22 research outputs found
A study of gamma ray bursts with afterglow plateau phases associated with supernovae
The analysis of 176 gamma ray burst (GRB) afterglow plateaus observed by
Swift from GRBs with known redshifts revealed that the subsample of long GRBs
associated with supernovae (LONG-SNe) - 19 events - presents a very high
correlation coefficient between the luminosity at the end of the plateau phase
La and the end time of the plateau T*a, hereafter Dainotti relation.
Furthermore, these SNe Ib/c associated with GRBs also obey the peak-magnitude
stretch relation, similar to that used to standardize the SNe Ia. We here
investigate a category of GRBs with plateau and associated with SNe to compare
the Dainotti correlation for this sample with the correlation for long GRBs for
which no associated SN has been observed (hereafter LONG-NO-SNe, 128 GRBs) and
to check whether there is a difference among these sub-samples. We first
adopted a non-parametric statistical method to take redshift evolution into
account and to check if and how this effect may steepen the slope for the
LONG-NO-SNe sample. Therefore, removing selection bias is the first step before
any comparison among samples observed at different redshifts could be properly
performed. Then, we applied the T-student test to evaluate a statistical
difference between the slopes of the two samples. We demonstrate that there is
no evolution for the slope of the LONG-NO-SNe sample and no evolution is
expected for the LONG-SNe sample at small redshifts. The difference between the
slope of the LONG-NO-SNe and the slope of LONG-SNe with firm spectral detection
of SN components, is statistically significant. This possibly suggests that,
unlike LONG-NO-SNe, LONG-SNe with firm spectroscopic features of the associated
SNe might not require a standard energy reservoir in the plateau phase.
Therefore, this analysis may open new perspectives in future theoretical
investigations of the GRBs with plateau emission and that are associated with
SNe.Comment: 11 pages, 10 figures, 2 Tables, in press on Astronomy and
Astrophysics, 8 dicember 201
Closure Relations of Synchrotron Self-Compton in Afterglow stratified medium and Fermi-LAT Detected Gamma-Ray Bursts
The Second Gamma-ray Burst Catalog (2FLGC) was announced by the Fermi Large
Area Telescope (Fermi-LAT) Collaboration. It includes 29 bursts with photon
energy higher than 10 GeV. Gamma-ray burst (GRB) afterglow observations have
been adequately explained by the classic synchrotron forward-shock model,
however, photon energies greater than 10 GeV from these transient events are
challenging, if not impossible, to characterize using this afterglow model.
Recently, the closure relations (CRs) of the synchrotron self-Compton (SSC)
forward-shock model evolving in a stellar wind and homogeneous medium was
presented to analyze the evolution of the spectral and temporal indexes of
those bursts reported in 2FLGC. In this work, we provide the CRs of the same
afterglow model, but evolving in an intermediate density profile () with , taking into account the
adiabatic/radiative regime and with/without energy injection for any value of
the electron spectral index. The results show that the current model accounts
for a considerable subset of GRBs that cannot be interpreted in either
stellar-wind or homogeneous afterglow SSC model. The analysis indicates that
the best-stratified scenario is most consistent with for
no-energy injection and for energy injection.Comment: 13 pages, 3 figure
Putting Flat CDM In The (Redshift) Bin
Flat CDM cosmology is specified by two constant fitting parameters
in the late Universe, the Hubble constant and matter density (today)
. In the cosmology literature, one typically \textit{assumes} that
there is no redshift evolution of cosmological parameters when one fits data
sets. Here, in mock observational Hubble data we demonstrate evolution in
distributions of best fit parameters with effective redshift. As a result,
considerably different best fits from Planck-CDM
cannot be precluded in high redshift bins. We explore if observational Hubble
data, Type Ia supernovae and standardisable quasar samples exhibit redshift
evolution of best fit CDM parameters. In all samples, we confirm an
increasing (decreasing ) trend with increasing bin redshift.
