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Register a new userObservations of the GRB afterglow ATLAS17aeu and its possible association with GW170104
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We report the discovery and multi-wavelength data analysis of the peculiar optical transient, ATLAS17aeu. This transient was identified in the skymap of the LIGO gravitational wave event GW170104 by our ATLAS and Pan-STARRS coverage. ATLAS17aeu was discovered 23.1hrs after GW170104 and rapidly faded over the next 3 nights, with a spectrum revealing a blue featureless continuum. The transient was also detected as a fading x-ray source by Swift and in the radio at 6 and 15 GHz. A gamma ray burst GRB170105A was detected by 3 satellites 19.04hrs after GW170104 and 4.10hrs before our first optical detection. We analyse the multi-wavelength fluxes in the context of the known GRB population and discuss the observed sky rates of GRBs and their afterglows. We find it statistically likely that ATLAS17aeu is an afterglow associated with GRB170105A, with a chance coincidence ruled out at the 99% confidence or 2.6$sigma$. A long, soft GRB within a redshift range of $1 lesssim z lesssim 2.9$ would be consistent with all the observed multi-wavelength data. The Poisson probability of a chance occurrence of GW170104 and ATLAS17aeu is $p=0.04$. This is the probability of a chance coincidence in 2D sky location and in time. These observations indicate that ATLAS17aeu is plausibly a normal GRB afterglow at significantly higher redshift than the distance constraint for GW170104 and therefore a chance coincidence. However if a redshift of the faint host were to place it within the GW170104 distance range, then physical association with GW170104 should be considered.
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The optical-infrared afterglow of the LAT-detected long duration burst, GRB 090902B, has been observed by several instruments. The earliest detection by ROTSE-IIIa occurred 80 minutes after detection by the GBM instrument onboard the Fermi Gamma-Ray Space Telescope, revealing a bright afterglow and a decay slope suggestive of a reverse shock origin. Subsequent optical-IR observations followed the light curve for 6.5 days. The temporal and spectral behavior at optical-infrared frequencies is consistent with synchrotron fireball model predictions; the cooling break lies between optical and XRT frequencies ~ 1.9 days after the burst. The inferred electron energy index is $p = 1.8 pm 0.2$, which would however imply an X-ray decay slope flatter than observed. The XRT and LAT data have similar spectral indices and the observed steeper value of the LAT temporal index is marginally consistent with the predicted temporal decay in the radiative regime of the forward shock model. Absence of a jet break during the first 6 days implies a collimation-corrected $gamma$-ray energy $E_{gamma} > 2.2times10^{52}rm$ ergs, one of the highest ever seen in a long-duration GRBs. More events combining GeV photon emission with multi-wavelength observations will be required to constrain the nature of the central engine powering these energetic explosions and to explore the correlations between energetic quanta and afterglow emission.
We describe the afterglows of the long gamma-ray-burst (GRB) 130427A within the context of a binary-driven hypernova (BdHN). The afterglows originate from the interaction between a newly born neutron star ($ u$NS), created by an Ic supernova (SN), and a mildly relativistic ejecta of a hypernova (HN). Such a HN in turn results from the impact of the GRB on the original SN Ic. The mildly relativistic expansion velocity of the afterglow ($Gamma sim 3$) is determined, using our model independent approach, from the thermal emission between $196$~s and $461$~s. The power-law in the optical and X-ray bands of the afterglow is shown to arise from the synchrotron emission of relativistic electrons in the expanding magnetized HN ejecta. Two components contribute to the injected energy: the kinetic energy of the mildly relativistic expanding HN and the rotational energy of the fast rotating highly magnetized $ u$NS. We reproduce the afterglow in all wavelengths from the optical ($10^{14}$~Hz) to the X-ray band ($10^{19}$~Hz) over times from $604$~s to $5.18times 10^6$~s relative to the Fermi-GBM trigger. Initially, the emission is dominated by the loss of kinetic energy of the HN component. After $10^5$~s the emission is dominated by the loss of rotational energy of the $ u$NS, for which we adopt an initial rotation period of $2$~ms and a dipole plus quadrupole magnetic field of $lesssim ! 7times 10^{12}$~G or $sim ! 10^{14}$~G. This scenario with a progenitor composed of a CO$_{rm core}$ and a NS companion differs from the traditional ultra-relativistic-jetted treatments of the afterglows originating from a single black hole.
We present the observations of the afterglow of gamma-ray burst GRB 090102. Optical data taken by the TAROT, REM, GROND, together with publicly available data from Palomar, IAC and NOT telescopes, and X-ray data taken by the XRT instrument on board the Swift spacecraft were used. This event features an unusual light curve. In X-rays, it presents a constant decrease with no hint of temporal break from 0.005 to 6 days after the burst. In the optical, the light curve presents a flattening after 1 ks. Before this break, the optical light curve is steeper than that of the X-ray. In the optical, no further break is observed up to 10 days after the burst. We failed to explain these observations in light of the standard fireball model. Several other models, including the cannonball model were investigated. The explanation of the broad band data by any model requires some fine tuning when taking into account both optical and X-ray bands.
We used data from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) to set upper-limits on the ${gamma}$-ray and hard X-ray prompt emission associated with the gravitational wave event GW170104, discovered by the LIGO/Virgo collaboration. The unique omni-directional viewing capability of the instruments on-board INTEGRAL allowed us to examine the full 90% confidence level localization region of the LIGO trigger. Depending on the particular spectral model assumed and the specific position within this region, the upper limits inferred from the INTEGRAL observations range from F${gamma}$=1.9x10-7 erg cm-2 to F${gamma}$=10-6 erg cm-2 (75 keV - 2 MeV energy range). This translates into a ratio between the prompt energy released in ${gamma}$-rays along the direction to the observer and the gravitational wave energy of E${gamma}$/EGW <2.6x10-5 . Using the INTEGRAL results, we can not confirm the ${gamma}$-ray proposed counterpart to GW170104 by the AGILE team with the MCAL instrument. The reported flux of the AGILE/MCAL event, E2, is not compatible with the INTEGRAL upper limits within most of the 90% LIGO localization region. There is only a relatively limited portion of the sky where the sensitivity of the INTEGRAL instruments was not optimal and the lowest allowed fluence estimated for E2 would still be compatible with the INTEGRAL results. This region was also observed independently by Fermi/GBM and AstroSAT, from which, as far as we are aware, there are no reports of any significant detection of a prompt high-energy event.
We present observations of the afterglow of GRB 080319B at optical, mm and radio frequencies from a few hours to 67 days after the burst. Present observations along with other published multi-wavelength data have been used to study the light-curves and spectral energy distributions of the burst afterglow. The nature of this brightest cosmic explosion has been explored based on the observed properties and its comparison with the afterglow models. Our results show that the observed features of the afterglow fits equally good with the Inter Stellar Matter and the Stellar Wind density profiles of the circum-burst medium. In case of both density profiles, location of the maximum synchrotron frequency $ u_m$ is below optical and the value of cooling break frequency $ u_c$ is below $X-$rays, $sim 10^{4}$s after the burst. Also, the derived value of the Lorentz factor at the time of naked eye brightness is $sim 300$ with the corresponding blast wave size of $sim 10^{18}$ cm. The numerical fit to the multi-wavelength afterglow data constraints the values of physical parameters and the emission mechanism of the burst.
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