Abstract
We present a population of 19 radio-luminous supernovae (SNe) with emission reaching
L
ν
∼ 10
26
–10
29
erg s
−1
Hz
−1
in the first epoch of the Very Large Array Sky Survey (VLASS) at 2–4 ...GHz. Our sample includes one long gamma-ray burst, SN 2017iuk/GRB 171205A, and 18 core-collapse SNe detected at ≈1–60 yr after explosion. No thermonuclear explosion shows evidence for bright radio emission, and hydrogen-poor progenitors dominate the subsample of core-collapse events with spectroscopic classification at the time of explosion (79%). We interpret these findings in the context of the expected radio emission from the forward shock interaction with the circumstellar medium (CSM). We conclude that these observations require a departure from the single wind–like density profile (i.e.,
ρ
CSM
∝
r
−2
) that is expected around massive stars and/or from a spherical Newtonian shock. Viable alternatives include the shock interaction with a detached, dense shell of CSM formed by a large effective progenitor mass-loss rate,
M
̇
∼
10
−
4
–
10
−
1
M
⊙
yr
−1
(for an assumed wind velocity of 1000 km s
−1
); emission from an off-axis relativistic jet entering our line of sight; or the emergence of emission from a newly born pulsar-wind nebula. The relativistic SN 2012ap that is detected 5.7 and 8.5 yr after explosion with
L
ν
∼ 10
28
erg s
−1
Hz
−1
might constitute the first detections of an off-axis jet+cocoon system in a massive star. However, none of the VLASS SNe with archival data points are consistent with our model off-axis jet light curves. Future multiwavelength observations will distinguish among these scenarios. Our VLASS source catalogs, which were used to perform the VLASS cross-matching, are publicly available at
https://doi.org/10.5281/zenodo.4895112
.
ABSTRACT
Fast-rotating pulsars and magnetars have been suggested as the central engines of superluminous supernovae (SLSNe) and fast radio bursts, and this scenario naturally predicts non-thermal ...synchrotron emission from their nascent pulsar wind nebulae (PWNe). We report results of high-frequency radio observations with ALMA and NOEMA for three SLSNe (SN 2015bn, SN 2016ard, and SN 2017egm), and present a detailed theoretical model to calculate non-thermal emission from PWNe with an age of ∼1−3 yr. We find that the ALMA data disfavours a PWN model motivated by the Crab nebula for SN 2015bn and SN 2017egm, and argue that this tension can be resolved if the nebular magnetization is very high or very low. Such models can be tested by future MeV–GeV gamma-ray telescopes such as AMEGO.
Abstract
We present a detailed compilation and analysis of the X-ray phase space of low- to intermediate-redshift (0 ≤
z
≤ 1) transients that consolidates observed light curves (and theory where ...necessary) for a large variety of classes of transient/variable phenomena in the 0.3–10 keV energy band. We include gamma-ray burst afterglows, supernovae, supernova shock breakouts and shocks interacting with the environment, tidal disruption events and active galactic nuclei, fast blue optical transients, cataclysmic variables, magnetar flares/outbursts and fast radio bursts, cool stellar flares, X-ray binary outbursts, and ultraluminous X-ray sources. Our overarching goal is to offer a comprehensive resource for the examination of these ephemeral events, extending the X-ray duration–luminosity phase space (DLPS) to show luminosity evolution. We use existing observations (both targeted and serendipitous) to characterize the behavior of various transient/variable populations. Contextualizing transient signals in the larger DLPS serves two primary purposes: to identify areas of interest (i.e., regions in the parameter space where one would expect detections, but in which observations have historically been lacking), and to provide initial qualitative guidance in classifying newly discovered transient signals. We find that while the most luminous (largely extragalactic) and least luminous (largely Galactic) part of the phase space is well populated at
t
> 0.1 days, intermediate-luminosity phenomena (
L
X
= 10
34
–10
42
erg s
−1
) represent a gap in the phase space. We thus identify
L
X
= 10
34
–10
42
erg s
−1
and
t
= 10
−4
to 0.1 days as a key discovery phase space in transient X-ray astronomy.
