Synergies of THESEUS with the large facilities of the 2030s and guest observer opportunities

Abstract

The proposed THESEUS mission will vastly expand the capabilities to monitor the high-energy sky. It will specifically exploit large samples of gamma-ray bursts to probe the early universe back to the first generation of stars, and to advance multi-messenger astrophysics by detecting and localizing the counterparts of gravitational waves and cosmic neutrino sources. The combination and coordination of these activities with multi-wavelength, multi-messenger facilities expected to be operating in the 2030s will open new avenues of exploration in many areas of astrophysics, cosmology and fundamental physics, thus adding considerable strength to the overall scientific impact of THESEUS and these facilities. We discuss here a number of these powerful synergies and guest observer opportunities.

Keywords: Gamma-ray bursts; Gravitation wave sources; Multi-messenger astrophysics; Neutrino sources; X-ray sources.

Fig. 1

THESEUS will work in synergy on a number of themes (bullets) with major multi-messenger facilities in the 2030s and will provide targets and triggers for follow-up observations with several of these facilities

Fig. 2

A simulated Athena/X-IFU spectrum of a medium bright (fluence: 4 × 10^− 7 erg cm^− 2) z = 7 GRB afterglow characterized by deep resonant lines from the ISM of the GRB host galaxy. An effective intrinsic column density of 2 × 10²² cm^− 2 was assumed [credit: Athena/X-IFU Consortium]

Fig. 3

Expected H-band light curves of the afterglow of high redshift GRBs and a kilonova from NS-NS merger at 300 Mpc. The shaded area indicates the median (black line) and 1-σ scatter of 100 simulated light curves drawn from GRB population models at z > 6 following [11]. The red curve represents the kilonova associated to GW170817, projected to a distance of 300 Mpc, using H-band photometry from [12]. Horizontal lines indicate the limiting magnitude of THESEUS IRT (600s and 1800s exposure for photometric and spectroscopic limit, with SNR= 5 and 3, respectively,) and ESO ELT-MICADO (1 h exposure with SNR = 5) in imaging and spectroscopic mode respectively (re-adapted from [13])

Fig. 4

Representation of the 21 cm absorption lines (known as the “21 cm forest”) produced by non-linear structures during the early stage of reionization [17]

Fig. 5

Strain sensitivities as a function of frequency for the next generation of GW observatories, ET [50] and CE Phase I [45] with respect to the sensitivities of the upgraded instruments of the existing LIGO, Virgo and Kagra expected to be operational in 2025 [47], and LIGO Voyager [48], a possible major upgrade of the LIGO inteferometers in the late 2020s

Fig. 6

Detection efficiency for binary neutron star mergers by ET alone, ET operating with CE located in USA, and ET operating with one CE in USA and one CE in Australia. Detection SNR threshold set equal to 8

Fig. 7

THESEUS can cover with a single exposure most of the sky uncertainty regions that will be obtained from GW source detection with both 2G and 3G interferometers (red contours), allowing independent detection of the electromagnetic counterpart and accurate sky localization down to arcmin/arcsec level, exploiting the SXI and IRT instruments

Fig. 8

Example of the ratio of the gravitational to electromagnetic luminosity distance in a modified gravity model, for different values of a parameter related to the energy scale of inflation. In the upper curve, the deviations of $d_L^{\text{gw}}(z)$ from $d_L^{\text{em}}(z)$ reaches 60% at large redshift (from [69])

Fig. 9

Schematic view of a neutrino telescope. An array of photo sensors is embedded in a large volume of a transparent medium (water or ice) to determine the direction and energy of secondary charged particles induced by neutrino interactions using the Cherenkov radiation. The figure shows the layout of the KM3NeT detector, in construction in the Mediterranean Sea with one of the multi-PMT sensor (credit: KM3NeT Collaboration, km3net.org)