28 results on '"Genet, F."'
Search Results
2. Browse species from Ethiopia: role in methane reduction and nematode control in goats
- Author
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Hendriks, Wouter, Pellikaan, Wilbert, Mengistu, Genet F., Hendriks, Wouter, Pellikaan, Wilbert, and Mengistu, Genet F.
- Abstract
The aim of the research reported in this thesis was to evaluate browse species collected from Ethiopia for preference by goats, and for their in vitro anthelmintic and methane (CH4) reduction properties. During the conduct of the studies observations were made warranting a further aim, to compare in vitro fermentation patterns of browse species using inocula from goats and cows kept on identical dietary regime. The preference of browse species using dry matter intake (DMI) as a proxy and in combination with polyethylene glycol (PEG), relationships between browse species intake and chemical composition were determined in Chapter 2. Air-dried leaves of Acacia etbaica, Cadaba farinosa, Capparis tomentosa, Dichrostachys cinerea, Dodonaea angustifolia, Euclea racemosa, Maerua angolensis, Maytenus senegalensis, Rhus natalensis and Senna singueana were used. Two cafeteria trials, each lasting 10 days were conducted using goats receiving a daily ration of grass hay and wheat bran, without (trial 1) or with (trial 2) the inclusion of PEG. Preference measured as the first 10 min browse DMI differed significantly among browse species and with PEG (P<0.0001). Browse with higher tannin content, D. cinerea, R. natalensis and A. etbaica were the most preferred species regardless of PEG presence. Preference appeared to be based on digestible fibre fraction, hemicellulose rather than tannin levels in the browse species. Extracts of the 10 browse species were evaluated for their anthelmintic activity against Haemonchus contortus (Chapter 3). The larval exsheathment inhibition assay (LEIA) was applied using H. contortus third stage larvae (L3) in a dose dependent manner with extract concentrations of 0, 150, 300, 600, 1200 µg/ml phosphate buffered saline (PBS). The role of polyphenols in the inhibition against L3 was evaluated using polyvinylpolypyrrolidone (PVPP). All browse extracts significantly (P<0.0001) inhibited larval exsheathment in a dose dependent manner with the dose requi
- Published
- 2017
3. Lag-luminosity relation in gamma-ray burst X-ray flares: a direct link to the prompt emission
- Author
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Margutti, R., Guidorzi, C., Chincarini, G., Bernardini, M. G., Genet, F., Mao, J., Pasotti, F., Margutti, R., Guidorzi, C., Chincarini, G., Bernardini, M. G., Genet, F., Mao, J., and Pasotti, F.
- Abstract
The temporal and spectral analysis of 9 bright X-ray flares out of a sample of 113 flares observed by Swift reveals that the flare phenomenology is strictly analogous to the prompt gamma-ray emission: high energy flare profiles rise faster, decay faster and peak before the low energy emission. However, flares and prompt pulses differ in one crucial aspect: flares evolve with time. As time proceeds flares become wider, with larger peak lag, lower luminosities and softer emission. The flare spectral peak energy E_{p,i} evolves to lower values following an exponential decay which tracks the decay of the flare flux. The two flares with best statistics show higher than expected isotropic energy E_{iso} and peak luminosity L_{p,iso} when compared to the E_{p,i}-E_{iso} and E_{p,i}-L_{iso} prompt correlations. E_{p,i} is found to correlate with L_{iso} within single flares, giving rise to a time resolved E_{p,i}(t)-L_{iso}(t). Like prompt pulses, flares define a lag-luminosity relation: L_{p,iso}^{0.3-10 keV} t_{lag}^{-0.95+/-0.23}. The lag-luminosity is proven to be a fundamental law extending 5 decades in time and 5 in energy. Moreover, this is direct evidence that GRB X-ray flares and prompt gamma-ray pulses are produced by the same mechanism. Finally we establish a flare-afterglow morphology connection: flares are preferentially detected superimposed to one-break or canonical X-ray afterglows., Comment: MNRAS accepted
- Published
- 2010
- Full Text
- View/download PDF
4. Lag-luminosity relation in gamma-ray burst X-ray flares: a direct link to the prompt emission
- Author
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Margutti, R., Guidorzi, C., Chincarini, G., Bernardini, M. G., Genet, F., Mao, J., Pasotti, F., Margutti, R., Guidorzi, C., Chincarini, G., Bernardini, M. G., Genet, F., Mao, J., and Pasotti, F.
