Christoph Winkler
European Space Research and Technology Centre
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Featured researches published by Christoph Winkler.
Nature | 2008
Georg Weidenspointner; Gerry Skinner; P. Jean; J. Knödlseder; Peter von Ballmoos; G. F. Bignami; R. Diehl; Andrew W. Strong; Bertrand Cordier; S. Schanne; Christoph Winkler
Gamma-ray line radiation at 511 keV is the signature of electron–positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk (∼10–50° from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV (‘hard’ LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron–positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 1041 positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.
Nature | 2012
S. A. Grebenev; A. A. Lutovinov; Sergei Tsygankov; Christoph Winkler
It is assumed that the radioactive decay of 44Ti powers the infrared, optical and ultraviolet emission of supernova remnants after the complete decay of 56Co and 57Co (the isotopes that dominated the energy balance during the first three to four years after the explosion) until the beginning of active interaction of the ejecta with the surrounding matter. Simulations show that the initial mass of 44Ti synthesized in core-collapse supernovae is (0.02–2.5) × 10−4 solar masses (). Hard X-rays and γ-rays from the decay of this 44Ti have been unambiguously observed from Cassiopeia A only, leading to the suggestion that values of the initial mass of 44Ti near the upper bound of the predictions occur only in exceptional cases. For the remnant of supernova 1987A, an upper limit to the initial mass of 44Ti of <10−3 has been obtained from direct X-ray observations, and an estimate of (1–2) × 10−4 has been made from infrared light curves and ultraviolet spectra by complex and model-dependent computations. Here we report observations of hard X-rays from the remnant of supernova 1987A in the narrow band containing two direct-escape lines of 44Ti at 67.9 and 78.4 keV. The measured line fluxes imply that this decay provided sufficient energy to power the remnant at late times. We estimate that the initial mass of 44Ti was (3.1 ± 0.8) × 10−4, which is near the upper bound of theoretical predictions.
The Astrophysical Journal | 1998
Bradley E. Schaefer; D. M. Palmer; B. L. Dingus; Edward J. Schneid; V. Schoenfelder; J. Ryan; Christoph Winkler; L. Hanlon; R. M. Kippen; Alanna Connors
We present three gamma-ray-burst spectra for bright bursts over very wide energy ranges. These were created from BATSE, COMPTEL, and OSSE data. The three spectra are for GRB 910503 (from 20 keV to 300 MeV), GRB 910601 (from 28 keV to 10.5 MeV), and GRB 910814 (from 103 keV to 500 MeV). A composite spectrum of 19 bright bursts is presented from 41 keV to 1.9 MeV (with no weak lines visible) for use in calculating average redshift corrections in cosmological models. Expanding fireball models with shocked synchrotron emission are predicted to have low-energy spectral slope (νFν ∝ να) that asymptotically approaches α = 4/3 such that α should never exceed 4/3. This prediction is tested with more than 100 bright bursts with BATSE and Ginga data. Over 90% of the bursts have spectral slopes in agreement with this prediction. For only one burst (GRB 870303, which has reported cyclotron lines) can a strong case be made that the slope violates the model limit, and then only from 2-5 keV.
SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation | 1996
Neil Gehrels; Christoph Winkler
The INTEGRAL observatory, due for launch in 2001, will address the fine spectroscopy (2 keV FWHM 1 MeV) and accurate imaging (12 arcminute FWHM) of celestial gamma-ray sources in the important 15 keV to 10 MeV energy range. The fine spectroscopy will permit spectral features to be uniquely identified and line profiles to be determined for in-depth studies of the source regions. Fine imaging will permit the accurate location and hence identification of the sources with counterparts at other wavelengths. ESA has completed the selection process for the scientific instruments to be flown on INTEGRAL, the data center and mission scientists, and the project is in its phase B development stage. The two main instruments onboard are a spectrometer which employs high-spectral-resolution germanium detectors and an imager which employs high- spatial-resolution arrays of cadmium telluride and cesium iodide detectors. Optical and x-ray monitors complete the scientific payload.
THE FIFTH COMPTON SYMPOSIUM | 2000
Christoph Winkler; W. Hermsen
The International Gamma-Ray Astrophysics Laboratory (INTEGRAL), to be launched in 2001, is dedicated to the fine spectroscopy (ΔE: 2 keV FWHM @ 1.3 MeV) and fine imaging (angular resolution: 12′ FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray (3–35 keV) and optical (V, 550 nm) range. The mission is conceived as an observatory led by ESA with contributions from Russia and NASA. The INTEGRAL observatory will provide to the science community at large an unprecedented combination of imaging and spectroscopy over a wide range of gamma-ray energies. This paper summarises the key scientific goals of the mission, the current development status of the payload and spacecraft and it will give an overview of the science ground segment including the science data center, science operations and key elements of the observing program.
arXiv: Astrophysics | 2008
Christoph Winkler
The gamma‐ray observatory INTEGRAL, launched in October 2002, produces a wealth of discoveries and new results on compact high energy Galactic objects, nuclear gamma‐ray line emission, diffuse line and continuum emission, cosmic background radiation, AGN, and high energy transients. Two important serendipitous discoveries made by the INTEGRAL mission are new classes of X‐ray binaries, namely the highly‐obscured high‐mass X‐ray binaries and the super‐giant fast transients. In this paper I will review the current status of these discoveries.
