198 research outputs found
Investigation of charge sharing among electrode strips for a CdZnTe detector
We have investigated charge sharing among the anode strips of a CdZnTe (CZT)
detector using a 30 micrometer collimated gamma-ray beam. We compared the
laboratory measurements with the predictions from our modeling of the charge
transport within the detector. The results indicate that charge sharing is a
function of the interaction depth and the energy of the incoming photon. Also,
depending on depth, a fraction of the electrons might drift to the inter-anode
region causing incomplete charge collection. Here, we show that photoelectron
range and diffusion of the charge cloud are the principal causes of charge
sharing and obtain limits on the size of the electron cloud as a function of
position in the detector.Comment: 16 pages 10 figures. Accepted for publication in Nuclear Instruments
and Methods -
State transitions and jet formation in black hole binaries
The daily monitoring observations of black hole transients with RXTE provided important clues on the conditions of the state transitions, both in terms of spectra and timing. The recent addition of monitoring in the optical-infrared and the radio band significantly extended our knowledge of the relation between the jets and the spectral states. However, there are still very important unanswered questions, most importantly, whether the formation of the jet triggers any change in the spectral and temporal properties of the source. The answer to this question is also intrinsically related to the origin of the hard X-ray emission. In this work, the relation between the jet and the state transitions is discussed, using the data from GX 339-4, 4U 1543-47, H 1743-322, and GRO J1655-40, concentrating on the evolution of spectral and temporal parameters before, during and after the formation of the jet
SEARCH FOR GRAVITATIONALLY REDSHIFTED 2.2 MEV LINE FROM 4U 1820-30
We have analyzed 1.7 Ms of the INTEGRAL data of the Low Mass X-Ray Binary (LMXB) 4U 1820-30 and searched for the redshifted 2.2 MeV neutron capture gamma-ray line. This source is unique in that it is
thought to be accreting pure Helium and might be a powerful 2.2 MeV line source. If detected, this line
would strongly constrain the neutron star equation of state, motivating this search. The line is expected to be redshifted to 1.30-1.72 MeV so we scanned the 1-2 MeV region. Although we failed to detect the redshifted 2.2 MeV line, mainly due to the intense background noise to which INTEGRAL is exposed, we placed upper limits on the source’s flux for different line widths. We plan to do analysis on the rest of the data (over 8 Ms) in the future
The effect of dust scattering on the timing properties of black holes
It has been known that sources with high absorption column density also have high dust column density along the line of sight. The differential delays caused by small angle scattering of X rays by dust may have important effects on the power spectra of Galactic black holes at low energies, and impact studies that use the relation between the rms amplitude of variability and energy to determine the origin of QPOs from these sources. We observed the high absorption column density (NH ˜1023 cm-2 ) GBH 1E1740.7-2942 for 20 ks simultaneously with XMM-Newton and RXTE. By comparing the power spectra from the events in the core of the point spread function (PSF) of XMM-Newton EPIC-PN (using imaging and excluding the scattering halo) and the RXTE data, we quantified the effects of small angle scattering on the timing properties of this source. The rms amplitude of variability in ˜2-6 keV band obtained from the XMM-Newton data is higher than that of the RXTE as expected from the a scattering halo contribution in the RXTE
Search for polarization from the prompt gamma-ray emission of GRB 041219a with SPI on INTEGRAL
Measuring the polarization of the prompt γ-ray emission from gamma-ray bursts (GRBs) can significantly improve our understanding of both the GRB emission mechanisms as well as the underlying engine driving the explosion. We searched for polarization in the prompt γ-ray emission of GRB 041219a with the SPI instrument on INTEGRAL. Using multiple-detector coincidence events in the 100-350 keV energy band, our analysis yields a polarization fraction from this GRB of 98%+/-33%. Statistically, we cannot claim a polarization detection from this source. Moreover, different event selection criteria lead to even less significant polarization fractions, e.g., lower polarization fractions are obtained when higher energies are included in the analysis. We cannot strongly rule out the possibility that the measured modulation is dominated by instrumental systematics. Therefore, SPI observations of GRB 041219a do not significantly constrain GRB models. However, this measurement demonstrates the capability of SPI to measure polarization, as well as the techniques developed for this analysis
Searching for annihilation radiation from SN 1006 with SPI on INTEGRAL
Historical Type Ia supernovae are a leading candidate for the source of
positrons observed through their diffuse annihilation emission in the Galaxy.
However, search for annihilation emission from individual Type Ia supernovae
has not been possible before the improved sensitivity of \integral. The total
511 keV annihilation flux from individual SNe Ia, as well as their contribution
to the overall diffuse emission, depends critically on the escape fraction of
positrons produced in Co decays. Late optical light curves suggest that
this fraction may be as high as 5%. We searched for positron annihilation
radiation from the historical Type Ia supernova SN 1006 using the SPI
instrument on \integral. We did not detect significant 511 keV line emission,
with a 3 flux upper limit of 0.59 x 10 ergs cm^-2 s^-1 for \wsim
1 Msec exposure time, assuming a FWHM of 2.5 keV. This upper limit corresponds
to a 7.5% escape fraction, 50% higher than the expected 5% escape scenario, and
rules out the possibility that Type Ia supernovae produce all of the positrons
in the Galaxy (~ 12% escape fraction), if the mean positron lifetime is less
than 10 years. Future observations with \integral will provide stronger
limits on the escape fraction of positrons, the mean positron lifetime, and the
contribution of Type Ia supernovae to the overall positron content of the
Galaxy.Comment: 3 pages, 2 figures, accepted for publication in ApJ
POLARIZATION MEASUREMENT OF GRB 041219A WITH SPI
Measuring the polarization of the prompt gamma-ray emission from GRBs can signicantly improve our understanding of both the GRB emission mechanisms, as well as of the underlying engine driving the explosion. We searched for polarization in the prompt gamma-ray emission of GRB 041219a with the SPI instrument. Using multiple detector coincidence events in the 100–350 keV energy band, our analysis yields a polarization fraction from this GRB of 98 +-33%. Statistically, we cannot claim a polarization detection from this source. We cannot strongly rule out the possibility that the measured modulation is dominated by instrumental systematics. Therefore, SPI observations of GRB 041219a do not significantly constrain GRB models. However, this measurement demonstrates the capability of SPI to measure polarization, and the techniques developed for this analysis
X-RAY OBSERVATIONS OF SN 1006 WITH INTEGRAL
We have used 1000 ksec of on-source, and 500 ksec of 10 degrees off-source INTEGRAL data of SN 1006 to characterize the synchrotron emission, and attempt to detect non-thermal bremsstrahlung, using the combination of IBIS and JEM-X spatial and spectral coverage. With the earlier 750 ksec on source data, we have detected the limbs of SN 1006 with JEM-X between 2.4 and 8.4 keV bands. The source was not detected with either ISGRI orSPI above 20 keV. The ISGRI upper limit is about a factor of four above current model predictions, but conrms the presence of steepening in the power-law extrapolated from lower energies (< 4 keV)
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