Multi-wavelength afterglow observations of the high redshift GRB 050730

¹ Instituto de Astrofísica de Andalucía, PO Box 03004, 18080 Granada, Spain e-mail: sbp2@mssl.ucl.ac.uk
² European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³ Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany
⁴ Departamento de Física (EPS), Universidad de Jaén, Campus Las Lagunillas s/n (Ed-A3), 23071 Jaén, Spain
⁵ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France
⁶ IAA-CSIC and Space Telescope Science Institute, St. Martin Dr., Baltimore, MA, USA
⁷ Department of Astronomy, Yale University, PO Box 208101, New Haven, CT 06520, USA
⁸ Nikolaev State University, Nikolska 24, Nikolaev 54030, Ukraine
⁹ Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK
¹⁰ Instituto de Astrofísica de Canarias, C/. Vía Láctea, s/n, 38200 La Laguna, Tenerife, Spain
¹¹ Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
¹² Center for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹³ Center for Research & Education in Science & Technology, Hosakote, Bangalore 562 114, India
¹⁴ Indian Institute of Astrophysics, Bangalore 560 034, India
¹⁵ Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Naini Tal 263129, Uttaranchal, India

Received: 11 February 2006
Accepted: 2 August 2006

Abstract

Context.GRB 050730 is a long duration high-redshift burst () that was discovered by Swift. The afterglow shows variability and was well monitored over a wide wavelength range. We present comprehensive temporal and spectral analysis of the afterglow of GRB 050730 including observations covering the wavelength range from the millimeter to X-rays.

Aims.We use multi-wavelength afterglow data to understand the complex temporal and spectral decay properties of this high redshift burst.

Methods.Five telescopes were used to study the decaying afterglow of GRB 050730 in the and K photometric pass bands. A spectral energy distribution was constructed at 2.9 h post-burst in the and K bands. X-ray data from the satellites Swift and XMM-Newton were used to study the afterglow evolution at higher energies.

Results.The early afterglow shows variability at early times and the slope steepens at 0.1 days (8.6 ks) in the and K passbands. The early afterglow light curve decayed with a powerlaw slope index and subsequently steepened to based on the R and I band data. A millimeter detection of the afterglow around 3 days after the burst shows an excess in comparison to theoretical predictions. The early X-ray light curve observed by Swift is complex and contains flares. At late times the X-ray light curve can be fit by a powerlaw decay with which is steeper than the optical light curve. A spectral energy distribution (SED) was constructed at ~2.9 h after the burst. An electron energy index, p, of ~2.3 was calculated using the SED and the photon index from the X-ray afterglow spectra and implies that the synchrotron cooling frequency is above the X-ray band.