Jacques PAUL - Academia.edu (original) (raw)

Papers by Jacques PAUL

An intriguing feature of extra dimensions is the possible production of Kaluza--Klein gravitons b... more An intriguing feature of extra dimensions is the possible production of Kaluza--Klein gravitons by nucleon-nucleon bremsstrahlung in the course of core collapse of massive stars, as pointed out by Hannestad and Raffelt. In this event Kaluza--Klein gravitons are copiously produced and a significant fraction of them remains trapped around the newly born neutron stars. They slowly decay into 2 gamma rays, making neutron stars gamma-ray sources. In this letter, we strengthen considerably the limits on the radius of compactification of extra-dimensions for small number n of them, or alternatively the fundamental scale of quantum gravity, considering the gamma-ray emission of the whole population of neutron stars sitting in the Galactic bulge, instead of the closest member of this category. For n=1 the constraint on the compactification radius is R<400μm, overlapping with the distance (180μm) at which Newtons law is directly measured. In addition, for n=1 and n=2, the fundamental energ...

Invited Papers

Nowadays, the studies of celestial gamma rays are of great interest for several areas of galactic... more Nowadays, the studies of celestial gamma rays are of great interest for several areas of galactic astronomy. On a large scale, an upper limit of about a factor 3 is placed on the possible increase in density of the interstellar gas in the ring at 5 Kpc from the galactic center with respect to the solar neighbourhood. Also the locations of enhanced gamma-ray emissivity seem to be preferentially distributed in accordance with a spiral pattern. Gamma rays from the local galactic environment appear to be a valuable probe of the content and structure of the local interstellar medium. On a smaller scale, the detection of numerous localized gamma-ray sources forces to explore some particular phases of clusters of young and massive stars.

Symposium - International Astronomical Union

Within the error circle of the COS-B gamma-ray source at ℓ = 288°, b = 0° lies the Carina Nebula,... more Within the error circle of the COS-B gamma-ray source at ℓ = 288°, b = 0° lies the Carina Nebula, one of the most active regions of star formation known, housing several OB associations and Wolf-Rayet stars (WRS), and perhaps also a supernova remnant (SNR). As a region containing intense mass-losing stars it belongs to the same species as the Rho Oph cloud (but much more active), suggested to be associated with the gamma-ray source at ℓ = 353°, b = +16° (Paul et al., this conference). As a group of OB association linked with a SNR, it belongs to the same species as…

Symposium - International Astronomical Union

Supersonic stellar winds have recently been proposed as active agents of cosmic-ray acceleration.... more Supersonic stellar winds have recently been proposed as active agents of cosmic-ray acceleration. We try to insert this potential acceleration mechanism in its general astrophysical context. Among galactic objects, OB associations have the narrowest latitude distribution, resembling to that of gamma-ray sources. Here we focus on the bulk rate of kinetic energy deposition in molecular clouds through stellar winds of individual stars pertaining to OB associations. Assuming that a minute fraction of this mechanical energy can be transferred to suprathermal particles, we examine whether OB associations are detectable high-energy gamma-ray sources, owing to the interaction of accelerated particles with the dense molecular cloud still present close to young and massive stars. The 3 factors that govern the gamma-ray “visibility” of a given OB association are i) the rate of kinetic energy deposition , where the summation is done on all mass-losing stars; is the mass-loss rate for the star i...

Le Journal de Physique Colloques

L'astronomie gamma à haute énergie a récemment connu un développement spectaculaire, notamment gr... more L'astronomie gamma à haute énergie a récemment connu un développement spectaculaire, notamment grâce aux résultats du satellite astronomique américain SAS IL Parmi ceux-ci, les plus intéressants portent sur la distribution de l'émission gamma à haute énergie (E > 100 MeV) le long de l'équateur galactique. Cette distribution, examinée en détail, semble être corrélée avec les principaux traits structurels de la galaxie et en particulier avec les bras galactiques. Si la plupart des astrophysiciens s'accordent pour attribuer ce rayonnement gamma à haute énergie à l'interaction des rayons cosmiques avec la matière interstellaire, la distribution relative de ces deux composants reste inconnue. Cependant, en étudiant simultanément l'émission gamma à haute énergie et l'émission radio non thermique provenant de la galaxie, il apparaît possible de proposer un modèle qui explique les résultats de SAS II et qui de plus réconcilie quantitativement les idées sur la structure spirale de la galaxie, sur le champ magnétique galactique, sur le confinement des rayons cosmiques par le champ magnétique et du champ magnétique par la matière. Dans cette communication, après avoir résumé l'état des observations et des théories sur l'émission gamma galactique, un modèle d'ensemble sera proposé dont les prédictions seront confrontées aux données les plus récentes.

