Showing papers by "Hartmut Sadrozinski published in 2009"
TL;DR: The Large Area Telescope (Fermi/LAT) as mentioned in this paper is the primary instrument on the Fermi Gamma-ray Space Telescope, which is an imaging, wide field-of-view, high-energy gamma-ray telescope, covering the energy range from below 20 MeV to more than 300 GeV.
Abstract: (Abridged) The Large Area Telescope (Fermi/LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy gamma-ray telescope, covering the energy range from below 20 MeV to more than 300 GeV. This paper describes the LAT, its pre-flight expected performance, and summarizes the key science objectives that will be addressed. On-orbit performance will be presented in detail in a subsequent paper. The LAT is a pair-conversion telescope with a precision tracker and calorimeter, each consisting of a 4x4 array of 16 modules, a segmented anticoincidence detector that covers the tracker array, and a programmable trigger and data acquisition system. Each tracker module has a vertical stack of 18 x,y tracking planes, including two layers (x and y) of single-sided silicon strip detectors and high-Z converter material (tungsten) per tray. Every calorimeter module has 96 CsI(Tl) crystals, arranged in an 8 layer hodoscopic configuration with a total depth of 8.6 radiation lengths. The aspect ratio of the tracker (height/width) is 0.4 allowing a large field-of-view (2.4 sr). Data obtained with the LAT are intended to (i) permit rapid notification of high-energy gamma-ray bursts (GRBs) and transients and facilitate monitoring of variable sources, (ii) yield an extensive catalog of several thousand high-energy sources obtained from an all-sky survey, (iii) measure spectra from 20 MeV to more than 50 GeV for several hundred sources, (iv) localize point sources to 0.3 - 2 arc minutes, (v) map and obtain spectra of extended sources such as SNRs, molecular clouds, and nearby galaxies, (vi) measure the diffuse isotropic gamma-ray background up to TeV energies, and (vii) explore the discovery space for dark matter.
3,666 citations
TL;DR: The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy, with the largest apparent energy release yet measured.
Abstract: Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gamma-ray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.
651 citations
TL;DR: The detection of emission up to ∼31 GeV from the distant and short GRB, and no evidence for the violation of Lorentz invariance is found, which disfavour quantum-gravity theories in which the quantum nature of space–time on a very small scale linearly alters the speed of light.
Abstract: A cornerstone of Einstein's special relativity is Lorentz invariance-the postulate that all observers measure exactly the same speed of light in vacuum, independent of photon-energy. While special relativity assumes that there is no fundamental length-scale associated with such invariance, there is a fundamental scale (the Planck scale, l(Planck) approximate to 1.62 x 10(-33) cm or E(Planck) = M(Planck)c(2) approximate to 1.22 x 10(19) GeV), at which quantum effects are expected to strongly affect the nature of space-time. There is great interest in the (not yet validated) idea that Lorentz invariance might break near the Planck scale. A key test of such violation of Lorentz invariance is a possible variation of photon speed with energy(1-7). Even a tiny variation in photon speed, when accumulated over cosmological light-travel times, may be revealed by observing sharp features in gamma-ray burst (GRB) light-curves(2). Here we report the detection of emission up to similar to 31GeV from the distant and short GRB090510. We find no evidence for the violation of Lorentz invariance, and place a lower limit of 1.2E(Planck) on the scale of a linear energy dependence (or an inverse wavelength dependence), subject to reasonable assumptions about the emission (equivalently we have an upper limit of l(Planck)/1.2 on the length scale of the effect). Our results disfavour quantum-gravity theories(3,6,7) in which the quantum nature of space-time on a very small scale linearly alters the speed of light.
586 citations
TL;DR: The LAT Bright AGN Sample (LBAS) as discussed by the authors contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 57 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 5 BLazars with uncertain classification.
Abstract: The first three months of sky-survey operation with the Fermi Gamma Ray Space Telescope (Fermi) Large Area Telescope (LAT) reveals 132 bright sources at |b|>10 deg with test statistic greater than 100 (corresponding to about 10 sigma). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known AGNs. This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 57 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 5 blazars with uncertain classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy peaked BL Lacs (HBLs), sources which were so far hard to detect in the GeV range. Another 10 lower-confidence associations are found. Only thirty three of the sources, plus two at |b|>10 deg, were previously detected with EGRET, probably due to the variable nature of these sources. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak gamma-ray fluxes is observed. Blazar log N - log S and luminosity functions are constructed to investigate the evolution of the different blazar classes, with positive evolution indicated for FSRQs but none for BLLacs. The contribution of LAT-blazars to the total extragalactic gamma-ray intensity is estimated.
