Person: Luna, Gerardo Juan Manuel
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23/12/1976
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Luna
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Gerardo Juan Manuel
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Publication The Remarkable Spin-down and Ultrafast Outflows of the Highly Pulsed Supersoft Source of Nova Herculis 2021(IOP Publishing, 2021) Drake, Jeremy; Ness, Jan Uwe; Page, Kim L.; Beardmore, Andrew P.; Orio, Marina; Osborne, Julian P.; Mróz, Przemek; Starrfield, Sumner; Banerjee, Dipankar P. K.; Balman, Solen; Darnley, Matt J; Bhargava, Yash; Dewangan, Gulab C.; Singh, Kulinder Pal; Luna, Gerardo Juan ManuelNova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye brightness and has been detected from radio to γ-rays. An extremely fast optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a high-mass white dwarf. The optical pre-outburst detection of a 501.42 s oscillation suggests a magnetic white dwarf. This is the first time that an oscillation of this magnitude has been detected in a classical nova prior to outburst. We report X-ray outburst observations from Swift and Chandra that uniquely show (1) a very strong modulation of supersoft X-rays at a different period from reported optical periods, (2) strong pulse profile variations and the possible presence of period variations of the order of 0.1-0.3 s, and (3) rich grating spectra that vary with modulation phase and show P Cygni-type emission lines with two dominant blueshifted absorption components at ∼3000 and 9000 km s-1 indicating expansion velocities up to 11,000 km s-1. X-ray oscillations most likely arise from inhomogeneous photospheric emission related to the magnetic field. Period differences between reported pre- and post-outburst optical observations, if not due to other period drift mechanisms, suggest a large ejected mass for such a fast nova, in the range 2 10-5-2 10-4 M o˙. A difference between the period found in the Chandra data and a reported contemporaneous post-outburst optical period, as well as the presence of period drifts, could be due to weakly nonrigid photospheric rotation.Publication NICER Monitoring of Supersoft X-Ray Sources(IOP Publishing, 2022) Luna, Gerardo Juan ManuelWe monitored four supersoft sources - two persistent ones, CAL 83 and MR Vel, and the recent novae YZ Ret (Nova Ret 2020), and V1674 Her (Nova Her 2021) - with NICER. The two persistent supersoft X-ray sources (SSS) were observed with unvaried X-ray flux level and spectrum, respectively, 13 and 20 yr after the last observations. Short-period modulations of the SSS appear where the spectrum of the luminous central source was fully visible (in CAL 83 and V1674 Her) and were absent in YZ Ret and MR Vel, in which the flux originated in photoionized or shocked plasma, while the white dwarf (WD) was not observable. We thus suggest that the pulsations occur on, or very close to, the WD surface. The pulsations of CAL 83 were almost unvaried after 15 yr, including an irregular drift of the ≃67 s period by 2.1 s. Simulations, including previous XMM-Newton data, indicate actual variations in period length within hours, rather than an artifact of the variable amplitude of the pulsations. Large amplitude pulsations with a period of 501.53 ± 0.30 s were always detected in V1674 Her, as long as the SSS was observable. This period seems to be due to rotation of a highly magnetized WD. We cannot confirm the maximum effective temperature of (≃145,000 K) previously inferred for this nova, and discuss the difficulty in interpreting its spectrum. The WD appears to present two surface zones, one of which does not emit SSS fluxPublication Expanding Bipolar X-Ray Structure after the 2006 Eruption of RS Oph(IOP Publishing, 2023) Luna, Gerardo Juan ManuelWe report on the detection and analysis of extended X-ray emission by the {\it Chandra} X-ray Observatory stemming from the 2006 eruption of the recurrent novae RS Oph. The extended emission was detected 1254 and 1927 days after the start of the 2006 eruption and is consistent with a bipolar flow oriented in the east-west direction of the sky with opening angles of approximately 70∘. The length of both lobes appeared to expand from 1.3 arcsec in 2009 to 2.0 arcsec in 2011, suggesting a projected expansion rate of 1.1±0.1 mas day−1 and an expansion velocity of 4600 km s−1 (D/2.4 kpc) in the plane of the sky. This expansion rate is consistent with previous estimates from optical and radio observations of material in a similar orientation. The X-ray emission does not show any evidence of cooling between 2009 and 2011, consistent with free expansion of the material. This discovery suggests