diego torres - Academia.edu (original) (raw)
Papers by diego torres
Astrophysical Journal, 2001
We present a correlative study between all unidentified EGRET sources at low Galactic latitudes a... more We present a correlative study between all unidentified EGRET sources at low Galactic latitudes and the newly discovered pulsars in the released portion of the Parkes multibeam radio survey. We note 14 positional coincidences: eight of these are ``Vela-like'' pulsars, with relatively small periods, small characteristic ages, and high spin-down luminosities. Three of these coincidences have been investigated by D'Amico et al. (2001) and Camilo et al. (2001). Among the others, we argue that PSR J1015-5719 may plausibly generate part of the high energy radiation observed from 3EG J1014-5705. Three additional interesting cases are: 3EG J1410-6147 and either of PSRs J1412-6145 or J1413-6141, if the pulsars are at the estimated distance of the coincident SNR G312.4-0.4; and 3EG J1639-4702/PSR J1637-4642. The remaining positional coincidences between the EGRET sources and the newly discovered pulsars are almost certainly spurious.
Inorganic Chemistry, 1997
The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared an... more The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared and used as a building block for four new macrocyclic ligands having mixed side-chain chelating groups. These ligands and their complexes with Mg II , Ca II , and Ln III were studied extensively by potentiometry, high-resolution NMR, and water proton relaxivity measurements. The protonation constants of all compounds compared well with those of other cyclen-based macrocyclic ligands. All Ca II complexes were found to be more stable than the corresponding Mg II complexes. Trends for the stabilities of the Ln III complexes are discussed and compared with literature data, incorporating the effects of water coordination numbers, Ln III contraction, and the nature of the side chains and the steric hindrance between them. 1 H NMR titrations of DO2A revealed that the first and second protonations take place preferentially at the secondary ring nitrogens, while the third and fourth involved protonation of the acetates. 17 O NMR shifts showed that the DyDO2A + complex had two inner-sphere water molecules. Water proton spin-lattice relaxation rates for the GdDO2A + complex were also consistent with water exchange between bulk water and two inner-sphere Gd III coordination positions. Upon formation of the diamagnetic complexes of DO2A (Ca II , Mg II , La III , and Lu III ), all of the macrocyclic ring protons became nonequivalent due to slow conformational rearrangements, while the signals for the acetate CH 2 protons remained a singlet. (8) Cox, J. P. L.; Jankowki, K. J.; Kataky, R.; Baker, D.; Beeley, R. A.; Boyce, B. A.; Eaton, M. A. W.; Miller, K.; Millican, A. T.; Harrison, S.; Warker, C.
Nature, 2002
It is thought that Galactic cosmic ray (CR) nuclei are gradually accelerated to high energies (up... more It is thought that Galactic cosmic ray (CR) nuclei are gradually accelerated to high energies (up to ~300 TeV/nucleon, where 1TeV=10^12eV) in the expanding shock-waves connected with the remnants of powerful supernova explosions. However, this conjecture has eluded direct observational confirmation^1,2 since it was first proposed in 1953 (ref. 3). Enomoto et al.^4 claim to have finally found definitive evidence that corroborates this model, proposing that the very-high-energy, TeV-range, gamma-rays from the supernova remnant (SNR) RX J1713.7-3946 are due to the interactions of energetic nuclei in this region. Here we argue that their claim is not supported by the existing multiwavelength spectrum of this source. The search for the origin(s) of Galactic cosmic ray nuclei may be closing in on the long-suspected supernova-remnant sources, but it is not yet over.
Astronomy & Astrophysics, 2003
The jets of microquasars with high-mass stellar companions are exposed to the dense matter field ... more The jets of microquasars with high-mass stellar companions are exposed to the dense matter field of the stellar wind. We present estimates of the gamma-ray emission expected from the jet-wind hadronic interaction and we discuss the detectability of the phenomenon at high energies. The proposed mechanism could explain some of the unidentified gamma-ray sources detected by EGRET instrument on the galactic plane.
