Publications (67)
Stellar flares cannot explain the Galactic 511 keV emission
Saurabh Mittal, Thomas Siegert, Francesca Calore +12
The authors assess whether stellar flares can produce enough positrons to explain the Milky Way’s 511 keV annihilation line and conclude that flares fall short by several orders of…
MHz to TeV expectations from scotogenic WIMP dark matter
Laura Eisenberger, Thomas Siegert, Karl Mannheim +1
The indirect search for dark matter is typically restricted to individual photon bands and instruments. In the context of multiwavelength observations, finding a weak signal in lar…
Al gamma rays from the Galaxy with INTEGRAL/SPI
Moritz M. M. Pleintinger, Roland Diehl, Thomas Siegert +2
The presence of radioactive Al at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way. Diffuse emission from its decay can be measured with gamma-ray telescopes in spa…
The Al Gamma-ray Line from Massive-Star Regions
Thomas Siegert, Roland Diehl
The measurement of gamma rays from the diffuse afterglow of radioactivity originating in massive-star nucleosynthesis is considered a laboratory for testing models, when specific s…
Positron Annihilation in the Galaxy
Carolyn A. Kierans, John F. Beacom, Steve Boggs +27
The 511 keV line from positron annihilation in the Galaxy was the first -ray line detected to originate from outside our solar system. Going into the fifth decade since the dis…
Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni
Thomas Siegert, Roland Diehl, Jochen Greiner +7
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 s…
Early 56Ni decay γ-rays from SN2014J suggest an unusual explosion
Roland Diehl, Thomas Siegert, Wolfgang Hillebrandt +7
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 56…
Enhancing Compton telescope imaging with maximum a posteriori estimation: a modified Richardson-Lucy algorithm for the Compton Spectrometer and Imager
Hiroki Yoneda, Thomas Siegert, Israel Martinez-Castellanos +23
We present a modified Richardson-Lucy (RL) algorithm tailored for image reconstruction in MeV gamma-ray observations, focusing on its application to the upcoming Compton Spectromet…
Background modelling for -ray spectroscopy with INTEGRAL/SPI
Thomas Siegert, Roland Diehl, Christoph Weinberger +3
The coded-mask spectrometer-telescope SPI on board the INTEGRAL observatory records photons in the energy range between 20 and 8000 keV. A robust and versatile method to model the…
Galactic Population Synthesis of Radioactive Nucleosynthesis Ejecta
Thomas Siegert, Moritz M. M. Pleintinger, Roland Diehl +3
Diffuse gamma-ray line emission traces freshly produced radioisotopes in the interstellar gas, providing a unique perspective on the entire Galactic cycle of matter from nucleosynt…
Nucleosynthesis constraints through -ray line measurements from classical novae
Thomas Siegert, Sohan Ghosh, Kalp Mathur +2
Classical novae are among the most frequent transient events in the Milky Way, and key agents of ongoing nucleosynthesis. Despite their large numbers, they have never been observed…
Revisiting INTEGRAL/SPI observations of 44Ti from Cassiopeia A
Thomas Siegert, Roland Diehl, Martin G. H. Krause +1
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 b…
Relaxation of Energy Constraints for Positrons Generating the Galactic Annihilation Signal
Souradeep Das, Mark R. Krumholz, Roland M. Crocker +2
Even 50 years after the discovery of a positron annihilation line from the inner Galaxy, no class of astrophysical sources has emerged as a definitive explanation for both the emis…
Detection of the 511 keV Galactic positron annihilation line with COSI
Carolyn A. Kierans, Steven E. Boggs, Andreas Zoglauer +10
The signature of positron annihilation, namely the 511 keV -ray line, was first detected coming from the direction of the Galactic center in the 1970's, but the source of Galac…
Search for 511 keV Emission in Satellite Galaxies of the Milky Way with INTEGRAL/SPI
Thomas Siegert, Roland Diehl, Aaron C. Vincent +3
The positron annihilation gamma-ray signal in the Milky Way (MW) shows a puzzling morphology: a very bright bulge and a very low surface-brightness disk. A coherent explanation of…
-Ray Lines -- Signatures of Nucleosynthesis, Cosmic Rays, Positron Annihilation, and Fundamental Physics
Thomas Siegert, Francesca Calore, Pierre Jean +6
The nuclear -ray lines in the MeV range of the electromagnetic spectrum hold a vast variety of astrophysical, particle-physical, and fundamental physical information that is ot…
A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1
Tristan Bouchet, Thomas Siegert, Victoria Grinberg +4
Recent X-ray and soft gamma-ray spectro-polarimetric observations of black hole X-ray binaries, such as Cygnus X-1, reveal discrepancies that challenge current models of accretion…
Evolution of radioactive elements in the LMC: predictions for future gamma-ray surveys
Arianna Vasini, Francesca Matteucci, Emanuele Spitoni +1
