Huei Sears
A5091681775- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Stellar, planetary, and galactic studies
- Neutrino Physics Research
- Second Language Learning and Teaching
- Tourism, Volunteerism, and Development
- Astronomical Observations and Instrumentation
- Astronomy and Astrophysical Research
- E-Learning and Knowledge Management
- Particle Accelerators and Free-Electron Lasers
- Entrepreneurship Studies and Influences
- Atmospheric Ozone and Climate
- University-Industry-Government Innovation Models
- Solar and Space Plasma Dynamics
- Ocean Waves and Remote Sensing
- Astro and Planetary Science
- Creativity in Education and Neuroscience
- Influenza Virus Research Studies
- Superconducting Materials and Applications
- CCD and CMOS Imaging Sensors
- Education in Rural Contexts
- Oceanographic and Atmospheric Processes
- Reservoir Engineering and Simulation Methods
Northwestern University
2022-2024
Abstract We present UV and/or optical observations and models of SN 2023ixf, a type II supernova (SN) located in Messier 101 at 6.9 Mpc. Early time ( flash ) spectroscopy obtained primarily Lick Observatory, reveals emission lines H i , He i/ii C iv N iii/iv/v with narrow core broad, symmetric wings arising from the photoionization dense, close-in circumstellar material (CSM) around progenitor star prior to shock breakout. These electron-scattering broadened line profiles persist for ∼8 days...
Abstract We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies fast radio bursts (FRBs). Our sample comprises 6 repeating FRBs 17 apparent nonrepeaters. 82 new photometric 8 spectroscopic these hosts. Using synthesis modeling employing nonparametric star formation histories (SFHs), we find that FRB hosts have median mass ≈10 9.9 M ⊙ , mass-weighted age ≈5.1 Gyr, ongoing rate ≈1.3 yr −1 but span wide ranges in all properties....
Abstract We present ultraviolet/optical/near-infrared observations and modeling of Type II supernovae (SNe II) whose early time ( δ t < 2 days) spectra show transient, narrow emission lines from shock ionization confined r 10 15 cm) circumstellar material (CSM). The observed electron-scattering broadened line profiles (i.e., IIn-like) H i , He i/ii C iv N iii/iv/v the CSM persist on a characteristic timescale IIn ) that marks transition to lower-density emergence Doppler-broadened...
Abstract Identifying the sites of r-process nucleosynthesis, a primary mechanism heavy element production, is key goal astrophysics. The discovery brightest gamma-ray burst (GRB) to date, GRB 221009A, presented an opportunity spectroscopically test idea that elements are produced following collapse rapidly rotating massive stars. Here we present James Webb Space Telescope observations 221009A obtained +168 and +170 rest-frame days after trigger, demonstrate they well described by SN...
Abstract Fast X-ray transients (FXTs) are a new observational class of phenomena with no clear physical origin. This is at least partially consequence limited multiwavelength follow-up this in real time. Here we present deep optical ( g - and i -band) photometry Keck, prompt radio observations the Very Large Array FXT 210423 obtained δ t ≈ 14–36 days since trigger. We use these multiband observations, combined publicly available data sets, to constrain presence properties on-axis off-axis...
Abstract We present the discovery of radio afterglow short gamma-ray burst (GRB) 210726A, localized to a galaxy at photometric redshift z ∼ 2.4. While observations commenced ≲1 day after burst, no emission was detected until ∼11 days. The subsequently brightened by factor ∼3 in span week, followed rapid decay (a “radio flare”). find that forward shock model cannot self-consistently describe multiwavelength X-ray and data, underpredicts flux flare ≈5. addition substantial energy injection,...
Abstract We present UV–optical–near-infrared observations and modeling of supernova (SN) 2024ggi, a type II (SN II) located in NGC 3621 at 7.2 Mpc. Early-time (“flash”) spectroscopy SN 2024ggi within +0.8 days discovery shows emission lines H i , He C iii N with narrow core broad, symmetric wings (i.e., “IIn-like”) arising from the photoionized, optically thick, unshocked circumstellar material (CSM) that surrounded progenitor star shock breakout (SBO). By next spectral epoch +1.5 days,...
