| 1. |
- Feroci, M., et al.
(författare)
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The large observatory for x-ray timing
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9780819496126
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Konferensbidrag (refereegranskat)abstract
- The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.
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| 2. |
- Feroci, M., et al.
(författare)
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LOFT - The large observatory for x-ray timing
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9780819491442 ; , s. 84432D-
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Konferensbidrag (refereegranskat)abstract
- The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (<1 degree field of view) experiment operating in the energy range 2-50 keV, with a 10 m2 peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of <5 arcmin. The LAD and WFM experiments will allow us to investigate variability from submillisecond QPO's to yearlong transient outbursts. In this paper we report the current status of the project.
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| 3. |
- de Graauw, Th., et al.
(författare)
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The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L6-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 4. |
- Falgarone, E., et al.
(författare)
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CH+(1-0) and 13CH+(1-0) absorption lines in the direction of massive star-forming regions
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of the ground-state rotational transition of the methylidyne cation CH+ and its isotopologue (CH+)-C-13 toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH+ absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH+ column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [(CH+)-C-12]/[(CH+)-C-13]> 35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH+)/N(HCO+), is found to vary by at least a factor 10, between 4 and > 40, in the Galactic foreground material. Line-of-sight 12CH+ average abundances relative to total hydrogen are estimated. Their average value, N(CH+)/NH > 2.6 x 10(-8), is higher than that observed in the solar neighborhood and confirms the high abundances of CH+ in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH+)/ N(HCO+) ratios, from 1 to similar to 50, is comparable to that observed.
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| 5. |
- Gerin, M., et al.
(författare)
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Interstellar OH+, H2O+ and H3O+ along the sight-line to G10.6-0.4
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:4, s. 110-
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of absorption lines by the reactive ions OH+, H2O+ and H3O+ along the line of sight to the submillimeter continuum source G10.6$-$0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+ at 971 GHz, H2O+ at 1115 and 607 GHz, and H3O+ at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6$-$0.4 as well as in the molecular gas directly associated with that source. The OH+ spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O+ lines remains lower than 1 in the same velocity range, and the H3O+ line shows only weak absorption. For LSR velocities between 7 and 50 kms$^{-1}$ we estimate total column densities of $N$(OH+) $> 2.5 \times 10^{14}$ cm$^{-2}$, $N$(H2O+) $\sim 6 \times 10^{13}$ cm$^{-2}$ and $N$(H3O+) $\sim 4.0 \times 10^{13}$ cm$^{-2}$. These detections confirm the role of O$^+$ and OH$^+$ in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH+ by the H2O+ column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.
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| 6. |
- Desforges, F. G., et al.
(författare)
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Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration
- 2014
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of ionization-induced electron injection in high density (similar to 1.2 x 10(19) cm(-3)) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism. (C) 2014 AIP Publishing LLC.
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| 7. |
- Persson, Carina, 1964, et al.
(författare)
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Nitrogen hydrides in interstellar gas Herschel/HIFI observations towards G10.6-0.4 (W31C)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L45 -
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Tidskriftsartikel (refereegranskat)abstract
- The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N = 1
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| 8. |
- Desforges, F. G., et al.
(författare)
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Reproducibility of electron beams from laser wakefield acceleration in capillary tubes
- 2014
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 740, s. 54-59
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Tidskriftsartikel (refereegranskat)abstract
- The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside capillary tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter capillary tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.
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| 9. |
- Hansson, Martin, et al.
(författare)
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Enhanced stability of laser wakefield acceleration using dielectric capillary tubes
- 2014
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Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:3
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Tidskriftsartikel (refereegranskat)abstract
- The stability of beams of laser wakefield accelerated electrons in dielectric capillary tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.
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| 10. |
- Ju, J., et al.
(författare)
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Enhancement of x-rays generated by a guided laser wakefield accelerator inside capillary tubes
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:19
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedElectrons accelerated in the nonlinear regime in a laser wakefield accelerator experience transverse oscillations inside the plasma cavity, giving rise to ultra-short pulsed x-rays, also called the betatron radiation. We show that the fluence of x-ray can be enhanced by more than one order of magnitude when the laser is guided by a 10 mm long capillary tube instead of interacting with a 2 mm gas jet. X-rays with a synchrotron-like spectrum and associated critical energy ∼ 5 keV, with a peak brightness of ∼ 1×1021 ph/s/mm2/mrad2/0.1%BW, were achieved by employing 16 TW laser pulses.
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| 11. |
- Neufeld, D. A., et al.
(författare)
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Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L10-
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1-0 transition of OH+ and the 1115 GHz 1(11)-0(00) transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s(-1) with respect to the local standard of rest. The inferred OH+/H2O+ abundance ratio ranges from similar to 3 to similar to 15, implying that the observed OH+ arises in clouds of small molecular fraction, in the 2-8% range. This conclusion is confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few x10(-8) suggests a cosmic ray ionization rate for atomic hydrogen of 0.6-2.4 x 10(-16) s(-1), in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H-3(+) and other species.
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