V. Schönfelder

Publications (179)111.53 Total impact

• Article: New COMPTEL Results on MeV Gamma Rays from the Orion/Monoceros Region

  H. Bloemen, A. M. Bykov, V. Bozhokin, R. Diehl, W. Hermsen, Meulen, U. Oberlack, J. Ryan, V. Schönfelder, W. Strong, and C. Winkler
  [show abstract] [hide abstract]
  ABSTRACT: We present new COMPTEL observations of the Orion/Monoceros region, confirming our previous report of excessive 3-7 MeV emission which we tentatively attributed to nuclear deexcitation lines at 4.44 and 6.13 MeV from accelerated 12C and 16O nuclei. We show first results from a combination of all data obtained during the first five years of the mission, with emphasis on the extent of the emission region. The 3-7 MeV radiation is observed at the 9 σ significance level with a flux of (12.8 ± 1.5) × 10-5 γ cm-2 s-1, consistent with our previous findings. In addition, we can firmly conclude now that one single source cannot explain the measured intensity distribution: we find that the emission extends over the complex (the Orion A and B and the Mon R2 clouds), but it may actually be due to a few localized source regions. Evidence (4.4 σ) for emission from the Mon OB1/OB2 area is appearing as well. We present a preliminary spectrum (not fully deconvolved), which indicates that the emission is widely spread over the 3-7 MeV range, suggesting a dominantly broad-line origin from energetic C and O nuclei if indeed caused by nuclear lines. The spectrum shows features that might be due to splitting of the C and O lines, but further substantiation should come from forthcoming spectral analyses and new observations.
  The Astrophysical Journal 01/2009; 475(1):L25. · 6.02 Impact Factor
• Article: The Soft Gamma-Ray Spectral Variability of Cygnus X-1

  M. L. McConnell, A. A. Zdziarski, K. Bennett, H. Bloemen, W. Collmar, W. Hermsen, L. Kuiper, W. Paciesas, B. F. Phlips, J. Poutanen, J. M. Ryan, V. Schönfelder, H. Steinle, and A. W. Strong
  [show abstract] [hide abstract]
  ABSTRACT: We have used observations of Cyg X-1 from the Compton Gamma Ray Observatory and BeppoSAX to study the variation in the MeV γ-ray emission between the hard and soft spectral states, using spectra that cover the energy range from 20 keV up to 10 MeV. These data provide evidence for significant spectral variability at energies above 1 MeV. In particular, whereas the hard X-ray flux decreases during the soft state, the flux at energies above 1 MeV increases, resulting in a significantly harder γ-ray spectrum at energies above 1 MeV. This behavior is consistent with the general picture of galactic black hole candidates having two distinct spectral forms at soft γ-ray energies. These data extend this picture, for the first time, to energies above 1 MeV. We have used two different hybrid thermal/nonthermal Comptonization models to fit broadband spectral data obtained in both the hard and soft spectral states. These fits provide a quantitative estimate of the electron distribution and allow us to probe the physical changes that take place during transitions between the low and high X-ray states. We find that there is a significant increase (by a factor of ~4) in the bolometric luminosity as the source moves from the hard state to the soft state. Furthermore, the presence of a nonthermal tail in the Comptonizing electron distribution provides significant constraints on the magnetic field in the source region.
  The Astrophysical Journal 12/2008; 572(2):984. · 6.02 Impact Factor
• Article: A High-Sensitivity Measurement of the MeV Gamma-Ray Spectrum of Cygnus X-1

