| 1. |
- Abramowski, A., et al.
(författare)
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The 2010 very high energy gamma-RAY flare and 10 years of multi-wavelength observations of M 87
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 746:2, s. 151-
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Tidskriftsartikel (refereegranskat)abstract
- The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3-6) x 10(9) M-circle dot) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) gamma-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE gamma-ray emitter since 2006. The VHE gamma-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE gamma-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of tau(rise)(d) = (1.69 +/- 0.30) days and tau(decay)(d) = (0.611 +/- 0.080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (similar to day), peak fluxes (Phi(>0.35 TeV) similar or equal to (1-3) x 10(-11) photons cm(-2) s(-1)), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken similar to 3 days after the peak of the VHE gamma-ray emission reveal an enhanced flux from the core (flux increased by factor similar to 2; variability timescale <2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE gamma-ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002-2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE gamma-ray emission from M 87 are reviewed in the light of the new data.
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| 2. |
- de Jong, R. S., et al.
(författare)
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4MOST : Project overview and information for the First Call for Proposals
- 2019
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Ingår i: The Messenger. - : European Southern Observatory. - 0722-6691. ; 175, s. 3-11
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We introduce the 4-metre Multi-Object Spectroscopic Telescope (4MOST), a new high-multiplex, wide-field spectroscopic survey facility under development for the four-metre-class Visible and Infrared Survey Telescope for Astronomy (VISTA) at Paranal. Its key specifications are: a large field of view (FoV) of 4.2 square degrees and a high multiplex capability, with 1624 fibres feeding two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20 000). After a description of the instrument and its expected performance, a short overview is given of its operational scheme and planned 4MOST Consortium science; these aspects are covered in more detail in other articles in this edition of The Messenger. Finally, the processes, schedules, and policies concerning the selection of ESO Community Surveys are presented, commencing with a singular opportunity to submit Letters of Intent for Public Surveys during the first five years of 4MOST operations.
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| 3. |
- Aguar-Bartolome, P., et al.
(författare)
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Measurement of the gamma p -> K-0 Sigma(+) reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron
- 2013
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:4
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Tidskriftsartikel (refereegranskat)abstract
- The gamma p -> K-0 Sigma(+) reaction has been measured from threshold to E-gamma = 1.45 GeV (W-CM = 1.9 GeV) using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. In the present experiment, this reaction was searched for in the 3 pi(0)p final state, by assuming K-S(0) -> pi(0)pi(0) and Sigma(+) -> pi(0)p. The experimental results include total and differential cross sections as well as the polarization of the recoil hyperon. The new data significantly improve empirical knowledge about the gamma p -> K-0 Sigma(+) reaction in the measured energy range. The results are compared to previous measurements and model predictions. It is demonstrated that adding the present gamma p -> K-0 Sigma(+) results to existing data allowed a better description of this reaction with various models.
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| 4. |
- Aguar-Bartolome, P., et al.
(författare)
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New determination of the eta transition form factor in the Dalitz decay eta -> e(+) e(-) gamma with the Crystal Ball/TAPS detectors at the Mainz Microtron
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:4
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Tidskriftsartikel (refereegranskat)abstract
- The Dalitz decay eta -> e(+) e(-) gamma has been measured in the gamma p -> eta p reaction with the Crystal Ball and TAPS multiphoton spectrometers, together with the photon-tagging facility at the Mainz Microtron MAMI. The experimental statistic used in this work is one order of magnitude greater than in any previous measurement of eta -> e(+) e(-) gamma. The value obtained for the slope parameter Lambda(-2) of the eta transition form factor, Lambda(-2) = (1.95 +/- 0.15(stat) +/- 0.10(syst)) GeV-2, is in good agreement with recent measurements conducted in eta -> e(+) e(-) gamma and eta -> mu(+) mu(-) gamma decays, as well as with recent form-factor calculations. The uncertainty obtained in the value of Lambda(-2) is lower compared to results from previous measurements of the eta -> e(+) e(-) gamma decay.
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| 5. |
- Kashevarov, V. L., et al.
