arXiv subjects

Ósmar Rodríguez

Publications and source records attributed to Ósmar Rodríguez.

11 recordsLinked to original sources

arXiv2026

Dark energy and negative compressibility of the Universe: A study based on cosmic equations of state

All cosmological models are defined through energy and matter, which describe the evolution of the targeted Universe. Whether the content is simple or complex, it can be defined through an effective equation of state (EoS). We study different cosmological models by analyzing the properties of the complete EoS of their fluid contents. We obtained general expressions for the ratio between pressure $p$ and energy density $ρ$, and for their derivative $dp/dρ$ in terms of deceleration and jerk parameters. We show that, in general, a cosmology whose energy density is constructed from multiple ideal gases cannot be described by the EoS of a single, ideal gas. This is directly related to a variation in the deceleration parameter during the evolution of the Universe. Furthermore, we studied the effective compressibility properties of the EoS, demonstrating that dark energy features of the fluid should be related to the negative compressibility of the contents. These features depend on the dynamics of the jerk parameter for each cosmological system, implying that the knowledge of dark energy evolution is encoded in the third-order derivatives of the scale factor. This approach to understanding the properties of cosmological models indicates that the accelerating evolution of some models, such as the lambda-cold dark matter model ($Λ$CDM) or the Chaplygin gas model, is due to the EoS of their nonideal content fluids rather than an associated anomalous (dark energy) nature. On the contrary, models such as $w$-cold dark matter ($w$CDM), $w_0$$w_a$-cold dark matter ($w_0$$w_a$CDM), or Dvali-Gabadadze-Porrati models, include by construction fluids with anomalous content, implying a negative compressibility and an effective dark energy behavior. Our work highlights the importance of treating all contents of the Universe as a nonideal fluid system, with a unique EoS.

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arXiv2026

Search For a Counterpart to the Subsolar Mass Gravitational Wave Candidate S251112cm

The recent candidate gravitational-wave (GW) alert from a compact object merger involving at least one subsolar mass (SSM) object has prompted questions about their origins. S251112cm is reported by LIGO/Virgo with a false alarm rate of 1 per 6.2 years, nearby luminosity distance $93 \pm 27$ Mpc, and probability of containing a SSM object of 100%. Such a system, if astrophysical, likely did not involve the supersolar neutron stars or black holes invoked to explain kilonovae. One must then also invoke hitherto unobserved and speculative models to produce SSM mergers which may have electromagnetic (EM) counterparts. We introduce a framework which vets and scores candidate counterparts to SSM GW events to inform follow-up in search of any among the zoo of potential EM transients: kilonovae, kilonovae-within-supernovae, super-kilonovae, or AGN flares from binary black hole mergers. We use a suite of telescopes to perform tiling, galaxy-targeted observations, and photometric/spectroscopic follow-up of promising candidates. In near-real time, we ingest candidates reported by the community, including some of the first observations reported by the Vera C. Rubin Observatory. We vet and score a total of 456 candidates, including 67 from Rubin, but find no likely counterpart. We nonetheless highlight candidates which demonstrate the ability of our framework to distinguish between different transient types and describe strategies to maximize the chances of detecting a counterpart to the next SSM event. Our framework will be implemented in the forthcoming Multimessenger Tool for Rapid Object Vetting and Examination (TROVE).

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arXiv2026

A new magnitude--redshift relation based on Type Ia supernovae

We present a new empirical relation between the standardized magnitude ($m$) of Type Ia supernovae (SNe Ia) and redshift ($z$). Using Pantheon+ and DES-SN5YR, we find a negative linear correlation between $m-5\log(z(1+z))$ and $z$, implying that their magnitude--redshift relation can be parametrized with just two parameters: an intercept $\mathcal{M}$ and a slope $b$. This relation corresponds to the luminosity distance $d_L(z)=c\,H_0^{-1}z(1+z)10^{bz/5}$ and is valid up to at least $z\simeq1.1$. It outperforms the $Λ$CDM and flat $w$CDM models and the (2,1) Padé approximant for $d_L(z)$, and performs comparably to the flat $Λ$CDM model and the (2,1) Padé($j_0=1$) model of Hu et al. Furthermore, the relation is stable in the absence of low-$z$ SNe, making it suitable for fitting Hubble diagrams of SNe Ia without the need to add a low-$z$ sample. In deep fields in particular, assuming that the large-scale density is independent of the comoving radial coordinate, $b\propto q_0+1$. We fit the empirical relation to SN data in eight deep-field regions and find that their fitted $\mathcal{M}$ and $b$ parameters are consistent within $1.6\,σ$, in agreement with isotropy. The inferred $q_0$ values, ranging from $-0.6$ to $-0.4$, are consistent within $1.5\,σ$ and significantly lower than zero, indicating statistically consistent cosmic acceleration across all eight regions. We apply the empirical relation to the DES-Dovekie and Amalgame SN samples, finding $b$ values consistent with those from DES-SN5YR and Pantheon+. Finally, using the empirical relation in the hemispheric comparison method applied to Pantheon+ up to $z=1.1$, we find no evidence for anisotropies in $\mathcal{M}$ and $b$.