Physical Review D, 1997
Analytical wormhole solutions in Brans-Dicke theory in the presence of matter are presented. It i... more Analytical wormhole solutions in Brans-Dicke theory in the presence of matter are presented. It is shown that the wormhole throat must not be necessarily threaded with exotic matter.
Astrophysical Journal, 2005
For about two decades, a population of relatively small and nearby molecular clouds has been know... more For about two decades, a population of relatively small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10Њ from the Galactic plane, these clouds have typical distances of ∼150 pc, angular sizes of ∼1Њ, and masses of order tens of solar masses. These objects are passive sources of high-energy g-rays through cosmic-ray-gas interactions. Using a new wide-angle CO survey of the northern sky, we show that typical high-latitude clouds are not bright enough in g-rays to have been detected by EGRET but that of order 100 of them will be detectable by the Large Area Telescope on the Gamma-Ray Large Area Space Telescope. Thus, we predict a new steady population of g-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.
Physical Review D, 1998
We present here analytical solutions of General Relativity that describe evolving wormholes with ... more We present here analytical solutions of General Relativity that describe evolving wormholes with a non-constant redshift function. We show that the matter that threads these wormholes is not necessarily exotic. Finally, we investigate some issues concerning WEC violation and human traversability in these time-dependent geometries.
Astrophysical Journal, 2003
It is proposed that TeV gamma-rays and neutrinos can be produced by cosmic rays (CRs) through had... more It is proposed that TeV gamma-rays and neutrinos can be produced by cosmic rays (CRs) through hadronic interactions in the innermost parts of the winds of massive O and B stars. Convection prevents low-energy particles from penetrating into the wind, leading to an absence of MeV-GeV counterparts. It is argued that groups of stars located close to the CR acceleration sites in OB stellar associations may be detectable by ground-based Cherenkov telescopes.
Astrophysical Journal, 2001
The non-thermal supernova remnant RX J1713.7-3946 (G347.3-0.5) has recently been shown to be a si... more The non-thermal supernova remnant RX J1713.7-3946 (G347.3-0.5) has recently been shown to be a site of cosmic ray (CR) electron acceleration to TeV energies (Muraishi et al. 2000). Here we present evidence that this remnant is also accelerating CR nuclei. Such nuclei can interact with ambient interstellar gas to produce high energy gamma-rays via the decay of neutral pions. We associate the unidentified EGRET GeV gamma- ray source 3EG J1714-3857 with a massive (~3*10 5 Mo) and dense (~500 nucleons cm -3) molecular cloud interacting with RX J1713.7-3946. Direct evidence for such interaction is provided by observations of the lowest two rotational transitions of CO in the cloud; as in other clear cases of interaction, the CO(J=2-1)/CO(J=1-0) ratio is significantly enhanced. Since the cloud is of low radio and X-ray brightness, CR electrons cannot be responsible for the bulk of its GeV emission there. A picture thus emerges where both electrons and nuclei are being accelerated by the SNR: whereas the CR electrons dominate the local non-thermal radio, X-ray and TeV emission, the shock accelerated CR protons and ions (hadrons) are revealed through their interactions in the adjacent massive cloud. Such a scenario had been anticipated by Aharonian, Drury and Volk (1994).
Reports on Progress in Physics, 2004
In the first part of this review we discuss the basic observational features at the end of the co... more In the first part of this review we discuss the basic observational features at the end of the cosmic ray energy spectrum. We also present there the main characteristics of each of the experiments involved in the detection of these particles. We then briefly discuss the status of the chemical composition and the distribution of arrival directions of cosmic rays. After that, we examine the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin (GZK) cutoff, and discuss the level of confidence with which each experiment have detected particles beyond the GZK energy limit. In the second part of the review, we discuss astrophysical environments able to accelerate particles up to such high energies, including active galactic nuclei, large scale galactic wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding galaxies, and gamma ray burst fireballs. In the third part of the review we provide a brief summary of scenarios which try to explain the super-GZK events with the help of new physics beyond the standard model. In the last section, we give an overview on neutrino telescopes and existing limits on the energy spectrum and discuss some of the prospects for a new (multi-particle) astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used to probe new physics beyond the electroweak scale.
