arXiv subjects

C. Hamadache

Publications and source records attributed to C. Hamadache.

At least 19 recordsLinked to original sources

arXiv2026

Gamma-ray production cross sections in proton interactions with natMg, natSi and 56Fe targets: measurement over the energy range of $E_p = 66$-125 MeV, data analysis, results and discussion. Astrophysical implications

We have measured nuclear gamma-ray line production cross sections in interactions of highly accelerated proton beams with various target nuclei abundant in astrophysical sites. The experiments were carried out at the 200-MV Separated Sector Cyclotron (SSC) of iThemba LABS (near Cape Town, in South Africa) using a high-energy resolution and high efficiency detection system for registering the emitted gamma-ray photons. We report and discuss in this paper the collected experimental data sets for various gamma-ray lines produced in bombarding natMg, natSi and 56Fe targets with proton beams of incident energies of Ep = 66, 80, 95, 110 and 125 MeV. After describing the experimental set up and the data analysis method used, we report and discuss our total experimental cross section results in comparisons to previous counterparts from the literature, to a semi-empirical compilation and to the predictions of nuclear reaction theory via performed TALYS code calculations. Significantly improved agreements between theory and experiment are point out when using our modified optical model potential and B\^eta (lambda) level deformation parameters instead of the default input parameters built in TALYS. Finally, we put into perspective the applications of our results in nuclear physics and astrophysics with drawing relevant conclusions. gammaKeywords: Proton-induced nuclear reactions; gamma-ray production cross sections; gamma-ray spectrometry; gamma-ray spectroscopy; Astrophysical implications

nucl-ex↗

arXiv2025

EROS light curve data base

The EROS project (Exp\'erience de Recherche d'Objets Sombres) carried out photometric surveys of dense stellar fields towards the Magellanic Clouds (LMC and SMC), the Galactic Bulge and Galactic spiral arms, over the period 1990-2003. The main goal of the experiment was to search for the Galactic Dark Matter in the form of massive compact objects (machos), through the gravitational microlensing effect. The historical record of the flux variations of the monitored stars by EROS-2 will be a unique asset for time domain astronomy and to complement current and future searches of transient sources. We describe the set of light curves obtained by EROS-2 program over the years 1996 to 2003, monitoring more than 86 million stars, which is publicly released through the Centre de Donn\'ees de Strasbourg (CDS). The numbers of light curves in this data set are 28.7 and 4.0 million in LMC, respectively SMC, 42.9 million in the Galactic Bulge and 10.4 million towards the Galactic spiral arms, with several hundred measurements for each object. Data from EROS-1 is also being released. The object catalog and light curves and images are accessible through the CDS portal. This will be useful for checking the past behavior of newly discovered variable objects.

astro-ph.GA↗

arXiv2022

Gamma-ray emission in proton-induced nuclear reactions on natC and Mylar targets over the incident energy range of Ep = 30-200 MeV. Astrophysical implications

We have measured the gamma-ray line production cross sections in proton-induced nuclear reactions on various target nuclei abundant in astrophysical sites over the incident energy range of Ep = 30 - 200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 cyclotron of iThemba LABS using a high-energy resolution, high-efficiency detection array composed of 8 Compton-suppressed clover detectors comprising 32 HP-Ge crystals for recording the gamma-ray spectra. In the current paper, we focus on de-excitation lines produced in proton irradiations of natC and Mylar targets. In particular, on the prominent 4.439 and 6.129 MeV lines of $^{12}$C and $^{16}$O which are among the strongest lines emitted in solar flares and in interactions of low-energy cosmic rays with the gas and dust of the inner galaxy. We report new gamma-ray production experimental cross section data for ten nuclear lines that we compare to previous low-energy data sets from the literature, to the predictions of the TALYS code of modern nuclear reactions and to a semi-empirical compilation. In first approach, performing calculations with default input parameters of TALYS we observed substantial deviations between the predicted cross sections and experimental data. Then, using modified optical model potential and nuclear level deformation parameters as input data we generated theoretical excitation functions for the above two main lines fully consistent with experimental data. In contrast, the experimental data sets for the other eight analyzed lines from the two proton-irradiated targets exhibit significant deviations with the predicted cross section values. We also report line-shape experimental data for the line complex observed at $E_g$ = 4.44 MeV in irradiations of the two targets. Finally, we emphasize the astrophysical implications of our results.