- Abstract
The temporal and spectral analysis of 9 bright X-ray flares out of a sample of 113 flares observed by Swift reveals that the flare phenomenology is strictly analogous to the prompt gamma-ray emission: high energy flare profiles rise faster, decay faster and peak before the low energy emission. However, flares and prompt pulses differ in one crucial aspect: flares evolve with time. As time proceeds flares become wider, with larger peak lag, lower luminosities and softer emission. The flare spectral peak energy E_{p,i} evolves to lower values following an exponential decay which tracks the decay of the flare flux. The two flares with best statistics show higher than expected isotropic energy E_{iso} and peak luminosity L_{p,iso} when compared to the E_{p,i}-E_{iso} and E_{p,i}-L_{iso} prompt correlations. E_{p,i} is found to correlate with L_{iso} within single flares, giving rise to a time resolved E_{p,i}(t)-L_{iso}(t). Like prompt pulses, flares define a lag-luminosity relation: L_{p,iso}^{0.3-10 keV} t_{lag}^{-0.95+/-0.23}. The lag-luminosity is proven to be a fundamental law extending 5 decades in time and 5 in energy. Moreover, this is direct evidence that GRB X-ray flares and prompt gamma-ray pulses are produced by the same mechanism. Finally we establish a flare-afterglow morphology connection: flares are preferentially detected superimposed to one-break or canonical X-ray afterglows., Comment: MNRAS accepted
- Published
- 2010
- Full Text
- View/download PDF
5. GRB081028 and its late-time afterglow re-brightening
- Author
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Margutti..[et al.], R., Genet, F., Granot, R., Fynbo, Johan Peter Uldall, Malesani, Daniele, Margutti..[et al.], R., Genet, F., Granot, R., Fynbo, Johan Peter Uldall, and Malesani, Daniele
- Published
- 2010
6. GRB 081028 and its late-time afterglow re-brightening
- Author
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Margutti....[et al.], R., Genet, F., Granot, J., Duran, R. B., Fynbo, Johan Peter Uldall, Malesani, Daniele, Margutti....[et al.], R., Genet, F., Granot, J., Duran, R. B., Fynbo, Johan Peter Uldall, and Malesani, Daniele
- Published
- 2010
7. Late-time Observations of GRB 080319B: Jet Break, Host Galaxy, and Accompanying Supernova
- Author
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Tanvir, N., Rol, E., Levan, A., Svensson, K., Fruchter, A., Granot, J., O’Brien, P., Wiersema, K., Starling, R., Jakobsson, P., Fynbo, J., Hjorth, J., Curran, Peter, van der Horst, A., Kouveliotou, C., Racusin, J., Burrows, D., Genet, F., Tanvir, N., Rol, E., Levan, A., Svensson, K., Fruchter, A., Granot, J., O’Brien, P., Wiersema, K., Starling, R., Jakobsson, P., Fynbo, J., Hjorth, J., Curran, Peter, van der Horst, A., Kouveliotou, C., Racusin, J., Burrows, D., and Genet, F.
- Abstract
The Swift-discovered GRB 080319B was by far the most distant source ever observed at naked-eye brightness,reaching a peak apparent magnitude of 5.3 at a redshift of z = 0.937. We present our late-time optical (HubbleSpace Telescope, Gemini, and Very Large Telescope) and X-ray (Chandra) observations, which confirm that anachromatic break occurred in the power-law afterglow light curve at~ 11 days post-burst. This most likely indicatesthat the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy inthe jet Ejet 1052 erg. Our observations also show a late-time excess of red light, which is well explained ifthe GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. Thelatest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy(r(AB) ˜ 27.0, rest frame MB ˜ -17.2). This galaxy is small even by the standards of other GRB hosts, whichis suggestive of a low-metallicity environment. Intriguingly, the properties of this extreme event—a small hostand bright SN—are entirely typical of the very low luminosity bursts such as GRB 980425 and GRB 060218.
- Published
- 2010
8. GRB081028 and its late-time afterglow re-brightening
- Author
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Margutti..[et al.], R., Genet, F., Granot, R., Fynbo, Johan Peter Uldall, Malesani, Daniele, Margutti..[et al.], R., Genet, F., Granot, R., Fynbo, Johan Peter Uldall, and Malesani, Daniele
- Published
- 2010
9. GRB 081028 and its late-time afterglow re-brightening
- Author
-
Margutti....[et al.], R., Genet, F., Granot, J., Duran, R. B., Fynbo, Johan Peter Uldall, Malesani, Daniele, Margutti....[et al.], R., Genet, F., Granot, J., Duran, R. B., Fynbo, Johan Peter Uldall, and Malesani, Daniele
- Published
- 2010
10. The spectral-temporal properties of the prompt pulses and rapid decay phase of GRBs
- Author
-
Willingale, R., Genet, F., Granot, J., O'Brien, P. T., Willingale, R., Genet, F., Granot, J., and O'Brien, P. T.
