Papers by Deborah Aguilera
arXiv (Cornell University), Dec 20, 2004
We study the phase structure and equation of state for two-flavor quark matter at low temperature... more We study the phase structure and equation of state for two-flavor quark matter at low temperature under compact star constraints within a nonlocal chiral quark model. We find that the occurence of a two-flavor color superconducting (2SC) phase is sensitive to variations of both the formfactor of the interaction and the ratio η between the coupling constants in the diquark and the scalar meson channels. Our study suggests that for standard values of the coupling ratio 0.5 < η < 0.75 either the 2SC phase does not occur (Gaussian formfactor) or it exists only in a mixed phase with normal quark matter (NQ-2SC) with a volume fraction less than 20 − 40 %, occuring at high baryon chemical potentials µ B > 1200 MeV and most likely not relevant for compact stars. We also present the relevant region of the phase diagram for compact star applications and obtain that no gapless 2SC occurs at low temperatures.
Nuclear Physics, Aug 1, 2005
We study the phase structure and equation of state for two-flavor quark matter at low temperature... more We study the phase structure and equation of state for two-flavor quark matter at low temperature under compact star constraints within a nonlocal chiral quark model. We find that the occurence of a two-flavor color superconducting (2SC) phase is sensitive to variations of both the formfactor of the interaction and the ratio η between the coupling constants in the diquark and the scalar meson channels. Our study suggests that for standard values of the coupling ratio 0.5 < η < 0.75 either the 2SC phase does not occur (Gaussian formfactor) or it exists only in a mixed phase with normal quark matter (NQ-2SC) with a volume fraction less than 20 − 40 %, occuring at high baryon chemical potentials µ B > 1200 MeV and most likely not relevant for compact stars. We also present the relevant region of the phase diagram for compact star applications and obtain that no gapless 2SC occurs at low temperatures.
Physical review, Jun 23, 2004
Physical review, Aug 9, 2005
We study a spin-1 single flavor color superconducting phase which results from a color-spin locki... more We study a spin-1 single flavor color superconducting phase which results from a color-spin locking (CSL) interaction in two-flavor quark matter. This phase is particularly interesting for compact star cooling applications since the CSL phase may survive under charge neutrality constraints implying a mismatch between up-and down-quark chemical potentials which can destroy the scalar diquark condensate. CSL gaps are evaluated within an NJL model and they are found to be consistent with cooling phenomenology if a density dependent coupling constant is used.
Proceedings of the International Astronomical Union, Sep 1, 2010
Accreting neutron stars can produce jets only if they are weakly magnetized (B ∼ 10 8 G). On the ... more Accreting neutron stars can produce jets only if they are weakly magnetized (B ∼ 10 8 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ∼ 10 12 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor star once the magnetic field has decayed due to accretion. We solve the induction equation for the magnetic field diffusion in a realistic neutron star crust and discuss the possibility of jet launching in systems like the recently detected Supergiant Fast X-ray Transients.
Astronomy and Astrophysics, Apr 22, 2015
Context. We monitored the quiescent thermal emission from neutron stars in low-mass X-ray binarie... more Context. We monitored the quiescent thermal emission from neutron stars in low-mass X-ray binaries after active periods of intense activity in X-rays (outbursts). Aims. The theoretical modeling of the thermal relaxation of the neutron star crust may be used to establish constraints on the crust composition and transport properties, depending on the astrophysical scenarios assumed. Methods. We numerically simulated the thermal evolution of the neutron star crust and compared them with inferred surface temperatures for five sources:
Astronomy and Astrophysics, Apr 22, 2008
Context. Many thermally emitting, isolated neutron stars have magnetic fields that are larger tha... more Context. Many thermally emitting, isolated neutron stars have magnetic fields that are larger than 10 13 G. A realistic cooling model that includes the presence of high magnetic fields should be reconsidered. Aims. We investigate the effects of an anisotropic temperature distribution and Joule heating on the cooling of magnetized neutron stars. Methods. The 2D heat transfer equation with anisotropic thermal conductivity tensor and including all relevant neutrino emission processes is solved for realistic models of the neutron star interior and crust. Results. The presence of the magnetic field affects significantly the thermal surface distribution and the cooling history during both, the early neutrino cooling era and the late photon cooling era. Conclusions. There is a large effect of Joule heating on the thermal evolution of strongly magnetized neutron stars. Both magnetic fields and Joule heating play an important role in keeping magnetars warm for a long time. Moreover, this effect is important for intermediate field neutron stars and should be considered in radio-quiet isolated neutron stars or high magnetic field radio-pulsars.
This report is generated with reference to the 39th DLR CE Study in August 2013, which was aimed ... more This report is generated with reference to the 39th DLR CE Study in August 2013, which was aimed to analyze the application of DLR’s Compact Satellite Bus for a Kennedy-Thorndike experiment in space, named “BOOst Symmetry Test (BOOST)”. While the CE study mainly focused on the payload, a subsequent workshop in September 2013 analyzed the experiment within the DLR compact satellite bus and post-processing up to now (November 2015) followed. For each study domain or subsystem as investigated during the study the elaborated options are covered in individual chapters. The chapters are chronologically subdivided into sections covering the results of the CE-study, the workshop and post-processing
International Journal of Modern Physics D, Jun 1, 2010
Context. We monitored the quiescent thermal emission from neutron stars in low-mass X-ray binarie... more Context. We monitored the quiescent thermal emission from neutron stars in low-mass X-ray binaries after active periods of intense activity in x-rays (outbursts). Aims. The theoretical modeling of the thermal relaxation of the neutron star crust may be used to establish constraints on the crust composition and transport properties, depending on the astrophysical scenarios assumed. Methods. We numerically simulated the thermal evolution of the neutron star crust and compared them with inferred surface temperatures for five sources:
arXiv (Cornell University), Oct 25, 2007
We present 2D simulations of the cooling of neutron stars with strong magnetic fields (B \geq 10^... more We present 2D simulations of the cooling of neutron stars with strong magnetic fields (B \geq 10^{13} G). We solve the diffusion equation in axial symmetry including the state of the art microphysics that controls the cooling such as slow/fast neutrino processes, superfluidity, as well as possible heating mechanisms. We study how the cooling curves depend on the the magnetic field strength and geometry. Special attention is given to discuss the influence of magnetic field decay. We show that Joule heating effects are very large and in some cases control the thermal evolution. We characterize the temperature anisotropy induced by the magnetic field for the early and late stages of the evolution of isolated neutron stars.
arXiv (Cornell University), May 20, 2015
The observation of thermal emission from isolated neutron stars and the modeling of the correspon... more The observation of thermal emission from isolated neutron stars and the modeling of the corresponding cooling curves has been very useful to get information on the properties of matter at very high densities. More recently, the detection of quiescent thermal emission from neutron stars in low mass X-ray binary systems after active periods opened a new window to the physics of matter at lower densities. Here we analyze a few sources that have been recently monitored and we show how the models can be used to establish constraints on the crust composition and their transport properties, depending on the astrophysical scenarios assumed.
arXiv (Cornell University), Mar 4, 2008
We present two-dimensional simulations for the cooling of neutron stars with strong magnetic fiel... more We present two-dimensional simulations for the cooling of neutron stars with strong magnetic fields (B ≥ 10 13 G). We study how the cooling curves are influenced by magnetic field decay. We show that the Joule heating effects are very large and in some cases control the thermal evolution. We characterize the temperature anisotropy induced by the magnetic field and predict the surface temperature distribution for the early and late stages of the evolution of isolated neutron stars, comparing our results with available observational data of isolated neutron stars.
Astrophysics and Space Science, Mar 15, 2007
We present a short general overview of the main features of exotic models of neutron stars, focus... more We present a short general overview of the main features of exotic models of neutron stars, focusing on the structural and dynamical predictions derived from them. In particular, we discuss the presence of "normal" quark matter and Color-Flavor Locked (CFL) states, including their possible self-bound versions, and mention some different proposals emerging from the study of QCD microphysics. A connection with actual observed data is the main goal to be addressed at this talk and along the meeting. It is demonstrated that exotic equations of state are not soft if the vacuum contributions are large enough, and argued that recent measurements of high pulsar masses (M ≥ 2 M ⊙) create problems for hadronic models in which hyperons should be present.