Short-lived radionuclides, such as 26Al and 60Fe, are tracers of star formation. Therefore, their abundances can unravel the recent star formation history of the host galaxy. In vi…
Gamma-Ray Light Curves and Spectra of Classical Novae
Shing-Chi Leung, Thomas Siegert
The nucleosynthesis in classical novae, in particular that of radioactive isotopes, is directly measurable by its -ray signature. Despite decades of observations, MeV -rays…
COSI: From Calibrations and Observations to All-sky Images
Andreas Zoglauer, Thomas Siegert, Alexander Lowell +13
The soft MeV gamma-ray sky, from a few hundred keV up to several MeV, is one of the least explored regions of the electromagnetic spectrum. The most promising technology to access…
Using Al to detect ongoing self-enrichment in young massive star clusters
Katarzyna Nowak, Martin G. H. Krause, Thomas Siegert +5
Self-enrichment is one of the leading explanations for chemical anomalies in globular clusters. In this scenario, various candidate polluter stars have been proposed to eject gas w…
Diffuse Galactic emission spectrum between 0.5 and 8.0 MeV
Thomas Siegert, Joanna Berteaud, Francesca Calore +2
The last measurement of the diffuse emission spectrum of the Milky Way in the megaelectronvolt (MeV) photon energy range was performed by CGRO/COMPTEL more than 20 years ago. We re…
Positron Annihilation in the Milky Way and beyond
Thomas Siegert
The electron-positron annihilation gamma-ray signal at 511 keV in the Milky Way is investigated towards a possible dark matter interpretation. If all bulge positrons were created b…
The Positron Puzzle
Thomas Siegert
The Positron Puzzle is a half-century old conundrum about the origin of the Galactic -ray emission line at photon energies of 511 keV, and the shape of its morphology, showing…
Cosmological - Pair-Production Background
Mika A. Gelowicz, Thomas Siegert, Saurabh Mittal +10
The paper calculates how photons from the cosmic photon background interact with each other to produce electron‑positron pairs across cosmic time, and evaluates the resulting secon…
Benchmarking simulations of the Compton Spectrometer and Imager with calibrations
Clio C. Sleator, Andreas Zoglauer, Alexander W. Lowell +9
The Compton Spectrometer and Imager (COSI) is a balloon-borne gamma-ray (0.2-5 MeV) telescope designed to study astrophysical sources. COSI employs a compact Compton telescope desi…
Line profile of nuclear de-excitation gamma-ray emission from very hot plasma
Hiroki Yoneda, Felix Aharonian, Paolo Coppi +2
De-excitation gamma-ray lines, produced by nuclei colliding with protons, provide information about astrophysical environments where particles have kinetic energies of MeV…
Search for Axion-Like Particles from Nearby Pre-Supernova Stars
Saurabh Mittal, Thomas Siegert, Francesca Calore +7
Axion-like particles (ALPs) are hypothetical pseudoscalar bosons that arise in many extensions of the Standard Model and are well-motivated dark matter candidates. Nearby massive s…
INTEGRAL reloaded: spacecraft, instruments and ground system
Erik Kuulkers, Carlo Ferrigno, Peter Kretschmar +85
ESA's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) was launched on 17 Oct 2002 at 06:41 CEST. Since then, it has been providing long, uninterrupted observations (up t…
Gamma-ray spectroscopy of galactic nucleosynthesis
Roland Diehl, Jochen Greiner, Martin Krause +2
Diffuse gamma-ray emission from the decay of radioactive Al is a messenger from the nucleosynthesis activity in our current-day galaxy. Because this material is attributed t…
The Compton Spectrometer and Imager
John A. Tomsick, Steven E. Boggs, Andreas Zoglauer +72
The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX) satellite mission in development with a planned launch in 2027. COSI is a wide-field gamma-ray telescope…
Imaging the 511 keV positron annihilation sky with COSI
Thomas Siegert, Steven E. Boggs, John A. Tomsick +10
The balloon-borne Compton Spectrometer and Imager (COSI) had a successful 46-day flight in 2016. The instrument is sensitive to photons in the energy range - MeV. Compton t…
Vertical position of the Sun with -rays
Thomas Siegert
We illustrate a method for estimating the vertical position of the Sun above the Galactic plane by -ray observations. Photons of -ray wavelengths are particularly well suit…
Gamma-Ray Observations of Nova Sgr 2015 No. 2 with INTEGRAL
Thomas Siegert, Alain Coc, Laura Delgado +11
INTEGRAL observed the nova V5668 Sgr around the time of its optical maximum on March 21, 2015. Studies at UV wavelengths showed spectral lines of freshly produced Be-7. This could…
Exploration of Aspherical Ejecta Properties in Type Ia Supernova: Progenitor Dependence and Applications to Progenitor Classification
Shing-Chi Leung, Roland Diehl, Ken'ichi Nomoto +1
Several explosions of thermonuclear supernovae (SNe Ia) have been found to exhibit deviations from spherical symmetry upon closer inspection. Examples are the gamma-ray lines from…
26Al kinematics: superbubbles following the spiral arms? Constraints from the statistics of star clusters and HI supershells
