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Register a new userA comparison between short GRB afterglows and AT2017gfo: shedding light on kilonovae properties
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Multi-messenger astronomy received a great boost following the discovery of kilonova AT2017gfo, the optical counterpart of the gravitational wave source GW170817 associated with the short gamma-ray burst GRB 170817A. AT2017gfo was the first kilonova that could be extensively monitored in time both photometrically and spectroscopically. Previously, only few candidates have been observed against the glare of short GRB afterglows. In this work, we aim to search the fingerprints of AT2017gfo-like kilonova emissions in the optical/NIR light curves of 39 short GRBs with known redshift. For the first time, our results allow us to study separately the range of luminosity of the blue and red components of AT2017gfo-like kilonovae in short GRBs. In particular, the red component is similar in luminosity to AT2017gfo, while the blue kilonova can be more than 10 times brighter. Finally, we find further evidence to support all the claimed kilonova detections and we exclude an AT2017gfo-like kilonova in GRBs 050509B and 061201.
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The combined detection of a gravitational-wave signal, kilonova, and short gamma-ray burst (sGRB) from GW170817 marked a scientific breakthrough in the field of multi-messenger astronomy. But even before GW170817, there have been a number of sGRBs with possible associated kilonova detections. In this work, we re-examine these historical sGRB afterglows with a combination of state-of-the-art afterglow and kilonova models. This allows us to include optical/near-infrared synchrotron emission produced by the sGRB as well as ultraviolet/optical/near-infrared emission powered by the radioactive decay of $r$-process elements (i.e., the kilonova). Fitting the lightcurves, we derive the velocity and the mass distribution as well as the composition of the ejected material. The posteriors on kilonova parameters obtained from the fit were turned into distributions for the peak magnitude of the kilonova emission in different bands and the time at which this peak occurs. From the sGRB with an associated kilonova, we found that the peak magnitude in H bands falls in the range [-16.2, -13.1] ($95%$ of confidence) and occurs within $0.8-3.6,rm days$ after the sGRB prompt emission. In g band instead we obtain a peak magnitude in range [-16.8, -12.3] occurring within the first $18,rm hr$ after the sGRB prompt. From the luminosity distributions of GW170817/AT2017gfo, kilonova candidates GRB130603B, GRB050709 and GRB060614 (with the possible inclusion of GRB150101B) and the upper limits from all the other sGRBs not associated with any kilonova detection we obtain for the first time a kilonova luminosity function in different bands.
We report on follow-up observations of 20 short-duration gamma-ray bursts performed in grizJHKs with the seven-channel imager GROND between mid-2007 and the end of 2010. This is one of the most comprehensive data sets on GRB afterglow observations of short bursts published so far. In three cases GROND was on target within less than 10 min after the trigger, leading to the discovery of the afterglow of GRB 081226A and its faint underlying host galaxy. In addition, GROND was able to image the optical afterglow and follow the light-curve evolution in further five cases, GRBs 090305, 090426, 090510, 090927, and 100117A. In all other cases optical/NIR upper limits can be provided on the afterglow magnitudes.
Aims: We investigate the behavior of the frequency-centered light curves expected within the standard model of Gamma Ray Bursts allowing the maximum electron energy to be a free parameter permitted to take low values. Methods: We solve the spatially averaged kinetic equations which describe the simultaneous evolution of particles and photons, obtaining the multi-wavelength spectra as a function of time. From these we construct the frequency-centered light curves giving emphasis in the X-ray and optical bands. Results: We show that in cases where the maximum electron energy takes low values, the produced X-ray light curves show a plateau as the synchrotron component gives its place to the Synhro Self-Compton one in the X-ray band.
The joint detection of the gravitational wave GW170817, of the short $gamma$-ray burst GRB170817A and of the kilonova AT2017gfo, generated by the the binary neutron star merger observed on August 17, 2017, is a milestone in multimessenger astronomy and provides new constraints on the neutron star equation of state. We perform Bayesian inference and model selection on AT2017gfo using semi-analytical, multi-components models that also account for non-spherical ejecta. Observational data favor anisotropic geometries to spherically symmetric profiles, with a log-Bayes factor of ${sim}10^{4}$, and favor multi-component models against single-component ones. The best fitting model is an anisotropic three-component composed of dynamical ejecta plus neutrino and viscous winds. Using the dynamical ejecta parameters inferred from the best-fitting model and numerical-relativity relations connecting the ejecta properties to the binary properties, we constrain the binary mass ratio to $q<1.54$ and the reduced tidal parameter to $120<tildeLambda<1110$. Finally, we combine the predictions from AT2017gfo with those from GW170817, constraining the radius of a neutron star of $1.4~{rm M}_odot$ to $12.2pm0.5~{rm km}$ ($1sigma$ level). This prediction could be further strengthened by improving kilonova models with numerical-relativity information.
We present optical observations of the Swift short-duration gamma-ray burst (GRB) GRB 161104A and its host galaxy at $z=0.793 pm 0.003$. We model the multiband photometry and spectroscopy with the stellar population inference code Prospector, and explore the posterior using nested sampling. We find that the mass-weighted age $t_m = 2.12^{+0.23}_{-0.21}$~Gyr, stellar mass $log{(M/M_odot)} = 10.21 pm 0.04$, metallicity $log{(Z/Z_odot)} = 0.08^{+0.05}_{-0.06}$, dust extinction $A_V = 0.08^{+0.08}_{-0.05}$ mag, and the star formation rate $text{SFR} = 9.9 times 10^{-2} M_odot$~yr$^{-1}$. These properties, along with a prominent 4000 Angstrom break and optical absorption lines classify this host as an early-type, quiescent galaxy. Using Dark Energy Survey galaxy catalogues, we demonstrate that the host of GRB 161104A resides on the outskirts of a galaxy cluster at $zapprox 0.8$, situated $approx 1$ Mpc from the likely brightest cluster galaxy. We also present new modeling for 20 additional short GRB hosts ($approx33%$ of which are early-type galaxies), finding population medians of $log(M/M_odot) = 9.94^{+0.88}_{-0.98}$ and $t_m = 1.07^{+1.98}_{-0.67}$~Gyr ($68%$ confidence). We further find that the host of GRB 161104A is more distant, less massive, and younger than the four other short GRB hosts known to be associated with galaxy clusters. Cluster short GRBs have faint afterglows, in the lower $approx 11%$ ($approx 30%$) of observed X-ray (optical) luminosities. We place a lower limit on the fraction of short GRBs in galaxy clusters versus those in the field of $approx 5-13%$, consistent with the fraction of stellar mass $approx 10-20%$ in galaxy clusters at redshifts $0.1 leq z leq 0.8$.
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