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We discuss applications of the study of the new and barely explored class of changing-look (CL) narrow-line Seyfert 1 (NLS1) galaxies and comment on their detection with the space mission SVOM (Space Variable Objects Monitor). We highlight the case of NGC 1566, which is outstanding in many respects, for instance as one of the nearest known CL AGN undergoing exceptional outbursts. Its NLS1 nature is discussed, and we take it as a nearby prototype for systems that could be discovered and studied in the near future, including with SVOM. Finally, we briefly examine the broader implications and applications of CL events in NLS1 galaxies and show that such systems, once discovered in larger numbers, will greatly advance our understanding of the physics of the environment of rapidly growing supermassive black holes. This White Paper is part of a sequence of publications which explore aspects of our understanding of (CL) NLS1 galaxy physics with future missions.

The Microchannel X-ray Telescope (MXT) will be the first focusing X-ray telescope based on a narrow field “Lobster-Eye” optical design to be flown on a satellite, namely the Sino-French mission SVOM. SVOM will be dedicated to the study of Gamma-Ray Bursts and more generally time-domain astrophysics. The MXT telescope is a compact (focal length ∼ 1.15 m) and light (< 42 kg) instrument, sensitive in the 0.2–10 keV energy range. It is composed of an optical system, based on micro-pore optics (MPOs) of 40 μ m pore size, coupled to a low-noise pnCDD X-ray detector. In this paper we describe the expected scientific performance of the MXT telescope, based on the End-to-End calibration campaign performed in fall 2021, before the integration of the SVOM payload on the satellite.

RECENT observations 1,2 with the γ-ray telescope SIGMA, on the GRANAT satellite, indicated that the hard X-ray source 1E1740.7 – 2942 may be the source of the strongest outbursts of 511-keV electron-positron annihilation radiation from the Galactic Centre region 3 . We have observed this source using the Very Large Array, and find that its radio structure is that of a doublesided jet emanating from a compact and variable core. The changes in flux density and spectral index of the core are correlated with variations in the hard X-ray output. The jets are symmetrical about the core, and end in edge-brightened radio lobes; they are probably a result of synchrotron emission of electrons and positrons from the compact core. Our observation suggest that 1E1740.7 – 2942 is a 'microquasar' stellar remnant near the Galactic Centre, which ejects positrons that travel more than a parsec before slowing and annihilating in the interstellar gas.

We discuss applications of the study of the new and barely explored class of changing-look (CL) narrow-line Seyfert 1 (NLS1) galaxies and comment on their detection with the space mission SVOM (Space Variable Objects Monitor). We highlight the case of NGC 1566, which is outstanding in many respects, for instance as one of the nearest known CL AGN undergoing exceptional outbursts. Its NLS1 nature is discussed, and we take it as a nearby prototype for systems that could be discovered and studied in the near future, including with SVOM. Finally, we briefly examine the broader implications and applications of CL events in NLS1 galaxies and show that such systems, once discovered in larger numbers, will greatly advance our understanding of the physics of the environment of rapidly growing supermassive black holes. This White Paper is part of a sequence of publications which explore aspects of our understanding of (CL) NLS1 galaxy physics with future missions.

THE centre of our Galaxy is known to contain a large condensation of mass 1 , and it has been suggested that a massive black hole (of several million solar masses) is located there. Massive black holes have been proposed to explain active galactic nuclei, and if the Galactic Centre is a less-powerful version of such sources it should radiate X-rays and γ-rays 1 . But although earlier observations 2–6 have shown that the region does emit X-rays and y-rays, the true centre, corresponding to the object Sagittarius A * , does not emit strongly at least up to energies of 30 keV (refs 4–6). Whether Sgr A * emits radiation at higher energies, however, was not resolved. Here we present the results of a deep imaging survey of the Galactic Centre, performed with the Sigma/GRANAT tele-scope. We determine the locations of the nine hard X-ray sources— six of them being observed for the first time in the spectral band— to an accuracy of about 2 arcmin, but find no source associated with Sgr A * . The hard X-ray luminosity of Sgr A * is a factor of 4 × 10 7 less than that expected for a black hole of a million solar masses accreting gas at the maximum stable rate, challenging the idea that there is a black hole at the Galactic Centre.

The Sino-French space mission SVOM is mainly designed to detect, localize and follow-up Gamma-Ray Bursts and other high-energy transients. The satellite, to be launched mid 2023, embarks two wide-field gamma-ray instruments and two narrow-field telescopes operating at X-ray and optical wavelengths. It is complemented by a dedicated ground segment encompassing a set of wide-field optical cameras and two 1-meter class follow-up telescopes. In this contribution, we describe the main characteristics of the mission and discuss its scientific rationale and some original GRB studies that it will enable.