- Abstract
The prompt emission from GRBs is the brightest electromagnetic emission known yet it's origin is not understood. The flux density of individual prompt pulses of a GRB can be represented by an analytical expression derived assuming the emission is from a thin, ultra-relativistically expanding, uniform, spherical shell over a finite range of radii. We present the results of fitting this analytical expression to the lightcurves from the four standard Swift BAT energy bands and two standard Swift XRT energy bands of 12 bursts. The expression includes the High Latitude Emission (HLE) component and the fits provide a rigourous demonstration that the HLE can explain the Rapid Decay Phase (RDP) of the prompt emission. The model also accommodates some aspects of energy-dependent lag and energy-dependent pulse width, but there are features in the data which are not well represented. Some pulses have a hard, narrow peak which is not well fitted or a rise and decay which is faster than expected using the standard indices derived assuming synchrotron emission from internal shocks, although it might be possible to accommodate these features using a different emission mechanism within the same overall framework. The luminosity of pulses is correlated with the peak energy of the pulse spectrum, Lf ~ (Epeak(1+z))^1.8, and anti-correlated with the time since ejection of the pulse, Lf ~ (Tf/(1 + z))^-2.0., Comment: Accepted for publication in MNRAS
- Published
- 2009
- Full Text
- View/download PDF
11. GRB081028 and its late-time afterglow re-brightening
- Author
-
Margutti, R., Genet, F., Granot, J., Duran, R. Barniol, Guidorzi, C., Chincarini, G., Mao, J., Schady, P., Sakamoto, T., Miller, A. A., Olofsson, G., Bloom, J. S., Evans, P. A., Fynbo, J. P. U., Malesani, D., Moretti, A., Pasotti, F., Starr, D., Burrows, D. N., Barthelmy, S. D., Roming, P. W. A., Gehrels, N., Margutti, R., Genet, F., Granot, J., Duran, R. Barniol, Guidorzi, C., Chincarini, G., Mao, J., Schady, P., Sakamoto, T., Miller, A. A., Olofsson, G., Bloom, J. S., Evans, P. A., Fynbo, J. P. U., Malesani, D., Moretti, A., Pasotti, F., Starr, D., Burrows, D. N., Barthelmy, S. D., Roming, P. W. A., and Gehrels, N.
- Abstract
Swift captured for the first time a smoothly rising X-ray re-brightening of clear non-flaring origin after the steep decay in a long gamma-ray burst (GRB): GRB081028. A rising phase is likely present in all GRBs but is usually hidden by the prompt tail emission and constitutes the first manifestation of what is later to give rise to the shallow decay phase. Contemporaneous optical observations reveal a rapid evolution of the injection frequency of a fast cooling synchrotron spectrum through the optical band, which disfavours the afterglow onset (start of the forward shock emission along our line of sight when the outflow is decelerated) as the origin of the observed re-brightening. We investigate alternative scenarios and find that the observations are consistent with the predictions for a narrow jet viewed off-axis. The high on-axis energy budget implied by this interpretation suggests different physical origins of the prompt and (late) afterglow emission. Strong spectral softening takes place from the prompt to the steep decay phase: we track the evolution of the spectral peak energy from the gamma-rays to the X-rays and highlight the problems of the high latitude and adiabatic cooling interpretations. Notably, a softening of both the high and low spectral slopes with time is also observed. We discuss the low on-axis radiative efficiency of GRB081028 comparing its properties against a sample of Swift long GRBs with secure E_gamma,iso measurements., Comment: 22 pages, 11 figures; MNRAS accepted
- Published
- 2009
- Full Text
- View/download PDF
12. Rise and fall of the X-ray flash 080330: an off-axis jet?
- Author
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Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N. P. M., Klotz, A., Fynbo, J. P. U., Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C. G., Steele, I. A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Kruehler, T., Yoldacs, A. Kupcu, Moretti, A., Mottram, C. J., O'Brien, P. T., Smith, R. J., Szokoly, G., Tagliaferri, G., Tanvir, N. R., Gehrels, N., Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N. P. M., Klotz, A., Fynbo, J. P. U., Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C. G., Steele, I. A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Kruehler, T., Yoldacs, A. Kupcu, Moretti, A., Mottram, C. J., O'Brien, P. T., Smith, R. J., Szokoly, G., Tagliaferri, G., Tanvir, N. R., and Gehrels, N.
