Abstract
We assemble a large set of 2–10 GHz radio flux density measurements and upper limits of 294 different supernovae (SNe), from the literature and our own and archival data. Only 31% of SNe ...were detected. We characterize the SN radio lightcurves near the peak using a two-parameter model, with
t
pk
being the time to rise to a peak and
L
pk
the spectral luminosity at that peak. Over all SNe in our sample at
D
< 100 Mpc, we find that
t
pk
= 10
1.7±0.9
days and that
L
pk
= 10
25.5±1.6
erg s
−1
Hz
−1
, and therefore that generally 50% of SNe will have
L
pk
< 10
25.5
erg s
−1
Hz
−1
. These
L
pk
values are ∼30 times lower than those for only detected SNe. Types Ib/c and II (excluding IIn’s) have similar mean values of
L
pk
but the former have a wider range, whereas Type IIn SNe have ∼10 times higher values with
L
pk
= 10
26.5±1.1
erg s
−1
Hz
−1
. As for
t
pk
, Type Ib/c have
t
pk
of only 10
1.1±0.5
days while Type II have
t
pk
= 10
1.6±1.0
and Type IIn the longest timescales with
t
pk
= 10
3.1±0.7
days. We also estimate the distribution of progenitor mass-loss rates,
, and find that the mean and standard deviation of
are −5.4 ± 1.2 (assuming
v
wind
= 1000 km s
−1
) for Type Ib/c SNe, and −6.9 ± 1.4 (assuming
v
wind
= 10 km s
−1
) for Type II SNe excluding Type IIn.
We present continued radio observations of the tidal disruption event Swift J164449.3+573451 extending to delta t approx = 216 days after discovery. The data were obtained with the EVLA, AMI Large ...Array, CARMA, the SMA, and the VLBA+Effelsberg as part of a long-term program to monitor the expansion and energy scale of the relativistic outflow, and to trace the parsec-scale environment around a previously dormant supermassive black hole (SMBH). The new observations reveal a significant change in the radio evolution starting at delta t approx = 1 month, with a brightening at all frequencies that requires an increase in the energy by about an order of magnitude, and an overall density profile around the SMBH of rho is proportional tor super(-3/2) (0.1-1.2 pc) with a significant flattening at r approx = 0.4-0.6 pc. The increase in energy cannot be explained with continuous injection from an L is proportional tot super(-5/3) tail, which is observed in the X-rays. Instead, we conclude that the relativistic jet was launched with a wide range of Lorentz factors, obeying E(> Gammaj)is proportional toGamma super(-2.5)j. The similar ratios of duration to dynamical timescale for Sw 1644+57 and gamma-ray bursts (GRBs) suggest that this result may be applicable to GRB jets as well. The radial density profile may be indicative of Bondi accretion, with the inferred flattening at r ~ 0.5 pc in good agreement with the Bondi radius for a ~few x 10 super(6) M black hole. The density at ~0.5 pc is about a factor of 30 times lower than inferred for the Milky Way Galactic Center, potentially due to a smaller number of mass-shedding massive stars. From our latest observations ( delta t approx = 216 days) we find that the jet energy is E sub(j, iso) approx = 5 x 10 super(53) erg (E sub(j) approx = 2.4 x 10 super(51) erg or thetaj = 0.1), the radius is r approx = 1.2 pc, the Lorentz factor is Gammaj approx = 2.2, the ambient density is n approx = 0.2 cm super(-3), and the projected angular size is r sub(proj) approx = 25 mu as, below the resolution of the VLBA+Effelsberg. Assuming no future changes in the observed evolution and a final integrated total energy of E sub(j) approx = 10 super(52) erg, we predict that the radio emission from Sw 1644+57 should be detectable with the EVLA for several decades and will be resolvable with very long baseline interferometry in a few years.
