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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2020

Caltech–NRAO Stripe 82 Survey (CNSS). III. The First Radio-discovered Tidal Disruption Event, CNSS J0019+00

We present the discovery of a nuclear transient with the Caltech–NRAO Stripe 82 Survey (CNSS), a dedicated radio transient survey carried out with the Karl G.Jansky Very Large Array (VLA). This transient, CNSS J001947.3+003527, exhibited a turn-on over a timescale of <~1 yr, increasing in flux density at 3 GHz from <0.14 mJy in 2014 February to 4.4 ± 0.1 mJy in 2015 March, reaching a peak luminosity of 5 x 10^28 erg s-1 Hz-1 around 2015 October. The association of CNSS J0019+00 with the nucleus (Gaia and our very-long baseline interferometry positions are consistent to within 1 pc) of a nearby S0 Seyfert galaxy at 77 Mpc, together with the radio spectral evolution, implies that this transient is most likely a tidal disruption event (TDE). Our equipartition analysis indicates the presence of a ∼15,000 km s−1 outflow, having energy ∼1049 erg. We derive the radial density profile for the circumnuclear material in the host galaxy to be proportional to R−2.5. All of these properties suggest resemblance with radio-detected thermal TDEs like ASASSN-14li and XMMSL1 J0740-85. No significant X-ray or optical emission is detected from CNSS J0019+00, although this may simply be due to the thermal emission being weak during our late-time follow-up observations. From the CNSS survey we have obtained the first unbiased measurement of the rate of radio TDEs, R(>500μJy) of about 2 × 10−3 deg−2, or equivalently a volumetric rate of about 10 Gpc−3 yr−1. This rate implies that all-sky radio surveys such as the VLA Sky Survey and those planned with ASKAP, will find many tens of radio TDEs over the next few years.

M M Anderson↗
NASA NTRS2021

The Peculiar X-Ray Transient Swift J0840.7-3516: An Unusual Low-mass X-Ray Binary or a Tidal Disruption Event?

We report on the X-ray properties of the new transient Swift J0840.7−3516, discovered with Swift/BAT in 2020February, using extensive data from Swift, MAXI, NICER, and NuSTAR. The source flux increased for∼103safter the discovery, decayed rapidly over∼5 orders of magnitude in five days, and then remained almost constant over nine months. Large-amplitude short-term variations on timescales of 1–104s were observed throughout the decay. In the initial flux rise, the source showed a hard power-law-shaped spectrum with a photon index of∼1.0extending up to∼30 keV, above which an exponential cutoff was present. The photon index increased in the following rapid decay and became∼2 at the end of the decay. A spectral absorption feature at 3–4 keV was detected in the decay. It is not straightforward to explain all the observed properties by any known class of X-ray sources. We discuss the possible nature of the source, including a Galactic low-mass X-ray binary with multiple extreme properties and a tidal disruption event by a supermassive black hole or a Galactic neutron star.

Megumi Shidatsu↗
NASA NTRS1989

Tidal disruption of open clusters in their parent molecular clouds

A simple model of tidal encounters has been applied to the problem of an open cluster in a clumpy molecular cloud. The parameters of the clumps are taken from the Blitz, Stark, and Long (1988) catalog of clumps in the Rosette molecular cloud. Encounters are modeled as impulsive, rectilinear collisions between Plummer spheres, but the tidal approximation is not invoked. Mass and binding energy changes during an encounter are computed by considering the velocity impulses given to individual stars in a random realization of a Plummer sphere. Mean rates of mass and binding energy loss are then computed by integrating over many encounters. Self-similar evolutionary calculations using these rates indicate that the disruption process is most sensitive to the cluster radius and relatively insensitive to cluster mass. The calculations indicate that clusters which are born in a cloud similar to the Rosette with a cluster radius greater than about 2.5 pc will not survive long enough to leave the cloud. The majority of clusters, however, have smaller radii and will survive the passage through their parent cloud.

Long, Kevin↗
NASA NTRS1990

Tidal disruption of solid bodies

The problem of stress, strain, and breakup in solid satellites and stray bodies subject to tidal perturbations is presently addressed in view of three novel considerations. After presenting a new analytic solution for the stress tensor in a homogeneous and compressible elastic sphere, where the inclusion of compressibility alters stresses by several percent, realistic failure criteria are noted to demonstrate the general failure of such ductile bodies as iron meteoroids by plastic shear, while brittle ice bodies fail by either tensile or shear fracture. A reexamination of crack propagation after initial failure allows the diverse breakup criteria to be reconciled.

Dobrovolskis, Anthony R.↗
NASA NTRS1966

Sun-grazing comets and tidal disruption.

Data interpretation for sun grazing family of comets deriving formulas for compressive and tensile stress in spherical bodies for tidal, rotational and self-gravitating fields

DATA ANALYSIS↗
NASA NTRS1994

Shoemaker-Levy 9 and the tidal disruption of comets

The break-up of Periodic Comet Shoemaker-Levy 9 into multiple pieces following its grazing encounter with Jupiter in July 1992 can be used to study tidally-induced fracture in comets. This spectacular event allows us not only to set limits on the size, strength and density of Shoemaker-Levy 9 itself, but provides invaluable guidance to numerical modeling of such encounters. In an extensive treatment of tidal breakup which assumed self-gravitating, homogeneous, perfectly elastic bodies, Dobrovolskis derived simple analytical expressions for the tidally-induced surface and central stresses. Both can be cast in such a way that Poisson's ratio is the only material dependent constant entering these expressions. Whether both surface and central failure must be initiated as a criterion for breakup, or either one of them is sufficient, remains a subject of disagreement. To resolve this debate, we model the details of cometary breakup using a three-dimensional Smooth Particle Hydrodynamics (SPH) code modified to simulate fracture in small solid objects. At lower stresses associated with brittle failure, we use a rate-dependent strength based on the nucleation of incipient flaws whose number density is given by a Weibull distribution.

Benz, W.↗
NASA NTRS1990

NGC 4438: Ram pressure sweeping of a tidally disrupted galaxy

NGC 4438 is the highly HI deficient peculiar spiral in the center of the Virgo cluster. Observations are given of the neutral hydrogen emission obtained with the Very Large Array (VLA) in the D-array configuration. These observations map out the total HI as determined from single dish measurements, and show the hydrogen to be confined to a region about one third the size of the optical disk and displaced to the side of the galaxy opposite M87. The hydrogen content of the galaxy is over an order of magnitude less than that expected for a galaxy of its type. The data suggest that the HI deficiency is a result of ram pressure stripping of the gas in the outer regions of the galaxy by the hot intracluster medium after being tidally perturbed.

Hibbard, J. E.↗