487 citations
TL;DR: In this article, the authors presented the initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than 10-sigma) gamma-ray sources in early-mission data.
Abstract: Following its launch in June 2008, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in 3 months produced a deeper and better-resolved map of the gamma-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than 10-sigma) gamma-ray sources in these data. These are the best-characterized and best-localized gamma-ray sources in the early-mission data.
476 citations
TL;DR: In this article, the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board the Fermi observatory were used to observe the long gamma-ray burst, GRB 090902B.
Abstract: We report on the observation of the bright, long gamma-ray burst (GRB), GRB 090902B, by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board the Fermi observatory. ...
462 citations
TL;DR: In this paper, the gamma-ray emission from three radio-loud narrow-line Seyfert 1 galaxies was detected with Fermi/LAT, and they may form an emerging new class of gamma ray active galactic nuclei (AGN).
Abstract: We report the discovery with Fermi/LAT of gamma-ray emission from three radio-loud narrow-line Seyfert 1 galaxies: PKS 1502+036 (z=0.409), 1H 0323+342 (z=0.061) and PKS 2004-447 (z=0.24). In addition to PMN J0948+0022 (z=0.585), the first source of this type to be detected in gamma rays, they may form an emerging new class of gamma-ray active galactic nuclei (AGN). These findings can have strong implications on our knowledge about relativistic jets and the unified model of AGN.
320 citations
TL;DR: The discovery of bright gamma-ray emission coincident with supernova remnant (SNR) W51C is reported using the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope as discussed by the authors.
Abstract: The discovery of bright gamma-ray emission coincident with supernova remnant (SNR) W51C is reported using the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. W51C is a middle-aged remnant (~10^4 yr) with intense radio synchrotron emission in its shell and known to be interacting with a molecular cloud. The gamma-ray emission is spatially extended, broadly consistent with the radio and X-ray extent of SNR W51C. The energy spectrum in the 0.2-50 GeV band exhibits steepening toward high energies. The luminosity is greater than 1x10^{36} erg/s given the distance constraint of D>5.5 kpc, which makes this object one of the most luminous gamma-ray sources in our Galaxy. The observed gamma-rays can be explained reasonably by a combination of efficient acceleration of nuclear cosmic rays at supernova shocks and shock-cloud interactions. The decay of neutral pi-mesons produced in hadronic collisions provides a plausible explanation for the gamma-ray emission. The product of the average gas density and the total energy content of the accelerated protons amounts to 5x10^{51}(D/6kpc)^2 erg/cm^3. Electron density constraints from the radio and X-ray bands render it difficult to explain the LAT signal as due to inverse Compton scattering. The Fermi LAT source coincident with SNR W51C sheds new light on the origin of Galactic cosmic rays.
302 citations
TL;DR: Fermi Large Area Telescope data is searched for pulsations from all known millisecond pulsars outside of stellar clusters, finding gamma-ray pulsations for eight of them, suggesting that they share the same basic emission mechanism with standard gamma-Ray pulsars.
Abstract: Pulsars are born with subsecond spin periods and slow by electromagnetic braking for several tens of millions of years, when detectable radiation ceases. A second life can occur for neutron stars in binary systems. They can acquire mass and angular momentum from their companions, to be spun up to millisecond periods and begin radiating again. We searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars (MSPs) outside of globular clusters, using rotation parameters from radio telescopes. Strong gamma-ray pulsations were detected for eight MSPs. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars. The basic emission mechanism seems to be the same for MSPs and young pulsars, with the emission originating in regions far from the neutron star surface.
263 citations
TL;DR: In this paper, the authors reported the discovery of high-energy (E>100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma ray Space Telescope.