Le Journal de Physique Colloques

L'intensité gamma galactique à haute énergie peut être utilisée comme traceur du milieu interstel... more L'intensité gamma galactique à haute énergie peut être utilisée comme traceur du milieu interstellaire. En effet l'interaction du rayonnement cosmique avec la matière produit des photons gamma à haute énergie soit par collisions p-p-» n°-»• 2 y soit par freinage des électrons. Après la présentation des récents résultats relatifs à l'émission galactique obtenus par le satellite européen d'astronomie gamma COS-B, il est proposé une vue d'ensemble du milieu interstellaire tenant compte de ces résultats et de ceux obtenus au moyen d'autres traceurs du milieu interstellaire. La matière interstellaire apparaît comme concentrée dans un disque mince, parfois décalé vers les latitudes galactiques négatives. Le maximum de densité se situe à une distance d'environ 5 kpc du Soleil. Cette matière ainsi que les autres constituants du milieu interstellaire (champ magnétique, rayons cosmiques) se répartissent préférentiellement suivant une structure spirale.

Astronomy Letters-a Journal of Astronomy and Space Astrophysics, 1999

The GRANAT/SIGMA hard X-ray observations of GRS 1758-258 in 1990-1998 are presented. The source l... more The GRANAT/SIGMA hard X-ray observations of GRS 1758-258 in 1990-1998 are presented. The source lies at 5 deg from the Galactic center and was within the SIGMA field of view during the Granat surveys of this region. The total exposure time of the Galactic center was 11 x 10^6 s. The regular SIGMA observations revealed great variability of the source:

AIP Conference Proceedings, 1994

X-ray binaries form the bulk of hard x-ray sources, in the 30–300 keV range. More than twenty of ... more X-ray binaries form the bulk of hard x-ray sources, in the 30–300 keV range. More than twenty of them have been detected by SIGMA. Suspected black hole systems seem to be particularly numerous among the sources emitting above 100 keV, and their spectra appear harder than those of neutron star systems. This amounts to a spectral distinction between the two

Astronomy and Astrophysics, May 1, 1976

Astronomy and Astrophysics, 1988

Presentation de nouvelles observations CCD de la contrepartie optique de Geminga (1E0630+178) qui... more Presentation de nouvelles observations CCD de la contrepartie optique de Geminga (1E0630+178) qui montrent que l'objet G″ est bien moins bleu que prevu. La faible luminosite de l'objet est a prendre en consideration pour l'interpretation correcte des donnees. On discute des mecanismes pouvant expliquer l'emission en bande V; en particulier du rayonnement cyclotron d'une etoile a neutrons magnetisee

New Views on Microquasars, 2003

AIP Conference Proceedings, 1994

The authors report the discovery of the radio and infrared counterpart of the hard X-ray transien... more The authors report the discovery of the radio and infrared counterpart of the hard X-ray transient GRS 1915+105 in the constellation of Aquila. The compact object is located beyond ≡30 mag of optical absorption. At radio wavelengths it exhibits drastic time variations in flux which are correlated with changes in the hard X rays. The source also shows unusual varibility

Astron Astrophys Suppl Series, 1993

We report the identification of the radio counterpart of 1E1740.7-2942 and the detection of a dou... more We report the identification of the radio counterpart of 1E1740.7-2942 and the detection of a double radio jet emanating from it. The jet is produced by synchrotron emission from charged particules streaming out from the high energy source. The compact radio source at the center of the double jet is time variable in flux and spectral index. We find that the changes in radio flux are correlated with the variations at hard X-rays observed by SIGMA. After September 1991 the radio flux of the compact source increased with the enhancement in hard X-ray activity. It appears that the central synchrotron source is self-absorbed during the high states of 1E1740.7-2942. Recent observations of GRS1768-258 reveal, as in 1E1740.7-2942, the presence of another triple radio source, whose central component is variable and falls inside the error circle (10 arcsec of radius) of ROSAT.

Astron Astrophys, 1991

Observations of molecular transitions at millimeter wavelengths show that the most powerful compa... more Observations of molecular transitions at millimeter wavelengths show that the most powerful compact source of radiation in the Galaxy resulting from matter-antimatter annihilation may be associated with dense interstellar gas. Coincident with the position of the high energy source 1E1740.7-2942, a molecular cloud is found . This cloud belongs to the inner molecular layer of the galactic center region, since it is located ∼50 arc min from the dynamical center of the Galaxy and has a Doppler shift of −140 km/s. At a distance of 8.5 kpc, it would have a size of ∼3 pc and a mass of ∼5×10 4 M ○ .

