Redshift-Driven Heterogeneity in the Amati Correlation of Long Gamma-Ray Bursts: Evidence and Implications

Основные понятия

The Amati correlation in long gamma-ray bursts exhibits significant heterogeneity across different redshift ranges, suggesting an evolution in GRB properties potentially linked to changes in host galaxy characteristics and challenging their use as standard candles in cosmology.

Аннотация

• Bibliographic Information: Singha, D., Singh, M., Verma, D., Pandey, K. L., & Gupta, S. (2024). Does the Amati Correlation Exhibit Redshift-Driven Heterogeneity in Long GRBs? arXiv preprint arXiv:2406.15993v2.
• Research Objective: This study investigates whether the Amati correlation, a relationship between the intrinsic peak energy and isotropic energy of long gamma-ray bursts (GRBs), remains consistent across different redshift ranges or exhibits heterogeneity.
• Methodology: The researchers analyzed a dataset of 221 long GRBs with redshifts ranging from 0.034 to 8.2. They divided the dataset into low- and high-redshift subgroups using thresholds of z = 1.5 and z = 2. Bayesian marginalization and Reichart's likelihood approach were employed to determine the best-fit values of the Amati parameters and assess their variations across the subgroups.
• Key Findings: The analysis revealed statistically significant differences in the Amati parameters between the low- and high-redshift GRB subgroups. The variations exceeded 2σ at z = 1.5 and 1σ at z = 2, indicating a potential evolution in the GRB population with redshift.
• Main Conclusions: The study concludes that the Amati relation in long GRBs is likely not universal and exhibits redshift-driven heterogeneity. This heterogeneity challenges the assumption of using GRBs as standard candles in cosmology and suggests potential changes in GRB properties or their progenitor populations over cosmic time.
• Significance: This research highlights the complexity of GRB physics and the need to account for redshift-dependent variations in their properties for accurate cosmological studies.
• Limitations and Future Research: The study acknowledges potential biases from instrumental limitations and selection effects. Future research with larger datasets from upcoming missions like THESEUS and eXTP is crucial to confirm these findings and refine our understanding of GRB evolution and its implications for cosmology.

Статистика

The study analyzed a dataset of 221 long GRBs.
The redshift range of the GRBs was from 0.034 to 8.2.
Two redshift thresholds were used to divide the data: z = 1.5 and z = 2.
At z = 1.5, the difference in Amati parameters between low- and high-redshift subgroups was greater than 2σ.
At z = 2, the difference in Amati parameters between low- and high-redshift subgroups was greater than 1σ.

Цитаты

"These variations, differing by approximately 2σ at z = 1.5 and more than 1σ at z = 2, suggest an evolution in the GRB population with redshift, possibly reflecting changes in host galaxy properties."
"Our results challenge the assumption of the Amati relation’s universality and underscore the need for larger datasets and more precise measurements from upcoming missions like Transient High-Energy Sky and Early Universe Surveyor (THESEUS), and enhanced X-ray Timing and Polarimetry mission (eXTP) to refine our understanding of GRB physics."

Ключевые выводы из

Does the Amati Correlation Exhibit Redshift-Driven Heterogeneity in Long GRBs?

by Darshan Sing... в arxiv.org 11-06-2024

https://arxiv.org/pdf/2406.15993.pdf

Дополнительные вопросы

How might the observed redshift-dependent heterogeneity in the Amati relation impact current models of GRB progenitor systems and their evolution?

The observed redshift-dependent heterogeneity in the Amati relation, if confirmed to be intrinsic to GRBs and not due to observational biases, presents a significant challenge to current models of GRB progenitor systems and their evolution. Here's how:

Challenging the Universality of GRB Physics: The Amati relation, connecting the intrinsic peak energy (Ep,i) and isotropic energy (Eiso) of GRBs, is thought to reflect fundamental physics governing these energetic explosions. A redshift-dependent heterogeneity suggests that this underlying physics might not be universal and could evolve over cosmic time. This challenges the assumption that we can extrapolate our understanding of nearby GRBs to understand the population at high redshifts.

Implications for Progenitor Models: The heterogeneity could imply different dominant progenitor channels for GRBs at different redshifts. For instance, the population of GRBs at high redshifts (where star formation is more active) might be dominated by the collapse of massive, low-metallicity stars. In contrast, at lower redshifts, a more diverse range of progenitors, including mergers of compact objects, might contribute.

Metallicity Dependence: The paper suggests that host galaxy metallicity could play a role in the observed heterogeneity. High-redshift GRBs are more likely to occur in low-metallicity environments, which could influence the properties of the progenitor stars and the resulting GRB. This highlights the need to incorporate metallicity effects in GRB progenitor models.

Evolution of Jet Properties: The Amati relation is also sensitive to the properties of the GRB jet, such as its opening angle and Lorentz factor. The observed heterogeneity could indicate an evolution in these jet properties with redshift, potentially linked to differences in the progenitor environment or the central engine driving the explosion.
In conclusion, the redshift-dependent heterogeneity in the Amati relation, if confirmed, would necessitate a reevaluation of current GRB progenitor models. It underscores the need to consider evolutionary effects, potentially linked to metallicity and jet properties, to fully understand the population of GRBs across cosmic time.

Could the observed differences in Amati parameters be attributed to systematic errors in redshift measurements or other observational biases, rather than intrinsic GRB evolution?

While the study highlights a statistically significant difference in Amati parameters for low- and high-redshift GRBs, it's crucial to acknowledge that observational biases could contribute to these differences. Here are some potential biases:

Redshift Measurement Uncertainties: Accurate redshift measurements are crucial for this analysis. At high redshifts, these measurements become more challenging and uncertain. Systematic errors in redshift determination could propagate through the analysis and lead to artificial trends in the Amati relation parameters.

Selection Effects: GRBs are detected based on their brightness. At high redshifts, only the most luminous GRBs are detectable, potentially introducing a Malmquist bias. This could skew the sample towards intrinsically brighter GRBs at high redshifts, influencing the Amati relation fit.

Instrumental Limitations: Different instruments (Swift, Fermi) with varying sensitivities and energy ranges are used to observe GRBs. These instrumental differences could introduce systematic uncertainties in the measured Ep,i and Eiso, particularly at high redshifts, potentially contributing to the observed heterogeneity.

Dust Extinction: Dust in both the host galaxy and the intergalactic medium can absorb and scatter GRB emission, particularly at higher redshifts. This dust extinction can make high-redshift GRBs appear fainter and redder, potentially affecting the determination of Ep,i and Eiso.

Evolution in Dust Properties: The properties of dust in galaxies have evolved over cosmic time. If not adequately accounted for, this evolution could introduce redshift-dependent systematic errors in the measured GRB properties, mimicking intrinsic evolution in the Amati relation.
Addressing these potential biases requires careful analysis and consideration of systematic uncertainties. Larger, more homogeneous datasets from future missions like THESEUS and eXTP, combined with improved modeling of selection effects and dust extinction, will be crucial to disentangle intrinsic GRB evolution from observational biases.

If the Amati relation is not universal, what other astrophysical objects or phenomena could be used as reliable standard candles for probing the early universe and constraining cosmological models?

If the Amati relation proves not to be a universal standard candle due to redshift-dependent evolution, several alternative astrophysical objects and phenomena hold promise for probing the early universe and constraining cosmological models:

Type Ia Supernovae (SNe Ia): These remain a cornerstone of cosmology. While limited to redshifts below z~1.75 with current telescopes, they offer high precision as standardizable candles. Future observatories like the Vera Rubin Observatory (LSST) will extend their use to higher redshifts.

Quasars: These extremely luminous active galactic nuclei can be observed at very high redshifts (z > 7). While not as intrinsically standard as SNe Ia, ongoing efforts to standardize their properties using relationships between their luminosity and emission line features show promise.

Baryon Acoustic Oscillations (BAO): These imprints of sound waves from the early universe on the distribution of galaxies provide a "standard ruler" to measure cosmic distances. BAO measurements are less affected by astrophysical uncertainties than SNe Ia or GRBs and can probe a wide range of redshifts.

Gravitational Waves (GW): Mergers of binary neutron stars and black holes generate GWs detectable with current and future instruments like LIGO, Virgo, and the planned Einstein Telescope. These events offer a new independent probe of cosmic distances and could become valuable standard sirens for cosmology.

Cosmic Microwave Background (CMB): While not a direct distance indicator, the CMB provides a snapshot of the early universe. Its anisotropies encode information about cosmological parameters, offering crucial constraints on cosmological models.

Other GRB Correlations: Even if the Amati relation exhibits redshift dependence, other correlations within GRB properties, such as the Ghirlanda relation or the Yonetoku relation, might prove more stable and serve as alternative standard candles.
A multi-messenger approach, combining observations from different sources like SNe Ia, quasars, BAO, GWs, and the CMB, will be crucial for robustly constraining cosmological models and understanding the evolution of the universe. Each method has its strengths and limitations, and their synergy will provide a more complete and accurate picture of the cosmos.