The Formation Rate and Luminosity Function of Fast X-ray transients from Einstein probe

Abstract

Following its launch on 2024 January 9, the Einstein Probe (EP) telescope has detected hundreds of fast X-ray transients (FXTs), yet their physical origins remain elusive. Understanding their luminosity function and formation rate is crucial for elucidating their nature. Recently, the EP team has provided the latest catalog of EP-detected FXTs. Based on this catalog, we present a model-independent nonparametric approach to derive the luminosity function and formation rate of FXTs. Our analysis reveals significant cosmological luminosity evolution, characterized by a scaling relationship of $(1+z{)}^{3.58}$. After accounting for this evolution, we establish that the local luminosity function is best represented by a broken power law, with a break luminosity of $(4.17\pm 0.34)\times 10^{46}$ erg/s. The formation rate exhibits a broken power law as $\rho (z)\propto (1+z{)}^{-4.25}$ at $z⪅0.9$ and $\rho (z)\propto (1+z{)}^{-0.26}$ at $z⪆0.9$, yielding a local rate of approximately $153.8_{-95.1}^{+249.4}$ Gpc${}^{-3}$ yr${}^{-1}$. This rate is higher than that of long gamma-ray bursts (LGRBs). Our findings indicate that a component of FXTs is associated with LGRBs.

9 pages, 4 figures, and 1 table. Accepted 2025 December 1 for publication in ApJL

References in corpus (28)

• On the normalisation of the cosmic star formation history
• Discovery of the X-Ray Afterglow of the Gamma-Ray Burst of February 28 1997
• An optical supernova associated with the X-ray flash XRF 060218
• The luminosity function and the rate of Swift's Gamma Ray Bursts
• Low Luminosity Gamma-Ray Bursts as a Unique Population: Luminosity Function, Local Rate, and Beaming Factor
• Extra-galactic high-energy transients: event rate densities and luminosity functions
• Cosmological Aspects of Gamma-Ray Bursts: Luminosity Evolution and an Estimate of the Star Formation Rate at High Redshifts
• Star Formation History up to z = 7.4: Implications for Gamma-Ray Bursts and the Cosmic Metallicity Evolution
• The Einstein Probe Mission
• The rate and luminosity function of long Gamma Ray Bursts
• Cosmological Evolution of Long Gamma-ray Bursts and Star Formation Rate
• Science objectives of the Einstein Probe mission
• An unexpectedly low-redshift excess of Swift gamma-ray burst rate
• X-ray Spectral Characteristics of Ginga Gamma-Ray Bursts
• On the Cosmological Evolution of Long Gamma-ray Burst Properties
• HETE Observations of the Gamma-Ray Burst GRB030329: Evidence for an Underlying Soft X-ray Component
• The formation rate of short gamma-ray bursts and gravitational waves
• The Luminosity Function and Formation Rate of A Complete Sample of Long Gamma-Ray Bursts
• Short Gamma Ray Burst Formation Rate from BATSE data using E_p-L_p correlation and the minimum gravitational wave event rate of coalescing compact binary
• GRANAT/WATCH catalogue of cosmic gamma-ray bursts: December 1989 to September 1994
• Gamma-Ray Bursts: the Isotropic-Equivalent-Energy Function and the Cosmic Formation Rate
• Binary neutron star merger rate via the luminosity function of short gamma-ray bursts
• Einstein Probe discovery of EP240408a: a peculiar X-ray transient with an intermediate timescale
• Cosmological Evolution of Fermi-LAT Gamma-ray Blazars Using Novel Nonparametric Methods
• Discovery of a Universal Correlation For Long and Short GRBs and Its Application on the Study of Luminosity Function and Formation Rate
• Revisiting the energy distribution and formation rate of CHIME fast radio bursts
• Do Pulsar Radio Fluxes violate the Inverse-Square Law?
• Source Count Distribution of Fermi LAT Gamma-Ray Blazars Using Novel Nonparametric Methods