| 1. |
- Nolan, P. L., et al.
(författare)
-
Fermi large area telescope second source catalog
- 2012
-
Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 199:2, s. 31-
-
Tidskriftsartikel (refereegranskat)abstract
- We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes.
|
|
| 2. |
- Abdo, A. A., et al.
(författare)
-
Fermi Observations of γ-Ray Emission from the Moon
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 758:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the detection of high-energy gamma-ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmic-ray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(> 100 MeV) = (1.04 +/- 0.01 [statistical error] +/- 0.1 [systematic error]) x 10(-6) cm(-2) s(-1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on boardthe Compton Gamma Ray Observatory, F(> 100 MeV) approximate to 5 x 10(-7) cm-2 s-1, when solar activity was relatively high. The higher gamma-ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across thesky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis ofthe lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.
|
|
| 3. |
- Ackermann, M., et al.
(författare)
-
The Second Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
- 2011
-
Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 743:2
-
Tidskriftsartikel (refereegranskat)abstract
- The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The second LAT AGN catalog (2LAC) includes 1017 γ-ray sources located at high Galactic latitudes (|b| > 10°) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However, some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently, we define a Clean Sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lac objects), 310 flat-spectrum radio quasars (FSRQs), 157 candidate blazars of unknown type (i.e., with broadband blazar characteristics but with no optical spectral measurement yet), 8 misaligned AGNs, 4 narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types, and 2 starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency <1014 Hz, about half of the BL Lac objects have a synchrotron-peak frequency >1015 Hz. The 2LAC represents a significant improvement relative to the first LAT AGN catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broadband data. Various properties, such as γ-ray fluxes and photon power-law spectral indices, redshifts, γ-ray luminosities, variability, and archival radio luminosities and their correlations are presented and discussed for the different blazar classes. The general trends observed in 1LAC are confirmed.
|
|
| 4. |
- Ackermann, M., et al.
(författare)
-
A STATISTICAL APPROACH TO RECOGNIZING SOURCE CLASSES FOR UNASSOCIATED SOURCES IN THE FIRST FERMI-LAT CATALOG
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:1, s. 83-
-
Tidskriftsartikel (refereegranskat)abstract
- The Fermi Large Area Telescope (LAT) First Source Catalog (1FGL) provided spatial, spectral, and temporal properties for a large number of gamma-ray sources using a uniform analysis method. After correlating with the most-complete catalogs of source types known to emit gamma rays, 630 of these sources are unassociated (i.e., have no obvious counterparts at other wavelengths). Here, we employ two statistical analyses of the primary gamma-ray characteristics for these unassociated sources in an effort to correlate their gamma-ray properties with the active galactic nucleus (AGN) and pulsar populations in 1FGL. Based on the correlation results, we classify 221 AGN-like and 134 pulsar-like sources in the 1FGL unassociated sources. The results of these source classifications appear to match the expected source distributions, especially at high Galactic latitudes. While useful for planning future multiwavelength follow-up observations, these analyses use limited inputs, and their predictions should not be considered equivalent to probable source classes for these sources. We discuss multiwavelength results and catalog cross-correlations to date, and provide new source associations for 229 Fermi-LAT sources that had no association listed in the 1FGL catalog. By validating the source classifications against these new associations, we find that the new association matches the predicted source class in similar to 80% of the sources.
|
|
| 5. |
- Ackermann, M., et al.
(författare)
-
The fermi large area telescope on orbit : Event classification, instrument response functions, and calibration
- 2012
-
Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 203:1, s. 4-
-
Tidskriftsartikel (refereegranskat)abstract
- The Fermi 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 γ-ray telescope, covering the energy range from 20MeV to more than 300GeV. During the first years of the mission, the LAT team has gained considerable insight into the in-flight performance of the instrument. Accordingly, we have updated the analysis used to reduce LAT data for public release as well as the instrument response functions (IRFs), the description of the instrument performance provided for data analysis. In this paper, we describe the effects that motivated these updates. Furthermore, we discuss how we originally derived IRFs from Monte Carlo simulations and later corrected those IRFs for discrepancies observed between flight and simulated data. We also give details of the validations performed using flight data and quantify the residual uncertainties in the IRFs. Finally, we describe techniques the LAT team has developed to propagate those uncertainties into estimates of the systematic errors on common measurements such as fluxes and spectra of astrophysical sources.
|
|
| 6. |
- Ackermann, M., et al.
(författare)
-
In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope
- 2012
-
Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 35:6, s. 346-353
-
Tidskriftsartikel (refereegranskat)abstract
- The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between ∌6 and ∌13 GeV with an estimated uncertainty of ∌2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.
|
|
| 7. |
- Ackermann, M., et al.
(författare)
-
MULTI-WAVELENGTH OBSERVATIONS OF BLAZAR AO 0235+164 IN THE 2008-2009 FLARING STATE
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 751:2
-
Tidskriftsartikel (refereegranskat)abstract
- The blazarAO 0235+164 (z=0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by Fermi, contemporaneous observations were carried out from the radio to gamma-ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the campaign (including F-GAMMA, GASP-WEBT, Kanata, OVRO, RXTE, SMARTS, Swift, and other instruments), examine the cross-correlation between the light curves measured in the different energy bands, and interpret the resulting spectral energy distributions in the context of well-known blazar emission models. We find that the gamma-ray activity is well correlated with a series of near-IR/optical flares, accompanied by an increase in the optical polarization degree. On the other hand, the X-ray light curve shows a distinct 20 day high state of unusually soft spectrum, which does not match the extrapolation of the optical/UV synchrotron spectrum. We tentatively interpret this feature as the bulk Compton emission by cold electrons contained in the jet, which requires an accretion disk corona with an effective covering factor of 19% at a distance of 100 R-g. We model the broadband spectra with a leptonic model with external radiation dominated by the infrared emission from the dusty torus.
|
|
| 8. |
- Ackermann, M., et al.
(författare)
-
Constraining Dark Matter Models from a Combined Analysis of Milky Way Satellites with the Fermi Large Area Telescope
- 2011
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 107:24
-
Tidskriftsartikel (refereegranskat)abstract
- Satellite galaxies of the Milky Way are among the most promising targets for dark matter searches in gamma rays. We present a search for dark matter consisting of weakly interacting massive particles, applying a joint likelihood analysis to 10 satellite galaxies with 24 months of data of the Fermi Large Area Telescope. No dark matter signal is detected. Including the uncertainty in the dark matter distribution, robust upper limits are placed on dark matter annihilation cross sections. The 95% confidence level upper limits range from about 10(-26) cm(3) s(-1) at 5 GeV to about 5 x 10(-23) cm(3) s(-1) at 1 TeV, depending on the dark matter annihilation final state. For the first time, using gamma rays, we are able to rule out models with the most generic cross section (similar to 3 x 10(-26) cm(3) s(-1) for a purely s-wave cross section), without assuming additional boost factors.
|
|
| 9. |
- Ackermann, M., et al.