Abstract: We report the discovery of high-energy (E>100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma ray Space Telescope. The positional center of the gamma-ray source is only ~3' away from the NGC 1275 nucleus, well within the 95% LAT error circle of ~5'.The spatial distribution of gamma-ray photons is consistent with a point source. The average flux and power-law photon index measured with the LAT from 2008 August 4 to 2008 December 5 are F_gamma = (2.10+-0.23)x 10^{-7} ph (>100 MeV) cm^{-2} s^{-1} and Gamma = 2.17+-0.05, respectively. The measurements are statistically consistent with constant flux during the four-month LAT observing period. Previous EGRET observations gave an upper limit of F_gamma 100 MeV) cm^{-2} s^{-1} to the gamma-ray flux from NGC 1275. This indicates that the source is variable on timescales of years to decades, and therefore restricts the fraction of emission that can be produced in extended regions of the galaxy cluster. Contemporaneous and historical radio observations are also reported. The broadband spectrum of NGC 1275 is modeled with a simple one-zone synchrotron/synchrotron self-Compton model and a model with a decelerating jet flow.
238 citations
TL;DR: In this paper, the authors reported the Fermi-LAT discovery of high energy (MeV/GeV) gamma-ray emission positionally consistent with the center of the radio galaxy M87, at a source significance of over 10 sigma in ten-months of all-sky survey data.
Abstract: We report the Fermi-LAT discovery of high-energy (MeV/GeV) gamma-ray emission positionally consistent with the center of the radio galaxy M87, at a source significance of over 10 sigma in ten-months of all-sky survey data. Following the detections of Cen A and Per A, this makes M87 the third radio galaxy seen with the LAT. The faint point-like gamma-ray source has a >100 MeV flux of 2.45 (+/- 0.63) x 10^-8 ph cm^-2 s^-1 (photon index = 2.26 +/- 0.13) with no significant variability detected within the LAT observation. This flux is comparable with the previous EGRET upper limit (< 2.18 x 10^-8 ph cm^-2 s^-1, 2 sigma), thus there is no evidence for a significant MeV/GeV flare on decade timescales. Contemporaneous Chandra and VLBA data indicate low activity in the unresolved X-ray and radio core relative to previous observations, suggesting M87 is in a quiescent overall level over the first year of Fermi-LAT observations. The LAT gamma-ray spectrum is modeled as synchrotron self-Compton (SSC) emission from the electron population producing the radio-to-X-ray emission in the core. The resultant SSC spectrum extrapolates smoothly from the LAT band to the historical-minimum TeV emission. Alternative models for the core and possible contributions from the kiloparsec-scale jet in M87 are considered, and can not be excluded.
TL;DR: The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET, and the LAT spectrum for this region of the sky is well reproduced by a diffuse galactic gamma-rays emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.
Abstract: The diffuse Galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission > 1 GeV relative to diffuse Galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called ``EGRET GeV excess''). The excess emission was observed in all directions on the sky, and a variety of explanations have been proposed, including beyond-the-Standard-Model scenarios like annihilating or decaying dark matter. The Large Area Telescope (LAT) instrument on the Fermi Gamma-ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements of the diffuse gamma-ray emission for energies 100 MeV to 10 GeV and Galactic latitudes 10 deg. <= |b| <= 20 deg. The LAT spectrum for this region of the sky is well reproduced by a diffuse Galactic gamma-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.
TL;DR: The first direct observation of a break in the spectrum of a high luminosity blazar above 100 MeV was reported in this article, and it is likely direct evidence for an intrinsic break of the energy distribution of the radiating particles.
Abstract: This is the first report of Fermi Gamma-ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope (LAT), covering 2008 July 7 - October 6, indicate strong, highly variable gamma-ray emission with an average flux of ~3 x 10^{-6} photons cm^{-2} s^{-1}, for energies above 100 MeV. The gamma-ray flux is variable, with strong, distinct, symmetrically-shaped flares for which the flux increases by a factor of several on a time scale of about three days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair-production implies relativistic beaming with Doppler factor delta > 8, consistent with the values inferred from VLBI observations of superluminal expansion (delta ~ 25). The observed gamma-ray spectrum is not consistent with a simple power-law, but instead steepens strongly above ~2 GeV, and is well described by a broken power-law with photon indices of ~2.3 and ~3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2 GeV could be due to gamma-ray absorption via photon-photon pair production on the soft X-ray photon field of the host AGN, but such an interpretation would require the dissipation region to be located very close (less than 100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.
