arXiv subjects

Roland Diehl

Publications and source records attributed to Roland Diehl.

At least 55 records · Page 3Linked to original sources

arXiv2016

White Paper on Nuclear Astrophysics

This white paper informs the nuclear astrophysics community and funding agencies about the scientific directions and priorities of the field and provides input from this community for the 2015 Nuclear Science Long Range Plan. It summarizes the outcome of the nuclear astrophysics town meeting that was held on August 21-23, 2014 in College Station at the campus of Texas A&M University in preparation of the NSAC Nuclear Science Long Range Plan. It also reflects the outcome of an earlier town meeting of the nuclear astrophysics community organized by the Joint Institute for Nuclear Astrophysics (JINA) on October 9- 10, 2012 Detroit, Michigan, with the purpose of developing a vision for nuclear astrophysics in light of the recent NRC decadal surveys in nuclear physics (NP2010) and astronomy (ASTRO2010). The white paper is furthermore informed by the town meeting of the Association of Research at University Nuclear Accelerators (ARUNA) that took place at the University of Notre Dame on June 12-13, 2014. In summary we find that nuclear astrophysics is a modern and vibrant field addressing fundamental science questions at the intersection of nuclear physics and astrophysics. These questions relate to the origin of the elements, the nuclear engines that drive life and death of stars, and the properties of dense matter. A broad range of nuclear accelerator facilities, astronomical observatories, theory efforts, and computational capabilities are needed. With the developments outlined in this white paper, answers to long standing key questions are well within reach in the coming decade.

astro-ph.SR↗

arXiv2016

New insights from cosmic gamma rays

The measurement of gamma rays from cosmic sources at MeV energies is one of the key tools for nuclear astrophysics, in its study of nuclear reactions and their impacts on objects and phenomena throughout the universe. Gamma rays trace nuclear processes most directly, as they originate from nuclear transitions following radioactive decays or high-energy collisions with excitation of nuclei. Additionally, the unique gamma-ray signature from the annihilation of positrons falls into this astronomical window and is discussed here: Cosmic positrons are often produced from beta-decays, thus also of nuclear physics origins. The nuclear reactions leading to radioactive isotopes occur inside stars and stellar explosions, which therefore constitute the main objects of such studies. In recent years, both thermonuclear and core-collapse supernova radioactivities have been measured, and complement conventional supernova observations with measurements of their prime energy sources. The diffuse radioactive afterglow of massive-star nucleosynthesis in gamma rays is now being analysed towards how massive stars feed back their energy and ejecta into interstellar gas. Large interstellar cavities and superbubbles have been recognised to be the dominating structures where new massive-star ejecta are injected, from 26Al gamma-ray spectroscopy. Finally, the puzzling bulge-dominated intensity distribution of positron annihilation gamma rays is measured in greater detail, but still not understood; a recent microquasar flare provided evidence that such objects may be prime sources for positrons in interstellar space, rather than distributed nucleosynthesis. We also briefly discuss the status and prospects for astronomy with telescopes for the nuclear-radiation energy window.

astro-ph.HE↗

arXiv2015

Gas expulsion in massive star clusters? Constraints from observations of young and gas-free objects

Gas expulsion is a central concept in some of the models for multiple populations and the light-element anticorrelations in globular clusters. If the star formation efficiency was around 30 per cent and the gas expulsion happened on the crossing timescale, this process could expel preferentially stars born with the chemical composition of the proto-cluster gas, while stars with special composition born in the centre would remain bound. Recently, a sample of extragalactic, gas-free, young massive clusters has been identified that has the potential to test the conditions for gas expulsion. We compute a large number of thin shell models, and calculate if the Rayleigh-Taylor instability is able to disrupt the shell before it reaches the escape speed. We show that the success of gas expulsion depends on the compactness index of a star cluster C5, proportionate to stellar mass over half-mass radius. For given C5, a certain critical, local star formation efficiency is required to remove the rest of the gas. Common stellar feedback processes may not lead to gas expulsion with significant loss of stars above C5 = 1. Considering pulsar winds and hypernovae, the limit increases to C5 = 30. If successful, gas expulsion generally takes place on the crossing timescale. Some observed young massive clusters have 1 < C5 < 10 and are gas-free at 10 Myr. This suggests that gas expulsion does not affect their stellar mass significantly, unless powerful pulsar winds and hypernovae are common in such objects. By comparison to observations, we show that C5 is a better predictor for the expression of multiple populations than stellar mass. The best separation between star clusters with and without multiple populations is achieved by a stellar winds-based gas expulsion model, where gas expulsion would occur exclusively in star clusters without multiple populations.

