TY - JOUR
T1 - Large-amplitude late-time radio variability in GRB 151027B
AU - Greiner, J.
AU - Bolmer, J.
AU - Wieringa, M.
AU - Van Der Horst, A. J.
AU - Petry, D.
AU - Schulze, S.
AU - Knust, F.
AU - De Bruyn, G.
AU - Krühler, T.
AU - Wiseman, P.
AU - Klose, S.
AU - Delvaux, C.
AU - Graham, J. F.
AU - Kann, D. A.
AU - Moin, A.
AU - Nicuesa-Guelbenzu, A.
AU - Schady, P.
AU - Schmidl, S.
AU - Schweyer, T.
AU - Tanga, M.
AU - Tingay, S.
AU - Van Eerten, H.
AU - Varela, K.
N1 - Funding Information:
Acknowledgements. During the writing of this paper, the radio astronomy community lost a great scientist, and we lost a dear colleague and collaborator, Ger de Bruyn. His insights in radio scintillation were crucial in the work presented in this paper, and he will be missed by many. J. G. is particularly grateful to Phil Edwards for scheduling the many ATCA ToO observations. S. K., A. N. G., S. S., and D. A. K. acknowledge support by DFG grant Kl 766/16–1. D. A. K. acknowledges financial support from the Spanish research project AYA 2014-58381-P, and from Juan de la Cierva Incorporación fellowships IJCI-2015-26153 and IJCI-2014-21669. J. F. G., T. K., and P. W. acknowledge support through the Sofja Kovalevskaja award to P. Schady from the A. von Humboldt foundation of Germany. Part of the funding for GROND (both hardware and personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). The Australia Telescope Compact Array is part of the Australia Telescope National Facility, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. Facilities: Max Planck:2.2 m (GROND), ATCA, ALMA, Swift
Publisher Copyright:
© ESO 2018.
PY - 2018/6/1
Y1 - 2018/6/1
N2 - Context. Deriving physical parameters from gamma-ray burst (GRB) afterglow observations remains a challenge, even 20 years after the discovery of afterglows. The main reason for the lack of progress is that the peak of the synchrotron emission is in the sub-mm range, thus requiring radio observations in conjunction with X-ray/optical/near-infrared data in order to measure the corresponding spectral slopes and consequently remove the ambiguity with respect to slow vs. fast cooling and the ordering of the characteristic frequencies. Aims. We have embarked on a multifrequency, multi-epoch observing campaign to obtain sufficient data for a given GRB that allows us to test the simplest version of the fireball afterglow model. Methods. We observed GRB 151027B, the 1000th Swift-detected GRB, with GROND in the optical-near-IR, ALMA in the sub-millimeter, ATCA in the radio band; we combined this with public Swift/XRT X-ray data. Results. While some observations at crucial times only return upper limits or surprising features, the fireball model is narrowly constrained by our data set, and allows us to draw a consistent picture with a fully determined parameter set. Surprisingly, we find rapid, large-amplitude flux density variations in the radio band which are extreme not only for GRBs, but generally for any radio source. We interpret them as scintillation effects, though their extreme nature requires the scattering screen to be at a much smaller distance than usually assumed, multiple screens, or a combination of the two. Conclusions. The data are consistent with the simplest fireball scenario for a blast wave moving into a constant-density medium, and slow-cooling electrons. All fireball parameters are constrained at or better than a factor of 2, except for the density and the fraction of the energy in the magnetic field which has a factor of 10 uncertainty in both directions.
AB - Context. Deriving physical parameters from gamma-ray burst (GRB) afterglow observations remains a challenge, even 20 years after the discovery of afterglows. The main reason for the lack of progress is that the peak of the synchrotron emission is in the sub-mm range, thus requiring radio observations in conjunction with X-ray/optical/near-infrared data in order to measure the corresponding spectral slopes and consequently remove the ambiguity with respect to slow vs. fast cooling and the ordering of the characteristic frequencies. Aims. We have embarked on a multifrequency, multi-epoch observing campaign to obtain sufficient data for a given GRB that allows us to test the simplest version of the fireball afterglow model. Methods. We observed GRB 151027B, the 1000th Swift-detected GRB, with GROND in the optical-near-IR, ALMA in the sub-millimeter, ATCA in the radio band; we combined this with public Swift/XRT X-ray data. Results. While some observations at crucial times only return upper limits or surprising features, the fireball model is narrowly constrained by our data set, and allows us to draw a consistent picture with a fully determined parameter set. Surprisingly, we find rapid, large-amplitude flux density variations in the radio band which are extreme not only for GRBs, but generally for any radio source. We interpret them as scintillation effects, though their extreme nature requires the scattering screen to be at a much smaller distance than usually assumed, multiple screens, or a combination of the two. Conclusions. The data are consistent with the simplest fireball scenario for a blast wave moving into a constant-density medium, and slow-cooling electrons. All fireball parameters are constrained at or better than a factor of 2, except for the density and the fraction of the energy in the magnetic field which has a factor of 10 uncertainty in both directions.
KW - Gamma-ray burst: general
KW - Gamma-ray burst: individual: GRB 151027B
KW - Radiation mechanisms: non-thermal
KW - Radio continuum: ISM
KW - Techniques: photometric
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U2 - 10.1051/0004-6361/201731755
DO - 10.1051/0004-6361/201731755
M3 - Article
AN - SCOPUS:85049004709
SN - 0004-6361
VL - 614
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A29
ER -