TL;DR: NASA's X-ray community capped a busy mid-September 2026 with open calls for XRISM legacy surveys, new polarization and timing clues to black-hole coronas and winds, and two deep Chandra catalogs tracing faint cosmic beacons.
A legacy window opens for XRISM
The X-ray Imaging and Spectroscopy Mission (XRISM) marked three years since launch during the weekend before September 14, 2026, and used the anniversary to open a new kind of observing opportunity.
According to NASA Science in "XRISM Key Program Call for Proposals," observations to date delivered results on the assembly of large-scale cosmic structures, the joint growth of galaxies and supermassive black holes, and plasma physics, while also producing unexpected discoveries that raised new questions.
The project response is Key Programs, described as strategic, large-scale observation programs intended to generate legacy data and results of broad value to the astronomical community. The first Key Programs are scheduled to begin in June 2027, with approximately 3 Ms of observing time allocated.
The proposal deadline is December 4, 2026, at 8:59 a.m. Japan Standard Time, which corresponds to December 3, 2026, at 6:59 p.m. Eastern and 3:59 p.m. Pacific. Data obtained through Key Program observations will be made publicly available without an exclusive access period. The announcement directs researchers worldwide to the Key Program webpage for guidelines and updated science objectives.
For U.S. researchers, the terms matter: no proprietary hold means student teams, small-college groups, and archival researchers can work with the same large uniform datasets as the proposing teams.
NGC 4151 polarization points to compact corona
A second thread concerns the shape of the hot X-ray source around a supermassive black hole.
A study published September 14, 2026, in The Astrophysical Journal as "Disk Reflection as the Origin of the X-Ray Polarization of NGC4151 with IXPE" re-examined the nearby type 1 active galactic nucleus NGC 4151 with two long Imaging X-ray Polarimetry Explorer (IXPE) observations from 2022 and 2024, supported by simultaneous XMM-Newton and NuSTAR spectroscopy.
IXPE measured a polarization degree of about 6%-7% above 4 keV, with a polarization angle parallel to the radio jet, plus a distinct low-energy component with a different angle. The authors interpret the pair as evidence for at least two polarized components in the 2-8 keV band.
Earlier work had read the hard X-ray polarization as evidence for a radially extended slab-like corona. The new paper tests an alternative in which the signal comes mostly from relativistic reflection from an accretion disk lit by a compact, lamp-post-like corona.
Fitting IXPE Stokes spectra with a lamp-post plus distant-torus geometry, including partial-covering absorption and an extra soft polarized power-law component, the team found the data require a low coronal height, less than 9 gravitational radii at 3 sigma, and a relatively large torus opening angle, greater than 45 degrees at 3 sigma. In that solution, disk reflection contributes about 20% of the 2-8 keV flux.
The soft polarized component carries only about 1%-5% of the flux but shows high polarization, above 10%, with an angle around 20 degrees. The same configuration also gives acceptable fits to the 0.4-79 keV XMM-Newton and NuSTAR spectra, indicating that disk reprocessing by a compact corona can account for both polarization and broadband spectral behavior.
The result is scheduled for community discussion at NASA's AGN SIG Spotlight Series on September 22 at 1 p.m. ET, according to NASA Science in "AGN SIG Spotlight Series, 22 Sept 2026." That listing describes speaker Elias Kammoun of the California Institute of Technology presenting the spectro-polarimetric study, alongside a separate presentation on ionized outflows in NGC 1365 from the MIRACLE program combining JWST/MIRI, MUSE, and ALMA observations of seven nearby Seyfert galaxies.
NuSTAR catches a high-energy heartbeat in 4U 1630-47
Stellar-mass black holes supplied the week's time-domain highlight.
According to Caltech's NuSTAR report "The Heartbeat of a Windy Black Hole," the past few weeks of the NuSTAR program were dominated by target-of-opportunity investigations, including X-ray binaries in outburst, Galactic novae, variable stars, and magnetars.
Over the past week, NuSTAR observed 4U 1630-47, described as a candidate black-hole X-ray binary in our Galaxy, as part of a spectroscopic campaign coordinated with IXPE, XMM-Newton, and XRISM. The source is noted for variable disk-wind signatures, abnormally high X-ray polarization, and multiple classes of outbursts on a quasi-annual recurrence time.
NuSTAR observations are identified as crucial for determining the temperature and distribution of the hot electron plasma near the black hole known as the corona. Those observations already sampled three different states of the central engine. Coordinated lower-energy observations by XMM and XRISM are intended to measure atomic transitions, enabling study of reflection of coronal emission off the accretion disk and the associated wind of ionized plasma.
Of particular note, NuSTAR made its first detection of 4U 1630-47 shifting between a high-energy-dominated heartbeat state and a more stable low-energy-dominated state. The report, authored by Maxime Parra of Ehime University, states that the NuSTAR heartbeat in 4U 1630-47 appears very different from the famed heartbeat of the Galactic black-hole binary GRS 1915+105, which is generally seen at lower X-ray energies.