astro-ph.GA↗

arXiv2015

Gamma-ray spectroscopy of Positron Annihilation in the Milky Way

The annihilation of positrons in the Galaxy's 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$σ$ significance in the line. The total Galactic line intensity amounts to $(2.7\pm0.3)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}$ 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 $(0.96\pm0.07)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}$ and an ortho-positronium continuum equivalent to a positronium fraction of ($1.08\pm0.03$). The 2D-Gaussian representing the disk has an extent of $60^{+10}_{-5}$ deg in longitude and a latitudinal extent of $10.5^{+2.5}_{-1.5}$ deg; the line intensity is $(1.7\pm0.4)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}$ with a marginal detection of ortho-positronium and an overall diffuse Galactic continuum of $(5.85\pm1.05)\times10^{-5}~\mathrm{ph~cm^{-2}~s^{-1}~keV^{-1}}$ at 511 keV. The disk shows no flux asymmetry between positive and negative longitudes, although spectral details differ. The flux ratio between bulge and disk is ($0.6\pm0.1$). The central source has an intensity of $(0.8\pm0.2)\times10^{-4}~\mathrm{ph~cm^{-2}~s^{-1}}$.

astro-ph.HE↗

arXiv2015

Stellar feedback efficiencies: supernovae versus stellar winds

Stellar winds and supernova (SN) explosions of massive stars ("stellar feedback") create bubbles in the interstellar medium (ISM) and insert newly produced heavy elements and kinetic energy into their surroundings, possibly driving turbulence. Most of this energy is thermalized and immediately removed from the ISM by radiative cooling. The rest is available for driving ISM dynamics. In this work we estimate the amount of feedback energy retained as kinetic energy when the bubble walls have decelerated to the sound speed of the ambient medium. We show that the feedback of the most massive star outweighs the feedback from less massive stars. For a giant molecular cloud (GMC) mass of 1e5 solar masses (as e.g. found in the Orion GMCs) and a star formation efficiency of 8% the initial mass function predicts a most massive star of approximately 60 solar masses. For this stellar evolution model we test the dependence of the retained kinetic energy of the cold GMC gas on the inclusion of stellar winds. In our model winds insert 2.34 times the energy of a SN and create stellar wind bubbles serving as pressure reservoirs. We find that during the pressure driven phases of the bubble evolution radiative losses peak near the contact discontinuity (CD), and thus, the retained energy depends critically on the scales of the mixing processes across the CD. Taking into account the winds of massive stars increases the amount of kinetic energy deposited in the cold ISM from 0.1% to a few percent of the feedback energy.

astro-ph.GA↗

arXiv2015

Squeezed between shells? On the origin of the Lupus I molecular cloud. APEX/LABOCA, Herschel, and Planck observations

The Lupus I cloud is found between the Upper-Scorpius (USco) and the Upper-Centaurus-Lupus (UCL) sub-groups of the Sco-Cen OB-association, where the expanding USco H I shell appears to interact with a bubble currently driven by the winds of the remaining B-stars of UCL.We want to study how collisions of large-scale interstellar gas flows form and influence new dense clouds in the ISM.We performed LABOCA continuum sub-mm observations of Lupus I that provide for the first time a direct view of the densest, coldest cloud clumps and cores at high angular resolution.We complemented those by Herschel and Planck data from which we constructed column density and temperature maps.We calculated PDFs to characterize the density structure of the cloud.The northern part of Lupus I is found to have on average lower densities and higher temperatures as well as no active star formation.The center-south part harbors dozens of pre-stellar cores where density and temperature reach their maximum and minimum, respectively.Our analysis of the column density PDFs from the Herschel data show double peak profiles for all parts of the cloud which we attribute to an external compression.In those parts with active star formation, the PDF shows a power-law tail at high densities.The PDFs we calculated from our LABOCA data trace the denser parts of the cloud showing one peak and a power-law tail.With LABOCA we find 15 cores with masses between 0.07 and 1.71 Msun and a total mass of ~8 Msun.The total gas and dust mass of the cloud is ~164 Msun and hence 5% of the mass is in cores.From the Herschel and Planck data we find a total mass of ~174 Msun and ~171 Msun, respectively.The position, orientation and elongated shape of Lupus I, the double peak PDFs and the population of pre-stellar and protostellar cores could be explained by the large-scale compression from the advancing USco H I shell and the UCL wind bubble.

