111 research outputs found
VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory
VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l.
in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design,
construction techniques and data acquisition system of the HAWC observatory.
HAWC is an air-shower array currently under construction at the same site of
VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water
Cherenkov detectors and two different data acquisition systems. It was in
operation between October 2011 and May 2012 with an average live time of 30%.
Besides the scientific verification purposes, the eight months of data were
used to obtain the results presented in this paper: the detector response to
the Forbush decrease of March 2012, and the analysis of possible emission, at
energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.Comment: Accepted for pubblication in Astroparticle Physics Journal (20 pages,
10 figures). Corresponding authors: A.Marinelli and D.Zaboro
Detection of Low-energy Breaks in Gamma-Ray Burst Prompt Emission Spectra
The radiative process responsible for gamma-ray burst (GRB) prompt emission has not been identified yet. If dominated by fast-cooling synchrotron radiation, the part of the spectrum immediately below the nF n peak energy should display a power-law behavior with slope a2 = -3 2, which breaks to a higher value a1 = -2 3 (i.e., to a harder spectral shape) at lower energies. Prompt emission spectral data (usually available down to 3c10 20 keV) are consistent with one single power-law behavior below the peak, with typical slope a = -1, higher than (and then inconsistent with) the expected value \u3b12= -3 2. To better characterize the spectral shape at low energy, we analyzed 14 GRBs for which the Swift X-ray Telescope started observations during the prompt. When available, Fermi-GBM observations have been included in the analysis. For 67% of the spectra, models that usually give a satisfactory description of the prompt (e.g., the Band model) fail to reproduce the 0.51000 keV spectra: lowenergy data outline the presence of a spectral break around a few keV. We then introduce an empirical fitting function that includes a low-energy power law a1, a break energy Ebreak, a second power law \u3b12, and a peak energy Epeak. We find \u3c31 = -0.66 (s = 0.35), log keV 0.63 ( ) Ebreak = (s = 0.20), \u3c32 = -1.46 (s = 0.31), and log keV 2.1 (Epeak) = (s = 0.56). The values \u3c31 and \u3c32 are very close to expectations from synchrotron radiation. In this context, Ebreak corresponds to the cooling break frequency. The relatively small ratio Epeak break E 3c 30 suggests a regime of moderately fast cooling, which might solve the long-lasting problem of the apparent inconsistency between measured and predicted low-energy spectral index
GRB091127/SN2009nz and the VLT/X-shooter spectroscopy of its host galaxy: probing the faint end of the mass-metallicity relation
We perform a detailed study of the gamma-ray burst GRB091127/SN2009nz host
galaxy at z=0.490 using the VLT/X-shooter spectrograph in slit and
integral-field unit (IFU). From the analysis of the optical and X-ray afterglow
data obtained from ground-based telescopes and Swift-XRT we confirm the
presence of a bump associated with SN2009nz and find evidence of a possible jet
break in the afterglow lightcurve. The X-shooter afterglow spectra reveal
several emission lines from the underlying host, from which we derive its
integrated properties. These are in agreement with those of previously studied
GRB-SN hosts and, more generally, with those of the long GRB host population.
We use the Hubble Space Telescope and ground based images of the host to
determine its stellar mass (M_star). Our results extend to lower M_star values
the M-Z plot derived for the sample of long GRB hosts at 0.3<z<1.0 adding new
information to probe the faint end of the M-Z relation and the shift of the
LGRB host M-Z relation from that found from emission line galaxy surveys.
Thanks to the IFU spectroscopy we can build the 2D velocity, velocity
dispersion and star formation rate (SFR) maps. They show that the host galaxy
has a perturbed rotation kinematics with evidence of a SFR enhancement
consistent with the afterglow position.Comment: 10 pages, 6 figures, accepted for publication in A&A. Major revision
on the host metallicit
The phenotypic spectrum of WWOX -related disorders: 20 additional cases of WOREE syndrome and review of the literature
Purpose: Germline WWOX pathogenic variants have been associated with disorder of sex differentiation (DSD), spinocerebellar ataxia (SCA), and WWOX-related epileptic encephalopathy (WOREE syndrome). We review clinical and molecular data on WWOX-related disorders, further describing WOREE syndrome and phenotype/genotype correlations. Methods: We report clinical and molecular findings in 20 additional patients from 18 unrelated families with WOREE syndrome and biallelic pathogenic variants in the WWOX gene. Different molecular screening approaches were used (quantitative polymerase chain reaction/multiplex ligation-dependent probe amplification [qPCR/MLPA], array comparative genomic hybridization [array-CGH], Sanger sequencing, epilepsy gene panel, exome sequencing). Results: Two copy-number variations (CNVs) or two single-nucleotide variations (SNVs) were found respectively in four and nine families, with compound heterozygosity for one SNV and one CNV in five families. Eight novel missense pathogenic variants have been described. By aggregating our patients with all cases reported in the literature, 37 patients from 27 families with WOREE syndrome are known. This review suggests WOREE syndrome is a very severe epileptic encephalopathy characterized by absence of language development and acquisition of walking, early-onset drug-resistant seizures, ophthalmological involvement, and a high likelihood of premature death. The most severe clinical presentation seems to be associated with null genotypes. Conclusion: Germline pathogenic variants in WWOX are clearly associated with a severe early-onset epileptic encephalopathy. We report here the largest cohort of individuals with WOREE syndrome
On the sensitivity of the HAWC observatory to gamma-ray bursts
We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very
high-energy gamma-ray observatory currently under construction in Mexico at an
altitude of 4100 m. It will observe atmospheric air showers via the water
Cherenkov method. HAWC will consist of 300 large water tanks instrumented with
4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main
DAQ system reads out coincident signals in the tanks and reconstructs the
direction and energy of individual atmospheric showers. The scaler DAQ counts
the hits in each photomultiplier tube (PMT) in the detector and searches for a
statistical excess over the noise of all PMTs. We show that HAWC has a
realistic opportunity to observe the high-energy power law components of GRBs
that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The
two DAQ systems have an energy threshold that is low enough to observe events
similar to GRB 090510 and GRB 090902b with the characteristics observed by
Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs
which in turn could help to understanding about e-pair attenuation in GRB jets,
extragalactic background light absorption, as well as establishing the highest
energy to which GRBs accelerate particles
Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).
Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and ≥1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (n = 5069) or prospectively (n = 5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (≤6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; p = 0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)
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