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Kunihito Ioka - One of the best experts on this subject based on the ideXlab platform.
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gamma ray burst formation rate inferred from the spectral peak energy peak Luminosity relation
The Astrophysical Journal, 2004Co-Authors: Daisuke Yonetoku, Ryo Yamazaki, Akio K. Inoue, T Murakami, T Nakamura, Kunihito IokaAbstract:We estimate a gamma-ray burst (GRB) formation rate based on the new relation between the spectral peak energy (Ep) and the peak Luminosity. The new relation is derived by combining the data of Ep and the peak luminosities by BeppoSAX and BATSE, and it looks considerably tighter and more reliable than the relations suggested by the previous works. Using the new Ep-Luminosity relation, we estimate redshifts of the 689 GRBs without known distances in the BATSE catalog and derive a GRB formation rate as a function of the redshift. For the redshift range of 0 ≤ z ≤ 2, the GRB formation rate increases and is well correlated with the star formation rate, while it keeps constant toward z ~ 12. We also discuss the Luminosity function and the redshift dependence of the intrinsic Luminosity (Luminosity evolution).
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grb formation rates inferred from the spectral peak energy Luminosity relation
arXiv: Astrophysics, 2003Co-Authors: Daisuke Yonetoku, Ryo Yamazaki, Akio K. Inoue, T Murakami, T Nakamura, Kunihito IokaAbstract:We investigate the GRB formation rate based on the relation between the spectral peak energy ($E_{p}$) and the isotropic Luminosity. The $E_{p}$--Luminosity relation covers the energy range of 50 -- 2000 keV and the Luminosity range of $10^{50}$--$10^{54} erg/s, respectively. We find that the relation is considerably tighter than similar relations suggested previously. Using $E_{p}$--Luminosity relation, we estimate the Luminosity and the redshift of 684 GRBs with the unknown distances and derive the GRB formation rate as a function of the redshift. For $0 \le z \le 2$, the GRB formation rate is well correlated with the star formation rate while it increases monotonously from $z\sim 2$ out to $z \sim 12$. This behavior is consistent with the results of previous works using the lag--Luminosity relation or the variability--Luminosity relation.
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peak Luminosity spectral lag relation caused by the viewing angle of the collimated gamma ray bursts
The Astrophysical Journal, 2001Co-Authors: Kunihito Ioka, T NakamuraAbstract:We compute the kinematical dependence of the peak Luminosity, the pulse width, and the spectral lag of the peak Luminosity on the viewing angle θv of a jet. For appropriate model parameters we obtain a peak Luminosity-spectral lag relation similar to the observed one including gamma-ray burst (GRB) 980425. A bright (dim) peak with short (long) spectral lag corresponds to a jet with small (large) viewing angle. This suggests that the viewing angle of the jet might cause various relations in GRBs such as the peak Luminosity-variability relation and the Luminosity-width relation. Our model also suggests that X-ray-rich GRBs (or X-ray flushes or fast X-ray transients) are typical GRBs observed from large θv with large spectral lag and low variability.
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peak Luminosity spectral lag relation caused by the viewing angle of the collimated gamma ray bursts
arXiv: Astrophysics, 2001Co-Authors: Kunihito Ioka, T NakamuraAbstract:We compute the kinematical dependence of the peak Luminosity, the pulse width and the spectral lag of the peak Luminosity on the viewing angle $\theta_v$ of a jet. For appropriate model parameters we obtain the peak Luminosity-spectral lag relation similar to the observed one including GRB980425. A bright (dim) peak with short (long) spectral lag corresponds to a jet with small (large) viewing angle. This suggests that the viewing angle of the jet might cause various relations in GRBs such as the peak Luminosity-variability relation and the Luminosity-width relation. Our model also suggests that X-ray rich GRBs (or X-ray flushes or Fast X-ray transients) are typical GRBs observed from large $\theta_v$ with large spectral lag and low variability.
T Nakamura - One of the best experts on this subject based on the ideXlab platform.