Physics Reports-review Section of Physics Letters, 2003
A review of the possible relationship between γ-ray sources and supernova remnants (SNRs) is pres... more A review of the possible relationship between γ-ray sources and supernova remnants (SNRs) is presented. Particular emphasis is given to the analysis of the observational status of the problem of cosmic ray acceleration at SNR shock fronts. All positional coincidences between SNRs and unidentified γ-ray sources listed in the Third EGRET Catalog at low Galactic latitudes are discussed on a
A review of the possible relationship between gamma-ray sources and supernova remnants (SNRs) is ... more A review of the possible relationship between gamma-ray sources and supernova remnants (SNRs) is presented. Particular emphasis is given to the analysis of the observational status of the problem of cosmic ray acceleration at SNR shock fronts. All positional coincidences between SNRs and unidentified gamma-ray sources listed in the Third EGRET Catalog at low Galactic latitudes are discussed on a case by case basis. For several coincidences of particular interest, new CO(J=1-0) and radio continuum maps are shown, and the mass content of the SNR surroundings is determined. The contribution to the gamma-ray flux observed that might come from cosmic ray particles (particularly nuclei) locally accelerated at the SNR shock fronts is evaluated. We discuss the prospects for future research in this field and remark on the possibilities for observations with forthcoming gamma-ray instruments.
Astronomische Nachrichten, 2001
We present a Monte Carlo analysis of the recently introduced variability indices tau\tautau (Tompkins... more We present a Monte Carlo analysis of the recently introduced variability indices tau\tautau (Tompkins 1999) and III (Zhang et al. 2000 & Torres et al. 2001) for gamma\gammagamma-ray sources. We explore different variability criteria and prove that these two indices, despite the very different approaches used to compute them, are statistically correlated (5 to 7$\sigma$). This conclusion is maintained also for the subset of AGNs and high latitude ($|b|>10$ deg) sources, whereas the correlation is lowered for the low latitude ones, where the influence of the diffuse galactic emission background is strong.
Astronomy & Astrophysics, 2001
We present a study of the unidentified gamma-ray source 3EG J0542+2610. This source is spatially ... more We present a study of the unidentified gamma-ray source 3EG J0542+2610. This source is spatially superposed to the supernova remnant G180.0-1.7, but its time variability makes unlikely a physical link. We have searched into the EGRET location error box for compact radio sources that could be the low energy counterpart of the gamma-ray source. Although 29 point-like radio sources were detected and measured, none of them is strong enough as to be considered the counterpart of a background gamma-ray emitting AGN. We suggest that the only object within the 95 % error box capable of producing the required gamma-ray flux is the X-ray transient A0535+26. We show that this Be/accreting pulsar can produce variable hadronic gamma-ray emission through the mechanism originally proposed by Cheng & Ruderman (1989), where a proton beam accelerated in a magnetospheric electrostatic gap impacts the transient accretion disk.
Physical Review D, 2001
We study the correlation between compact radio quasars or 3EG gamma-ray blazars and the arrival d... more We study the correlation between compact radio quasars or 3EG gamma-ray blazars and the arrival directions of cosmic rays above 10^19 eV using an updated list of air shower detections. Our Monte Carlo simulations reveal no significant correlations above random and some previous positive results appear to be an effect of the small sample size. Consequently, unless somehow severely deflected, there is no evidence for ultra-high energy cosmic ray primaries being new particles or particles with new interactions beyond the electroweak scale, produced in high-redshift active galactic nuclei.
