A5059224409- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- GNSS positioning and interference
- Astronomy and Astrophysical Research
- Ionosphere and magnetosphere dynamics
- Astro and Planetary Science
- Particle Accelerators and Free-Electron Lasers
- Radio Astronomy Observations and Technology
- Solar and Space Plasma Dynamics
- Advanced X-ray and CT Imaging
- Galaxies: Formation, Evolution, Phenomena
- Atomic and Subatomic Physics Research
- Geomagnetism and Paleomagnetism Studies
- Geophysics and Gravity Measurements
- Spacecraft and Cryogenic Technologies
- Earthquake Detection and Analysis
- Paleopathology and ancient diseases
- Adaptive optics and wavefront sensing
- Nuclear Physics and Applications
- High-pressure geophysics and materials
- Superconducting and THz Device Technology
University of Copenhagen
2023-2024
Northwestern University
2018-2023
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 radio observations of 23 optically discovered tidal disruption events (TDEs) on timescales ∼500–3200 days postdiscovery. detect nine new TDEs that did not have detectable emission at earlier times, indicating a late-time brightening after several hundred (and up to 2300) days; an additional seven exhibit whose origin is ambiguous or may be attributed the host galaxy active galactic nucleus. also report rising component in one TDE previously detected ∼10 3 days. While some...
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 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...
Time domain science has undergone a revolution over the past decade, with tens of thousands new supernovae (SNe) discovered each year. However, several observational domains, including SNe within days or hours explosion and faint, red transients, are just beginning to be explored. Here, we present Young Supernova Experiment (YSE), novel optical time-domain survey on Pan-STARRS telescopes. Our is designed obtain well-sampled $griz$ light curves for transient events up $z \approx 0.2$. This...
For the first $\sim3$ years after binary neutron star merger event GW 170817 radio and X-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into low-density medium with n $< 0.01\,\rm{cm^{-3}}$. We report on observational evidence for an excess of at $\delta t>900$ days merger. With $L_x\approx5\times 10^{38}\,\rm{erg\,s^{-1}}$ 1234 days, recently detected represents $\ge 3.2\,\sigma$ (Gaussian equivalent) deviation universal post jet-break...
Abstract We present late-time radio/millimeter (as well as optical/UV and X-ray) detections of tidal disruption event (TDE) AT2018hyz, spanning 970–1300 d after optical discovery. In conjunction with earlier deeper limits, including those at ≈700 days, our observations reveal rapidly rising emission 0.8–240 GHz, steeper than F ν ∝ t 5 relative to the time Such a steep rise cannot be explained in any reasonable scenario an outflow launched (e.g., off-axis jet, sudden increase ambient...
Quasi-periodic eruptions (QPEs) are luminous bursts of soft X-rays from the nuclei galaxies, repeating on timescales hours to weeks
We present a new constraint on the Hubble constant ${H}_{0}$ using latest measurements of electromagnetic counterpart to gravitational wave (GW) event GW170817. use optical, x-ray and radio observations afterglow up $\ensuremath{\sim}3.5\text{ }\text{ }\mathrm{years}$ after GW detection, properly take into account impact host galaxy peculiar velocity. find ${75.46}_{\ensuremath{-}5.39}^{+5.34}\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$...
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 panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in star-forming galaxy M100 ( d ≈ 16.2 Mpc) starting 10 hr after explosion continuing for ∼300 days. SN shows a double-peaked optical light curve peaking at t = 3 15 The first peak is coincident with luminous, rapidly decaying Swift-XRT–discovered X-ray emission <?CDATA ${L}_{{\rm{x}}}\approx {10}^{41}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$?> days; L x ∝ −3 ), Shane/Kast spectral detection narrow H...
The discovery of the electromagnetic counterpart to binary neutron star merger GW170817 has opened era gravitational-wave multi-messenger astronomy. Rapid identification optical/infrared kilonova enabled a precise localization source, which paved way deep multi-wavelength follow-up and its myriad related science results. Fully exploiting this new territory exploration requires acquisition data from samples mergers other gravitational wave sources. After GW170817, frontier is now map...