We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d 16.2 Mpc) starting 10 hr after explosion and continuing for ∼300 days. ...SN 2019ehk shows a double-peaked optical light curve peaking at t = 3 and 15 days. The first peak is coincident with luminous, rapidly decaying Swift-XRT-discovered X-ray emission ( at 3 days; Lx ∝ t−3), and a Shane/Kast spectral detection of narrow H and He ii emission lines (v 500 ) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r < 1015 cm and the resulting cooling emission. We calculate a total CSM mass of ∼7 × 10−3 (MHe/MH 6) with particle density n 109 cm−3. Radio observations indicate a significantly lower density n < 104 cm−3 at larger radii r > (0.1-1) × 1017 cm. The photometric and spectroscopic properties during the second light-curve peak are consistent with those of Ca-rich transients (rise-time of tr = 13.4 0.210 days and a peak B-band magnitude of MB = −15.1 0.200 mag). We find that SN 2019ehk synthesized (3.1 0.11) × 10−2 of and ejected Mej = (0.72 0.040) total with a kinetic energy Ek = (1.8 0.10) × 1050 erg. Finally, deep HST pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (∼10 ) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD+CO WD binaries.
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 the first look at the evolution of ...a young extragalactic SN in the 0.3–80 keV energy range in the years after core collapse. We find that the spectroscopic metamorphosis of SN 2014C from an ordinary type Ib SN into an interacting SN with copious hydrogen emission is accompanied by luminous X-rays reaching
L
x
≈ 5.6 × 10
40
erg s
−1
(0.3–100 keV) at ∼1000 days post-explosion and declining as
L
x
∝
t
−1
afterwards. The broadband X-ray spectrum is of thermal origin and shows clear evidence for cooling after peak, with
T
(
t
)
≈
20
keV
(
t
/
t
pk
)
−
0.5
. Soft X-rays of sub-keV energy suffer from large photoelectric absorption originating from the local SN environment with
NH
int
(
t
)
≈
3
×
10
22
(
t
/
400
days
)
−
1.4
cm
−
2
. We interpret these findings as the result of the interaction of the SN shock with a dense (
n
≈ 10
5
− 10
6
cm
−3
), H-rich disk-like circumstellar medium (CSM) with inner radius ∼2 × 10
16
cm and extending to ∼10
17
cm. Based on the declining NH
int
(
t
) and X-ray luminosity evolution, we infer a CSM mass of ∼(1.2
f
–2.0
f
)
M
⊙
, where
f
is the volume filling factor. We place SN 2014C in the context of 121 core-collapse SNe with evidence for strong shock interaction with a thick circumstellar medium. Finally, we highlight the challenges that the current mass-loss theories (including wave-driven mass loss, binary interaction, and line-driven winds) face when interpreting the wide dynamic ranges of CSM parameters inferred from observations.
We present 8-12 GHz radio light curves of five dwarf nova (DN) type cataclysmic variable stars (CVs) in outburst (RX And, U Gem, and Z Cam), or superoutburst (SU UMa and YZ Cnc), increasing the ...number of radio-detected DN by a factor of 2. The observed radio emission was variable on time-scales of minutes to days, and we argue that it is likely to be synchrotron emission. This sample shows no correlation between the radio luminosity and optical luminosity, orbital period, CV class, or outburst type; however, higher cadence observations are necessary to test this, as the measured luminosity is dependent on the timing of the observations in these variable objects. The observations show that the previously detected radio emission from SS Cyg is not unique in type, luminosity (in the plateau phase of the outburst), or variability time-scales. Our results prove that DN, as a class, are radio emitters in outburst.
Radio spectra of bright compact sources at z > 4.5 Coppejans, Rocco; van Velzen, Sjoert; Intema, Huib T ...
Monthly notices of the Royal Astronomical Society,
01/2017, Letnik:
467, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
High-redshift quasars are important to study galaxy and active galactic nuclei evolution, test cosmological models and study supermassive black hole growth. Optical searches for ...high-redshift sources have been very successful, but radio searches are not hampered by dust obscuration and should be more effective at finding sources at even higher redshifts. Identifying high-redshift sources based on radio data is, however, not trivial. Here we report on new multifrequency Giant Metrewave Radio Telescope observations of eight z > 4.5 sources previously studied at high angular resolution with very long baseline interferometry (VLBI). Combining these observations with those from the literature, we construct broad-band radio spectra of all 30 z > 4.5 sources that have been observed with VLBI. In the sample we found flat, steep and peaked spectra in approximately equal proportions. Despite several selection effects, we conclude that the z > 4.5 VLBI (and likely also non-VLBI) sources have diverse spectra and that only about a quarter of the sources in the sample have flat spectra. Previously, the majority of high-redshift radio sources were identified based on their ultrasteep spectra. Recently, a new method has been proposed to identify these objects based on their megahertz-peaked spectra. No method would have identified more than 18 per cent of the high-redshift sources in this sample. More effective methods are necessary to reliably identify complete samples of high-redshift sources based on radio data.
The Radio to GeV Afterglow of GRB 221009A Laskar, Tanmoy; Alexander, Kate D.; Margutti, Raffaella ...
Astrophysical journal. Letters,
03/2023, Letnik:
946, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
GRB 221009A (
z
= 0.151) is one of the closest known long
γ
-ray bursts (GRBs). Its extreme brightness across all electromagnetic wavelengths provides an unprecedented opportunity to study a ...member of this still-mysterious class of transients in exquisite detail. We present multiwavelength observations of this extraordinary event, spanning 15 orders of magnitude in photon energy from radio to
γ
-rays. We find that the data can be partially explained by a forward shock (FS) from a highly collimated relativistic jet interacting with a low-density, wind-like medium. Under this model, the jet’s beaming-corrected kinetic energy (
E
K
∼ 4 × 10
50
erg) is typical for the GRB population. The radio and millimeter data provide strong limiting constraints on the FS model, but require the presence of an additional emission component. From equipartition arguments, we find that the radio emission is likely produced by a small amount of mass (≲6 × 10
−7
M
⊙
) moving relativistically (Γ ≳ 9) with a large kinetic energy (≳10
49
erg). However, the temporal evolution of this component does not follow prescriptions for synchrotron radiation from a single power-law distribution of electrons (e.g., in a reverse shock or two-component jet), or a thermal-electron population, perhaps suggesting that one of the standard assumptions of afterglow theory is violated. GRB 221009A will likely remain detectable with radio telescopes for years to come, providing a valuable opportunity to track the full lifecycle of a powerful relativistic jet.
A Reverse Shock in GRB 181201A Laskar, Tanmoy; Eerten, Hendrik van; Schady, Patricia ...
The Astrophysical journal,
10/2019, Letnik:
884, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present comprehensive multiwavelength radio to X-ray observations of GRB 181201A spanning from 150 s to 163 days after the burst, comprising the first joint ALMA-VLA-GMRT observations of a ...gamma-ray burst (GRB) afterglow. The radio and millimeter-band data reveal a distinct signature at 3.9 days, which we interpret as reverse-shock (RS) emission. Our observations present the first time that a single radio-frequency spectral energy distribution can be decomposed directly into RS and forward shock (FS) components. We perform detailed modeling of the full multiwavelength data set, using Markov Chain Monte Carlo sampling to construct the joint posterior density function of the underlying physical parameters describing the RS and FS synchrotron emission. We uncover and account for all discovered degeneracies in the model parameters. The joint RS-FS modeling reveals a weakly magnetized ( 3 × 10−3), mildly relativistic RS, from which we derive an initial bulk Lorentz factor of Γ0 103 for the GRB jet. Our results support the hypothesis that low-density environments are conducive to the observability of RS emission. We compare our observations to other events with strong RS detections and find a likely observational bias selecting for longer lasting, nonrelativistic RSs. We present and begin to address new challenges in modeling posed by the present generation of comprehensive, multifrequency data sets.
The outburst catalogue contains a wide variety of observational properties for 722 dwarf nova (DN)-type cataclysmic variables (CVs) and 309 CVs of other types from the Catalina Real-time Transient ...Survey. In particular, it includes the apparent outburst and quiescent V-band magnitudes, duty cycles, limits on the recurrence time, upper and lower limits on the distance and absolute quiescent magnitudes, colour information, orbital parameters and X-ray counterparts. These properties were determined by means of a classification script presented in this paper. The DN in the catalogue show a correlation between the outburst duty cycle and the orbital period (and outburst recurrence time), as well as between the quiescent absolute magnitude and the orbital period (and duty cycle). This is the largest sample of DN properties collected to date. Besides serving as a useful reference for individual systems and a means of selecting objects for targetted studies, it will prove valuable for statistical studies that aim to shed light on the formation and evolution of cataclysmic variables.
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