TL;DR: In this paper, the first detection of orbital periodicity in high-energy gamma rays (20 MeV-100 GeV, HE) was made using LS I +61°303 data from the Fermi Gamma-Ray Space Telescope between 2008 August and 2009 March.
Abstract: This Letter presents the first results from the observations of LS I +61°303 using Large Area Telescope data from the Fermi Gamma-Ray Space Telescope between 2008 August and 2009 March. Our results indicate variability that is consistent with the binary period, with the emission being modulated at 26.6 ± 0.5 days. This constitutes the first detection of orbital periodicity in high-energy gamma rays (20 MeV-100 GeV, HE). The light curve is characterized by a broad peak after periastron, as well as a smaller peak just before apastron. The spectrum is best represented by a power law with an exponential cutoff, yielding an overall flux above 100 MeV of 0.82 ± 0.03(stat) ± 0.07(syst) 10–6 ph cm–2 s–1, with a cutoff at 6.3 ± 1.1(stat) ± 0.4(syst) GeV and photon index Γ = 2.21 ± 0.04(stat) ± 0.06(syst). There is no significant spectral change with orbital phase. The phase of maximum emission, close to periastron, hints at inverse Compton scattering as the main radiation mechanism. However, previous very high-energy gamma ray (>100 GeV, VHE) observations by MAGIC and VERITAS show peak emission close to apastron. This and the energy cutoff seen with Fermi suggest that the link between HE and VHE gamma rays is nontrivial.
TL;DR: The first results from observations of the high mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented in this article.
Abstract: The first results from observations of the high mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. Our results indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 +/- 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV - 300 GeV) of 4.9 +/- 0.5(stat) +/- 1.8(syst) x 10^-7 photon cm^-2 s^-1, with a cutoff at 2.1 +/- 0.3(stat) +/- 1.1(syst) GeV and photon index Gamma = 1.9 +/- 0.1(stat) +/- 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. We suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.
TL;DR: In this article, the authors report on observations of TeV-selected active galactic nuclei (AGNs) made during the first 55 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi).
Abstract: We report on observations of TeV-selected active galactic nuclei (AGNs) made during the first 55 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi) In total, 96 AGNs were selected for study, each being either (1) a source detected at TeV energies (28 sources) or (2) an object that has been studied with TeV instruments and for which an upper limit has been reported (68 objects) The Fermi observations show clear detections of 38 of these TeV-selected objects, of which 21 are joint GeV-TeV sources, and 29 were not in the third EGRET catalog For each of the 38 Fermi-detected sources, spectra and light curves are presented Most can be described with a power law of spectral index harder than 20, with a spectral break generally required to accommodate the TeV measurements Based on an extrapolation of the Fermi spectrum, we identify sources, not previously detected at TeV energies, which are promising targets for TeV instruments Evidence for systematic evolution of the γ-ray spectrum with redshift is presented and discussed in the context of interaction with the extragalactic background light
TL;DR: In this paper, the authors describe on-orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector, which have been used to calibrate the LAT datasets to be publicly released in August 2009.
TL;DR: In this paper, the Vela pulsar was used to verify Fermi timing and angular resolution, and the high energy behavior of the pulsed emission was examined; initial spectra suggest a phase-averaged power law index of Gamma=1.51{+0.05/-0.04} with an exponential cut-off at E_c=2.1 GeV.
Abstract: The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new gamma-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high quality pulse profile, with some 32,400 pulsed photons at E>0.03 GeV, shows new features, including pulse structure as fine as 0.3ms and a distinct third peak, which shifts in phase with energy. We examine the high energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power law index of Gamma=1.51{+0.05/-0.04} with an exponential cut-off at E_c=2.9+/-0.1 GeV. Spectral fits with generalized cut-offs of the form e^{-(E/E_c)^b} require b<1, which is inconsistent with magnetic pair attenuation, and thus favor outer magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding synchrotron wind nebula (PWN).
TL;DR: In this paper, observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse gamma-rays in a mid-latitude region in the third quadrant (Galactic longitude $l$ from $200\arcdeg$ to $260\arcdegree) are reported.
