Browsing by Author "Clocchiatti García, Alejandro"

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    ATClean: a novel method for detecting low-luminosity transients and application to pre-explosion counterparts from SN 2023ixf
    (2024) Rest, S.; Rest, A.; Kilpatrick, C. D.; Jencson, J. E.; Coelln, S. von; Strolger, L.; Smartt, S.; Anderson, J. P.; Clocchiatti García, Alejandro; Coulter, D. A.; Denneau, L.; Gómez, S.; Heinze, A.; Ridden-Harper, R.; Smith, K. W.; Stalder, B.; Tonry, J. l.; Wang, Q.; Zenati, Y.
    In an effort to search for faint sources of emission over arbitrary timescales, we present a novel method for analyzing forced photometry light curves in difference imaging from optical surveys. Our method “ATLAS Clean” or ATClean, utilizes the reported fluxes, uncertainties, and fits to the point-spread function from difference images to quantify the statistical significance of individual measurements. We apply this method to control light curves across the image to determine whether any source of flux is present in the data for a range of specific timescales. From ATLAS o-band imaging at the site of the Type II supernova (SN) 2023ixf in M101 from 2015–2023, we show that this method accurately reproduces the 3σ flux limits produced from other, more computationally expensive methods. We derive limits for emission on timescales of 5 days and 80-300 days at the site of SN 2023ixf, which are 19.8 and 21.3 mag, respectively. The latter limits rule out variability for inextinguished red supergiants (RSG) with initial masses >22 M⊙, comparable to the most luminous predictions for the SN 2023ixf progenitor system. We also compare our limits to short timescale outbursts, similar to those expected for Type IIn SN progenitor stars or the Type II SN 2020tlf, and rule out outburst ejecta masses of >0.021 M⊙, much lower than the inferred mass of circumstellar matter around SN 2023ixf in the literature. In the future, these methods can be applied to any forced point-spread function photometry on difference imaging from other surveys, such as Rubin optical imaging.
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    Global Anisotropies of ΩΛ
    (IOP Publishing Ltd, 2024) Clocchiatti García, Alejandro; Rodríguez Suárez, Osmar Ali; Órdenes Morales, Ariel Antonio; Cuevas Tapia, Benjamín Exequiel; Instituto Milenio de Astrofísica (MAS)
    An analysis of the Cosmological Constant ΩΛ fitted to subsamples of the Pantheon+ Type Ia SN sample spanning 2π 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∼ 217.5 ◦ Dec∼ −26.4 ◦ , ∼50.9 degrees from the CMB dipole Apex. The signal to noise ratio (S/N) of the multiple ΩΛ measurements in these directions is 3.2 ≲ S/N ≲ 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 ΩΛ 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, ΩΛ would not be a physical entity, a real Dark Energy, but an apparent effect associated with the relativistic frame of reference transformation.