astro-ph.SR↗

arXiv2015

A very luminous magnetar-powered supernova associated with an ultra-long gamma-ray burst

A new class of ultra-long duration (>10,000 s) gamma-ray bursts has recently been suggested. They may originate in the explosion of stars with much larger radii than normal long gamma-ray bursts or in the tidal disruptions of a star. No clear supernova had yet been associated with an ultra-long gamma-ray burst. Here we report that a supernova (2011kl) was associated with the ultra-long duration burst 111209A, at z=0.677. This supernova is more than 3 times more luminous than type Ic supernovae associated with long gamma-ray bursts, and its spectrum is distinctly different. The continuum slope resembles those of super-luminous supernovae, but extends farther down into the rest-frame ultra-violet implying a low metal content. The light curve evolves much more rapidly than super-luminous supernovae. The combination of high luminosity and low metal-line opacity cannot be reconciled with typical type Ic supernovae, but can be reproduced by a model where extra energy is injected by a strongly magnetized neutron star (a magnetar), which has also been proposed as the explanation for super-luminous supernovae.

astro-ph.HE↗

arXiv2015

Gamma rays from a supernova of type Ia: SN2014J

SN2014J is the closest supernova of type Ia that occured in the last 40 years. This provides an opportunity for unprecedented observational detail and coverage in many astronomical bands, which will help to better understand the still unknown astrophysics of these supernovae. For the first time, such an event occurs sufficiently nearby so that also gamma rays are able to contribute to such investigations. This is important, as the primary source of the supernova light is the radioactive energy from about 0.5 M$_\odot$ of $^{56}$Ni produced in the explosion, and the gamma rays associated with this decay make the supernova shine for months. The INTEGRAL gamma-ray observatory of ESA has followed the supernova emission for almost 5 months. The characteristic gamma ray lines from the $^{56}$Ni decay chain through $^{56}$Co to $^{56}$Fe have been measured. We discuss these observations, and the implications of the measured gamma-ray line characteristics as they evolve.

astro-ph.HE↗

arXiv2015

Revisiting INTEGRAL/SPI observations of 44Ti from Cassiopeia A

The 340-year old supernova remnant Cassiopeia A at 3.4 kpc distance is the best-studied young core-collapse supernova remnant. Nucleosynthesis yields in radioactive isotopes have been studied with different methods, in particular for production and ejection of $^{44}$Ti and $^{56}$Ni which originate from the innermost regions of the supernova. $^{44}$Ti was first discovered in this remnant, but is not seen consistently in other core-collapse sources. We analyse the observations accumulated with the SPI spectrometer on INTEGRAL, together with an improved instrumental background method, to achieve high spectroscopic resolution which enables interpretation towards a velocity constraint on $^{44}$Ti ejecta from the 1.157 MeV $γ$-ray line of the $^{44}$Sc decay. We observe both the hard X-ray line at 78 keV and the $γ$-ray line at 1157 keV from the $^{44}$Ti decay chain, at a combined significance of 3.8 $σ$. Measured fluxes are $(2.1\pm0.4)~10^{-5}~\mathrm{ph~cm^{-2}~s^{-1}}$ and $(3.5\pm1.2)~10^{-5}~\mathrm{ph~cm^{-2}~s^{-1}}$, which corresponds to $(1.5\pm0.4)~10^{-4}$ and $(2.4\pm0.9)~10^{-4}~\mathrm{M}_{\odot}$ of $^{44}$Ti, respectively. The measured Doppler broadening of the lines implies expansion velocities of $4300$ and $2200~\mathrm{km~s^{-1}}$, respectively. Combining our results with previous studies, we determine a more precise estimate of ejected $^{44}$Ti of $(1.37\pm0.19)~10^{-4}~\mathrm{M}_{\odot}$. The measurements of both lines are consistent with previous studies. The flux in the line originating from excited $^{44}$Ca is significantly higher than the flux determined in the lines from $^{44}$Sc. Cosmic ray acceleration within the supernova remnant may be responsible for an additional contribution to this line from nuclear de-excitation following energetic particle collisions in the remnant and swept-up material.