Abstract We present multiwavelength observations of the Swift short γ -ray burst GRB 231117A, localized to an underlying galaxy at redshift z = 0.257 a small projected offset (∼2 kpc). uncover long-lived X-ray Chandra Observatory and radio/millimeter (VLA, MeerKAT, ALMA) afterglow emission, detected ∼37 days ∼20 (rest frame), respectively. measure wide jet (∼10 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow>...
The current bias in the STEM academy favors English-language research publications, creating a barrier between English-speaking and non-English speaking researchers that is detrimental to continuity evolution of research. In this paper, we lay out policy measures employ U.S. government resources create infrastructure standardizes facilitates language translation process hosting multilingual publications. This proposal aims increase linguistic diversity academic publications for ultimate goal...
Abstract We report multiwavelength observations and characterization of the ultraluminous transient AT 2021lwx (ZTF20abrbeie; aka “Barbie”) identified in alert stream Zwicky Transient Facility (ZTF) using a Recommender Engine For Intelligent Tracking filter on ANTARES broker. From spectroscopically measured redshift 0.995, we estimate peak-observed pseudo-bolometric luminosity log( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow>...
We present ultraviolet/optical/near-infrared observations and modeling of Type II supernovae (SNe II) whose early-time ($\delta t < 2$ days) spectra show transient, narrow emission lines from shock ionization confined ($r 10^{15}$ cm) circumstellar material (CSM). The observed electron-scattering broadened line profiles (i.e., IIn-like) HI, He I/II, C III/IV, N III/IV/V the CSM persist on a characteristic timescale ($t_{\rm IIn}$) that marks transition to lower-density emergence...
Abstract We present rest-frame UV Hubble Space Telescope imaging of the largest and most complete sample 23 long-duration gamma-ray burst (GRB) host galaxies between redshifts 4 6. Of these 23, we new WFC3/F110W for 19 hosts, which combine with archival WFC3/F140W remaining four. use photometry from this to characterize both luminosity function (LF) size–luminosity relation sample. find that when assuming standard Schechter-function parameterization LF, GRB is best fit <mml:math...
Abstract We present the tidal disruption event (TDE) AT2022lri, hosted in a nearby (≈144 Mpc) quiescent galaxy with low-mass massive black hole (10 4 M ⊙ < BH 10 6 ). AT2022lri belongs to TDE-H+He subtype. More than 1 Ms of X-ray data were collected NICER, Swift, and XMM-Newton from 187 672 days after peak. The luminosity gradually declined 1.5 × 44 erg s −1 43 remains much above UV optical luminosity, consistent super-Eddington accretion flow viewed face-on. Sporadic strong dips atop...
The detonation of a thin ($\lesssim$$0.03\,\mathrm{M_\odot}$) helium shell (He-shell) atop $\sim$$1\,\mathrm{M_\odot}$ white dwarf (WD) is promising mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker He-shells and less massive WDs may some recently observed peculiar SNe Ia. We present observations SN 2020jgb, discovered by the Zwicky Transient Facility (ZTF). Near maximum light, 2020jgb slightly subluminous (ZTF $g$-band absolute magnitude $M_g$ between $-18.2$ $-18.7$...
Abstract Gamma-ray bursts (GRBs) are divided into two populations [1, 2]; long GRBs that derive from the core-collapse of massive stars [e.g., 3] and short form in merger compact objects [4]. While it is common to divide at a γ-ray duration seconds, classification based on does not always cleanly map progenitor. This notable with bright, GRB 211211A 3 (≲ 2 seconds) spikes prompt emission followed by more prolonged, spectrally-softer extended (EE-SGRBs), which have been suggested arise object...
We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies fast radio bursts (FRBs). Our sample comprises six repeating FRBs 17 apparent non-repeaters. 82 new photometric eight spectroscopic these hosts. Using synthesis modeling employing non-parametric star formation histories (SFHs), we find that FRB hosts have median mass $\approx 10^{9.9}\,M_{\odot}$, mass-weighted age 5.1$ Gyr, ongoing rate 1.3\,M_{\odot}$ yr$^{-1}$ but span...
