Search Publications
Deep XMM-Newton Observations of an X-ray Weak Broad Absorption Line Quasar at z = 6.5
Fan, Xiaohui; Keeton, Charles R.; Walter, Fabian +14 more
We report X-ray observations of the most distant known gravitationally lensed quasar, J0439+1634 at z = 6.52, which is also a broad absorption line (BAL) quasar, using the XMM-Newton Observatory. With a 130 ks exposure, the quasar is significantly detected as a point source at the optical position with a total of ${358}_{-19}^{+19}$ net counts usi…
The "Singular" Behavior of the Solar Wind Scaling Features during Parker Solar Probe-BepiColombo Radial Alignment
Richter, Ingo; Auster, Hans-Ulrich; Hadid, Lina Z. +4 more
At the end of 2020 September, the Parker Solar Probe (PSP) and BepiColombo were radially aligned: PSP was orbiting near 0.17 au and BepiColombo near 0.6 au. This geometry is of particular interest for investigating the evolution of solar wind properties at different heliocentric distances by observing the same solar wind plasma parcels. In this wo…
A Partial Filament Eruption in Three Steps Induced by External Magnetic Reconnection
Xu, Zhe; Li, Leping; Zhang, Qingmin +6 more
We present an investigation of partial filament eruption on 2012 June 17 in the active region NOAA 11504. For the first time, we observed the vertical splitting process during the partial eruption with high-resolution narrowband images at 10830 Å. The active filament was rooted in a small δ-sunspot of the active region. Particularly, it underwent …
MARS: A New Maximum-entropy-regularized Strong Lensing Mass Reconstruction Method
Jee, M. James; Cha, Sangjun
Free-form strong-lensing (SL) mass reconstructions typically suffer from overfitting, which manifests itself as false-positive small-scale fluctuations. We present a new free-form MAximum-entropy ReconStruction (MARS) method without the assumption that light traces mass (LTM). The MARS algorithm enables us to achieve excellent convergence in sourc…
The Nascent Milliquasar VT J154843.06+220812.6: Tidal Disruption Event or Extreme Accretion State Change?
Hallinan, Gregg; Graham, Matthew; Lu, Wenbin +5 more
We present a detailed multiwavelength follow-up of the nuclear radio flare VT J154843.06+220812.6, hereafter VT J1548. VT J1548 was selected as a ~1 mJy radio flare in 3 GHz observations from the Very Large Array Sky Survey. It is located in the nucleus of a low-mass ( $\mathrm{log}{M}_{\mathrm{BH}}/{M}_{\odot }\sim 6$ ) host galaxy with weak or n…
A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A
McQuinn, Kristen B. W.; Williams, Benjamin F.; Choi, Yumi +17 more
We characterize massive stars (M > 8 M ⊙) in the nearby (D ∼ 0.8 Mpc) extremely metal-poor (Z ∼ 5% Z ⊙) galaxy Leo A using Hubble Space Telescope ultraviolet (UV), optical, and near-infrared (NIR) imaging along with Keck/Low-Resolution Imaging Spectrograph and MMT/Binospec optical spectroscopy for 18 main-sequence OB stars…
A Multiepoch X-Ray Study of the Nearby Seyfert 2 Galaxy NGC 7479: Linking Column Density Variability to the Torus Geometry
Ajello, M.; Marchesi, S.; Torres-Albà, N. +3 more
Active galactic nuclei are powered by accreting supermassive black holes, surrounded by a torus of obscuring material. Recent studies have shown how the torus structure, formerly thought to be homogeneous, appears to be "patchy": the detection of variability in the line-of-sight hydrogen column density, in fact, matches the description of an obscu…
An Improved Magnetohydrodynamic Simulation of the 2006 December 13 Coronal Mass Ejection of NOAA Active Region 10930
Fan, Yuhong
We present a magnetohydrodynamic simulation of the coronal mass ejection on 2006 December 13 in the emerging δ-sunspot NOAA Active Region 10930, improving upon a previous simulation by Fan as follows. (1) Incorporate an ambient solar wind instead of using a static potential magnetic field extrapolation as the initial state. (2) In addition to impo…
Testing High-energy Emission Models for Blazars with X-Ray Polarimetry
Liodakis, Ioannis; Peirson, Abel L.; Romani, Roger W.
Both leptonic and hadronic emission processes may contribute to blazar jet emission; which dominates in blazars' high-energy emission component remains an open question. Some intermediate synchrotron peaked blazars transition from their low- to high-energy emission components in the X-ray band making them excellent laboratories to probe both compo…
Photometric and Spectroscopic Study of the EXor-like Eruptive Young Star Gaia19fct
Pál, András; Lee, Jeong-Eun; Ábrahám, Péter +19 more
Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multifilter optical and near-infrared photometry, as well as near-infrared spectroscopy, to understand the physical properties of Gaia19fct and investigate whether it fits into the historically defined…