NuSTAR's broadband coverage will be essential for testing whether the two oscillation modes share the same physical origin. The multi-facility campaign is framed as a way to clarify how matter falls into stellar-mass black holes and how released energy drives material outward in a powerful wind.
Chandra maps 327 sources behind a cosmic lens
Deep-survey science advanced with a new catalog in one of the sky's most studied lensing fields.
According to reporting on September 17, 2026, in "Chandra catalogs 327 X-ray sources near cluster Abell 2744," astronomers released the first catalog from the Chandra Lensing-cluster Ultradeep Extragalactic Survey, or CLUES, an ultradeep survey around galaxy cluster Abell 2744. Results were described in a preprint posted on arXiv.
The survey combines 101 archival observations with Chandra's ACIS-I camera into a single dataset with total exposure of 2 million seconds, covering 369 square arcminutes. Sources were searched simultaneously in soft, hard, and full bands covering 0.5-2 keV, 2-7 keV, and 0.5-7 keV.
The catalog contains 327 X-ray point sources, most interpreted as distant galaxies hosting active nuclei. Depth rivals the classic Chandra Deep Fields, while the massive cluster at redshift z=0.3 acts as a natural telescope, magnifying background objects through strong gravitational lensing. The same lensing effect previously helped the James Webb Space Telescope identify distant galaxies in this field.
A central technical challenge was bright, structured emission from hot intracluster gas between the cluster's galaxies. That glow can hide faint point sources or create false detections. The team fit each candidate with Chandra's point-spread function, improving positions and filtering artifacts in the crowded central region.
Simulations place 50% flux completeness at 6.3x10^-16 erg/cm²/s in the full band, 2.8x10^-16 in the soft band, and 4.9x10^-16 in the hard band. Source counts versus brightness broadly match blank-sky fields without massive clusters, within about a factor of two. The authors note a small excess above roughly 10^-14 erg/cm²/s among the brightest catalog objects, possibly tied to the cluster or lensing, but remain cautious.
The catalog's value lies in overlap: Abell 2744 already has intensive Hubble and Webb coverage of shapes and spectra. Adding an equally deep X-ray layer opens searches for active nuclei among Webb-classified objects and tests whether early galaxies host actively growing supermassive black holes. All products — catalog, images, exposure maps, background maps, and sensitivity maps — were made publicly available.
84 hypersoft sources expose an EUV blind spot
A second Chandra result reframes what archives can still reveal.
According to SpaceDaily reporting on September 12, 2026, astronomers mining NASA's Chandra archive assembled 84 unusually soft sources in six nearby galaxies. The objects show significant signal between 0.15 and 0.3 keV, no significant detection above 0.3 keV, and a photon ratio greater than eight between the lower band and the 0.3-1.0 keV band.
The search covered M31, M101, NGC 3115, NGC 3379, NGC 4697, and NGC 4472, with seven to 21 candidates per host. The Nature Astronomy paper appeared September 9 from Mustafa Muhibullah and Jimmy A. Irwin of the University of Alabama with Rosanne Di Stefano of the Center for Astrophysics | Harvard & Smithsonian. A few nearest faint objects had earlier catalog matches, including novae in Andromeda, but the shared spectral signature was not previously recognized as a population.
The team calls them hypersoft X-ray sources, an observed spectrum rather than a proven engine. Likely categories include compact binaries, but the physical nature remains unsettled. Proposed possibilities include accreting white dwarfs or post-nova systems and systems hosting accreting black holes.
The sources appear away from galactic nuclei, separating them from diffuse hot gas and central supermassive black holes. In M101 they tend to follow spiral structure; in NGC 3379 many lie closer to the center, suggesting occurrences in both star-forming and older stellar populations. Archive exposures ranged from hundreds of kiloseconds to more than one megasecond, so the count of 84 is not a direct ranking of true abundance.
The most luminous examples approach 10^38 ergs per second in the narrow detected band alone. Researchers argue most energy may emerge in extreme ultraviolet, an inference from the low-energy tail and thermal models rather than direct ultraviolet detection, because interstellar hydrogen and helium absorb most EUV photons. In blackbody examples, moving from 25 electronvolts to 10 electronvolts raises the bolometric correction from single digits to thousands.
Instrumental change was checked with repeated observations of galaxy cluster Abell 1795 to model time-dependent response, addressing sensitivity loss from contaminant buildup on the detector system. Two sources in NGC 4472 recur in images from different epochs, supporting a persistent or repeating population rather than one-time artifacts.
Together, the week's items show X-ray astrophysics working across scales: XRISM planning kilosecond-to-megasecond legacy maps, IXPE and NuSTAR dissecting coronas and winds near black holes, and Chandra pairing lens-assisted depth with archival mining to find emission the sky had kept hidden.