A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set
Pablo Torné, Kuo Liu, Ralph P. Eatough, J. Wongphechauxsorn, J. M. Cordes, G. Desvignes, Mariafelicia De Laurentis, Michael Kramer, S. M. Ransom, Shami Chatterjee, Robert Wharton, R. Karuppusamy, Lindy Blackburn, Michaël Janssen, Chi‐kwan Chan, G. Crew, Lynn D. Matthews, C. Goddi, Helge Rottmann, Jan Wagner, Salvador Sánchez, Ignacio Ruiz, Federico Abbate, Geoffrey C. Bower, Juan J. Salamanca, Arturo I. Gómez-Ruiz, Alfredo Herrera–Aguilar, Wu Jiang, Ru-Sen Lu, Ue‐Li Pen, Alexander W. Raymond, Lijing Shao, Zhi-Qiang Shen, G. Paubert, M. Sánchez‐Portal, C. Krämer, Manuel Castillo, S. Navarro, John David, K. Schüster, Michael D. Johnson, K. L. J. Rygl, Kazunori Akiyama, A. Alberdi, W. Alef, Juan Carlos Algaba, Richard Anantua, Keiichi Asada, Rebecca Azulay, U. Bach, Anne-Kathrin Baczko, David Ball, Mislav Baloković, John Barrett, Michi Bauböck, B. A. Benson, Dan Bintley, R. Blundell, Katherine L. Bouman, Hope Boyce, Michael Bremer, Christiaan D. Brinkerink, Roger Brissenden, S. Britzen, Avery E. Broderick, Dominique Broguière, Thomas Bronzwaer, Sandra Bustamante, Do‐Young Byun, J. E. Carlstrom, Chiara Ceccobello, Andrew Chael, Dominic O. Chang, Koushik Chatterjee, Ming‐Tang Chen, Yongjun 永军 Chen 陈, Xiaopeng Cheng, Ilje Cho, Pierre Christian, Nicholas S. Conroy, J. E. Conway, T. M. Crawford, Alejandro Cruz-Osorio, Yuzhu Cui, Rohan Dahale, Jordy Davelaar, Roger Deane, Jessica Dempsey, Jason Dexter, Vedant Dhruv, Sheperd S. Doeleman, Sean Dougal, Sergio A. Dzib, Razieh Emami, H. Falcke, Joseph Farah, Vincent L. Fish, Ed Fomalont, H. Alyson Ford, Marianna Foschi
Abstract
Abstract In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz ( λ = 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars—which typically exhibit steep emission spectra—are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (≲2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.