Abstract: Observations by the Large Area Telescope (LAT) on the \textit{Fermi} mission of diffuse $\gamma$-rays in a mid-latitude region in the third quadrant (Galactic longitude $l$ from $200\arcdeg$ to $260\arcdeg$ and latitude $| b |$ from $22\arcdeg$ to $60\arcdeg$) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of $\gamma$-ray point sources and inverse Compton scattering are estimated and subtracted. The residual $\gamma$-ray intensity exhibits a linear correlation with the atomic gas column density in energy from 100 MeV to 10 GeV. The measured integrated $\gamma$-ray emissivity is $(1.63 \pm 0.05) \times 10^{-26} {\rm photons s^{-1} sr^{-1} H\mathchar`-atom^{-1}}$ and $(0.66 \pm 0.02) \times 10^{-26} {\rm photons s^{-1} sr^{-1} H\mathchar`-atom^{-1}}$ above 100 MeV and above 300 MeV, respectively, with additional systematic error of $\sim 10%$. The differential emissivity in 100 MeV--10 GeV agrees with calculations based on cosmic ray spectra consistent with those directly measured, at the 10% level. The results obtained indicate that cosmic ray nuclei spectra within 1 kpc from the solar system in regions studied are close to the local interstellar spectra inferred from direct measurements at the Earth within $\sim 10%$.
TL;DR: In this paper, the authors reported the detection of gamma-ray emissions above 200 megaelectron volts at a significance level of 17σ from the globular cluster 47 Tucanae, using data obtained with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope.
Abstract: We report the detection of gamma-ray emissions above 200 megaelectron volts at a significance level of 17σ from the globular cluster 47 Tucanae, using data obtained with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. Globular clusters are expected to emit gamma rays because of the large populations of millisecond pulsars that they contain. The spectral shape of 47 Tucanae is consistent with gamma-ray emission from a population of millisecond pulsars. The observed gamma-ray luminosity implies an upper limit of 60 millisecond pulsars present in 47 Tucanae.
TL;DR: In this paper, the authors report on measurements of the cosmic-ray induced gamma-ray emission of Earth's atmosphere by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope.
Abstract: We report on measurements of the cosmic-ray induced gamma-ray emission of Earth's atmosphere by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. The LAT has observed the Earth during its commissioning phase and with a dedicated Earth-limb following observation in September 2008. These measurements yielded 6.4 x 10^6 photons with energies >100MeV and ~250hours total livetime for the highest quality data selection. This allows the study of the spatial and spectral distributions of these photons with unprecedented detail. The spectrum of the emission - often referred to as Earth albedo gamma-ray emission - has a power-law shape up to 500 GeV with spectral index Gamma = 2.79+-0.06.
TL;DR: In this article, the authors reported the detection of pulsed gamma-rays from the young spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST).
Abstract: We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 +/- 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 +/- 0.004 +/- 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 +/- 3 +/- 11) x 10^{-8} /cm2/s. The photon spectrum is well-described by an exponentially cut-off power law of the form dF/dE = kE^{-\Gamma} e^(-E/E_c) where the energy E is expressed in GeV. The photon index is \Gamma = 1.5 +/- 0.1 +/- 0.1 and the exponential cut-off is E_c = 2.4 +/- 0.3 +/- 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is <10% of the pulsed emission at the 95% confidence level. Radio polarization measurements yield a rotation measure of RM = 524 +/- 4 rad/m^2 but a poorly constrained magnetic geometry. Re-analysis of Chandra data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase-aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.
TL;DR: In this article, the authors reported the discovery of gamma-ray pulsations from the nearby isolated millisecond pulsar PSR J0030+0451 with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST).
