Cornelia B. Wunderer

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.

Radioactive 26Al and massive stars in the Galaxy

Gamma-rays from radioactive 26Al (half-life ∼7.2 × 105u2009years) provide a ‘snapshot’ view of continuing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such γ-rays, and emission has been found concentrated along its plane. This led to the conclusion that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show evidence for locally produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent γ-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65u2009keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (± 0.8) solar masses of 26Al. We use this to determine that the frequency of core collapse (that is, type Ib/c and type II) supernovae is 1.9u2009(± 1.1) events per century.

26Al in the inner Galaxy : Large-scale spectral characteristics derived with SPI/INTEGRAL

Aims. We performed a spectroscopic study of the 1809 keV gamma-ray line from 26 Al decay in the Galaxy using the SPI imaging spectrometer with its high-resolution Ge detector camera on the INTEGRAL observatory. Methods. 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 26 Al sky. Instrumental background is estimated from independent tracers of cosmic-ray activation. The shape of the 26 Al signal is compared to the instrumental response to extract the width of the celestial line. Results. We detect the 26 Al line at ≃16σ significance. The line is broadened only slightly, if at all; we constrain the width to be below 2.8 keV (FWHM, 2cr). The average Doppler velocities of 26 Al at the time of its decay in the interstellar medium (τ ∼ 1.04 My) therefore are probably around 100 km s -1 , in agreement with expectations from Galactic rotation and interstellar turbulence. The flux (3.3 (±0.4) x 10 -4 ph cm -2 s -1 rad -1 ) and spatial distribution of the emission are found consistent with previous observations. The derived amount of 26 Al in the Galaxy is 2.8 (±0.8) M ⊙ .

Search for Millisecond Flares in INTEGRAL and RHESSI GRBs — towards probing Quantum Gravity with GRBs

Since the discovery of the cosmological origin of GRBs there has been growing interest in using these transient events to probe the Quantum Gravity energy scale in the range 1016–1019 GeV, up to the Planck mass scale. This energy scale can manifest itself through a modification in the electromagnetic radiation dispersion relation, specifically, an energy‐dependence of the velocity of light. To impose stringent limits on a possible modification, a flare within a GRB must be both short and significant over a wide energy band to provide a sufficient baseline for determining dt/dE, the difference in the arrival times of photons of different energies. To approach the Planck mass scale, we must measure arrival time differences on the order of 0.5 ms from soft to hard (∼10 MeV) photons within a flare for a GRB at a redshift of a few. We have searched INTEGRAL‐ and RHESSI‐observed GRBs for suitable flares, requiring a 5σ trigger on a 2 ms, 10 ms, or 100 ms time scale using only photons above 1 MeV. We present met...