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Register a new userExploiting the IRT-THESEUS capability to observe lensed Quasars
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THESEUS is an ESA space based project, aiming to explore the early universe by unveiling a complete census of Gamma-Ray Burst (GRB) population in the first billion years. This goal is expected to be achieved by combined observations of its three instruments: the Soft X-ray Imager (SXI), the X and Gamma Imaging Spectrometer (XGIS) and the InfraRed Telescope (IRT). In particular, the IRT instrument will help to identify, localise and study the afterglow of the GRBs detected by SXI and XGIS, and about $40%$ of its time will be devoted to an all-sky photometric survey, which will certainly detect a relevant number of extragalactic sources, including Quasars. In this paper, we focus on the capability of IRT-THESEUS Telescope to observe Quasars and, in particular, those objects lensed by foreground galaxies. In our analysis, we consider the Quasar Luminosity Function (QLF) in the infrared band based obtained by the Spitzer Space Telescope imaging survey. Furthermore, by using the mass-luminosity distribution function of galaxies and the galaxy/Quasar redshift distributions, we preformed Monte Carlo simulations to estimate the number of lensed Quasars. We predict that up to $2.14 times 10^5$ Quasars can be observed during gthe IRT-Theseus sky survey, and about $140$ of them could be lensed by foreground galaxies. Detailed studies of these events would provide a powerful probe of the physical properties of Quasars and the mass distribution models of the galaxies.
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The Infra-Red Telescope (IRT) is part of the payload of the THESEUS mission, which is one of the two ESA M5 candidates within the Cosmic Vision program, planned for launch in 2032. The THESEUS payload, composed by two high energy wide field monitors (SXI and XGIS) and a near infra-red telescope (IRT), is optimized to detect, localize and characterize Gamma-Ray Bursts and other high-energy transients. The main goal of the IRT is to identify and precisely localize the NIR counterparts of the high-energy sources and to measure their distance. Here we present the design of the IRT and its expected performance.
With the discovery of the electromagnetic counterpart of the gravitational wave source GW170817 the multi-messenger era is started. The identification of an electromagnetic counterpart is crucial to understand the nature of the detected gravitational wave sources and to maximize the scientific return of their detections. The role of the instrument THESEUS/IRT will be crucial in this field, in particular in localizing afterglows of gamma-ray bursts within few minutes from the trigger and in identifying optical/NIR isotropic emissions such as kilonovae.
The large optical reflector (~ 100 m^2) of a H.E.S.S. Cherenkov telescope was used to search for very fast optical transients of astrophysical origin. 43 hours of observations targeting stellar-mass black holes and neutron stars were obtained using a dedicated photometer with microsecond time resolution. The photometer consists of seven photomultiplier tube pixels: a central one to monitor the target and a surrounding ring of six pixels to veto background events. The light curves of all pixels were recorded continuously and were searched offline with a matched-filtering technique for flares with a duration of 2 us to 100 ms. As expected, many unresolved (<3 us) and many long (>500 us) background events originating in the earths atmosphere were detected. In the time range 3 to 500 us the measurement is essentially background-free, with only eight events detected in 43 h; five from lightning and three presumably from a piece of space debris. The detection of flashes of brightness ~ 0.1 Jy and only 20 us duration from the space debris shows the potential of this setup to find rare optical flares on timescales of tens of microseconds. This timescale corresponds to the light crossing time of stellar-mass black holes and neutron stars.
Recent work has demonstrated the potential of gravitationally lensed quasars to extend measurements of black hole spin out to high-redshift with the current generation of X-ray observatories. Here we present an analysis of a large sample of 27 lensed quasars in the redshift range 1.0<z<4.5 observed with Chandra, utilizing over 1.6 Ms of total observing time, focusing on the rest-frame iron K emission from these sources. Although the X-ray signal-to-noise (S/N) currently available does not permit the detection of iron emission from the inner accretion disk in individual cases in our sample, we find significant structure in the stacked residuals. In addition to the narrow core, seen almost ubiquitously in local AGN, we find evidence for an additional underlying broad component from the inner accretion disk, with a clear red wing to the emission profile. Based on simulations, we find the detection of this broader component to be significant at greater than the 3-sigma level. This implies that iron emission from the inner disk is relatively common in the population of lensed quasars, and in turn further demonstrates that, with additional observations, this population represents an opportunity to significantly extend the sample of AGN spin measurements out to high-redshift.
Gravitational lens systems containing lensed quasars are important as cosmological probes, as diagnostics of structural properties of the lensing galaxies and as tools to study the quasars themselves. The largest lensed quasar sample is the SDSS Quasar Lens Search, drawn from the Sloan Digital Sky Survey (SDSS). We are attempting to extend this survey using observations of lens candidates selected from a combination of the quasar sample from the SDSS and the UKIRT Infrared Deep Sky Survey (UKIDSS). This adds somewhat higher image quality together with a wider range of wavelength for the selection process. In previous pilot surveys we observed 5 objects, finding 2 lenses; here we present further observations of 20 objects in which we find 4 lenses, of which 2 are independently discovered in SQLS (in preparation). Following earlier work on the combination of these two surveys, we have refined our method and find that use of a colour-separation diagnostic, where we select for separations between components which appear to decrease in wavelength, is an efficient method to find lensed quasars and may be useful in ongoing and future large-scale strong lensing surveys with instruments such as Pan-STARRS and LSST. The new lenses have mostly high flux ratios, with faint secondaries buried in the lensing galaxy and typically 6-10 times less bright than the primary. Our survey brings the total number of lenses discovered in the SDSS quasar sample to 46, plus 13 lenses already known. This is likely to be up to 60-70% of the total number of lensed quasars; we briefly discuss strategies by which the rest might be found.
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