Dark GRBs constitute a significant fraction of the GRB population. In this paper, we present the multiwavelength analysis of an intense two-episodic GRB 150309A observed early on to ~114 days ...post-burst. Despite the strong gamma-ray emission, no optical afterglow was detected for this burst. However, we discovered near-infrared afterglow (\(K_{\rm S}\)-band), ~5.2 hours post burst, with the CIRCE instrument mounted at the 10.4m GTC. We used Fermi observations of GRB 150309A to understand the prompt emission mechanisms and jet composition. We performed the early optical observations using the BOOTES robotic telescope and late-time afterglow observations using the GTC. A potential faint host galaxy is also detected at optical wavelength using the GTC. We modelled the potential host galaxy of GRB 150309A in order to explore the environment of the burst. The time-resolved spectral analysis of Fermi data indicates a hybrid jet composition consisting of a matter-dominated fireball and magnetic-dominated Poynting flux. GTC observations of the afterglow revealed that the counterpart of GRB 150309A was very red, with H-\(K_{\rm S}\) > 2.1 mag (95 \(\%\) confidence). The red counterpart was not discovered in any bluer filters of Swift UVOT, indicative of high redshift origin. This possibility was discarded based on multiple arguments, such as spectral analysis of X-ray afterglow constrain z < 4.15 and a moderate redshift value obtained using spectral energy distribution modelling of the potential galaxy. The broadband afterglow SED implies a very dusty host galaxy with deeply embedded GRB (suggesting \(A_{\rm V}\) \(\gtrsim\) 35 mag). The environment of GRB 150309A demands a high extinction towards the line of sight, demanding dust obscuration is the most probable origin of optical darkness and the very red afterglow of GRB 150309A. This result makes GRB 150309A the highest extinguished GRB known to date.
We present and perform a detailed analysis of multi-wavelength observations of \thisgrb, an optical bright GRB with an observed reverse shock (RS) signature. Observations of this GRB were acquired ...with the BOOTES-4 robotic telescope, the \fermi, and the \swift missions. Time-resolved spectroscopy of the prompt emission shows that changes to the peak energy (\Ep) tracks intensity and the low-energy spectral index seems to follow the intensity for the first episode, whereas this tracking behavior is less clear during the second episode. The fit to the afterglow light curves shows that the early optical afterglow can be described with RS emission and is consistent with the thin shell scenario of the constant ambient medium. The late time afterglow decay is also consistent with the prediction of the external forward shock (FS) model. We determine the properties of the shocks, Lorentz factor, magnetization parameters, and ambient density of \thisgrb, and compare these parameters with another 12 GRBs, consistent with having RS produced by thin shells in an ISM-like medium. The value of the magnetization parameter (\(R_{\rm B} \approx 18\)) indicates a moderately magnetized baryonic dominant jet composition for \thisgrb. We also report the host galaxy photometric observations of \thisgrb obtained with 10.4m GTC, 3.5m CAHA, and 3.6m DOT telescopes and find the host (photo \(z\) = \(2.8^{+0.7}_{-0.9}\)) to be a high mass, star-forming galaxy with a star formation rate of \(20 \pm 10 \msun\) \(\rm yr^{-1}\).
GRB 070610: Flares from a peculiar Galactic source de Ugarte Postigo, A; Castro-Tirado, A J; Gorosabel, J ...
Gamma-Ray Bursts 2007: Proceedings of the Santa Fe Conference (AIP Conference Proceedings Volume 1000),
01/2008, Letnik:
1000
Journal Article
Recenzirano
The majority of bright gamma-ray transients that we observe in the sky, are produced by extragalactic gamma-ray bursts (GRBs). However, we know that there are other kinds of sources that can produce ...intense bursts of high-energy photons within our own Galaxy. GRB 070610/Swift J195509+261406, being just 1 degree away from the Galactic plane, is one of these sources and presents a peculiar behavior, as it shows strong flaring activity that has been observed in the optical and near infrared.We have gathered multi-wavelength observations of GRB 070610 including optical, near infrared, millimeter and radio observations. Our dataset covers the time from 1 minute after the burst onset to more than 4 months later. Following the burst in the gamma-ray band, the source displayed more than 40 flaring episodes in the optical bands (reaching up to Ic~15) over a time span of three days, plus a faint infrared flare that was observed at late times. After this time, the source slowly faded away until it became undetectable.
We investigate the long GRB140629A through multiwavelength observations, which cover optical, infrared and X-rays between 40s and 3yr after the burst, to derive the properties of the dominant jet and ...its host galaxy. Polarisation observations by the MASTER telescope indicate that this burst is weakly polarised. The optical spectrum contains absorption features, from which we confirm the redshift of the GRB as originating at z=2.276. We performed spectral fitting of the X-rays to optical afterglow data and find there is no strong spectral evolution. We determine the hydrogen column density to be 7.2x10^21cm^-2 along the line of sight. The afterglow in this burst can be explained by a blast wave jet with a long-lasting central engine expanding into a uniform medium in the slow cooling regime. At the end of energy injection, a normal decay phase is observed in both the optical and X-ray bands. An achromatic jet break is also found in the afterglow light curves 0.4d after trigger. We fit the multiwavelength data simultaneously with a model based on a numerical simulation and find that the observations can be explained by a narrow uniform jet in a dense environment with an opening angle of 6.7deg viewed 3.8deg off-axis, which released a total energy of 1.4x10^54erg. Using the redshift and opening angle, we find GRB 140629A follows both the Ghirlanda and Amati relations. From the peak time of the light curve, identified as the onset of the forward shock (181s after trigger), the initial Lorentz factor is constrained in the range 82-118. Fitting the host galaxy photometry, we find the host to be a low mass, star-forming galaxy with a star formation rate of logSFR=1.1^+0.9_-0.4Myr^-1. We obtain a value of the neutral hydrogen density by fitting the optical spectrum, logN(HI)=21.0+-0.3, classifying this host as a damped Lyman-alpha. High ionisation lines are also detected in the spectrum.
The Burst Observer and Optical Transient Exploring System (BOOTES) is a network of telescopes that allows the continuous monitoring of transient astrophysical sources. It was originally devoted to ...the study of the optical emission from gamma-ray bursts (GRBs) that occur in the Universe. In this paper we show the initial results obtained using the spectrograph COLORES (mounted on BOOTES-2), when observing compact objects of diverse nature.
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