  M. L. McConnell, J. M. Ryan, W. Collmar, V. Schönfelder, H. Steinle, A. W. Strong, H. Bloemen, W. Hermsen, L. Kuiper, K. Bennett, B. F. Phlips, and J. C. Ling
  [show abstract] [hide abstract]
  ABSTRACT: The Compton Gamma Ray Observatory (CGRO) has observed the Cygnus region on several occasions since its launch in 1991. The data collected by the COMPTEL experiment on CGRO represent the most sensitive observations to date of Cygnus X-1 in the 0.75-30 MeV range. A spectrum accumulated by COMPTEL over 10 weeks of observation time shows significant evidence for emission extending out to several MeV. We have combined these data with contemporaneous data from both BATSE and OSSE to produce a broadband γ-ray spectrum, corresponding to the low X-ray state of Cygnus X-1, extending from 50 keV up to ~5 MeV. Although there is no evidence for any broad-line-like emissions in the MeV region, these data further confirm the presence of a hard tail at energies above several hundred keV. In particular, the spectrum at MeV energies can be described as a power law with a photon spectral index of α = -3.2, with no evidence for a cutoff at high energies. For the 200 keV-5 MeV spectrum, we provide a quantitative description of the underlying electron spectrum, in the context of a hybrid thermal/nonthermal model for the emission. The electron spectrum can be described by a thermal Maxwellian with a temperature of kTe = 86 keV and a nonthermal power-law component with a spectral index of pe = 4.5. The spectral data presented here should provide a useful basis for further theoretical modeling.
  The Astrophysical Journal 12/2008; 543(2):928. · 6.02 Impact Factor
• Source

  Available from: ArXiv

  Article: INTEGRAL SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane

  B. J. Teegarden, K. Watanabe, P. Jean, J. Knödlseder, V. Lonjou, J. P. Roques, G. K. Skinner, P. von Ballmoos, G. Weidenspointner, A. Bazzano, [......], W. H. G. Lewin, K. Makishima, A. Malzac, J. Miller, A. N. Parmar, S. P. Reynolds, R. E. Rothschild, V. Schönfelder, J. A. Tomsick, and J. Vink
  [show abstract] [hide abstract]
  ABSTRACT: The center of our Galaxy is a known strong source of electron-positron 511 keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (International Gamma-Ray Astrophysics Laboratory) mission, launched in 2002 October, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high-resolution, coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution, and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic plane. No positive annihilation flux was detected outside of the central region ( l > 40°) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511 keV flux.
  The Astrophysical Journal 12/2008; 621(1):296. · 6.02 Impact Factor
• Article: The Revised COMPTEL Orion Results

  H. Bloemen, D. Morris, J. Knödlseder, K. Bennett, R. Diehl, W. Hermsen, G. Lichti, R. D. van der Meulen, U. Oberlack, J. Ryan, V. Schönfelder, A. W. Strong, C. de Vries, and C. Winkler
  [show abstract] [hide abstract]
  ABSTRACT: COMPTEL observations of the Orion/Monoceros region have shown distinct evidence for excessive 3-7 MeV emission that was attributed to nuclear de-excitation lines from accelerated 12C and 16O nuclei. Unfortunately, we must conclude now that this appears to be a spurious result. This conclusion follows from a better understanding of the instrumental background, from a better exposure of the region, and from an improved analysis method. We show here how the impact of each of these gradually reduces the signal to a less than 3 σ result. The prime underlying cause seems to be 24Na activation in and around the upper COMPTEL detectors. Combining all available data, we now set a 2 σ flux upper limit on the 3-7 MeV emission of Orion of 3 × 10-5 γ cm-2 s-1, to be compared with the previously derived flux of ~10-4 γ cm-2 s-1.
  The Astrophysical Journal 12/2008; 521(2):L137. · 6.02 Impact Factor
• Source