- Abstract
X-ray flashes (XRFs) are a class of gamma-ray bursts (GRBs) with the peak energy of the time-integrated spectrum, Ep, below 30 keV, whereas classical GRBs have Ep of a few hundreds keV. Apart from Ep and the lower luminosity, the properties of XRFs are typical of the classical GRBs. Yet, the nature of XRFs and the differences from that of GRBs are not understood. In addition, there is no consensus on the interpretation of the shallow decay phase observed in most X-ray afterglows of both XRFs and GRBs. We examine in detail the case of XRF 080330 discovered by Swift at the redshift of 1.51. This burst is representative of the XRF class and exhibits an X-ray shallow decay. The rich and broadband (from NIR to UV) photometric data set we collected across this phase makes it an ideal candidate to test the off-axis jet interpretation proposed to explain both the softness of XRFs and the shallow decay phase. We present prompt gamma-ray, early and late IR/visible/UV and X-ray observations of the XRF 080330. We derive a SED from NIR to X-ray bands across the plateau phase with a power-law index of 0.79 +- 0.01 and negligible rest-frame dust extinction. The multi-wavelength evolution of the afterglow is achromatic from ~10^2 s out to ~8x10^4 s. We describe the temporal evolution of the multi-wavelength afterglow within the context of the standard afterglow model and show that a single-component jet viewed off-axis explains the observations (abriged)., Comment: accepted to A&A, 19 pages, 11 figures
- Published
- 2009
- Full Text
- View/download PDF
13. Is the Rapid Decay Phase from High Latitude Emission?
- Author
-
Genet, F., Granot, J., Genet, F., and Granot, J.
- Abstract
There is good observationnal evidence that the Steep Decay Phase (SDP) that is observed in most Swift GRBs is the tail of the prompt emission. The most popular model to explain the SDP is Hight Latitude Emission (HLE). Many models for the prompt emission give rise to HLE, like the popular internal shocks (IS) model, but some models do not, such as sporadic magnetic reconnection events. Knowing if the SDP is consistent with HLE would thus help distinguish between different prompt emission models. In order to test this, we model the prompt emission (and its tail) as the sum of independent pulses (and their tails). A single pulse is modeled as emission arising from an ultra-relativistic thin spherical expanding shell. We obtain analytic expressions for the flux in the IS model with a Band function spectrum. We find that in this framework the observed spectrum is also a Band function, and naturally softens with time. The decay of the SDP is initially dominated by the tail of the last pulse, but other pulses can dominate later. Modeling several overlapping pulses as a single broader pulse would overestimates the SDP flux. One should thus be careful when testing the HLE., Comment: 3 pages, submitted to the proceedings of the Sixth Huntsville gamma-ray bursts symposium
- Published
- 2009
- Full Text
- View/download PDF
14. The spectral-temporal properties of the prompt pulses and rapid decay phase of GRBs
- Author
-
Willingale, R., Genet, F., Granot, J., O'Brien, P. T., Willingale, R., Genet, F., Granot, J., and O'Brien, P. T.
- Abstract
The prompt emission from GRBs is the brightest electromagnetic emission known yet it's origin is not understood. The flux density of individual prompt pulses of a GRB can be represented by an analytical expression derived assuming the emission is from a thin, ultra-relativistically expanding, uniform, spherical shell over a finite range of radii. We present the results of fitting this analytical expression to the lightcurves from the four standard Swift BAT energy bands and two standard Swift XRT energy bands of 12 bursts. The expression includes the High Latitude Emission (HLE) component and the fits provide a rigourous demonstration that the HLE can explain the Rapid Decay Phase (RDP) of the prompt emission. The model also accommodates some aspects of energy-dependent lag and energy-dependent pulse width, but there are features in the data which are not well represented. Some pulses have a hard, narrow peak which is not well fitted or a rise and decay which is faster than expected using the standard indices derived assuming synchrotron emission from internal shocks, although it might be possible to accommodate these features using a different emission mechanism within the same overall framework. The luminosity of pulses is correlated with the peak energy of the pulse spectrum, Lf ~ (Epeak(1+z))^1.8, and anti-correlated with the time since ejection of the pulse, Lf ~ (Tf/(1 + z))^-2.0., Comment: Accepted for publication in MNRAS
- Published
- 2009
- Full Text
- View/download PDF
15. GRB081028 and its late-time afterglow re-brightening
- Author
-
Margutti, R., Genet, F., Granot, J., Duran, R. Barniol, Guidorzi, C., Chincarini, G., Mao, J., Schady, P., Sakamoto, T., Miller, A. A., Olofsson, G., Bloom, J. S., Evans, P. A., Fynbo, J. P. U., Malesani, D., Moretti, A., Pasotti, F., Starr, D., Burrows, D. N., Barthelmy, S. D., Roming, P. W. A., Gehrels, N., Margutti, R., Genet, F., Granot, J., Duran, R. Barniol, Guidorzi, C., Chincarini, G., Mao, J., Schady, P., Sakamoto, T., Miller, A. A., Olofsson, G., Bloom, J. S., Evans, P. A., Fynbo, J. P. U., Malesani, D., Moretti, A., Pasotti, F., Starr, D., Burrows, D. N., Barthelmy, S. D., Roming, P. W. A., and Gehrels, N.
