Diego F. Torres' research

Observational and theoretical inquiries on compact objects, relativistic environments, and cosmic-ray astrophysics

Some of the questions tackled in my research

Radiation and dynamics of pulsar wind nebulae

Multifrequency emission from pulsars and magnetars

Gamma-ray binaries and transitional pulsars

Cosmic-ray feedback and ultra-high energy cosmic rays

A few selected, recent papers

Pulsar wind nebulae beyond reverberation

R. Bandiera, N. Bucciantini, B. Olmi &  DFT; MNRAS 2023 [paper]

The vast majority of pulsar wind nebulae (PWNe) present in the Galaxy is formed by middle-aged systems characterized by a strong interaction of the PWN itself with the supernova remnant (SNR). Unfortunately, modelling these systems can be quite complex and numerically expensive, due to the non-linearity of the PWN-SNR evolution even in the simple one-dimensional (1D)/one-zone case when the reverse shock of the SNR reaches the PWN, and the two begin to interact (and reverberation starts). Here, we introduce a new numerical technique that couples the numerical efficiency of the one-zone thin shell approach with the reliability of a full 'Lagrangian' evolution, able to correctly reproduce the PWN-SNR interaction during the reverberation, and to consistently evolve the particle spectrum beyond. Based on our previous findings, we show that our novel strategy resolves many of the uncertainties present in previous approaches, as the arbitrariness in the SNR structure, and ensure a robust evolution, compatible with results that can be obtained with more complex 1D dynamical approaches. Our approach enable us for the first time to provide reliable spectral models of the later compression phases in the evolution of PWNe. While in general, we found that the compression is less extreme than that obtained without such detailed dynamical considerations, leading to the formation of less structured spectral energy distributions, we still find that a non-negligible fraction of PWNe might experience a super-efficient phase, with the optical and/or X-ray luminosity exceeding the spin-down one.

Visualizing the pulsar population using graph theory

C. R. García,  DFT, A. Patruno; MNRAS 2022 [paper]

C. R. García,  DFT, MNRAS 2023 [paper]

The PP˙-diagram is a cornerstone of pulsar research. It is used in multiple ways for classifying the population, understanding evolutionary tracks, identifying issues in our theoretical reach, and more. However, we have been looking at the same plot for more than five decades. A fresh appraisal may be healthy. Is the PP˙-diagram the most useful or complete way to visualize the pulsars we know? Here we pose a fresh look at the information we have on the pulsar population. First, we use principal components analysis over magnitudes depending on the intrinsic pulsar's timing properties (proxies to relevant physical pulsar features), to analyze whether the information contained by the pulsar's period and period derivative is enough to describe the variety of the pulsar population. Even when the variables of interest depend on P and P˙, we show that they are not principal components. Thus, any distance ranking or visualization based only on P and P˙ is potentially misleading. Next, we define and compute a properly normalized distance to measure pulsar nearness, calculate the minimum spanning tree of the population, and discuss possible applications. The pulsar tree hosts information about pulsar similarities that go beyond P and P˙, and are thus naturally difficult to read from the PP˙-diagram. We use this work to introduce the pulsar tree website containing visualization tools and data to allow users to gather information in terms of MST and distance ranking. 

Radio pulsations from a neutron star within the gamma-ray binary LS I +61 303

S. Weng*, L. Qian, B. Wang, DFT*, A. Papitto, P. Jiang, R. Xu, J. Li, J. Yan, Q. Liu, M. Ge, Q. Yuan; Nature Astronomy (2022) [paper] [*: corresponding authors]

LS I +61 303 is one of the rare gamma-ray binaries emitting most of their luminosity in photons with energies beyond 100 MeV.  The 26.5 d orbital period is clearly detected  at many wavelengths. Additional aspects of its multi-frequency behavior make it the most interesting example of the class. The morphology of high-resolution radio images changes with orbital phase displaying a cometary tail pointing away from the high-mass star. LS I +61 303 also shows superorbital variability. A couple of energetic (~ 10^37 erg s^-1), short, magnetar-like bursts have been plausibly ascribed to it. LS I +61 303's phenomenology has been put under theoretical scrutiny for decades, but the lack of certainty regarding the nature of the compact object in the binary has prevented  advancing our understanding of the source. Here, using observations done with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we report on the existence of transient radio pulsations from the direction of LS I +61 303. We find a period P=269.15508 \pm 0.00016 ms at a significance of > 20\sigma. This is the first evidence for pulsations from this source at any frequency, and strongly argues for the existence of a rotating neutron star in LS I +61 303.

The website cover image was produced by D. F. Torres on the ocassion of the paper 'Order parameters for the high-energy spectra of pulsars', Nature Astronomy, Volume 2, p. 247-256 (2018).