nucl-ex↗

arXiv2022

New limits from microlensing on Galactic Black Holes in the mass range $10M_{\odot}<M<1000M_{\odot}$

We have searched for long duration microlensing events originating from intermediate mass Black Holes (BH) in the halo of the Milky Way, using archival data from EROS-2 and MACHO photometric surveys towards the Large Magellanic Cloud. We combined data from these two surveys to create a common database of light curves for 14.1 million objects in LMC, covering a total duration of 10.6 years, with flux series measured through four wide passbands. We have carried out a microlensing search on these light curves, complemented by the light curves of 22.7 million objects, observed by EROS-2 only or MACHO only over about 7 years, with flux series measured through only two passbands. A likelihood analysis, taking into account LMC self lensing and Milky Way disk contributions allows us to conclude that compact objects with masses in the range $10 - 100 M_{\odot}$ cannot make up more than $\sim 15\%$ of a standard halo total mass (at $95\%$ confidence level). Our analysis sensitivity weakens for heavier objects, although we still exclude that $\sim 50\%$ of the halo be made of $\sim 1000 M_{\odot}$ BHs. Combined with previous EROS results, an upper limit of $\sim 15\%$ of the total halo mass can be obtained for the contribution of compact halo objects in the mass range $10^{-6} - 10^2 M_{\odot}$.

astro-ph.GA↗

arXiv2020

Sub-threshold states in $^{19}$Ne relevant to $^{18}$F(p,$\alpha$)$^{15}$O

Classical novae result from thermonuclear explosions producing several $\gamma$-ray emitters which are prime targets for satellites observing in the MeV range. The early 511 keV gamma-ray emission depends critically on the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate which, despite many experimental and theoretical efforts, still remains uncertain. One of the main uncertainties in the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate is the contribution in the Gamow window of interference between sub-threshold $^{19}$Ne states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states. States in the $^{19}$Ne compound nucleus were studied at the Tandem-ALTO facility using the $^{19}$F($^3$He,t)$^{19}$Ne charge exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or $\alpha$-particles from unbound $^{19}$Ne states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established. The coincidence yield at $E_x$ = 6.29 MeV was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high spin and low spin components. Evidence for a broad, low spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. R-matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold. The levels schemes of $^{19}$Ne and $^{19}$F are still not sufficiently well known and further studies of the analogue assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.

nucl-ex↗

arXiv2020

Measurement and analysis of nuclear $\gamma$-ray production cross sections in proton interactions with Mg, Si and Fe nuclei abundant in astrophysical sites over the incident energy range $E=30-66$ MeV

Gamma-ray production cross section excitation functions have been measured for $30$, $42$, $54$ and $66$ MeV proton beams accelerated onto targets of astrophysical interest, $^{nat}$C, C + O (Mylar), $^{nat}$Mg, $^{nat}$Si and $^{56}$Fe, at the Sector Separated Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with 8 Compton suppressed HPGe clover detectors was used to record $\gamma$-ray data. For known, intense $\gamma$-ray lines the previously reported experimental data measured up to $E_{p}\simeq$ $25$ MeV at the Washington and Orsay tandem accelerators were extended to higher proton energies. Our experimental data for the last 3 targets are reported here and discussed with respect to previous data and the Murphy \textit{et al.} compilation [ApJS 183, 142 (2009)], as well as to predictions of the nuclear reaction code TALYS. The overall agreement between theory and experiment obtained in first-approach calculations using default input parameters of TALYS has been appreciably improved by using modified optical model potential (OMP), deformation, and level density parameters. The OMP parameters have been extracted from theoretical fits to available experimental elastic/inelastic nucleon scattering angular distribution data by means of the coupled-channels reaction code OPTMAN. Experimental data for several new $\gamma$-ray lines are also reported and discussed. The astrophysical implications of our results are emphasised.

nucl-ex↗

arXiv2020

Gamma-ray emission in alpha-particle reactions with C, Mg, Si, Fe

Cross sections for the strongest gamma-ray emission lines produced in alpha-particle reactions with C, Mg, Si, Fe have been measured in the range E_alpha = 50 - 90 MeV at the center for proton therapy at the Helmholtz-Zentrum Berlin. Data for more than 60 different gamma-ray lines were determined, with particular efforts for lines that are in cross section compilations/evaluations with astrophysical purpose, and where data exist at lower projectile energies. The data are compared with predictions of a modern nuclear reaction code and cross-section curves of the latest evaluation for gamma-ray line emission in accelerated-particle interactions in solar flares.

