Highly magnified stars at cosmological distances (z ≳ 0.7) become detectable thanks to microlensing by intracluster stars near the critical curves of galaxy clusters. Multi-epoch photometric campaigns targeting caustic crossing galaxies magnified by massive galaxy clusters enable the detection of these objects as transient events. Such stars provide unique opportunities to study stellar populations at early cosmic times, probe the nature of dark matter, reveal small-scale structure in the cluster, and improve lens models. To date, only a few dozen high-redshift stars have been reported, with a single lensed galaxy, the Dragon, holding the current record of 44 detections. These numbers, however, remain insufficient to exploit their full potential. In this paper, owing to the inclusion of new observations, we report the identification of more than 100 magnified stellar events in the Dragon, behind the massive galaxy cluster Abell 370. The relatively low redshift of the Dragon (z _ facilitates the detection of its most massive stars. Using imaging data from three different cycles (2022--2024) with the James Webb Space Telescope, we applied a time-domain technique to identify flux variations associated with caustic-crossing events. From the spatial distribution of stellar events, we constrained the high-end slope of the stellar luminosity function, finding β=2.18^ +0.20 -0.30 . Alternatively, assuming a fixed slope, we constrained the microlens surface mass density. In addition, we examined the parity asymmetry of the detected caustic-crossing events, a proposed probe of wave dark matter, and found that it remains present in our fiducial lens model. We also used the events to trace the regions of highest magnification, offering an alternative way to map the system critical curves.
The first statistical study of over 100 magnified stellar events at a redshift z ≈ 0.725 with JWST
J. M. Palencia·Adi Zitrin·J. M. Diego·Yoshinobu Fudamoto·Anton M. Koekemoer·Christopher N. A. Willmer·Eduardo Iani·Xiaojing Lin·Justin Pierel·Alfred Amruth·Franz E. Bauer·T. Broadhurst·W. Chen·Liang Dai·Daniel Espada·Alexei V. Filippenko·Seiji Fujimoto·Patrick L. Kelly·Mingyu Li·Sung Kei Li·Ashish Kumar Meena·Jordi Miralda-Escudé·P. Morilla·Mitchell F. Struble·Hayley Williams·Rogier A. Windhorst·E. Zackrisson·Ruwen Zhou·Fengwu Sun

