Article

# Multiple Component Analysis of Time Resolved Spectra of GRB041006: A Clue to the Nature of Underlying Soft Component of GRBs

• ##### G. Pizzichini
Publications- Astronomical Society of Japan (Impact Factor: 2.44). 02/2008; DOI: 10.1093/pasj/60.4.919
Source: arXiv

ABSTRACT GRB 041006 was detected by HETE-2 at 12:18:08 UT on 06 October 2004. This GRB displays a soft X-ray emission, a precursor before the onset of the main event, and also a soft X-ray tail after the end of the main peak. The light curves in four different energy bands display different features; At higher energy bands several peaks are seen in the light curve, while at lower energy bands a single broader bump dominates. It is expected that these different features are the result of a mixture of several components each of which has different energetics and variability. To reveal the nature of each component, we analysed the time resolved spectra and they are successfully resolved into several components. We also found that these components can be classified into two distinct classes; One is a component which has an exponential decay of $E_{p}$ with a characteristic timescale shorter than $\sim$ 30 sec, and its spectrum is well represented by a broken power law function, which is frequently observed in many prompt GRB emissions, so it should have an internal-shock origin. Another is a component whose $E_{p}$ is almost unchanged with characteristic timescale longer than $\sim$ 60 sec, and shows a very soft emission and slower variability. The spectrum of the soft component is characterized by either a broken power law or a black body spectrum. This component might originate from a relatively wider and lower velocity jet or a photosphere of the fireball. By assuming that the soft component is a thermal emission, the radiation radius is initially $4.4 \times 10^{6}$ km, which is a typical radius of a blue supergiant, and its expansion velocity is $2.4 \times 10^{5}$ km/s in the source frame. Comment: 19 pages, 10 figures, accepted for publication in PASJ, replaced with the accepted version (minor correction)

0 Bookmarks
·
55 Views
• Source
##### Article: X-Ray-rich Gamma-Ray Bursts, Photospheres, and Variability
[Hide abstract]
ABSTRACT: We investigate the relationship between the quasi-thermal baryon-related photosphere in relativistic outflows and the internal shocks arising outside them, which out to a limiting radius may be able to create enough pairs to extend the optically thick region. Variable gamma-ray light curves are likely to arise outside this limiting pair-forming shock radius, while X-ray excess bursts may arise from shocks occurring below it; a possible relation to X-ray flashes is discussed. This model leads to a simple physical interpretation of the observational gamma-ray variability-luminosity relation.
The Astrophysical Journal 12/2008; 578(2):812. · 6.73 Impact Factor
• Source
##### Article: The Ep,i–Eiso correlation in gamma‐ray bursts: updated observational status, re‐analysis and main implications
[Hide abstract]
ABSTRACT: The correlation between the cosmological rest-frame νFν spectrum peak energy, Ep,i, and the isotropic-equivalent radiated energy, Eiso, discovered by Amati et al. in 2002 and confirmed/extended by subsequent osbervations, is one of the most intriguing and debated observational evidences in gamma-ray burst (GRB) astrophysics. In this paper, I provide an update and a re-analysis of the Ep,i–Eiso correlation basing on an updated sample consisting of 41 long GRBs/X-ray flashes (XRFs) with firm estimates of z and observed peak energy, Ep,obs, 12 GRBs with uncertain values of z and/or Ep,obs, two short GRBs with firm estimates of z and Ep,obs and the peculiar subenergetic events GRB 980425/SN1998bw and GRB 031203/SN2003lw. In addition to standard correlation analysis and power-law fitting, the data analysis here reported includes modelling that accounts for sample variance. All 53 classical long GRBs and XRFs, including 11 Swift events with published spectral parameters and fluences, have Ep,i and Eiso values, or upper/lower limits, consistent with the correlation, which shows a chance probability as low as ∼7 × 10−15, a slope of ∼0.57 (∼0.5 when fitting by accounting for sample variance) and an extra-Poissonian logarithmic dispersion of ∼0.15, it extends over ∼5 orders of magnitude in Eiso and ∼3 orders of magnitude in Ep,i and holds from the closer to the higher z GRBs. Subenergetic GRBs (980425 and possibly 031203) and short GRBs are found to be inconsistent with the Ep,i–Eiso correlation, showing that it can be a powerful tool for discriminating different classes of GRBs and understanding their nature and differences. I also discuss the main implications of the updated Ep,i–Eiso correlation for the models of the physics and geometry of GRB emission, its use as a pseudo-redshift estimator and the tests of possible selection effects with GRBs of unknown redshift.
Monthly Notices of the Royal Astronomical Society 10/2006; 372(1):233 - 245. · 5.52 Impact Factor
• Source
##### Article: On the temporal variability classes found in long gamma-ray bursts with known redshift
[Hide abstract]
ABSTRACT: Based on the analysis of a small sample of BATSE and Konus gamma-ray bursts (GRBs) with know redshift it has been reported that the width of the autocorrelation function (ACF) shows a remarkable bimodal distribution in the rest-frame of the source. However, the origin of these two well-separated ACF classes remains unexplained.We complement previous ACF analysis studying the corresponding power density spectra (PDS). With the addition of Beppo-SAX data and taken advantage of its broad-band capability, we not only increase the burst sample but we extend the analysis to X-ray energies. The rest-frame PDS analysis at gamma-ray energies shows that the two ACF classes are not simply characterised by a different low frequency cut-off, but they have a distinct variability as a whole in the studied frequency range. Both classes exhibit average PDS with power-law behaviour at high frequencies (f' > 0.1 Hz) but significantly different slopes, with index values close to those of Brownian (-2) and Kolmogorov (-5/3) spectra for the narrow and broad classes respectively. The latter spectrum presents an additional PDS component, a low-frequency noise excess with a sharp cut-off. At X-ray energies we find the power-law index unchanged for the broad class, but a significantly steeper slope in the narrow case (~ -3). We interpret this as an indication that the broad class bursts have weaker spectral evolution than the narrow ones, as suggested also by our analysis of the ACF energy dependence. The low and high frequency PDS components may then arise from two radiating regions involving different emission mechanisms.
Astronomy and Astrophysics 03/2007; · 5.08 Impact Factor