[ { "id": "authors:ex3s5-zsy06", "collection": "authors", "collection_id": "ex3s5-zsy06", "cite_using_url": "https://authors.library.caltech.edu/records/ex3s5-zsy06", "type": "article", "title": "Resolving Oblique Star\u2013Disk Collisions in Quasiperiodic Eruptions: Numerical Requirements and the Importance of Geometry", "author": [ { "family_name": "Huang \u9ec4", "given_name": "Shunquan \u987a\u6743", "orcid": "0000-0002-7276-3694" }, { "family_name": "Huang \u9ec4", "given_name": "Xiaoshan \u5c0f\u73ca", "orcid": "0000-0003-2868-489X", "clpid": "Huang-Xiaoshan" }, { "family_name": "Zhu \u6731", "given_name": "Zhaohuan \u7167\u5bf0", "orcid": "0000-0003-3616-6822" }, { "family_name": "Martin", "given_name": "Rebecca G.", "orcid": "0000-0003-2401-7168" } ], "abstract": "

Star–disk collisions have been proposed as a promising mechanism for producing quasiperiodic eruptions (QPEs) in galactic nuclei. Because the stellar atmospheric scale height is orders of magnitude smaller than the stellar radius, studying the shock launching by stars poses a significant numerical challenge. We implement an immersed solid-boundary method in Athena++ to study bow-shock formation and ejecta launching when a solid sphere crosses an accretion disk at supersonic speed. After validating the method against experimental results for solid bodies in uniform flows, we perform 2D and 3D adiabatic simulations of star–disk collisions. We find that resolving the bow-shock stand-off distance during the compression phase is essential: under-resolved simulations severely underestimate the ejecta mass and energy. When adequately resolved, the ejecta properties agree well with analytical estimates. We further show that collision geometry plays a critical role. Oblique encounters, which arise naturally due to disk rotation, allow for easier shock breakout from the disk's backside and substantially reduce the luminosity contrast between forward and backward ejecta compared to perpendicular collisions. These results emphasize the importance of both numerical resolution and 3D geometry in modeling star–disk collisions and interpreting QPEs.