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arXiv2024

Global Anisotropies of $Ω_Λ$

An analysis of the Cosmological Constant $Ω_Λ$ fitted to subsamples of the Pantheon+ Type Ia SN sample spanning 2$π$ sterradians for a grid of 432 pole positions covering the whole sky reveals two large scale asymmetries. One of them is closely aligned with the Galactic North-South direction and the other points approximately towards RA$\sim 217.5^\circ$ Dec$\sim -26.4^\circ$, $\sim$50.9 degrees from the CMB dipole Apex. The signal to noise ratio (S/N) of the multiple $Ω_Λ$ measurements in these directions is $3.2\lesssim $ S/N $\lesssim 8.4$. The first asymmetry is puzzling, and would indicate a systematic effect related with the distribution of Pantheon+ SNe on the sky and, probably, how the correction for reddening in the Galaxy is calculated. The second one, which entails a 2.8-$σ$ tension between $Ω_Λ$ measure in opposite directions, bears strong implications on its interpretation as Dark Energy: It is consistent with the prediction for tilted observers located in a Friedmann-Robertson-Walker universe who could measure an acceleration or a deceleration with a dipolar asymmetry, irrespective of what the universe as a whole is doing. In this case, $Ω_Λ$ would not be a physical entity, a real Dark Energy, but an apparent effect associated with the relativistic frame of reference transformation.

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arXiv2024

Stripped-envelope supernova light curves argue for central engine activity

The luminosity of ``stripped-envelope supernovae'', a common type of stellar explosions, has been generally thought to be driven by the radioactive decay of the nickel synthesized in the explosion and carried in its ejecta. Additional possible energy sources have been previously suggested, but these claims have been statistically inconclusive or model-dependent. Here, we analyse the energy budget of a sample of 54 well-observed stripped-envelope supernovae of all sub-types, and present statistically significant, largely model-independent, observational evidence for a non-radioactive power source in most of them (and possibly in all). We consider various energy sources, or alternatively, plausible systematic errors, that could drive this result, and conclude that the most likely option is the existence of a ``central engine'', such as a magnetar (a highly magnetic neutron star) or an accreting neutron star or black hole, operating over hours to days after the explosion. We infer from the observations constraints on the engines, finding that if these are magnetars, then their initial magnetic fields are about $10^{15}\,$G and their initial rotation period is 1--100 ms, implying that stripped-envelope supernovae could be the formative events of magnetars.

