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

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

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

Peering into the dark side: Magnesium lines establish a massive neutron star in PSR J2215+5135

New millisecond pulsars (MSPs) in compact binaries provide a good opportunity to search for the most massive neutron stars. Their main-sequence companion stars are often strongly irradiated by the pulsar, displacing the effective center of light from their barycenter and making mass measurements uncertain. We present a series of optical spectroscopic and photometric observations of PSR J2215+5135, a “redback” binary MSP in a 4.14 hr orbit, and measure a drastic temperature contrast between the dark/cold (TN = 5660- + 380 260 K) and bright/hot (TD = 8080- + 280 470 K) sides of the companion star. We find that the radial velocities depend systematically on the atmospheric absorption lines used to measure them. Namely, the semi-amplitude of the radial velocity curve (RVC) of J2215 measured with magnesium triplet lines is systematically higher than that measured with hydrogen Balmer lines, by 10%. We interpret this as a consequence of strong irradiation, whereby metallic lines dominate the dark side of the companion (which moves faster) and Balmer lines trace its bright (slower) side. Further, using a physical model of an irradiated star to fit simultaneously the two-species RVCs and the three-band light curves, we find a center-of-mass velocity of K2=412.3±5.0 km s-1 and an orbital inclination i=63°.9- + 2.7 2.4. Our model is able to reproduce the observed fluxes and velocities without invoking irradiation by an extended source. We measure masses of M1=2.27- + 0.15 0.17Me and M2=0.33- + 0.02 0.03Me for the neutron star and the companion star, respectively. If confirmed, such a massive pulsar would rule out some of the proposed equations of state for the neutron star interior.Peer Reviewe