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gamma ray burst formation rate inferred from the spectral peak energy peak Luminosity relation
The Astrophysical Journal, 2004Co-Authors: Daisuke Yonetoku, Ryo Yamazaki, Akio K. Inoue, T Murakami, T Nakamura, Kunihito IokaAbstract:We estimate a gamma-ray burst (GRB) formation rate based on the new relation between the spectral peak energy (Ep) and the peak Luminosity. The new relation is derived by combining the data of Ep and the peak luminosities by BeppoSAX and BATSE, and it looks considerably tighter and more reliable than the relations suggested by the previous works. Using the new Ep-Luminosity relation, we estimate redshifts of the 689 GRBs without known distances in the BATSE catalog and derive a GRB formation rate as a function of the redshift. For the redshift range of 0 ≤ z ≤ 2, the GRB formation rate increases and is well correlated with the star formation rate, while it keeps constant toward z ~ 12. We also discuss the Luminosity function and the redshift dependence of the intrinsic Luminosity (Luminosity evolution).
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grb formation rates inferred from the spectral peak energy Luminosity relation
arXiv: Astrophysics, 2003Co-Authors: Daisuke Yonetoku, Ryo Yamazaki, Akio K. Inoue, T Murakami, T Nakamura, Kunihito IokaAbstract:We investigate the GRB formation rate based on the relation between the spectral peak energy ($E_{p}$) and the isotropic Luminosity. The $E_{p}$--Luminosity relation covers the energy range of 50 -- 2000 keV and the Luminosity range of $10^{50}$--$10^{54} erg/s, respectively. We find that the relation is considerably tighter than similar relations suggested previously. Using $E_{p}$--Luminosity relation, we estimate the Luminosity and the redshift of 684 GRBs with the unknown distances and derive the GRB formation rate as a function of the redshift. For $0 \le z \le 2$, the GRB formation rate is well correlated with the star formation rate while it increases monotonously from $z\sim 2$ out to $z \sim 12$. This behavior is consistent with the results of previous works using the lag--Luminosity relation or the variability--Luminosity relation.
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peak Luminosity spectral lag relation caused by the viewing angle of the collimated gamma ray bursts
The Astrophysical Journal, 2001Co-Authors: Kunihito Ioka, T NakamuraAbstract:We compute the kinematical dependence of the peak Luminosity, the pulse width, and the spectral lag of the peak Luminosity on the viewing angle θv of a jet. For appropriate model parameters we obtain a peak Luminosity-spectral lag relation similar to the observed one including gamma-ray burst (GRB) 980425. A bright (dim) peak with short (long) spectral lag corresponds to a jet with small (large) viewing angle. This suggests that the viewing angle of the jet might cause various relations in GRBs such as the peak Luminosity-variability relation and the Luminosity-width relation. Our model also suggests that X-ray-rich GRBs (or X-ray flushes or fast X-ray transients) are typical GRBs observed from large θv with large spectral lag and low variability.
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peak Luminosity spectral lag relation caused by the viewing angle of the collimated gamma ray bursts
arXiv: Astrophysics, 2001Co-Authors: Kunihito Ioka, T NakamuraAbstract:We compute the kinematical dependence of the peak Luminosity, the pulse width and the spectral lag of the peak Luminosity on the viewing angle $\theta_v$ of a jet. For appropriate model parameters we obtain the peak Luminosity-spectral lag relation similar to the observed one including GRB980425. A bright (dim) peak with short (long) spectral lag corresponds to a jet with small (large) viewing angle. This suggests that the viewing angle of the jet might cause various relations in GRBs such as the peak Luminosity-variability relation and the Luminosity-width relation. Our model also suggests that X-ray rich GRBs (or X-ray flushes or Fast X-ray transients) are typical GRBs observed from large $\theta_v$ with large spectral lag and low variability.
A Pescalli - One of the best experts on this subject based on the ideXlab platform.