(författare)
-
Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
- 2013
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 339:6121, s. 807-811
-
Tidskriftsartikel (refereegranskat)abstract
- Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.
|
|
| 10. |
- Ackermann, M., et al.
(författare)
-
Determination of the point-spread function for the fermi large area telescope from on-orbit data and limits on pair halos of active galactic nuclei
- 2013
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 765:1, s. 54-
-
Tidskriftsartikel (refereegranskat)abstract
- The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from approximate to 20 MeV to > 300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of gamma rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broader than the pre-launch PSF. We checked for dependence of the PSF on the class of gamma-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. We found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low-and high-redshift BL Lac AGNs and the TeV blazars 1ES0229 + 200 and 1ES0347-121.
|
|
| 11. |
- Ackermann, M., et al.
(författare)
-
Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope
- 2012
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:1
-
Tidskriftsartikel (refereegranskat)abstract
- We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 GeV. We confirm that the fraction rises with energy in the 20-100 GeV range. The three new spectral points between 100 and 200 GeVare consistent with a fraction that is continuing to rise with energy.
|
|
| 12. |
- Ackermann, M., et al.
(författare)
-
SEARCH FOR DARK MATTER SATELLITES USING FERMI-LAT
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 747:2, s. 121-
-
Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations based on the ACDM model of cosmology predict a large number of as yet unobserved Galactic dark matter satellites. We report the results of a Large Area Telescope (LAT) search for these satellites via the gamma-ray emission expected from the annihilation of weakly interacting massive particle (WIMP) dark matter. Some dark matter satellites are expected to have hard gamma-ray spectra, finite angular extents, and a lack of counterparts at other wavelengths. We sought to identify LAT sources with these characteristics, focusing on gamma-ray spectra consistent with WIMP annihilation through the b (b) over bar channel. We found no viable dark matter satellite candidates using one year of data, and we present a framework for interpreting this result in the context of numerical simulations to constrain the velocity-averaged annihilation cross section for a conventional 100 GeV WIMP annihilating through the b (b) over bar channel.
|
|
| 13. |
- Abdo, A. A., et al.
(författare)
-
DISCOVERY OF HIGH-ENERGY GAMMA-RAY EMISSION FROM THE BINARY SYSTEM PSR B1259-63/LS 2883 AROUND PERIASTRON WITH FERMI
- 2011
-
Ingår i: Astrophysical Journal Letters. - 2041-8205. ; 736:1, s. L11-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the discovery of >= 100 MeV gamma-rays from the binary system PSR B1259-63/LS 2883 using the Large Area Telescope (LAT) on board Fermi. The system comprises a radio pulsar in orbit around a Be star. We report on LAT observations from near apastron to similar to 128 days after the time of periastron, t(p), on 2010 December 15. No gamma-ray emission was detected from this source when it was far from periastron. Faint gamma-ray emission appeared as the pulsar approached periastron. At similar to t(p) + 30 days, the >= 100 MeV gamma-ray flux increased over a period of a few days to a peak flux 20-30 times that seen during the pre-periastron period, but with a softer spectrum. For the following month, it was seen to be variable on daily timescales, but remained at similar to(1-4) x 10(-6) cm(-2) s(-1) before starting to fade at similar to t(p) + 57 days. The total gamma-ray luminosity observed during this period is comparable to the spin-down power of the pulsar. Simultaneous radio and X-ray observations of the source showed no corresponding dramatic changes in radio and X-ray flux between the pre-periastron and post-periastron flares. We discuss possible explanations for the observed gamma-ray-only flaring of the source.
|
|
| 14. |
- Ackermann, M., et al.
(författare)
-
A Cocoon of Freshly Accelerated Cosmic Rays Detected by Fermi in the Cygnus Superbubble
- 2011
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 334:6059, s. 1103-1107
-
Tidskriftsartikel (refereegranskat)abstract
- The origin of Galactic cosmic rays is a century-long puzzle. Indirect evidence points to their acceleration by supernova shockwaves, but we know little of their escape from the shock and their evolution through the turbulent medium surrounding massive stars. Gamma rays can probe their spreading through theambient gas and radiation fields. The Fermi Large Area Telescope (LAT) has observed the star-forming region of Cygnus X. The 1- to 100-gigaelectronvolt images reveal a 50-parsec-wide cocoon of freshly accelerated cosmic rays that flood the cavities carved by the stellar winds and ionization fronts from young stellar clusters. It provides an example to study the youth of cosmic rays in a superbubble environment before they merge into the older Galactic population.
|
|
| 15. |
- Ackermann, M., et al.
(författare)
-
Dark matter constraints from observations of 25 Milky Way satellite galaxies with the Fermi Large Area Telescope
- 2014
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:4
-
Tidskriftsartikel (refereegranskat)abstract
- The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via gamma rays. Here we report on.-ray observations of 25 Milky Way dwarf spheroidal satellite galaxies based on 4 years of Fermi Large Area Telescope (LAT) data. None of the dwarf galaxies are significantly detected in. rays, and we present.-ray flux upper limits between 500 MeV and 500 GeV. We determine the dark matter content of 18 dwarf spheroidal galaxies from stellar kinematic data and combine LAT observations of 15 dwarf galaxies to constrain the dark matter annihilation cross section. We set some of the tightest constraints to date on the annihilation of dark matter particles with masses between 2 GeV and 10 TeV into prototypical standard model channels. We find these results to be robust against systematic uncertainties in the LAT instrument performance, diffuse.-ray background modeling, and assumed dark matter density profile.
|
|
| 16. |
- Ackermann, M., et al.
(författare)
-
FERMI-LAT OBSERVATIONS OF THE DIFFUSE γ-RAY EMISSION : IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 750:1, s. 3-
-
Tidskriftsartikel (refereegranskat)abstract
- The gamma-ray sky >100MeVis dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse gamma-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. To assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X-CO factor, the ratio between integrated CO-line intensity and H-2 column density, the fluxes and spectra of the gamma-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as gamma-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. We also provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.
|
|
| 17. |
- Ackermann, M., et al.
