arXiv subjects

K. Kretschmer

Publications and source records attributed to K. Kretschmer.

13 recordsLinked to original sources

arXiv2009

Spectral and intensity variations of Galactic 26^Al emission

Gamma-ray line emission from the radioactive decay of 26Al reflects nucleosynthesis in massive stars and supernovae. We use INTEGRAL 26Al measurements to characterize the distribution and characteristics of 26Al source regions throughout the Galaxy. We detect the 26Al line from the inner Galaxy at 28σsignificance. The line appears narrow, and we constrain broadening in the source regions to <1.3 keV (2σ). Different sky distribution models do not significantly affect those large-scale results. The 26Al intensity for the inner Galaxy is derived as (2.9\pm 0.2)\times 10^{-4}ph\ cm^{-2} s^{-1} rad^{-1}, consistent with earlier results from COMPTEL and SPI data. This can be translated to an 26Al mass of 2.7\pm 0.7 solar mass in the Galaxy as a whole. The 26Al intensity is also confirmed to be somewhat brighter in the 4th than in the 1st quadrant (ratio 1.3\pm 0.2). 26Al spectra separately derived for regions along the Galactic plane show clear line centroid shifts, attributed largely to the Galaxy's large-scale rotation. The 26Al line toward the direction of the Aquila region (20deg < l < 40deg) appears somewhat broadened. Latitudinal variations of 26Al emission towards the inner Galaxy are studied, finding a latitudinal scale height of 130^{+120}_{-70} pc (1σ) for 26Al in the inner Galaxy and a hint of peculiar 26Al emission towards the region l<0deg, b>5deg.

astro-ph.HE↗

arXiv2007

SPI observations of the diffuse 60Fe emission in the Galaxy

Gamma-ray line emission from radioactive decay of 60Fe provides constraints on nucleosynthesis in massive stars and supernovae. The spectrometer SPI on board INTEGRAL has accumulated nearly three years of data on gamma-ray emission from the Galactic plane. We have analyzed these data with suitable instrumental-background models and sky distributions to produce high-resolution spectra of Galactic emission. We detect the gamma-ray lines from 60Fe decay at 1173 and 1333 keV, obtaining an improvement over our earlier measurement of both lines with now 4.9 sigma significance for the combination of the two lines. The average flux per line is (4.4 \pm 0.9) \times 10^{-5} ph cm^{-2} s^{-1} rad^{-1} for the inner Galaxy region. Deriving the Galactic 26Al gamma-ray line flux with using the same set of observations and analysis method, we determine the flux ratio of 60Fe/26Al gamma-rays as 0.148 \pm 0.06. The current theoretical predictions are still consistent with our result.

astro-ph↗

arXiv2005

26Al in the inner Galaxy

We performed a spectroscopic study of the 1809 keV gamma-ray line from 26Al decay in the Galaxy using the SPI imaging spectrometer with its high-resolution Ge detector camera on the INTEGRAL observatory. We analyzed observations of the first two mission years, fitting spectra from all 7130 telescope pointings in narrow energy bins to models of instrumental background and the 26Al sky. Instrumental background is estimated from independent tracers of cosmic-ray activation. The shape of the 26Al signal is compared to the instrumental response to extract the width of the celestial line. We detect the 26Al line at \~16sigma significance. The line is broadened only slightly, if at all; we constrain the width to be below 2.8 keV (FWHM, 2 sigma). The average Doppler velocities of 26Al at the time of its decay in the interstellar medium (decay time~1.04 My) therefore are probably around 100 km/s, in agreement with expectations from Galactic rotation and interstellar turbulence. The flux and spatial distribution of the emission are found consistent with previous observations. The derived amount of 26Al in the Galaxy is 2.8 (+/-0.8) M_solar.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

arXiv2004

Search for gamma-ray line emission from the radioactive decay of 60Fe with SPI

The search for gamma-ray line emission from the radioactive decay of 60Fe figures among the prime scientific objectives of the INTEGRAL mission. 60Fe is believed to be primarily produced in core-collapse supernovae, although other sites, such as carbon deflagration supernovae or intermediate mass AGB stars have also been suggested. We present first results of our search for the 1173 and 1332 keV gamma-ray lines of 60Fe decay in the SPI data of the first mission year. So far we can only report upper flux limits whose levels are determined by systematic uncertainties in the treatment of the instrumental background. Once we understand the background uncertainties better, the SPI data should provide stringent constraints on 60Fe nucleosynthesis in our Galaxy.

astro-ph↗

arXiv2003

Line shape diagnostics of Galactic 26Al

The shape of the gamma-ray line from radioactive 26Al, at 1808.7 keV energy in the frame of the decaying isotope, is determined by its kinematics when it decays, typically 10^6 y after its ejection into the interstellar medium from its nucleosynthesis source. Three measurements of the line width exist: HEAO-C's 1982 value of (0+3) keV FWHM, the GRIS 1996 value of (5.4 +/- 1.3) keV FWHM, and the recent RHESSI value of (2.0 +/- 0.8) keV FWHM, suggesting either "cold", "hot", or "warm" 26Al in the ISM. We model the line width as expected from Galactic rotation, expanding supernova ejecta, and/or Wolf-Rayet winds, and predict a value below 1 keV (FWHM) with plausible assumptions about 26Al initial velocities and expansion history. Even though the recent RHESSI measurement reduces the need to explain a broad line corresponding to 540 km/s mean 26Al velocity through extreme assumptions about grain transport of 26Al or huge interstellar cavities, our results suggest that standard 26Al ejection models produce a line on the narrow side of what is observed by RHESSI and INTEGRAL. Improved INTEGRAL and RHESSI spatially-resolved line width measurements should help to disentangle the effects of Galactic rotation from the ISM trajectories of 26Al.