Abstract We present the photometric and spectroscopic evolution of SN 2022oqm, a nearby multipeaked hydrogen- helium-weak calcium-rich transient (CaRT). 2022oqm was detected 13.1 kpc from its host galaxy, face-on spiral galaxy NGC 5875. Extensive coverage reveals an early hot ( T ≥ 40,000 K) continuum carbon features observed ∼1 day after discovery, Ic-like photospheric-phase spectra, strong forbidden calcium emission starting 38 days discovery. has relatively high peak luminosity M B = −17...
Identifying the astrophysical sites of $r$-process, one primary mechanisms by which heavy elements are formed, is a key goal modern astrophysics. The discovery brightest gamma-ray burst all time, GRB 221009A, at relatively nearby redshift, presented first opportunity to spectroscopically test idea that $r$-process produced following collapse rapidly rotating massive stars. Here we present spectroscopic and photometric $\textit{James Webb Space Telescope}$ (JWST) observations 221009A obtained...
We present the photometric and spectroscopic evolution of SN 2022oqm, a nearby multi-peaked hydrogen- helium-weak calcium-rich transient (CaRT). 2022oqm was detected 13.1 kpc from its host galaxy, face-on spiral galaxy NGC 5875. Extensive coverage reveals an early hot (T >= 40,000 K) continuum carbon features observed $\sim$1~day after discovery, Ic-like photospheric-phase spectra, strong forbidden calcium emission starting 38 days discovery. has relatively high peak luminosity (MB = -17...
Abstract We present observations of SN 2022joj, a peculiar Type Ia supernova discovered by the Zwicky Transient Facility. 2022joj exhibits an unusually red g ZTF − r color at early times and rapid blueward evolution afterward. Around maximum brightness, shows high luminosity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mi>g</mml:mi> <mml:mi>ZTF</mml:mi> </mml:msub> <mml:mo>,</mml:mo>...
We present observations of SN 2022joj, a peculiar Type Ia supernova (SN Ia) discovered by the Zwicky Transient Facility (ZTF). 2022joj exhibits an unusually red $g_\mathrm{ZTF}-r_\mathrm{ZTF}$ color at early times and rapid blueward evolution afterward. Around maximum brightness, shows high luminosity ($M_{g_\mathrm{ZTF},\mathrm{max}}\simeq-19.7$ mag), blue broadband ($g_\mathrm{ZTF}-r_\mathrm{ZTF}\simeq-0.2$ shallow Si II absorption lines, consistent with those overluminous, 1991T-like...
Fast X-ray Transients (FXTs) are a new observational class of phenomena with no clear physical origin. This is at least partially consequence limited multi-wavelength follow up this transients in real time. Here we present deep optical ($g-$ and $i-$ band) photometry Keck, prompt radio observations the VLA FXT 210423 obtained ${\delta t \approx 14-36}$ days since trigger. We use these multi-band observations, combined publicly available data sets, to constrain presence properties on-axis...
GRB 221009A is one of the brightest transients ever observed with highest peak gamma-ray flux for a burst (GRB). A type Ic-BL supernova (SN), SN 2022xiw, was definitively detected in late-time JWST spectroscopy (t = 195 days, observer-frame). However, photometric studies have found 2022xiw to be less luminous (10-70%) than canonical GRB-SN, 1998bw. We present Hubble Space Telescope (HST)/WFC3 and JWST/NIRCam imaging afterglow host galaxy at t ~ 185, 277, 345 days post-trigger. Our joint...
We present the tidal disruption event (TDE) AT2022lri, hosted in a nearby ($\approx\!144$ Mpc) quiescent galaxy with low-mass massive black hole ($10^4\,M_\odot < M_{\rm BH} 10^6\,M_\odot$). AT2022lri belongs to TDE-H+He subtype. More than 1 Ms of X-ray data were collected NICER, Swift, and XMM-Newton from 187 d 672 after peak. The luminosity gradually declined $1.5\times 10^{44}\,{\rm erg\,s^{-1}}$ 10^{43}\,{\rm remains much above UV optical luminosity, consistent super-Eddington accretion...