GRB 020813: Polarization in the case of a smooth optical decay

Gorosabel, J.; Rol, E.; Covino, S.; Castro-Tirado, A. J.; Cerón, J. M. Castro; Lazzati, Davide; Hjorth, J.; Malesani, D.; Valle, M. Della; Alighieri, S. di Serego; Fiore, F.; Fruchter, A. S.; Fynbo, J. P. U.; Ghisellini, G.; Goldoni, P.; Greiner, J.; Israel, G. L.; Kaper, L.; Kawai, N.; Klose, S.; Kouveliotou, C.; Floc’h, E. Le; Masetti, N.; Mirabel, F.; Møller, P.; Ortolani, S.; Palazzi, E.; Pian, E.; Rhoads, James E.; Ricker, G.; Saracco, P.; Stella, L.; Tagliaferri, G.; Tanvir, N. R.; Heuvel, E. P. J. van den; Vietri, M.; Vreeswijk, P.M.; Wijers, R. A. M. J.; Zerbi, F. M.

doi:10.1051/0004-6361:20034409

Cited by 30 publications

(40 citation statements)

References 24 publications

(60 reference statements)

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“…Since then, there have been a number of other detections of polarisation in afterglows (e.g. Covino et al 2004;Gorosabel et al 2004). The polarisation is observed to be at about the 1-3% level and is reasonably constant when associated with a smooth afterglow lightcurve (Covino et al 2003).…”

Section: Discussionmentioning

confidence: 99%

Polarisation studies of the prompt gamma-ray emission from GRB 041219a using the spectrometer aboard INTEGRAL

McGlynn

Clark

Dean

et al. 2007

A&A

155

138

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Context. Linear polarisation in gamma-ray burst prompt emission is an important diagnostic with the potential to significantly constrain models. The spectrometer aboard INTEGRAL, SPI, has the capability to detect the signature of polarised emission from a bright γ-ray source. GRB 041219a is the most intense burst localised by INTEGRAL with a fluence of 5.7 ×10 −4 erg cm −2 over the energy range 20 keV-8 MeV and is an ideal candidate for such a study. Aims. Polarisation can be measured using multiple events scattered into adjacent detectors because the Compton scatter angle depends on the polarisation of the incoming photon. A search for linear polarisation in the most intense pulse of duration 66 seconds and in the brightest 12 seconds of GRB 041219a was performed in the 100-350 keV, 100-500 keV and 100 keV-1 MeV energy ranges. It was possible to divide the events into six directions in the energy ranges of 100-350 keV and 100-500 keV using the kinematics of the Compton scatter interactions. Methods. The multiple event data from the spectrometer was analysed and compared with the predicted instrument response obtained from Monte-Carlo simulations using the GEANT 4 INTEGRAL mass model. The χ 2 distribution between the real and simulated data as a function of the percentage polarisation and polarisation angle was calculated for all three energy ranges. The degree and angle of polarisation were obtained from the best-fit value of χ 2 . Results. A weak signal consistent with polarisation was found throughout the analyses. The degree of linear polarisation in the brightest pulse of duration 66 s was found to be 63 +31 −30 % at an angle of 70 +14 −11 degrees in the 100-350 keV energy range. The degree of polarisation was also constrained in the brightest 12 s of the GRB and a polarisation fraction of 96 +39 −40 % at an angle of 60 +12 −14 degrees was determined over the same energy range. However, despite extensive analysis and simulations, a systematic effect that could mimic the weak polarisation signal could not be definitively excluded. Conclusions. Our results over several energy ranges and time intervals are consistent with a polarisation signal of about 60% but at a low level of significance (∼2σ). The polarisation results are compared with predictions from the synchrotron and Compton drag processes. The spectrum of this GRB can also be well fit by a combined black body and power law model which could arise from a combination of the Compton and synchrotron processes, with different degrees of polarisation. We therefore conclude that the procedure described here demonstrates the effectiveness of using SPI as a polarimeter, and is a viable method of measuring polarisation levels in intense gamma-ray bursts.

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Section: Discussionmentioning

confidence: 99%

Polarisation studies of the prompt gamma-ray emission from GRB 041219a using the spectrometer aboard INTEGRAL

McGlynn

Clark

Dean

et al. 2007

A&A

155

138

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“…Polarized optical emission has been claimed for a few classical GRBs, usually P = 1-2% (Gorosabel et al 2004) and rarely up to 10% (Steele et al 2009). P ∼ 1.5 % was measured for SN 2003dh / GRB 030329 (Greiner et al 2003).…”

Section: Polarimetric Observations Of Grb Afterglows and Hypernovaementioning

confidence: 99%

Multiwavelength observations of GRB afterglows

Castro-Tirado

2011

Proc. IAU

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Abstract. Multiwavelength observations of gamma-ray burst afterglows are presented, in particular those in the optical and millimetre wavelengths. I will focus on the observations mostly carried out at Spanish ground-based observatories (mainly the 10.4m GTC) and at the Plateau de Bure Interferometer in the French Alps. The importance of global networks of robotic telescopes (like BOOTES, established worldwide) for early time observations in order to put constraints on the physical mechanisms of the GRB early time emission phase is also discussed. The overall observational efforts provide additional clues for a better understanding of the reverse and forward shock. Finally I will report on the Lomonosov/UFFO-p capabilities taking into account its launch in 2012.

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“…GRB 020813 (see the accompanying paper, Gorosabel et al 2004, for more details) had an extremely smooth light curve (Laursen & Stanek 2003;Gorosabel et al 2004), successfully fitted by a smoothly broken power-law with an rms scatter of the residuals of <0.01 mag in the optical filters. This ensures that inhomogeneities in the fireball structure and/or in the surrounding interstellar medium (ISM) are not significant and therefore can not affect the polarization measurement.…”

Section: Introductionmentioning

confidence: 99%

On the jet structure and magnetic field configuration of GRB 020813

Lazzati

Covino

Gorosabel

et al. 2004

A&A

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Abstract. The polarization curve of GRB 020813 is discussed and compared to different models for the structure, evolution and magnetisation properties of the jet and the interstellar medium onto which the fireball impacts. GRB 020813 is best suited for this kind of analysis for the smoothness of its afterglow light curve, ensuring the applicability of current models. The polarization dataset allows us to rule out the standard GRB jet, in which the energy and Lorentz factor have a well defined value inside the jet opening angle and the magnetic field is generated at the shock front. We explore alternative models finding that a structured jet or a jet with a toroidal component of the magnetic field can fit equally well the polarization curve. Stronger conclusions cannot be drawn due to the incomplete sampling of the polarization curve. A more dense sampling, especially at early times, is required to pin down the structure of the jet and the geometry of its magnetic field.

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GRB 020813: Polarization in the case of a smooth optical decay

Cited by 30 publications

References 24 publications

Polarisation studies of the prompt gamma-ray emission from GRB 041219a using the spectrometer aboard INTEGRAL

Polarisation studies of the prompt gamma-ray emission from GRB 041219a using the spectrometer aboard INTEGRAL

Multiwavelength observations of GRB afterglows

On the jet structure and magnetic field configuration of GRB 020813

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