Title：Observing Radio Transients with ALMA

Speaker: Prof. Dr. Marilyn Cruces (Pontifical Catholic University of Chile)

Time：3:00 pm Dec.11th (Thursday)

Tencent Meeting：46822606747 password: 6360

Location: Lecture Hall, 3rd floor

Abstract：

Radio transients, such as pulsars and fast radio bursts (FRBs), are primarily detected at centimetre (cm) radio wavelengths, where higher luminosities are found. However, could we study them at millimetre (mm) waves? For pulsars, this window remains poorly studied, but it represents a stepping stone to discerning where the transition from coherent to incoherent emission occurs. For FRBs, detections have been made up to 8 GHz. Thus, studying radio-emitting neutron stars at mm-waves offers a direct link to FRBs and may indicate whether they can be detected above the classic cm- window.

In this presentation, we will explore new capabilities at ALMA that enable the observation of radio transients from 35 up to 300 GHz. The Phased ALMA Mode (PAM) was introduced in Cycle 8 (2021) to enable observations of weak radio sources (< 50 mJy), but only recently, in Cycle 11 (2024), it became available with its low-frequency instrument, Band 1 (35–50 GHz), with full polarisation. Importantly, when ALMA’s 12-m antennas are coherently combined, they reach an equivalent sensitivity to an 80+ metre dish, enabling high-time resolution at mm-wavelengths with unparalleled sensitivity. We will present the results from the ongoing campaigns, with a focus on our pilot study of the Galactic Centre magnetar, PSR J1745–2900. For this source, we have detected a large sample of highly polarised pulses at 86 GHz and used them to study the stability of the PAM system for transient searches, as well as the potential to detect bursts from repeating FRBs.

Given the complex and strongly scattered environment around Sgr A*, this region offers a unique laboratory for testing the behaviour of magnetars in extreme, magneto-turbulent conditions and for probing possible connections with FRBs.

CV：

Prof. Cruces is based at the Center for Astroengineering UC in Chile, where she leads the Max Planck Partner Group of the Max Planck Institute for Radio Astronomy (MPIfR). Her group focuses on short-duration time-domain events, such as fast radio bursts (FRBs) and neutron-star populations including pulsars and magnetars, from centimetric to millimetric wavelengths. Their work aims to understand the emission mechanisms that drive transient phenomena in the Universe.

Prof. Cruces completed her PhD at the University of Bonn as part of the International Max Planck Research School for Astronomy & Astrophysics (IMPRS). She then joined the MPIfR as a postdoctoral researcher, contributing to the collaboration between Max Planck Society (MPG)–CAS on low-frequency gravitational-wave detection and gravitational physics (LEGACY project). After that, she moved to the European Southern Observatory (ESO) as an ALMA Fellow, where she explored the potential of ALMA for time-domain astronomy. Since August 2024, she has been at UC Chile, where she leads the Radio Transients Lab, an interdisciplinary group of astronomers, engineers, and data scientists working on transient radio emission and developing new software and hardware techniques for their detection, with an emphasis on reducing the cost and complexity of the required instrumentation.

Since May of this year, Prof. Cruces has been appointed PIFI Fellow of the Chinese Academy of Sciences.