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Diego F. Torres

Publications and source records attributed to Diego F. Torres.

At least 181 records · Page 10Linked to original sources
arXiv2001

On the time variability of gamma-ray sources: A numerical analysis of variability indices

We present a Monte Carlo analysis of the recently introduced variability indices $τ$ (Tompkins 1999) and $I$ (Zhang et al. 2000 & Torres et al. 2001) for $γ$-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$σ$). 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.

astro-ph↗
arXiv2001

The Mysterious Ultrahigh Energy Cosmic Ray Clustering

We examine the correlation between compact radio quasars (redshifts in the range $z = 0.3 - 2.2$) and the arrival direction of ultrahigh energy cosmic rays forming clusters. Our Monte Carlo simulation reveals a statistically significant correlation on the AGASA sample: the chance probability of this effect being less than 1%. The implications of this result on the origin of ultrahigh energy cosmic rays are discussed.

astro-ph↗
arXiv2001

Is the Supernova Remnant RX J1713.7-3946 a Hadronic Cosmic Ray Accelerator ?

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).

astro-ph↗
arXiv2001

Recently discovered pulsars and unidentified EGRET sources

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.

astro-ph↗
arXiv2001

Variable gamma-ray emission from the Be/X-ray transient A0535+26?

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.

astro-ph↗
arXiv2001

Self-existing objects and auto-generated information in chronology-violating space-times: A philosophical discussion

Closed time-like curves naturally appear in a variety of chronology-violating space-times. In these space-times, the Principle of Self-Consistency demands an harmony between local and global affairs that excludes grandfather-like paradoxes. However, self-existing objects trapped in CTCs are not seemingly avoided by the standard interpretation of this principle, usually constrained to a dynamical framework. In this paper we discuss whether we are committed to accept an ontology with self-existing objects if CTCs actually occur in the universe. In addition, the epistemological status of the Principle of Self-Consistency is analyzed and a discussion on the information flux through CTCs is presented.

gr-qc↗
arXiv2001

Microlensing by natural wormholes: theory and simulations

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.

gr-qc↗
arXiv2001

Statistical mechanics and the description of the early universe I.: Foundations for a slightly non-extensive cosmology

We analyze how the thermal history of the universe is influenced by the statistical description, assuming a deviation from the usual Bose-Einstein, Fermi-Dirac and Boltzmann-Gibbs distribution functions. These deviations represent the possible appearance of non-extensive effects related with the existence of long range forces, memory effects, or evolution in fractal or multi-fractal space. In the early universe, it is usually assumed that the distribution functions are the standard ones. Then, considering the evolution in a larger theoretical framework will allow to test this assumption and to place limits to the range of its validity. The corrections obtained will change with temperature, and consequently, the bounds on the possible amount of non-extensivity will also change with time. We generalize results which can be used in other contexts as well, as the Boltzmann equation and the Saha law, and provide an estimate on how known cosmological bounds on the masses of neutrinos are modified by a change in the statistics. We particularly analyze here the recombination epoch, making explicit use of the chemical potentials involved in order to attain the necessary corrections. All these results constitute the basic tools needed for placing bounds on the amount of non-extensivity that could be present at different eras and will be later used to study primordial nucleosynthesis.

gr-qc↗
arXiv2001

Statistical mechanics and the description of the early universe II. Principle of detailed balance and primordial 4He formation

If the universe is slightly non-extensive, and the distribution functions are not exactly given by those of Boltzmann-Gibbs, the primordial production of light elements will be non-trivially modified. In particular, the principle of detailed balance (PDB), of fundamental importance in the standard analytical analysis, is no longer valid, and a non-extensive correction appears. This correction is computed and its influence is studied and compared with previous works, where, even when the universe was considered as an slightly non-extensive system, the PDB was assumed valid. We analytically track the formation of Helium and Deuterium, and study the kind of deviation one could expect from the standard regime. The correction to the capture time, the moment in which Deuterium can no longer be substantially photo-disintegrated, is also presented. This allows us to take into account the process of the free decay of neutrons, which was absent in all previous treatments of the topic. We show that even when considering a first (linear) order correction in the quantum distribution functions, the final output on the primordial nucleosynthesis yields cannot be reduced to a linear correction in the abundances. We finally obtain new bounds upon the non-extensive parameter, both comparing the range of physical viability of the theory, and using the latest observational data.

gr-qc↗
arXiv2001

Chromaticity effects in microlensing by wormholes

Chromaticity effects introduced by the finite source size in microlensing events by presumed natural wormholes are studied. It is shown that these effects provide a specific signature that allow to discriminate between ordinary and negative mass lenses through the spectral analysis of the microlensing events. Both galactic and extragalactic situations are discussed.

