41 research outputs found
Studies of EGRET sources with a novel image restoration technique
We have developed an image restoration technique based on the Richardson-Lucy
algorithm optimized for GLAST-LAT image analysis. Our algorithm is original
since it utilizes the PSF (point spread function) that is calculated for each
event. This is critical for EGRET and GLAST-LAT image analysis since the PSF
depends on the energy and angle of incident gamma-rays and varies by more than
one order of magnitude. EGRET and GLAST-LAT image analysis also faces Poisson
noise due to low photon statistics. Our technique incorporates wavelet
filtering to minimize noise effects. We present studies of EGRET sources using
this novel image restoration technique for possible identification of extended
gamma-ray sources.Comment: 5 pages, 3 figures. Presented at First GLAST Symposium, Stanford
University, Stanford, CA, USA, February 5-8, 200
Studies of Cosmic Rays with GeV Gamma Rays
We describe the role of GeV gamma-ray observations with GLAST-LAT (Gamma-ray
Large Area Space Telescope - Large Area Telescope) in identifying interaction
sites of cosmic-ray proton (or hadrons) with interstellar medium (ISM). We
expect to detect gamma rays from neutral pion decays in high-density ISM
regions in the Galaxy, Large Magellanic Cloud, and other satellite galaxies.
These gamma-ray sources have been detected already with EGRET (Energetic Gamma
Ray Experiment Telescope) as extended sources (eg. LMC and Orion clouds) and
GLAST-LAT will detect many more with a higher spatial resolution and in a wider
spectral range. We have developed a novel image restoration technique based on
the Richardson-Lucy algorithm optimized for GLAST-LAT observation of extended
sources. Our algorithm calculates PSF (point spread function) for each event.
This step is very important for GLAST-LAT and EGRET image analysis since PSF
varies more than one order of magnitude from one gamma ray to another depending
on its energy as well as its impact point and angle in the instrument. The
GLAST-LAT and EGRET image analysis has to cope with Poisson fluctuation due to
low number of detected photons for most sources. Our technique incorporates
wavelet filtering to minimize effects due to the fluctuation. Preliminary
studies on some EGRET sources are presented, which shows potential of this
novel image restoration technique for the identification and characterisation
of extended gamma-ray sources.Comment: 9 pages, 6 figures, Invited Talk at International Workshop on
"Cosmic-Rays and High Energy Universe," Aoyama-Gakuin University, Shibuya,
Tokyo, Japan, March 5-6, 200
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
ADHERE: randomized controlled trial comparing renal function in de novo kidney transplant recipients receiving prolonged-release tacrolimus plus mycophenolate mofetil or sirolimus
ADHERE was a randomized, open-label, Phase IV study comparing renal function at Week 52 postkidney transplant, in patients who received prolongedrelease tacrolimus-based immunosuppressive regimens. On Days 0?27, patients received prolonged-release tacrolimus (initially 0.2 mg/kg/day), corticosteroids, and mycophenolate mofetil (MMF). Patients were randomized on Day 28 to receive either prolonged-release tacrolimus plus MMF (Arm 1) or prolongedrelease tacrolimus (?25% dose reduction on Day 42) plus sirolimus (Arm 2). The primary endpoint was glomerular filtration rate by iohexol clearance (mGFR) at Week 52. Secondary endpoints included eGFR, creatinine clearance (CrCl), efficacy failure (patient withdrawal or graft loss), and patient/graft survival. Tolerability was analyzed. The full-analysis set comprised 569 patients (Arm 1: 287; Arm 2: 282). Week 52 mean mGFR was similar in Arm 1 versus Arm 2 (40.73 vs. 41.75 ml/min/1.73 m2; P = 0.405), as were the secondary endpoints, except composite efficacy failure, which was higher in Arm 2 versus 1 (18.2% vs. 11.5%; P = 0.002) owing to a higher postrandomization withdrawal rate due to adverse events (AEs) (14.4% vs. 5.2%). Results from this study show comparable renal function between arms at Week 52, with fewer AEs leading to study discontinuation with prolonged-release tacrolimus plus MMF (Arm 1) versus lower dose prolonged-release tacrolimus plus sirolimus (Arm 2)
Detection of High-Energy Gamma-Ray Emission from the Globular Cluster 47 Tucanae with Fermi
Gamma-Ray Pulsar Bonanza
Most of the pulsars we know about were detected through their radio emission; a few are known to pulse gamma rays but were first detected at other wavelengths (see the Perspective by
Halpern
). Using the Fermi Gamma-Ray Space Telescope,
Abdo
et al.
(p.
840
, published online 2 July; see the cover) report the detection of 16 previously unknown pulsars based on their gamma-ray emission alone. Thirteen of these coincide with previously unidentified gamma-ray sources, solving the 30-year-old mystery of their identities. Pulsars are fast-rotating neutron stars. With time they slow down and cease to radiate; however, if they are in a binary system, they can have their spin rates increased by mass transfer from their companion stars, starting a new life as millisecond pulsars. In another study,
Abdo
et al.
(p.
845
) report the detection of gamma-ray emission from the globular cluster 47 Tucanae, which is coming from an ensemble of millisecond pulsars in the cluster's core. The data imply that there are up to 60 millisecond pulsars in 47 Tucanae, twice as many as predicted by radio observations. In a further companion study,
Abdo
et al.
(p.
848
, published online 2 July) searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars outside of stellar clusters, finding gamma-ray pulsations for eight of them. Their properties resemble those of other gamma-ray pulsars, suggesting that they share the same basic emission mechanism. Indeed, both sets of pulsars favor emission models in which the gamma rays are produced in the outer magnetosphere of the neutron star
A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope
Gamma-Ray Pulsar Bonanza
Most of the pulsars we know about were detected through their radio emission; a few are known to pulse gamma rays but were first detected at other wavelengths (see the Perspective by
Halpern
). Using the Fermi Gamma-Ray Space Telescope,
Abdo
et al.
(p.
840
, published online 2 July; see the cover) report the detection of 16 previously unknown pulsars based on their gamma-ray emission alone. Thirteen of these coincide with previously unidentified gamma-ray sources, solving the 30-year-old mystery of their identities. Pulsars are fast-rotating neutron stars. With time they slow down and cease to radiate; however, if they are in a binary system, they can have their spin rates increased by mass transfer from their companion stars, starting a new life as millisecond pulsars. In another study,
Abdo
et al.
(p.
845
) report the detection of gamma-ray emission from the globular cluster 47 Tucanae, which is coming from an ensemble of millisecond pulsars in the cluster's core. The data imply that there are up to 60 millisecond pulsars in 47 Tucanae, twice as many as predicted by radio observations. In a further companion study,
Abdo
et al.
(p.
848
, published online 2 July) searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars outside of stellar clusters, finding gamma-ray pulsations for eight of them. Their properties resemble those of other gamma-ray pulsars, suggesting that they share the same basic emission mechanism. Indeed, both sets of pulsars favor emission models in which the gamma rays are produced in the outer magnetosphere of the neutron star
ERRATUM: "FERMI DETECTION OF γ-RAY EMISSION FROM THE M2 SOFT X-RAY FLARE ON 2010 JUNE 12" (2012, ApJ, 745, 144)
Due to an error at the publisher, the times given for the major tick marks in the X-axis in Figure 1 of the published article are incorrect. The correctly labeled times should be "00:52:00," "00:54:00," ... , and "01:04:00." The correct version of Figure 1 and its caption is shown below. IOP Publishing sincerely regrets this error