We present a study on the possible association of unidentified γ-ray sources in the Third EGRET (... more We present a study on the possible association of unidentified γ-ray sources in the Third EGRET (3EG) catalog with different types of galactic objects such as Wolf-Rayet and Of stars, supernova remnants (SNRs), and OB associations (considered as pulsar tracers). We have made use of numerical simulations of galactic populations of γ-ray point sources in order to determine the statistical significance of the positional coincidences. New constraints on pure chance association are presented for SNRs and OB associations. There is overwhelming statistical support for the hypothesis that some SNRs are γray sources (we obtain probabilities of pure chance association < 10 −5 ). OB star associations present higher, but still negligible probabilities (< 10 −3 ). It is also shown that although massive stars present just marginally significant correlation with 3EG sources, there is a posteriori support for at least three candidates.
Physical Review D, 2001
We provide an in depth study of the theoretical peculiarities that arise in effective negative ma... more We provide an in depth study of the theoretical peculiarities that arise in effective negative mass lensing, both for the case of a point mass lens and source, and for extended source situations. We describe novel observational signatures arising in the case of a source lensed by a negative mass. We show that a negative mass lens produces total or partial eclipse of the source in the umbra region and also show that the usual Shapiro time delay is replaced with an equivalent time gain. We describe these features both theoretically, as well as through numerical simulations. We provide negative mass microlensing simulations for various intensity profiles and discuss the differences between them. The light curves for microlensing events are presented and contrasted with those due to lensing produced by normal matter. Presence or absence of these features in the observed microlensing events can shed light on the existence of natural wormholes in the Universe.
Physical Review D, 1998
The extragalactic microlensing scenario for natural wormholes is examined. It is shown that the m... more The extragalactic microlensing scenario for natural wormholes is examined. It is shown that the main features of wormhole lensing events upon the light of distant Active Galactic Nuclei (AGNs) are similar to some types of already observed Gamma Ray Bursts (GRBs). Using recent satellite data on GRBs, an upper limit to the negative mass density -- calO(10−36){\cal O} (10^{-36})calO(10−36) g cm$^{-3}$ -- under the form of wormhole-like objects is presented.
Astrophysical Journal, 2001
We present a correlative study between all unidentified EGRET sources at low Galactic latitudes a... more We present a correlative study between all unidentified EGRET sources at low Galactic latitudes and the newly discovered pulsars in the released portion of the Parkes multibeam radio survey. We note 14 positional coincidences: eight of these are ``Vela-like'' pulsars, with relatively small periods, small characteristic ages, and high spin-down luminosities. Three of these coincidences have been investigated by D'Amico et al. (2001) and Camilo et al. (2001). Among the others, we argue that PSR J1015-5719 may plausibly generate part of the high energy radiation observed from 3EG J1014-5705. Three additional interesting cases are: 3EG J1410-6147 and either of PSRs J1412-6145 or J1413-6141, if the pulsars are at the estimated distance of the coincident SNR G312.4-0.4; and 3EG J1639-4702/PSR J1637-4642. The remaining positional coincidences between the EGRET sources and the newly discovered pulsars are almost certainly spurious.
Inorganic Chemistry, 1997
The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared an... more The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared and used as a building block for four new macrocyclic ligands having mixed side-chain chelating groups. These ligands and their complexes with Mg II , Ca II , and Ln III were studied extensively by potentiometry, high-resolution NMR, and water proton relaxivity measurements. The protonation constants of all compounds compared well with those of other cyclen-based macrocyclic ligands. All Ca II complexes were found to be more stable than the corresponding Mg II complexes. Trends for the stabilities of the Ln III complexes are discussed and compared with literature data, incorporating the effects of water coordination numbers, Ln III contraction, and the nature of the side chains and the steric hindrance between them. 1 H NMR titrations of DO2A revealed that the first and second protonations take place preferentially at the secondary ring nitrogens, while the third and fourth involved protonation of the acetates. 17 O NMR shifts showed that the DyDO2A + complex had two inner-sphere water molecules. Water proton spin-lattice relaxation rates for the GdDO2A + complex were also consistent with water exchange between bulk water and two inner-sphere Gd III coordination positions. Upon formation of the diamagnetic complexes of DO2A (Ca II , Mg II , La III , and Lu III ), all of the macrocyclic ring protons became nonequivalent due to slow conformational rearrangements, while the signals for the acetate CH 2 protons remained a singlet. (8) Cox, J. P. L.; Jankowki, K. J.; Kataky, R.; Baker, D.; Beeley, R. A.; Boyce, B. A.; Eaton, M. A. W.; Miller, K.; Millican, A. T.; Harrison, S.; Warker, C.