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arXiv2023

The Iron Yield of Core-collapse Supernovae

We present a systematic analysis of 191 stripped-envelope supernovae (SE SNe), aimed to compute their $^{56}$Ni masses from the luminosity in their radioactive tails ($M_\mathrm{Ni}^\mathrm{tail}$) and/or in their maximum light, and the mean $^{56}$Ni and iron yields of SE SNe and core-collapse SNe. Our sample consists of SNe IIb, Ib, and Ic from the literature and from the Zwicky Transient Facility Bright Transient Survey. To calculate luminosities from optical photometry, we compute bolometric corrections using 49 SE SNe with optical and near-IR photometry, and develop corrections to account for the unobserved UV and IR flux. We find that the equation of Khatami & Kasen for radioactive $^{56}$Ni-powered transients with a single free parameter does not fit the observed peak time-luminosity relation of SE SNe. Instead, we find a correlation between $M_\mathrm{Ni}^\mathrm{tail}$, peak time, peak luminosity, and decline rate, which allows measuring individual $^{56}$Ni masses to a precision of 14%. Applying this method to the whole sample, we find, for SNe IIb, Ib, and Ic, mean $^{56}$Ni masses of $0.066\pm0.006$, $0.082\pm0.009$, and $0.132\pm0.011\,\mathrm{M}_{\odot}$, respectively. After accounting for their relative rates, for SE SNe as a whole we compute mean $^{56}$Ni and iron yields of $0.090\pm0.005$ and $0.097\pm0.007\,\mathrm{M}_{\odot}$, respectively. Combining these results with the recent Type II SN mean $^{56}$Ni mass derived by Rodríguez et al., core-collapse SNe, as a whole, have mean $^{56}$Ni and iron yields of $0.055\pm0.006$ and $0.058\pm0.007\,\mathrm{M}_{\odot}$, respectively. We also find that radioactive $^{56}$Ni-powered models typically underestimate the peak luminosity of SE SNe by 60-70%, suggesting the presence of an additional power source contributing to the luminosity at peak.

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arXiv2022

Luminosity distribution of Type II supernova progenitors

I present progenitor luminosities ($L$) for a sample of 112 Type II supernovae (SNe II), computed directly from progenitor photometry and the bolometric correction technique, or indirectly from empirical correlations between progenitor luminosity and [OI] $λλ$6300, 6364 line luminosity at 350 d since explosion, $^{56}$Ni mass, or absolute $V$-band magnitude at 50 d since explosion. To calibrate these correlations, I use twelve SNe II with progenitor luminosities measured from progenitor photometry. I find that the correlations mentioned above are strong and statistically significant, and allow to estimate progenitor luminosities to a precision between 20 and 24 per cent. I correct the SN sample for selection bias and define a subsample of 112 SNe II with progenitor luminosities between $\log(L/L_{\odot})=4.6$ dex, corresponding to the completeness limit of the corrected sample, and the maximum observed progenitor luminosity of $\log(L/L_{\odot})=5.091$ dex. The luminosity distribution for this subsample is statistically consistent with those for red supergiants (RSGs) in LMC, SMC, M31, and M33 with $4.6\leq\log(L/L_{\odot})\leq5.091$. This supports that SN II progenitors correspond to RSGs. The conspicuous absence of SN II progenitors with $\log(L/L_{\odot})>5.1$ dex with respect to what is observed in RSG luminosity distributions, known as the RSG problem, is significant at a $5.2\pm0.5\,σ$ level.

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arXiv2021

The Gravity Collective: A Search for the Electromagnetic Counterpart to the Neutron Star-Black Hole Merger GW190814

We present optical follow-up imaging obtained with the Katzman Automatic Imaging Telescope, Las Cumbres Observatory Global Telescope Network, Nickel Telescope, Swope Telescope, and Thacher Telescope of the LIGO/Virgo gravitational wave (GW) signal from the neutron star-black hole (NSBH) merger GW190814. We searched the GW190814 localization region (19 deg$^{2}$ for the 90th percentile best localization), covering a total of 51 deg$^{2}$ and 94.6% of the two-dimensional localization region. Analyzing the properties of 189 transients that we consider as candidate counterparts to the NSBH merger, including their localizations, discovery times from merger, optical spectra, likely host-galaxy redshifts, and photometric evolution, we conclude that none of these objects are likely to be associated with GW190814. Based on this finding, we consider the likely optical properties of an electromagnetic counterpart to GW190814, including possible kilonovae and short gamma-ray burst afterglows. Using the joint limits from our follow-up imaging, we conclude that a counterpart with an $r$-band decline rate of 0.68 mag day$^{-1}$, similar to the kilonova AT 2017gfo, could peak at an absolute magnitude of at most $-17.8$ mag (50% confidence). Our data are not constraining for ''red'' kilonovae and rule out ''blue'' kilonovae with $M>0.5 M_{\odot}$ (30% confidence). We strongly rule out all known types of short gamma-ray burst afterglows with viewing angles $<$17$^{\circ}$ assuming an initial jet opening angle of $\sim$$5.2^{\circ}$ and explosion energies and circumburst densities similar to afterglows explored in the literature. Finally, we explore the possibility that GW190814 merged in the disk of an active galactic nucleus, of which we find four in the localization region, but we do not find any candidate counterparts among these sources.

