iPTF16geu: A multiply imaged, gravitationally lensed type Ia supernova (1611.00014v2)

Abstract: We report the discovery of a multiply-imaged gravitationally lensed Type Ia supernova, iPTF16geu (SN 2016geu), at redshift $z=0.409$. This phenomenon could be identified because the light from the stellar explosion was magnified more than fifty times by the curvature of space around matter in an intervening galaxy. We used high spatial resolution observations to resolve four images of the lensed supernova, approximately 0.3" from the center of the foreground galaxy. The observations probe a physical scale of $\sim$1 kiloparsec, smaller than what is typical in other studies of extragalactic gravitational lensing. The large magnification and symmetric image configuration implies close alignment between the line-of-sight to the supernova and the lens. The relative magnifications of the four images provide evidence for sub-structures in the lensing galaxy.

iPTF16geu: A Multiply Imaged, Gravitationally Lensed Type Ia Supernova

This paper presents the discovery and analysis of the gravitationally lensed Type Ia supernova, iPTF16geu. The supernova was detected at a redshift of $z=0.409$, with its light being significantly magnified by more than fifty times due to a foreground galaxy's gravitational lensing effect. Such strong lensing phenomena are critical for astrophysical paper, as they provide insights into both the properties of the lensed astronomical objects and the structures of the lensing galaxies themselves.

Key Observations and Methodology

The researchers discovered four distinct images of the iPTF16geu supernova, with these images being approximately \ang{;;0.3} from the lensing galaxy's center. This configuration offered a rare opportunity to explore gravitational lensing on an unprecedented small scale, around one kiloparsec, as opposed to larger scales typically examined in other extragalactic lensing studies.

Spectroscopic verification established iPTF16geu as a normal Type Ia supernova, known for its consistent peak luminosity—a characteristic that makes SNe Ia excellent standard candles in cosmology. The spectroscopic data revealed the redshifts of both the lensed supernova and the lensing galaxy, enabling precise modeling of the system's gravitational lensing.

Results and Implications

The researchers determined a lensing magnification in the range of 4.1 to 4.8 magnitudes, considering possible differential extinction due to dust in the lensing galaxy. This magnification aligns with the intrinsic brightness predictions for standard SNe Ia at such a redshift, illustrating gravitational lensing's profound impact on observational brightness.

A smooth lens model, specifically an isothermal ellipsoid, was developed to describe the lensing effect. Nonetheless, observed discrepancies in brightness differences among the lensed images suggest potential contributions from microlensing by sub-structures in the lensing galaxy, such as dark matter sub-halos or stellar disruptions. This deviation highlights complexities in lensing phenomena not fully explicable by smooth, continuous mass distributions.

Future Prospects

The paper underscores the rarity of discovering multiply-imaged lensed supernovae, especially with such high magnification. It suggests the need for further exploration into the prevalence of sub-structures within lensing galaxies, which seem to influence gravitational lensing to a greater extent than previously modeled.

The implications for cosmology and astrophysics are significant. Gravitational lenses like iPTF16geu offer direct methods to measure the Hubble constant and test the cosmic scale structure. Future telescopic surveys could increase the detection rate of similar systems, enabling researchers to explore the matter distribution at kiloparsec scales and thereby refine models of dark matter halos and their mass concentration.

In conclusion, the iPTF16geu discovery enriches our understanding of strong lensing phenomena and the structural intricacies of intervening galaxies. As future technologies improve observational capacity, the paper anticipates a transformative breadth of data, further probing the universe's expansion and structure through such lensing events.