13 research outputs found
Hypernovae as possible sources of Galactic positrons
INTEGRAL/SPI has recently observed a strong and extended emission resulting
from electron-positron annihilation located in the Galactic center region,
consistent with the Galactic bulge geometry, without any counterpart at high
gamma-ray energies, nor in the 1809 keV Al decay line. In order to
explain the rate of positron injection in the Galactic bulge, estimated to more
than 10 s, the most commonly considered positron injection
sources are type Ia supernovae. However, SN Ia rate estimations show that those
sources fall short to explain the observed positron production rate, raising a
challenging question about the nature of the Galactic positron source. In this
context, a possible source of Galactic positrons could be supernova events of a
new type, as the recently observed SN2003dh/GRB030329, an exploding Wolf-Rayet
star (type Ic supernova) associated with a hypernova/gamma-ray burst; the
question about the rate of this kind of events remains open, but could be
problematically low.
In this paper, we explore the possibility of positron production and escape
by such an event in the framework of an asymmetric model, in which a huge
amount of Ni is ejected in a cone with a very high velocity; the ejected
material becomes quickly transparent to positrons, which spread out in the
interstellar medium.Comment: 8 pages, 2 figures. To appear in the Proceedings of the 5th INTEGRAL
Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munich, German
Evidence for 1809 keV Gamma-Ray Emission from 26Al Decays in the Vela Region with INTEGRAL/SPI
The Vela region is a promising target for the detection of 1.8 MeV gamma-rays
emitted by the decays of radioactive 26Al isotopes produced in hydrostatic or
explosive stellar nucleosynthesis processes. COMPTEL has claimed 1.8 MeV
gamma-ray detection from Vela at a 3sigma level with a flux of 3.6 10^-5
ph/cm^2/s. In this paper, we present first results of our search for 1.8 MeV
gamma-rays from Vela with the spectrometer SPI aboard INTEGRAL. Using the data
set acquired during 1.7 Ms at the end of 2005 in the frame of our AO-3
open-time observation, we determine a flux of (6.5 \pm 1.9(stat) \pm 2.4(syst))
10^-5 ph/cm^2/s from 26Al decays in the Vela region.Comment: 4 pages, 8 figures. Accepted for publication in ESA SP-622
(Proceedings of the 6th INTEGRAL Workshop, Moscow, 2006 07 03-07
Radioactive 26Al and massive stars in the Galaxy
Gamma-rays from radioactive 26Al (half life ~7.2 10^5 yr) provide a
'snapshot' view of ongoing nucleosynthesis in the Galaxy. The Galaxy is
relatively transparent to such gamma-rays, and emission has been found
concentrated along the plane of the Galaxy. This led to the conclusion1 that
massive stars throughout the Galaxy dominate the production of 26Al. On the
other hand, meteoritic data show locally-produced 26Al, perhaps from spallation
reactions in the protosolar disk. Furthermore, prominent gamma-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 1808.65 keV, 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) M_sol of
26Al. We use this to estimate that the frequency of core collapse (i.e. type
Ib/c and type II) supernovae to be 1.9(+/- 1.1) events per century.Comment: accepted for publication in Nature, 24 pages including Online
Supplements, 11 figures, 1 tabl
Large Observatory for x-ray Timing (LOFT-P): a Probe-class mission concept study
LOFT-P is a concept for a NASA Astrophysics Probe-Class (<$1B) X-ray timing
mission, based on the LOFT concept originally proposed to ESAs M3 and M4 calls.