", "doi": "10.3847/1538-4357/ae78d4", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2026-07-10", "series_number": "2", "volume": "1005", "issue": "2", "pages": "235" }, { "id": "authors:2h94d-w9e28", "collection": "authors", "collection_id": "2h94d-w9e28", "cite_using_url": "https://authors.library.caltech.edu/records/2h94d-w9e28", "type": "article", "title": "AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events", "author": [ { "family_name": "Yao", "given_name": "Yuhan", "orcid": "0000-0001-6747-8509" }, { "family_name": "Chornock", "given_name": "Ryan", "orcid": "0000-0002-7706-5668" }, { "family_name": "Mummery", "given_name": "Andrew" }, { "family_name": "Margutti", "given_name": "Raffaella", "orcid": "0000-0003-4768-7586" }, { "family_name": "Gilfanov", "given_name": "Marat" }, { "family_name": "Guolo", "given_name": "Muryel", "orcid": "0000-0002-5063-0751" }, { "family_name": "Coughlin", "given_name": "Eric R", "orcid": "0000-0003-3765-6401" }, { "family_name": "Lu", "given_name": "Wenbin", "orcid": "0000-0002-1568-7461" }, { "family_name": "Chakraborty", "given_name": "Joheen", "orcid": "0000-0002-0568-6000" }, { "family_name": "Pasham", "given_name": "Dheeraj R", "orcid": "0000-0003-1386-7861" }, { "family_name": "Alexander", "given_name": "Kate D", "orcid": "0000-0002-8297-2473" }, { "family_name": "Aspegren", "given_name": "Olivia", "orcid": "0000-0001-5674-8403" }, { "family_name": "Angus", "given_name": "Charlotte R", "orcid": "0000-0002-4269-7999" }, { "family_name": "Guo", "given_name": "Xinze", "orcid": "0009-0002-9727-8326" }, { "family_name": "Hall", "given_name": "Xander J", "orcid": "0000-0002-9364-5419" }, { "family_name": "Hammerstein", "given_name": "Erica", "orcid": "0000-0002-5698-8703" }, { "family_name": "Hinds", "given_name": "K -Ryan", "orcid": "0000-0002-0129-806X" }, { "family_name": "Ho", "given_name": "Anna Y Q", "orcid": "0000-0002-9017-3567" }, { "family_name": "Huang", "given_name": "Xiaoshan", "orcid": "0000-0003-2868-489X", "clpid": "Huang-Xiaoshan" }, { "family_name": "Kammoun", "given_name": "Elias", "orcid": "0000-0002-0273-218X", "clpid": "Kammoun-Elias" }, { "family_name": "LeBaron", "given_name": "Natalie", "orcid": "0000-0002-2249-0595" }, { "family_name": "Lucchini", "given_name": "Matteo", "orcid": "0000-0002-2235-3347" }, { "family_name": "McGrath", "given_name": "Zo\u00eb", "orcid": "0009-0006-0726-1328" }, { "family_name": "Nicholl", "given_name": "Matt", "orcid": "0000-0002-2555-3192" }, { "family_name": "Perley", "given_name": "Daniel A", "orcid": "0000-0001-8472-1996" }, { "family_name": "Rich", "given_name": "R Michael", "orcid": "0000-0003-0427-8387" }, { "family_name": "Schroeder", "given_name": "Genevieve", "orcid": "0000-0001-9915-8147" }, { "family_name": "Sheng", "given_name": "Xinyue", "orcid": "0000-0002-6527-1368" }, { "family_name": "Sollerman", "given_name": "Jesper", "orcid": "0000-0003-1546-6615" }, { "family_name": "Somalwar", "given_name": "Jean", "orcid": "0000-0001-8426-5732" }, { "family_name": "Wise", "given_name": "Jacob L", "orcid": "0000-0003-0733-2916" }, { "family_name": "Coughlin", "given_name": "Michael W", "orcid": "0000-0002-8262-2924" }, { "family_name": "Drake", "given_name": "Andrew", "orcid": "0000-0003-0228-6594", "clpid": "Drake-Andrew" }, { "family_name": "Graham", "given_name": "Matthew J", "orcid": "0000-0002-3168-0139", "clpid": "Graham-M-J" }, { "family_name": "Helou", "given_name": "George", "orcid": "0000-0003-3367-3415", "clpid": "Helou-G" }, { "family_name": "Jaimes", "given_name": "Joahan C", "orcid": "0000-0002-0987-3372", "clpid": "Jaimes-Joahan-C" }, { "family_name": "Kasliwal", "given_name": "Mansi M", "orcid": "0000-0002-5619-4938", "clpid": "Kasliwal-M-M" }, { "family_name": "Mahabal", "given_name": "Ashish A", "orcid": "0000-0003-2242-0244", "clpid": "Mahabal-A-A" }, { "family_name": "Medvedev", "given_name": "Pavel", "orcid": "0000-0002-9380-8708" }, { "family_name": "Purdum", "given_name": "Josiah", "orcid": "0000-0003-1227-3738", "clpid": "Purdum-Josiah-N" }, { "family_name": "Rusholme", "given_name": "Ben", "orcid": "0000-0001-7648-4142", "clpid": "Rusholme-Benjamin" }, { "family_name": "Sunyaev", "given_name": "Rashid" } ], "abstract": "

We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ($M_{\\rm BH}\\sim 10^8\\, \\mathrm{ M}_\\odot$). Both events show optical precursors consistent with shock dissipation from stream self-intersection. Their X-ray emission is luminous ($L_{\\rm X}\\sim 10^{44}\\, {\\rm erg\\, s^{-1}}$), highly variable (with minimum observed variability time-scales of 1.3 and 4.8 h for factor of ∼3 flux changes), long-lasting (>1 yr), emerging no later than the optical peak, and well characterized by power laws with $1.7\\lt \\Gamma \\lt 3$ (where $f_\\nu \\propto \\nu ^{1-\\Gamma }$). The X-ray properties and radio non-detections support a compact corona ($\\lesssim 10 r_{\\rm g}$) producing Comptonized X-ray emission. Using all published featureless TDEs, we find statistically significant bimodality in the distribution of their peak ultraviolet/optical blackbody luminosities and radii. We assemble a comparison TDE sample with early-time X-ray observations with eROSITA, in which we find different $M_{\\rm BH}$ distributions in TDEs with different X-ray spectral evolution properties: low-mass black holes ($M_{\\rm BH} \\sim 10^6 \\mathrm{ M}_\\odot$) remain soft ($\\Gamma \\gt 4$) within $t\\lesssim 2$ yr, intermediate masses ($\\sim 10^7 \\mathrm{ M}_\\odot$) transition from soft to hard at $\\sim$1 yr, while high masses ($\\sim 10^8 \\mathrm{ M}_\\odot$) are hard ($1.5\\lt \\Gamma \\lesssim 3$) from the outset. We interpret this result as evidence that the soft-to-hard state transition in TDEs occurs at the critical threshold of $\\dot{M}_{\\rm acc} \\sim 0.03 \\dot{M}_{\\rm Edd}$ (similar to X-ray binaries), using the fact that the transition time-scale predicted by simple disc theory scales with black hole mass as $t_{\\rm tr}\\propto M_{\\rm BH}^{-3/4}$.