- Abstract
Swift captured for the first time a smoothly rising X-ray re-brightening of clear non-flaring origin after the steep decay in a long gamma-ray burst (GRB): GRB081028. A rising phase is likely present in all GRBs but is usually hidden by the prompt tail emission and constitutes the first manifestation of what is later to give rise to the shallow decay phase. Contemporaneous optical observations reveal a rapid evolution of the injection frequency of a fast cooling synchrotron spectrum through the optical band, which disfavours the afterglow onset (start of the forward shock emission along our line of sight when the outflow is decelerated) as the origin of the observed re-brightening. We investigate alternative scenarios and find that the observations are consistent with the predictions for a narrow jet viewed off-axis. The high on-axis energy budget implied by this interpretation suggests different physical origins of the prompt and (late) afterglow emission. Strong spectral softening takes place from the prompt to the steep decay phase: we track the evolution of the spectral peak energy from the gamma-rays to the X-rays and highlight the problems of the high latitude and adiabatic cooling interpretations. Notably, a softening of both the high and low spectral slopes with time is also observed. We discuss the low on-axis radiative efficiency of GRB081028 comparing its properties against a sample of Swift long GRBs with secure E_gamma,iso measurements., Comment: 22 pages, 11 figures; MNRAS accepted
- Published
- 2009
- Full Text
- View/download PDF
16. Rise and fall of the X-ray flash 080330: an off-axis jet?
- Author
-
Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N. P. M., Klotz, A., Fynbo, J. P. U., Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C. G., Steele, I. A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Kruehler, T., Yoldacs, A. Kupcu, Moretti, A., Mottram, C. J., O'Brien, P. T., Smith, R. J., Szokoly, G., Tagliaferri, G., Tanvir, N. R., Gehrels, N., Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N. P. M., Klotz, A., Fynbo, J. P. U., Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C. G., Steele, I. A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Kruehler, T., Yoldacs, A. Kupcu, Moretti, A., Mottram, C. J., O'Brien, P. T., Smith, R. J., Szokoly, G., Tagliaferri, G., Tanvir, N. R., and Gehrels, N.
- Abstract
X-ray flashes (XRFs) are a class of gamma-ray bursts (GRBs) with the peak energy of the time-integrated spectrum, Ep, below 30 keV, whereas classical GRBs have Ep of a few hundreds keV. Apart from Ep and the lower luminosity, the properties of XRFs are typical of the classical GRBs. Yet, the nature of XRFs and the differences from that of GRBs are not understood. In addition, there is no consensus on the interpretation of the shallow decay phase observed in most X-ray afterglows of both XRFs and GRBs. We examine in detail the case of XRF 080330 discovered by Swift at the redshift of 1.51. This burst is representative of the XRF class and exhibits an X-ray shallow decay. The rich and broadband (from NIR to UV) photometric data set we collected across this phase makes it an ideal candidate to test the off-axis jet interpretation proposed to explain both the softness of XRFs and the shallow decay phase. We present prompt gamma-ray, early and late IR/visible/UV and X-ray observations of the XRF 080330. We derive a SED from NIR to X-ray bands across the plateau phase with a power-law index of 0.79 +- 0.01 and negligible rest-frame dust extinction. The multi-wavelength evolution of the afterglow is achromatic from ~10^2 s out to ~8x10^4 s. We describe the temporal evolution of the multi-wavelength afterglow within the context of the standard afterglow model and show that a single-component jet viewed off-axis explains the observations (abriged)., Comment: accepted to A&A, 19 pages, 11 figures
- Published
- 2009
- Full Text
- View/download PDF
17. Is the Rapid Decay Phase from High Latitude Emission?
- Author
-
Genet, F., Granot, J., Genet, F., and Granot, J.
- Abstract
There is good observationnal evidence that the Steep Decay Phase (SDP) that is observed in most Swift GRBs is the tail of the prompt emission. The most popular model to explain the SDP is Hight Latitude Emission (HLE). Many models for the prompt emission give rise to HLE, like the popular internal shocks (IS) model, but some models do not, such as sporadic magnetic reconnection events. Knowing if the SDP is consistent with HLE would thus help distinguish between different prompt emission models. In order to test this, we model the prompt emission (and its tail) as the sum of independent pulses (and their tails). A single pulse is modeled as emission arising from an ultra-relativistic thin spherical expanding shell. We obtain analytic expressions for the flux in the IS model with a Band function spectrum. We find that in this framework the observed spectrum is also a Band function, and naturally softens with time. The decay of the SDP is initially dominated by the tail of the last pulse, but other pulses can dominate later. Modeling several overlapping pulses as a single broader pulse would overestimates the SDP flux. One should thus be careful when testing the HLE., Comment: 3 pages, submitted to the proceedings of the Sixth Huntsville gamma-ray bursts symposium