(författare)
-
Search for gamma-ray spectral lines with the Fermi Large Area Telescope and dark matter implications
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:8, s. 082002-
-
Tidskriftsartikel (refereegranskat)abstract
- Weakly interacting massive particles (WIMPs) are a theoretical class of particles that are excellent dark matter candidates. WIMP annihilation or decay may produce essentially monochromatic gamma rays detectable by the Fermi Large Area Telescope (LAT) against the astrophysical gamma-ray emission of the Galaxy. We have searched for spectral lines in the energy range 5-300 GeV using 3.7 years of data, reprocessed with updated instrument calibrations and an improved energy dispersion model compared to the previous Fermi-LAT Collaboration line searches. We searched in five regions selected to optimize sensitivity to different theoretically motivated dark matter density distributions. We did not find any globally significant lines in our a priori search regions and present 95% confidence limits for annihilation cross sections of self-conjugate WIMPs and decay lifetimes. Our most significant fit occurred at 133 GeV in our smallest search region and had a local significance of 3.3 standard deviations, which translates to a global significance of 1.5 standard deviations. We discuss potential systematic effects in this search, and examine the feature at 133 GeV in detail. We find that the use both of reprocessed data and of additional
|
|
| 18. |
- Ackermann, M., et al.
(författare)
-
The cosmic-ray and gas content of the Cygnus region as measured in gamma-rays by the Fermi Large Area Telescope
- 2012
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 538, s. A71-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The Cygnus region hosts a giant molecular-cloud complex that actively forms massive stars. Interactions of cosmic rays with interstellar gas and radiation fields make it shine at gamma-ray energies. Several gamma-ray pulsars and other energetic sources are seen in this direction. Aims. In this paper we analyze the gamma-ray emission measured by the Fermi Large Area Telescope (LAT) in the energy range from 100 MeV to 100 GeV in order to probe the gas and cosmic-ray content on the scale of the whole Cygnus complex. The gamma-ray emission on the scale of the central massive stellar clusters and from individual sources is addressed elsewhere. Methods. The signal from bright pulsars is greatly reduced by selecting photons in their off-pulse phase intervals. We compare the diffuse gamma-ray emission with interstellar gas maps derived from radio/mm-wave lines and visual extinction data. A general model of the region, including other pulsars and gamma-ray sources, is sought. Results. The integral HI emissivity above 100 MeV averaged over the whole Cygnus complex amounts to [2.06 +/- 0.11 (stat.) (+0.15)(-0.84) (syst.)] x 10(-26) photons s(-1) sr(-1) H-atom(-1), where the systematic error is dominated by the uncertainty on the HI opacity to calculate its column densities. The integral emissivity and its spectral energy distribution are both consistent within the systematics with LAT measurements in the interstellar space near the solar system. The average X-CO = N(H-2)/W-CO ratio is found to be [1.68 +/- 0.05 (stat.) (+0.87)(-0.10) (H I opacity)] x 10(20) molecules cm(-2) (K km s(-1))(-1), consistent with other LAT measurements in the Local Arm. We detect significant gamma-ray emission from dark neutral gas for a mass corresponding to similar to 40% of what is traced by CO. The total interstellar mass in the Cygnus complex inferred from its gamma-ray emission amounts to 8 (+5)(-1) x 10(6) M-circle dot at a distance of 1.4 kpc. Conclusions. Despite the conspicuous star formation activity and high masses of the interstellar clouds, the cosmic-ray population in the Cygnus complex averaged over a few hundred parsecs is similar to that of the local interstellar space.
|
|
| 19. |
- Ajello, M., et al.
(författare)
-
Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun
- 2011
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 84:3, s. 032007-
-
Tidskriftsartikel (refereegranskat)abstract
- During its first year of data taking, the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy cosmic-ray electrons and positrons (CREs). We present the results of a directional analysis of the CRE events, in which we searched for a flux excess correlated with the direction of the Sun. Two different and complementary analysis approaches were implemented, and neither yielded evidence of a significant CRE flux excess from the Sun. We derive upper limits on the CRE flux from the Sun's direction, and use these bounds to constrain two classes of dark matter models which predict a solar CRE flux: (1) models in which dark matter annihilates to CREs via a light intermediate state, and (2) inelastic dark matter models in which dark matter annihilates to CREs.
|
|
| 20. |
- Ajello, M., et al.
(författare)
-
FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE SUPERNOVA REMNANT G8.7-0.1
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 744:1, s. 80-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a detailed analysis of the GeV gamma-ray emission toward the supernova remnant (SNR) G8.7-0.1 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. An investigation of the relationship between G8.7-0.1 and the TeV unidentified source HESS J1804-216 provides us with an important clue on diffusion process of cosmic rays if particle acceleration operates in the SNR. The GeV gamma-ray emission is extended with most of the emission in positional coincidence with the SNR G8.7-0.1 and a lesser part located outside the western boundary of G8.7-0.1. The region of the gamma-ray emission overlaps spatially connected molecular clouds, implying a physical connection for the gamma-ray structure. The total gamma-ray spectrum measured with LAT from 200 MeV-100 GeV can be described by a broken power-law function with a break of 2.4 +/- 0.6 (stat) +/- 1.2 (sys) GeV, and photon indices of 2.10 +/- 0.06 (stat) +/- 0.10 (sys) below the break and 2.70 +/- 0.12 (stat) +/- 0.14 (sys) above the break. Given the spatial association among the gamma rays, the radio emission of G8.7-0.1, and the molecular clouds, the decay of pi(0)s produced by particles accelerated in the SNR and hitting the molecular clouds naturally explains the GeV gamma-ray spectrum. We also find that the GeV morphology is not well represented by the TeV emission from HESS J1804-216 and that the spectrum in the GeV band is not consistent with the extrapolation of the TeV gamma-ray spectrum. The spectral index of the TeV emission is consistent with the particle spectral index predicted by a theory that assumes energy-dependent diffusion of particles accelerated in an SNR. We discuss the possibility that the TeV spectrum originates from the interaction of particles accelerated in G8.7-0.1 with molecular clouds, and we constrain the diffusion coefficient of the particles.
|
|
| 21. |
- Ajello, M., et al.