Abstract: We report the discovery of gamma-ray pulsations from the nearby isolated millisecond pulsar PSR J0030+0451 with the Large Area Telescope (LAT) on the \emph{Fermi} Gamma-ray Space Telescope (formerly GLAST). This discovery makes PSR J0030+0451 the second millisecond pulsar to be detected in gamma-rays after PSR J0218+4232, observed by the EGRET instrument on the Compton Gamma Ray Observatory. The spin-down power $\dot E = $ 3.5 $\times$ 10$^{33}$ ergs s$^{-1}$ is an order of magnitude lower than the empirical lower bound of previously known gamma-ray pulsars. The emission profile is characterized by two narrow peaks, respectively 0.07 $\pm$ 0.01 and 0.08 $\pm$ 0.02 wide, separated by 0.44 $\pm$ 0.02 in phase. The first gamma-ray peak falls 0.15 $\pm$ 0.01 after the main radio peak. The pulse shape is similar to that of the "normal" gamma-ray pulsars. An exponentially cut-off power-law fit of the emission spectrum leads to an integral photon flux above 100 MeV of (6.76 $\pm$ 1.05 $\pm$ 1.35) $\times 10^{-8}$ cm$^{-2}$ s$^{-1}$ with cut-off energy (1.7 $\pm$ 0.4 $\pm$ 0.5) GeV. Based on its parallax distance of $(300 \pm 90)$ pc, we obtain a gamma-ray efficiency $L_\gamma / \dot{E} \simeq 15%$ for the conversion of spin-down energy rate into gamma-ray radiation, assuming isotropic emission.
TL;DR: In this article, the authors reported the detection of gamma-ray pulsations (> 0.1 GeV) from PSR J2229+6114 and PSRJ1048-5832, the latter having been detected as a low-significance pulsar by EGRET.
Abstract: We report the detection of gamma-ray pulsations (> 0.1 GeV) from PSR J2229+6114 and PSR J1048-5832, the latter having been detected as a low-significance pulsar by EGRET. Data in the gamma-ray band were acquired by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope, while the radio rotational ephemerides used to fold the gamma-ray light curves were obtained using the Green Bank Telescope, the Lovell telescope at Jodrell Bank, and the Parkes telescope. The two young radio pulsars, located within the error circles of the previously unidentified EGRET sources 3EG J1048-5840 and 3EG J2227+6122, present spin-down characteristics similar to the Vela pulsar. PSR J1048-5832 shows two sharp peaks at phases 0.15 \pm 0.01 and 0.57 \pm 0.01 relative to the radio pulse confirming the EGRET light curve, while PSR J2229+6114 presents a very broad peak at phase 0.49 \pm 0.01. The gamma-ray spectra above 0.1 GeV of both pulsars are fit with power laws having exponential cutoffs near 3 GeV, leading to integral photon fluxes of (2.19 \pm 0.22 \pm 0.32) x 10^{-7} cm^{-2} ^{-1} for PSR J1048-5832 and (3.77 \pm 0.22 \pm 0.44) x 10^{-7} cm^{-2} s^{-1} for PSR J2229+6114. The first uncertainty is statistical and the second is systematic. PSR J1048-5832 is one of two LAT sources which were entangled together as 3EG J1048-5840. These detections add to the growing number of young gamma-ray pulsars that make up the dominant population of GeV gamma-ray sources in the Galactic plane.
TL;DR: In this article, the authors reported the discovery of γ-ray pulsations from the young radio and X-ray PSR J0205 + 6449 located in the Galactic supernova remnant 3C 58.4 GeV.
Abstract: We report the discovery of γ-ray pulsations (≥0.1 GeV) from the young radio and X-ray pulsar PSR J0205 + 6449 located in the Galactic supernova remnant 3C 58. Data in the γ-ray band were acquired by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope (formerly GLAST), while the radio rotational ephemeris used to fold γ-rays was obtained using both the Green Bank Telescope and the Lovell telescope at Jodrell Bank. The light curve consists of two peaks separated by 0.49 ± 0.01 ± 0.01 cycles which are aligned with the X-ray peaks. The first γ-ray peak trails the radio pulse by 0.08 ± 0.01 ± 0.01, while its amplitude decreases with increasing energy as for the other γ-ray pulsars. Spectral analysis of the pulsed γ-ray emission suggests a simple power law of index –2.1 ± 0.1 ± 0.2 with an exponential cutoff at 3.0+1.1 –0.7 ± 0.4 GeV. The first uncertainty is statistical and the second is systematic. The integral γ-ray photon flux above 0.1 GeV is (13.7 ± 1.4 ± 3.0) × 10–8 cm–2 s–1, which implies for a distance of 3.2 kpc and assuming a broad fan-like beam a luminosity of 8.3 × 1034 erg s–1 and an efficiency η of 0.3%. Finally, we report a 95% upper limit on the flux of 1.7 × 10–8 cm–2 s–1 for off-pulse emission from the object.
TL;DR: In this article, a radio pulsar PSR J1028-5819 was discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic gamma-ray Experiment Telescope (EGRET) source.
