The high energy Universe at ultra-high resolution: the power and promise of X-ray interferometry

Uttley, P.; Hartog, R. den; Bambi, Cosimo; Barret, D.; Bianchi, S.; Bursa, Michal; Cappi, M.; Casella, P.; Cash, Webster; Costantini, E.; Dauser, Thomas; Trigo, María Díaz; Gendreau, Keith C.; Grinberg, V.; Herder, Jan-Willem den; Ingram, Adam; Kara, Erin; Markoff, Sera; Mingo, B.; Panessa, F.; Poppenhäger, Katja; Różáńska, A.; Svoboda, Jiří; Wijers, R. A. M. J.; Willingale, R.; Wilms, J.; Wise, Michael

doi:10.1007/s10686-021-09724-w

Cited by 17 publications

(13 citation statements)

References 74 publications

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“…However, X-ray interferometry would be able to make a much larger impact. Such a mission concept has been proposed for the ESA Vision 2050 Programme [42], but it is not at all clear that the mission will be approved and/or technically feasible, as the technology challenges are considerable.…”

Section: Other Results and Future Prospectsmentioning

confidence: 99%

Probing Spacetime Foam with Extragalactic Sources of High-Energy Photons

Perlman

2022

Universe

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Quantum fluctuations can endow spacetime with a foamy structure. In this review article, we discuss our various proposals to observationally constrain models of spacetime foam. One way is to examine if the light wave-front from a distant quasar or GRB can be noticeably distorted by spacetime-foam-induced phase incoherence. As the phase fluctuations are proportional to the distance to the source but inversely proportional to the wavelength, ultra-high energy photons (>1 TeV) from distant sources are particularly useful. We elaborate on several proposals, including the possibility of detecting spacetime foam by observing “seeing disks” in the images of distant quasars and active galactic nuclei. We also discuss the appropriate distance measure for calculating the expected angular broadening. In addition, we discuss our more recent work in which we investigate whether wave-front distortions on small scales (due to spacetime foam) can cause distant objects become undetectable because the phase fluctuations have accumulated to the point at which image formation is impossible. Another possibility that has recently become accessible is to use interferometers to observe cosmologically distant sources, thereby giving a large baseline perpendicular to the local wave vector over which the wave front could become corrugated and thus distorted, reducing or eliminating its fringe visibility. We argue that all these methods ultimately depend on the availability of ways (if any) to carry out proper averaging of contributions from different light paths from the source to the telescope.

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Section: Other Results and Future Prospectsmentioning

confidence: 99%

Probing Spacetime Foam with Extragalactic Sources of High-Energy Photons

Perlman

2022

Universe

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“…Moving away from VLBI techniques, and further down the timeline, an interesting possibility is that of using constellations of satellites to perform X-ray interferometry (XRI). By ∼2060, XRI may be able to achieve sub-µas angular resolution [223]. It should be noted, however, that XRI is best suited for imaging SMBHs with optically thick disks: in this case, what is being observed (which we refer to as the "XRI BH shadow") is no longer the apparent image of the photon sphere, but the inner edge of the accretion disk.…”

Section: Discussionmentioning

confidence: 99%

Superradiance evolution of black hole shadows revisited

Roy,

Vagnozzi,

Visinelli

2021

Preprint

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Black hole (BH) shadows can be used to probe new physics in the form of ultra-light particles via the phenomenon of superradiant instability. By directly affecting the BH mass and spin, superradiance can lead to a time evolution of the BH shadow, which nonetheless has been argued to be unobservable through Very Long Baseline Interferometry (VLBI) over realistic observation timescales. We revisit the superradiance-induced BH shadow evolution including the competing effects of gas accretion and gravitational wave (GW) emission and, as a first step towards modelling realistic new physics scenarios which predict the existence of multiple ultra-light species, we study the system in the presence of two ultra-light bosons, whose combined effect could help reducing the shadow evolution timescale. We find that accretion and GW emission play a negligible role in our results (justifying previous simplified analyses), and that contrary to our intuition the inclusion of an additional ultra-light boson does not shorten the BH shadow evolution timescale and hence improve detection prospects. However, we point out an important subtlety concerning the observationally meaningful definition of the superradiance-induced BH shadow evolution timescale, which reduces the latter by about an order of magnitude, opening up the possibility of observing the superradiance-induced BH shadow evolution with upcoming VLBI arrays, provided angular resolutions just below the µas level can be reached. As a concrete example, we show that the angular size of the shadow of SgrA * can change by up to 0.6 µas over a period as short as 16 years, which further strengthens the scientific case for targeting the shadow of SgrA * with next-generation VLBI arrays.

