Thomas Siegert

Early 56Ni decay gamma rays from SN2014J suggest an unusual explosion

Surprise found by γ-ray metal detector Astronomers commonly use type-Ia supernovae as standard distance measurement tools, though the physics of these bright sources are not fully understood. One product of the thermonuclear explosion is 56Ni, which probably lies at the heart of the supernova cloud. Diehl et al. detected the gamma-ray emission from 56Ni in SN2014J much earlier than expected, only about 20 days after the initial explosion. This early exposure suggests both an asymmetric event and the production of 56Ni farther out in the ejecta than predicted. These sources will help astronomers measure distances far beyond where supernovae have been studied. Science, this issue p. 1162 Early exposure of material produced in a supernova suggests an asymmetric explosion from the white dwarf progenitor. Type Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 solar mass of radioactive 56Ni. The 56Ni is commonly believed to be buried deeply in the expanding supernova cloud. In SN2014J, we detected the lines at 158 and 812 kiloelectron volts from 56Ni decay (time ~8.8 days) earlier than the expected several-week time scale, only ~20 days after the explosion and with flux levels corresponding to roughly 10% of the total expected amount of 56Ni. Some mechanism must break the spherical symmetry of the supernova and at the same time create a major amount of 56Ni at the outskirts. A plausible explanation is that a belt of helium from the companion star is accreted by the white dwarf, where this material explodes and then triggers the supernova event.

Correlated optical, X-ray, and γ-ray flaring activity seen with INTEGRAL during the 2015 outburst of V404 Cygni

After 25 years of quiescence, the microquasar V404 Cyg entered a new period of activity in June 2015. This X-ray source is known to undergo extremely bright and variable outbursts seen at all wavelengths. It is therefore an object of prime interest to understand the accretion-ejection connections. These can, however, only be probed through simultaneous observations at several wavelengths. We made use of the INTEGRAL instruments to obtain long, almost uninterrupted observations from 2015 June 20, 15:50 UTC to June 25, 4:05 UTC, from the optical V band up to the soft γ-rays. V404 Cyg was extremely variable in all bands, with the detection of 18 flares with fluxes exceeding 6 Crab (20–40 keV) within three days. The flare recurrence can be as short as ~20 min from peak to peak. A model-independent analysis shows that the >6 Crab flares have a hard spectrum. A simple 10–400 keV spectral analysis of the off-flare and flare periods shows that the variation in intensity is likely to be only due to variations of a cut-off power-law component. The optical flares seem to be at least of two different types: one occurring in simultaneity with the X-ray flares, the other showing a delay greater than 10 min. The former could be associated with X-ray reprocessing by either an accretion disk or the companion star. We suggest that the latter are associated with plasma ejections that have also been seen in radio.

SN2014J gamma rays from the 56Ni decay chain

R. Diehl, et al., “SN2014J gamma rays from the 56Ni decay chain”, Astronomy & Astrophysics, Vol. 574, January 2015. The version of record is available online at: https://www.aanda.org/articles/aa/abs/2015/02/aa24991-14/aa24991-14.html Reproduced with Permission from Astronomy and Astrophysics,

Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni

Microquasars are stellar-mass black holes accreting matter from a companion star and ejecting plasma jets at almost the speed of light. They are analogues of quasars that contain supermassive black holes of 106 to 1010 solar masses. Accretion in microquasars varies on much shorter timescales than in quasars and occasionally produces exceptionally bright X-ray flares. How the flares are produced is unclear, as is the mechanism for launching the relativistic jets and their composition. An emission line near 511 kiloelectronvolts has long been sought in the emission spectrum of microquasars as evidence for the expected electron–positron plasma. Transient high-energy spectral features have been reported in two objects, but their positron interpretation remains contentious. Here we report observations of γ-ray emission from the microquasar V404 Cygni during a recent period of strong flaring activity. The emission spectrum around 511 kiloelectronvolts shows clear signatures of variable positron annihilation, which implies a high rate of positron production. This supports the earlier conjecture that microquasars may be the main sources of the electron–positron plasma responsible for the bright diffuse emission of annihilation γ-rays in the bulge region of our Galaxy. Additionally, microquasars could be the origin of the observed megaelectronvolt continuum excess in the inner Galaxy.

Gamma-ray spectroscopy of positron annihilation in the Milky Way

The annihilation of positrons in the Galaxys interstellar medium produces characteristic gamma-rays with a line at 511 keV. This emission has been observed with the spectrometer SPI on INTEGRAL, confirming a puzzling morphology with bright emission from an extended bulge-like region, and faint disk emission. Most plausible sources of positrons are believed to be distributed throughout the disk of the Galaxy. We aim to constrain characteristic spectral shapes for different spatial components in the disk and bulge with the high-resolution gamma-ray spectrometer SPI, based on a new instrumental background method and detailed multi-component sky model fitting. We confirm the detection of the main extended components of characteristic annihilation gamma-ray signatures at 58

Prospective slice-by-slice motion correction reduces false positive activations in fMRI with task-correlated motion

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Revisiting INTEGRAL/SPI observations of 44Ti from Cassiopeia A

significance in the line. The total Galactic line intensity amounts to

Search for 511 keV emission in satellite galaxies of the Milky Way with INTEGRAL/SPI

(2.7\pm0.3)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}

26Al kinematics: superbubbles following the spiral arms? - Constraints from the statistics of star clusters and HI supershells

for our assumed spatial model. We derive spectra for the bulge and disk, and a central point-like and at the position of Sgr A*, and discuss spectral differences. The bulge shows a 511 keV line intensity of

INTEGRAL IBIS, SPI, and JEM-X observations of LVT151012

(0.96\pm0.07)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}