astro-ph.HE↗

arXiv2015

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

High energy resolution spectroscopy of the 1.8 MeV radioactive decay line of 26Al with the SPI instrument on board the INTEGRAL satellite has recently revealed that diffuse 26Al has large velocities in comparison to other components of the interstellar medium in the Milky Way. 26Al shows Galactic rotation in the same sense as the stars and other gas tracers, but reaches excess velocities up to 300 km/s. We investigate if this result can be understood in the context of superbubbles, taking into account the statistics of young star clusters and H I supershells, as well as the association of young star clusters with spiral arms. We derive energy output and 26Al mass of star clusters as a function of the cluster mass via population synthesis from stellar evolutionary tracks of massive stars. [...] We link this to the size distribution of HI supershells and assess the properties of likely 26Al-carrying superbubbles. 26Al is produced by star clusters of all masses above about 200 solar masses, roughly equally contributed over a logarithmic star cluster mass scale, and strongly linked to the injection of feedback energy. The observed superbubble size distribution cannot be related to the star cluster mass function in a straight forward manner. In order to avoid that the added volume of all superbubbles exceeds the volume of the Milky Way, individual superbubbles have to merge frequently. If any two superbubbles merge, or if 26Al is injected off-centre in a bigger HI supershell we expect the hot 26Al-carrying gas to obtain velocities of the order of the typical sound speed in superbubbles, about 300 km/s before decay. [...]

astro-ph.GA↗

arXiv2015

Gamma-ray lines from SN2014J

On 21 January 2014, SN2014J was discovered in M82 and found to be the closest type Ia supernova (SN Ia) in the last four decades. INTEGRAL observed SN2014J from the end of January until late June for a total exposure time of about 7 Ms. SNe Ia light curves are understood to be powered by the radioactive decay of iron peak elements of which $^{56}$Ni is dominantly synthesized during the thermonuclear disruption of a CO white dwarf (WD). The measurement of $γ$-ray lines from the decay chain $^{56}$Ni$\rightarrow$$^{56}$Co$\rightarrow$$^{56}$Fe provides unique information about the explosion in supernovae. Canonical models assume $^{56}$Ni buried deeply in the supernova cloud, absorbing most of the early $γ$-rays, and only the consecutive decay of $^{56}$Co should become directly observable through the overlaying material several weeks after the explosion when the supernova envelope dilutes as it expands. Surprisingly, with the spectrometer on INTEGRAL, SPI, we detected $^{56}$Ni $γ$-ray lines at 158 and 812 keV at early times with flux levels corresponding to roughly 10% of the total expected amount of $^{56}$Ni, and at relatively small velocities. This implies some mechanism to create a major amout of $^{56}$Ni at the outskirts, and at the same time to break the spherical symmetry of the supernova. One plausible explanation would be a belt accreted from a He companion star, exploding, and triggering the explosion of the white dwarf. The full set of observations of SN2014J show $^{56}$Co $γ$-ray lines at 847 and 1238 keV, and we determine for the first time a SN Ia $γ$-ray light curve. The irregular appearance of these $γ$-ray lines allows deeper insights about the explosion morphology from its temporal evolution and provides additional evidence for an asymmetric explosion, from our high-resolution spectroscopy and comparisons with recent models.