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“…Archival Very Large Array (VLA) data show that these objects do align with the FP at lower angular resolution (∼500 mas, or 30-100 pc), suggesting that whatever is responsible for the apparent correlation between SMBH mass and X-ray/radio emission paradoxically occurs on larger physical scales, at least beyond the largest angular scale of the VLBA observations (∼50 mas, or 3-10 pc for the typical distances of the sample), far larger than the scales of the AGN corona where X-ray emission is generally considered to arise. On the other hand, for radio-loud (RL) AGNs, X-ray emission could be a superposition of different components such as synchrotron radiation from a jet, synchrotron self-Compton, emission from the accretion flow, and inverse Compton scattering of lowerenergy photons off a corona (Plotkin et al 2012), but for our sample AGNs, which are almost entirely radio-quiet (RQ; the exception is NGC 1052), the most likely explanation for the X-ray emission is the accretion disk corona, and so far no current or planned future missions can resolve the X-ray-emitting corona region in AGNs (although see Uttley et al 2021). Despite the proximity of AGNs in the volume-complete sample and their selection at hard X-rays (Oh et al 2018), only nine out of the 25 AGNs were detected in the VLBA observations with a sensitivity level of ∼20 μJy beam −1 from Paper I, raising the prospect of true "radio-silent" AGNs.…”

Section: Introductionmentioning

confidence: 92%

FRAMEx. III. Radio Emission in the Immediate Vicinity of Radio-quiet AGNs

Shuvo

Johnson

Secrest

et al. 2022

ApJ

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We present follow-up results from the first Fundamental Reference AGN Monitoring Experiment (FRAMEx) X-ray/radio snapshot program of a volume-complete sample of local hard X-ray-selected active galactic nuclei (AGNs). Here, we added nine new sources to our previous volume-complete snapshot campaign, two of which are detected in 6 cm Very Long Baseline Array (VLBA) observations. We also obtained deeper VLBA observations for a sample of nine AGNs not detected by our previous snapshot campaign. We recovered three sources with approximately twice the observing sensitivity. In contrast with lower-angular-resolution Very Large Array (VLA) studies, the majority of our sources continue to be undetected with the VLBA. The subparsec radio (6 cm) and X-ray (2–10 keV) emission shows no significant correlation, with L R/L X ranging from 10−8 to 10−4, and the majority of our sample lies well below the fiducial 10−5 relationship for coronal synchrotron emission. Additionally, our sources are not aligned with any of the proposed “fundamental” planes of black hole activity, which purport to unify black hole accretion in the M BH–L X–L R parameter space. The new detections in our deeper observations suggest that the radio emission may be produced by the synchrotron radiation of particles accelerated in low-luminosity outflows. Nondetections may be a result of synchrotron self-absorption at 6 cm in the radio core, similar to what has been observed in X-ray binaries transitioning from the radiatively inefficient state to a radiatively efficient state.

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The high energy Universe at ultra-high resolution: the power and promise of X-ray interferometry

Cited by 17 publications

References 74 publications

Probing Spacetime Foam with Extragalactic Sources of High-Energy Photons

Probing Spacetime Foam with Extragalactic Sources of High-Energy Photons

Superradiance evolution of black hole shadows revisited

FRAMEx. III. Radio Emission in the Immediate Vicinity of Radio-quiet AGNs

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