Article

Towards the Properties of Long Gamma-Ray Burst Progenitors with Swift Data

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 09/2009; DOI: 10.1111/j.1365-2966.2009.15760.x
Source: arXiv

ABSTRACT We investigate the properties of both the prompt and X-ray afterglows of gamma-ray bursts (GRBs) in the burst frame with a sample of 33 Swift GRBs. Assuming that the steep decay segment in the canonical X-ray afterglow lightcurves is due to the curvature effect, we fit the lightcurves with a broken power-law to derive the zero time of the last emission epoch of the prompt emission (t1) and the beginning as well as the end time of the shallow decay segment (t2 and t3).We show that both the isotropic peak gamma-ray luminosity and gamma-ray energy are correlated with the isotropic X-ray energy of the shallow decay phase and the isotropic X-ray luminosity at t2. We infer the properties of the progenitor stars based on a model proposed by Kumar et al. who suggested that both the prompt gamma-rays and the X-ray afterglows are due to the accretions of different layers of materials of the GRB progenitor star by a central black hole (BH). We find that most of the derived masses of the core layers are 0.1-5 solar mass with a radius of 10^8-10^10 cm. The rotation parameter is correlated with the burst duration, being consistent with the expectation of collapsar models. The estimated radii and the masses of the fall-back materials for the envelope layers are 10^10-10^12 cm and 10^-3~1 solar mass, respectively. The average accretion rates in the shallow decay phase are correlated with those in the prompt gamma-ray phase, but they are much lower. The derived radii of the envelope are smaller than the photospheric radii of Wolf-Rayet (WR) stars. It is interesting that the assembled mass density profile for the bursts in our sample is also well consistent with the simulation for a pre-supernova star with 25 solar mass. Comment: 12 pages in MNRAS two-column style, 8 figures, 3 tables, accepted for publication in MNRAS

0 Bookmarks
 · 
52 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: (shortened) It has been proposed that the envelopes of luminous stars may be subject to substantial radius inflation. The inflation effect has been discussed in relation to the radius problem of WR stars, but has yet failed to explain the large observed radii of Galactic WR stars. We wish to obtain a physical perspective of the inflation effect, and study the consequences for the radii of WR stars, and LBVs. For WR stars the observed radii are up to an order of magnitude larger than predicted by theory, whilst S Doradus-type LBVs are subject to humongous radius variations, which remain as yet ill-explained. We use a dual approach to investigate the envelope inflation, based on numerical models for stars near the Eddington limit, and a new analytic formalism to describe the effect. An additional new aspect is that we take the effect of density inhomogeneities (clumping) within the outer stellar envelopes into account. Due to the effect of clumping we are able to bring the observed WR radii in agreement with theory. Based on our new formalism, we find that the radial inflation is a function of a dimensionless parameter W, which largely depends on the topology of the Fe-opacity peak, i.e., on material properties. For W>1, we discover an instability limit, for which the stellar envelope becomes gravitationally unbound, i.e. there no longer exists a static solution. Within this framework we are also able to explain the S Doradus-type instabilities for LBVs like AG Car, with a possible triggering due to changes in stellar rotation. The stellar effective temperatures in the upper HR diagram are potentially strongly affected by the inflation effect. This may have particularly strong effects on the evolved massive LBV and WR stars just prior to their final collapse, as the progenitors of SNe Ibc, SNe II, and long GRBs.
    Astronomy and Astrophysics 12/2011; · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the analysis of a large sample of gamma-ray burst (GRB) X-ray light curves in the rest frame to characterise their intrinsic properties in the context of different theoretical scenarios. We determine the morphology, time scales, and energetics of 64 long GRBs observed by \emph{Swift}/XRT \emph{without} flaring activity. We furthermore provide a one-to-one comparison to the properties of GRBs \emph{with} X-ray flares. We find that the steep decay morphology and its connection with X-ray flares favour a scenario in which a central engine origin. We show that this scenario can also account for the shallow decay phase, provided that the GRB progenitor star has a self-similar structure with a constant envelope-to-core mass ratio $\sim 0.02-0.03$. However, difficulties arise for very long duration ($t_p\gtrsim10^4$ s) shallow phases. Alternatively, a spinning-down magnetar whose emitted power refreshes the forward shock can quantitatively account for the shallow decay properties. In particular we demonstrate that this model can account for the plateau luminosity vs. end time anticorrelation.
    Astronomy and Astrophysics 12/2011; · 5.08 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We analyze the emission plateaus in the X-ray afterglow light curves of gamma-ray bursts (GRBs) and those in the optical light curves of type II plateau supernovae (SNe II-P) in order to study whether they have similar late energy injection behaviors. We show that correlations of bolometric energies (or luminosities) between the prompt explosions and the plateaus for the two phenomena are similar. The energy emitted by SNe II-P are at the lower end of the range of possible energies for GRBs. The bolometric energies (or luminosities) in the prompt phase Eexpl (or Lexpl) and in the plateau phase Eplateau (or Lplateau) share relations of Eexpl ∝ E0.73±0.14plateau and Lexpl ∝ L~0.70plateau. These results may indicate a similar late energy injection behavior that produces the observed plateaus in these two phenomena.
    Research in Astronomy and Astrophysics 06/2013; 13(6):671. · 1.35 Impact Factor

Full-text (2 Sources)

View
33 Downloads
Available from
May 16, 2014