* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Gamma-ray burst -> GRB 090618
Post Info TOPIC: GRB 090618
Blobrana


L

Posts: 131433
Date:
RE: GRB 090618
Permalink  
 

Title: AA double component in GRB 090618: a proto-black hole and a genuinely long GRB
Authors: L. Izzo, R. Ruffini, A. V. Penacchioni, C. L. Bianco, L. Caito, S. K. Chakrabarti, Jorge A. Rueda, A. Nandi, B. Patricelli

The joint X and gamma-ray observations of GRB 090618 by a large number of satellites offer an unprecedented possibility of testing crucial aspects of theoretical models. In particular, it allows us to test (a) the formation of an optically thick e+e- baryon plasma self-accelerating to Lorentz factors in the range 200 < g < 3000; (b) its transparency condition with the emission of a component of 10^{53-54} baryons in the TeV region and (c) the collision of these baryons with the circumburst medium clouds, characterized by dimensions of 10^{15-16} cm. In addition, these observations offer the possibility of testing a new understanding of the thermal and power-law components in the early phase of this GRB. We test the fireshell model of GRBs in one of the closest (z = 0.54) and most energetic (Eiso = 2.90 x 10^{53} ergs) GRBs, namely GRB 090618. We analyse its emission using several spectral models, with special attention to the thermal and power-law components. We determine the fundamental parameters of a canonical GRB within the context of the fireshell model. We find evidences of the existence of two different episodes in GRB 090618. The first episode lasts 50 s and is characterized by a spectrum consisting of thermal component, which evolves between kT = 54 keV and kT = 12 keV. The second episode, which lasts for ~ 100s, behaves as a canonical long GRB with a Lorentz gamma factor at transparency of g = 495, a temperature at transparency of 29.22 keV and with characteristic masses of the surrounding clouds of ~ 10^{22-24} g. We support the recently proposed two-component nature of GRB 090618 by using specific theoretical analysis and illustrate that the episode 1 cannot be considered to be either a GRB or a part of a GRB event, but it appears to be related to the progenitor of the collapsing bare core leading to the formation of the black hole which we call a proto-black hole.

Read more (949kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: GRB 090618: different pulse temporal and spectral characteristics within a burst
Authors: Fu-Wen Zhang

GRB 090618 was simultaneously detected by Swift-BAT and Fermi-GBM. Its light curve shows two emission episodes consisting of four prominent pulses. The pulse in the first episode (episode A) has a smoother morphology than the three pulses in the second episode (episode B). Using the pulse peak-fit method, we have performed a detailed analysis of the temporal and spectral characteristics of these four pulses and found out that the first pulse (pulse A) exhibits distinctly different properties than the others in episode B (pulses B1, B2 and B3) in the following aspects. (i) Both the pulse width (w) and the rise-to-decay ratio of pulse (r/d, pulse asymmetry) in GRB 090618 are found to be energy-dependent. The indices of the power-law correlation between w and E for the pulses in episode B however are larger than that in episode A. Moreover the pulses B1, B2 and B3 tend to be more symmetric at the higher energy bands while the pulse A displays a reverse trend. (ii) Pulse A shows a hard-to-soft spectral evolution pattern, while the three pulses in the episode B follow the light curve trend. (iii) Pulse A has a longer lag than the pulses B1, B2 and B3. The mechanism which causes the different pulse characteristics within one single GRB is unclear.

Read more (117kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: A double component in the prompt emission of GRB 090618
Authors: L. Izzo, R. Ruffini, A. V. Penacchioni, C. L. Bianco, M. Muccino, L. Caito, B. Patricelli, S. K. Chakrabarti, A. Nandi

GRB 090618 offered an unprecedented opportunity to have coordinated data, by the best of the X and Gamma Ray observatories, of the nearest (z = 0.54) energetic source (10^{54} erg). Using the Fermi-GBM observations of this GRB, we have analysed this source to explore the possibility of having components yet to be observed in other sources. We show that it is not possible to interpret GRB 090618 within the framework of the traditional single component GRB model. We argue that the observation of the first episode of duration of around 50s could not be a part of a canonical GRB, while the residual emission could be modelled easily with the models existing in literature. In this work we have considered the case of the fireshell scenario.

Read more (168kb, PDF)



__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Gamma-ray burst -> GRB 090618


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard