scholarly journals Signature of Temporary Burning Front Stalling from a Non-Photospheric Radius Expansion Double-peaked Burst

2006 ◽  
Vol 641 (1) ◽  
pp. L53-L56 ◽  
Author(s):  
Sudip Bhattacharyya ◽  
Tod E. Strohmayer
Keyword(s):  
Burning Front ◽  
Photospheric Radius

scholarly journals Thermonuclear X-ray bursts from 4U 1636 − 536  observed with AstroSat

2021 ◽  
Vol 508 (2) ◽  
pp. 2123-2133
Author(s):  
Pinaki Roy ◽  
Aru Beri ◽  
Sudip Bhattacharyya
Keyword(s):  
Neutron Star ◽  
Flame Spreading ◽  
Rapid Rotation ◽  
X Ray ◽  
Surface Modes ◽  
Doppler Shifts ◽  
Amplitude Profile ◽  
Photospheric Radius ◽  
Rms Amplitude ◽  
Very High

ABSTRACT We report results obtained from the study of 12 thermonuclear X-ray bursts in six AstroSat observations of a neutron star X-ray binary and well-known X-ray burster, 4U 1636 − 536. Burst oscillations (BOs) at ∼ 581 Hz are observed with 4–5σ confidence in three of these X-ray bursts. The rising phase BOs show a decreasing trend of the fractional rms amplitude at 3σ confidence, by far the strongest evidence of thermonuclear flame spreading observed with AstroSat. During the initial 0.25 s of the rise a very high value ($34.0\pm 6.7{{{\ \rm per\ cent}}}$) is observed. The concave shape of the fractional amplitude profile provides a strong evidence of latitude-dependent flame speeds, possibly due to the effects of the Coriolis force. We observe decay phase oscillations with amplitudes comparable to that observed during the rising phase, plausibly due to the combined effect of both surface modes, as well as the cooling wake. The Doppler shifts due to the rapid rotation of the neutron star might cause hard pulses to precede the soft pulses, resulting in a soft lag. The distance to the source estimated using the photospheric radius expansion bursts is consistent with the known value of ∼6 kpc.

scholarly journals Photospheric radius expansion X-ray bursts as standard candles

2003 ◽  
Vol 399 (2) ◽  
pp. 663-680 ◽  
Author(s):  
E. Kuulkers ◽  
P. R. den Hartog ◽  
J. J. M. in 't Zand ◽  
F. W. M. Verbunt ◽  
W. E. Harris ◽  
...  
Keyword(s):  
X Ray ◽  
Photospheric Radius

scholarly journals On the Properties of Wolf-Rayet Stars and Their Mass Loss

1982 ◽  
Vol 99 ◽  
pp. 203-207
Author(s):  
N. Panagia ◽  
M. Felli
Keyword(s):  
Mass Loss ◽  
Multiple Scattering ◽  
Radiation Temperature ◽  
List Type ◽  
Type Number ◽  
Lyman Continuum ◽  
Stellar Radiation ◽  
Total Luminosity ◽  
Continuous Radiation ◽  
Photospheric Radius

From consideration of the observed properties of the envelopes produced by mass loss in WR stars we find that: a)The velocity at the optical photosphere is in the range 200–800 km sb)The effective photospheric radius for the continuous radiation capable to ionize helium twice (γ < 228 A) is typically 5 to 15 times the optical photospheric radius.c)The radiation temperature in the Lyman continuum (γ < 912 Å) is around 5 × 104K. Therefore, most of the stellar radiation is emitted in the far UV and the total luminosity is considerably higher than currently estimated.d)Multiple scattering (N ≃ 20) of radiation in the interval 228–504 Å can provide most of the momentum needed to accelerate the wind up to the observed terminal velocities.

scholarly journals A catalogue of intermediate-duration Type I X-ray bursts observed with the INTEGRAL satellite

2020 ◽  
Vol 494 (2) ◽  
pp. 2509-2522 ◽  
Author(s):  
K Alizai ◽  
J Chenevez ◽  
S Brandt ◽  
N Lund
Keyword(s):  
Accretion Rate ◽  
Type I ◽  
Emission Method ◽  
X Ray ◽  
Long Duration ◽  
Photospheric Radius