  Available from: Hans Bloemen

  Chapter: 26Al radioactivity in the galaxy

  R. Diehl, U. Oberlack, J. Knödlseder, K. Bennett, H. Bloemen, W. Hermsen, J. Ryan, V. Schönfelder, P. von Ballmoos
  [show abstract] [hide abstract]
  ABSTRACT: 26Al radioactivity is believed to originate predominantly from massive stars, ejected into interstellar medium in wind phases and/or supernova events. With its million-year decay time, penetrating γ-rays from 26Al decay measure the massive-star history averaged over a time scale of ≃million years, thus extending times cales accessible otherwise. The COMPTEL 1.809 MeV all-sky data from 5 years of observations show irregularities and features at intermediate latitudes, which may have a more local origin (≃1 kpc). We find that the large scale emission can be characterized by a Galactic scale height of ≃130 pc, and a Galactocentric scale radius of ≃5 kpc, with features from spiral structure. Catalogues from massive-star related objects do not significantly improve the description of COMPTEL data above this. Emission associated with nearby structures such as the Gould Belt, Loop I, or stellar aggregates, is indicated, yet cannot be clearly detected. Combined with our imaging results, this suggests that 26Al yields from massive star ensembles depend on specifics of those stars and their history. Further 26Al γ-ray studies are underway to help mapping of the massive star history in the solar vicinity.
  05/2007: pages 393-396;
• Conference Proceeding: $^26$Al Gamma-Ray Line Observations of the Galaxy

  R Diehl, H Halloin, K Kretschmer, G ~G Lichti, V Schönfelder, A ~W Strong, A Kienlin, W Wang, P Jean, J Knödlseder, J -P Roques, G Weidenspointner, S Schanne, C Winkler, C Wunderer
  ESA Special Publication; 01/2007
• Article: Highlights from the COMPTEL 1 to 30 MeV Sky Survey

  V. SCHÖNFELDER, K. BENNETT, H. BLOEMEN, W. COLLMAR, R. DIEHL, W. HERMSEN, L. KUIPER, G. LICHTI, M. MCCONNELL, J. RYAN, A. STRONG, C. WINKLER
  Annals of the New York Academy of Sciences 12/2006; 759(1):226 - 231. · 3.15 Impact Factor
• Article: Evidence for 56Co Line Emission from the Type Ia Supernova 1991T using COMPTELa

  D.J. MORRIS, K. BENNETT, H. BLOEMEN, W. HERMSEN, G.G. LICHTI, M. L. McCONNELL, J.M. RYAN, V. SCHÖNFELDER
  Annals of the New York Academy of Sciences 12/2006; 759(1):397 - 400. · 3.15 Impact Factor
• Article: COMPTEL Observations of Gamma‐ray Burstsa

  R. M. KIPPEN, J. RYAN, A. CONNORS, M. MCCONNELL, V. SCHÖNFELDER, J. GREINER, M. VARENDORFF, W. COLLMAR, W. HERMSEN, L. KUIPER, C. WINKLER, L. O. HANLON, K. S. O'FLAHERTY
  Annals of the New York Academy of Sciences 12/2006; 759(1):425 - 428. · 3.15 Impact Factor
• Source

  Available from: Robert Georgii

  Article: The SPI Spectrometer for the Integral Mission

  G Vedrenne, P Jean, B Kandel, F Albernhe, V Borrel, P Mandrou, J P Roques, P von Ballmoos, Ph Durouchoux, B Cordier, [......], H Seifert, S Sturner, J Matteson, R Lin, S Slassi, F Sanchez, P Caraveo, P Leleux, G K Skinner, P Connell
  [show abstract] [hide abstract]
  ABSTRACT: SPI (Spectrometer for INTEGRAL) is a high spectral resolution gamma-ray telescope to be flown on board the ESA mission INTEGRAL. It consists of an array of 19 closely packed Germanium detectors surrounded by an active anticoincidence shield of BGO. The imaging capabilities of the instrument are obtained with a tungsten coded aperture mask located 1.7 m from the Ge array. The fully coded field-of-view is 16° and the angular resolution ≈2°. The energy range extends from 20 keV to 8 MeV with a typical energy resolution ≈2 keV at 1 MeV. The point-source narrow-line sensitivity is estimated to be (3–7) × 10−6 ph/cm−2 s−1 over most of the energy range of the instrument (E > 200 keV) for a 106 s observing time. With these expected performances a major step forward can be expected in fine gamma-ray spectroscopy of astrophysical objects.
  Physica Scripta 12/2006; 1998(T77):35. · 1.20 Impact Factor
• Article: Are 44Ti-producing supernovae exceptional?

