arXiv subjects

C. Winkler

Publications and source records attributed to C. Winkler.

35 records · Page 2Linked to original sources

arXiv2004

SPI/INTEGRAL observation of 1809 keV gamma-ray line emission from the Cygnus X region

We present first results on the observation of 1809 keV gamma-ray line emission from the Cygnus X region with the SPI imaging spectrometer. Our analysis is based on data from the performance verification phase of the INTEGRAL instruments and comprises 1.3 Ms of exposure time. We observe a 1809 keV line flux of (7.3 +/- 0.9) x 10-5 ph cm-2 s-1 from a region delimited by galactic longitudes 73-93 deg and |b| < 7 deg at a significance level of 8 sigma. The 1809 keV line appears moderately broadened, with an intrinsic FWHM of 3.3 +/- 1.3 keV. Although this broadening is only marginal (at the 2 sigma level our data are compatible with an unbroadened line), it could reflect the 26Al ejecta kinematics.

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arXiv2004

Al(26) Studies with INTEGRAL's Spectrometer SPI

Al(26) radioactivity traces recent nucleosynthesis throughout the Galaxy, and is known to be produced in massive stars and novae. The map from its decay gamma-ray line suggests massive stars to dominate, but high-resolution line spectroscopy is expected to supplement imaging of Al(26) source regions and thus to help decide about the Al(26) injection process and interstellar environment, hence about the specific massive-star subgroup and phase which produces interstellar Al(26). The INTEGRAL Spectrometer SPI has observed Galactic Al(26) radioactivity in its 1809 keV gamma-ray line during its first inner-Galaxy survey. Instrumental background lines make analysis difficult; yet, a clear signal from the inner Galaxy agrees with expectations. In particular, SPI has constrained the line width to exclude previously-reported line broadenings corresponding to velocities >500 km/s. The signal-to-background ratio of percent implies that detector response and background modeling need to be fine-tuned to eventually enable line shape deconvolution in order to extract source location information along the line of sight.

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arXiv2003

Early SPI/INTEGRAL measurements of galactic 511 keV line emission from positron annihilation

We report the first measurements of the 511 keV line emission from the Galactic Centre (GC) region performed with the spectrometer SPI on the space observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory). Taking into account the range of spatial distribution models which are consistent with the data, we derive a flux of $9.9^{+4.7}_{-2.1} \times 10^{-4}$ ph cm$^{-2}$ s$^{-1}$ and an intrinsic line width of $2.95^{+0.45}_{-0.51}$ keV (FWHM). The results are consistent with other high-spectroscopy measurements, though the width is found to be at the upper bound of previously reported values.

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arXiv2003

SPI Measurements of Galactic 26Al

The precision measurement of the 1809 keV gamma-ray line from Galactic $^{26}$Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge detector camera. We aim for determination of the detailed shape of this gamma-ray line, and its variation for different source regions along the plane of the Galaxy. Data from the first part of the core program observations of the first mission year have been inspected. A clear detection of the \Al line at about 5--7 $σ$ significance demonstrates that SPI will deepen \Al studies. The line intensity is consistent with expectations from previous experiments, and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more consistent with RHESSI's recent value. Only preliminary statements can be made at this time, however, due to the multi-component background underlying the signal at \about 40 times higher intensity than the signal from Galactic $^{26}$Al.

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arXiv2003

The INTEGRAL ground segment and its science operations centre

The INTEGRAL ground segment is divided into operational and scientific components. The operational component consists of the Mission Operations Centre, the ground stations and communications lines while the scientific component comprises of a Science Operations Centre and Science Data Centre. The overall architecture of the ground segment is described paying particular attention to the tasks and functionalities of the INTEGRAL Science Operations Centre.

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arXiv2003

The INTEGRAL Science Data Centre (ISDC)

The INTEGRAL Science Data Centre (ISDC) provides the INTEGRAL data and means to analyse them to the scientific community. The ISDC runs a gamma ray burst alert system that provides the position of gamma ray bursts on the sky within seconds to the community. It operates a quick-look analysis of the data within few hours that detects new and unexpected sources as well as it monitors the instruments. The ISDC processes the data through a standard analysis the results of which are provided to the observers together with their data.