- Published
- 2009
- Full Text
- View/download PDF
18. Rise and fall of the X-ray flash 080330:an off-axis jet ?
- Author
-
Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N.~P.~M., Klotz, A., Fynbo, Johan Peter Uldall, Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C.~G., Steele, I.~A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Krühler, T., Küpcü Yoldas, A., Moretti, A., Mottram, C.~J., O'Brien, P.~T., Smith, R.~J., Szokoly, G., Tagliaferri, G., Tanvir, N.~R., Gehrels, N., Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N.~P.~M., Klotz, A., Fynbo, Johan Peter Uldall, Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C.~G., Steele, I.~A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Krühler, T., Küpcü Yoldas, A., Moretti, A., Mottram, C.~J., O'Brien, P.~T., Smith, R.~J., Szokoly, G., Tagliaferri, G., Tanvir, N.~R., and Gehrels, N.
- Abstract
Udgivelsesdato: May
- Published
- 2009
19. Rise and fall of the X-ray flash 080330:an off-axis jet ?
- Author
-
Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N.~P.~M., Klotz, A., Fynbo, Johan Peter Uldall, Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C.~G., Steele, I.~A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Krühler, T., Küpcü Yoldas, A., Moretti, A., Mottram, C.~J., O'Brien, P.~T., Smith, R.~J., Szokoly, G., Tagliaferri, G., Tanvir, N.~R., Gehrels, N., Guidorzi, C., Clemens, C., Kobayashi, S., Granot, J., Melandri, A., D'Avanzo, P., Kuin, N.~P.~M., Klotz, A., Fynbo, Johan Peter Uldall, Covino, S., Greiner, J., Malesani, D., Mao, J., Mundell, C.~G., Steele, I.~A., Jakobsson, P., Margutti, R., Bersier, D., Campana, S., Chincarini, G., D'Elia, V., Fugazza, D., Genet, F., Gomboc, A., Krühler, T., Küpcü Yoldas, A., Moretti, A., Mottram, C.~J., O'Brien, P.~T., Smith, R.~J., Szokoly, G., Tagliaferri, G., Tanvir, N.~R., and Gehrels, N.
- Abstract
Udgivelsesdato: May
- Published
- 2009
20. Realistic analytic model for the prompt and high latitude emission in GRBs
- Author
-
Genet, F., Granot, J., Genet, F., and Granot, J.
- Abstract
Most gamma-ray bursts (GRBs) observed by the Swift satellite show an early rapid decay phase (RDP) in their X-ray lightcurve, which is usually a smooth continuation of the prompt gamma-ray emission, strongly suggesting that it is its tail. However, the mechanism behind it is still not clear. The most popular model for this RDP is High Latitude Emission (HLE). While HLE is expected in many models for the prompt GRB emission, such as the popular internal shocks model, there are models in which it is not expected, such as sporadic magnetic reconnection events. Therefore, testing whether the RDP is consistent with HLE can help distinguish between different prompt emission models. We address this question by modeling the prompt emission as the sum of its individual pulses with their HLE tails. Analytic expressions for the observed flux density are obtained for power-law and Band function emission spectra. For internal shocks the observed instantaneous spectrum is very close to the emitted one, and should be well described by a Band function also during the RDP. Our model naturally produces, the observed spectral softening and steepening of the flux decay. The observed flux during the RDP is initially dominated by the tail of the last pulse, but the tails of one or more earlier pulses can become dominant later on. Moreover, modeling several overlapping pulses as a single wider pulse would over-predict the emission tail. Thus, one should be very careful when testing the predictions of HLE and do a combined temporal and spectral fit of the prompt GRB emission and the RDP., Comment: 24 pages, 9 figures. Text reorganized. Accepted by MNRAS
- Published
- 2008
- Full Text
- View/download PDF
21. Realistic analytic model for the prompt and high latitude emission in GRBs
- Author
-
Genet, F., Granot, J., Genet, F., and Granot, J.
- Abstract
Most gamma-ray bursts (GRBs) observed by the Swift satellite show an early rapid decay phase (RDP) in their X-ray lightcurve, which is usually a smooth continuation of the prompt gamma-ray emission, strongly suggesting that it is its tail. However, the mechanism behind it is still not clear. The most popular model for this RDP is High Latitude Emission (HLE). While HLE is expected in many models for the prompt GRB emission, such as the popular internal shocks model, there are models in which it is not expected, such as sporadic magnetic reconnection events. Therefore, testing whether the RDP is consistent with HLE can help distinguish between different prompt emission models. We address this question by modeling the prompt emission as the sum of its individual pulses with their HLE tails. Analytic expressions for the observed flux density are obtained for power-law and Band function emission spectra. For internal shocks the observed instantaneous spectrum is very close to the emitted one, and should be well described by a Band function also during the RDP. Our model naturally produces, the observed spectral softening and steepening of the flux decay. The observed flux during the RDP is initially dominated by the tail of the last pulse, but the tails of one or more earlier pulses can become dominant later on. Moreover, modeling several overlapping pulses as a single wider pulse would over-predict the emission tail. Thus, one should be very careful when testing the predictions of HLE and do a combined temporal and spectral fit of the prompt GRB emission and the RDP., Comment: 24 pages, 9 figures. Text reorganized. Accepted by MNRAS
- Published
- 2008
- Full Text
- View/download PDF
22. The rise of the afterglow in GRB 050820a
- Author
-
Genet, F., Daigne, F., Mochkovitch, R., Genet, F., Daigne, F., and Mochkovitch, R.