Nature, 2002
It is thought that Galactic cosmic ray (CR) nuclei are gradually accelerated to high energies (up... more It is thought that Galactic cosmic ray (CR) nuclei are gradually accelerated to high energies (up to ~300 TeV/nucleon, where 1TeV=10^12eV) in the expanding shock-waves connected with the remnants of powerful supernova explosions. However, this conjecture has eluded direct observational confirmation^1,2 since it was first proposed in 1953 (ref. 3). Enomoto et al.^4 claim to have finally found definitive evidence that corroborates this model, proposing that the very-high-energy, TeV-range, gamma-rays from the supernova remnant (SNR) RX J1713.7-3946 are due to the interactions of energetic nuclei in this region. Here we argue that their claim is not supported by the existing multiwavelength spectrum of this source. The search for the origin(s) of Galactic cosmic ray nuclei may be closing in on the long-suspected supernova-remnant sources, but it is not yet over.
Astronomy & Astrophysics, 2003
The jets of microquasars with high-mass stellar companions are exposed to the dense matter field ... more The jets of microquasars with high-mass stellar companions are exposed to the dense matter field of the stellar wind. We present estimates of the gamma-ray emission expected from the jet-wind hadronic interaction and we discuss the detectability of the phenomenon at high energies. The proposed mechanism could explain some of the unidentified gamma-ray sources detected by EGRET instrument on the galactic plane.
Physical Review D, 1997
Analytical wormhole solutions in Brans-Dicke theory in the presence of matter are presented. It i... more Analytical wormhole solutions in Brans-Dicke theory in the presence of matter are presented. It is shown that the wormhole throat must not be necessarily threaded with exotic matter.
Astrophysical Journal, 2005
For about two decades, a population of relatively small and nearby molecular clouds has been know... more For about two decades, a population of relatively small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10Њ from the Galactic plane, these clouds have typical distances of ∼150 pc, angular sizes of ∼1Њ, and masses of order tens of solar masses. These objects are passive sources of high-energy g-rays through cosmic-ray-gas interactions. Using a new wide-angle CO survey of the northern sky, we show that typical high-latitude clouds are not bright enough in g-rays to have been detected by EGRET but that of order 100 of them will be detectable by the Large Area Telescope on the Gamma-Ray Large Area Space Telescope. Thus, we predict a new steady population of g-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.
Physical Review D, 1998
We present here analytical solutions of General Relativity that describe evolving wormholes with ... more We present here analytical solutions of General Relativity that describe evolving wormholes with a non-constant redshift function. We show that the matter that threads these wormholes is not necessarily exotic. Finally, we investigate some issues concerning WEC violation and human traversability in these time-dependent geometries.
Astrophysical Journal, 2003
It is proposed that TeV gamma-rays and neutrinos can be produced by cosmic rays (CRs) through had... more It is proposed that TeV gamma-rays and neutrinos can be produced by cosmic rays (CRs) through hadronic interactions in the innermost parts of the winds of massive O and B stars. Convection prevents low-energy particles from penetrating into the wind, leading to an absence of MeV-GeV counterparts. It is argued that groups of stars located close to the CR acceleration sites in OB stellar associations may be detectable by ground-based Cherenkov telescopes.
