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A possible planet candidate in an external galaxy detected through X-ray transit according to Financial Times (9-october-2021)
The X-xay binary M51-ULS-1.The X-ray observations we employed from both Chandra and XMM-Newton are summarized in Extended Data Figs. During a 190 ks Chandra pointing, the X-ray light curve exhibited a fall from baseline to zero flux and then an approximately symmetric rise back to base-line. The event, shown in Fig. Extended Data Fig. before and after the flux dip,had been estimated to be RX = 2.5+4.1 109 cm 7. X-ray data collected just prior to and after the dip to zero flux. Hubble Space Telescope image, consistent with stellar type, Second, based on the visual field, there is a probability of only 0.17 that a star this bright would happen to be at the location of M51-ULS-1 by chance. In addition, the HST image of the region around M51-ULS-1, shown next to the Chandra image in Fig. Nature of the X-ray dip To determine whether the characteristics of the event we identified set it apart, we compare it with other types of dipping events. Accretion-related dips were first observed in low-mass XRBs, binaries in which a black hole or neutron star accretes matter from a companion with 3 shows the light curve containing the event in context with light curves that were not selected. He average effective radius of the X-ray-emitting region during this observation, mass between a few tenths of a solar mass and a few solar masses. XRBs exhibit both eclipses and dips, with single or multiple dips in flux occurring between eclipses, often within a specific range of orbital phases. The most obvious difference between a dip and an eclipse is, however, that dips display energy dependence. Accretion dips occur in other types of XRBs and even in young stars. Figure 3 shows a dipping ultra luminous soft XRS in M101,M101-ULS, exhibiting considerable intensity and spectral variability during a Chandra observation. The middle panel shows the spectral variations explicitly, with each dot representing a photon of a given energy that arrived at a given time. The running median energy over the 16 nearest photons in time is shown as the teal curve, with vertical dotted lines marking every 17th photon. The spectrum softens significantly during the dip compared to its state just prior to it. There is no evidence for a sharp change in the spectrum with intensity. Furthermore, a formal two-sample Kolmogorov–Smirnov test on the energy distributions of the photons obtained during periods of the intensity decrease, the minimum and the intensity increase, compared with the energy distributions obtained during the baseline, yields p values of 0.76, 0.93 and 0.85 respectively, showing that the spectrum obtained during the event cannot be distinguished from that outside the event. These characteristics suggest that the event is caused by the passage of an opaque body with sharp borders in front of the source. Note that this type of spectral stability is also exhibited by eclipses of an XRS by its donor star. M51-ULS-1 data include evidence of both an ingress to and an egress from eclipse. Data Fig. In addition, the XRS in M51-ULS-1, whose spectrum is fit by a thermal model, can also be well modelled in two dimensions as a circle. Finally, we note that the shape of the sharp wall-like structures observed in many planetary transits is associated with the very small size of the planet relative to the star. When, however, the sizes of the planet and star are more similar to each other, the decline and subsequent recovery of the flux are more gradual. We model the intensity dip seen at ~150ks into the observation as an eclipse in which an opaque circular body obscures the We limit the time range of fit to a small interval around the dip so that the intensity of the XRS may be assumed to be constant. The events are binned at t=471.156s, corresponding to 150 times the charged couple device readout duration, yield ing an XRS intensity of cX≈7.5 counts per bin. We carry out the fit using a method optimized to analyse low-count X-ray data explicitly using the Poisson likelihood, as it is appropriate in this regime. First, the value of the mode of the distribution of transiter radii is fec=0.74, corresponding to a physical size com-parable to Saturn’s. Second, the mode of the relative speed between the transiter and the XRS is only 17 kms−1. This indicates that the distance between the XRB and the transiting object is much larger than the radius of the inner binary . The probability distribution of transiter radii is shown in Fig. 5, supplemented by additional information about the physical radii of possible transiters. Extended Data Figs. 8–10 show, respectively, the model-derived nominal and cumulative probability distributions of transiter radii, the marginalized posterior distributions of other fit parameters and several joint posterior distributions. The nature of the transiting object 5 represents the probability distribution of transiter radii. Superposed is information about the galactic population of planets, brown dwarfs and M dwarfs. These planetary radii fall within the 90% uncertainty interval of the probability distribution, but have a peak at about 1.4 Jupiter radii. Neptune below the mode and Saturn slightly above it, followed by There is a significant probability that the transiting object is smaller than Jupiter. The red dashed line farther to the right corresponds to the radius of the young brown dwarf, RIK 72b. RIK 72b illustrates, the probabilities of large-radii transiters are small. The youth of the XRB also serves to make it highly unlikely that the transiter is either a brown dwarf or an M dwarf. Members of each of these two classes are born with radii larger than our 90% limit. The radius of a 0.1M⊙ M dwarf takes roughly 50Myr to decrease to 2RJ. Beyond that, M dwarf radii tend to be 5–10%larger than predicted by theory, and can be ‘inflated’ by up to 50%, even for stars older than 100Myr. In addition, brown dwarfs are rare relative to planets, a phenomenon known as the ‘brown dwarf desert’ 19,20. At this distance, the incoming flux can be com-parable to the flux received by a ‘hot Jupiter’ from a Sun-like star. We can gain insight from a number of investigations that consider the effects of comparable received flux on planetary atmospheres, some even considering stars with energy output at ultraviolet or X-ray wavelengths21,22. The transiter in M51-ULS-1 shows no signs of ablation, which would likely alter the eclipse profile and introduce energy dependence detectable through a change in hardness ratio. 2Myr and younger than 108 yr and with orbital separations between The catalog includes brown dwarfs as well as planets. Note that when the source and eclipse are of the same size and perfectly aligned , then X = ec = arccos d Here we describe the MCMC based fitting29 that we carry out to estimate the parameters of the eclipse light curve model described in Modeling the short-duration event as a transit’. We do not explicitly tie together fec and b, although the fact that an eclipse is observed requires that b40kms−1 are predominantly obtained when fec>2RJ, which itself has a lowered probability of explaining the data. Thus, the preponderance of the probability suggests that the system is better described with smaller values of fec and vpl.