198 research outputs found
Discovery of a tight correlation for gamma ray burst afterglows with `canonical' light curves
Gamma Ray Bursts (GRB) observed up to redshifts are fascinating objects
to study due to their still unexplained relativistic outburst mechanisms and a
possible use to test cosmological models. Our analysis of 77 GRB afterglows
with known redshifts revealed a physical subsample of long GRBs with canonical
{\it plateau breaking to power-law} light curves with a significant {\it
luminosity - break time } correlation in the GRB rest frame.
This subsample forms approximately the {\it upper envelope} of the studied
distribution. We have also found a similar relation for a small sample of GRB
afterglows that belong to the intermediate class (IC) between the short and the
long ones. It proves that within the full sample of afterglows there exist
physical subclasses revealed here by tight correlations of their afterglow
properties. The afterglows with regular (`canonical') light curves obey not
only a mentioned tight physical scaling, but -- for a given -- the more
regular progenitor explosions lead to preferentially brighter afterglows.Comment: 15 pages, 5 figures accepted to ApJ
Toward a standard Gamma Ray Burst: tight correlations between the prompt and the afterglow plateau phase emission
To reveal and understand astrophysical processes responsible for the Gamma
Ray Burst (GRB) phenomenon, it is crucial to discover and understand relations
between their observational properties. The presented study is performed in the
GRB rest frames and it uses a sample of 62 long GRBs from our sample of 77
Swift GRBs with known redshifts. Following the earlier analysis of the
afterglow {\it characteristic luminosity -- break time }
correlation for a sample of long GRBs \citep{Dainotti2010} we extend it to
correlations between the afterglow and the prompt emission GRB physical
parameters. We reveal a tight physical scaling between the mentioned afterglow
luminosity and the prompt emission {\it mean} luminosity . The distribution, with the Spearman correlation
coefficient reaching 0.95 for the data subsample with most regular light
curves, can be fitted with approximately .
We also analyzed correlations of with several other prompt emission
parameters, including the isotropic energy , the peak energy in the
spectrum, , and the variability parameter, , defined
by \cite{N000}. As a result, we reveal significant correlations also between
these quantities, with an exception of the variability parameter. The main
result of the present study is the discovery that the highest correlated GRB
subsample in the \citet{Dainotti2010} afterglow analysis, for the GRBs with
canonical X\,-\,ray light curves, leads also to the highest {\it
prompt-afterglow} correlations and such events can be considered to form a
sample of standard GRBs for astrophysics and cosmology.Comment: The Data Table will appear after the paper will be accepte
Tensions with the flat CDM model from high-redshift cosmography
The longstanding search for the cosmological model that best describes the
Universe has been made more intriguing since the recent discovery of the Hubble
constant, , tension observed between the value of from the
Cosmic Microwave Background and from type Ia supernovae (SNe Ia). Hence, the
commonly trusted flat CDM model is under investigation. In this
scenario, cosmography is a very powerful technique to investigate the evolution
of the Universe without any cosmological assumption, thus revealing tensions
between observational data and predictions from cosmological models in a
completely model-independent way. We here employ a robust cosmographic
technique based on an orthogonal logarithmic polynomial expansion of the
luminosity distance to fit quasars (QSOs) alone and QSOs combined with
Gamma-Ray Bursts (GRBs), SNe Ia, and Baryon Acoustic Oscillations. To apply
QSOs and GRBs as probes we use, respectively, the Risaliti-Lusso relation
between ultraviolet and X-ray luminosities and the ``Dainotti GRB 3D relation"
among the rest-frame end time of the X-ray plateau emission, its corresponding
luminosity, and the peak prompt luminosity. We also correct QSOs and GRBs for
selection biases and redshift evolution and we employ both the traditional
Gaussian likelihood and the newly discovered best-fit likelihoods for each
probe investigated. This comprehensive analysis reveals a strong tension () between our data sets and the flat CDM model proving the
power of both the cosmographic approach and high-redshift sources, such as QSOs
and GRBs, which can probe the Universe at early epochs.Comment: 13 pages, 4 figures, 4 tables. Comments are welcome. Accepted for
publication in MNRA
Constraining cosmological parameters by Gamma Ray Burst X - ray afterglow lightcurves
We present the Hubble diagram (HD) of 66 Gamma Ray Bursts (GRBs) derived
using only data from their X - ray afterglow lightcurve. To this end, we use
the recently updated L_X - T_a correlation between the break time T_a and the X
- ray luminosity L_X measured at T_a calibrated from a sample of Swift GRBs
with lightcurves well fitted by the Willingale et al. (2007) model. We then
investigate the use of this HD to constrain cosmological parameters when used
alone or in combination with other data showing that the use of GRBs leads to
constraints in agreement with previous results in literature. We finally argue
that a larger sample of high luminosity GRBs can provide a valuable information
in the search for the correct cosmological model.Comment: 6 pages, 2 figures, 2 tables, submitte
GRB970228 and the class of GRBs with an initial spikelike emission: do they follow the Amati relation?
On the basis of the recent understanding of GRB050315 and GRB060218, we
return to GRB970228, the first Gamma-Ray Burst (GRB) with detected afterglow.