An intriguing feature of extra dimensions is the possible production of Kaluza--Klein gravitons b... more An intriguing feature of extra dimensions is the possible production of Kaluza--Klein gravitons by nucleon-nucleon bremsstrahlung in the course of core collapse of massive stars, as pointed out by Hannestad and Raffelt. In this event Kaluza--Klein gravitons are copiously produced and a significant fraction of them remains trapped around the newly born neutron stars. They slowly decay into 2 gamma rays, making neutron stars gamma-ray sources. In this letter, we strengthen considerably the limits on the radius of compactification of extra-dimensions for small number n of them, or alternatively the fundamental scale of quantum gravity, considering the gamma-ray emission of the whole population of neutron stars sitting in the Galactic bulge, instead of the closest member of this category. For n=1 the constraint on the compactification radius is R<400μm, overlapping with the distance (180μm) at which Newtons law is directly measured. In addition, for n=1 and n=2, the fundamental energ...

Invited Papers

Nowadays, the studies of celestial gamma rays are of great interest for several areas of galactic... more Nowadays, the studies of celestial gamma rays are of great interest for several areas of galactic astronomy. On a large scale, an upper limit of about a factor 3 is placed on the possible increase in density of the interstellar gas in the ring at 5 Kpc from the galactic center with respect to the solar neighbourhood. Also the locations of enhanced gamma-ray emissivity seem to be preferentially distributed in accordance with a spiral pattern. Gamma rays from the local galactic environment appear to be a valuable probe of the content and structure of the local interstellar medium. On a smaller scale, the detection of numerous localized gamma-ray sources forces to explore some particular phases of clusters of young and massive stars.

Symposium - International Astronomical Union

Within the error circle of the COS-B gamma-ray source at ℓ = 288°, b = 0° lies the Carina Nebula,... more Within the error circle of the COS-B gamma-ray source at ℓ = 288°, b = 0° lies the Carina Nebula, one of the most active regions of star formation known, housing several OB associations and Wolf-Rayet stars (WRS), and perhaps also a supernova remnant (SNR). As a region containing intense mass-losing stars it belongs to the same species as the Rho Oph cloud (but much more active), suggested to be associated with the gamma-ray source at ℓ = 353°, b = +16° (Paul et al., this conference). As a group of OB association linked with a SNR, it belongs to the same species as…

Symposium - International Astronomical Union

Supersonic stellar winds have recently been proposed as active agents of cosmic-ray acceleration.... more Supersonic stellar winds have recently been proposed as active agents of cosmic-ray acceleration. We try to insert this potential acceleration mechanism in its general astrophysical context. Among galactic objects, OB associations have the narrowest latitude distribution, resembling to that of gamma-ray sources. Here we focus on the bulk rate of kinetic energy deposition in molecular clouds through stellar winds of individual stars pertaining to OB associations. Assuming that a minute fraction of this mechanical energy can be transferred to suprathermal particles, we examine whether OB associations are detectable high-energy gamma-ray sources, owing to the interaction of accelerated particles with the dense molecular cloud still present close to young and massive stars. The 3 factors that govern the gamma-ray “visibility” of a given OB association are i) the rate of kinetic energy deposition , where the summation is done on all mass-losing stars; is the mass-loss rate for the star i...

Le Journal de Physique Colloques

L'astronomie gamma à haute énergie a récemment connu un développement spectaculaire, notamment gr... more L'astronomie gamma à haute énergie a récemment connu un développement spectaculaire, notamment grâce aux résultats du satellite astronomique américain SAS IL Parmi ceux-ci, les plus intéressants portent sur la distribution de l'émission gamma à haute énergie (E > 100 MeV) le long de l'équateur galactique. Cette distribution, examinée en détail, semble être corrélée avec les principaux traits structurels de la galaxie et en particulier avec les bras galactiques. Si la plupart des astrophysiciens s'accordent pour attribuer ce rayonnement gamma à haute énergie à l'interaction des rayons cosmiques avec la matière interstellaire, la distribution relative de ces deux composants reste inconnue. Cependant, en étudiant simultanément l'émission gamma à haute énergie et l'émission radio non thermique provenant de la galaxie, il apparaît possible de proposer un modèle qui explique les résultats de SAS II et qui de plus réconcilie quantitativement les idées sur la structure spirale de la galaxie, sur le champ magnétique galactique, sur le confinement des rayons cosmiques par le champ magnétique et du champ magnétique par la matière. Dans cette communication, après avoir résumé l'état des observations et des théories sur l'émission gamma galactique, un modèle d'ensemble sera proposé dont les prédictions seront confrontées aux données les plus récentes.