", "doi": "10.1093/mnras/stag920", "issn": "0035-8711", "publisher": "Royal Astronomical Society", "publication": "Monthly Notices of the Royal Astronomical Society", "publication_date": "2026-06", "series_number": "2", "volume": "549", "issue": "2", "pages": "stag920" }, { "id": "authors:s3yhb-0t926", "collection": "authors", "collection_id": "s3yhb-0t926", "cite_using_url": "https://authors.library.caltech.edu/records/s3yhb-0t926", "type": "article", "title": "Radiation-magnetohydrodynamic Simulations of Accretion Flow Formation After a Tidal Disruption Event", "author": [ { "family_name": "Meza", "given_name": "Maria Renee", "orcid": "0009-0002-8615-6403" }, { "family_name": "Huang \u9ec4", "given_name": "Xiaoshan \u5c0f\u73ca", "orcid": "0000-0003-2868-489X", "clpid": "Huang-Xiaoshan" }, { "family_name": "Davis", "given_name": "Shane W.", "orcid": "0000-0001-7488-4468" }, { "family_name": "Jiang \u59dc", "given_name": "Yan-Fei \u71d5\u98de", "orcid": "0000-0002-2624-3399" } ], "abstract": "
\n

We perform 3D radiation-magnetohydrodynamic simulations of the evolution of the fallback debris after a tidal disruption event (TDE). We focus on studying the effects of magnetic fields on the formation and early evolution of the accretion flow. We find that large magnetic fields can increase the debris stream thickness, moderately reducing the efficiency of the radiative acceleration of outflows during the first self-intersecting collisions. As gas accumulates and the collisions happen instead between the infalling stream and the accretion flow, magnetized and nonmagnetized systems evolve similarly at these early times: radiation-driven outflows dominate early after the initial stream–stream collision, and a few days later, the accretion rate exceeds the mass outflow rate. We find that magnetorotational instability does not play a significant role in angular momentum transport and dissipation. Nor do we find evidence of a magnetocentrifugal-driven outflow. Instead, collisions continue to dissipate kinetic energy into radiation that launches outflows and powers TDE luminosities reaching L ∼ 4–6 × 1044 erg s−1. Shock-driven outflows and inflows redistribute angular momentum throughout the extent (∼50rs) of the forming eccentric disk. Even in the presence of magnetic stresses, the accretion flow remains mostly eccentric with e ∼ 0.2–0.3 for r \u2272 8rs and e ∼ 0.4–0.5 for 10 \u2272 r (rs) \u2272 50. Lastly, we find a polar angle-dependent density structure compatible with the viewing-angle effect, along with an additional azimuthal angle dependence established by the collisions.