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arXiv2003

The Peculiar X-ray Transient IGR 16358-4726

The new transient IGR 16358-4726 was discovered on 2003 March 19 with INTEGRAL. We detected the source serendipitously during our 2003 March 24 observation of SGR 1627-41 with the Chandra X-ray Observatory at the 1.7 x 10^{-10} ergs s^{-1} cm^{-2} flux level (2-10 keV) with a very high absorption column (N_H=3.3(1) x 10^{23} cm^{-2}) and a hard power law spectrum of index 0.5(1). We discovered a very strong flux modulation with a period of 5880(50) s and peak-to-peak pulse fraction of 70(6)% (2-10 keV), clearly visible in the x-ray data. The nature of IGR 16358-4726 remains unresolved. The only neutron star systems known with similar spin periods are low luminosity persistent wind-fed pulsars; if this is a spin period, this transient is a new kind of object. If this is an orbital period, then the system could be a compact Low Mass X-ray Binary (LMXB).

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arXiv2003

INTEGRAL observations of the black hole candidate H 1743-322 in outburst

INTEGRAL made 3 observations in 2003 April of the black hole candidate H 1743-322 during the rising part, and close to the maximum, of an outburst. H 1743-322 was previously observed in outburst in 1977-1978. The source is located in a crowded region of the sky (l = 357 deg, b = -2 deg) and at least 18 sources are clearly detected in the field of view of the gamma-ray imager during a 277 ksec exposure. These are well known persistent X-ray binaries and 3 transient sources in outburst. The combined 5-200 keV JEM-X and SPI spectrum of H 1743-322 is well fit with an absorbed ((2.5 10E22 atom/cm2) soft (photon index 2.70 +/- 0.09) power-law model consistent with J 1743-322 being in a high/soft state.

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arXiv2003

Observation of GRB 030131 with the INTEGRAL satellite

A long Gamma-Ray Burst (GRB) was detected with the instruments on board the INTEGRAL satellite on January 31 2003. Although most of the GRB, which lasted $\sim$150 seconds, occurred during a satellite slew, the automatic software of the INTEGRAL Burst Alert System was able to detect it in near-real time. Here we report the results obtained with the IBIS instrument, which detected GRB 030131 in the 15 keV - 200 keV energy range, and ESO/VLT observations of its optical transient. The burst displays a complex time profile with numerous peaks. The peak spectrum can be described by a single power law with photon index $Γ\simeq$1.7 and has a flux of $\sim$2 photons cm$^{-2}$ s$^{-1}$ in the 20-200 keV energy band. The high sensitivity of IBIS has made it possible for the first time to perform detailed time-resolved spectroscopy of a GRB with a fluence of 7$\times10^{-6}$ erg cm$^{-2}$ (20-200 keV).

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arXiv2003

First results from the INTEGRAL Galactic plane scans

Scans of the Galactic plane performed at regular intervals constitute a key element of the guaranteed time observations of the INTEGRAL observing programme. These scans are done for two reasons: frequent monitoring of the Galactic plane in order to detect transient sources, and time resolved mapping of the Galactic plane in continuum and diffuse line emission. This paper describes first results obtained from the Galactic plane scans executed so far during the early phase (Dec 2002 - May 2003) of the nominal mission.

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arXiv2003

INTEGRAL and XMM-Newton observations of the weak GRB 030227

We present INTEGRAL and XMM-Newton observations of the prompt gamma-ray emission and the X-ray afterglow of GRB030227, the first GRB for which the quick localization obtained with the INTEGRAL Burst Alert System (IBAS) has led to the discovery of X-ray and optical afterglows. GRB030227 had a duration of about 20 s and a peak flux of 1.1 photons cm^-2 s^-1 in the 20-200 keV energy range. The time averaged spectrum can be fit by a single power law with photon index about 2 and we find some evidence for a hard to soft spectral evolution. The X-ray afterglow has been detected starting only 8 hours after the prompt emission, with a 0.2-10 keV flux decreasing as t^-1 from 1.3x10e-12 to 5x10e-13 erg cm^-2 s^-1. The afterglow spectrum is well described by a power law with photon index 1.94+/-0.05 modified by a redshifted neutral absorber with column density of several 10e22 cm^-2. A possible emission line at 1.67 keV could be due to Fe for a redshift z=3, consistent with the value inferred from the absorption.