Astrophysical Journal, 2001
The non-thermal supernova remnant RX J1713.7-3946 (G347.3-0.5) has recently been shown to be a si... more The non-thermal supernova remnant RX J1713.7-3946 (G347.3-0.5) has recently been shown to be a site of cosmic ray (CR) electron acceleration to TeV energies (Muraishi et al. 2000). Here we present evidence that this remnant is also accelerating CR nuclei. Such nuclei can interact with ambient interstellar gas to produce high energy gamma-rays via the decay of neutral pions. We associate the unidentified EGRET GeV gamma- ray source 3EG J1714-3857 with a massive (~3*10 5 Mo) and dense (~500 nucleons cm -3) molecular cloud interacting with RX J1713.7-3946. Direct evidence for such interaction is provided by observations of the lowest two rotational transitions of CO in the cloud; as in other clear cases of interaction, the CO(J=2-1)/CO(J=1-0) ratio is significantly enhanced. Since the cloud is of low radio and X-ray brightness, CR electrons cannot be responsible for the bulk of its GeV emission there. A picture thus emerges where both electrons and nuclei are being accelerated by the SNR: whereas the CR electrons dominate the local non-thermal radio, X-ray and TeV emission, the shock accelerated CR protons and ions (hadrons) are revealed through their interactions in the adjacent massive cloud. Such a scenario had been anticipated by Aharonian, Drury and Volk (1994).
Reports on Progress in Physics, 2004
In the first part of this review we discuss the basic observational features at the end of the co... more In the first part of this review we discuss the basic observational features at the end of the cosmic ray energy spectrum. We also present there the main characteristics of each of the experiments involved in the detection of these particles. We then briefly discuss the status of the chemical composition and the distribution of arrival directions of cosmic rays. After that, we examine the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin (GZK) cutoff, and discuss the level of confidence with which each experiment have detected particles beyond the GZK energy limit. In the second part of the review, we discuss astrophysical environments able to accelerate particles up to such high energies, including active galactic nuclei, large scale galactic wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding galaxies, and gamma ray burst fireballs. In the third part of the review we provide a brief summary of scenarios which try to explain the super-GZK events with the help of new physics beyond the standard model. In the last section, we give an overview on neutrino telescopes and existing limits on the energy spectrum and discuss some of the prospects for a new (multi-particle) astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used to probe new physics beyond the electroweak scale.
Physics Reports-review Section of Physics Letters, 2003
A review of the possible relationship between γ-ray sources and supernova remnants (SNRs) is pres... more A review of the possible relationship between γ-ray sources and supernova remnants (SNRs) is presented. Particular emphasis is given to the analysis of the observational status of the problem of cosmic ray acceleration at SNR shock fronts. All positional coincidences between SNRs and unidentified γ-ray sources listed in the Third EGRET Catalog at low Galactic latitudes are discussed on a
A review of the possible relationship between gamma-ray sources and supernova remnants (SNRs) is ... more A review of the possible relationship between gamma-ray sources and supernova remnants (SNRs) is presented. Particular emphasis is given to the analysis of the observational status of the problem of cosmic ray acceleration at SNR shock fronts. All positional coincidences between SNRs and unidentified gamma-ray sources listed in the Third EGRET Catalog at low Galactic latitudes are discussed on a case by case basis. For several coincidences of particular interest, new CO(J=1-0) and radio continuum maps are shown, and the mass content of the SNR surroundings is determined. The contribution to the gamma-ray flux observed that might come from cosmic ray particles (particularly nuclei) locally accelerated at the SNR shock fronts is evaluated. We discuss the prospects for future research in this field and remark on the possibilities for observations with forthcoming gamma-ray instruments.
Astronomische Nachrichten, 2001
We present a Monte Carlo analysis of the recently introduced variability indices tau\tautau (Tompkins... more We present a Monte Carlo analysis of the recently introduced variability indices tau\tautau (Tompkins 1999) and III (Zhang et al. 2000 & Torres et al. 2001) for gamma\gammagamma-ray sources. We explore different variability criteria and prove that these two indices, despite the very different approaches used to compute them, are statistically correlated (5 to 7$\sigma$). This conclusion is maintained also for the subset of AGNs and high latitude ($|b|>10$ deg) sources, whereas the correlation is lowered for the low latitude ones, where the influence of the diffuse galactic emission background is strong.