(författare)
-
Limits on large extra dimensions based on observations of neutron stars with the Fermi-LAT
- 2012
-
Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :2, s. 012-
-
Tidskriftsartikel (refereegranskat)abstract
- We present limits for the compactification scale in the theory of Large Extra Dimensions (LED) proposed by Arkani-Hamed, Dimopoulos, and Dvali. We use 11 months of data from the Fermi Large Area Telescope (Fermi-LAT) to set gamma ray flux limits for 6 gamma-ray faint neutron stars (NS). To set limits on LED we use the model of Hannestad and Raffelt (HR) that calculates the Kaluza-Klein (KK) graviton production in supernova cores and the large fraction subsequently gravitationally bound around the resulting NS. The predicted decay of the bound KK gravitons to gamma gamma should contribute to the flux from NSs. Considering 2 to 7 extra dimensions of the same size in the context of the HR model, we use Monte Carlo techniques to calculate the expected differential flux of gamma-rays arising from these KK gravitons, including the effects of the age of the NS, graviton orbit, and absorption of gamma-rays in the magnetosphere of the NS. We compare our Monte Carlo-based differential flux to the experimental differential flux using maximum likelihood techniques to obtain our limits on LED. Our limits are more restrictive than past EGRET-based optimistic limits that do not include these important corrections. Additionally, our limits are more stringent than LHC based limits for 3 or fewer LED, and comparable for 4 LED. We conclude that if the effective Planck scale is around a TeV, then for 2 or 3 LED the compactification topology must be more complicated than a torus.
|
|
| 22. |
- Lister, M. L., et al.
(författare)
-
gamma-RAY AND PARSEC-SCALE JET PROPERTIES OF A COMPLETE SAMPLE OF BLAZARS FROM THE MOJAVE PROGRAM
- 2011
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 742:1, s. 27-
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the Fermi Large Area Telescope gamma-ray and 15 GHz Very Long Baseline Array radio properties of a joint gamma-ay and radio-selected sample of active galactic nuclei (AGNs) obtained during the first 11 months of the Fermi mission (2008 August 4-2009 July 5). Our sample contains the brightest 173 AGNs in these bands above declination -30 degrees during this period, and thus probes the full range of gamma-ray loudness (gamma-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least 4 orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing gamma-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the gamma-ray emission in these BL Lac objects over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED-peak-gamma-ray-loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQs) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lac objects have generally lower Doppler factors than the lower-synchrotron peaked BL Lac objects or FSRQs in our sample.
|
|
| 23. |
- Pletsch, H. J., et al.
(författare)
-
Binary Millisecond Pulsar Discovery via Gamma-Ray Pulsations
- 2012
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 338:6112, s. 1314-1317
-
Tidskriftsartikel (refereegranskat)abstract
- Millisecond pulsars, old neutron stars spun up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such "recycled" rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311-3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found.
|
|
| 24. |
- Ackermann, M., et al.
(författare)
-
Anisotropies in the diffuse gamma-ray background measured by the Fermi LAT
- 2012
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 85:8
-
Tidskriftsartikel (refereegranskat)abstract
- The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales. We analyze the angular power spectrum of the diffuse emission measured by the Fermi Large Area Telescope at Galactic latitudes vertical bar b vertical bar > 30 degrees in four energy bins spanning 1-50 GeV. At multipoles l >= 155, corresponding to angular scales less than or similar to 2 degrees, angular power above the photon noise level is detected at >99.99% confidence level in the 1-2 GeV, 2-5 GeV, and 5-10 GeV energy bins, and at >99% confidence level at 10-50 GeV. Within each energy bin the measured angular power takes approximately the same value at all multipoles l >= 155, suggesting that it originates from the contribution of one or more unclustered source populations. The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies, C-P/< I >(2) 9.05 +/- 0.84 x 10(-6) sr, while the energy dependence of C-P is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index Gamma(s) = 2.40 +/- 0.07. We discuss the implications of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray background.
|
|
| 25. |
- Ackermann, M., et al.
(författare)
-
Constraints on the galactic halo dark matter from fermi-lat diffuse measurements
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 761:2, s. 91-
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope (LAT) in the Milky Way halo region, searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e(+)/e(-) produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum, and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. The resulting limits impact the range of particle masses over which dark matter thermal production in the early universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as the annihilation of dark matter.
|
|
| 26. |
- Ackermann, M., et al.
(författare)
-
FERMI LARGE AREA TELESCOPE STUDY OF COSMIC RAYS AND THE INTERSTELLAR MEDIUM IN NEARBY MOLECULAR CLOUDS
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 755:1
-
Tidskriftsartikel (refereegranskat)abstract
- We report an analysis of the interstellar gamma-ray emission from the Chamaeleon, R Coronae Australis (R CrA), and Cepheus and Polaris flare regions with the Fermi Large Area Telescope. They are among the nearest molecular cloud complexes, within similar to 300 pc from the solar system. The gamma-ray emission produced by interactions of cosmic rays (CRs) and interstellar gas in those molecular clouds is useful to study the CR densities and distributions of molecular gas close to the solar system. The obtained gamma-ray emissivities above 250 MeV are (5.9 +/- 0.1(stat-1.0sys)(+0.9)) x 10(-27) photons s(-1) sr(-1) H-atom(-1), (10.2 +/- 0.4(stat-1.7sys)(+1.2)) x 10(-27) photons s(-1) sr(-1) H-atom(-1), and (9.1 +/- 0.3(stat-0.6sys)(+1.5)) x 10(-27) photons s(-1) sr(-1) H-atom(-1) for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively. Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by similar to 20% in the neighborhood of the solar system, even if we consider systematic uncertainties. The molecular mass calibrating ratio, X-CO = N(H-2)/W-CO, is found to be (0.96 +/- 0.06(stat-0.12sys)(+0.15)) x 10(20) H-2-molecule cm(-2) (K km s(-1))(-1), (0.99 +/- 0.08(stat-0.10sys)(+0.18)) x 10(20) H-2-molecule cm(-2) (K km s(-1))(-1), and (0.63 +/- 0.02(stat-0.07sys)(+0.09)) x 10(20) H-2-molecule cm(-2) (K km s(-1))(-1) for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively, suggesting a variation of X-CO in the vicinity of the solar system. From the obtained values of X-CO, the masses of molecular gas traced by W-CO in the Chamaeleon, R CrA, and Cepheus and Polaris flare regions are estimated to be similar to 5 x 10(3)M(circle dot), similar to 10(3)M(circle dot), and similar to 3.3 x 10(4)M(circle dot), respectively. A comparable amount of gas not traced well by standard Hi and CO surveys is found in the regions investigated.
|
|
| 27. |
- Ackermann, M., et al.
