Observations of the intense and ultra-long burst GRB 041219a with the Germanium spectrometer on INTEGRAL

¹ Research and Scientific Support Department of ESA, ESTEC, Noordwijk, The Netherlands e-mail: smcbreen@mpe.mpg.de
² Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany
³ School of Physics, University College Dublin, Dublin 4, Ireland
⁴ Department of Physics, University of Alabama at Huntsville, USA
⁵ ISOC, ESA/ESAC, Urb. Villafranca del Castillo, Madrid, Spain

Received: 14 March 2006
Accepted: 18 April 2006

Abstract

Context.GRB 041219a is the brightest burst localised by INTEGRAL. The peak flux of 43 ph cm^-2 s^-1 ( erg cm^-2 s^-1, 20 keV–8 MeV, 1 s integration) is greater than that for ~98% of all bursts and the T₉₀ duration of ~186 s (~20 keV–8 MeV) is longer than all but a small number of bursts. The intense burst occurred about ~250 s after the precursor and the long delay enabled optical and near infrared telescopes to observe the prompt emission.

Aims.We present comprehensive results of the temporal and spectral analyses, including line and afterglow searches using the spectrometer, SPI, aboard INTEGRAL, BAT on Swift and ASM on Rossi X-ray Timing Explorer. We avail of multi-wavelength data to generate broadband spectra of GRB 041219a and afterglow.

Methods.Spectra for the burst and sub-intervals were fit by the Band model and also by the quasithermal model. The high resolution Germanium spectrometer data were searched for emission and absorption features and for γ-ray afterglow.

Results. The overall burst and sub-intervals are well fit by the Band model. The photon index below the break energy shows a marked change after the quiescent time interval. In addition the spectra are well described by a black body component with a power law. The burst was detected by BAT and ASM during the long quiescent interval in SPI indicating the central engine might not be dormant but that the emission occurs in different bands. No significant emission or absorption features were found and limits of 900 eV and 120 eV are set on the most significant features. No γ-ray afterglow was detected from the end of the prompt phase to ~12 h post-burst. Broadband spectra of the prompt emission were generated in 7 time intervals using γ-ray, X-ray, optical and near-infrared data and these were compared to the high-redshift burst GRB 050904. The optical and γ-ray emission are correlated in GRB 041219a. We estimate isotropic radiated energy (E_iso) to be ~ erg. The spectral lag was determined using data from the BAT and it changes throughout the burst. A number of pseudo-redshifts were evaluated and large dispersion in values was found.