\n
", "doi": "10.3847/1538-4357/ae044c", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2025-11-01", "series_number": "1", "volume": "993", "issue": "1", "pages": "57" }, { "id": "authors:y7ery-5ge55", "collection": "authors", "collection_id": "y7ery-5ge55", "cite_using_url": "https://authors.library.caltech.edu/records/y7ery-5ge55", "type": "article", "title": "The Most Luminous Known Fast Blue Optical Transient AT 2024wpp: Unprecedented Evolution and Properties in the X-Rays and Radio", "author": [ { "family_name": "A. J.", "given_name": "Nayana", "orcid": "0000-0002-8070-5400" }, { "family_name": "Margutti", "given_name": "Raffaella", "orcid": "0000-0003-4768-7586" }, { "family_name": "Wiston", "given_name": "Eli", "orcid": "0009-0002-4843-2913" }, { "family_name": "Laskar", "given_name": "Tanmoy", "orcid": "0000-0003-1792-2338" }, { "family_name": "Migliori", "given_name": "Giulia", "orcid": "0000-0003-0216-8053" }, { "family_name": "Chornock", "given_name": "Ryan", "orcid": "0000-0002-7706-5668" }, { "family_name": "Galvin", "given_name": "Timothy J.", "orcid": "0000-0002-2801-766X" }, { "family_name": "LeBaron", "given_name": "Natalie", "orcid": "0000-0002-2249-0595" }, { "family_name": "Hajela", "given_name": "Aprajita", "orcid": "0000-0003-2349-101X" }, { "family_name": "Christy", "given_name": "Collin T.", "orcid": "0000-0003-0528-202X" }, { "family_name": "Sfaradi", "given_name": "Itai", "orcid": "0000-0003-0466-3779" }, { "family_name": "Tsuna", "given_name": "Daichi", "orcid": "0000-0002-6347-3089", "clpid": "Tsuna-Daichi" }, { "family_name": "Aspegren", "given_name": "Olivia", "orcid": "0000-0001-5674-8403" }, { "family_name": "De Colle", "given_name": "Fabio", "orcid": "0000-0002-3137-4633" }, { "family_name": "Metzger", "given_name": "Brian D.", "orcid": "0000-0002-4670-7509" }, { "family_name": "Lu", "given_name": "Wenbin", "orcid": "0000-0002-1568-7461" }, { "family_name": "Beniamini", "given_name": "Paz", "orcid": "0000-0001-7833-1043" }, { "family_name": "Kasen", "given_name": "Daniel", "orcid": "0000-0002-5981-1022" }, { "family_name": "Berger", "given_name": "Edo", "orcid": "0000-0002-9392-9681" }, { "family_name": "Grefenstette", "given_name": "Brian W.", "orcid": "0000-0002-1984-2932", "clpid": "Grefenstette-B-W" }, { "family_name": "Alexander", "given_name": "Kate D.", "orcid": "0000-0002-8297-2473" }, { "family_name": "Anupama", "given_name": "G. C.", "orcid": "0000-0003-3533-7183" }, { "family_name": "Coppejans", "given_name": "Deanne L.", "orcid": "0000-0001-5126-6237" }, { "family_name": "Cruz", "given_name": "Luigi F.", "orcid": "0000-0001-5576-2254" }, { "family_name": "DeBoer", "given_name": "David R", "orcid": "0000-0003-3197-2294" }, { "family_name": "Drout", "given_name": "Maria R.", "orcid": "0000-0001-7081-0082" }, { "family_name": "Farah", "given_name": "Wael", "orcid": "0000-0002-0161-7243" }, { "family_name": "Huang", "given_name": "Xiaoshan", "orcid": "0000-0003-2868-489X", "clpid": "Huang-Xiaoshan" }, { "family_name": "Jacobson-Gal\u00e1n", "given_name": "W. V.", "orcid": "0000-0003-1103-3409", "clpid": "Jacobson-Gal\u00e1n-W-V" }, { "family_name": "Milisavljevic", "given_name": "Dan", "orcid": "0000-0002-0763-3885" }, { "family_name": "Pollak", "given_name": "Alexander W.", "orcid": "0000-0002-3430-7671" }, { "family_name": "Roth", "given_name": "Nathan J.", "orcid": "0000-0002-6485-2259" }, { "family_name": "Sears", "given_name": "Huei", "orcid": "0000-0001-8023-4912" }, { "family_name": "Siemion", "given_name": "Andrew", "orcid": "0000-0003-2828-7720" }, { "family_name": "Sheikh", "given_name": "Sofia Z.", "orcid": "0000-0001-7057-4999" }, { "family_name": "Steiner", "given_name": "James F.", "orcid": "0000-0002-5872-6061" }, { "family_name": "Vurm", "given_name": "Indrek", "orcid": "0000-0003-1336-4746" } ], "abstract": "

We present X-ray (0.3–79 keV) and radio (0.25–203 GHz) observations of the most luminous fast blue optical transient (LFBOT) AT 2024wpp at z = 0.0868, spanning 2–280 days after first light. AT 2024wpp shows luminous (LX ≈ 1.5 × 1043 erg s−1), variable X-ray emission with a Compton hump peaking at δt ≈ 50 days. The X-ray spectrum evolves from a soft (Fν ∝ ν−0.6) to an extremely hard state (Fν ∝ ν1.26) accompanied by a rebrightening at δt ≈ 50 days. The X-ray emission properties favor an embedded high-energy source shining through asymmetric expanding ejecta. We detect radio emission peaking at L9 GHz ≈ 1.7 × 1029 erg s−1 Hz−1 at δt ≈ 73 days. The spectral evolution is unprecedented: the early millimeter fluxes rise nearly an order of magnitude during δt ≈ 17–32 days, followed by a decline in spectral peak fluxes. We model the radio emission as synchrotron radiation from an expanding blast wave interacting with a dense environment (M \u0307∼10−³ M\u2299 yr−1 for vw = 1000 km s−1). The inferred outflow velocities increase from Γβc ≈ 0.07c to 0.42c during δt ≈ 32–73 days, indicating an accelerating blast wave. We interpret these observations as a shock propagating through a dense shell of radius ≈1016 cm and then accelerating into a steep density profile ρCSM(r) ∝ r−3.1. All radio-bright LFBOTs exhibit similar circumstellar medium (CSM) density profiles (ρCSM ∝ r−3), suggesting similar progenitor processes. The X-ray and radio properties favor a progenitor involving super-Eddington accretion onto a compact object launching mildly relativistic disk wind outflows.