ABSTRACT We present a catalogue of long-duration bursts observed with the Joint European X-ray Monitor and IBIS/ISGRI instruments onboard the INTEGRAL satellite. The 14 bursts have e-folding times ranging from 55 s to ≈17 min, and are therefore classified as intermediate-duration bursts, caused by the ignition of an unusually thick helium layer. Though seven events have already been reported in literature, we have systematically reanalysed the whole sample. We find three new photospheric radius expansion bursts, which are not reported in the literature, allowing us to provide a new estimate of the distances to these sources. We apply the enhanced persistent emission method (also known as the fa method) on sources with detectable persistent emission prior to a burst, in order to follow the evolution of the accretion rate during the burst. Although we do not get significantly better fits, the evolution of the fa factor shows an indicative behaviour, which we discuss.

scholarly journals PHOTOSPHERIC RADIUS EXPANSION DURING MAGNETAR BURSTS

2010 ◽  
Vol 719 (1) ◽  
pp. 190-200 ◽  
Author(s):  
Anna L. Watts ◽  
Chryssa Kouveliotou ◽  
Alexander J. van der Horst ◽  
Ersin Göğüş ◽  
Yuki Kaneko ◽  
...  
Keyword(s):  
Photospheric Radius

scholarly journals Diffusive photospheres in gamma-ray bursts

2020 ◽  
Vol 494 (1) ◽  
pp. 1463-1469
Author(s):  
G V Vereshchagin ◽  
I A Siutsou
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Total Flux ◽  
Thermal Component ◽  
Radiative Diffusion ◽  
Relativistic Outflows ◽  
Photospheric Radius

ABSTRACT Photospheric emission may originate from relativistic outflows in two qualitatively different regimes: last scattering of photons inside the outflow at the photospheric radius or radiative diffusion to the boundary of the outflow. In this work, the measurement of temperature and flux of the thermal component in the early afterglows of several gamma-ray bursts along with the total flux in the prompt phase is used to determine initial radii of the outflow as well as its Lorentz factors. Results indicate that in some cases the outflow has relatively low Lorentz factors (Γ &lt; 10), favouring cocoon interpretation, while in other cases Lorentz factors are larger (Γ &gt; 10), indicating diffusive photospheric origin of the thermal component, associated with an ultrarelativistic outflow.

scholarly journals Design and Operation of Laboratory Combustion Tubes

1966 ◽  
Vol 6 (02) ◽  
pp. 183-198 ◽  
Author(s):  
W.L. Penberthy ◽  
H.J. Ramey
Keyword(s):  
Experimental Data ◽  
Heat Loss ◽  
Oil Recovery ◽  
Combustion Process ◽  
Recovery Process ◽  
Combustion Tube ◽  
Design Procedures ◽  
Fuel Concentration ◽  
Burning Front ◽  
Design Construction

Abstract Experimental work on the combustion oil recovery process has consisted of both laboratory and field studies. Although field experiments are the ultimate test of any oil recovery process, they are costly, time consuming and difficult to analyze quantitatively. Laboratory combustion tube experiments can be operated far more rapidly and cheaply, but are subject to scaling and interpretation problems. This paper points out some important design problems, operational criteria and considerations important to interpretation of results. An analytical heat model of movement of a burning front axially along a cylinder with heat loss through an annular insulation was developed. The result was used to identify steady-state temperature distributions both ahead of and behind the burning front, with and without heat loss. Results indicate potential operating limitations on the minimum burning front velocity (or air flux) which may be used for any given combustion tube. Results also enable estimating the effective thermal diffusivity and over-all heat loss from experimental data and thickness of the burning zone. Results of operation of a combustion tube constructed recently verify this preliminary theory in the region immediately ahead of and behind the burning front surprisingly well. Introduction Many field and laboratory studies of the forward combustion oil recovery process have been conducted since the early publications of Kuhn and Koch and Grant and Szasz in 1953 and 1954. In view of the complex and costly nature of this type of investigation, it is not surprising that no complete theory of the nature of the forward combustion process is yet available. However, gross effects are understood well enough that reasonable design procedures are available for planning field operations. Nelson and McNeil have published two comprehensive papers concerning design procedures. One major consideration in planning field operations is the fuel concentration at the burning front. Fuel concentration controls air requirements - an important cost factor in forward combustion. Although fuel concentration can be estimated from field test results by various methods, results are subject to great uncertainty in view of natural limitations on experimental observations. Nelson and McNeil recommend that fuel concentration be determined from laboratory combustion tube studies. Fuel concentration is only one of many important factors which can be studied by combustion tube experimentation. An obvious goal of importance must be development of a comprehensive theory of the forward combustion process. If a theory of this process can be established which matches controlled laboratory experimentation, it should be possible to apply this theory to field operating conditions with some confidence. Laboratory combustion tube studies have already yielded important information concerning the combustion process. However, details concerning the design, construction and operation of combustion tubes are rare. Combustion tubes used by various investigators vary in size, length and mode of operation. Therefore, one purpose of this paper is to present considerations important to design, construction and operation of a combustion tube. In regard to previous combustion tube studies, attention is called to Refs. 1 through 9. These references describe a wide variety of equipment types and present a great deal of pertinent experimental data. In general, combustion tubes usually consist of thin-walled stainless steel tubes containing an oil sand pack mounted within a pressure jacket. Provisions have often been made to heat the tube externally by separately controlled heaters to reduce heat losses. This step usually permits operation at low air fluxes (air rate per square foot burning front surface) similar to those encountered in field operations. Burning is usually conducted from the air inlet end of the tube to the outflow end. The tube orientation used has been vertical or horizontal. For vertical tubes, burning has been conducted vertically downwards. SPEJ P. 183ˆ

