Constraints on dark photon dark matter using data from LIGO's and Virgo's third observing run

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Ram-pressure stripping of a kicked Hill sphere:Prompt electromagnetic emission from the merger of stellar mass black holes in an AGN accretion disk

Accretion disks around supermassive black holes (SMBHs) are promising sites for stellar mass black hole (BH) mergers due to mass segregation and merger acceleration by disk gas torques. Here we show that a gravitational-wave (GW) kick at BH merger causes ram-pressure stripping of gas within the BH Hill sphere. If R_H ≥ H, the disk height, an off-center UV flare at a_(BH) ~ 10³ r_g, emerges within t_(UV) ~ O(2 days)(a_(BH)/10³ r_g)(M_(SMBH)/10⁸ M_⊙)(v_(kick)/10² km s⁻¹) postmerger and lasts O(R_H/v_(kick)) ~ O(5t_(UV)). The flare emerges with luminosity O(10⁴² erg s⁻¹(t_(UV)/2 days)⁻¹(M_(Hill)/1M_⊙)(v_(kick)/10² km s⁻¹)². Active galactic nucleus optical/UV photometry is altered and asymmetric broad emission line profiles can develop after weeks. If R_H 50M_⊙

Multi-messenger Observations of a Binary Neutron Star Merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 {{s}} with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of {40}-8+8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 {M}ȯ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 {{Mpc}}) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.</p