Enabling Transformational ngEHT Science via the Inclusion of 86 GHz Capabilities

Abstract

We present a case for significantly enhancing the utility and efficiency of the ngEHT by incorporating an additional 86 GHz observing band. In contrast to 230 or 345 GHz, weather conditions at the ngEHT sites are reliably good enough for 86 GHz to enable year-round observations. Multi-frequency imaging that incorporates 86 GHz observations would sufficiently augment the (u,v) coverage at 230 and 345 GHz to permit detection of the M87 jet structure without requiring EHT stations to join the array. The general calibration and sensitivity of the ngEHT would also be enhanced by leveraging frequency phase transfer techniques, whereby simultaneous observations at 86 GHz and higher-frequency bands have the potential to increase the effective coherence times from a few seconds to tens of minutes. When observation at the higher frequencies is not possible, there are opportunities for standalone 86 GHz science, such as studies of black hole jets and spectral lines. Finally, the addition of 86 GHz capabilities to the ngEHT would enable it to integrate into a community of other VLBI facilities—such as the GMVA and ngVLA—that are expected to operate at 86 GHz but not at the higher ngEHT observing frequencies.

Multifrequency Black Hole Imaging for the Next-generation Event Horizon Telescope

“…In this section, we present multifrequency reconstructions of synthetic GRMHD simulation models of the emission from M87 * as observed by the ngEHT. For ngEHT station locations and telescope parameters, we use the proposed ngEHT reference array presented in Issaoun et al (2023) that was developed from the site-selection considerations presented in Raymond et al (2021). The ngEHT sites we use in generating synthetic data are summarized in Table 1 and are mapped in Figure 1.…”

“…The geographical and weather properties of these sites were described in Raymond et al (2021). The potential ngEHT station configuration used in this paper and its 86 GHz capabilities are described in Issaoun et al (2023).…”

“…The resulting decrease in sensitivity limits the overall number of detected data points and reduces the signal-to-noise ratio (S/N) of the data points that are detected, relative to observations at lower frequencies. We note that for the ngEHT, it may be possible to use frequency phase transfer (FPT) techniques (e.g., Rioja & Dodson 2011;Dodson et al 2017;Rioja & Dodson 2020) to bootstrap atmospheric phase solutions from lower-frequency observations up to 345 GHz, thereby substantially extending the coherent integration time and enabling additional detections (e.g., Issaoun et al 2023). However, in this paper we do not simulate observations that take advantage of FPT techniques.…”

“…Rapid filling of the u − v plane from these additional sites will also allow for robust imaging of rapid variability in the accretion flow around Sgr A * . In addition to adding new sites, the ngEHT will also increase the observing bandwidth and the range of observed frequencies up to 345 GHz and (potentially) down to 86 GHz (Doeleman et al 2019;Issaoun et al 2023).…”

Key Science Goals for the Next-Generation Event Horizon Telescope

“…The next-generation EHT (ngEHT) is a project to design and build a significantly enhanced EHT array through the upgrade, integration, or deployment of additional stations (e.g., [37][38][39][40][41][42][43][44]), the use of simultaneous observations at three observing frequencies [45][46][47], and observations that extend over several months or more with a dense coverage in time [48]. The ngEHT currently envisions two primary development phases.…”