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arXiv2018

The e-ASTROGAM gamma-ray space observatory for the multimessenger astronomy of the 2030s

e-ASTROGAM is a concept for a breakthrough observatory space mission carrying a gamma-ray telescope dedicated to the study of the non-thermal Universe in the photon energy range from 0.15 MeV to 3 GeV. The lower energy limit can be pushed down to energies as low as 30 keV for gamma-ray burst detection with the calorimeter. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with remarkable polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous and current generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will be a major player of the multiwavelength, multimessenger time-domain astronomy of the 2030s, and provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LISA, LIGO, Virgo, KAGRA, the Einstein Telescope and the Cosmic Explorer, IceCube-Gen2 and KM3NeT, SKA, ALMA, JWST, E-ELT, LSST, Athena, and the Cherenkov Telescope Array.

astro-ph.HE↗

arXiv2017

The e-ASTROGAM gamma-ray space mission

The e-ASTROGAM is a gamma-ray space mission to be proposed as the M5 Medium-size mission of the European Space Agency. It is dedicated to the observation of the Universe with unprecedented sensitivity in the energy range 0.2 - 100 MeV, extending up to GeV energies, together with a groundbreaking polarization capability. It is designed to substantially improve the COMPTEL and Fermi sensitivities in the MeV-GeV energy range and to open new windows of opportunity for astrophysical and fundamental physics space research. e-ASTROGAM will operate as an open astronomical observatory, with a core science focused on (1) the activity from extreme particle accelerators, including gamma-ray bursts and active galactic nuclei and the link of jet astrophysics to the new astronomy of gravitational waves, neutrinos, ultra-high energy cosmic rays, (2) the high-energy mysteries of the Galactic center and inner Galaxy, including the activity of the supermassive black hole, the Fermi Bubbles, the origin of the Galactic positrons, and the search for dark matter signatures in a new energy window; (3) nucleosynthesis and chemical evolution, including the life cycle of elements produced by supernovae in the Milky Way and the Local Group of galaxies. e-ASTROGAM will be ideal for the study of high-energy sources in general, including pulsars and pulsar wind nebulae, accreting neutron stars and black holes, novae, supernova remnants, and magnetars. And it will also provide important contributions to solar and terrestrial physics. The e-ASTROGAM telescope is optimized for the simultaneous detection of Compton and pair-producing gamma-ray events over a large spectral band. It is based on a very high technology readiness level for all subsystems and includes many innovative features for the detectors and associated electronics.

astro-ph.IM↗

arXiv2015

Fast-neutron induced background in LaBr3:Ce detectors

The response of a scintillation detector with a cylindrical 1.5-inch LaBr3:Ce crystal to incident neutrons has been measured in the energy range En = 2-12 MeV. Neutrons were produced by proton irradiation of a Li target at Ep = 5-14.6 MeV with pulsed proton beams. Using the time-of-flight information between target and detector, energy spectra of the LaBr3:Ce detector resulting from fast neutron interactions have been obtained at 4 different neutron energies. Neutron-induced gamma rays emitted by the LaBr3:Ce crystal were also measured in a nearby Ge detector at the lowest proton beam energy. In addition, we obtained data for neutron irradiation of a large-volume high-purity Ge detector and of a NE-213 liquid scintillator detector, both serving as monitor detectors in the experiment. Monte-Carlo type simulations for neutron interactions in the liquid scintillator, the Ge and LaBr3:Ce crystals have been performed and compared with measured data. Good agreement being obtained with the data, we present the results of simulations to predict the response of LaBr3:Ce detectors for a range of crystal sizes to neutron irradiation in the energy range En = 0.5-10 MeV

physics.ins-det↗

arXiv2015

Gamma ray production cross sections in proton induced reactions on natural Mg, Si and Fe targets over the proton energy range 30 up to 66 MeV

Gamma-ray excitation functions have been measured for 30, 42, 54 and 66 MeV proton beams accelerated onto C + O (Mylar), Mg, Si, and Fe targets of astrophysical interest at the separate-sector cyclotron of iThemba LABS in Somerset West (Cape Town, South Africa). A large solid angle, high energy resolution detection system of the Eurogam type was used to record Gamma-ray energy spectra. Derived preliminary results of Gamma-ray line production cross sections for the Mg, Si and Fe target nuclei are reported and discussed. The current cross section data for known, intense Gamma-ray lines from these nuclei consistently extend to higher proton energies previous experimental data measured up to Ep ~ 25 MeV at the Orsay and Washington tandem accelerators. Data for new Gamma-ray lines observed for the first time in this work are also reported.

