Detection of Polarization in the Afterglow of GRB 990510 with the ESO Very Large Telescope

Following a BeppoSAX alert and the discovery of the OT at SAAO, we observed GRB 990510 with the FORS instrument on ESO's VLT Unit 1 (Antu). The burst is unremarkable in gamma rays, but in optical is the first one to show good evidence for jetlike outflow. We report the detection of significant linear polarization in the afterglow: it is 1.6 ± 0.2% 0.86 days after trigger, and after 1.81 days is consistent with that same value, but much more uncertain. The polarization angle is constant on a timescale of hours and may be constant over one day. We conclude that the polarization is intrinsic to the source and due to the synchrotron nature of the emission, and discuss the random and ordered field geometries that may be responsible for it.

[1]  Jose Miguel Rodriguez Espinosa,et al.  Instrumentation for large telescopes , 1997 .

[2]  Hjorth,et al.  Polarimetric constraints on the optical afterglow emission from GRB 990123 , 1999, Science.

[3]  Wijers,et al.  UvA-DARE ( Digital Academic Repository ) Physical parametres of GRB 970508 and GRB 971214 from their afterglow synchroton emission , 1999 .

[4]  P. Mészáros,et al.  Rings in Fireball Afterglows , 1997, astro-ph/9709284.

[5]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[6]  Cambridge,et al.  The Radio-to-X-Ray Spectrum of GRB 970508 on 1997 May 21.0 UT , 1998, astro-ph/9804191.

[7]  P. Hughes.  Beams and jets in astrophysics , 1991 .

[8]  Abraham Loeb,et al.  Generation of Magnetic Fields in the Relativistic Shock of Gamma-Ray Burst Sources , 1999, astro-ph/9904363.

[9]  D. Palmer,et al.  BATSE observations of gamma-ray burst spectra. I: Spectral diversity , 1993 .

[10]  Sperello di Serego Alighieri,et al.  Instrumentation for Large Telescopes: Polarimetry with large telescopes , 1997 .

[11]  Eli Waxman.  Angular Size and Emission Timescales of Relativistic Fireballs , 1997 .

[12]  R. Preece,et al.  The nu F nu Peak Energy Distributions of Gamma-Ray Bursts Observed by BATSE , 1995 .

[13]  M. Rees,et al.  Optical and Long-Wavelength Afterglow from Gamma-Ray Bursts , 1996, astro-ph/9606043.

[14]  Geometrical Accuracy Test Obtained on the OUR Rotating γ-System , 1999 .

[15]  M. Rees,et al.  Relativistic fireballs: energy conversion and time-scales , 1992 .

[16]  M. Rees,et al.  Shocked by GRB 970228: the afterglow of a cosmological fireball , 1997, astro-ph/9704153.

[17]  J. Angel,et al.  Optical and Infrared Polarization of Active Extragalactic Objects , 1980 .

[18]  Eli Waxman,et al.  Gamma-ray burst afterglow: Polarization and analytic light curves , 1999 .

[19]  Abraham Loeb,et al.  Microlensing of Gamma-Ray Burst Afterglows , 1997, astro-ph/9708159.

[20]  Thanu Padmanabhan.  Inter-University Centre for Astronomy and Astrophysics (IUCAA) , 1998 .

[21]  T. Piran,et al.  Spectra and Light Curves of Gamma-Ray Burst Afterglows , 1997, astro-ph/9712005.

[22]  C. Kouveliotou,et al.  Identification of two classes of gamma-ray bursts , 1993 .

[23]  T. Muxlow,et al.  Observations of large scale extragalactic jets , 1991 .