124 research outputs found
Quark nova inside supernova: Application to GRBs and XROs
In this paper we consider a quark nova occurring inside an exploding star.
The quark nova ejecta will shock when interacting with the stellar envelope.
When this shock reaches the surface of the star, the energy is radiated away.
We suggest that this energy may be seen in X-rays, and show here that this may
explain some flares seen in the X-ray afterglow of long gamma ray bursts
(GRBs). A quark nova inside an exploding star need not be followed by a GRB, or
the GRB may not be beamed towards us. However, the shock breakout is likely not
beamed and could be seen even in the absence of a GRB. We suggest that XRO
080109 is such an event in which a quark nova occurs inside an exploding star.
No GRB is formed, but the break out of the shock leads to the XRO.Comment: 13 pages, 3 figures, 1 table. To appear in Proceedings for "Compact
stars in the QCD phase diagram II (CSQCD II), May 20-24, 2009, KIAA at Peking
University, Beijing - P. R. China [http://vega.bac.pku.edu.cn/rxxu/csqcd.htm
Quark-Novae in Low-mass X-ray Binaries II: Application to G87-7 and to GRB 110328A
We propose a simple model explaining two outstanding astrophysical problems
related to compact objects: (1) that of stars such as G87-7 (alias EG 50) that
constitute a class of relatively low-mass white dwarfs which nevertheless fall
away from the C/O composition and (2) that of GRB 110328A/Swift J164449.3+57345
which showed spectacularly long-lived strong X-ray flaring, posing a challenge
to standard GRB models. We argue that both these observations may have an
explanation within the unified framework of a Quark-Nova occurring in a
low-mass X-ray binary (neutron star- white dwarf). For LMXBs where the binary
separation is sufficiently tight, ejecta from the exploding Neutron Star
triggers nuclear burning in the white dwarf on impact, possibly leading to
Fe-rich composition compact white dwarfs with mass 0.43M_sun < M_WD <
0.72M_sun, reminiscent of G87-7. Our results rely on the assumption, which
ultimately needs to be tested by hydrodynamic and nucleosynthesis simulations,
that under certain circumstances the WD can avoid the thermonuclear runaway.
For heavier white dwarfs (i.e. M_WD > 0.72M_sun) experiencing the QN shock,
degeneracy will not be lifted when Carbon burning begins, and a
sub-Chandrasekhar Type Ia Supernovae may result in our model. Under slightly
different conditions, and for pure He white dwarfs (i.e. M_WD < 0.43M_sun), the
white dwarf is ablated and its ashes raining down on the Quark star leads to
accretion-driven X-ray luminosity with energetics and duration reminiscent of
GRB 110328A. We predict additional flaring activity towards the end of the
accretion phase if the Quark star turns into a Black Hole.Comment: Accepted for publication in ApJ. Extended paper size to 6 journal
pages (from 4). Table is extended and more detailed. Related animations at:
http://quarknova.ucalgary.ca/media/ (find paper I of the series here:
http://adsabs.harvard.edu/abs/2011ApJ...729...60O
Quark-nova explosion inside a collapsar: application to Gamma Ray Bursts
If a quark-nova occurs inside a collapsar, the interaction between the
quark-nova ejecta (relativistic iron-rich chunks) and the collapsar envelope,
leads to features indicative of those observed in Gamma Ray Bursts. The
quark-nova ejecta collides with the stellar envelope creating an outward moving
cap
(Gamma ~ 1-10) above the polar funnel. Prompt gamma-ray burst emission from
internal shocks in relativistic jets (following accretion onto the quark star)
become visible after the cap becomes optically thin. Model features include:
(i) precursor activity (optical, X-ray, gamma-ray), (ii) prompt gamma-ray
emission, and (iii) afterglow emission. We discuss SN-less long duration GRBs,
short hard GRBs (including association and non-association with star forming
regions), dark GRBs, the energetic X-ray flares detected in Swift GRBs, and the
near-simultaneous optical and gamma-ray prompt emission observed in GRBs in the
context of our model.Comment: 10 journal pages and 5 figures (updated references and extended
discussions; accepted for publication in Advances in Astronomy
Considerations on the Role of Fall-Back Discs in the Final Stages of the Common Envelope Binary Interaction
The common envelope interaction is thought to be the gateway to all evolved
compact binaries and mergers. Hydrodynamic simulations of the common envelope
interaction between giant stars and their companions are restricted to the
dynamical, fast, in-spiral phase. They find that the giant envelope is lifted
during this phase, but remains mostly bound to the system. At the same time,
the orbital separation is greatly reduced, but in most simulations it levels
off? at values larger than measured from observations. We conjectured that
during the post-in-spiral phase the bound envelope gas will return to the
system. Using hydrodynamic simulations, we generate initial conditions for our
simulation that result in a fall-back disk with total mass and angular momentum
in line with quantities from the simulations of Passy et al. We find that the
simulated fall-back event reduces the orbital separation efficiently, but fails
to unbind the gas before the separation levels off once again. We also find