Martin G. H. Krause, Roland Diehl, Yiannis Bagetakos +6
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 ha…
Probing the Galactic Diffuse Continuum Emission with COSI
Christopher Karwin, Thomas Siegert, Jacqueline Beechert +9
In 2016 the Compton Spectrometer and Imager (COSI) had a successful 46-day flight onboard NASA's Super Pressure Balloon platform. In this work we report measurements of the Galacti…
The Compton Spectrometer and Imager
John A. Tomsick, Andreas Zoglauer, Clio Sleator +21
In this Astro2020 APC White Paper, we describe a Small Explorer (SMEX) mission concept called the Compton Spectrometer and Imager. COSI is a Compton telescope that covers the bandp…
Steady-state nucleosynthesis throughout the Galaxy
Roland Diehl, Martin G. H. Krause, Karsten Kretschmer +6
Measurement and astrophysical interpretation of characteristic gamma-ray lines from nucleosynthesis was one of the prominent science goals of the INTEGRAL mission and in particular…
Calibrations of the Compton Spectrometer and Imager
Jacqueline Beechert, Hadar Lazar, Steven E. Boggs +12
The Compton Spectrometer and Imager (COSI) is a balloon-borne soft -ray telescope (0.2-5 MeV) designed to study astrophysical sources. COSI employs a compact Compton telescope…
Sub-GeV Dark Matter Annihilation: Limits from Milky Way observations with INTEGRAL
Thomas Siegert, Francesca Calore, Pasquale Dario Serpico
From 16 years of INTEGRAL/SPI -ray observations, we derive bounds on annihilating light dark matter particles in the halo of the Milky Way up to masses of about 300 MeV. We tes…
Improving INTEGRAL/SPI data analysis of GRBs
Björn Biltzinger, Jochen Greiner, J. Michael Burgess +1
INTEGRAL/SPI is a coded mask instrument observing since 2002 in the keV to MeV energy range, which covers the peak of the spectrum of most Gamma-Ray Bursts (GRBs). Since it…
The Compton Spectrometer and Imager Project for MeV Astronomy
John A. Tomsick, Steven E. Boggs, Andreas Zoglauer +33
The Compton Spectrometer and Imager (COSI) is a 0.2-5 MeV Compton telescope capable of imaging, spectroscopy, and polarimetry of astrophysical sources. Such capabilities are made p…
ejecta in young supernova remnants
Christoph Weinberger, Roland Diehl, Moritz M. M. Pleintinger +2
Context: Tracing unstable isotopes produced in supernova nucleosynthesis provides a direct diagnostic of supernova explosion physics. Theoretical models predict an extensive variet…
Gamma-ray line emission from the Local Bubble
Thomas Siegert, Michael M. Schulreich, Niklas Bauer +3
Deep-sea archives that include intermediate-lived radioactive particles suggest the occurrence of several recent supernovae inside the present-day volume of the…
Reticulum II: Particle Dark Matter and Primordial Black Holes Limits
Thomas Siegert, Celine Boehm, Francesca Calore +4
Reticulum II (Ret II) is a satellite galaxy of the Milky Way and presents a prime target to investigate the nature of dark matter (DM) because of its high mass-to-light ratio. We e…
INTEGRAL/SPI -ray line spectroscopy
Roland Diehl, Thomas Siegert, Jochen Greiner +7
INTEGRAL/SPI is a space-based coded mask telescope featuring a 19-element Germanium detector array for high-resolution gamma-ray spectroscopy, encapsulated in a scintillation detec…
Atmospheric Response for MeV Gamma Rays Observed with Balloon-Borne Detectors
Chris Karwin, Carolyn Kierans, Albert Shih +9
The atmospheric response for MeV gamma rays (~ 0.1 - 10 MeV) can be characterized in terms of two observed components. The first component is due to photons that reach the detector…
Constraints on positron annihilation kinematics in the inner Galaxy
Thomas Siegert, Roland M. Crocker, Roland Diehl +4
The annihilation of cosmic positrons () with electrons in the interstellar medium (ISM) results in the strongest persistent gamma-ray line signal in the sky. For 50 years, thi…
Imaging and Spectral Fitting of Bright Gamma-ray Sources with the COSI Balloon Payload
Jarred M. Roberts, Steven Boggs, Thomas Siegert +17
The Compton Spectrometer and Imager balloon payload (COSI-Balloon) is a wide-field-of-view Compton -ray telescope that operates in the 0.2 - 5 MeV bandpass. COSI-Balloon had a…
Gamma-ray lines from SN2014J
Thomas Siegert, Roland Diehl
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…
Telescope Concepts in Gamma-Ray Astronomy
Thomas Siegert, Deirdre Horan, Gottfried Kanbach
This chapter outlines the general principles for the detection and characterisation of high-energy -ray photons in the energy range from MeV to GeV. Applications of these funda…
On the Possibility of an Extragalactic Positron Annihilation Signal
Thomas Siegert, Hiroki Yoneda
With 20 years of INTEGRAL/SPI observations, Yoneda et al. (2025) created the most detailed map of the positron annihilation line at 511keV. While central bulge and extended disk ar…
Measuring the smearing of the Galactic 511 keV signal: positron propagation or supernova kicks?