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arXiv2001

The Comptel 1.809 Mev Survey

We present the latest update of the 1.809 MeV sky survey obtained with COMPTEL. Based on all observations taken since the launch of CGRO in spring 1991 to early summer this year we obtain 1.809 MeV all sky maps using different imaging methods. The background is modelled on the basis of an adjacent energy approach. We confirm the previously reported characteristics of the galactic 1.809 MeV emission, specifically excesses in regions away from the inner Galaxy. The observed 1.8 MeV gamma-ray line is ascribed to the radioactive decay of 26Al in the interstellar medium. 26Al has been found to be predominantly synthesised in massive stars and their subsequent core-collapse supernovae, which is confirmed in tracer comparisons. Due to this, one anticipates flux enhancements aligned with regions of recent star formation, such as apparently observed in the Cygnus and Vela regions.

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arXiv1999

Observations of GRB 990123 by the Compton Gamma-Ray Observatory

GRB 990123 was the first burst from which simultaneous optical, X-ray and gamma-ray emission was detected; its afterglow has been followed by an extensive set of radio, optical and X-ray observations. We have studied the gamma-ray burst itself as observed by the CGRO detectors. We find that gamma-ray fluxes are not correlated with the simultaneous optical observations, and the gamma-ray spectra cannot be extrapolated simply to the optical fluxes. The burst is well fit by the standard four-parameter GRB function, with the exception that excess emission compared to this function is observed below ~15 keV during some time intervals. The burst is characterized by the typical hard-to-soft and hardness-intensity correlation spectral evolution patterns. The energy of the peak of the nu f_nu spectrum, E_p, reaches an unusually high value during the first intensity spike, 1470 +/- 110 keV, and then falls to \~300 keV during the tail of the burst. The high-energy spectrum above ~MeV is consistent with a power law with a photon index of about -3. By fluence, GRB 990123 is brighter than all but 0.4% of the GRBs observed with BATSE, clearly placing it on the -3/2 power-law portion of the intensity distribution. However, the redshift measured for the afterglow is inconsistent with the Euclidean interpretation of the -3/2 power-law. Using the redshift value of >= 1.61 and assuming isotropic emission, the gamma-ray fluence exceeds 10E54 ergs.

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arXiv1999

COMPTEL Observations of AGN at MeV-Energies

The COMPTEL experiment aboard CGRO, exploring the previously unknown sky at MeV-energies, has so far detected 10 Active Galactic Nuclei (AGN): 9 blazars and the radio galaxy Centaurus A. No Seyfert galaxy has been found yet. With these results COMPTEL has opened the field of extragalactic Gamma-ray astronomy in the MeV-band.

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arXiv1999

INTEGRAL: The Current Status

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is dedicated to the fine spectroscopy (Delta-E: 2 keV FWHM @ 1.3 MeV) and fine imaging (angular resolution: 12 arcmin 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 energies. Most of the observing time will be open to the scientific community. 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 data centre, science operations and the key elements of the observing programme

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arXiv1999

The INTEGRAL Core Observing Programme

The Core Programme of the INTEGRAL mission is defined as the portion of the scientific programme covering the guaranteed time observations for the INTEGRAL Science Working Team. This paper describes the current status of the Core Programme preparations and summarizes the key elements of the observing programme.

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arXiv1995

The gamma-ray burst GB 920622

We have analyzed the Ulysses, BATSE, and COMPTEL spectral data from the $γ$-ray burst of June 22, 1992 (GB 920622). COMPTEL data reveal a hard to soft evolution within the first pulse of the burst, while the mean hardness ratios of the three pulses are the same. Unlike the single instrument spectra, the composite spectrum of GB 920622 averaged over the total burst duration ranging from 20 keV up to 10 MeV cannot be fit by a single power law. Instead, the spectrum shows continuous curvature across the full energy range. COMPTEL imaging and BATSE/Ulysses triangulation constrain the source location of GB 920622 to a ring sector 1.1 arcmin wide and 2 degrees long. This area has been searched for quiescent X-ray sources using \ros survey data collected about two years before the burst. After the optical identification of the X-ray sources in and near the GRB location we conclude that no quiescent X-ray counterpart candidate for GB 920622 has been found.

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