Cystinosis is an autosomal recessive disorder characterized by intra‐lysosomal accumulation of cystine. Three disease forms exist, infantile, juvenile, and ocular nonnephropathic cystinosis, delineated on the basis of severity of symptoms and age of onset. Mutations in the causative gene, CTNS, which encodes cystinosin, the seven transmembrane domain lysosomal cystine transporter, have been identified in all forms confirming their allelic status. By screening for mutations in the CTNS exons and promotor region, we report 14 novel mutations associated with cystinosis: 11 underlying infantile cystinosis, two juvenile cystinosis, and one associated with an atypical form of the disease. These mutations, all situated in the exons or immediately flanking intronic sequences, comprise in‐frame insertions and deletions, as well as missense, nonsense, and putative splice‐site mutations. Furthermore, we confirmed the putative splice‐site mutations we have reported to date (five novel and two previously reported) by isolation of RNA from the affected carriers and characterization of the resultant transcripts using RT‐PCR. Since the cloning of CTNS, we have screened for mutations in 108 affected individuals, which has resulted in a high mutation detection rate of 95.8%. Interestingly, the few undetectable mono‐ or bi‐allelic mutations segregated mostly in the noninfantile forms, suggesting that these individuals carry mutations either in the introns or in unidentified regulatory sequences. Hum Mutat 20:439–446, 2002. © 2002 Wiley‐Liss, Inc.

The majority of energetic long-duration gamma-ray bursts (GRBs) are thought to arise from the collapse of massive stars, making them powerful tracers of star formation across cosmic time. Evidence for this origin comes from the presence of supernovae in the aftermath of the GRB event, whose properties in turn link back to those of the collapsing star. In principle, with GRBs we can study the properties of individual stars in the distant universe. Here, we present JWST/NIRCAM observations that detect both the host galaxy and likely supernova in the SVOM GRB 250314A with a spectroscopically measured redshift of z \\(\\simeq\\) 7.3, deep in the era of reionisation. The data are well described by a combination of faint blue host, similar to many z \\(\\sim\\) 7 galaxies, with a supernova of similar luminosity to the proto-type GRB supernova, SN 1998bw. Although larger galaxy contributions cannot be robustly excluded, given the evidence from the blue afterglow colours of low dust extinction, supernovae much brighter than SN 1998bw can be. These observations suggest that, despite disparate physical conditions, the star that created GRB 250314A was similar to GRB progenitors in the local universe.

The SVOM mission under development will carry various instruments, and in particular the coded-mask telescope ECLAIRs, with a large field of view of about 2 sr, operating in the 4--150 keV energy band, whose goal is to detect high energy transients such as gamma-ray bursts. The trigger software onboard ECLAIRs will search for new hard X-ray sources appearing in the sky, as well as peculiar behaviour (e.g. strong outbursts) from known sources, in order to repoint the satellite to perform follow-up observations with its onboard narrow field of view instruments. The presence of known X-ray sources must be disentangled from the appearance of new sources. This is done with the help of an onboard source catalogue, which we present in this paper. As an input we use catalogues of X-ray sources detected by Swift/BAT and MAXI/GSC and we study the influence of the sources on ECLAIRs' background level and on the quality of the sky image reconstruction process. We show that the influence of the sources depends on the pointing direction on the sky, on the energy band and on the exposure time. In the Galactic centre, the known sources contribution largely dominates the cosmic X-ray background, which is, on the contrary, the main background in sky regions empty of strong sources. We also demonstrate the need to clean the sources contributions in order to maintain a low noise level in the sky images and to keep the threshold applied for the detection of new sources as low as possible, without introducing false triggers. We briefly describe one of our cleaning methods and its challenges. Finally, we present the overall structure of the onboard catalogue and the way it will be used to perform the source cleaning and disentangle the detections of new sources from outbursts of known sources.

The Microchannel X-ray Telescope (MXT) will be the first focusing X-ray telescope based on a \"Lobster-Eye\" optical design to be flown on Sino-French mission SVOM. SVOM will be dedicated to the study of Gamma-Ray Bursts and more generally time-domain astrophysics. The MXT telescope is a compact (focal length ~ 1.15 m) and light (< 42 kg) instrument, sensitive in the 0.2--10 keV energy range. It is composed of an optical system, based on micro-pore optics (MPOs) of 40 micron pore size, coupled to a low-noise pnCDD X-ray detector. In this paper we describe the expected scientific performance of the MXT telescope, based on the End-to-End calibration campaign performed in fall 2021, before the integration of the SVOM payload on the satellite.