Thomas Siegert, Roland M. Crocker, Oscar Macias +4
We use 15 years of -ray data from INTEGRAL/SPI in a refined investigation of the morphology of the Galactic bulge positron annihilation signal. Our spatial analysis confirms th…
Catching Element Formation In The Act
Chris L. Fryer, Frank Timmes, Aimee L. Hungerford +216
Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects…
Light WIMPs and MeV Gamma-ray Detection with COSI
Yu Watanabe, Shigeki Matsumoto, Christopher M. Karwin +6
Light weakly interacting massive particles (WIMPs), whose masses are in the sub-GeV scale, have been attracting more attention due to the negative results searching for traditional…
Constraints on light decaying dark matter candidates from 16 years of INTEGRAL/SPI observations
Francesca Calore, Ariane Dekker, Pasquale Dario Serpico +1
We apply the recently developed analysis of 16 years of INTEGRAL/SPI data including a dark matter spatial template to derive bounds on dark matter candidates lighter than WIMPs (li…
The effect of positron-alkali metal atom interactions in the diffuse ISM
Fiona H. Panther, Ivo R. Seitenzahl, Roland M. Crocker +4
In the Milky Way galaxy, positrons, which are responsible for the diffuse gamma ray emission observed by space-based gamma ray observatories, are thought to ann…
Gamma-ray spectroscopy of Positron Annihilation in the Milky Way
Thomas Siegert, Roland Diehl, Gerasim Khachatryan +5
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 S…
Surround & Squash: The Interstellar Medium around Scorpius Centaurus OB2
Martin G. H. Krause, Andreas Burkert, Roland Diehl +7
We exploited observational constraints on stars, gas and nucleosynthesis ashes for the closest region of recent massive-star formation, Scorpius-Centaurus OB2, and combined them wi…
Prospects of direct detection of V gamma-rays from thermonuclear supernovae
Fiona H. Panther, Ivo R. Seitenzahl, Ashley J. Ruiter +3
Detection of gamma-rays emitted by radioactive isotopes synthesized in stellar explosions can give important insights into the processes that power transients such as supernovae, a…
The cosipy library: COSI's high-level analysis software
Israel Martinez-Castellanos, Savitri Gallego, Chien-You Huang +72
The Compton Spectrometer and Imager (COSI) is a selected Small Explorer (SMEX) mission launching in 2027. It consists of a large field-of-view Compton telescope that will probe wit…
Comparing simulated Al maps to gamma-ray measurements
Moritz M. M. Pleintinger, Thomas Siegert, Roland Diehl +4
Context. The diffuse gamma-ray emission of at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way, and traces massive-star feedback in the interstellar medium…
Measurement of Galactic Al with the Compton Spectrometer and Imager
Jacqueline Beechert, Thomas Siegert, John A. Tomsick +11
The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the 0.2-5 MeV sky. COSI's energy resolution of 0.2% at 1.8 MeV, sin…
Time-Variable Diffuse -ray Foreground
Thomas Siegert
While the data analysis of -ray telescopes has now become more robust, some signals may be misinterpretations of a time-variable foreground emission from the Solar System, indu…
SN2014J gamma-rays from the 56Ni decay chain
Roland Diehl, Thomas Siegert, Wolfgang Hillebrandt +7
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…
Imaging the positron annihilation line with 20 years of INTEGRAL/SPI observations
Hiroki Yoneda, Thomas Siegert, Saurabh Mittal
The e e annihilation line at 511 keV provides a unique probe for studying the distribution and origin of positrons in our Galaxy. The SPI spectrometer on INTEGRAL has obser…