(författare)
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Experimental study of the gamma p -> pi (0)pi(0) p reaction with the Crystal Ball/TAPS detector system at the Mainz Microtron
- 2012
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 85:6
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Tidskriftsartikel (refereegranskat)abstract
- The gamma p -> pi(0)pi(0) p reaction has been measured from threshold to 1.4 GeV using the Crystal Ball and TAPS photon spectrometers together with the photon tagging facility at the Mainz Microtron. The experimental results include total and differential cross sections as well as specific angular distributions, which were used to extract partial-wave amplitudes. In particular, the energy region below the D-13(1520) resonance was studied.
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| 6. |
- Acciari, V. A., et al.
(författare)
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Radio Imaging of the Very-High-Energy gamma-Ray Emission Region in the Central Engine of a Radio Galaxy
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 325:5939, s. 444-448
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Tidskriftsartikel (refereegranskat)abstract
- The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.
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| 7. |
- Adolph, C., et al.
(författare)
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Interplay among transversity induced asymmetries in hadron leptoproduction
- 2016
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 753, s. 406-411
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Tidskriftsartikel (refereegranskat)abstract
- In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as the Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows quantitative relationships to be established among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.
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| 8. |
- Adolph, C., et al.
(författare)
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Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data
- 2017
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Ingår i: European Physical Journal C. - : SPRINGER. - 1434-6044 .- 1434-6052. ; 77:4
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Tidskriftsartikel (refereegranskat)abstract
- Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality Q(2) > 1 ( GeV/c)(2). The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised (LiD)-Li-6 target. By analysing the full range in hadron transverse momentum p(T), the different pT-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation Delta g/g is evaluated at leading order in pQCD at a hard scale of mu(2) = < Q(2) > = 3( GeV/c)(2). It is determined in three intervals of the nucleon momentum fraction carried by gluons, x(g), covering the range 0.04< x(g)< 0.28 and does not exhibit a significant dependence on xg. The average over the three intervals, < Delta g/g > = 0.113 +/- 0.038(stat) +/- 0.036( syst) at < x(g) > approximate to 0.10, suggests that the gluon polarisation is positive in the measured x(g) range.
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| 9. |
- Adolph, C., et al.
(författare)
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Multiplicities of charged pions and charged hadrons from deep-inelastic scattering of muons off an isoscalar target
- 2017
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Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 764, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Multiplicities of charged pions and charged hadrons produced in deep-inelastic scattering were measured in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y and the relative hadron energy z. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and an isoscalar target ((LiD)-Li-6). They cover the kinematic domain in the photon virtuality Q(2) > 1 (GeV/c) 2, 0.004 < x < 0.4, 0.2 < z < 0.85 and 0.1 < y < 0.7. In addition, a leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions.
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| 10. |
- Adolph, C., et al.
(författare)
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Resonance production and pi pi S-wave in pi(-) + p -> pi(-) pi(-) pi(+) + p(recoil) at 190 GeV/c
- 2017
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 95:3
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Tidskriftsartikel (refereegranskat)abstract
- The COMPASS collaboration has collected the currently largest data set on diffractively produced pi(-) pi(-) pi(+) final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, 0.5 < m(3 pi) < 2.5 GeV/c(2), and in 11 bins of the reduced four-momentum transfer squared, 0.1 < t' < 1.0 (GeV/c)(2). This two-dimensional analysis offers sensitivity to genuine one-step resonance production, i.e. the production of a state followed by its decay, as well as to more complex dynamical effects in nonresonant 3 pi production. In this paper, we present detailed studies on selected 3p partial waves with J(PC) = 0(-+) ,1(++) ,2(-+) ,2(++) ,and 4(++). In these waves, we observe the well-known groundstate mesons as well as a new narrow axial-vector meson a(1)(1420) decaying into f(0) (980)pi. In addition, we present the results of a novel method to extract the amplitude of the pi(-)pi(+) subsystem with I(G)J(PC) = 0(+)0(++) in various partial waves from the pi(-)pi(-)pi(+) data. Evidence is found for correlation of the f (0)(980) and f(0)(1500) appearing as intermediate pi(-)pi(+) isobars in the decay of the known pi(1800) and pi(2)(1880).
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