The 26.3-h orbit and multiwavelength properties of the 'redback' millisecond pulsar PSR J1306-40

We present the discovery of the variable optical and X-ray counterparts to the radio millisecond pulsar (MSP) PSR J1306–40, recently discovered by Keane et al. We find that both the optical and X-ray fluxes are modulated with the same period, which allows us to measure for the first time the orbital period Porb = 1.097¿16[6] d. The optical properties are consistent with a main-sequence companion with spectral type G to mid K and, together with the X-ray luminosity (8.8¿×¿1031¿erg¿s-1 in the 0.5–10¿keV band, for a distance of 1.2¿kpc), confirm the redback classification of this pulsar. Our results establish the binary nature of PSR J1306–40, which has the longest Porb among all known compact binary MSPs in the Galactic disc. We briefly discuss these findings in the context of irradiation and intrabinary shock emission in compact binary MSPs.Postprint (published version

A Gaia view of the optical and X-ray luminosities of compact binary millisecond pulsars

In this paper, we study compact binary millisecond pulsars with low- and very low-mass companion stars (spiders) in the Galactic field, using data from the latest Gaia data release (DR3). We infer the parallax distances of the optical counterparts to spiders, which we use to estimate optical and X-ray luminosities. We compare the parallax distances to those derived from radio pulse dispersion measures and find that they have systematically larger values, by 40 per cent on average. We also test the correlation between X-ray and spin-down luminosities, finding that most redbacks have a spin-down to X-ray luminosity conversion efficiency of ~0.1 per cent, indicating a contribution from the intrabinary shock. On the other hand, most black widows have an efficiency of ~0.01 per cent, similar to the majority of the pulsar population. Finally, we find that the bolometric optical luminosity significantly correlates with the orbital period, with a large scatter due to different irradiated stellar temperatures and binary properties. We interpret this correlation as the effect of the increasing size of the Roche Lobe radius with the orbital period. With this newly found correlation, an estimate of the optical magnitude can be obtained from the orbital period and a distance estimate.Peer ReviewedPostprint (published version

The binary millisecond pulsar PSR J1023+0038-II. Optical spectroscopy

We present time-resolved optical spectroscopy of the ‘redback’ binary millisecond pulsar system PSR¿J1023+0038 during both its radio pulsar (2009) and accretion disc states (2014 and 2016). We provide observational evidence for the companion star being heated during the disc state. We observe a spectral type change along the orbit, from ~G5 to ~F6 at the secondary star’s superior and inferior conjunction, respectively, and find that the corresponding irradiating luminosity can be powered by the high-energy accretion luminosity or the spin-down luminosity of the neutron star. We determine the secondary star’s radial velocity semi-amplitude from the metallic (primarily Fe and Ca) and Ha absorption lines during these different states. The metallic and Ha radial velocity semi-amplitude determined from the 2009 pulsar-state observations allows us to constrain the secondary star’s true radial velocity K2 = 276.3 ± 5.6 ¿km¿s-1 and the binary mass ratio q = 0.137 ± 0.003. By comparing the observed metallic and Ha absorption-line radial velocity semi-amplitudes with model predictions, we can explain the observed semi-amplitude changes during the pulsar state and during the pulsar/disc-state transition as being due to different amounts of heating and the presence of an accretion disc, respectively.Postprint (published version

The 1989 and 2015 outbursts of V404 Cygni: a global study of wind-related optical features

Peer ReviewedPreprin

XIPE: the x-ray imaging polarimetry explorer

XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially-resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics. Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega launcher. XIPE is designed as an observatory for X-ray astronomers with 75 % of the time dedicated to a Guest Observer competitive program and it is organized as a consortium across Europe with main contributions from Italy, Germany, Spain, United Kingdom, Poland, Sweden

Multiband study of RX J0838-2827 and XMM J083850.4-282759: a new asynchronous magnetic cataclysmic variable and a candidate transitional millisecond pulsar

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017. The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.In a search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we performed a multiwavelength campaign: in the X-ray band with Swift and XMM-Newton; in the infrared and optical with OAGH, ESO-NTT and IAC80; and in the radio with ATCA observations. We also used archival hard X-ray data obtained by INTEGRAL. We report on three X-ray sources consistent with the position of the Fermi-LAT source.We confirm the identification of the brightest object, RX J0838-2827, as a magnetic cataclysmic variable that we recognize as an asynchronous system (not associated with the Fermi-LAT source). RX J0838-2827 is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as being caused by the binary system orbital period of ~1.64 h and the white dwarf spin period of ~1.47 h. A strong flux modulation at ~15 h is observed at all energy bands, consistent with the beat frequency between spin and orbital periods. Optical spectra show prominent Hß, He I and He II emission lines that are Doppler-modulated at the orbital period and at the beat period. Therefore, RX J0838-2827 accretes through a disc-less configuration and could be either a strongly asynchronous polar or a rare example of a pre-polar system on its way to reaching synchronism. Regarding the other two X-ray sources, XMM J083850.4-282759 showed a variable X-ray emission, with a powerful flare lasting for ~600 s, similar to what is observed in transitional millisecond pulsars during the subluminous disc state: this observation possibly means that this source can be associated with the Fermi-LAT source.Peer ReviewedPostprint (published version