astro-ph↗

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.

astro-ph↗

arXiv2002

Disturbance Ecology from nearby Supernovae

Monte Carlo simulations of Galactic Supernovae are carried out to study the rate of nearby events, which may have a direct effect on Earth's ecology though ionizing radiation and cosmic ray bombardment. A nearby supernova may have left a radioactive imprint (60Fe) in recent galactic history.

astro-ph↗

arXiv2001

Diffuse gamma-ray line emission from multiple OB Associations in Cygnus

The COMPTEL observations of the diffuse galactic 1.809 MeV emission attributed to the radioactive decay of 26Al have confirmed the diffuse nature of this interstellar emission line. One of the most significant features of the reconstructed intensity pattern is a flux enhancement in the direction of the Cygnus region. This region is fairly young and contains a wealth of massive stars, most of them grouped in the Cygnus OB associations. Multi-frequency model fitting strongly supports the hypothesis of massive stars and their descendent supernovae being the dominant sources of interstellar 26Al as observed by COMPTEL. Massive stars and supernovae are known to impart a large amount of kinetic energy into the surrounding ISM which lead to shockregions and large cavities. In addition, a large fraction of the electro-magnetic radiation of massive stars lies in the extreme ultra-violet causing photoionisation of the surrounding interstellar medium. We applied a population synthesis model in combination with an analytic model of the expansion of superbubbles to the Cygnus OB associations. The model predicts the expected 1.809 MeV flux and the gamma-ray line intensity due to interstellar 60Fe. We compute the sizes and expansion parameters of the expected HI-structures and the free-free emission intensities due to the photoionizing radiation from massive stars within this region of the sky. We discuss our present understanding of the Cygnus region with respect to the massive star census and history. Our model assigns about 70% of the 1.809 MeV intensity to six known OB associations, about 20% to known isolated sources and roughly 10% to an unkown diffuse component.

astro-ph↗

arXiv2001

Gamma-Ray Line Emission from Superbubbles in the Interstellar Medium: The Cygnus Region

The star forming process in the Milky Way is non-uniform in time and space. The scale of star forming regions ranges from groups within a few pc to large segments of spiral arms with linear dimension of order kpc. When many stars form in a relatively small volume over a short duration, a localized starburst ensues. The energetic impact of such a burst of star formation can severely affect the dynamic structure of the gaseous disk. Stellar winds and supernova explosions drive an expanding superbubble, whose size eventually exceeds the scale height of the disk and thus drives a disk-wind blowing metal enriched gas into the halo. We discuss the basic scenario of superbubble evolution, emphasizing the associated gamma-ray line signatures. In particular, we discuss nuclear line emission from 26Al and 60Fe in the Cygnus region.

astro-ph↗

arXiv2001

The Cygnus Region: 26Al from OB Associations

The COMPTEL map of the 1.809 MeV gamma-ray line, which is attributed to the radioactive decay of 26Al, shows significant excess emission in the Cygnus region. Cygnus is a region of recent star formation activity, which is rich in massive, early-type stars concentrated in OB associations. We perform population synthesis studies of this region to model the production and distribution of 26Al, which is predominantly synthesized in massive stars and distributed through stellar winds and core-collapse supernovae. Our simulations of the Cygnus OB associations determine the time-dependent production rate of 26Al. We also estimate the associated production of radioactive 60Fe, which is primarily synthesized in core-collapse supernovae. Gamma-ray line emission from this isotope has yet to be detected. We also track the temporal evolution of the mechanical "luminosity" due to the kinetic energy of stellar winds and supernova ejecta, and the ionizing EUV emission from early-type stars. Together with a simple one-dimensional model of the superbubble driven into the ISM by this energy flux one can constrain key parameters of the stellar associations in the Cygnus region.

astro-ph↗

arXiv2001

Radioactivities in Population Studies: 26Al and 60Fe from OB Associations

The observation of the interstellar 1.809 MeV decay-line of radioactive 26Al by the imaging gamma-ray telescope COMPTEL have let to the conclusion, that massive stars and their subsequent core-collapse supernovae are the dominant sources of the interstellar 26Al abundance. Massive stars are known to affect the surrounding interstellar medium by their energetic stellar winds and by the emission of ionising radiation. We present a population synthesis model allowing the correlated investigation of the gamma-ray emission characteristics with integrated matter, kinetic energy and extreme ultra-violet radiation emission of associations of massive stars. We study the time evolution of the various observables. In addition, we discuss systematic as well as statistical uncertainties affecting the model. Beside uncertainties in the input stellar physics such as stellar rotation, mass loss rates or internal mixing modifications due to a unknown binary component may lead to significant uncertainties.

astro-ph↗