Black hole masses of tidal disruption event host galaxies

The mass of the central black hole in a galaxy that hosted a tidal disruption event (TDE) is an important parameter in understanding its energetics and dynamics. We present the first homogeneously measured black hole masses of a complete sample of 12 optically/UV selected TDE host galaxies (down to $g_{host}$$\leq$22 mag and $z$=0.37) in the Northern sky. The mass estimates are based on velocity dispersion measurements, performed on late time optical spectroscopic observations. We find black hole masses in the range 3$\times$10$^5$ M$_{\odot}$$\leq$M$_{\rm BH}$$\leq$2$\times$10$^7$ M$_{\odot}$. The TDE host galaxy sample is dominated by low mass black holes ($\sim$10$^6$ M$_{\odot}$), as expected from theoretical predictions. The blackbody peak luminosity of TDEs with M$_{\rm BH}$$\leq$10$^{7.1}$ M$_{\odot}$ is consistent with the Eddington limit of the SMBH, whereas the two TDEs with M$_{\rm BH}$$\geq$10$^{7.1}$ M$_{\odot}$ have peak luminosities below their SMBH Eddington luminosity, in line with the theoretical expectation that the fallback rate for M$_{\rm BH}$$\geq$10$^{7.1}$ M$_{\odot}$ is sub-Eddington. In addition, our observations suggest that TDEs around lower mass black holes evolve faster. These findings corroborate the standard TDE picture in 10$^6$ M$_{\odot}$ black holes. Our results imply an increased tension between observational and theoretical TDE rates. By comparing the blackbody emission radius with theoretical predictions, we conclude that the optical/UV emission is produced in a region consistent with the stream self-intersection radius of shallow encounters, ruling out a compact accretion disk as the direct origin of the blackbody radiation at peak brightness.Comment: 16 pages, 9 figures. Submitted to MNRAS; including minor revisions suggested by the refere

Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li

We carried out the first multi-wavelength (optical/UV and X-ray) photometric reverberation mapping of a tidal disruption flare (TDF) ASASSN-14li. We find that its X-ray variations are correlated with and lag the optical/UV fluctuations by 32$\pm$4 days. Based on the direction and the magnitude of the X-ray time lag, we rule out X-ray reprocessing and direct emission from a standard circular thin disk as the dominant source of its optical/UV emission. The lag magnitude also rules out an AGN disk-driven instability as the origin of ASASSN-14li and thus strongly supports the tidal disruption picture for this event and similar objects. We suggest that the majority of the optical/UV emission likely originates from debris stream self-interactions. Perturbations at the self-interaction sites produce optical/UV variability and travel down to the black hole where they modulate the X-rays. The time lag between the optical/UV and the X-rays variations thus correspond to the time taken by these fluctuations to travel from the self-interaction site to close to the black hole. We further discuss these time lags within the context of the three variants of the self-interaction model. High-cadence monitoring observations of future TDFs will be sensitive enough to detect these echoes and would allow us to establish the origin of optical/UV emission in TDFs in general.Comment: Publish in ApJ Letter

Green school outdoor environments, greater equity? Assessing environmental justice in green spaces around Dutch primary schools

Green spaces around schools contribute to children's health and wellbeing. However, only a few studies have examined whether green space provision around schools in urban and rural areas are equally available across socioeconomic groups. We assessed whether and to what extent the green space provision of public primary schoolyards differs cross-sectionally across demographic and socioeconomic neighborhood profiles in the Netherlands. A fine-grained measure of green space (e.g., lawns, hedges, and trees) was applied to 5,773 school locations centering buffers at 50 m, 100 m, and 500 m. Fitting spatial lag regression models to the data, our results showed robust and inverse associations between available green school outdoor environments and low-income and less-educated neighborhoods. The percentage of non-Western migrants was positively associated. No evidence showed greenness around schools differing across levels of urbanization; however, schools with subsidy schemes supporting schoolyard greening tended to be greener. Our overall findings highlight socioeconomic disparities in green school outdoor environments across the Netherlands. To bridge this gap in environmental justice, we advocate for each child to have the ability to benefit equally from schoolyard green spaces by enabling more comprehensive greening subsidy schemes

Land Sold from Rev. Simon van Velzen to Dr. G. C. de Moen

Rev. Simon van Velzen sold a piece of propety in Gramsberen, Province of Overijssel to Dr. G. C. de Moen, a doctor in Leiden for 2,390.50 guilders. Van Velzen had inherited a share in the propety from his deceased wife, a sister of de Moen and Mrs. Christina Van Raalte.https://digitalcommons.hope.edu/vrp_1840s/1002/thumbnail.jp