  L.-S. The, D. D. Clayton, R. Diehl, D. H. Hartmann, A. F. Iyudin, M. D. Leising, B. S. Meyer, Y. Motizuki, V. Schönfelder
  [show abstract] [hide abstract]
  ABSTRACT: According to standard models supernovae produce radioactive 44Ti, which should be visible in gamma-rays following decay to 44Ca for a few centuries. 44Ti production is believed to be the source of cosmic 44Ca, whose abundance is well established. Yet, gamma-ray telescopes have not seen the expected young remnants of core collapse events. The 44Ti mean life of τ ≃ 89 y and the Galactic supernova rate of ≃3/100 y imply ≃several detectable 44Ti gamma-ray sources, but only one is clearly seen, the 340-year-old Cas A SNR. Furthermore, supernovae which produce much 44Ti are expected to occur primarily in the inner part of the Galaxy, where young massive stars are most abundant. Because the Galaxy is transparent to gamma-rays, this should be the dominant location of expected gamma-ray sources. Yet the Cas A SNR as the only one source is located far from the inner Galaxy (at longitude 112°). We evaluate the surprising absence of detectable supernovae from the past three centuries. We discuss whether our understanding of SN explosions, their 44Ti yields, their spatial distributions, and statistical arguments can be stretched so that this apparent disagreement may be accommodated within reasonable expectations, or if we have to revise some or all of the above aspects to bring expectations in agreement with the observations. We conclude that either core collapse supernovae have been improbably rare in the Galaxy during the past few centuries, or 44Ti-producing supernovae are atypical supernovae. We also present a new argument based on 44Ca/40Ca ratios in mainstream SiC stardust grains that may cast doubt on massive-He-cap type I supernovae as the source of most galactic 44Ca.
  Astronomy and Astrophysics 04/2006; 450:1037-1050. · 4.59 Impact Factor
• Article: $^26$Al in the inner Galaxy. Large-scale spectral characteristics derived with SPI/INTEGRAL

  R Diehl, H Halloin, K Kretschmer, A ~W Strong, W Wang, P Jean, G ~G Lichti, J Knödlseder, J -P Roques, S Schanne, V Schönfelder, A Kienlin, G Weidenspointner, C Winkler, C Wunderer
  åp. 04/2006; 449:1025-1031.
• Conference Proceeding: A Mystery of the Galactic Bulge: SPI Observations of Positron Annihilation

  G Weidenspointner, J Knödlseder, P Jean, V Lonjou, P Ballmoos, W Gillard, J ~M Harris, A Marcowith, G ~K Skinner, G Vedrenne, C ~R Shrader, B ~J Teegarden, N Guessoum, R Diehl, V Schönfelder, S Schanne, C Winkler
  SF2A-2005: Semaine de l'Astrophysique Francaise; 12/2005
• Source

  Available from: Christoph Winkler

  Article: The all-sky distribution of 511 keV electron-positron annihilation emission