ABSTRACT
We present high-cadence multifrequency radio observations of the long gamma-ray burst (GRB) 190829A, which was detected at photon energies above 100 GeV by the High Energy Stereoscopic ...System (H.E.S.S.). Observations with the Meer Karoo Array Telescope (MeerKAT, 1.3 GHz) and Arcminute Microkelvin Imager – Large Array (AMI-LA, 15.5 GHz) began one day post-burst and lasted nearly 200 d. We used complementary data from Swift X-Ray Telescope (XRT), which ran to 100 d post-burst. We detected a likely forward shock component with both MeerKAT and XRT up to over 100 d post-burst. Conversely, the AMI-LA light curve appears to be dominated by reverse shock emission until around 70 d post-burst when the afterglow flux drops below the level of the host galaxy. We also present previously unpublished observations of the other H.E.S.S.-detected GRB, GRB 180720B from AMI-LA, which shows likely forward shock emission that fades in less than 10 d. We present a comparison between the radio emission from the three GRBs with detected very high energy (VHE) gamma-ray emission and a sensitivity-limited radio afterglow sample. GRB 190829A has the lowest isotropic radio luminosity of any GRB in our sample, but the distribution of luminosities is otherwise consistent, as expected, with the VHE GRBs being drawn from the same parent distribution as the other radio-detected long GRBs.
The energy source powering the extreme optical luminosity of hydrogen-stripped superluminous supernovae (SLSNe-I) is not known, but recent studies have highlighted the case for a central engine. ...Radio and/or X-ray observations are best placed to track the fastest ejecta and probe the presence of outflows from a central engine. We compile all the published radio observations of SLSNe-I to date and present three new observations of two new SLSNe-I. None were detected. Through modeling the radio emission, we constrain the subparsec environments and possible outflows in SLSNe-I. In this sample, we rule out on-axis collimated relativistic jets of the kind detected in gamma-ray bursts (GRBs). We constrain off-axis jets with opening angles of 5° (30°) to energies of E k < 4 × 10 50 erg ( E k < 10 50 erg ) in environments shaped by progenitors with mass-loss rates of M ˙ < 10 − 4 M yr − 1 ( M ˙ < 10 − 5 M yr − 1 ) for all off-axis angles, assuming fiducial values ϵ e = 0.1 and ϵ B = 0.01 . The deepest limits rule out emission of the kind seen in faint uncollimated GRBs (with the exception of GRB 060218) and from relativistic SNe. Finally, for the closest SLSN-I, SN 2017egm, we constrain the energy of an uncollimated nonrelativistic outflow like those observed in normal SNe to E k 10 48 erg.
We present continued multi-frequency radio observations of the relativistic tidal disruption event Swift J164449.3+573451 extending to t approximate 600 days. The data were obtained with the JVLA and ...AMI Large Array as part of our on-going study of the jet energetics and the density structure of the parsec-scale environment around the disrupting super-massive black hole. We combine these data with public Swift/XRT and Chandra X-ray observations over the same time-frame to show that the jet has undergone a dramatic transition starting at approximate 500 days, with a sharp decline in the X-ray flux by about a factor of 170 on a timescale of delta t/t < or = 0.2. On the other hand, our radio data uniquely demonstrate that the low X-ray flux measured by Chandra at approximate 610 days is consistent with emission from the forward shock. Projecting forward, we predict that the emission in the radio and X-ray bands will evolve in tandem with similar decline rates.
Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce relativistic jets with lifetimes of at least one million years, and the observation of ...the birth of such a jet is therefore unlikely. Transient accretion onto a supermassive black hole, for example through the tidal disruption of a stray star, thus offers a rare opportunity to study the birth of a relativistic jet. On 25 March 2011, an unusual transient source (Swift J164449.3+573451) was found, potentially representing such an accretion event. Here we report observations spanning centimetre to millimetre wavelengths and covering the first month of evolution of a luminous radio transient associated with Swift J164449.3+573451. The radio transient coincides with the nucleus of an inactive galaxy. We conclude that we are seeing a newly formed relativistic outflow, launched by transient accretion onto a million-solar-mass black hole. A relativistic outflow is not predicted in this situation, but we show that the tidal disruption of a star naturally explains the observed high-energy properties and radio luminosity and the inferred rate of such events. The weaker beaming in the radio-frequency spectrum relative to γ-rays or X-rays suggests that radio searches may uncover similar events out to redshifts of z ≈ 6.
