Spectral-luminosity relation within individualFermigamma rays bursts

Abstract

We study the spectra of all long gamma ray bursts (GRBs) of known redshift detected by the Fermi satellite untill the end of July 2009. Their fluxes and fluences are large enough to allow a time dependent study of their spectral characteristics in the 8 keV-1 MeV energy range. We find that the peak energy E peak of their EL(E) spectrum correlates with the luminosity in a remarkably tight way within individual bursts. This time-resolved E peak − L iso correlation is very similar for all the considered bursts and has a slope and normalisation similar to the analogous E peak − L iso correlation defined by the time-integrated spectra of different bursts detected by several different satellites. For a few of the considered GRBs, we could also study the behaviour of the E peak − L iso correlation during the rising and decaying phases of individual pulses within each burst, finding no differences. Our results indicate the presence of a similar physical mechanism, operating for the duration of different GRBs, tightly linking the burst luminosity with the peak energy of the spectrum emitted at different times. Such a physical mechanism is the same during the rise and decay phase of individual pulses composing a GRB. While calling for a robust physical interpretation, these results strongly indicate that the E peak − L iso spectral energy correlation found considering the time-integrated spectra of different bursts is real and not the result of instrumental selection effects.

TheEpeak–Eisorelation revisited withFermiGRBs

“…The observation of an E pi -E iso relation in time-resolved spectra (e.g. Ghirlanda et al 2010;Frontera et al 2012;Basak & Rao 2012;Lu et al 2012) may also provide insights into the origin of the E pi -E iso boundary. Finally, Since the E pi -E iso relation is not an intrinsic property of GRBs, it may be difficult to use it to standardize GRBs (Ghirlanda et al 2006;Mészáros & Gehrels 2012).…”

The rest-frame Golenetskii correlation via a hierarchical Bayesian analysis

“…A key feature of gamma-ray bursts (GRBs) is the observed relation within a burst between the luminosity and the νFν peak energy (E rest peak ) (Golenetskii et al 1983;Kargatis 1994;Borgonovo & Ryde 2001;Ryde et al 2006;Ghirlanda et al 2010;Lu et al 2010;Zhang & Chen 2012;Guiriec et al 2013;Burgess et al 2014). This luminosity-E rest peak relation was first discovered by Golenetskii et al (1983) and has been found in several GRBs regardless of their lightcurve shape.…”

“…Other attempts to explain the observed GCs invoked non-thermal synchrotron emission (Zhang & Meszaros 2002;Dermer 2004) in both single (Ghirlanda et al 2010) and multi-component Preece et al 2014) time-resolved spectra. For synchrotron emission, one expects L ∝ NeB 2 Γ 2 γ 2 e and E peak ∝ BΓγ 2 e where Ne is the number of emitting electrons, B in the magnetic field, γe is the characteristic electron Lorentz factor and Γ is the bulk Lorentz factor.…”

Determination of cosmological parameters from gamma ray burst characteristics and afterglow correlations

“…These two correlations were then used to create a GRB Hubble diagram (Schaefer 2003). Other luminosity and energy correlations were soon discovered, such as: the Amati relation (Amati et al 2002;Amati 2006;Amati et al 2008Amati et al , 2009) which relates the intrinsic spectral peak energy, E p,i , to the equivalent isotropic energy, E iso ; the Yonetoku relation (Yonetoku et al 2004) which is a correlation between E p,i and the isotropic peak luminosity, L iso ; the Ghirlanda relation (Ghirlanda et al , 2006(Ghirlanda et al , 2010 which is a correlation between E p,i and the collimation corrected energy E γ ; and the Liang-Zhang relation (Liang and Zhang 2005) which relates E iso to both E p,i and the break time of the optical afterglow light curves, T a .…”