", "doi": "10.3847/2041-8213/ae0b4d", "issn": "2041-8205", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal Letters", "publication_date": "2025-11-01", "series_number": "1", "volume": "993", "issue": "1", "pages": "L6" }, { "id": "authors:w65f1-1d093", "collection": "authors", "collection_id": "w65f1-1d093", "cite_using_url": "https://authors.library.caltech.edu/records/w65f1-1d093", "type": "article", "title": "Disk Draining in LIGO Progenitor Black Hole Binaries and Its Significance to Electromagnetic Counterparts", "author": [ { "family_name": "Huang", "given_name": "Xiaoshan", "orcid": "0000-0003-2868-489X", "clpid": "Huang-Xiaoshan" }, { "family_name": "Dodd", "given_name": "Sierra", "orcid": "0000-0002-3696-8035" }, { "family_name": "Schr\u00f8der", "given_name": "Sophie Lund", "orcid": "0000-0003-1735-8263" }, { "family_name": "Davis", "given_name": "Shane W.", "orcid": "0000-0001-7488-4468" }, { "family_name": "Ramirez-Ruiz", "given_name": "Enrico", "orcid": "0000-0003-2558-3102" } ], "abstract": "

The effect of tidal forces on transport within a relic accretion disk in binary black holes is studied here with a suite of two-dimensional hydrodynamic simulations. As the binary contracts owing to the emission of gravitational waves, the accretion disk is truncated, and a two-armed spiral wave is excited, which remains stationary in the rotating reference frame of the coalescing binary. Such spiral waves lead to increased transport of mass and angular momentum. Our findings suggest that even in the case of weakly ionized accretion disks spiral density waves will drain the disk long before the orbit of the two black holes decays enough for them to merge, thus dimming prospects for a detectable electromagnetic counterpart.

", "doi": "10.3847/2041-8213/adbb62", "issn": "2041-8205", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal Letters", "publication_date": "2025-03-20", "series_number": "1", "volume": "982", "issue": "1", "pages": "L11" }, { "id": "authors:hayww-2h259", "collection": "authors", "collection_id": "hayww-2h259", "cite_using_url": "https://authors.library.caltech.edu/records/hayww-2h259", "type": "article", "title": "Transients by Black Hole Formation from Red Supergiants: Impact of Dense Circumstellar Matter", "author": [ { "family_name": "Tsuna", "given_name": "Daichi", "orcid": "0000-0002-6347-3089", "clpid": "Tsuna-Daichi" }, { "family_name": "Huang", "given_name": "Xiaoshan", "orcid": "0000-0003-2868-489X", "clpid": "Huang-Xiaoshan" }, { "family_name": "Fuller", "given_name": "Jim", "orcid": "0000-0002-4544-0750", "clpid": "Fuller-J" }, { "family_name": "Piro", "given_name": "Anthony L.", "orcid": "0000-0001-6806-0673" } ], "abstract": "
\n

Failed supernovae (SNe), which are likely the main channel for forming stellar-mass black holes, are predicted to accompany mass ejections much weaker than typical core-collapse SNe. We conduct a grid of one-dimensional radiation hydrodynamical simulations to explore the emission of failed SNe from red supergiant progenitors, leveraging recent understanding of the weak explosion and the dense circumstellar matter (CSM) surrounding these stars. We find from these simulations and semianalytical modeling that diffusion in the CSM prolongs the early emission powered by shock breakout/cooling. The early emission has peak luminosities of ~107–108 L\u2299 in optical and UV and durations of days to weeks. The presence of dense CSM aids in the detection of the early bright peak from these events via near-future wide-field surveys such as Rubin Observatory, ULTRASAT, and UVEX.

\n
", "doi": "10.3847/1538-4357/ad9bad", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2025-01-20", "series_number": "1", "volume": "979", "issue": "1", "pages": "20" } ]