Abstract: Radio pulsar PSR J1028-5819 was recently discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic Gamma-Ray Experiment Telescope (EGRET) source 3EG J1027-5817. The sp ...
31 Mar 2009
TL;DR: Proton computed tomography (pCT) as mentioned in this paper has been used to estimate the Bragg peak position in proton therapy using the electron density and ratio of effective atomic number and mass (Z/A) of the body tissues traversed.
Abstract: Determination of the Bragg peak position in proton therapy requires accurate knowledge of the electron density and ratio of effective atomic number and mass (Z/A) of the body tissues traversed While the Z/A ratio is fairly constant for human tissues, the density of tissues varies significantly One possibility to obtain accurate electron density information of tissues is to use protons of sufficient energy to penetrate the patient and measure their energy loss From these transmission measurements, it is possible to reconstruct a three‐dimensional map of electron densities using algebraic techniques The interest in proton computed tomography (pCT) has considerably increased in recent years due to the more common use of proton accelerators for cancer treatment world‐wide and a modern design concept based on current high‐energy physics technology has been suggested This contribution gives a status update on the pCT project carried out by the pCT Collaboration, a group of institutions sharing interest and expertise in the development of pCT We will present updated imaging data obtained with a small pCT prototype developed in collaboration with the Santa Cruz Institute of Particle Physics and installed on the proton research beam line at Loma Linda University Medical Center We will discuss hardware decisions regarding the next‐generation pCT scanner, which will permit scanning of head‐sized objects Progress has also been made in the formulation of the most likely path of protons through an object and parallelizable iterative reconstruction algorithms that can be implemented on general‐purpose commodity graphics processing units Finally, we will present simulation studies for utilizing pCT technology for on‐line proton dose verification and tumor imaging with positron emission tomography (PET)
11 Jun 2009-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the relative merits of the latest generations of IBM SiGe HBT BiCMOS technologies, the 8WL and 8HP platforms, were evaluated at multiple gamma and neutron irradiation levels.
Abstract: Silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) technologies promise several advantages over CMOS for the front-end readout electronics for the ATLAS upgrade. We have evaluated the relative merits of the latest generations of IBM SiGe HBT BiCMOS technologies, the 8WL and 8HP platforms. These 130 nm SiGe technologies show promise to operate at lower power than do CMOS technologies and would provide a viable alternative for the silicon strip detector and liquid argon calorimeter upgrades, provided that the radiation tolerance studies at multiple gamma and neutron irradiation levels, included in this investigation, show them to be sufficiently radiation tolerant.
TL;DR: In this article, the bias voltage dependence of the collected charge and the hit detection efficiency have been measured before and after accelerated annealing, and predictions of the performance at the SuperLHC are derived.
Abstract: The charge collected from p-type silicon strip sensors irradiated to SuperLHC fluences has been determined with a beta source using fast front-end electronics. The bias voltage dependence of the collected charge and the hit detection efficiency have been measured before and after accelerated annealing. Predictions of the performance at the SuperLHC are derived.
31 Mar 2009
TL;DR: The purpose of this ongoing work is to characterize systematic errors that are introduced by regions of bone and air density and how this affects the accuracy of proton CT in surrounding voxels both in terms of spatial and density reconstruction accuracy.
Abstract: Maintaining a high degree of spatial resolution in proton computed tomography (pCT) is a challenge due to the statistical nature of the proton path through the object. Recent work has focused on the formulation of the most likely path (MLP) of protons through a homogeneous water object and the accuracy of this approach has been tested experimentally with a homogeneous PMMA phantom. Inhomogeneities inside the phantom, consisting of, for example, air and bone will lead to unavoidable inaccuracies of this approach. The purpose of this ongoing work is to characterize systematic errors that are introduced by regions of bone and air density and how this affects the accuracy of proton CT in surrounding voxels both in terms of spatial and density reconstruction accuracy. Phantoms containing tissue‐equivalent inhomogeneities have been designed and proton transport through them has been simulated with the GEANT 4.9.0 Monte Carlo tool kit. Various iterative reconstruction techniques, including the classical fully sequential algebraic reconstruction technique (ART) and block‐iterative techniques, are currently being tested, and we will select the most accurate method for this study.