- Abstract
The early optical afterglow of GRB 050820a recorded by the RAPTOR telescope shows both a contribution from the prompt emission and the initial rise of the afterglow. It is therefore well-suited for the study of the dynamical evolution of the GRB ejecta when it first undergoes the decelerating effect of the environment. This is a complex phase where the internal, reverse, and forward shocks can all be present simultaneously. We have developed a simplified model that can follow these different shocks in an approximate, but self-consistent way. It is applied to the case of GRB 050820a to obtain the prompt and afterglow light curves. We show that the rise of the afterglow during the course of the prompt emission has some important consequences. The reverse shock propagates back into the ejecta before internal shocks are completed, which affects the shape of the gamma-ray profile. We get the best results when the external medium has a uniform density, but obtaining a simultaneous fit of the prompt and afterglow emission is not easy. We discuss a few possibilities that could help to improve this situation., Comment: 6 pages, 9 figures, accepted for publication in A&A
- Published
- 2007
- Full Text
- View/download PDF
23. The rise of the afterglow in GRB 050820a
- Author
-
Genet, F., Daigne, F., Mochkovitch, R., Genet, F., Daigne, F., and Mochkovitch, R.
- Abstract
The early optical afterglow of GRB 050820a recorded by the RAPTOR telescope shows both a contribution from the prompt emission and the initial rise of the afterglow. It is therefore well-suited for the study of the dynamical evolution of the GRB ejecta when it first undergoes the decelerating effect of the environment. This is a complex phase where the internal, reverse, and forward shocks can all be present simultaneously. We have developed a simplified model that can follow these different shocks in an approximate, but self-consistent way. It is applied to the case of GRB 050820a to obtain the prompt and afterglow light curves. We show that the rise of the afterglow during the course of the prompt emission has some important consequences. The reverse shock propagates back into the ejecta before internal shocks are completed, which affects the shape of the gamma-ray profile. We get the best results when the external medium has a uniform density, but obtaining a simultaneous fit of the prompt and afterglow emission is not easy. We discuss a few possibilities that could help to improve this situation., Comment: 6 pages, 9 figures, accepted for publication in A&A
- Published
- 2007
- Full Text
- View/download PDF
24. The rise of the afterglow in GRB 050820a
- Author
-
Genet, F., Daigne, F., Mochkovitch, R., Genet, F., Daigne, F., and Mochkovitch, R.
- Abstract
The early optical afterglow of GRB 050820a recorded by the RAPTOR telescope shows both a contribution from the prompt emission and the initial rise of the afterglow. It is therefore well-suited for the study of the dynamical evolution of the GRB ejecta when it first undergoes the decelerating effect of the environment. This is a complex phase where the internal, reverse, and forward shocks can all be present simultaneously. We have developed a simplified model that can follow these different shocks in an approximate, but self-consistent way. It is applied to the case of GRB 050820a to obtain the prompt and afterglow light curves. We show that the rise of the afterglow during the course of the prompt emission has some important consequences. The reverse shock propagates back into the ejecta before internal shocks are completed, which affects the shape of the gamma-ray profile. We get the best results when the external medium has a uniform density, but obtaining a simultaneous fit of the prompt and afterglow emission is not easy. We discuss a few possibilities that could help to improve this situation., Comment: 6 pages, 9 figures, accepted for publication in A&A
- Published
- 2007
- Full Text
- View/download PDF
25. Afterglow calculation in the electromagnetic model for gamma-ray bursts
- Author
-
Genet, F., Daigne, F., Mochkovitch, R., Genet, F., Daigne, F., and Mochkovitch, R.