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arXiv2019

SN2018kzr: a rapidly declining transient from the destruction of a white dwarf

We present SN2018kzr, the fastest declining supernova-like transient, second only to the kilonova, AT2017gfo. SN2018kzr is characterized by a peak magnitude of $M_r = -17.98$, peak bolometric luminosity of ${\sim} 1.4 \times 10^{43}$erg s$^{\mathrm{-1}}$ and a rapid decline rate of $0.48 \pm 0.03$ mag day$^{\textrm{-1}}$ in the $r$ band. The bolometric luminosity evolves too quickly to be explained by pure $^{\mathrm{56}}$Ni heating, necessitating the inclusion of an alternative powering source. Incorporating the spin-down of a magnetized neutron star adequately describes the lightcurve and we estimate a small ejecta mass of $M_\mathrm{ej} = 0.10 \pm 0.05$ $\textrm{M}_{\odot}$. Our spectral modelling suggests the ejecta is composed of intermediate mass elements including O, Si and Mg and trace amounts of Fe-peak elements, which disfavours a binary neutron star merger. We discuss three explosion scenarios for SN2018kzr, given the low ejecta mass, intermediate mass element composition and the high likelihood of additional powering - core collapse of an ultra-stripped progenitor, the accretion induced collapse of a white dwarf and the merger of a white dwarf and neutron star. The requirement for an alternative input energy source favours either the accretion induced collapse with magnetar powering or a white dwarf - neutron star merger with energy from disk wind shocks.

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arXiv2019

Signatures of Circumstellar Interaction in the Type IIL Supernova ASASSN-15oz

Hydrogen-rich, core-collapse supernovae are typically divided into four classes: IIP, IIL, IIn, and IIb. In general, interaction with circumstellar material is only considered for Type IIn supernovae. However, recent hydrodynamic modeling of IIP and IIL supernovae requires circumstellar material to reproduce their early light curves. In this scenario, IIL supernovae experience large amounts of mass loss before exploding. We test this hypothesis on ASASSN-15oz, a Type IIL supernova. With extensive follow-up in the X- ray, UV, optical, IR, and radio we present our search for signs of interaction, and the mass-loss history indicated by their detection. We find evidence of short-lived intense mass-loss just prior to explosion from light curve modeling, amounting in 1.5 M$_{\odot}$ of material within 1800 R$_{\odot}$ of the progenitor. We also detect the supernova in the radio, indicating mass-loss rates of $10^{-6}-10^{-7}$ M$_{\odot}$ yr$^{-1}$ prior to the extreme mass-loss period. Our failure to detect the supernova in the X-ray and the lack of narrow emission lines in the UV, optical, and NIR do not contradict this picture and place an upper limit on the mass-loss rate outside the extreme period of $<10^{-4}$ M$_{\odot}$ yr$^{-1}$. This paper highlights the importance gathering comprehensive data on more Type II supernovae to enable detailed modeling of the progenitor and supernova which can elucidate their mass-loss histories and envelope structures and thus inform stellar evolution models.

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arXiv2014

Photospheric Magnitude Diagrams for Type II Supernovae: A Promising Tool to Compute Distances

We develop an empirical color-based standardization for Type II supernovae (SNe II), equivalent to the classical surface brightness method given in Wesselink (1969). We calibrate it with SNe II with host galaxy distance measured with Cepheids, and well-constrained shock breakout epoch and extinction due to the host galaxy. We estimate the reddening with an analysis of the B-V versus V-I color-color curves, similar to that of Natali et al. (1994). With four SNe II meeting the above requirements, we build a photospheric magnitude versus color diagram (similar to an HR diagram) with a dispersion of 0.29 mag. We also show that when using time since shock breakout instead of color as independent variable, the same standardization gives a dispersion of 0.09 mag. Moreover, we show that the above time-based standardization corresponds to the generalization of the standardized candle method of Hamuy & Pinto (2002) for various epochs throughout the photospheric phase. To test the new tool, we construct Hubble diagrams to different subsamples of 50 low-redshift (cz<10^4 km s^-1) SNe II. For 13 SNe within the Hubble flow (cz_CMB>3000 km s^-1) and with well-constrained shock breakout epoch we obtain values of 68-69 km s^-1 Mpc^-1 for the Hubble constant, and an mean intrinsic scatter of 0.12 mag or 6% in relative distances.

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