Abstract We present a revised and complete optical afterglow light curve of the binary neutron star merger GW170817, enabled by deep Hubble Space Telescope ( HST ) F606W observations at ≈584 days post-merger, which provide robust template. The spans ≈110–362 days, is fully consistent with emission from relativistic structured jet viewed off-axis, as previously indicated radio X-ray data. Combined contemporaneous observations, we find no spectral evolution, weighted average index <mml:math...
Abstract We present the results from our 7 yr long broadband X-ray observing campaign of SN 2014C with Chandra and NuSTAR. These coordinated observations represent first look at evolution a young extragalactic in 0.3–80 keV energy range years after core collapse. find that spectroscopic metamorphosis an ordinary type Ib into interacting copious hydrogen emission is accompanied by luminous X-rays reaching L x ≈ 5.6 × 10 40 erg s −1 (0.3–100 keV) ∼1000 days post-explosion declining as ∝ t...
We present the complete set of {\it Hubble Space Telescope} imaging binary neutron star merger GW170817 and its optical counterpart AT 2017gfo. Including deep template in F814W, F110W, F140W, F160W at 3.4 years post-merger, we re-analyze full light curve 2017gfo across 12 bands from 5--1273 rest-frame days after merger. obtain four new detections short $\gamma$-ray burst (GRB) 170817A afterglow 109--170 post-merger. These are consistent with previously observed $\beta=-0.6$ spectral index no...
Abstract We present results from an extensive follow-up campaign of the tidal disruption event (TDE) ASASSN-15oi spanning δt ∼ 10–3000 days, offering unprecedented window into multiwavelength properties a TDE during its first ≈8 yr evolution. is one few TDEs with strong detections at X-ray, optical/UV, and radio wavelengths it also featured two delayed flares 180 days 1400 days. Our observations > reveal absence thermal X-rays, late-time variability in nonthermal X-ray emission, sharp...
Abstract The tidal disruption event (TDE) AT2022cmc represents the fourth known example of a relativistic jet produced by stray star, providing unique probe formation and evolution jets in otherwise dormant supermassive black holes (SMBHs). Here we present deep, late-time Chandra observations extending to t obs ≈ 400 days after disruption. Our reveal sudden decrease X-ray brightness factor ≳14 over ≈2.3 time, deviation from earlier power-law decline with steepening α ≳ 3.2 ( F X ∝ − ),...
A tidal disruption event (TDE) occurs when a supermassive black hole rips apart passing star. Part of the stellar material falls toward hole, forming an accretion disk that in some cases launches relativistic jet. We performed optical polarimetry observations TDE, AT 2020mot. find peak linear polarization degree 25 ± 4%, consistent with highly polarized synchrotron radiation, as is typically observed from jets. However, our radio observations, taken up to 8 months after peak, do not detect...
Abstract The binary neutron star merger GW170817 is the first and only astronomical object with a joint detection of gravitational waves electromagnetic radiation. Here we report results from deep Chandra X-ray observations at δt ∼ 940 days post merger. We find evidence for emission flux F x = <?CDATA $({2.24}_{+0.97}^{-0.96})\times {10}^{-15}\,\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo...
ABSTRACT We have carried out a dedicated transient survey of 300 deg2 the SDSS Stripe 82 region using Giant Metrewave Radio Telescope (GMRT) at 150 MHz. Our multi-epoch observations, together with TGSS survey, allow us to probe variability and activity on four different time-scales, beginning 4 h up yr. Data calibration, RFI flagging, source finding, search were in semi-automated pipeline incorporating SPAM recipe. This has enabled produce superior-quality images carry reliable over entire...
Quasi-periodic Eruptions (QPEs) are luminous bursts of soft X-rays from the nuclei galaxies, repeating on timescales hours to weeks. The mechanism behind these rare systems is uncertain, but most theories involve accretion disks around supermassive black holes (SMBHs), undergoing instabilities or interacting with a stellar object in close orbit. It has been suggested that this disk could be created when SMBH disrupts passing star, implying many QPEs should preceded by observable tidal...
The field of time-domain astrophysics has entered the era Multi-messenger Astronomy (MMA). One key science goal for next decade (and beyond) will be to characterize gravitational wave (GW) and neutrino sources using generation Extremely Large Telescopes (ELTs). These studies have a broad impact across astrophysics, informing our knowledge production enrichment history heaviest chemical elements, constrain dense matter equation state, provide independent constraints on cosmology, increase...