Through comparison with mocks, we confirm that similar behaviour can arise
randomly within the flat CDM model with probabilities as low as ().Comment: 5 pages, 10 figures; v2 added explanations and appendi
The unprecedented flaring activities around Mrk 421 in 2012 and 2013: The test for neutrino and UHECR event connection
Since its mission, Fermi Collaboration reported the highest flux observed
during July - September 2012 for the BL Lac Markarian 421 (Mrk 421). The
integrated flux was eight times greater than the average flux reported in the
second Fermi catalog. During April 2013, Mrk 421 exhibited the highest TeV
-ray and optical fluxes recorded. The Telescope Array (TA)
collaboration reported the arrival of 72 ultra-high-energy cosmic rays
(UHECRs), two in temporal and positional coincidence with the flaring activity
observed in 2012 and one with the flaring activity in 2013. The IceCube
collaboration has reported around 100 neutrino events in the High-Energy
Starting Events (HESE) catalog. Although no neutrino track-like event has been
associated with this source, a neutrino shower-like event (IC31) is in temporal
and positional coincidence with the flare in 2012. Describing the broadband
spectral energy distribution during the flaring activities exhibited in 2012
and 2013 with one- and two-zone lepto-hadronic scenarios and one-zone SSC
model, we study a possible correlation between the neutrino event IC31 and the
three UHECRs. We estimate the number of neutrino and UHECR events generated
from the proposed models, and show that while the neutrino events are low to
associate the event IC31 with Mrk 421, the number of UHECRs are similar to
those reported by TA collaboration.Comment: 20 pages, 5 figures, 7 Table
A Stochastic Approach To Reconstruct Gamma Ray Burst Lightcurves
Gamma-Ray Bursts (GRBs), being observed at high redshift (z = 9.4), vital to
cosmological studies and investigating Population III stars. To tackle these
studies, we need correlations among relevant GRB variables with the requirement
of small uncertainties on their variables. Thus, we must have good coverage of
GRB light curves (LCs). However, gaps in the LC hinder the precise
determination of GRB properties and are often unavoidable. Therefore, extensive
categorization of GRB LCs remains a hurdle. We address LC gaps using a
'stochastic reconstruction,' wherein we fit two pre-existing models (Willingale
2007; W07 and Broken Power Law; BPL) to the observed LC, then use the
distribution of flux residuals from the original data to generate data to fill
in the temporal gaps. We also demonstrate a model-independent LC reconstruction
via Gaussian Processes. At 10% noise, the uncertainty of the end time of the
plateau, its correspondent flux, and the temporal decay index after the plateau
decreases, on average, by 33.3% 35.03%, and 43.32%, respectively for the W07,
and by 33.3%, 30.78%, 43.9% for the BPL. The slope of the plateau decreases by
14.76% in the BPL. After using the Gaussian Process technique, we see similar
trends of a decrease in uncertainty for all model parameters for both the W07
and BPL models. These improvements are essential for the application of GRBs as
standard candles in cosmology, for the investigation of theoretical models and
for inferring the redshift of GRBs with future machine learning analysis.Comment: 20 pages, 6 tables, 11 figure
GRB Optical and X-ray Plateau Properties Classifier Using Unsupervised Machine Learning
The division of Gamma-ray bursts (GRBs) into different classes, other than
the "short" and "long", has been an active field of research. We investigate
whether GRBs can be classified based on a broader set of parameters, including
prompt and plateau emission ones. Observational evidence suggests the existence
of more GRB sub-classes, but results so far are either conflicting or not
statistically significant. The novelty here is producing a
machine-learning-based classification of GRBs using their observed X-rays and
optical properties. We used two data samples: the first, composed of 203 GRBs,
is from the Neil Gehrels Swift Observatory (Swift/XRT), and the latter,
composed of 134 GRBs, is from the ground-based Telescopes and Swift/UVOT. Both
samples possess the plateau emission (a flat part of the light curve happening
after the prompt emission, the main GRB event). We have applied the Gaussian
Mixture Model (GMM) to explore multiple parameter spaces and sub-class
combinations to reveal if there is a match between the current observational
sub-classes and the statistical classification. With these samples and the
algorithm, we spot a few micro-trends in certain cases, but we cannot conclude
that any clear trend exists in classifying GRBs. These microtrends could point
towards a deeper understanding of the physical meaning of these classes (e.g.,
a different environment of the same progenitor or different progenitors).
However, a larger sample and different algorithms could achieve such goals.