(författare)
-
SEARCH FOR COSMIC-RAY-INDUCED GAMMA-RAY EMISSION IN GALAXY CLUSTERS
- 2014
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 787:1
-
Tidskriftsartikel (refereegranskat)abstract
- Current theories predict relativistic hadronic particle populations in clusters of galaxies in addition to the already observed relativistic leptons. In these scenarios hadronic interactions give rise to neutral pions which decay into gamma rays that are potentially observable with the Large Area Telescope (LAT) on board the Fermi space telescope. We present a joint likelihood analysis searching for spatially extended gamma-ray emission at the locations of 50 galaxy clusters in four years of Fermi-LAT data under the assumption of the universal cosmic-ray (CR) model proposed by Pinzke & Pfrommer. We find an excess at a significance of 2.7 sigma, which upon closer inspection, however, is correlated to individual excess emission toward three galaxy clusters: A400, A1367, and A3112. We discuss these cases in detail and conservatively attribute the emission to unmodeled background systems (for example, radio galaxies within the clusters). Through the combined analysis of 50 clusters, we exclude hadronic injection efficiencies in simple hadronic models above 21% and establish limits on the CR to thermal pressure ratio within the virial radius, R-200, to be below 1.25%-1.4% depending on the morphological classification. In addition, we derive new limits on the gamma-ray flux from individual clusters in our sample.
|
|
| 28. |
- Ackermann, M., et al.
(författare)
-
SEARCH FOR GAMMA-RAY EMISSION FROM X-RAY-SELECTED SEYFERT GALAXIES WITH FERMI-LAT
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 747:2, s. 104-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a systematic investigation of the gamma-ray properties of 120 hard X-ray-selected Seyfert galaxies classified as radio-quiet objects, utilizing the three-year accumulation of Fermi Large Area Telescope (LAT) data. Our sample of Seyfert galaxies is selected using the Swift Burst Alert Telescope 58 month catalog, restricting the analysis to the bright sources with average hard X-ray fluxes F14-195 keV >= 2.5 x 10(-11) erg cm(-2) s(-1) at high Galactic latitudes (|b| > 10 degrees). In order to remove radio-loud objects from the sample, we use the hard X-ray radio loudness parameter, RrX, defined as the ratio of the total 1.4 GHz radio to 14-195 keV hard X-ray energy fluxes. Among 120 X-ray bright Seyfert galaxies with RrX < 10(-4), we did not find a statistically significant g-ray excess (TS > 25) positionally coincident with any target Seyferts, with possible exceptions of ESO 323-G077 and NGC 6814. The mean value of the 95% confidence level gamma-ray upper limit for the integrated photon flux above 100 MeV from the analyzed Seyferts is similar or equal to 4 x 10(-9) photons cm(-2) s(-1), and the upper limits derived for several objects reach similar or equal to 1 x 10(-9) photons cm(-2) s(-1). Our results indicate that no prominent gamma-ray emission component related to active galactic nucleus activity is present in the spectra of Seyferts around GeV energies. The Fermi-LAT upper limits derived for our sample probe the ratio of gamma-ray to X-ray luminosities L-gamma/L-X < 0.1, and even <0.01 in some cases. The obtained results impose novel constraints on the models for high-energy radiation of radio-quiet Seyfert galaxies.
|
|
| 29. |
- Freire, P. C. C., et al.
(författare)
-
Fermi Detection of a Luminous gamma-Ray Pulsar in a Globular Cluster
- 2011
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 334:6059, s. 1107-1110
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the Fermi Large Area Telescope's detection of gamma-ray (>100 mega-electron volts) pulsations from pulsar J1823-3021A in the globular cluster NGC 6624 with high significance (similar to 7 sigma). Its gamma-ray luminosity, L(gamma) = (8.4 +/- 1.6) x 10(34) ergs per second, is the highest observed for any millisecond pulsar (MSP) to date, and it accounts for most of the cluster emission. The nondetection of the cluster in the off-pulse phase implies that it contains <32 gamma-ray MSPs, not similar to 100 as previously estimated. The gamma-ray luminosity indicates that the unusually large rate of change of its period is caused by its intrinsic spin-down. This implies that J1823-3021A has the largest magnetic field and is the youngest MSP ever detected and that such anomalous objects might be forming at rates comparable to those of the more normal MSPs.
|
|
| 30. |
- Ackermann, M., et al.
(författare)
-
Gamma-ray observations of the orion molecular clouds with the fermi large area telescope
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 756:1, s. 4-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between similar to 100 MeV and similar to 100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to similar to 10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (W-CO) at a 1 degrees x 1 degrees pixel level. The correlation is found to be linear over a W-CO range of similar to 10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W-CO-to-mass conversion factor, X-CO, is found to be similar to 2.3 x 10(20) cm(-2) (K km s(-1))(-1) for the high-longitude part of Orion A (l > 212 degrees), similar to 1.7 times higher than similar to 1.3 x 10(20) found for the rest of Orion A and B. We interpret the apparent high XCO in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H-2 and CO densities in the diffuse molecular gas. W-CO decreases faster than the H-2 column density in the region making the gas "darker" to W-CO.
|
|
| 31. |
- Ackermann, M., et al.
(författare)
-
Periodic Emission from the Gamma-Ray Binary 1FGL J1018.6-5856
- 2012
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 335:6065, s. 189-193
-
Tidskriftsartikel (refereegranskat)abstract
- Gamma-ray binaries are stellar systems containing a neutron star or black hole, with gamma-ray emission produced by an interaction between the components. These systems are rare, even though binary evolution models predict dozens in our Galaxy. A search for gamma-ray binaries with the Fermi Large Area Telescope (LAT) shows that 1FGL J1018.6-5856 exhibits intensity and spectral modulation with a 16.6-day period. We identified a variable x-ray counterpart, which shows a sharp maximum coinciding with maximum gamma-ray emission, as well as an O6V((f)) star optical counterpart and a radio counterpart that is also apparently modulated on the orbital period. 1FGL J1018.6-5856 is thus a gamma-ray binary, and its detection suggests the presence of other fainter binaries in the Galaxy.
|
|
| 32. |
- Ackermann, M., et al.
