Journal of the Korean Physical Society

pISSN 0374-4884 eISSN 1976-8524
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< PreviousNext >J. Korean Phy. Soc. 2010; 56(5(1)): 1575~1699
  • 2010-05-14

    GRB970228 in the "canonical GRB" scenario

    Maria Grazia Bernardini, Carlo Luciano Bianco, Letizia Caito, Maria Giovanna Dainotti, Roberto Guida, Remo Ruffini
    J. Korean Phy. Soc. 2010; 56(5(1)): 1575-1578

    Abstract : Within the "fireshell" model we define a "canonical GRB" light curve with two sharply different components: theProper-GRB (P-GRB), emitted when the optically thick fireshell of electron-positron plasma originating the phenomenonreaches transparency, and the afterglow, emitted due to the collision between the remaining optically thin fireshell and theCircumBurst Medium (CBM). On the basis of the recent understanding of GRB970228 as the prototype for a new class of GRBs with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission" we outline our "canonical GRB" scenario, originating from the gravitational collapse to a black hole, with a special emphasis on the discrimination between "genuine" and "fake" short GRBs. Furthermore, we investigate how the GRB970228 analysis provides a theoretical explanation for the apparent absence of such correlation for the GRBs belonging to this new class.

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  • 2010-05-14

    GRB 060614: a preliminary result

    Letizia Caito, Maria Grazia Bernardini, Carlo Luciano Bianco, Maria Giovanna Dainotti, Roberto Guida, Remo Ruffini
    J. Korean Phy. Soc. 2010; 56(5(1)): 1579-1582

    Abstract : The explosion of GRB 060614 produced a deep break in the GRB scenario and opened new horizons of investigation because it can't be traced back to any traditional scheme of classification. In fact, it manifests peculiarities both of long bursts and of short bursts and, above all, it is the first case of long duration near GRB without any bright Ib/c associated Supernova.We will show that, in our canonical GRB scenario (cite{APJ645Ruffini}), this "anomalous" situation finds a natural interpretation and allows us to discuss a possible variation to the traditional classification scheme, introducing the distinction between "genuine" and "fake" short bursts.

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  • 2010-05-14

    A direct link between the prompt emission and the afterglow: the case of GRB~070311

    Cristiano Guidorzi, Susanna D. Vergani
    J. Korean Phy. Soc. 2010; 56(5(1)): 1583-1587

    Abstract : GRB~070311 was a long burst discovered by {em INTEGRAL}.Here we present prompt $gamma$-ray, early NIR/optical, late optical and X-ray data onthis burst. We fitted the gamma-ray and optical light curves and scaledthe result to the late time optical and X-rays.The $H$-band light curve acquired by REM shows two pulses at 80 and140~s after the peak of the $gamma$-ray burst, with marginal evidence for a faint$gamma$-ray tail.Notably, the late optical and X-ray afterglow experienceda rebrightening between $3 imes10^4$ and $2 imes10^5$~s afterthe burst with energy comparable with that of the prompt emission extrapolated in the X-ray band.We describe the time profile of the late rebrightening as the combination of atime-rescaled version of the prompt $gamma$-ray pulse and an underlying power law.This result supports a common origin for both prompt and late X-ray/optical afterglowrebrightening of GRB~070311 within the external shock scenario.

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  • 2010-05-14

    The astrophysical trypthic: GRB, SN and URCA can be extended to GRB060218?

    Maria Giovanna Dainotti, Maria Grazia Bernardini, Carlo Luciano Bianco, Letizia Caito, Roberto Guida , Remo Ruffini
    J. Korean Phy. Soc. 2010; 56(5(1)): 1588-1593