We report on new 5-GHz Very Large Array (VLA) radio observations of the pulsar-powered supernova remnant G21.5−0.9. These observations have allowed us to make a high-quality radio image of this ...remnant with a resolution of ∼0.7 arcsec. It has a filamentary structure similar to that seen in the Crab Nebula. Radio structure suggestive of the torus seen around the Crab pulsar is tentatively identified. We also compared the new image with one taken ∼15 yr earlier at 1.5 GHz, both to find the expansion speed of the remnant and to make a spectral index image. Between 1991 and 2006, we find that the average expansion rate of the remnant is 0.11 ± 0.02 per cent yr−1, corresponding, for a distance of 5 kpc, to a speed of 910 ± 160 km s−1 with respect to the centre of the nebula. Assuming undecelerated expansion, this expansion speed implies that the age of G21.5−0.9 is 870+200−150 yr, which makes PSR J1833−1034 one of the youngest, if not the youngest, known pulsars in the Galaxy.
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 at 0.8–240 GHz, steeper than
F
ν
∝
t
5
relative to the time of optical discovery. Such a steep rise cannot be explained in any reasonable scenario of an outflow launched at the time of disruption (e.g., off-axis jet, sudden increase in the ambient density), and instead points to a delayed launch. Our multifrequency data allow us to directly determine the radius and energy of the radio-emitting outflow, and we find from our modeling that the outflow was launched ≈750 days after optical discovery. The outflow velocity is mildly relativistic, with
β
≈ 0.25 and ≈0.6 for a spherical geometry and a 10° jet geometry, respectively, and the minimum kinetic energy is
E
K
≈ 5.8 × 10
49
and ≈6.3 × 10
49
erg, respectively. This is the first definitive evidence for the production of a delayed mildly relativistic outflow in a TDE; a comparison to the recently published radio light curve of ASASSN-15oi suggests that the final rebrightening observed in that event (at a single frequency and time) may be due to a similar outflow with a comparable velocity and energy. Finally, we note that the energy and velocity of the delayed outflow in AT2018hyz are intermediate between those of past nonrelativistic TDEs (e.g., ASASSN-14li, AT2019dsg) and the relativistic TDE Sw J1644+57. We suggest that such delayed outflows may be common in TDEs.
We report on a Very Large Array survey for late-time radio emission from 59 supernovae (SNe) of the Type I b/c, which is associated with long-duration gamma-ray bursts (GRBs). An 'off-axis' GRB burst ...(i.e. whose relativistic jet points away from us) is expected to have late-time radio emission even in the absence of significant prompt gamma-ray emission. From our sample, we detected only SN 2003gk with an 8.4 GHz flux density of 2260 ± 130 μJy. Our subsequent very long baseline interferometry (VLBI) observations of SN 2003gk, at an age of ∼8 yr, allowed us to determine its radius to be (2.4 ± 0.4) × 1017 cm, or 94 ± 15 light days. This radius rules out relativistic expansion as expected for an off-axis GRB jet, and instead suggests an expansion speed of ∼10 000 km s−1 typical for non-relativistic core-collapse SNe. We attribute the late-onset radio emission to interaction of the ejecta with a dense shell caused by episodic mass-loss from the progenitor.
In addition, we present new calculations for the expected radio light curves from GRB jets at various angles to the line of sight, and compare these to our observed limits on the flux densities of the remainder of our SN sample. From this comparison, we can say that only a fraction of broadlined Type I b/c SNe have a radio-bright jet similar to those seen for GRB afterglows at cosmological distances. However, we also find that for a reasonable range of parameters, as might be representative of the actual population of GRB events rather than the detected bright ones, the radio emission from the GRB jets can be quite faint, and that at present, radio observations do not place strong constraints on off-axis GRB jets.
Long duration gamma-ray bursts (GRBs) mark the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. They are distinguished by the production of an energetic and ...collimated relativistic outflow powered by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested in the pulse of gamma-rays and a long-lived radio afterglow. Until now, central-engine-driven supernovae have been discovered exclusively through their gamma-ray emission, yet it is expected that a larger population goes undetected because of limited satellite sensitivity or beaming of the collimated emission away from our line of sight. In this framework, the recovery of undetected GRBs may be possible through radio searches for type Ibc supernovae with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. A comparison with our radio survey of type Ibc supernovae reveals that the fraction harbouring central engines is low, about one per cent, measured independently from, but consistent with, the inferred rate of nearby GRBs. Independently, a second mildly relativistic supernova has been reported.