Thus, this methodology can lead to deeper insights in the future.Comment: 20 pages, 10 figures (one has 4 panels, two have a single panel, six
have 8 panels, one has 6 panels), 4 tables. Accepted for publication in MNRA
The Blackholic energy and the canonical Gamma-Ray Burst IV: the "long", "genuine short" and "fake - disguised short" GRBs
(Shortened) [...] After recalling the basic features of the "fireshell
model", we emphasize the following novel results: 1) the interpretation of the
X-ray flares in GRB afterglows as due to the interaction of the optically thin
fireshell with isolated clouds in the CircumBurst Medium (CBM); 2) an
interpretation as "fake - disguised" short GRBs of the GRBs belonging to the
class identified by Norris & Bonnell [...] consistent with an origin from the
final coalescence of a binary system in the halo of their host galaxies with
particularly low CBM density [...]; 3) the first attempt to study a genuine
short GRB with the analysis of GRB 050509B, that reveals indeed still an open
question; 4) the interpretation of the GRB-SN association in the case of GRB
060218 via the "induced gravitational collapse" process; 5) a first attempt to
understand the nature of the "Amati relation", a phenomenological correlation
between the isotropic-equivalent radiated energy of the prompt emission E_{iso}
with the cosmological rest-frame \nu F_{\nu} spectrum peak energy E_{p,i}. In
addition, recent progress on the thermalization of the electron-positron plasma
close to their formation phase, as well as the structure of the electrodynamics
of Kerr-Newman Black Holes are presented. An outlook for possible explanation
of high-energy phenomena in GRBs to be expected from the AGILE and the Fermi
satellites are discussed. As an example of high energy process, the work by
Enrico Fermi dealing with ultrarelativistic collisions is examined. It is clear
that all the GRB physics points to the existence of overcritical
electrodynamical fields. In this sense we present some progresses on a unified
approach to heavy nuclei and neutron stars cores, which leads to the existence
of overcritical fields under the neutron star crust.Comment: 68 pages, 50 figures, in the Proceedings of the XIII Brazilian School
on Cosmology and Gravitation, M. Novello, S.E. Perez-Bergliaffa, editor
Modeling Gamma-ray burst Afterglow observations with an Off-axis Jet emission
Gamma-ray bursts (GRBs) are fascinating extragalactic objects. They represent
a fantastic opportunity to investigate unique properties not exhibited in other
sources. Multi-wavelength afterglow observations from some short- and
long-duration GRBs reveal an atypical long-lasting emission that evolves
differently from the canonical afterglow light curves favoring the off-axis
emission. We present an analytical synchrotron afterglow scenario, and the
hydrodynamical evolution of an off-axis top-hat jet decelerated in a stratified
surrounding environment. The analytical synchrotron afterglow model is shown
during the coasting, deceleration (off- and on-axis emission), and the
post-jet-break decay phases, and the hydrodynamical evolution is computed by
numerical simulations showing the time evolution of the Doppler factor, the
half-opening angle, the bulk Lorentz factor, and the deceleration radius. We
show that numerical simulations are in good agreement with those derived with
our analytical approach. We apply the current synchrotron model and describe
successfully the delayed non-thermal emission observed in a sample of long and
short GRBs with evidence of off-axis emission. Furthermore, we provide
constraints on the possible afterglow emission by requiring the
multi-wavelength upper limits derived for the closest Swift-detected GRBs and
promising gravitational-wave events.Comment: 36 pages, 16 figures, accepted for publication in Ap
The canonical Gamma-Ray Bursts and their "precursors"
The fireshell model for Gamma-Ray Bursts (GRBs) naturally leads to a
canonical GRB composed of a proper-GRB (P-GRB) and an afterglow. P-GRBs,
introduced by us in 2001, are sometimes considered "precursors" of the main GRB
event in the current literature. We show in this paper how the fireshell model
leads to the understanding of the structure of GRBs, with precise estimates of
the time sequence and intensities of the P-GRB and the of the afterglow. It
leads as well to a natural classification of the canonical GRBs which overcomes
the traditional one in short and long GRBs.Comment: 4 pages, 3 figures, Proceedings of the 2008 Nanjing GRB conferenc
Machine-Learning Enhanced Photometric Analysis of the Extremely Bright GRB 210822A
We present analytical and numerical models of the bright long GRB 210822A at
. The intrinsic extreme brightness exhibited in the optical, which is
very similar to other bright GRBs (e.g., GRBs 080319B, 130427A, 160625A
190114C, and 221009A), makes GRB 210822A an ideal case for studying the
evolution of this particular kind of GRB. We use optical data from the RATIR
instrument starting at s, with publicly available optical data from
other ground-based observatories, as well as X-ray data from the Swift/X-ray
Telescope (XRT) and data from the Swift/Ultraviolet/Optical Telescope (UVOT).
The temporal profiles and spectral properties during the late stages align
consistently with the conventional forward shock model, complemented by a
reverse shock element that dominates optical emissions during the initial
phases ( s). Furthermore, we observe a break at s that we
interpreted as evidence of a jet break, which constrains the opening angle to
be about degrees. Finally, we apply a
machine-learning technique to model the multi-wavelength light curve of GRB
210822A using the AFTERGLOWPY library. We estimate the angle of sight
degrees, the energy ergs, the electron index , the thermal
energy fraction in electrons and in
the magnetic field , the efficiency
, and the density of the surrounding medium .Comment: Submitted to MNRAS, 11 pages, 6 figures. Fixed typo