    Abstract : The emph{Swift} satellite has given continuous data in the range $0.3$--$150$ keV from $0$ s to $10^6$ s for GRB060218 associated with SN2006aj. This GRB is the fourth GRB spectroscopically associated with SNe after the cases of GRB980425-SN1998bw, GRB031203-SN2003lw, GRB 030329-SN2003dh. It has an unusually long duration ($T_{90}sim 2100$ s). These data offer the opportunity to probe theoretical models for Gamma-Ray Bursts (GRBs) connected with Supernovae (SNe).We plan to fit the complete $gamma$- and X-ray light curves of this long duration GRB, including the prompt emission, in order to clarify the nature of the progenitors and the astrophysical scenario of the class of GRBs associated to SNe Ib/c. We apply our "fireshell" model based on the formation of a black hole, giving the relevant references. The initial total energy of the electron-positron plasma $E_{e^pm}^{tot} = 2.32 imes 10^{50}$ erg has a particularly low value similarly to the other GRBs associated with SNe. For the first time we observe a baryon loading $B =10^{-2}$ which coincides with the upper limit for the dynamical stability of the fireshell. The effective CircumBurst Medium (CBM) density shows a radial dependence $n_{cbm} propto r^{-alpha}$ with $1.0 lesssim alpha lesssim 1.7$ and monotonically decreases from $1$ to $10^{-6}$ particles/cm$^3$. Such a behavior is interpreted as due to a fragmentation in the fireshell. Such a fragmentation is crucial in explaining both the unusually large $T_{90}$ and the consequently inferred abnormal low value of the CBM effective density. We fit GRB060218, usually considered as an X-Ray Flash (XRF), as a "canonical GRB" within our theoretical model. The smallest possible black hole, formed by the gravitational collapse of a neutron star in a binary system, is consistent with the especially low energetics of the class of GRBs associated with SNe Ib/c. We present the URCA process and the connection between the GRBs associated with SNe extended also to the case of GRB060218.

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  • 2010-05-14

    On the lqlq electric Meissner effect'' in the field of a Reissner-Nordstr

    D. Bini, A. Geralico, R. Ruffini
    J. Korean Phy. Soc. 2010; 56(5(1)): 1594-1597

    Abstract : A perturbative solution describing atwo-body system consisting of a Reissner-Nordstrom black hole and acharged massive particle at rest is presented. The general propertiesof the perturbed metric, completely reconstructed analytically, are discussed.The perturbed electromagnetic field is also analyzed by plottingthe associated lines of force.

  • 2010-05-14

    GRB early afterglow observations with the REM robotic telescope

    Susanna Diana Vergani, Stefano Covino, Daniele Malesani, Cristiano Guidorzi, Paolo D'Avanzo, Eliana Palazzi
    J. Korean Phy. Soc. 2010; 56(5(1)): 1598-1602

    Abstract : Gamma-ray burst are thought to be produced by highly relativistic outflows. Althoughupper and lower limits for the outflow initial Lorentz factor $Gamma_0$ are available, observationalefforts to derive a direct determination of $Gamma_0$ have so far failed or provided ambiguousresults. As a matter of fact, the shape of the early-time afterglow light curve is strongly sensitive on $Gamma_0$which determines the time of the afterglow peak, i.e. when the outflow and the shocked circumburstmaterial share a comparable amount of energy.We now comment early-time observations of the near-infrared afterglows of GRB,060418 and GRB,060607Aperformed by the REM robotic telescope.For both events, the afterglow peak was singled out and allowed us to determine the initial fireball Lorentz,$Gamma_0sim400$.

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  • 2010-05-14

    The correlation between peak photon energy and radiated energy in Gamma--Ray Bursts

    Lorenzo Amati
    J. Korean Phy. Soc. 2010; 56(5(1)): 1603-1606

    Abstract : The correlation between the photon energy at which the redshift corrected ufnu spectrum peaks (hence called "peak energy", epi) and the isotropic equivalent radiated energy (eiso), is one of the most intriguing and debated observational evidences in Gamma--Ray Bursts (GRB) astrophysics. I present the updated epeiso correlation and discuss its main implications for the physics and geometry of the GRB emission, with particular emphasis on the properties of emph{Swift} GRB and the location in the epeiso plane of sub--energetic long GRB, GRB/SN events, short GRB and the recently discovered sub--class of long GRB without association with a hypernova.