Le Journal de Physique Colloques

L'intensité gamma galactique à haute énergie peut être utilisée comme traceur du milieu interstel... more L'intensité gamma galactique à haute énergie peut être utilisée comme traceur du milieu interstellaire. En effet l'interaction du rayonnement cosmique avec la matière produit des photons gamma à haute énergie soit par collisions p-p-» n°-»• 2 y soit par freinage des électrons. Après la présentation des récents résultats relatifs à l'émission galactique obtenus par le satellite européen d'astronomie gamma COS-B, il est proposé une vue d'ensemble du milieu interstellaire tenant compte de ces résultats et de ceux obtenus au moyen d'autres traceurs du milieu interstellaire. La matière interstellaire apparaît comme concentrée dans un disque mince, parfois décalé vers les latitudes galactiques négatives. Le maximum de densité se situe à une distance d'environ 5 kpc du Soleil. Cette matière ainsi que les autres constituants du milieu interstellaire (champ magnétique, rayons cosmiques) se répartissent préférentiellement suivant une structure spirale.

Astronomy Letters-a Journal of Astronomy and Space Astrophysics, 1999

The GRANAT/SIGMA hard X-ray observations of GRS 1758-258 in 1990-1998 are presented. The source l... more The GRANAT/SIGMA hard X-ray observations of GRS 1758-258 in 1990-1998 are presented. The source lies at 5 deg from the Galactic center and was within the SIGMA field of view during the Granat surveys of this region. The total exposure time of the Galactic center was 11 x 10^6 s. The regular SIGMA observations revealed great variability of the source:

AIP Conference Proceedings, 1994

X-ray binaries form the bulk of hard x-ray sources, in the 30–300 keV range. More than twenty of ... more X-ray binaries form the bulk of hard x-ray sources, in the 30–300 keV range. More than twenty of them have been detected by SIGMA. Suspected black hole systems seem to be particularly numerous among the sources emitting above 100 keV, and their spectra appear harder than those of neutron star systems. This amounts to a spectral distinction between the two

Astronomy and Astrophysics, May 1, 1976

Astronomy and Astrophysics, 1988

Presentation de nouvelles observations CCD de la contrepartie optique de Geminga (1E0630+178) qui... more Presentation de nouvelles observations CCD de la contrepartie optique de Geminga (1E0630+178) qui montrent que l'objet G″ est bien moins bleu que prevu. La faible luminosite de l'objet est a prendre en consideration pour l'interpretation correcte des donnees. On discute des mecanismes pouvant expliquer l'emission en bande V; en particulier du rayonnement cyclotron d'une etoile a neutrons magnetisee

New Views on Microquasars, 2003

AIP Conference Proceedings, 1994

The authors report the discovery of the radio and infrared counterpart of the hard X-ray transien... more The authors report the discovery of the radio and infrared counterpart of the hard X-ray transient GRS 1915+105 in the constellation of Aquila. The compact object is located beyond ≡30 mag of optical absorption. At radio wavelengths it exhibits drastic time variations in flux which are correlated with changes in the hard X rays. The source also shows unusual varibility

Astron Astrophys Suppl Series, 1993

We report the identification of the radio counterpart of 1E1740.7-2942 and the detection of a dou... more We report the identification of the radio counterpart of 1E1740.7-2942 and the detection of a double radio jet emanating from it. The jet is produced by synchrotron emission from charged particules streaming out from the high energy source. The compact radio source at the center of the double jet is time variable in flux and spectral index. We find that the changes in radio flux are correlated with the variations at hard X-rays observed by SIGMA. After September 1991 the radio flux of the compact source increased with the enhancement in hard X-ray activity. It appears that the central synchrotron source is self-absorbed during the high states of 1E1740.7-2942. Recent observations of GRS1768-258 reveal, as in 1E1740.7-2942, the presence of another triple radio source, whose central component is variable and falls inside the error circle (10 arcsec of radius) of ROSAT.

Astron Astrophys, 1991

Observations of molecular transitions at millimeter wavelengths show that the most powerful compa... more Observations of molecular transitions at millimeter wavelengths show that the most powerful compact source of radiation in the Galaxy resulting from matter-antimatter annihilation may be associated with dense interstellar gas. Coincident with the position of the high energy source 1E1740.7-2942, a molecular cloud is found . This cloud belongs to the inner molecular layer of the galactic center region, since it is located ∼50 arc min from the dynamical center of the Galaxy and has a Doppler shift of −140 km/s. At a distance of 8.5 kpc, it would have a size of ∼3 pc and a mass of ∼5×10 4 M ○ .