3 research outputs found
The complex light-curve of the afterglow of GRB071010A
We present and discuss the results of an extensive observational campaign
devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift
satellite. This event was followed for almost a month in the
optical/near-infrared (NIR) with various telescopes starting from about 2min
after the high-energy event. Swift-XRT observations started only later at about
0.4d. The light-curve evolution allows us to single out an initial rising phase
with a maximum at about 7min, possibly the afterglow onset in the context of
the standard fireball model, which is then followed by a smooth decay
interrupted by a sharp rebrightening at about 0.6d. The rebrightening was
visible in both the optical/NIR and X-rays and can be interpreted as an episode
of discrete energy injection, although various alternatives are possible. A
steepening of the afterglow light curve is recorded at about 1d. The entire
evolution of the optical/NIR afterglow is consistent with being achromatic.
This could be one of the few identified GRB afterglows with an achromatic break
in the X-ray through the optical/NIR bands. Polarimetry was also obtained at
about 1d, just after the rebrightening and almost coincident with the
steepening. This provided a fairly tight upper limit of 0.9% for the
polarized-flux fraction.Comment: 11 pages, 3 figures, MNRAS, in pres
The complex light-curve of the afterglow of GRB071010A
We present and discuss the results of an extensive observational campaign
devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift
satellite. This event was followed for almost a month in the
optical/near-infrared (NIR) with various telescopes starting from about 2min
after the high-energy event. Swift-XRT observations started only later at about
0.4d. The light-curve evolution allows us to single out an initial rising phase
with a maximum at about 7min, possibly the afterglow onset in the context of
the standard fireball model, which is then followed by a smooth decay
interrupted by a sharp rebrightening at about 0.6d. The rebrightening was
visible in both the optical/NIR and X-rays and can be interpreted as an episode
of discrete energy injection, although various alternatives are possible. A
steepening of the afterglow light curve is recorded at about 1d. The entire
evolution of the optical/NIR afterglow is consistent with being achromatic.
This could be one of the few identified GRB afterglows with an achromatic break
in the X-ray through the optical/NIR bands. Polarimetry was also obtained at
about 1d, just after the rebrightening and almost coincident with the
steepening. This provided a fairly tight upper limit of 0.9% for the
polarized-flux fraction.Comment: 11 pages, 3 figures, MNRAS, in pres
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta