Radio Properties of Tidal Disruption Events Alexander, Kate D.; van Velzen, Sjoert; Horesh, Assaf ...
Space science reviews,
08/2020, Letnik:
216, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Radio observations of tidal disruption events (TDEs) probe material ejected by the disruption of stars by supermassive black holes (SMBHs), uniquely tracing the formation and evolution of jets and ...outflows, revealing details of the disruption hydrodynamics, and illuminating the environments around previously-dormant SMBHs. To date, observations reveal a surprisingly diverse population. A small fraction of TDEs (at most a few percent) have been observed to produce radio-luminous mildly relativistic jets. The remainder of the population are radio quiet, producing less luminous jets, non-relativistic outflows or, possibly, no radio emission at all. Here, we review the radio observations that have been made of TDEs to date and discuss possible explanations for their properties, focusing on detected sources and, in particular, on the two best-studied events: Sw J1644+57 and ASASSN-14li. We also discuss what we have learned about the host galaxies of TDEs from radio observations and review constraints on the rates of bright and faint radio outflows in TDEs. Upcoming X-ray, optical, near-IR, and radio surveys will greatly expand the sample of TDEs, and technological advances open the exciting possibility of discovering a sample of TDEs in the radio band unbiased by host galaxy extinction.
Abstract
We present an expansion of FLEET, a machine-learning algorithm optimized to select transients that are most likely tidal disruption events (TDEs). FLEET is based on a random forest algorithm ...trained on both the light curves and host galaxy information of 4779 spectroscopically classified transients. We find that for transients with a probability of being a TDE,
P
(TDE) > 0.5, we can successfully recover TDEs with ≈40% completeness and ≈30% purity when using their first 20 days of photometry or a similar completeness and ≈50% purity when including 40 days of photometry, an improvement of almost 2 orders of magnitude compared to random selection. Alternatively, we can recover TDEs with a maximum purity of ≈80% and a completeness of ≈30% when considering only transients with
P
(TDE) > 0.8. We explore the use of FLEET for future time-domain surveys such as the Legacy Survey of Space and Time on the Vera C. Rubin Observatory (Rubin) and the Nancy Grace Roman Space Telescope (Roman). We estimate that ∼10
4
well-observed TDEs could be discovered every year by Rubin and ∼200 TDEs by Roman. Finally, we run FLEET on the TDEs from our Rubin survey simulation and find that we can recover ∼30% of them at redshift
z
< 0.5 with
P
(TDE) > 0.5, or ∼3000 TDEs yr
–1
that FLEET could uncover from the Rubin stream. We have demonstrated that we will be able to run FLEET on Rubin photometry as soon as this survey begins. FLEET is provided as an open source package on GitHub:
https://github.com/gmzsebastian/FLEET
.
Abstract
Massive, rapidly spinning magnetar remnants produced as a result of binary neutron-star (BNS) mergers may deposit a fraction of their energy into the surrounding kilonova ejecta, powering a ...synchrotron radio signal from the interaction of the ejecta with the circumburst medium. Here, we present 6.0 GHz Very Large Array (VLA) observations of nine, low-redshift short gamma-ray bursts (GRBs;
z
< 0.5) on rest-frame timescales of ≈2.4–13.9 yr following the bursts. We place 3
σ
limits on radio continuum emission of
F
ν
≲ 6–20
μ
Jy at the burst positions, or
L
ν
≲ (0.6–8.3) × 10
28
erg s
−1
Hz
−1
. Comparing these limits with new light-curve modeling that properly incorporates relativistic effects, we obtain limits on the energy deposited into the ejecta of
E
ej
≲ (0.6–6.7) × 10
52
erg (
erg) for an ejecta mass of 0.03
M
⊙
(0.1
M
⊙
). We present a uniform reanalysis of 27 short GRBs with 5.5–6.0 GHz observations, and find that ≳50% of short GRBs did not form stable magnetar remnants in their mergers. Assuming short GRBs are produced by BNS mergers drawn from the Galactic BNS population plus an additional component of high-mass GW194025-like mergers in a fraction
f
GW190425
of cases, we place constraints on the maximum mass of a nonrotating neutron star (NS; Tolman–Oppenheimer–Volkoff mass;
M
TOV
), finding
for
f
GW190425
= 0.4; this limit increases for larger values of
f
GW190425
. The detection (or lack thereof) of radio remnants in untargeted surveys such as the VLA Sky Survey (VLASS) could provide more stringent constraints on the fraction of mergers that produce stable remnants. If
radio remnants are discovered in VLASS, this suggests that short GRBs are a biased population of BNS mergers in terms of the stability of the remnants they produce.
We present Atacama Large Millimeter/submillimeter Array 97.5 GHz total intensity and linear polarization observations of the mm-band afterglow of GRB 190114C spanning 2.2-5.2 hr after the burst. We ...detect linear polarization at the 5 level, decreasing from = (0.87 0.13)% to (0.60 0.19)%, and evolving in polarization position angle from (10 5)° to (−44 12)° during the course of the observations. This represents the first detection and measurement of the temporal evolution of polarized radio/millimeter emission in a γ-ray burst. We show that the optical and X-ray observations between 0.03 days and ∼0.3 days are consistent with a fast-cooling forward shock expanding into a wind environment. However, the optical observations at 0.03 days, as well as the radio and millimeter observations, arise from a separate component, which we interpret as emission from the reverse-shocked ejecta. Using the measured linear polarization, we constrain the coherence scale of tangled magnetic fields in the ejecta to an angular size of θB 10−3 radian, while the rotation of the polarization angle rules out the presence of large-scale, ordered axisymmetric magnetic fields, and in particular a large-scale toroidal field, in the jet.
Abstract
We present the complete set of Hubble Space Telescope imaging of the binary neutron star merger GW170817 and its optical counterpart AT 2017gfo. Including deep template imaging in F814W, ...F110W, F140W, and F160W at 3.4 yr post-merger, we reanalyze the full light curve of AT 2017gfo across 12 bands from 5 to 1273 rest-frame days after merger. We obtain four new detections of the short
γ
-ray burst 170817A afterglow from 109 to 170 rest-frame days post-merger. These detections are consistent with the previously observed
β
= −0.6 spectral index in the afterglow light curve with no evidence for spectral evolution. We also analyze our limits in the context of kilonova afterglow or IR dust echo emission but find that our limits are not constraining for these models. We use the new data to construct deep optical and IR stacks, reaching limits of
M
= −6.3 to −4.6 mag, to analyze the local environment around AT 2017gfo and low surface brightness features in its host galaxy NGC 4993. We rule out the presence of any globular cluster at the position of AT 2017gfo to 2.3 × 10
4
L
⊙
, including those with the reddest
V
−
H
colors. Finally, we analyze the substructure of NGC 4993 in deep residual imaging and find shell features that extend up to 71.″8 (14.2 kpc) from NGC 4993. The shells have a cumulative stellar mass of 6.3 × 10
8
M
⊙
, roughly 2% of NGC 4993, and mass-weighted ages of >3 Gyr. We conclude that it was unlikely that the GW170817 progenitor system formed in the galaxy merger.
A REVERSE SHOCK IN GRB 160509A Laskar, Tanmoy; Alexander, Kate D.; Berger, Edo ...
The Astrophysical journal,
12/2016, Letnik:
833, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We present the second multi-frequency radio detection of a reverse shock in a γ-ray burst. By combining our extensive radio observations of the Fermi-Large Area Telescope γ-ray burst 160509A ...at z = 1.17 up to 20 days after the burst with Swift X-ray observations and ground-based optical and near-infrared data, we show that the afterglow emission comprises distinct reverse shock and forward shock contributions: the reverse shock emission dominates in the radio band at 10 days, while the forward shock emission dominates in the X-ray, optical, and near-infrared bands. Through multi-wavelength modeling, we determine a circumburst density of , supporting our previous suggestion that a low-density circumburst environment is conducive to the production of long-lasting reverse shock radiation in the radio band. We infer the presence of a large excess X-ray absorption column, NH 1.5 × 1022 , and a high rest-frame optical extinction, AV 3.4 mag. We identify a jet break in the X-ray light curve at , and thus derive a jet opening angle of , yielding a beaming-corrected kinetic energy and radiated γ-ray energy of erg and erg (1-104 keV, rest frame), respectively. Consistency arguments connecting the forward shocks and reverse shocks suggest a deceleration time of s T90, a Lorentz factor of , and a reverse-shock-to-forward-shock fractional magnetic energy density ratio of . Our study highlights the power of rapid-response radio observations in the study of the properties and dynamics of γ-ray burst ejecta.
We present detailed multiwavelength observations of GRB 161219B at z = 0.1475, spanning the radio to X-ray regimes, and the first Atacama Large Millimeter/submillimeter Array (ALMA) light curve of a ...γ-ray burst (GRB) afterglow. The centimeter- and millimeter-band observations before 8.5 days require emission in excess of that produced by the afterglow forward shock (FS). These data are consistent with radiation from a refreshed reverse shock (RS) produced by the injection of energy into the FS, signatures of which are also present in the X-ray and optical light curves. We infer a constant-density circumburst environment with an extremely low density, , and show that this is a characteristic of all strong RS detections to date. The Karl G. Lansky Very Large Array (VLA) observations exhibit unexpected rapid variability on roughly minute timescales, indicative of strong interstellar scintillation. The X-ray, ALMA, and VLA observations together constrain the jet break time, days, yielding a wide jet opening angle of , implying beaming-corrected γ-ray and kinetic energies of erg and erg, respectively. Comparing the RS and FS emission, we show that the ejecta are only weakly magnetized, with relative magnetization, , compared to the FS. These direct, multifrequency measurements of a refreshed RS spanning the optical to radio bands highlight the impact of radio and millimeter data in probing the production and nature of GRB jets.
"Epitranscriptomics" is the new RNA code that represents an ensemble of posttranscriptional RNA chemical modifications, which can precisely coordinate gene expression and biological processes. There ...are several RNA base modifications, such as N6-methyladenosine (m6A), 5-methylcytosine (m5C), and pseudouridine (Ψ), etc. that play pivotal roles in fine-tuning gene expression in almost all eukaryotes and emerging evidences suggest that parasitic protists are no exception. In this review, we primarily focus on m6A, which is the most abundant epitranscriptomic mark and regulates numerous cellular processes, ranging from nuclear export, mRNA splicing, polyadenylation, stability, and translation. We highlight the universal features of spatiotemporal m6A RNA modifications in eukaryotic phylogeny, their homologs, and unique processes in 3 unicellular parasites-Plasmodium sp., Toxoplasma sp., and Trypanosoma sp. and some technological advances in this rapidly developing research area that can significantly improve our understandings of gene expression regulation in parasites.
We present detailed multifrequency, multiepoch radio observations of GRB 140304A at z = 5.283 from 1 to 86 GHz and from 0.45 to 89 days. The radio and millimeter data exhibit unusual multiple ...spectral components, which cannot be simply explained by standard forward and reverse shock scenarios. Through detailed multiwavelength analysis spanning radio to X-rays, we constrain the forward shock parameters to Ek,iso 4.9 × 1054 erg, A * 2.6 × 10−2, ϵ e 2.5 × 10−2, ϵ B 5.9 × 10−2, p 2.6, and θ jet 1 1, yielding a beaming-corrected γ-ray and kinetic energy, E γ 2.3 × 1049 erg and E K 9.5 × 1050 erg, respectively. We model the excess radio emission as due to a combination of a late-time reverse shock (RS) launched by a shell collision, which also produces a rebrightening in the X-rays at 0.26 days, and either a standard RS or diffractive interstellar scintillation (ISS). Under the standard RS interpretation, we invoke consistency arguments between the forward and reverse shocks to derive a deceleration time, tdec 100 s, the ejecta Lorentz factor, Γ(tdec) 300, and a low RS magnetization, RB 0.6. Our observations highlight both the power of radio observations in capturing RS emission and thus constraining the properties of GRB ejecta and central engines and the challenge presented by ISS in conclusively identifying RS emission in GRB radio afterglows.
Abstract
We present 1.3 mm (230 GHz) observations of the recent and nearby Type II supernova, SN 2023ixf, obtained with the Submillimeter Array (SMA) at 2.6–18.6 days after explosion. The ...observations were obtained as part the SMA Large Program, POETS (Pursuit of Extragalactic Transients with the SMA). We do not detect any emission at the location of SN 2023ixf, with the deepest limits of
L
ν
(230 GHz) ≲ 8.6 × 10
25
erg s
−1
Hz
−1
at 2.7 and 7.7 days, and
L
ν
(230 GHz) ≲ 3.4 × 10
25
erg s
−1
Hz
−1
at 18.6 days. These limits are about a factor of 2 times dimmer than the millimeter emission from SN 2011dh (IIb), about 1 order of magnitude dimmer compared to SN 1993J (IIb) and SN 2018ivc (IIL), and about 30 times dimmer than the most luminous nonrelativistic SNe in the millimeter band (Type IIb/Ib/Ic). Using these limits in the context of analytical models that include synchrotron self-absorption and free–free absorption, we place constraints on the proximate circumstellar medium around the progenitor star, to a scale of ∼2 × 10
15
cm, excluding the range
M
̇
∼
few
×
10
−
6
−
10
−
2
M
⊙
yr
−1
(for a wind velocity,
v
w
= 115 km s
−1
, and ejecta velocity,
v
ej
∼ (1 − 2) × 10
4
km s
−1
). These results are consistent with an inference of the mass-loss rate based on optical spectroscopy (∼2 × 10
−2
M
⊙
yr
−1
for
v
w
= 115 km s
−1
), but are in tension with the inference from hard X-rays (∼7 × 10
−4
M
⊙
yr
−1
for
v
w
= 115 km s
−1
). This tension may be alleviated by a nonhomogeneous and confined CSM, consistent with results from high-resolution optical spectroscopy.
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