that some mechanism collimates ejecta away from the equatorial plane, and that after that material passes through the red-giant wind, it expands freely into the cavity left by the 1985 eruption. We expect similar structures to arise from latest eruption and to expand into the cavity shaped by the 2006 eruption.Publication Optical spectroscopy and X-ray observations of the D-type symbiotic star EF Aql(Wiley Blackwell, 2020) Stoyanov, K. A.; Ilkiewicz, K.; Mikołajewska, J.; Mukai, K.; Martí, J; Latev, G; Boeva, S.; Zamanov, R. K.; Luna, Gerardo Juan ManuelWe performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with the Southern African Large Telescope (SALT), we determine the temperature (∼55 000 K) and the luminosity (∼5.3 L⊙) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements.We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10-12 erg cm-2 s-1, whichmeans that EF Aql is consistent with the faintestX-ray systems detected so far. Otherwise we detected it with the UltraViolet and Optical Telescope (UVOT) instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4 ± 0.3 d caused by the pulsations of the Mira-type donor star.Publication Discovery of the most luminous quasar of the last 9 Gyr(Astronomical Society of Australia, 2021) Onken, Christopher A.; Lai, Samuel; Wolf, Christian; Lucy, Adrian B.; Hon,Wei Jeat; Tisserand, Patrick; Sokoloski, Jennifer L.; Manick, Rajeev; Fan, Xiaohui; Bian, Fuyan; Pérez, Mariana Valeria; Luna, Gerardo Juan ManuelWe report the discovery of a bright (g = 14.5 mag (AB), K = 11.9 mag (Vega)) quasar at redshift z = 0.83 — the optically brightest (unbeamed) quasar at z > 0.4. SMSS J114447.77-430859.3, at a Galactic latitude of b = +18.1◦, was identified by its optical colours from the SkyMapper Southern Survey (SMSS) during a search for symbiotic binary stars. Optical and near-infrared spectroscopy reveals broad Mg II, Hβ, Hα, and Paβ emission lines, from which we measure a black hole mass of log10(MBH/M) = 9.4 ± 0.5. With its high luminosity, Lbol = (4.7 ± 1.0) × 1047 erg s−1 or Mi(z = 2) = −29.74 mag (AB), we estimate an Eddington ratio of ≈ 1.4. As the most luminous quasar known over the last ∼9 Gyr of cosmic history, having a luminosity 8× greater than 3C 273, the source offers a range of potential follow-up opportunities.Publication Transient and asymmetric dust structures in the TeV-bright nova RS Oph revealed by spectropolarimetry(EDP Sciences, 2023) Nikolov, Y.; Luna, Gerardo Juan Manuel; Stoyanov, K. A.; Borisov, G.; Mukai, K.; Sokoloski, Jennifer L.; Avramova Boncheva, A.A long-standing question related to nova eruptions is how these eruptions might lead to dust formation, despite the ostensibly inhospitable environment for dust within the hot, irradiated ejecta. In the novae of systems such as the symbiotic binary RS Ophiuchi (RS Oph), ejecta from the white dwarf collide with pre-existing circumstellar material fed by the wind from the red-giant companion, offering a particularly clear view of some nova shocks and any associated dust production. In this work, we use the spectropolarimetric monitoring of the recurrent nova RS Oph starting two days after its eruption in August 2021 to show that: 1) dust was present in the RS Oph system as early as two days into the 2021 eruption; 2) the spatial distribution of this early dust was asymmetric, with components both aligned with and perpendicular to the orbital plane of the binary; 3) between two and nine days after the start of the eruption, this early dust was gradually destroyed; and 4) dust was again created, aligned roughly with the orbital plane of the binary more than 80 days after the start of the outburst, most likely as a result of shocks that arose as the ejecta interacted with circumbinary material concentrated in the orbital plane. The modeling of X-rays and very-high-energy (GeV and TeV) emission from RS Oph days to months into the 2021 eruption suggests that collisions between the ejecta and the circumbinary material may have led to shock formation in two distinct regions: the polar regions perpendicular to the orbital plane, where collimated outflows have been observed after prior eruptions, and a circumbinary torus in the orbital plane. The observations described here indicate that dust formed in approximately the same two regions, supporting the connection between shocks and dust in novae and revealing a very early onset of asymmetry. The spectropolarimetric signatures of RS Oph in the first week into the 2021 outburst indicate: 1) polarized flux across the Hα emission line and 2) the position angle orientation relative to the radio axis is similar to what is seen from the spectropolarimetric signatures of active galactic nuclei (AGNs)