(författare)
-
Fermi LAT search for dark matter in gamma-ray lines and the inclusive photon spectrum
- 2012
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 86:2
-
Tidskriftsartikel (refereegranskat)abstract
- Dark matter particle annihilation or decay can produce monochromatic gamma-ray lines and contribute to the diffuse gamma-ray background. Flux upper limits are presented for gamma-ray spectral lines from 7 to 200 GeV and for the diffuse gamma-ray background from 4.8 GeV to 264 GeV obtained from two years of Fermi Large Area Telescope data integrated over most of the sky. We give cross-section upper limits and decay lifetime lower limits for dark matter models that produce gamma-ray lines or contribute to the diffuse spectrum, including models proposed as explanations of the PAMELA and Fermi cosmic-ray data.
|
|
| 33. |
- Atwood, W. B., et al.
(författare)
-
NEW FERMI-LAT EVENT RECONSTRUCTION REVEALS MORE HIGH-ENERGY GAMMA RAYS FROM GAMMA-RAY BURSTS
- 2013
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 774:1, s. 76-
-
Tidskriftsartikel (refereegranskat)abstract
- Based on the experience gained during the four and a half years of the mission, the Fermi-LAT Collaboration has undertaken a comprehensive revision of the event-level analysis going under the name of Pass 8. Although it is not yet finalized, we can test the improvements in the new event reconstruction with the special case of the prompt phase of bright gamma-ray bursts (GRBs), where the signal-to-noise ratio is large enough that loose selection cuts are sufficient to identify gamma rays associated with the source. Using the new event reconstruction, we have re-analyzed 10 GRBs previously detected by the Large Area Telescope (LAT) for which an X-ray/optical follow-up was possible and found four new gamma rays with energies greater than 10 GeV in addition to the seven previously known. Among these four is a 27.4 GeV gamma ray from GRB 080916C, which has a redshift of 4.35, thus making it the gamma ray with the highest intrinsic energy (similar to 147 GeV) detected from a GRB. We present here the salient aspects of the new event reconstruction and discuss the scientific implications of these new high-energy gamma rays, such as constraining extragalactic background light models, Lorentz invariance violation tests, the prompt emission mechanism, and the bulk Lorentz factor of the emitting region.
|
|
| 34. |
|
|
| 35. |
- Wunderer, C. B., et al.
(författare)
-
The PERCIVAL soft X-ray imager
- 2014
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 9:3
-
Tidskriftsartikel (refereegranskat)abstract
- With the increased brilliance of state-of-the-art Synchrotron radiation sources and the advent of Free Electron Lasers enabling revolutionary science with EUV to X-ray photons comes an urgent need for suitable photon imaging detectors. Requirements include high frame rates, very large dynamic range, single-photon counting capability with low probability of false positives, and (multi)-megapixels. PERCIVAL (''Pixelated Energy Resolving CMOS Imager, Versatile and Large'') is currently being developed by a collaboration of DESY, RAL, Elettra and DLS to address this need for the soft X-ray regime. PERCIVAL is a monolithic active pixel sensor (MAPS), i.e. based on CMOS technology. It will be back-thinned to access its primary energy range of 250 eV to 1 keV with target efficiencies above 90%. According to its preliminary specifications, the roughly 10 × 10 cm2, 3520 × 3710 pixel monolithic sensor will operate at frame rates up to 120 Hz (commensurate with most FELs) and use multiple gains within its 27 μm pixels to measure (e.g. at 500 eV) 1 to ∼ 105 simultaneously-arriving photons. Currently, small-scale front-illuminated prototype systems (160 × 210 pixels) are undergoing detailed testing with visible-light as well as X-ray photons. © 2014 IOP Publishing Ltd and Sissa Medialab srl.
|
|
| 36. |
- Allahgholi, A., et al.
(författare)
-
AGIPD 1.0 : The high-speed high dynamic range readout ASIC for the adaptive gain integrating pixel detector at the European XFEL
- 2014
-
Ingår i: 2014 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS/MIC 2014. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479960972
-
Konferensbidrag (refereegranskat)abstract
- AGIPD is a hybrid pixel X-ray detector developed by a collaboration between Deutsches Elektronen-Synchrotron (DESY), Paul-Scherrer-Institute (PSI), University of Hamburg and the University of Bonn. The detector is designed to comply with the requirements of the European XFEL. The radiation tolerant Application Specific Integrated Circuit (ASIC) is designed with the following highlights: high dynamic range, spanning from single photon sensitivity up to 104 × 12.4 keV photons, achieved by the use of dynamic gain switching, auto-selecting one of 3 gains of the charge sensitive pre-amplifier. To cope with the unique features of the European XFEL source, image data is stored in 352 analogue memory cells per pixel. The selected gain is stored in the same way and depth, encoded as one of 3 voltage levels. These memories are operated in random-access mode at 4.5MHz frame rate. Data is read out on a row-by-row basis via multiplexers to the DAQ system for digitisation during the 99.4ms gap between the bunch trains of the European XFEL. The AGIPD 1.0 ASIC features 64×64 pixels with a pixel area of 200×200 μm2. It is bump-bonded to a 500 μm thick silicon sensor. The principles of the chip architecture were proven in different experiments and the ASIC characterization was performed with a series of development prototypes. The mechanical concept of the detector system was developed in close contact with the XFEL beamline scientists to ensure a seamless integration into the beamline setup and is currently being manufactured. The first single module system was successfully tested at APS1 the high dynamic range allows imaging of the direct synchrotron beam along with single photon sensitivity and burst imaging of 352 subsequent frames synchronized to the source.
|
|
| 37. |
- Allahgholi, A., et al.
(författare)
-
AGIPD, the electronics for a high speed X-ray imager at the Eu-XFEL
- 2014
-
Ingår i: Proceedings of Science. - : Proceedings of Science (PoS).