The proposal Autonomous X-ray Pulsar-based Deep Space Navigation System will be presented as a pr... more The proposal Autonomous X-ray Pulsar-based Deep Space Navigation System will be presented as a project of the Institute of Space Systems at the German Aerospace Center (DLR). The aim of this project is to develop enabling technologies for autonomous navigation in deep space using pulsars visible in X-rays. These include the investigation of synchronization of high performance frequency standards with X-ray pulses and the development of the corresponding navigation algorithms
An equation of state for 2-flavor quark matter (QM) with diquark condensation under the condition... more An equation of state for 2-flavor quark matter (QM) with diquark condensation under the conditions for compact stars-β-equilibrium, charge and color neutrality-is presented. Trapped antineutrinos prevent the formation of the diquark condensate at moderate densities above a critical value of the antineutrino chemical potential µ c νe. The following consequences are presented: 1) The star develops a 2-phase structure (µν e ≥ µ c νe): a color superconducting QM core and a normal QM shell. 2)During the cooling, when the temperature is small enough (T < 1 MeV) the antineutrino mean free path becomes larger than the thickness of the normal QM shell and the antineutrinos get untrapped in a sudden burst. The energy release is estimated as ≃ 10 52 erg and an antineutrino pulse is expected to be observed.
Springer eBooks, 2006
We investigate a nonlocal chiral quark model with separable 4-fermion interaction for the case of... more We investigate a nonlocal chiral quark model with separable 4-fermion interaction for the case of U(3) flavor symmetry and show that strange quark matter is unlikely to occur in a large enough volume of a compact star to entail remarkable observational consequences. The phase diagram in the two-flavor sector of such model has a critical end point of the line of first order chiral/deconfinement phase transitions on which a triple point marks the junction with the critical line for second order phase transitions to two-flavor color superconductivity (2SC) below T ~ 80 MeV. Stable hybrid star configurations with large quark matter core in a color superconducting phase can exist. We suggest that for accreting compact stars in Low-mass X-ray binary (LMXB) systems a population gap in the phase diagram (Ω-M plane) for rotating compact star configurations would be an observable indicator of such a quark matter core. A consistent cooling phenomenology for such hybrid stars requires that no direct Urca type fast cooling process in the hadronic shell occurs and that all quark species be gapped, with the minimum pairing gap being a decreasing function of the chemical potential in the range of 1 MeV to 10 keV. We discuss possible implications of a QCD phase transition for the early evolution of hot proto-neutron stars regarding delayed energy release by neutrinos and a possible gamma-ray burst (GRB) mechanism.
Astronomy and Astrophysics, May 1, 2014
Context. In the magneto-centrifugal mechanism for jet formation, accreting neutron stars are assu... more Context. In the magneto-centrifugal mechanism for jet formation, accreting neutron stars are assumed to produce relativistic jets only if their surface magnetic field is weak enough (B ∼ 10 8 G). However, the most common manifestation of neutron stars are pulsars, whose magnetic field distribution peaks at B ∼ 10 12 G. If the neutron star magnetic field has at least this strength at birth, it must decay considerably before jets can be launched in binary systems. Aims. We study the magnetic field evolution of a neutron star that accretes matter from the wind of a high-mass stellar companion so that we can constrain the accretion rate and the impurities in the crust, which are necessary conditions for jet formation. Methods. We solved the induction equation for the diffusion and convection of the neutron star magnetic field confined to the crust, assuming spherical accretion in a simpliflied one-dimensional treatment. We incorporated state-of-the-art microphysics, including consistent thermal evolution profiles, and assumed two different neutron star cooling scenarios based on the superfluidity conditions at the core. Results. We find that in this scenario, magnetic field decay at long timescales is governed mainly by the accretion rate, while the impurity content and thermal evolution of the neutron star play a secondary role. For accretion ratesṀ > ∼ 10 −10 M yr −1 , surface magnetic fields can decay up to four orders of magnitude in ∼10 7 yr, which is the timescale imposed by the evolution of the high-mass stellar companion in these systems. Based on these results, we discuss the possibility of transient jet-launching in strong windaccreting high-mass binary systems like supergiant fast X-ray transients.
Astronomy and Astrophysics, Mar 1, 2004
We study the consequences of antineutrino trapping in hot quark matter for quark star configurati... more We study the consequences of antineutrino trapping in hot quark matter for quark star configurations with possible diquark condensation. Due to the conditions of charge neutrality and β-equilibrium the flavor asymmetry increases with the number density of trapped antineutrinos. Above a critical value of the antineutrino chemical potential of 30 MeV, diquark condensation is inhibited at low densities and a two-phase structure emerges: a superconducting quark matter core surrounded by a shell of normal quark matter. When the quark star cools below a temperature T ∼ 1 MeV, the mean free path of antineutrinos becomes larger than the thickness of the normal quark matter shell so that they become suddenly untrapped. By comparing the masses of configurations with the same baryon number we estimate that the release of energy due to the antineutrino untrapping transition can be in the range of 10 51-10 52 erg.
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Papers by Deborah Aguilera