An 86 GHz Search for Pulsars in the Galactic Center with the Atacama Large Millimeter / submillimeter Array

Abstract

We report on the first pulsar and transient survey of the Galactic Center (GC) with the Atacama Large Millimeter/ submillimeter Array (ALMA). The observations were conducted during the Global Millimeter VLBI Array campaign in 2017 and 2018. We carry out searches using time series of both total intensity and other polarization components in the form of Stokes parameters. We incorporate acceleration and its derivative in the pulsar search, and also search in segments of the entire observation to compensate for potential orbital motion of the pulsar. While no new pulsar is found, our observations yield the polarization profile of the GC magnetar PSR J1745−2900 at millimeter wavelength for the first time, which turns out to be nearly 100% linearly polarized. Additionally, we estimate the survey sensitivity placed by both system and red noise, and evaluate its capability of finding pulsars in orbital motion with either Sgr A * or a binary companion. We show that the survey is sensitive to only the most luminous pulsars in the known population and future observations with ALMA in Band-1 will deliver significantly deeper survey sensitivity on the GC pulsar population.

4–8 GHz Fourier-domain Searches for Galactic Center Pulsars

“…Motivated by the rich rewards of GC pulsar timing, numerous extensive surveys of the GC have been previously undertaken over a broad range of radio frequencies (e.g., Johnston et al 2006;Deneva et al 2009;Macquart et al 2010;Bates et al 2011;Eatough et al 2013aEatough et al , 2013bSiemion et al 2013;Eatough et al 2021;Liu et al 2021;Torne et al 2021, etc.). To date, these endeavors have revealed a single magnetar, namely PSR J1745−2900 (Eatough et al 2013b) at 2 4 offset from Sgr A * , and five pulsars, all located 10′ away from Sgr A * .…”

Submillimeter pulsations from the magnetar XTE J1810-197

“…However, if we would select only the broad component from 6 GHz to fit a single power law, the measured spectral index α c would be even more inverted and would not improve the fit to the points above 200 GHz. Full-polarization information at the millimeter and submillimeter wavelengths would enable a better understanding of the viewing geometry (e.g., Liu et al 2021), and a comparison with the measurements at centimeter wavelengths (Kramer et al 2007;Camilo et al 2007a;Dai et al 2019). The polarization degree and position angle could help to identify equivalent components among frequency bands.…”

A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set

“…The exact relationship between sensitivity, pulsar spin period, acceleration (or orbital period), jerk, pipeline parameters, and observing time is complex (see, e.g., Eatough et al 2021;Liu et al 2021). Nonetheless, with the parameters zmax and wmax chosen here, we can correct for the line-of-sight acceleration of virtually any pulsar orbiting Sgr A * down to orbital periods P b 2.5 yr (assuming circular orbits).…”

“…In practice, Equation ( 5) is known to overestimate the realistic sensitivity of a pulsar search. This is particularly true for slow pulsars with large duty cycles, when red noise is prominent in the data (Lazarus et al 2015;Eatough et al 2021;Liu et al 2021). Therefore, a more practical, accurate estimate is obtained empirically by injecting synthetic pulsar signals each time of a different flux density into the real data, conducting the search, and obtaining the minimum detectable flux density.…”

“…The first attempts at searching the GC for pulsars at millimeter wavelengths were undertaken with the IRAM 30 m Telescope (λ ; 2, 3 mm; Torne et al 2021) and the Atacama Large Millimeter/submillimeter Array (ALMA; λ ; 3.5 mm; Liu et al 2021). In this work we report the first 1.3 mm searches for GC pulsars using data from the EHT 2017 campaign on Sgr A * .…”