Gamma-ray bursts: 3rd Huntsville symposium | 2008
J. Gregory Stacy; Peter D. Jackson; Tj. Romke Bontekoe; Christoph Winkler
We report on the status of our ongoing project to search the database of the COBE Differential Microwave Radiometer (DMR) experiment for transient signals at microwave wavelengths simultaneous with cosmic gamma-ray bursts (GRBs). To date we have carried out a complete search of the DMR database using burst positions taken from the original BATSE 1B catalog for the eight-month period of overlap (May–December 1991) corresponding to the first public release of COBE data. We are currently repeating our original search of the COBE DMR database using the revised burst positions of the newly-released BATSE 3B catalog. Using BATSE 1B positions, at least two apparent simultaneous observations of GRBs by the COBE DMR occurred in 1991, along with a number of “near misses” within 30 seconds in time. At present, only upper limits to burst microwave emission are indicated. Even in the event of a non-detection of a GRB by the COBE DMR, unprecedented observational limits will still be obtained, constraining the predictio...
arXiv: Astrophysics | 2007
Jurgen Knodlseder; V. Lonjou; Georg Weidenspointner; P. Jean; Andrew W. Strong; R. Diehl; Bertrand Cordier; S. Schanne; Christoph Winkler
The origin of the soft gamma-ray (200 keV - 1 MeV) galactic ridge emission is one of the long-standing mysteries in the field of high-energy astrophysics. Population studies at lower energies have shown that emission from accreting compact objects gradually recedes in this domain, leaving place to another source of gamma-ray emission that is characterised by a hard power-law spectrum extending from 100 keV up to 100 MeV The nature of this hard component has remained so far elusive, partly due to the lack of sufficiently sensitive imaging telescopes that would be able to unveil the spatial distribution of the emission. The SPI telescope aboard INTEGRAL allows now for the first time the simultaneous imaging of diffuse and point-like emission in the soft gamma-ray regime. We present here all-sky images of the soft gamma-ray continuum emission that clearly reveal the morphology of the different emission components. We discuss the implications of our results on the nature of underlying emission processes and we put our results in perspective of GLAST studies of diffuse galactic continuum emission.
AIP Conference Proceedings | 2007
J. Gregory Stacy; Gary Lee Case; Daniel R. Hart; Peter D. Jackson; Christoph Winkler
We report on a new program to search the public time‐ordered datasets acquired with the Wilkinson Microwave Anisotropy Probe (WMAP) for transient signals associated with gamma‐ray bursts (GRBs) and other high‐energy sources. This program is an extension of earlier work in which we established the first limits on prompt microwave emission from GRBs using archival datasets from the Differential Microwave Radiometers (DMR) aboard the COBE satellite. The increased sensitivity and angular resolution of the WMAP radiometers compared to the COBE/DMR lead to a factor of ∼10,000 improvement in overall point‐source sensitivity. Such limits approach the signal levels predicted in the microwave band for the peak prompt emission arising from reverse shocks in GRBs. In the first phase of our program we are verifying our analysis software and assessing sensitivity limits by searching for microwave transients or flaring signals from known blazars and similar sources that are detected in the cumulative WMAP data as “foreg...
GAMMA-RAY BURSTS: 5th Huntsville Symposium | 2001
Louis J. Beathley; J. Gregory Stacy; Tj. Romke Bontekoe; Peter D. Jackson; Christoph Winkler
We report on an extension of earlier work to search the archival database of the Differential Microwave Radiometers (DMR) aboard the COBE satellite for evidence of transient events at microwave wavelengths associated with cosmic gamma-ray bursts (GRBs). Over its four-year lifetime the DMR experiment repeatedly surveyed the sky to measure fluctuations in the cosmic microwave background. On a number of occasions at least one of the horns of the DMR was also serendipitously pointing in the direction of a cosmic gamma-ray burst at the moment of burst occurrence. Our original investigation covered the eight-month period April–December 1991 when a number of GRBs were observed by the COBE/DMR at or within a few seconds of the CGRO/BATSE trigger time. Upper limits only were obtained for any simultaneous microwave flux from these events, in the range 7–42 kJy. Most recently, we have extended our search using the additional 24 months of COBE DMR data now publicly available, covering the time period January 1992 thr...