  J. Knödlseder, P. Jean, V. Lonjou, G. Weidenspointner, N. Guessoum, W. Gillard, G. Skinner, P. von Ballmoos, G. Vedrenne, J. P. Roques, S. Schanne, B. Teegarden, V. Schönfelder, C. Winkler
  [show abstract] [hide abstract]
  ABSTRACT: We present a map of 511 keV electron-positron annihilation emission, based on data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray observatory, that covers approximately 95% of the celestial sphere. 511 keV line emission is significantly detected towards the galactic bulge region and, at a very low level, from the galactic disk. The bulge emission is highly symmetric and is centred on the galactic centre with an extension of 8 deg. The emission is equally well described by models that represent the stellar bulge or halo populations. The disk morphology is only weakly constrained by the present data, being compatible with both the distribution of young and old stellar populations. The 511 keV line flux from the bulge and disk components is 1.05e-3 ph cm-2 s-1 and 0.7e-3 ph cm-2 s-1, respectively, corresponding to a bulge-to-disk flux ratio in the range 1-3. Assuming a positronium fraction of 0.93 this translates into annihilation rates of 1.5e43 s-1 and 3e42 s-1, respectively. The ratio of the bulge luminosity to that of the disk is in the range 3-9. We find no evidence for a point-like source in addition to the diffuse emission, down to a typical flux limit of 1e-4 ph cm-2 s-1. We also find no evidence for the positive latitude enhancement that has been reported from OSSE measurements; our 3 sigma upper flux limit for this feature is 1.5e-4 ph cm-2 s-1. The disk emission can be attributed to the beta+ decay of the radioactive species 26Al and 44Ti. The bulge emission arises from a different source which has only a weak or no disk component. We suggest that Type Ia supernovae and/or low-mass X-ray binaries are the prime candidates for the source of the galactic bulge positrons. Light dark matter annihilation could also explain the observed 511 keV bulge emission characteristics.
  07/2005;
• Conference Proceeding: Foreword

  V Schönfelder, G Lichti, C Winkler
  5th INTEGRAL Workshop on the INTEGRAL Universe; 10/2004
• Source

  Available from: Nidhal Guessoum

  Conference Proceeding: Status of the 511 keV Line from the Galactic Centre Region

  P Jean, P Ballmoos, J Knödlseder, V Lonjou, G Weidenspointer, G ~K Skinner, M Allain, E Cisana, M Valsesia, N Guessoum, R Diehl, A ~W Strong, M Casse, G Vedrenne, V Schönfelder, C Winkler
  5th INTEGRAL Workshop on the INTEGRAL Universe; 10/2004
• Source

  Available from: Andreas von Kienlin

  Article: First Observations of Cygnus X-1 with SPI/INTEGRAL

  E. Jourdain, J. P. Roques, L. Bouchet, P. Mandrou, G. Vedrenne, V. Schönfelder, S. Boggs, P. Caraveo, B. Cordier, R. Diehl, P. Durouchoux, A. von Kienlin, J. Knödlseder, G. Lichti, J. Matteson, F. Sanchez, S. Schanne, A. Strong, P. von Ballmoos, C. Wunderer
  09/2004; 552:195.
• Source

  Available from: articles.adsabs.harvard.edu

  Article: The SPI/INTEGRAL Survey of the Galactic Plane After One Year

  L. Bouchet, E. Jourdain, J. P. Roques, P. Mandrou, P. Jean, G. Skinner, G. Vedrenne, R. Diehl, V. Schönfelder, A. Strong, B. Cordier, P. Durouchoux, P. Caraveo, S. Boggs, C. Wunderer, P. Leleux
  09/2004; 552:147.
• Article: The GLAST Burst Monitor

  P. N. Bhat, C. A. Meegan, G. G. Lichti, M. S. Briggs, V. Connaughton, R. Diehl, G. J. Fishman, J. Greiner, R. M. Kippen, C. Kouveliotou, W. S. Paciesas, R. D. Preece, V. Schönfelder, R. B. Wilson, A. von Kienlin
  [show abstract] [hide abstract]
  ABSTRACT: The Gamma Ray Large Area Space Telescope (GLAST) mission is a followup to the successful EGRET experiment onboard the Compton Gamma Ray Observatory (CGRO). It will provide a high‐sensitivity survey of the sky in high‐energy γ‐rays, and will perform detailed observations of persistent and transient sources. There are two experiments onboard the GLAST — the Large Area Telescope (LAT) and the GLAST Burst Monitor (GBM).
  AIP Conference Proceedings. 09/2004; 727(1):684-687.