We proposed it as the prototype for a new class of GRBs with "an occasional
softer extended emission lasting tenths of seconds after an initial spikelike
emission". Detailed theoretical computation of the GRB970228 light curves in
selected energy bands for the prompt emission are presented and compared with
observational BeppoSAX data. From our analysis we conclude that GRB970228 and
likely the ones of the above mentioned new class of GRBs are "canonical GRBs"
have only one peculiarity: they exploded in a galactic environment, possibly
the halo, with a very low value of CBM density. Here we investigate how
GRB970228 unveils another peculiarity of this class of GRBs: they do not
fulfill the "Amati relation". We provide a theoretical explanation within the
fireshell model for the apparent absence of such correlation for the GRBs
belonging to this new class.Comment: 5 pages, 3 figures, in the Proceedings of the "4th Italian-Sino
Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28,
2007, C.L. Bianco, S.-S. Xue, Editor
Gamma-Ray Bursts, Quasars, Baryonic Acoustic Oscillations, and Supernovae Ia: new statistical insights and cosmological constraints
The recent Hubble constant, , tension is observed
between the value of from the Cosmic Microwave Background (CMB) and
Type Ia Supernovae (SNe Ia). It is a decade since this tension is excruciating
the modern astrophysical community. To shed light on this problem is key to
consider probes at intermediate redshifts between SNe Ia and CMB and reduce the
uncertainty on . Toward these goals, we fill the redshift gap by employing
Gamma-Ray Bursts (GRBs) and Quasars (QSOs), reaching and ,
respectively, combined with Baryonic Acoustic Oscillations (BAO) and SNe Ia. To
this end, we employ the ``Dainotti GRB 3D relation" among the rest-frame end
time of the X-ray plateau emission, its corresponding luminosity, and the peak
prompt luminosity, and the ``Risaliti-Lusso" QSO relation between ultraviolet
and X-ray luminosities. We inquire the commonly adopted Gaussianity assumption
on GRBs, QSOs, and BAO. With the joint sample, we fit the flat Cold
Dark Matter model with both the Gaussian and the newly discovered likelihoods.
We also investigate the impact of the calibration assumed for \textit{Pantheon}
and \textit{Pantheon +} SNe Ia on this analysis. Remarkably, we show that only
GRBs fulfill the Gaussianity assumption. We achieve small uncertainties on the
matter density parameter and . We find values compatible
within 2 with the one from the Tip of the Red Giant Branch. Finally,
we show that the cosmological results are heavily biased against the arbitrary
calibration choice for SNe Ia.Comment: 17 pages, 6 figures, 1 table, accepted in MNRA
Constraining properties of GRB magnetar central engines using the observed plateau luminosity and duration correlation
An intrinsic correlation has been identified between the luminosity and
duration of plateaus in the X-ray afterglows of Gamma-Ray Bursts (GRBs;
Dainotti et al. 2008), suggesting a central engine origin. The magnetar central
engine model predicts an observable plateau phase, with plateau durations and
luminosities being determined by the magnetic fields and spin periods of the
newly formed magnetar. This paper analytically shows that the magnetar central
engine model can explain, within the 1 uncertainties, the correlation
between plateau luminosity and duration. The observed scatter in the
correlation most likely originates in the spread of initial spin periods of the
newly formed magnetar and provides an estimate of the maximum spin period of
~35 ms (assuming a constant mass, efficiency and beaming across the GRB
sample). Additionally, by combining the observed data and simulations, we show
that the magnetar emission is most likely narrowly beamed and has 20%
efficiency in conversion of rotational energy from the magnetar into the
observed plateau luminosity. The beaming angles and efficiencies obtained by
this method are fully consistent with both predicted and observed values. We
find that Short GRBs and Short GRBs with Extended Emission lie on the same
correlation but are statistically inconsistent with being drawn from the same
distribution as Long GRBs, this is consistent with them having a wider beaming
angle than Long GRBs.Comment: MNRAS Accepte
The Amati relation in the "fireshell" model
(Shortened) CONTEXT: [...] AIMS: Motivated by the relation proposed by Amati
and collaborators, we look within the ``fireshell'' model for a relation
between the peak energy E_p of the \nu F_\nu total time-integrated spectrum of
the afterglow and the total energy of the afterglow E_{aft}, which in our model
encompasses and extends the prompt emission. METODS: [...] Within the fireshell
model [...] We can then build two sets of ``gedanken'' GRBs varying the total
energy of the electron-positron plasma E^{e^\pm}_{tot} and keeping the same
baryon loading B of GRB050315. The first set assumes for the effective CBM
density the one obtained in the fit of GRB050315. The second set assumes
instead a constant CBM density equal to the average value of the GRB050315
prompt phase. RESULTS: For the first set of ``gedanken'' GRBs we find a
relation E_p\propto (E_{aft})^a, with a = 0.45 \pm 0.01, whose slope strictly
agrees with the Amati one. Such a relation, in the limit B \to 10^{-2},
coincides with the Amati one. Instead, in the second set of ``gedanken'' GRBs
no correlation is found. CONCLUSIONS: Our analysis excludes the Proper-GRB
(P-GRB) from the prompt emission, extends all the way to the latest afterglow
phases and is independent on the assumed cosmological model, since all
``gedanken'' GRBs are at the same redshift. The Amati relation, on the other
hand, includes also the P-GRB, focuses on the prompt emission only, and is
therefore influenced by the instrumental threshold which fixes the end of the
prompt emission, and depends on the assumed cosmology. This may well explain
the intrinsic scatter observed in the Amati relation.Comment: 4 pages, 5 figures, to appear on A&A Letter
ACM SIGCOMM Workshop on Big Data Analytics and Machine Learning for Data Communication Networks
The explosion in volume and heterogeneity of data communication network measurements opens the door to the massive applica- tion of machine learning and artificial intelligence technology in networking. While machine learning is today systematically and successfully applied in many other data-driven domains, its appli- cation is in an infancy stage of development in the networking domain. The ACM SIGCOMM Workshop on Big Data Analytics and Machine Learning for Data Communication Networks, Big- DAMA, fosters the research and development of novel analytical approaches and technical solutions that can exploit Big Data tech- nology in the analysis of complex communication networks such as the Internet
- …