nucl-ex↗

arXiv2013

Search for new resonant states in 10C and 11C and their impact on the cosmological lithium problem

The observed primordial 7Li abundance in metal-poor halo stars is found to be lower than its Big-Bang nucleosynthesis (BBN) calculated value by a factor of approximately three. Some recent works suggested the possibility that this discrepancy originates from missing resonant reactions which would destroy the 7Be, parent of 7Li. The most promising candidate resonances which were found include a possibly missed 1- or 2- narrow state around 15 MeV in the compound nucleus 10C formed by 7Be+3He and a state close to 7.8 MeV in the compound nucleus 11C formed by 7Be+4He. In this work, we studied the high excitation energy region of 10C and the low excitation energy region in 11C via the reactions 10B(3He,t)10C and 11B(3He,t)11C, respectively, at the incident energy of 35 MeV. Our results for 10C do not support 7Be+3He as a possible solution for the 7Li problem. Concerning 11C results, the data show no new resonances in the excitation energy region of interest and this excludes 7Be+4He reaction channel as an explanation for the 7Li deficit.

nucl-ex↗

arXiv2013

Using INTEGRAL/SPI to study the Sun

Solar energetic particle (SEP) events are a prime opportunity to probe astrophysical particle acceleration by combining in-situ measurements of particles in space with remote sensing of the hard X-ray (HXR) and γ-ray emitting particles in the solar atmosphere. For the space environment SEPs are among the biggest hazards, particularly for spacecraft and human exploration of the solar system. Unfortunately our current understanding of the acceleration and transport of SEPs is weak. With the increasing onset of the space age it is vitally important that we increase our knowledge of the physical mechanisms related to SEPs. In this direction, the SEPServer project aims at building an on-line server that will provide the space research community with SEP data and related observations of solar electromagnetic emission. INTEGRAL/SPI acquires observations from many X-ray/γ-ray flares associated with SEP events. To make this data accessible for SEP studies we have undertaken a major effort to specify the solar observing conditionS of INTEGRAL through Monte-Carlo simulations of its BGO-detector response for several flares associated with selected SEP events.

astro-ph.SR↗

arXiv2010

Measurements of nuclear $γ$-ray line emission in interactions of protons and $α$ particles with N, O, Ne and Si

$γ$-ray production cross sections have been measured in proton irradiations of N, Ne and Si and $α$-particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong $γ$-ray lines of $^{16}$O produced in proton and $α$-particle irradiations of O. For the measurements gas targets were used for N, O and Ne and a thick foil was used for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for $α$-particles have been delivered by the IPN-Orsay tandem accelerator. The $γ$ rays have been detected with four HP-Ge detectors in the angular range 30$^{\circ}$ to 135$^{\circ}$. We extracted 36 cross section excitation functions for proton reactions and 14 for $α$-particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular the agreement of cross section calculations in the nuclear reaction code TALYS with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei $^{14}$N, $^{20,22}$Ne and $^{28}$Si. The importance of these results for the modeling of nuclear $γ$-ray line emission in astrophysical sites is discussed.

nucl-ex↗

arXiv2009

The EROS2 search for microlensing events towards the spiral arms: the complete seven season results

The EROS-2 project has been designed to search for microlensing events towards any dense stellar field. The densest parts of the Galactic spiral arms have been monitored to maximize the microlensing signal expected from the stars of the Galactic disk and bulge. 12.9 million stars have been monitored during 7 seasons towards 4 directions in the Galactic plane, away from the Galactic center. A total of 27 microlensing event candidates have been found. Estimates of the optical depths from the 22 best events are provided. A first order interpretation shows that simple Galactic models with a standard disk and an elongated bulge are in agreement with our observations. We find that the average microlensing optical depth towards the complete EROS-cataloged stars of the spiral arms is $\barτ =0.51\pm .13\times 10^{-6}$, a number that is stable when the selection criteria are moderately varied. As the EROS catalog is almost complete up to $I_C=18.5$, the optical depth estimated for the sub-sample of bright target stars with $I_C<18.5$ ($\barτ=0.39\pm >.11\times 10^{-6}$) is easier to interpret. The set of microlensing events that we have observed is consistent with a simple Galactic model. A more precise interpretation would require either a better knowledge of the distance distribution of the target stars, or a simulation based on a Galactic model. For this purpose, we define and discuss the concept of optical depth for a given catalog or for a limiting magnitude.