gr-qc↗
arXiv2001

A Study of the Unidentified Gamma-Ray Source 3EG J1828+0142

We present a study of the radio environment of the gamma-ray source 3EG J1828+0142. This source presents a very high variability index in its gamma emission and a steep high-energy spectral index $Γ\sim-2.8$. Large-scale radio maps at different frequencies show the presence of a shell-type non-thermal structure when the diffuse emission from the Galactic disk is eliminated. At small scales, VLA radio images reveal the existence of several weak point sources within the 95 % gamma-ray confidence location contour. Most of these sources present non-thermal spectral indices, but it is not clear whether they are extragalactic or not. We discuss the possibility of a scenario where the large structure is a SNR and one of the compact radio sources is an isolated black hole also produced in the original supernova explosion. The black hole could be responsible for the variable gamma-ray emission according to Punsly's (1998) model. INTEGRAL observations with IBIS imager could detect the inverse Compton and blueshifted pair annihilation radiation from the relativistic electron-positron jets of the hole. Some estimates are presented in this regard.

astro-ph↗
arXiv2001

Non-extensivity Effects and the Highest Energy Cosmic Ray Affair

Recent measurements of the cosmic microwave background confirm that it is described by a Planckian distribution with high precision. It is non-extensivity bounded to be less than some parts in $10^5$, or to some parts in $10^4$ at most. This deviation may appear minuscule, but may have a non-negligible effect on a particle propagating through this background over the course of millions of years. In this paper we analyze the possible influence of such a slight deviation upon the propagation of nuclei and protons of ultra-high energy. These particles interact via photopion and photodisintegration processes which we examine taking into account a slight non-extensive background. We show that such a deviation does not exhibit a significant difference in the energy attenuation length of extremely high energy cosmic rays.

cond-mat↗
arXiv2001

Macrolensing signatures of large-scale violations of the weak energy condition

We present a set of simulations of the macrolensing effects produced by large-scale cosmological violations of the energy conditions. These simulations show how the appearance of a background field of galaxies is affected when lensed by a region with an energy density equivalent to a negative mass ranging from $10^{12}$ to $10^{17}$ solar masses. We compare with the macrolensing results of equal amounts of positive mass, and show that, contrary to the usual case where tangential arc-like structures are expected, there appear radial arcs-runaway filaments-and a central void. These results make the cosmological macrolensing produced by space-time domains where the weak energy conditions is violated, observationally distinguishable from standard regions. Whether large domains with negative energy density indeed exist in the universe can now be decided by future observations of deep fields.

astro-ph↗
arXiv2001

A variability analysis of low-latitude unidentified gamma-ray sources

We present a study of 40 low-latitude unidentified 3EG gamma-ray sources which were found to be not positionally coincident with any known class of potential gamma-ray emitters in the Galaxy (Romero, Benaglia & Torres, 1999). We have performed a variability analysis which reveals that many of these 40 sources are variable. These sources have, in addition, a steep mean value of the gamma-ray spectral index, $<Γ> = 2.41 \pm 0.2$, which, combined with the high level of variability seems to rule out a pulsar origin. The positional coincidences with uncatalogued candidates to supernova remnants were also studied. Only 7 sources in the sample are spatially coincident with these candidates, a result that is shown to be consistent with the expected level of pure chance association. A complementary search for weak radio counterparts was also conducted and the results are presented as an extensive table containing all significant point-like radio sources within the 40 EGRET fields. We argue that in order to produce the high variability, steep gamma-ray spectra, and absence of strong radio counterparts observed in some of the gamma-ray sources of our sample a new class of objects should be postulated, and we analyze a viable candidate.

astro-ph↗
arXiv2001

Variable Unidentified Gamma-Ray Sources Near the Galactic Plane

In a recent paper, Romero et al. (1999) have presented the results of a positional correlation analysis of the low-latitude unidentified gamma-ray sources in the Third EGRET catalog with complete lists of galactic objects like supernova remnants, early type stars with strong stellar winds, and OB associations (considered as pulsar tracers). We have now carried out a study of those 42 sources at |b|<10 deg for which no counterpart was found at all. A variability analysis shows that this sample contains a population of sources with high levels of variability at gamma-rays. The surface density of these variable sources is 5 times higher than what is expected for unidentified AGNs seen through the Galactic plane. We discuss the origin of this presumed Galactic population of gamma-ray objects and the role that INTEGRAL could play in their physical identification.

astro-ph↗
arXiv2000

Supermassive boson stars: prospects for observational detection

In a recent work (Torres, Capozziello and Lambiase, Physical Review D62, 104012 (2000)), it was shown that a supermassive boson star could provide an alternative model for the galactic center, usually assumed as a black hole. Here we comment on some of the possibilities to actually detect this object, and how can it be distinguished from the standard and other alternative models.

gr-qc↗
arXiv2000

Positional correlation between low-latitude gamma-ray sources and SNRs

We present the results of a spatial correlation analysis between unidentified gamma-ray sources in the 3EG catalog and candidates to supernova remnants. This work extends a previous study made by Romero, Benaglia & Torres (1999). We also consider the gamma-ray emission variability and the spectral index for the sources with positional coincidence.

astro-ph↗