Bad prospects for the detection of giant stars’ tidal disruption: effect of the ambient medium on bound debris

AbstractThis study presents a tomographic survey of a subset of the outer halo (10–40 kpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure on spatial scales of >3 degrees is revealed as an excess in the local density of sub-giant stars. With an appropriate assumption of a model stellar isochrone it is possible for us to then derive distances to the sub-giant population. We describe three new candidate halo substructures; the 160- and 180-degree over-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and 1.5 kpc respectively) and an extended feature at 28 kpc that covers at least 162 deg2, the Virgo Equatorial Stream. In addition, we recover the Sagittarius dwarf galaxy (Sgr) leading-arm material and the Virgo Over-Density.The derived distances, together with the number of sub-giant stars associated with each substructure, enables us to derive the integrated luminosity for the features. The tenuous, low surface brightness of the features strongly suggests an origin from the tidal disruption of an accreted galaxy or galaxies. Given the dominance of the tidal debris of Sgr in this region of the sky we investigate if our observations can be accommodated by tidal disruption models for Sgr. The clear discordance between observations and model predictions for known Sgr features means it is difficult to tell unambiguously if the new substructures are related to Sgr or not. Radial velocities in the stellar over-densities will be critical in establishing their origins.

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THE TIDAL DISRUPTION OF GIANT STARS AND THEIR CONTRIBUTION TO THE FLARING SUPERMASSIVE BLACK HOLE POPULATION

The Astrophysical Journal ◽

10.1088/0004-637x/757/2/134 ◽

2012 ◽

Vol 757 (2) ◽

pp. 134 ◽

Cited By ~ 91

Author(s):

Morgan MacLeod ◽

James Guillochon ◽

Enrico Ramirez-Ruiz

Keyword(s):

Black Hole ◽

Tidal Disruption ◽

Giant Stars ◽

Supermassive Black Hole

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Exploring Halo Substructure with Giant Stars. X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy

The Astrophysical Journal ◽

10.1086/518302 ◽

2007 ◽

Vol 663 (2) ◽

pp. 960-989 ◽

Cited By ~ 94

Author(s):

Sangmo Tony Sohn ◽

Steven R. Majewski ◽

Ricardo R. Munoz ◽

William E. Kunkel ◽

Kathryn V. Johnston ◽

...

Keyword(s):

Dark Matter ◽

Tidal Disruption ◽

Giant Stars

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A New Population of Highly Energetic Nuclear Transients

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318002387 ◽

2017 ◽

Vol 14 (S339) ◽

pp. 131-134

Author(s):

E. Kankare ◽

R. Kotak ◽

S. Mattila ◽

P. Lundqvist

Keyword(s):

Active Galactic Nucleus ◽

Ambient Medium ◽

Seyfert Galaxies ◽

Energy Output ◽

Broad Line ◽

Spectral Evolution ◽

Tidal Disruption ◽

Broad Line Region ◽

Supermassive Black Hole ◽

Line Region

AbstractWe have identified a new population of luminous, optical, narrow-lined transients (FWHM ∼1000 km s−1) coincident with the nuclear region of Seyfert galaxies. According to extensive spectrophotometric follow-ups of the main event (PS1-10adi), we could exclude both normal active galactic nucleus activity and changing-look quasars as the origin. The integrated energy output and spectral evolution over a time-scale of several years point to two possible paths of origin: a tidal disruption of a star by a supermassive black hole, or an extremely energetic supernova occurring within the Seyfert galaxy’s narrow-line (or broad-line) region. The former model would require invoking a specific variant of a tidal disruption, while the latter would require an extremely efficient conversion of kinetic energy via shock interaction between the supernova ejecta and the dense ambient medium.

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Self-intersection of the fallback stream in tidal disruption events

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3405 ◽

2019 ◽

Vol 492 (1) ◽

pp. 686-707 ◽

Cited By ~ 22

Author(s):

Wenbin Lu ◽

Clément Bonnerot

Keyword(s):

Ambient Medium ◽

Large Fraction ◽

Intersection Point ◽

Tidal Disruption ◽

Density Profiles ◽

Accretion Flow ◽

Volumetric Rate ◽

Low Mass ◽

Bound Orbits ◽

Optical Surveys

ABSTRACT We propose a semi-analytical model for the self-intersection of the fallback stream in tidal disruption events (TDEs). When the initial periapsis is less than about 15 gravitational radii, a large fraction of the shocked gas is unbound in the form of a collision-induced outflow (CIO). This is because large apsidal precession causes the stream to self-intersect near the local escape speed at radius much below the apocentre. The rest of the fallback gas is left in more tightly bound orbits and quickly joins the accretion flow. We propose that the CIO is responsible for reprocessing the hard emission from the accretion flow into the optical band. This picture naturally explains the large photospheric radius [or low blackbody (BB) temperature] and typical line widths for optical TDEs. We predict the CIO-reprocessed spectrum in the infrared to be Lν ∝ ν∼0.5, shallower than a BB. The partial sky coverage of the CIO also provides a unification of the diverse X-ray behaviours of optical TDEs. According to this picture, optical surveys filter out a large fraction of TDEs with low-mass blackholes due to lack of a reprocessing layer, and the volumetric rate of optical TDEs is nearly flat wrt. the blackhole mass in the range $M\lesssim 10^7\, \mathrm{M_{\odot }}$. This filtering also causes the optical TDE rate to be lower than the total rate by a factor of ∼10 or more. When the CIO is decelerated by the ambient medium, radio emission at the level of that in ASASSN-14li is produced, but the time-scales and peak luminosities can be highly diverse. Finally, our method paves the way for global simulations of the disc formation process by injecting gas at the intersection point according to the prescribed velocity and density profiles.

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Radio emission from the unbound debris of tidal disruption events

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1567 ◽

2019 ◽

Vol 487 (3) ◽

pp. 4083-4092 ◽

Cited By ~ 9

Author(s):

A Yalinewich ◽

E Steinberg ◽

T Piran ◽

J H Krolik

Keyword(s):

Radio Emission ◽

Ambient Medium ◽

Accurate Estimate ◽

Bow Shock ◽

Moving Mesh ◽

Host Galaxy ◽

Tidal Disruption ◽

Supermassive Black Hole ◽

Tidal Forces ◽

Disruption Event

ABSTRACT When a star gets too close to a supermassive black hole, it is torn apart by the tidal forces. Roughly half of the stellar mass becomes unbound and flies away at tremendous velocities – around 104 km s−1. In this work, we explore the idea that the shock produced by the interaction of the unbound debris with the ambient medium gives rise to the synchrotron radio emission observed in several tidal disruption event (TDE). We use a moving mesh numerical simulation to study the evolution of the unbound debris and the bow shock around it. We find that as the periapse distance of the star decreases, the outflow becomes faster and wider. A TDE whose periapse distance is a factor of 7 smaller than the tidal radius can account for the radio emission observed in ASASSN-14li. This model also allows us to obtain a more accurate estimate for the gas density around the centre of the host galaxy of ASASSN-14li.

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Surface Brightness Scale of Galactic Cepheids

Symposium - International Astronomical Union ◽

10.1017/s0074180900118996 ◽

1999 ◽

Vol 190 ◽

pp. 561-562

Author(s):

G. P. Di Benedetto

Keyword(s):

Surface Brightness ◽

Variable Stars ◽

Giant Stars ◽

Near Ir

An accurate calibration of the surface brightness scaleSVas a function of the near-IR color (V–K) has been recently measured for non-variable Galactic dwarf and giant stars. It can be shown that this correlation can be applied to theSVscale of Galactic Cepheid variable stars, which are of major cosmological interest.

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