astro-ph.GA↗

arXiv2009

The beat Cepheids in the Magellanic Clouds: an analysis from the EROS-2 database

A number of microlensing dark-matter surveys have produced tens of millions of light curves of individual background stars. These data provide an unprecedented opportunity for systematic studies of whole classes of variable stars and their host galaxies. We aim to use the EROS-2 survey of the Magellanic Clouds to detect and study the population of beat Cepheids (BCs) in both Clouds. BCs pulsating simultaneously in the first overtone and fundamental modes (FO/F) or in the second and first overtone modes (SO/FO) are of particular interest. Using special software designed to search for periodic variables, we have scanned the EROS-2 data base for variables in the typical period range of Cepheids. Metallicities of FO/F objects were then calculated from linear nonadiabatic convective stellar models. We identify 74 FO/F BCs in the LMC and 41 in the SMC, and 173 and 129 SO/FO pulsators in the LMC and SMC, respectively; 185 of these stars are new discoveries. For nearly all the FO/F objects we determine minimum, mean, and maximum values of the metallicity. The EROS data have expanded the samples of known BCs in the LMC by 31%, in the SMC by 110%. The FO/F objects provide independent measures of metallicities in these galaxies. The mean value of metallicity is 0.0045 in the LMC and 0.0018 in the SMC.

astro-ph.SR↗

arXiv2008

Discovery of a peculiar Cepheid-like star towards the northern edge of the Small Magellanic Cloud

For seven years, the EROS-2 project obtained a mass of photometric data on variable stars. We present a peculiar Cepheid-like star, in the direction of the Small Magellanic Cloud, which demonstrates unusual photometric behaviour over a short time interval. We report on data of the photometry acquired by the MARLY telescope and spectroscopy from the EFOSC instrument for this star, called EROS2 J005135-714459(sm0060n13842), which resembles the unusual Cepheid HR 7308. The light curve of our target is analysed using the Analysis of Variance method to determine a pulsational period of 5.5675 days. A fit of time-dependent Fourier coefficients is performed and a search for proper motion is conducted. The light curve exhibits a previously unobserved and spectacular change in both mean magnitude and amplitude, which has no clear theoretical explanation. Our analysis of the spectrum implies a radial velocity of 104 km s$^{-1}$ and a metallicity of -0.4$\pm$0.2 dex. In the direction of right ascension, we measure a proper motion of 17.4$\pm$6.0 mas yr$^{-1}$ using EROS astrometry, which is compatible with data from the NOMAD catalogue. The nature of EROS2 J005135-714459(sm0060n13842) remains unclear. For this star, we may have detected a non-zero proper motion for this star, which would imply that it is a foreground object. Its radial velocity, pulsational characteristics, and photometric data, however, suggest that it is instead a Cepheid-like object located in the SMC. In such a case, it would present a challenge to conventional Cepheid models.

astro-ph↗

arXiv2008

R Coronae Borealis stars in the Galactic Bulge discovered by EROS-2

Rare types of variable star may give unique insight into short-lived stages of stellar evolution. The systematic monitoring of millions of stars and advanced light curve analysis techniques of microlensing surveys make them ideal for discovering also such rare variable stars. One example is the R Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. We have conducted a systematic search of the EROS-2 database for the Galactic catalogue Bulge and spiral arms to find Galactic RCB stars. The light curves of $\sim$100 million stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCB stars, large and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm the photometric candidates. We have discovered 14 new RCB stars, all in the direction of the Galactic Bulge, bringing the total number of confirmed Galactic RCB stars to about 51. After reddening correction, the colours and absolute magnitudes of at least 9 of the stars are similar to those of Magellanic RCB stars. This suggests that these stars are in fact located in the Galactic Bulge, making them the first RCB stars discovered in the Bulge. The localisation of the 5 remaining RCBs is more uncertain: 4 are either located behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual thick circumstellar shell; the other is a DY Per RCB which may be located in the Bulge, even if it is fainter than the known Magellanic DY Per. From the small scale height found using the 9 new Bulge RCBs, $61<h^{RCB}_{Bulge}<246$ pc (95% C.L.), we conclude that the RCB stars follow a disk-like distribution inside the Bulge.

astro-ph↗