Multi-wavelength afterglow observations of the high redshift GRB 050730
McBreen, S.; Bremer, M.; Tanvir, N.; Bhatt, B. C.; Pandey, S. B.; Bailyn, C. D.; Guerrero, M. A.; Combi, J. A.; Gorosabel, J.; Muñoz-Darias, T.; Castro-Tirado, A. J.; Jelínek, M.; Monfardini, A.; Levan, A. J.; de Ugarte Postigo, A.; Guidorzi, C.; Sharma, S.; Sota, A.; Gomboc, A.; Mundell, C. G.; Sahu, D. K.; Cobb, B. E.; Guziy, S.; Pérez-Ramírez, M. D.; Bogdanov, O.
Spain, Netherlands, Germany, France, United States, Ukraine, United Kingdom, Slovenia, India
Abstract
Context: .GRB 050730 is a long duration high-redshift burst (z=3.967) 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 B, V, r', R, i', I, J and K photometric pass bands. A spectral energy distribution was constructed at 2.9 h post-burst in the B, V, R, I, J 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 B, V, r', R, i', I, J and K passbands. The early afterglow light curve decayed with a powerlaw slope index α1 = -0.60±0.07 and subsequently steepened to α2 = -1.71±0.06 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 αx = -2.5±0.15 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 νc is above the X-ray band.