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The rate and Luminosity function of long gamma ray bursts
Astronomy and Astrophysics - A&A, 2016Co-Authors: A Pescalli, G Ghirlanda, O S Salafia, G Ghisellini, F Nappo, R Salvaterra, S. D. Vergani, A. Melandri, S. Covino, D. GötzAbstract:We derive, adopting a direct method, the Luminosity function and the formation rate of long Gamma Ray Bursts through a complete, flux-limited, sample of Swift bursts which has a high level of completeness in redshift z (~82%). We parametrise the redshift evolution of the GRB Luminosity as L = L0(1 + z)k and we derive k = 2.5, consistently with recent estimates. The de-evolved Luminosity function φ(L0) of GRBs can be represented by a broken power law with slopes a = −1.32 ± 0.21 and b = −1.84 ± 0.24 below and above, respectively, a break Luminosity L0,b = 1051.45±0.15 erg/s. Under the hypothesis of Luminosity evolution we find that the GRB formation rate increases with redshift up to z ~ 2, where it peaks, and then decreases in agreement with the shape of the cosmic star formation rate. We test the direct method through numerical simulations and we show that if it is applied to incomplete (both in redshift and/or flux) GRB samples it can misleadingly result in an excess of the GRB formation rate at low redshifts.
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the rate and Luminosity function of long gamma ray bursts
arXiv: High Energy Astrophysical Phenomena, 2015Co-Authors: A Pescalli, G Ghirlanda, G Ghisellini, F Nappo, R Salvaterra, S. D. Vergani, O S SalafiaAbstract:We derive, adopting a direct method, the Luminosity function and the formation rate of long Gamma Ray Bursts through a complete, flux-limited, sample of Swift bursts which has a high level of completeness in redshift z (~82%). We parametrise the redshift evolution of the GRB Luminosity as L = L_0(1+ z)^k and we derive k = 2.5, consistently with recent estimates. The de-evolved Luminosity function of GRBs can be represented by a broken power law with slopes a = -1.32 +- 0.21 and b = -1.84 +- 0.24 below and above, respectively, a characteristic break Luminosity L_0,b = 10^51.45+-0.15 erg/s. Under the hypothesis of Luminosity evolution we find that the GRB formation rate increases with redshift up to z~2, where it peaks, and then decreases in agreement with the shape of the cosmic star formation rate. We test the direct method through numerical simulations and we show that if it is applied to incomplete (both in redshift and/or flux) GRB samples it can misleadingly result in an excess of the GRB formation rate at low redshifts.
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Luminosity function and jet structure of gamma ray burst
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: A Pescalli, G Ghirlanda, O S Salafia, G Ghisellini, F Nappo, R SalvaterraAbstract:The structure of Gamma Ray Burst (GRB) jets impacts on their prompt and afterglow emission properties. The jet of GRBs could be uniform, with constant energy per unit solid angle within the jet aperture, or it could instead be structured, namely with energy and velocity that depend on the angular distance from the axis of the jet. We try to get some insight about the still unknown structure of GRBs by studying their Luminosity function. We show that low (1e46-1e48 erg/s) and high (i.e. with L > 1e50 erg/s) Luminosity GRBs can be described by a unique Luminosity function, which is also consistent with current lower limits in the intermediate Luminosity range (1e48-1e50} erg/s). We derive analytical expressions for the Luminosity function of GRBs in uniform and structured jet models and compare them with the data. Uniform jets can reproduce the entire Luminosity function with reasonable values of the free parameters. A structured jet can also fit adequately the current data, provided that the energy within the jet is relatively strongly structured, i.e. E propto theta^{-k} with k > 4. The classical E propto theta^{-2} structured jet model is excluded by the current data.
Joseph F Hennawi - One of the best experts on this subject based on the ideXlab platform.