astro-ph.HE↗

arXiv2014

SN2014J gamma-rays from the 56Ni decay chain

The measurement of gamma-ray lines from the decay chain of 56Ni provides unique information about the explosion in supernovae. The 56Ni freshly-produced in the supernova powers the optical light curve, as it emits gamma-rays upon its radioactive decay to 56Co and then 56Fe. Gamma-ray lines from 56Co decay are expected to become directly visible through the overlying white dwarf material several weeks after the explosion, as they progressively penetrate the overlying material of the supernova envelope, diluted as it expands. The lines are expected to be Doppler-shifted or broadened from the kinematics of the 56Ni ejecta. With the SPI spectrometer on INTEGRAL and using an improved instrumental background method, we detect the two main lines from 56Co decay at 847 and 1238 keV from SN2014J at 3.3 Mpc, significantly Doppler-broadened, and at intensities (3.65+/-1.21) 10^-4 and (2.27+/-0.69) 10^-4 ph cm^-2s^-1, respectively, at brightness maximum. We measure their rise towards a maximum after about 60-100 days and decline thereafter. The intensity ratio of the two lines is found consistent with expectations from 56Co decay (0.62+/-0.28 at brightness maximum, expected is 0.68). We find that the broad lines seen in the late, gamma-ray transparent phase are not representative for the early gamma-ray emission, and rather notice the emission spectrum to be complex and irregular until the supernova is fully transparent to gamma-rays, with progressive uncovering of the bulk of 56Ni. We infer that the explosion morphology is not spherically symmetric, both in the distribution of 56Ni and of the unburnt material which occults the 56Co emission. Comparing light curves from different plausible models, the resulting 56Ni mass is determined as 0.49+/-0.09 M_sol.

astro-ph.HE↗

arXiv2014

Synchrotron Cooling in Energetic Gamma-Ray Bursts Observed by the Fermi Gamma-Ray Burst Monitor

We study the time-resolved spectra of eight GRBs observed by Fermi GBM in its first five years of mission, with 1 keV - 1 MeV fluence $f>1.0\times10^{-4}$ erg cm$^{-2}$ and signal-to-noise level $\text{S/N}\geq10.0$ above 900 keV. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. We perform time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We fit the Band function to all spectra and obtain the distributions for the low-energy power-law index $α$, the high-energy power-law index $β$, the peak energy in the observed $νF_ν$ spectrum $E_\text{p}$, and the difference between the low- and high-energy power-law indices $Δs=α-β$. Using the distributions of $Δs$ and $β$, the electron population index $p$ is found to be consistent with the "moderately fast" scenario which fast- and slow-cooling scenarios cannot be distinguished. We also apply a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test for consistency with a synchrotron origin for the prompt emission and obtain the distributions for the two break energies $E_\text{b,1}$ and $E_\text{b,2}$, the middle segment power-law index $β$, and the Planck function temperature $kT$. A synchrotron model is found consistent with the majority of time-resolved spectra for these eight energetic Fermi GBM bursts with good high-energy photon statistics, as long as both the cooling and injection break are included and the leftmost spectral slope is lifted either by inclusion of a thermal component or when an evolving magnetic field is accounted for.

astro-ph.HE↗

arXiv2014

Dynamics and Energy Loss in Superbubbles

Interstellar bubbles appear to be smaller in observations than expected from calculations. Instabilities at the shell boundaries create three-dimensional ef- fects, and are probably responsible for part of this discrepancy. We investigate instabilities and dynamics in superbubbles by 3D hydrodynamics simulations with time-resolved energy input from massive stars, including the supernova explosions. We find that the superbubble shells are accelerated by supernova explosions, coincident with substantial brightening in soft X-ray emission. In between the explosions, the superbubbles lose energy efficiently, approaching the momentum-conserving snowplow limit. This and enhanced radiative losses due to instabilities reduce the expansion compared to the corresponding radiative bubbles in pressure-driven snowplow models with constant energy input. We note generally good agreement with observations of superbubbles and some open issues. In particular, there are hints that the shell velocities in the X-ray-bright phases is underpredicted.

astro-ph.GA↗

arXiv2014

Early 56Ni decay γ-rays from SN2014J suggest an unusual explosion

Type-Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 M_solar of radioactive 56Ni. The 56Ni is commonly believed to be buried deeply in the expanding supernova cloud. Surprisingly, in SN2014J we detected the lines at 158 and 812 keV from 56Ni decay (τ~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.

