T. Eftekhari
A5039943457- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Astronomical Observations and Instrumentation
- Astronomy and Astrophysical Research
- Radio Astronomy Observations and Technology
- Stellar, planetary, and galactic studies
- Geophysics and Gravity Measurements
- Ionosphere and magnetosphere dynamics
- GNSS positioning and interference
- Superconducting and THz Device Technology
- Galaxies: Formation, Evolution, Phenomena
- Computational Physics and Python Applications
- Solar and Space Plasma Dynamics
- Statistical and numerical algorithms
- Atmospheric Ozone and Climate
- Geophysics and Sensor Technology
- Advanced X-ray and CT Imaging
- SAS software applications and methods
- Calibration and Measurement Techniques
- Particle Accelerators and Free-Electron Lasers
- Inertial Sensor and Navigation
- Antenna Design and Optimization
- Interdisciplinary Research and Collaboration
Northwestern University
2022-2025
Center for Astrophysics Harvard & Smithsonian
2016-2022
University of New Mexico
2014-2018
Time Domain (United States)
2017
We present UV, optical, and NIR photometry of the first electromagnetic counterpart to a gravitational wave source from Advanced LIGO/Virgo, binary neutron star merger GW170817. Our data set extends discovery optical at $0.47$ days $18.5$ post-merger, includes observations with Dark Energy Camera (DECam), Gemini-South/FLAMINGOS-2 (GS/F2), {\it Hubble Space Telescope} ({\it HST}). The spectral energy distribution (SED) inferred this $0.6$ is well described by blackbody model $T\approx 8300$...
Abstract We present the Dark Energy Camera (DECam) discovery of optical counterpart first binary neutron star merger detected through gravitational-wave emission, GW170817. Our observations commenced 10.5 hr post-merger, as soon localization region became accessible from Chile. imaged 70 deg 2 in i and z bands, covering 93% initial integrated probability, to a depth necessary identify likely counterparts (e.g., kilonova). At 11.4 post-merger we bright transient located nucleus NGC 4993 at...
We report the discovery of rising X-ray emission from binary neutron star (BNS) merger event GW170817. This is first detection a gravitational-wave source. Observations acquired with Chandra Observatory (CXO) at t~2.3 days post reveal no significant emission, L_x<=3.2x10^38 erg/s (isotropic-equivalent). Continued monitoring revealed presence an source that brightened time, reaching L_x\sim 9x10^39 ~15.1 merger. interpret these findings in context isotropic and collimated relativistic...
We present Very Large Array (VLA) and Atacama Millimeter/sub-millimeter ALMA radio observations of GW\,170817, the first Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo gravitational wave (GW) event from a binary neutron star merger GW with an electromagnetic (EM) counterpart. Our data include following discovery optical transient at both centimeter ($13.7$ hours post merger) millimeter ($2.41$ days bands. detect faint emission 6 GHz 19.47 39.23 after merger, but not in...
We present a near-infrared spectral sequence of the electromagnetic counterpart to binary neutron star merger GW170817 detected by Advanced LIGO/Virgo. Our dataset comprises seven epochs J+H spectra taken with FLAMINGOS-2 on Gemini-South between 1.5 and 10.5 days after merger. In initial epoch, spectrum is dominated smooth blue continuum due high-velocity, lanthanide-poor kilonova component. Starting following night, all subsequent instead show features that are similar those predicted in...
Abstract We present the first effort to aggregate, homogenize, and uniformly model combined ultraviolet, optical, near-infrared data set for electromagnetic counterpart of binary neutron star merger GW170817. By assembling all available from 18 different papers 46 instruments, we are able identify mitigate systematic offsets between individual sets clear outlying measurements, with resulting pruned adjusted offering an opportunity expand study kilonova. The unified includes 647 flux spanning...
Abstract We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 9.5 days post-merger, using Southern Astrophysical Research Magellan telescopes; UV spectrum was with Hubble Space Telescope at 5.5 days. Our data reveal rapidly fading blue component ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>T</mml:mi>...
Abstract We report deep Chandra X-ray Observatory ( CXO ), Hubble Space Telescope HST and Karl J. Jansky Very Large Array (VLA) observations of the binary neutron star event GW170817 at t < 160 days after merger. These show that has been steadily brightening with time might have now reached its peak, constrain emission process as non-thermal synchrotron where cooling frequency ν c is above band m below radio band. The very simple power-law spectrum extending for eight orders magnitude in...
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....
GRB 221009A ($z=0.151$) is one of the closest known long $\gamma$-ray bursts (GRBs). Its extreme brightness across all electromagnetic wavelengths provides an unprecedented opportunity to study a member this still-mysterious class transients in exquisite detail. We present multi-wavelength observations extraordinary event, spanning 15 orders magnitude photon energy from radio $\gamma$-rays. find that data can be partially explained by forward shock (FS) highly-collimated relativistic jet...
We present the discovery of as-of-yet non-repeating Fast Radio Burst (FRB), FRB 20210117A, with Australian Square Kilometer Array Pathfinder (ASKAP) as a part Commensal Real-time ASKAP Transients (CRAFT) Survey. The sub-arcsecond localization burst led to identification its host galaxy at $z=0.214(1)$. This redshift is much lower than what would be expected for source dispersion measure (DM) 729 pc cm$^{-3}$, given typical contributions from intergalactic medium and galaxy. Optical...
