightforward from morphology alone. Using deep Hubble ...Space Telescope/Advanced Camera for Surveys data, we have derived further constraints in the form of quantitative star formation histories (SFHs) for 14 inner halo fields which sample diverse substructures. In agreement with our previous analysis of colour-magnitude diagram morphologies, we find the resultant behaviours can be broadly separated into two categories. The SFHs of 'disc-like' fields indicate that most of their mass has formed since z ... 1, with one quarter of the mass formed in the last 5 Gyr. We find 'stream-like' fields to be on average 1.5 Gyr older, with ... 10 per cent of their stellar mass formed within the last 5 Gyr. These fields are also characterized by an age-metallicity relation showing rapid chemical enrichment to solar metallicity by z = 1, suggestive of an early-type progenitor. We confirm a significant burst of star formation 2 Gyr ago, discovered in our previous work, in all the fields studied here. The presence of these young stars in our most remote fields suggests that they have not formed in situ but have been kicked-out from the thin disc through disc heating in the recent past. (ProQuest: ... denotes formulae/symbols omitted.)
We present new Jansky Very Large Array observations of five pre-Swift gamma-ray bursts for which an ultraluminous star formation rate (SFR) >100 M... yr super( -1) dusty host galaxy had previously ...been inferred from radio or submillimetre observations taken within a few years after the burst. In four of the five cases, we no longer detect any source at the host location to limits much fainter than the original observations, ruling out the existence of an ultraluminous galaxy hosting any of these gamma-ray bursts (GRBs). We continue to detect a source at the position of GRB 980703, but it is much fainter than it was a decade ago and the inferred radio SFR (~80 M...) is relatively modest. The radio flattening at 200-1000 d observed in the light curve of this GRB may have been caused by a decelerating counterjet oriented 180 deg away from the viewer, although an unjetted wind model can also explain the data. Our results eliminate all well-established ultraluminous infrared galaxies (ULIRGs) among the pre-Swift host population. They also rule out all cases for which an unobscured GRB was found in a galaxy dominated by heavily obscured star formation. When GRBs do occur in ULIRGs, the afterglow is almost always observed to be heavily obscured, consistent with the large dust opacities and high dust covering fractions characteristic of these systems. (ProQuest: ... denotes formulae/symbols omitted.)
M31 has a giant stream of stars extending far to the south and a great deal of other tidal debris in its halo, much of which is thought to be directly associated with the southern stream. We model ...this structure by means of Bayesian sampling of parameter space, where each sample uses an N-body simulation of a satellite disrupting in M31's potential. We combine constraints on stellar surface densities from the Isaac Newton Telescope survey of M31 with kinematic data and photometric distances. This combination of data tightly constrains the model, indicating a stellar mass at last pericentric passage of log10 (M
s
/M) = 9.5 ± 0.1, comparable to the Large Magellanic Cloud. Any existing remnant of the satellite is expected to lie in the Northeast (NE) Shelf region beside M31's disc, at velocities more negative than M31's disc in this region. This rules out the prominent satellites M32 or NGC 205 as the progenitor, but an overdensity recently discovered in M31's NE disc sits at the edge of the progenitor locations found in the model. M31's virial mass is constrained in this model to be log10 M
200 = 12.3 ± 0.1, alleviating the previous tension between observational virial mass estimates and expectations from the general galactic population and the timing argument. The techniques used in this paper, which should be more generally applicable, are a powerful method of extracting physical inferences from observational data on tidal debris structures.
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