448 research outputs found
Gamma Ray Bursts Spectral--Energy correlations: recent results
The correlations between the rest frame peak of the EF_E spectrum of GRBs
Epeak and their isotropic energy (E_iso) or luminosity (L_iso) could have
several implications for the understanding of the GRB prompt emission. These
correlations are presently founded on the time-averaged spectral properties of
a sample of 95 bursts, with measured redshifts, collected by different
instruments in the last 13 years (pre-Fermi). One still open issue is wether
these correlations have a physical origin or are due to instrumental selection
effects. By studying 10 long and 14 short GRBs detected by Fermi we find that a
strong time-resolved correlation between E_peak and the luminosity L_iso is
present within individual GRBs and that it is consistent with the
time-integrated correlation. This result is a direct proof of the existence in
both short and long GRBs of a similar physical link between the hardness and
the luminosity which is not due to instrumental selection effects. The origin
of the E_peak-L_iso correlation should be searched in the radiation mechanism
of the prompt emission.Comment: 5 pages, 3 figures, to appear in the proceedings of the 275 IAU Symp:
"Jets at all scales", Buenos Aires, Sept. 201
Factor analysis of the spectral and time behavior of long GRBs
A sample of 197 long BATSE GRBs is studied statistically. In the sample 11
variables, describing for any burst the time behavior of the spectra and other
quantities, are collected. The application of the factor analysis on this
sample shows that five factors describe the sample satisfactorily. Both the
pseudo-redshifts coming from the variability and the Amati-relation in its
original form are disfavored.Comment: In GAMMA-RAY BURSTS 2007: Proceedings of the Santa Fe Conferenc
A Comparative Study of Dark Energy Constraints from Current Observational Data
We examine how dark energy constraints from current observational data depend
on the analysis methods used: the analysis of Type Ia supernovae (SNe Ia), and
that of galaxy clustering data. We generalize the flux-averaging analysis
method of SNe Ia to allow correlated errors of SNe Ia, in order to reduce the
systematic bias due to weak lensing of SNe Ia. We find that flux-averaging
leads to larger errors on dark energy and cosmological parameters if only SN Ia
data are used. When SN Ia data (the latest compilation by the SNLS team) are
combined with WMAP 7 year results (in terms of our Gaussian fits to the
probability distributions of the CMB shift parameters), the latest Hubble
constant (H_0) measurement using the Hubble Space Telescope (HST), and gamma
ray burst (GRB) data, flux-averaging of SNe Ia increases the concordance with
other data, and leads to significantly tighter constraints on the dark energy
density at z=1, and the cosmic curvature \Omega_k. The galaxy clustering
measurements of H(z=0.35)r_s(z_d) and r_s(z_d)/D_A(z=0.35) (where H(z) is the
Hubble parameter, D_A(z) is the angular diameter distance, and r_s(z_d) is the
sound horizon at the drag epoch) by Chuang & Wang (2011) are consistent with SN
Ia data, given the same pirors (CMB+H_0+GRB), and lead to significantly
improved dark energy constraints when combined. Current data are fully
consistent with a cosmological constant and a flat universe.Comment: 11 pages, 9 figures. Slightly revised version, to appear in PRD.
Supernova flux-averaging code available at
http://www.nhn.ou.edu/~wang/SNcode
Extremely energetic Fermi Gamma-Ray Bursts obey spectral energy correlations
The extremely energetic Fermi GRBs 080916C, with its Eiso of ~ 10^{55} erg in
1 keV - 10 GeV and intense GeV emission, and 090323 give us a unique
opportunity to test the reliability and extension of spectral energy
correlations. Based on Konus/WIND and Fermi spectral measurements, we find that
both events are fully consistent with the updated (95 events as of April 2009)
Ep,i - Eiso correlation, thus further confirming and extending it and pointing
against a possible flattening or increased dispersion at very high energies.
This also suggests that the physics behind the emission of peculiarly bright
and hard GRBs is the same as for softer and weaker ones. In addition, we find
that the normalization of the correlation obtained by considering these two
GRBs and the other long ones for which Ep,i was measured with high accuracy by
the Fermi/GBM are fully consistent with those obtained by other instruments
(e.g., BeppoSAX, Swift, Konus-WIND), thus indicating that the correlation is
not affected significantly by detectors limited thresholds and energy bands.
Prompted by the extension of the spectrum of GRB 080916C up to several GeVs
without any excess or cut-off, we also investigated if the evaluation of Eiso
in the commonly adopted 1 keV - 10 MeV energy band may bias the Ep,i - Eiso
correlation contributing to its scatter. By computing Eiso from 1 keV to 10
GeV, the slope of the correlation becomes slightly flatter, while its
dispersion does not change significantly. Finally, we find that GRB 080916C is
also consistent with most of the other spectral energy correlations derived
from it, with the possible exception of the Ep,i - Eiso - tb correlation.Comment: 9 pages, 5 figures, final revised version accepted for pubblication
in Astronomy & Astrophysics (main Journal
Comparative Analysis of a Transition Region Bright Point with a Blinker and Coronal Bright Point Using Multiple EIS Emission Lines
Since their discovery twenty year ago, transition region bright points
(TRBPs) have never been observed spectroscopically. Bright point properties
have not been compared with similar transition region and coronal structures.
In this work we have investigated three transient quiet Sun brightenings
including a TRBP, a coronal BP (CBP) and a blinker. We use time-series
observations of the extreme ultraviolet emission lines of a wide range of
temperature T (log T = 5.3 - 6.4) from the EUV imaging spectrometer (EIS)
onboard the Hinode satellite. We present the EIS temperature maps and Doppler
maps, which are compared with magnetograms from the Michelson Doppler Imager
(MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker
are <,25 km s, which is typical of transient TR phenomena. The Dopper
velocities of the CBP were found to be < 20 km s^{-1} with exception of those
measured at log T = 6.2 where a distinct bi-directional jet is observed. From
an EM loci analysis we find evidence of single and double isothermal components
in the TRBP and CBP, respectively. TRBP and CBP loci curves are characterized
by broad distributions suggesting the existence of unresolved structure. By
comparing and contrasting the physical characteristics of the events we find
the BP phenomena are an indication of multi-scaled self similarity, given
similarities in both their underlying magnetic field configuration and
evolution in relation to EUV flux changes. In contrast, the blinker phenomena
and the TRBP are sufficiently dissimilar in their observed properties as to
constitute different event classes. Our work indicates that the measurement of
similar characteristics across multiple event types holds class-predictive
power, and is a significant step towards automated solar atmospheric
multi-class classification of unresolved transient EUV sources.Comment: 38 pages, 16 figure
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