Thermoelectric self-potential and resistivity data localize the burning front of underground coal fires

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. B259-B273 ◽  
Author(s):  
A. Revil ◽  
M. Karaoulis ◽  
S. Srivastava ◽  
S. Byrdina
Keyword(s):  
Coal Seam ◽  
Joint Inversion ◽  
Synthetic Data ◽  
Ground Surface ◽  
Thermal Anomaly ◽  
Silica Sand ◽  
Geophysical Field ◽  
Burning Front ◽  
Resistivity Data ◽  
Self Potential

Self-potential signals and resistivity data can be jointly inverted or analyzed to track the position of the burning front of an underground coal-seam fire. We first investigate the magnitude of the thermoelectric coupling associated with the presence of a thermal anomaly (thermoelectric current associated with a thermal gradient). A sandbox experiment is developed and modeled to show that in presence of a heat source, a negative self-potential anomaly is expected at the ground surface. The expected sensitivity coefficient is typically on the order of [Formula: see text] in a silica sand saturated by demineralized water. Geophysical field measurements gathered at Marshall (near Boulder, CO) show clearly the position of the burning front in the electrical resistivity tomogram and in the self-potential data gathered at the ground surface with a negative self-potential anomaly of about [Formula: see text]. To localize more accurately the position of the burning front, we developed a strategy based on two steps: (1) We first jointly invert resistivity and self-potential data using a cross-gradient approach, and (2) a joint interpretation of the resistivity and self-potential data is made using a normalized burning front index (NBI). The value of the NBI ranges from 0 to 1 with 1 indicating a high probability to find the burning front (strictly speaking, the NBI is, however, not a probably density). We validate first this strategy using synthetic data and then we apply it to the field data. A clear source is localized at the expected position of the burning front of the coal-seam fire. The NBI determined from the joint inversion is only slightly better than the value determined from independent inversion of the two geophysical data sets.

scholarly journals On the Coronal Activity of RS CVn Systems

1991 ◽  
Vol 130 ◽  
pp. 501-503
Author(s):  
Osman Demircan ◽  
Ethem Derman
Keyword(s):  
Effective Temperature ◽  
Strongly Correlated ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Long Period ◽  
Emission Area ◽  
Coronal Activity ◽  
New Evidence ◽  
Photospheric Radius

An analysis of the X-ray emission of a large sample of single MS stars shows that X-ray luminosity is strongly correlated with the photospheric radius (Fleming et al., 1989) which implies the dependence of activity on bolometric luminosity Lbol, effective temperature Teff, and thus stellar mass M (Micela et al., 1985; Bookbinder et al., 1986). The role of the emission area on the coronal activity of RS CVn systems has been noted independently by Majer et al. (1986), and Demircan (1986).By using new data on some well known RS CVn systems, we produce new evidence that above idea is indeed valid. A plot of X-ray luminosity Lx versus (B – V) for the sample of well known RS CVn systems in Fig. 1 shows that cooler, long period, more evolved systems with larger surface area have stronger X-ray emission.

Sign in / Sign up

Export Citation Format

Share Document