Gamma-ray observations of MAXI J1820+070 during the 2018 outburst

MAXI J1820+070 is a low-mass X-ray binary with a black hole (BH) as a compact object. This binary underwent an exceptionally bright X-ray outburst from 2018 March to October, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 h of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy (HE) gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to ~500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential HE and very-HE gamma-ray emitting region should be located at a distance from the BH ranging between 1011 and 1013 cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA.Peer ReviewedPostprint (author's final draft

The Neutron Star Population in M28: A Joint Chandra/GBT Look at Pulsar Paradise

We present the results of a deep study of the neutron star (NS) population in the globular cluster M28 (NGC 6626), using the full 330 ks 2002–2015 ACIS data set from the Chandra X-ray Observatory and coordinated radio observations taken with the Green Bank Telescope (GBT) in 2015. We investigate the X-ray luminosity (LX), spectrum, and orbital modulation of the seven known compact binary millisecond pulsars in the cluster. We report two simultaneous detections of the redback PSR J1824-2452I (M28I) and its X-ray counterpart at LX = [8.3 ± 0.9] × 1031 erg s-1. We discover a double-peaked X-ray orbital flux modulation in M28I during its pulsar state, centered around pulsar inferior conjunction. We analyze the spectrum of the quiescent NS low-mass X-ray binary to constrain its mass and radius. Using both hydrogen and helium NS atmosphere models, we find an NS radius of R = 9.2–11.5 km and R = 13.0–17.5 km, respectively, for an NS mass of 1.4 M¿ (68% confidence ranges). We also search for long-term variability in the 46 brightest X-ray sources and report the discovery of six new variable low-luminosity X-ray sources in M28.Peer ReviewedPostprint (published version

Curs 0: preparació per als estudis a l’EEBE

Aquest article presenta el desenvolupament i primers resultats d'ús d'un conjunt de cursos virtuals que pretenen proporcionar uns coneixements inicials bàsics de Matemàtiques, Física i !ímica als estudiants que accedeixen a estudis de grau a l'Escola d'Enginyeria de Barcelona Est (EEBE). Els cursos han estat desenvolupats sobre la plataforma Atenea (Moodle). El seu nucli el constitueixen un conjunt de materials per a autoaprenentatge que inclouen documents escrits, vídeos i tests d'autoavaluació. Els documents escrits i els vídeos corresponen tant a explicacions de teoria com a la resolució detallada d'exercicis. En el marc d'una prova pilot, els cursos, de seguiment voluntari durant el període transcorregut entre la matricula (mitjans de juliol) i l'inici de les classes (mitjans de setembre), van ser publicitats a tots els estudiants de nou accés del curs 2021-2022. Encara que la participació va ser més limitada del que s'esperava (únicament el 22% dels estudiants de nou accés es van inscriure), cal destacar que els estudiants que sí que van seguir els cursos van expressar majoritàriament una bona valoració dels mateixos (al respondre un qüestionari de satisfacció). Del desenvolupament dels cursos i de la realització de la prova pilot s'han obtingut unes quantes conclusions que també queden reflectides al final de l'article

The 26.3-h orbit and multiwavelength properties of the 'redback' millisecond pulsar PSR J1306-40

We present the discovery of the variable optical and X-ray counterparts to the radio millisecond pulsar (MSP) PSR J1306–40, recently discovered by Keane et al. We find that both the optical and X-ray fluxes are modulated with the same period, which allows us to measure for the first time the orbital period Porb = 1.097¿16[6] d. The optical properties are consistent with a main-sequence companion with spectral type G to mid K and, together with the X-ray luminosity (8.8¿×¿1031¿erg¿s-1 in the 0.5–10¿keV band, for a distance of 1.2¿kpc), confirm the redback classification of this pulsar. Our results establish the binary nature of PSR J1306–40, which has the longest Porb among all known compact binary MSPs in the Galactic disc. We briefly discuss these findings in the context of irradiation and intrabinary shock emission in compact binary MSPs