-
Konferensbidrag (refereegranskat)abstract
- The AGIPD (Adaptive Gain Integrated Pixel Detector) X-ray imaging camera will be operated at the X-ray Free Electron Laser, Eu-XFEL, under construction in Hamburg, Germany. Key parameters are 1 million 200 μm square pixels, single 12.4 keV photon detection and a dynamic range to 10 000/pixel/image. The developed sensors, ASICs, PCB-electronics and FPGA firmware acquire individual images per bunch at 27 000 bunches/s, packed into 10 bunch-trains/s with a bunch separation of 222 ns. Bunch-trains are handled by 352 analogue storage cells within each pixel of the ASIC and written during the 0.6msec train delivery. Therefore AGIPD can store 3520 images/s from the delivered 27 000 bunches/s. Random addressing provides reusability of each cell after an image has been declared as low-quality, so that good images can be selected. Digitization is performed between trains (99.4 msec). In the paper all functional blocks are introduced. The details concentrate on the DAQ-chain PCB-electronics and the slow control. A dense area of 1024 ADC-channels, each with a pickup-noise filtering and sampling of up to 50 MS/s/ADC and a serial output of 700 Mbit/s/ADC. FPGAs operate the ASICs synchronized to the bunch structure and collect the bit streams from 64 ADCs/FPGA. Pre-sorted data is transmitted on 10 GbE links out of the camera head using the time between trains. The control and monitoring of the camera with 600 A current consumption is based on a micro-controller and I2C bus with an addressing architecture allowing many devices and identical modules. The high currents require planned return paths at the system level. First experimental experience with the constructed components will be presented.
|
|
| 38. |
- Becker, J., et al.
(författare)
-
High speed cameras for X-rays : AGIPD and others
- 2013
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 8:1, s. Art. no. C01042-
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments at high pulse rate Free Electron Laser (FEL) facilities require new cameras capable of acquiring 2D images at high rates, handling large signal dynamic ranges and resolving images from individual pulses. The Adaptive Gain Integrated Pixel Detector (AGIPD) will operated with pulse rates and separations of 27000/s and 220 ns, respectively at European XFEL. Si-sensors, ASICs, PCBs, and FPGA logic are developed for a 1 Mega-pixel camera with 200 μm square pixels with per-pulse occupancies 104. Data from 3520 images/s will be transferred with 80 Gbits/s to a DAQ-system. The electronics have been adapted for use in other synchrotron light source detectors.
|
|
| 39. |
- Becker, J., et al.
(författare)
-
The high speed, high dynamic range camera AGIPD
- 2013
-
Ingår i: IEEE Nuclear Science Symposium Conference Record. - : IEEE conference proceedings. - 9781479905348 ; , s. Art. no. 6829504-
-
Konferensbidrag (refereegranskat)abstract
- The European X-Ray Free Electron Laser (XFEL) will provide ultra short, highly coherent X-ray pulses which will revolutionize scientific experiments in a variety of disciplines spanning physics, chemistry, materials science, and biology. One of the differences between the European XFEL and other free electron laser sources is the high pulse frequency of 4.5 MHz. The European XFEL will provide pulse trains, consisting of up to 2700 pulses separated by 220 ns (600 μs in total) followed by an idle time of 99.4 ms, resulting in a supercycle of 10 Hz. Dedicated fast 2D detectors are being developed, one of which is the Adaptive Gain Integrating Pixel Detector (AGIPD). AGIPD is based on the hybrid pixel technology. The design goals of the recently produced, radiation hard Application Specific Integrated Circuit (ASIC) with dynamic gain switching amplifiers are (for each pixel) a dynamic range of more than 10 4 12.4 keV photons in the lowest gain, single photon sensitivity in the highest gain, an analog memory capable of storing 352 images, and operation at 4.5 MHz frame rate. A vetoing scheme allows to maximize the number of useful images that are acquired by providing the possibility to overwrite any previously recorded image during the pulse train. The AGIPD will feature a pixel size of (200 μm)2 and a silicon sensor with a thickness of 500 μm. The image data is read out and digitized between pulse trains. © 2013 IEEE.
|
|
| 40. |
|
|
| 41. |
- Doro, M., et al.
(författare)
-
Dark matter and fundamental physics with the Cherenkov Telescope Array
- 2013
-
Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 43, s. 189-214
-
Tidskriftsartikel (refereegranskat)abstract
- The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV-TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2-3 different sizes, distributed over a large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10 degrees. In the following study, we investigate the prospects for CIA to study several science questions that can profoundly influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations currently under discussion, we employ a Monte Carlo based approach to evaluate the prospects for detection and characterisation of new physics with the array. First, we discuss cm prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, which are virtually void of astrophysical background and have a relatively well known dark matter density; in the region close to the Galactic Centre, where the dark matter density is expected to be large while the astrophysical background due to the Galactic Centre can be excluded; and in clusters of galaxies, where the intrinsic flux may be boosted significantly by the large number of halo substructures. The possible search for spatial signatures, facilitated by the larger field of view of CIA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma-rays from very distant blazars. We establish the axion mass range CIA could probe through observation of long-lasting flares in distant sources. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.
|
|
| 42. |
- Graafsma, Heinz, et al.
(författare)
-
PERCIVAL soft X-ray imager
- 2013
-
Ingår i: IEEE Nuclear Science Symposium Conference Record. - : IEEE conference proceedings. - 9781479905348 ; , s. Art. no. 6829506-
-
Konferensbidrag (refereegranskat)abstract
- Our goal is to provide the scientific community with a large (10cm × 10cm) pixellated detector featuring a large dynamic range (1-105 photons), good spatial resolution (27μm), good Quantum Efficiency (QE) in the low energy range (250eV-1keV), variable readout speed (up to 120 frames/s), i.e. with characteristics compatible with user needs at today's of low-energy Free Electron Lasers (FEL) and synchrotron sources. © 2013 IEEE.
|
|
| 43. |
- Greiffenberg, D., et al.
(författare)
-
Optimization of the noise performance of the AGIPD prototype chips
- 2013
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 8:10, s. Art. no. P10022-
-
Tidskriftsartikel (refereegranskat)abstract
- The charge integrating readout electronics AGIPD (adaptive gain integrating pixel detector) is a hybrid detector system developed for the European XFEL. It features a threefold dynamic gain switching to be able to resolve single photons and to cover a dynamic range of 104·12.4 keV photons. As a result of dynamic gain switching, single photon resolution will be achieved in the high gain stage, while the maximum dynamic range will be reached in the low gain stage. The specification to resolve single photons requires a signal-over-noise ratio of at least 10 for a single incoming photon with an energy of 12.4 keV. When using a silicon sensor, that translates to an equivalent noise charge of less than 343 e-. Several AGIPD prototype chips have been designed and characterized, particularly focusing on the noise performance. During the testing phase, the dominant noise sources were identified and the corresponding circuit blocks were improved in the subsequent ASICs. This paper reports on the procedures to identify the dominating noise sources, the optimization process of the circuit blocks and discusses the effect of the optimization on the noise performance.© 2013 IOP Publishing Ltd and Sissa Medialab srl.
|
|
| 44. |
- Greiffenberg, D., et al.