Astronomy & Astrophysics, 2001
We present a study of the unidentified gamma-ray source 3EG J0542+2610. This source is spatially ... more We present a study of the unidentified gamma-ray source 3EG J0542+2610. This source is spatially superposed to the supernova remnant G180.0-1.7, but its time variability makes unlikely a physical link. We have searched into the EGRET location error box for compact radio sources that could be the low energy counterpart of the gamma-ray source. Although 29 point-like radio sources were detected and measured, none of them is strong enough as to be considered the counterpart of a background gamma-ray emitting AGN. We suggest that the only object within the 95 % error box capable of producing the required gamma-ray flux is the X-ray transient A0535+26. We show that this Be/accreting pulsar can produce variable hadronic gamma-ray emission through the mechanism originally proposed by Cheng & Ruderman (1989), where a proton beam accelerated in a magnetospheric electrostatic gap impacts the transient accretion disk.
Physical Review D, 2001
We study the correlation between compact radio quasars or 3EG gamma-ray blazars and the arrival d... more We study the correlation between compact radio quasars or 3EG gamma-ray blazars and the arrival directions of cosmic rays above 10^19 eV using an updated list of air shower detections. Our Monte Carlo simulations reveal no significant correlations above random and some previous positive results appear to be an effect of the small sample size. Consequently, unless somehow severely deflected, there is no evidence for ultra-high energy cosmic ray primaries being new particles or particles with new interactions beyond the electroweak scale, produced in high-redshift active galactic nuclei.
We present a study on the possible association of unidentified γ-ray sources in the Third EGRET (... more We present a study on the possible association of unidentified γ-ray sources in the Third EGRET (3EG) catalog with different types of galactic objects such as Wolf-Rayet and Of stars, supernova remnants (SNRs), and OB associations (considered as pulsar tracers). We have made use of numerical simulations of galactic populations of γ-ray point sources in order to determine the statistical significance of the positional coincidences. New constraints on pure chance association are presented for SNRs and OB associations. There is overwhelming statistical support for the hypothesis that some SNRs are γray sources (we obtain probabilities of pure chance association < 10 −5 ). OB star associations present higher, but still negligible probabilities (< 10 −3 ). It is also shown that although massive stars present just marginally significant correlation with 3EG sources, there is a posteriori support for at least three candidates.
Physical Review D, 2001
We provide an in depth study of the theoretical peculiarities that arise in effective negative ma... more We provide an in depth study of the theoretical peculiarities that arise in effective negative mass lensing, both for the case of a point mass lens and source, and for extended source situations. We describe novel observational signatures arising in the case of a source lensed by a negative mass. We show that a negative mass lens produces total or partial eclipse of the source in the umbra region and also show that the usual Shapiro time delay is replaced with an equivalent time gain. We describe these features both theoretically, as well as through numerical simulations. We provide negative mass microlensing simulations for various intensity profiles and discuss the differences between them. The light curves for microlensing events are presented and contrasted with those due to lensing produced by normal matter. Presence or absence of these features in the observed microlensing events can shed light on the existence of natural wormholes in the Universe.
Physical Review D, 1998
The extragalactic microlensing scenario for natural wormholes is examined. It is shown that the m... more The extragalactic microlensing scenario for natural wormholes is examined. It is shown that the main features of wormhole lensing events upon the light of distant Active Galactic Nuclei (AGNs) are similar to some types of already observed Gamma Ray Bursts (GRBs). Using recent satellite data on GRBs, an upper limit to the negative mass density -- calO(10−36){\cal O} (10^{-36})calO(10−36) g cm$^{-3}$ -- under the form of wormhole-like objects is presented.