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 We report the discovery of repeating fast radio burst (FRB) source FRB 20240209A using Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB telescope. detected 22 bursts from this repeater between 2024 February and July, 6 which were also recorded at Outrigger station k’niʔatn k’l ⌣ stk’masqt (KKO). The multiple very long baseline interferometry localizations 66 km CHIME–KKO baseline, each with a different vector orientation due to repeater’s high decl. ∼86°, enabled combined...
Abstract The discovery and localization of FRB 20240209A by the Canadian Hydrogen Intensity Mapping Fast Radio Burst (CHIME/FRB) experiment marks first repeating localized with CHIME/FRB Outriggers adds to small sample FRBs associated host galaxies. Here we present Keck Gemini observations that reveal a redshift z = 0.1384 ± 0.0004. We perform stellar population modeling jointly fit optical through mid-IR data infer median mass log( M * / ⊙ ) 11.35 0.01 mass-weighted age ~11 Gyr,...
The Large-aperture Experiment to Detect the Dark Age (LEDA) was designed detect predicted O(100) mK sky-averaged absorption of cosmic microwave background by hydrogen in neutral pre- and intergalactic medium just after cosmological Age. spectral signature would be associated with emergence a diffuse Lyα from starlight during 'Cosmic Dawn'. Recently, Bowman et al. have reported detection this feature, an unexpectedly large amplitude 530 mK, centred at 78 MHz. Verification result independent...
We present the properties of NGC 4993, host galaxy GW170817, first gravitational wave (GW) event from merger a binary neutron star (BNS) system and with an electromagnetic (EM) counterpart. use both archival photometry new optical/near-IR imaging spectroscopy, together stellar population synthesis models to infer global galaxy. formation history peaked at $\gtrsim 10$ Gyr ago, subsequent exponential decline leading low current rate 0.01 M$_{\odot}$ yr$^{-1}$, which we convert into timescale...
Abstract We present Chandra and Very Large Array observations of GW170817 at ∼521–743 days post-merger, a homogeneous analysis the entire data set. find that late-time nonthermal emission follows expected evolution an off-axis relativistic jet, with steep temporal decay <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mi>ν</mml:mi> </mml:msub> <mml:mo>∝</mml:mo> <mml:msup> <mml:mi>t</mml:mi>...
We present a comprehensive comparison of the properties radio through X-ray counterpart GW170817 and short-duration gamma-ray bursts (GRBs). For this effort, we utilize sample 36 short GRBs spanning redshift range $z \approx 0.12-2.6$ discovered over 2004-2017. find that to has an isotropic-equivalent luminosity is $\approx 3000$ times less than median value on-axis GRB afterglows, $\gtrsim10^{4}$ for detected afterglows. Moreover, allowed jet energies particle densities inferred from...
The birth of the first luminous sources and ensuing epoch reionization are best studied via redshifted 21-cm emission line, signature two imprinting last. In this work we present a fully-Bayesian method, \textsc{hibayes}, for extracting faint, global (sky-averaged) signal from much brighter foreground emission. We show that simplified (but plausible), Gaussian model Cosmic Dawn ($15 \lesssim z 30$), parameterized by an amplitude $A_{\rm HI}$, frequency peak $\nu_{\rm HI}$ width $\sigma_{\rm...
We present new observations of the binary neutron star merger GW170817 at $\Delta t\approx 220-290$ days post-merger, radio (Karl G. Jansky Very Large Array; VLA), X-ray (Chandra Observatory) and optical (Hubble Space Telescope; HST) wavelengths. These provide first evidence for a turnover in light curve, mirroring decline emission $\gtrsim5\sigma$ significance. The radio-to-X-ray spectral energy distribution exhibits no evolution into declining phase. Our full multi-wavelength dataset is...
Abstract We present the first extensive radio to γ -ray observations of a fast-rising blue optical transient, AT 2018cow, over its ∼100 days. 2018cow rose few days peak luminosity L pk ∼ 4 × 10 44 erg s −1 , exceeding that superluminous supernovae (SNe), before declining as ∝ t −2 . Initial spectra at δt ≲ 15 were mostly featureless and indicated large expansion velocities v 0.1 c temperatures reaching T 3 K. Later revealed persistent optically thick photosphere emergence H He emission...
Young, rapidly spinning magnetars are invoked as central engines behind a diverse set of transient astrophysical phenomena, including gamma-ray bursts (GRB), super-luminous supernovae (SLSNe), fast radio (FRB), and binary neutron star (NS) mergers. However, barrier to direct confirmation the magnetar hypothesis is challenge directly observing non-thermal emission from engine at early times (when it most powerful thus detectable) due dense surrounding ejecta. We present CLOUDY calculations...
Abstract On 2019 April 25.346 and 26.640 UT the Laser Interferometer Gravitational-Wave Observatory (LIGO) Virgo gravitational-wave (GW) observatory announced detection of first candidate events in Observing Run 3 that contained at least one neutron star (NS). S190425z is a likely binary (BNS) merger d L = 156 ± 41 Mpc, while S190426c possibly NS–black hole (BH) ever detected, 377 100 although with marginal statistical significance. Here we report our optical follow-up observations for both...
Abstract We present the discovery of radio afterglow and near-infrared (NIR) counterpart Swift short gamma-ray burst (GRB) GRB 200522A, located at a small projected offset ≈1 kpc from center young, star-forming host galaxy z = 0.5536. The X-ray luminosities are consistent with those on-axis cosmological GRBs. NIR counterpart, revealed by our Hubble Space Telescope observations rest-frame time ≈2.3 days, has luminosity ≈(1.3–1.7) × 10 42 erg s −1 . This is substantially lower than detections...