(författare)
-
Towards AGIPD1.0 : Optimization of the dynamic range and investigation of a pixel input protection
- 2014
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 9:6, s. Art. no. P06001-
-
Tidskriftsartikel (refereegranskat)abstract
- AGIPD is a charge integrating, hybrid pixel readout ASIC, which is under development for the European XFEL [1,2]. A dynamic gain switching logic at the output of the preamplifier (preamp) is used to provide single photon resolution as well as covering a dynamic range of at least 104·12.4 keV photons [3,4]. Moreover, at each point of the dynamic range the electronics noise should be lower than the Poisson fluctuations, which is especially challenging at the points of gain switching. This paper reports on the progress of the chip design on the way to the first full-scale chip AGIPD1.0, focusing on the optimization of the dynamic range and the implementation of protection circuits at the preamplifier input to avoid pixel destruction due to high intense spots. © 2014 IOP Publishing Ltd and Sissa Medialab srl.
|
|
| 45. |
- Haileselassie, Yeneneh, et al.
(författare)
-
Lactobacilli Regulate Staphylococcus aureus 161:2-Induced Pro-Inflammatory T-Cell Responses In Vitro
- 2013
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:10
-
Tidskriftsartikel (refereegranskat)abstract
- There seems to be a correlation between early gut microbiota composition and postnatal immune development. Alteration in the microbial composition early in life has been associated with immune mediated diseases, such as autoimmunity and allergy. We have previously observed associations between the presence of lactobacilli and Staphylococcus (S.) aureus in the early-life gut microbiota, cytokine responses and allergy development in children. Consistent with the objective to understand how bacteria modulate the cytokine response of intestinal epithelial cell (IEC) lines and immune cells, we exposed IEC lines (HT29, SW480) to UV-killed bacteria and/or culture supernatants (-sn) from seven Lactobacillus strains and three S. aureus strains, while peripheral blood mononuclear cells (PBMC) and cord blood mononuclear cells (CBMC) from healthy donors were stimulated by bacteria-sn or with bacteria conditioned IEC-sn. Although the overall IEC response to bacterial exposure was characterized by limited sets of cytokine and chemokine production, S. aureus 161: 2-sn induced an inflammatory response in the IEC, characterized by CXCL1/GROa and CXCL8/IL-8 production, partly in a MyD88-dependent manner. UV-killed bacteria did not induce a response in the IEC line, and a combination of both UV-killed bacteria and the bacteria-sn had no additive effect to that of the supernatant alone. In PBMC, most of the Lactobacillus-sn and S. aureus-sn strains were able to induce a wide array of cytokines, but only S. aureus-sn induced the T-cell associated cytokines IL-2, IL-17 and IFN-gamma, independently of IEC-produced factors, and induced up regulation of CTLA-4 expression and IL-10 production by T-regulatory cells. Notably, S. aureus-sn-induced T-cell production of IFN-gamma and IL-17 was down regulated by the simultaneous presence of any of the different Lactobacillus strains, while the IEC CXCL8/IL-8 response was unaltered. Thus these studies present a possible role for lactobacilli in induction of immune cell regulation, although the mechanisms need to be further elucidated.
|
|
| 46. |
- Hauptman, P. J., et al.
(författare)
-
Clinical course of patients with hyponatremia and decompensated systolic heart failure and the effect of vasopressin receptor antagonism with tolvaptan
- 2013
-
Ingår i: Journal of Cardiac Failure. - : Elsevier BV. - 1071-9164 .- 1532-8414. ; 19:6, s. 390-7
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Patients with decompensated heart failure, volume overload, and hyponatremia are challenging to manage. Relatively little has been documented regarding the clinical course of these patients during standard in-hospital management or with vasopressin antagonism. METHODS AND RESULTS: The Efficacy of Vasopressin Antagonism in Heart Failure Outcome Study With Tolvaptan database was examined to assess the short-term clinical course of patients hospitalized with heart failure and hyponatremia and the effect of tolvaptan on outcomes. In the placebo group, patients with hyponatremia (serum Na(+) <135mEq/L; n = 232), compared with those with normonatremia at baseline (n = 1785), had less relief of dyspnea despite receiving higher doses of diuretics (59.2% vs 69.2% improved; P < .01) and worse long-term outcomes. In the hyponatremia subgroup from the entire trial cohort (n = 475), tolvaptan was associated with greater likelihood of normalization of serum sodium than placebo (58% vs 20% and 64% vs 29% for day 1 and discharge, respectively; P < .001 for both comparisons), greater weight reduction at day 1 and discharge (0.7 kg and 0.8 kg differences, respectively; P < .001 and P = .008), and greater relief of dyspnea (P = .03). Among all hyponatremic patients, there was no effect of tolvaptan on long-term outcomes compared with placebo. In patients with pronounced hyponatremia (<130 mEq/L; n = 92), tolvaptan was associated with reduced cardiovascular morbidity and mortality after discharge (P = .04). CONCLUSIONS: In patients with decompensated heart failure and hyponatremia, standard therapy is associated with less weight loss and dyspnea relief, and unfavorable longer-term outcomes compared to those with normonatremia. Tolvaptan is associated with more favorable in-hospital effects and, possibly, long-term outcomes in patients with severe hyponatremia.
|
|
| 47. |
- Marras, A., et al.
(författare)
-
Vertically integrated circuits : Example of an application to an x-ray detector
- 2014
-
Ingår i: 2014 21st IEEE International Conference on Electronics, Circuits and Systems, ICECS 2014. - 9781479942428 ; , s. 243-246
-
Konferensbidrag (refereegranskat)abstract
- Replacing planar circuits with vertically integrated ones allows to increment circuit functionalities on a given silicon area, while avoiding some of the problems associated with aggressively scaled technology nodes. This is particularly true for applications likely to subject circuits to high doses of ionizing radiation (such of x-ray detectors to be used in synchrotron rings and Free Electron Lasers), since the degradation mechanisms of some of the innovative materials to be used in most recent nodes have not been fully characterized yet. In this paper, an evolution is presented for the readout ASIC of a pixelated x-ray detector to be used for such applications. The readout circuit is distributed in a stack of two vertically interconnected tiers, thus doubling the circuitry resident in each pixel without increasing the pixel pitch (and thus compromising spatial resolution of the detector). A first prototype has been designed and manufactured, using a commercial 130 nm CMOS technology. Design issues are discussed, along with preliminary characterization results. © 2014 IEEE.
|
|
| 48. |
|
|
| 49. |
|
|
