NEWS: THESEUS 2021 Conference
The THESEUS mission
THESEUS is a mission concept proposed in response to the ESA call for medium-size mission (M5) within the Cosmic Vision Programme and selected by ESA on 2018 May 7 to enter an assessment phase study (part of banner image credits: Loeb 2006 & ESO).
The mission is designed to vastly increase the discovery space of the high energy transient phenomena over the entirety of cosmic history. Its primary scientific goals will address the Early Universe ESA Cosmic Vision themes “How did the Universe originate and what is made of?” (4.1, 4.2 and 4.3) and will also impact on “The gravitational wave Universe” (3.2) and “The hot and energetic Universe” themes. This is achieved via a unique payload providing an unprecedented combination of: 1) wide and deep sky monitoring in a broad energy band (0.3 keV - 20 MeV); 2) focusing capabilities in the soft X-ray band providing large grasp and high angular resolution; and 3) on board near-IR capabilities for immediate transient identification and redshift determination.
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Left: long gamma-ray bursts in the cosmological context (adapted from the NASA/WMAP team). Right: short gamma-ray bursts as electromagnetic counter-parts of the gravitational wave signal emitted by merging neutron stars (credits: LIGO/VIRGO collaboration). |
The foreseen payload of THESEUS includes the following instrumentation:
- Soft X-ray Imager (SXI, 0.3 – 5 keV): a set of 2 lobster-eye telescopes units, covering a total field of view (FOV) of ~0.5sr with source location accuracy < 1-2’;
- InfraRed Telescope (IRT, 0.7 – 1.8 μm): a 0.7m class IR telescope with 15’x15’ FOV, for fast response, with both imaging and spectroscopy capabilities;
- X-Gamma rays Imaging Spectrometer (XGIS, 2 keV – 20 MeV): a set of 2 coded-mask cameras using monolithic X-gamma rays detectors based on bars of Silicon diodes coupled with CsI crystal scintillator, granting a ~2sr FOV and a source location accuracy of ~10 arcmin in the 2-150 keV, as well as a >4sr FoV at energies >150 keV.
A sketch of the THESEUS satellite showing the instruments accommodation is shown on the left panel (credits: ESA). |
The mission profile includes: an onboard data handling units (DHUs) system capable of detecting, identifying and localizing likely transients in the SXI and XGIS FOV; the capability of promptly (within a few tens of seconds at most) transmitting to ground the trigger time and position of GRBs (and other transients of interest); and a spacecraft slewing capability of at least 6°/minute. The baseline launcher / orbit configuration is a launch with Vega-C to a low inclination low Earth orbit (LEO, ~600 km, <5°), which has the unique advantages of granting a low and stable background level in the high-energy instruments, allowing the exploitation of the Earth’s magnetic field for spacecraft fast slewing and facilitating the prompt transmission of transient triggers and positions to the ground.
The left panel shows the cumulative distribution of GRBs with redshift determination as a function of the redshift for Swift (in 10 yr) and the prediction for THESEUS (in 3 yr). The panel on the right shows the sensitivity of THESEUS for different classes of sources. |
The main scientific goals of the proposed mission are to:
By satisfying the requirements coming from the above main science drivers, the THESEUS payload will also automatically enable excellent observatory science opportunities, including, e.g., performing IR observatory science, especially providing capability for response to external triggers, thus allowing strong community involvement. We remark that THESEUS has survey capabilities for high-energy transient phenomena complementary to the Large Synoptic Survey Telescope (LSST) in the optical. Their joint availability in the next decade would enable a remarkable scientific synergy between them. |
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Top left: THESEUS will have the ideal combination of instrumentation and mission profile for detecting all types of GRBs (long, short/hard, weak/soft, high-redshift), localizing them from a few arcmindown to arsecand measure the redshift for a large fraction of them. Top right: the detection, study and arcsecond localization of afterglow and kilonova emission from short GRB/GW events will be possible with THESEUS/IRT. In this figure, we show in particular the light curve of the kilonova associated to the gravitational wave/short GRB event GW170817/GRB170817A in the IRT filters. The continuous and dashed red lines indicate the THESEUS/IRT limiting H magnitudes for imaging and prism spectroscopy, respectively, with 300s of exposure.Bottom: expected X-ray fluxes at peak luminosity for z=0.05 and from different models of magnetar-powered X-ray emission from long-lived NS-NS merger remnants. Predictions from each model are represented by a coloured region and/or by single dots that are indicative of fiducial cases (see the legend on the right). Grey solid lines show typical GRB X-ray afterglows observed with Swift/XRT. The dashed/solid curves show the SXI sensitivity vs. exposure time, assuming a source column density of 5x1020 cm−2 (i.e., well out of the Galactic plane and very little intrinsic absorption, solid line) and 1022 cm−2 (significant intrinsic absorption, dashed line). |
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THESEUS synergies in the field of the early Universe exploration (top) and the time-domain multi-messenger Astrophysics (bottom). |