158 research outputs found
Fast and Reliable Time Delay Estimation of Strong Lens Systems Using Method of Smoothing and Cross-Correlation
The observable time delays between the multiple images of strong lensing
systems with time variable sources can provide us with some valuable
information to probe the expansion history of the Universe. Estimation of these
time delays can be very challenging due to complexities of the observed data
where there are seasonal gaps, various noises and systematics such as unknown
microlensing effects. In this paper we introduce a novel approach to estimate
the time delays for strong lensing systems implementing various statistical
methods of data analysis including the method of smoothing and
cross-correlation. The method we introduce in this paper has been recently used
in TDC0 and TDC1 Strong Lens Time Delay Challenges and has shown its power in
reliable and precise estimation of time delays dealing with data with different
complexities.Comment: 23 pages, 9 figures, 3 tables, discussions extended, references
added, results unchanged, matches final version published in Ap
Testing Isotropic Universe Using the Gamma-Ray Burst Data of Fermi / GBM
The sky distribution of Gamma-Ray Bursts (GRBs) has been intensively studied
by various groups for more than two decades. Most of these studies test the
isotropy of GRBs based on their sky number density distribution. In this work
we propose an approach to test the isotropy of the Universe through inspecting
the isotropy of the properties of GRBs such as their duration, fluences and
peak fluxes at various energy bands and different time scales. We apply this
method on the {\em Fermi} / Gamma-ray Burst Monitor (GBM) data sample
containing 1591 GRBs. The most noticeable feature we found is near the Galactic
coordinates , and radius . The inferred probability for the occurrence of such an
anisotropic signal (in a random isotropic sample) is derived to be less than a
percent in some of the tests while the other tests give results consistent with
isotropy. These are based on the comparison of the results from the real data
with the randomly shuffled data samples. Considering large number of statistics
we used in this work (which some of them are correlated to each other) we can
anticipate that the detected feature could be result of statistical
fluctuations. Moreover, we noticed a considerably low number of GRBs in this
particular patch which might be due to some instrumentation or observational
effects that can consequently affect our statistics through some systematics.
Further investigation is highly desirable in order clarify about this result,
e.g. utilizing a larger future {\em Fermi} / GBM data sample as well as data
samples of other GRB missions and also looking for possible systematics.Comment: 17 pages, 10 figures, 4 tables, accepted for publication in The
Astrophysical Journa
Update on Testing the Isotropy of the Properties of Gamma-Ray Bursts
Previously we proposed a novel method to inspect the isotropy of the
properties of gamma-ray bursts (GRBs) such as their duration, fluences and peak
fluxes at various energy bands and different time scales, complementary to
existing studies of spatial distribution of GRBs by other authors. The method
was then applied on the Fermi GBM Burst Catalog containing 1591 GRBs and except
one particular direction where we noticed some hints of violation from
statistical isotropy, the rest of the data showed consistency with isotropy. In
this work we apply our method with some minor modifications to the updated
Fermi/GBM data sample containing 2266 GRBs, thus % larger. We also
test two other major GRB catalogs, the BATSE Current GRB Catalog of the CGRO
satellite containing bursts and the Swift/BAT Gamma-Ray Burst
Catalog containing bursts. The new results using the updated data
are consistent with our previous findings and no statistically significant
anisotropic feature in the observed properties of these samples of all GRBs is
found.Comment: 15 pages, 2 figures, 13 tables. Accepted for publication in MNRAS.
arXiv admin note: text overlap with arXiv:1706.0355
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