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evolution of the agn uv Luminosity function from redshift 7 5
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Joseph F Hennawi, Girish Kulkarni, Gabor WorseckAbstract:Determinations of the UV Luminosity function of AGN at high redshifts are important for constraining the AGN contribution to reionization and understanding the growth of supermassive black holes. Recent inferences of the Luminosity function suffer from inconsistencies arising from inhomogeneous selection and analysis of AGN data. We address this problem by constructing a sample of more than 80,000 colour-selected AGN from redshift z=0 to 7.5. While this sample is composed of multiple data sets with spectroscopic redshifts and completeness estimates, we homogenise these data sets to identical cosmologies, intrinsic AGN spectra, and magnitude systems. Using this sample, we derive the AGN UV Luminosity function from redshift z=0 to 7.5. The Luminosity function has a double power law form at all redshifts. The break magnitude $M_*$ of the AGN Luminosity function shows a steep brightening from $M_*\sim -24$ at z=0.7 to $M_*\sim -29$ at z=6. The faint-end slope $\beta$ significantly steepens from $-1.7$ at $z<2.2$ to $-2.4$ at $z\simeq 6$. In spite of this steepening, the contribution of AGN to the hydrogen photoionization rate at $z\sim 6$ is subdominant (< 3%), although it can be non-negligible (~10%) if these Luminosity functions hold down to $M_{1450}=-18$. Under reasonable assumptions, AGN can reionize HeII by redshift z=2.9. At low redshifts (z<0.5), AGN can produce about half of the hydrogen photoionization rate inferred from the statistics of HI absorption lines in the IGM. Our global analysis of the Luminosity function also reveals important systematic errors in the data, particularly at z=2.2--3.5, which need to be addressed and incorporated in the AGN selection function in future in order to improve our results. We make various fitting functions, Luminosity function analysis codes, and homogenised AGN data publicly available.
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the obscured fraction of active galactic nuclei in the xmm cosmos survey a spectral energy distribution perspective
The Astrophysical Journal, 2013Co-Authors: E Lusso, G Zamorani, Ezequiel Treister, Joseph F Hennawi, A Comastri, G T Richards, C Vignali, Kevin Schawinski, M Salvato, R GilliAbstract:The fraction of active galactic nucleus (AGN) Luminosity obscured by dust and re-emitted in the mid-IR is critical for understanding AGN evolution, unification, and parsec-scale AGN physics. For unobscured (Type?1) AGNs, where we have a direct view of the accretion disk, the dust covering factor can be measured by computing the ratio of re-processed mid-IR emission to intrinsic nuclear bolometric Luminosity. We use this technique to estimate the obscured AGN fraction as a function of Luminosity and redshift for 513 Type?1 AGNs from the XMM-COSMOS survey. The re-processed and intrinsic luminosities are computed by fitting the 18 band COSMOS photometry with a custom spectral energy distribution fitting code, which jointly models emission from hot dust in the AGN torus, from the accretion disk, and from the host galaxy. We find a relatively shallow decrease of the Luminosity ratio as a function of L bol, which we interpret as a corresponding decrease in the obscured fraction. In the context of the receding torus model, where dust sublimation reduces the covering factor of more luminous AGNs, our measurements require a torus height that increases with Luminosity as . Our obscured-fraction-Luminosity relation agrees with determinations from Sloan Digital Sky Survey censuses of Type?1 and Type?2 quasars and favors a torus optically thin to mid-IR radiation. We find a much weaker dependence of the obscured fraction on 2-10?keV Luminosity than previous determinations from X-ray surveys and argue that X-ray surveys miss a significant population of highly obscured Compton-thick AGNs. Our analysis shows no clear evidence for evolution of the obscured fraction with redshift.