LOFT-P requires very large collecting area (>6 m^2, >10x RXTE), high time
resolution, good spectral resolution, broad-band spectral coverage (2-30 keV),
highly flexible scheduling, and an ability to detect and respond promptly to
time-critical targets of opportunity. It addresses science questions such as:
What is the equation of state of ultra dense matter? What are the effects of
strong gravity on matter spiraling into black holes? It would be optimized for
sub-millisecond timing to study phenomena at the natural timescales of neutron
star surfaces and black hole event horizons and to measure mass and spin of
black holes. These measurements are synergistic to imaging and high-resolution
spectroscopy instruments, addressing much smaller distance scales than are
possible without very long baseline X-ray interferometry, and using
complementary techniques to address the geometry and dynamics of emission
regions. A sky monitor (2-50 keV) acts as a trigger for pointed observations,
providing high duty cycle, high time resolution monitoring of the X-ray sky
with ~20 times the sensitivity of the RXTE All-Sky Monitor, enabling
multi-wavelength and multi-messenger studies. A probe-class mission concept
would employ lightweight collimator technology and large-area solid-state
detectors, technologies which have been recently greatly advanced during the
ESA M3 study. Given the large community interested in LOFT (>800 supporters,
the scientific productivity of this mission is expected to be very high,
similar to or greater than RXTE (~2000 refereed publications). We describe the
results of a study, recently completed by the MSFC Advanced Concepts Office,
that demonstrates that LOFT-P is feasible within a NASA probe-class mission
budget.Comment: Proc. SPIE 9905, Space Telescopes and Instrumentation 2016:
Ultraviolet to Gamma Ray, 99054Y (July 18, 2016
The large area detector onboard the eXTP mission
The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument onboard the eXTP mission, a flagship
mission of the Chinese Academy of Sciences and the China National Space Administration, with a large European
participation coordinated by Italy and Spain. The eXTP mission is currently performing its phase B study, with a target
launch at the end-2027. The eXTP scientific payload includes four instruments (SFA, PFA, LAD and WFM) offering
unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The LAD instrument is based on the
design originally proposed for the LOFT mission. It envisages a deployed 3.2 m2 effective area in the 2-30 keV energy
range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to
200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper
we will provide an overview of the LAD instrument design, its current status of development and anticipated
performance
Asymmetric 511 keV Positron Annihilation Line Emission from the Inner Galactic Disk
A recently reported asymmetry in the 511 keV gamma-ray line emission from the inner galactic disk is unexpected and mimics an equally unexpected one in the distribution of LMXBs seen at hard X-ray energies. A possible conclusion is that LMXBs are an important source of the positrons whose annihilation gives rise to the line. We will discuss these results, their statistical significance and that of any link between the two. The implication of any association between LMXBs and positrons for the strong annihilation radiation from the galactic bulge will be reviewed
The space-borne INTEGRAL-SPI gamma ray telescope: Test and calibration campaigns
The spectrometer SPI aboard the ESA INTEGRAL satellite, which will be launched in 2002, will study the gamma ray sky in the 20-keV to 8-MeV energy band. It achieves the excellent spectral resolution of about 2 keV for photons of 1 MeV thanks to its 19 germanium detectors. A coded mask imaging technique provides an angular resolution of 2degrees. An active BGO veto shield is used for the definition of the field of view and for background rejection. After integration and testing at ONES in Toulouse, the flight model of SPI recently underwent a one-month prelaunch calibration at the CEA center of Bruyeres le Ch (a) over cap tel, using an accelerator for homogeneity measurements and high-activity radioactive sources for imaging performance measurements. This paper presents the scientific goals and the different detector components of SPI and reports on the testing and calibration campaigns. The methods used to achieve good timing alignment using the digital front end electronics are described and the first detector performance and imaging capabilities are presented
The large area detector onboard the eXTP mission
The eXTP (enhanced X-ray Timing and Polarimetry) mission is a major project of the Chinese Academy of Sciences
(CAS) and China National Space Administration (CNSA) currently performing an extended phase A study and proposed
for a launch by 2025 in a low-earth orbit. The eXTP scientific payload envisages a suite of instruments (Spectroscopy
Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented
simultaneous wide-band X-ray spectral, timing and polarimetry sensitivity. A large European consortium is contributing
to the eXTP study and it is expected to provide key hardware elements, including a Large Area Detector (LAD). The
LAD instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA context. The
eXTP/LAD envisages a deployed 3.4 m2 effective area in the 2-30 keV energy range, achieved through the technology of
the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary
plate collimators - limiting the field of view to about 1 degree. In this paper we provide an overview of the LAD
instrument design, including new elements with respect to the earlier LOFT configuration
The enhanced X-ray Timing and Polarimetry missionâeXTP
International audienceIn this paper we present the enhanced X-ray Timing and Polarimetry missionâeXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring effects of QED, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, eXTP will be a very powerful observatory for astrophysics that will provide observations of unprecedented quality on a variety of galactic and extragalactic objects. In particular, its wide field monitoring capabilities will be highly instrumental to detect the electro-magnetic counterparts of gravitational wave sources. The paper provides a detailed description of: (1) the technological and technical aspects, and the expected performance of the instruments of the scientific payload, (2) the elements and functions of the mission, from the spacecraft to the ground segment