that more massive fall-back disks reduce the orbital separation more
efficiently, but the efficiency of unbinding remains invariably very low. From
these results we deduce that unless a further energy source contributes to
unbinding the envelope (such as was recently tested by Nandez et al.), all
common envelope interactions would result in mergers. On the other hand,
additional energy sources are unlikely to help, on their own, to reduce the
orbital separation. We conclude by discussing our dynamical fall-back event in
the context of a thermally-regulated post-common envelope phase.Comment: 12 pages, 12 pages, Accepted to MNRA
Disk wind feedback from high-mass protostars
We perform a sequence of 3D magnetohydrodynamic (MHD) simulations of the
outflow-core interaction for a massive protostar forming via collapse of an
initial cloud core of . This allows us to characterize the
properties of disk wind driven outflows from massive protostars, which can
allow testing of different massive star formation theories. It also enables us
to assess quantitatively the impact of outflow feedback on protostellar core
morphology and overall star formation efficiency. We find that the opening
angle of the flow increases with increasing protostellar mass, in agreement
with a simple semi-analytic model. Once the protostar reaches
the outflow's opening angle is so wide that it has blown
away most of the envelope, thereby nearly ending its own accretion. We thus
find an overall star formation efficiency of , similar to that
expected from low-mass protostellar cores. Our simulation results therefore
indicate that the MHD disk wind outflow is the dominant feedback mechanism for
helping to shape the stellar initial mass function from a given prestellar core
mass function.Comment: Accepted for publication in Ap
Outflow-Confined HII regions. II. The Early Break-Out Phase
In this series of papers, we model the formation and evolution of the
photoionized region and its observational signatures during massive star
formation. Here we focus on the early break out of the photoionized region into
the outflow cavity. Using results of 3-D magnetohydrodynamic-outflow
simulations and protostellar evolution calculations, we perform post-processing
radiative-transfer. The photoionized region first appears at a protostellar
mass of 10Msun in our fiducial model, and is confined to within 10-100AU by the
dense inner outflow, similar to some observed very small hypercompact HII
regions. Since the ionizing luminosity of the massive protostar increases
dramatically as Kelvin-Helmholz (KH) contraction proceeds, the photoionized
region breaks out to the entire outflow region in <10,000yr. Accordingly, the
radio free-free emission brightens significantly in this stage. In our fiducial
model, the radio luminosity at 10 GHz changes from 0.1 mJy kpc2 at m=11Msun to
100 mJy kpc2 at 16Msun, while the infrared luminosity increases by less than a
factor of two. The radio spectral index also changes in the break-out phase
from the optically thick value of 2 to the partially optically thin value of
0.6. Additionally, we demonstrate that short-timescale variation in free-free
flux would be induced by an accretion burst. The outflow density is enhanced in
the accretion burst phase, which leads to a smaller ionized region and weaker
free-free emission. The radio luminosity may decrease by one order of magnitude
during such bursts, while the infrared luminosity is much less affected, since
internal protostellar luminosity dominates over accretion luminosity after KH
contraction starts. Such variability may be observable on timescales as short
10-100 yr, if accretion bursts are driven by disk instabilities.Comment: 9 pages, 5 figures, accepted for publication in Ap
Quark-Novae Ia in the Hubble diagram: Implications For Dark Energy
The accelerated expansion of the Universe was proposed through the use of
Type-Ia SNe as standard candles. The standardization depends on an empirical
correlation between the stretch/color and peak luminosity of the light curves.
The use of Type Ia SN as standard candles rests on the assumption that their
properties (and this correlation) do not vary with red-shift. We consider the
possibility that the majority of Type-Ia SNe are in fact caused by a Quark-Nova
detonation in a tight neutron-star-CO-white-dwarf binary system; a Quark-Nova
Ia. The spin-down energy injected by the Quark Nova remnant (the quark star)
contributes to the post-peak light curve and neatly explains the observed
correlation between peak luminosity and light curve shape. We demonstrate that
the parameters describing Quark-Novae Ia are NOT constant in red-shift.
Simulated Quark-Nova Ia light curves provide a test of the stretch/color
correlation by comparing the true distance modulus with that determined using
SN light curve fitters. We determine a correction between the true and fitted
distance moduli which when applied to Type-Ia SNe in the Hubble diagram
recovers the Omega_M = 1 cosmology. We conclude that Type-Ia SNe observations
do not necessitate the need for an accelerating expansion of the Universe (if
the observed SNe-Ia are dominated by QNe-Ia) and by association the need for
Dark Energy.Comment: 22 pages, 6 figures. Accepted for publication in Research in
Astronomy and Astrophysic
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