astro-ph.HE↗

arXiv2014

Feedback by massive stars and the emergence of superbubbles II. X-ray properties

In a previous paper we investigated the energy transfer of massive stars to the interstellar medium as a function of time and the geometrical configuration of three massive stars via 3D-mesh-refining hydrodynamics simulations, following the complete evolution of the massive stars and their supernovae except non-thermal processes . We analysed our ISM simulation results with the help of spectra for plasma temperatures between 0.1 and 10 keV and computed the spectral evolution and the spatio-temporal distribution of the hot gas. Results. Despite significant input of high temperature gas from supernovae and fast stellar winds, the resulting thermal X-ray spectra are generally very soft, with most of the emission well below 1 keV. We show that this is due to mixing triggered by resolved hydrodynamic instabilities. Supernovae enhance the X-ray luminosity of a superbubble by 1-2 orders of magnitude for a time span of about 0.1 Myr; longer if a supernova occurs in a larger superbubble and shorter in higher energy bands. Peak superbubble luminosities of the order of 10^{36} erg/s are reproduced well. The strong decay of the X-ray luminosity is due to bubble expansion, hydrodynamic instabilities related to the acceleration of the superbubble's shell thanks to the sudden energy input, and subsequent mixing. We also find global oscillations of our simulated superbubbles, which produce spatial variations of the X-ray spectrum, similar to what we see in the Orion-Eridanus cavity. We calculated the fraction of energy emitted in X-rays and find that with a value of a few times 10^{-4}, it is about a factor of ten below the measurements for nearby galaxies.

astro-ph.GA↗

arXiv2014

The Fermi GBM Gamma-Ray Burst Spectral Catalog: Four Years Of Data

In this catalog we present the updated set of spectral analyses of GRBs detected by the Fermi Gamma-Ray Burst Monitor (GBM) during its first four years of operation. It contains two types of spectra, time-integrated spectral fits and spectral fits at the brightest time bin, from 943 triggered GRBs. Four different spectral models were fitted to the data, resulting in a compendium of more than 7500 spectra. The analysis was performed similarly, but not identically to Goldstein et al. 2012. All 487 GRBs from the first two years have been re-fitted using the same methodology as that of the 456 GRBs in years three and four. We describe, in detail, our procedure and criteria for the analysis, and present the results in the form of parameter distributions both for the observer-frame and rest-frame quantities. The data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC).

astro-ph.HE↗

arXiv2013

Kinematics of massive star ejecta in the Milky Way as traced by 26Al

Massive stars form in groups and their winds and supernova explosions create superbubbles up to kpc in size. Their ejecta are important for the dynamics of the interstellar medium and chemical evolution models. However, ejecta kinematics and the characteristic scales in space and time are rather unexplored beyond ~10 ka. Through measurement of radioactive 26Al with its decay time constant of ~10^6 years, we aim to trace the kinematics of massive-star and supernova ejecta over million-year time scales. Our goal is to identify the mixing time scale and the spatio-kinematics of such ejecta from the pc to kpc scale. We use the SPI spectrometer on INTEGRAL and its observations along the Galactic ridge to trace the line shape of the 1808.63 keV gamma-ray line from 26Al decay. We determine line centroids and compare these to Doppler shift expectations from large-scale systematic rotation around the Galaxy's center, as observed in other Galactic objects. We measure the radial velocities of gas traced by 26Al, averaged over the line of sight, as a function of Galactic longitude. We find substantially higher velocities than expected from Galactic rotation, the average bulk velocity being ~200 km s^-1 larger than the Galactic-rotation prediction. The observed radial velocity spread implies a Doppler-broadening of the gamma-ray line that is consistent with our measurements of the overall line width. We can reproduce the observed characteristics with 26Al sources located along the inner spiral arms, when we add a global blow-out into the forward direction away from arms, such as expected from massive stars offset towards the spiral-arm leading edge. The superbubbles-halo connection implies angular-momentum transfer in the disk-halo system and also radial gas flows.

astro-ph.HE↗