- Abstract
We compute the afterglow of gamma-ray bursts produced by purely electromagnetic outflows to see if it shows characteristic signatures differing from those obtained with the standard internal/external shock model. Using a simple approach for the injection of electromagnetic energy to the forward shock we obtain the afterglow evolution both during the period of activity of the central source and after. Our method equally applies to a variable source. Afterglow light curves in the visible and X-ray bands are computed both for a uniform medium and a stellar wind environment. They are brighter at early times than afterglows obtained with the internal/external shock model but relying only on these differences to discriminate between models is not sufficient., Comment: 5 pages, 10 figures. to appear in A&A
- Published
- 2006
- Full Text
- View/download PDF
26. Afterglow calculation in the electromagnetic model for gamma-ray bursts
- Author
-
Genet, F., Daigne, F., Mochkovitch, R., Genet, F., Daigne, F., and Mochkovitch, R.
- Abstract
We compute the afterglow of gamma-ray bursts produced by purely electromagnetic outflows to see if it shows characteristic signatures differing from those obtained with the standard internal/external shock model. Using a simple approach for the injection of electromagnetic energy to the forward shock we obtain the afterglow evolution both during the period of activity of the central source and after. Our method equally applies to a variable source. Afterglow light curves in the visible and X-ray bands are computed both for a uniform medium and a stellar wind environment. They are brighter at early times than afterglows obtained with the internal/external shock model but relying only on these differences to discriminate between models is not sufficient., Comment: 5 pages, 10 figures. to appear in A&A
- Published
- 2006
- Full Text
- View/download PDF
27. The circumstellar environment of Wolf-Rayet stars & Gamma-ray burst afterglows
- Author
-
Eldridge, J. J., Genet, F., Daigne, F., Mochkovitch, R., Eldridge, J. J., Genet, F., Daigne, F., and Mochkovitch, R.
- Abstract
We study the evolution of the circumstellar medium of massive stars. We pay particular attention to Wolf-Rayet stars that are thought to be the progenitors of some long Gamma-Ray Bursts. We detail the mass-loss rates we use in our stellar evolution models and how we estimate the stellar wind speeds during different phases. With these details we simulate the interactions between the wind and the interstellar medium to predict the circumstellar environment around the stars at the time of core-collapse. We then investigate how the structure of the environment might affect the GRB afterglow. We find that when the afterglow jet encounters the free-wind to stalled-wind interface that rebrightening occurs and a bump is seen in the afterglow light curve. However our predicted positions of this interface are too distant from the site of the GRB to reach while the afterglow remains observable. The values of the final-wind density, A_{*}, from our stellar models are similar to the values inferred from observed afterglow lightcurves and those from observed Wolf-Rayet stars. However we do not reproduce the lowest observed A_{*} values below 0.3. For these cases we suggest that the progenitors could have been a WO type Wolf-Rayet star, be in a close binary or very low metallicity star. Finally we turn our attention to the matter of stellar wind material producing absorption lines in the afterglow spectra. We discuss the observational signatures of two Wolf-Rayet stellar types, WC and WO, in the afterglow lightcurve and spectra. We also indicate how it may be possible to constrain the initial mass and metallicity of a GRB progenitor by using the inferred wind density and wind velocity., Comment: 36 pages, third draft changed by referees comments and resubmitted to MNRAS
- Published
- 2005
- Full Text
- View/download PDF
28. The circumstellar environment of Wolf-Rayet stars & Gamma-ray burst afterglows
- Author
-
Eldridge, J. J., Genet, F., Daigne, F., Mochkovitch, R., Eldridge, J. J., Genet, F., Daigne, F., and Mochkovitch, R.
- Abstract
We study the evolution of the circumstellar medium of massive stars. We pay particular attention to Wolf-Rayet stars that are thought to be the progenitors of some long Gamma-Ray Bursts. We detail the mass-loss rates we use in our stellar evolution models and how we estimate the stellar wind speeds during different phases. With these details we simulate the interactions between the wind and the interstellar medium to predict the circumstellar environment around the stars at the time of core-collapse. We then investigate how the structure of the environment might affect the GRB afterglow. We find that when the afterglow jet encounters the free-wind to stalled-wind interface that rebrightening occurs and a bump is seen in the afterglow light curve. However our predicted positions of this interface are too distant from the site of the GRB to reach while the afterglow remains observable. The values of the final-wind density, A_{*}, from our stellar models are similar to the values inferred from observed afterglow lightcurves and those from observed Wolf-Rayet stars. However we do not reproduce the lowest observed A_{*} values below 0.3. For these cases we suggest that the progenitors could have been a WO type Wolf-Rayet star, be in a close binary or very low metallicity star. Finally we turn our attention to the matter of stellar wind material producing absorption lines in the afterglow spectra. We discuss the observational signatures of two Wolf-Rayet stellar types, WC and WO, in the afterglow lightcurve and spectra. We also indicate how it may be possible to constrain the initial mass and metallicity of a GRB progenitor by using the inferred wind density and wind velocity., Comment: 36 pages, third draft changed by referees comments and resubmitted to MNRAS
- Published
- 2005
- Full Text
- View/download PDF
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