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  • 2010-05-14

    Swift observations of GRB~060614

    Vanessa Mangano, Giancarlo Cusumano, Daniele Malesani, Guido Chincarini
    J. Korean Phy. Soc. 2010; 56(5(1)): 1607-1611

    Abstract : GRB 060614 is a remarkable nearby gamma-ray burst (GRB; $z=0.125$)observed by Swift with puzzling properties,which challenge current progenitor models:the lack of any bright supernova down to very strict limitsand the vanishing spectral lags are typical of short GRBs, strikinglyat odds with the long (102~s) duration of this event. However, theburst presents optical, UV and X-ray afterglows in remarkableagreement with standard jetted fireball models. In particular,spectral analysis of BAT and XRT data during the overlap time interval andafter shows that the peak energy of the burst decays and crosses theXRT energy band within 500 s from the trigger. The afterglow shows a clearcase of jet break simultaneously detected in optical, UV and X-rays, possiblythe best among Swift GRBs.Moreover, the UVOT light curves possibly show evidence of the passageof the injection frequency across the optical band between 10 and 30ks from the trigger.

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  • 2010-05-14

    Some consequences of gravitationally induced electromagnetic fields in microphysics

    Kjell Rosquist
    J. Korean Phy. Soc. 2010; 56(5(1)): 1612-1618

    Abstract : We discuss the relation between the gravitational and electromagnetic fields as governed by the Einstein-Maxwell field equations. It is emphasized that the tendency of the gravitational field to induce electromagnetic effects increases as the size of the system decreases. This is because the charge-to-mass ratio $Q/M$ is typically larger in smaller systems. For most astrophysical systems, $Q/M$ is $ll 1$ while for a Millikan oil drop, $Q/M sim 10^6$. Going all the way down to elementary particles, the value for the electron is $Q/M sim 10^{21}$. For subatomic systems there is an additional phenomenon which comes into play. In fact, according to general relativity, the gravitational field tends to become dominated by the spin at distances of the order of the Compton wavelength.The relevant quantity which governs this behavior is the ratio $S/M^2$ where $S$ is the (spin) angular momentum. For an electron, $S/M^2 sim 10^{44}$.As a consequence, the gravitational field becomes dominated by gravitomagnetic effects in the subatomic domain.This fact has important consequences for the electromagnetic fields of spinning charged particles.To analyze this situation we use the asymptotic structure in the form of the multipole fields.%Such an approach avoids the pitfalls should one try to use a near-field approach using some kind of semi-classical formulation of the Einstein-Maxwell equations for example. To obtain more exact results however, one must take quantum effects into account including radiative contributions. Although such effects are not considered in this work, the order of magnitude of the considered effects are not expected to change drastically when going to a quantum mechanical treatment. The most relevant solution of the Einstein-Maxwell equations in this context is the Kerr-Newman metric. It is the preferred solution which is in accord with all the four known multipole moments of the electron to an accuracy of one part in a thousand. Our main result is that general relativity predicts corrections to the Coulomb field for charged spinning sources. Experimentally verifiable consequences include a predicted electric quadrupole moment for the electron, possible quasi-bound states in positron-heavy ion scattering with sizes corresponding to observed anomalous peaks, as well as small corrections to energy levels in microscopic bound systems such as the hydrogen atom.

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  • 2010-05-14

    Local rate of Short-Hard Gamma-Ray Bursts and SHB Progenitor life time

    Chang-Hwan Lee, Soomin Jeong
    J. Korean Phy. Soc. 2010; 56(5(1)): 1619-1623

    Abstract : Gamma ray bursts have been divided into two classes, long-soft gamma ray burst and short-hard gamma ray burst accordingto the bimodal distribution in duration time. Due to the harder spectrum and the lack of afterglows of short-hardbursts in optical and radio observations, different progenitors for short-hard bursts and long-soft bursts have beensuggested. Based on the X-ray afterglow observation and the cumulative red-shift distribution of short-hard bursts,citet{Nak06} found that the progenitors of short-hard bursts are consistent with old populations, such as mergers ofbinary neutron stars.%Recently, the existence of two subclasses in long-soft bursts has been suggested after considering multiplecharacteristics of gamma-ray bursts, including fluences and the duration time.In this work, we extended the analysis of cumulative red-shift distribution to two possible subclasses in L-GRBs. Wefound that two possible subclass GRBs show different red-shift distributions, especially for red-shifts $z > 1$. Ourresults indicate that the accumulative red-shift distribution can be used as a tool to constrain the progenitorcharacteristics of possible subclasses in L-GRBs.

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Journal of the Korean Physical Society

pISSN 0374-4884 eISSN 1976-8524