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the obscured fraction of agn in the xmm cosmos survey a spectral energy distribution perspective
arXiv: Cosmology and Nongalactic Astrophysics, 2013Co-Authors: E Lusso, G Zamorani, Ezequiel Treister, Joseph F Hennawi, A Comastri, G T Richards, C Vignali, Kevin Schawinski, M Salvato, R GilliAbstract:The fraction of AGN Luminosity obscured by dust and re-emitted in the mid-IR is critical for understanding AGN evolution, unification, and parsec-scale AGN physics. For unobscured (Type-1) AGN, where we have a direct view of the accretion disk, the dust covering factor can be measured by computing the ratio of re-processed mid-IR emission to intrinsic nuclear bolometric Luminosity. We use this technique to estimate the obscured AGN fraction as a function of Luminosity and redshift for 513 Type-1 AGN from the XMM-COSMOS survey. The re-processed and intrinsic luminosities are computed by fitting the 18-band COSMOS photometry with a custom SED-fitting code, which jointly models emission from: hot-dust in the AGN torus, the accretion disk, and the host-galaxy. We find a relatively shallow decrease of the Luminosity ratio as a function of Lbol, which we interpret as a corresponding decrease in the obscured fraction. In the context of the receding torus model, where dust sublimation reduces the covering factor of more luminous AGN, our measurements require a torus height which increases with Luminosity as h ~ Lbol^{0.3-0.4}. Our obscured fraction-Luminosity relation agrees with determinations from SDSS censuses of Type-1 and Type-2 quasars, and favors a torus optically thin to mid-IR radiation. We find a much weaker dependence of obscured fraction on 2-10 keV Luminosity than previous determinations from X-ray surveys, and argue that X-ray surveys miss a significant population of highly obscured Compton-thick AGN. Our analysis shows no clear evidence for evolution of obscured fraction with redshift.
O S Salafia - One of the best experts on this subject based on the ideXlab platform.
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The rate and Luminosity function of long gamma ray bursts
Astronomy and Astrophysics - A&A, 2016Co-Authors: A Pescalli, G Ghirlanda, O S Salafia, G Ghisellini, F Nappo, R Salvaterra, S. D. Vergani, A. Melandri, S. Covino, D. GötzAbstract:We derive, adopting a direct method, the Luminosity function and the formation rate of long Gamma Ray Bursts through a complete, flux-limited, sample of Swift bursts which has a high level of completeness in redshift z (~82%). We parametrise the redshift evolution of the GRB Luminosity as L = L0(1 + z)k and we derive k = 2.5, consistently with recent estimates. The de-evolved Luminosity function φ(L0) of GRBs can be represented by a broken power law with slopes a = −1.32 ± 0.21 and b = −1.84 ± 0.24 below and above, respectively, a break Luminosity L0,b = 1051.45±0.15 erg/s. Under the hypothesis of Luminosity evolution we find that the GRB formation rate increases with redshift up to z ~ 2, where it peaks, and then decreases in agreement with the shape of the cosmic star formation rate. We test the direct method through numerical simulations and we show that if it is applied to incomplete (both in redshift and/or flux) GRB samples it can misleadingly result in an excess of the GRB formation rate at low redshifts.
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the rate and Luminosity function of long gamma ray bursts
arXiv: High Energy Astrophysical Phenomena, 2015Co-Authors: A Pescalli, G Ghirlanda, G Ghisellini, F Nappo, R Salvaterra, S. D. Vergani, O S SalafiaAbstract:We derive, adopting a direct method, the Luminosity function and the formation rate of long Gamma Ray Bursts through a complete, flux-limited, sample of Swift bursts which has a high level of completeness in redshift z (~82%). We parametrise the redshift evolution of the GRB Luminosity as L = L_0(1+ z)^k and we derive k = 2.5, consistently with recent estimates. The de-evolved Luminosity function of GRBs can be represented by a broken power law with slopes a = -1.32 +- 0.21 and b = -1.84 +- 0.24 below and above, respectively, a characteristic break Luminosity L_0,b = 10^51.45+-0.15 erg/s. Under the hypothesis of Luminosity evolution we find that the GRB formation rate increases with redshift up to z~2, where it peaks, and then decreases in agreement with the shape of the cosmic star formation rate. We test the direct method through numerical simulations and we show that if it is applied to incomplete (both in redshift and/or flux) GRB samples it can misleadingly result in an excess of the GRB formation rate at low redshifts.
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Luminosity function and jet structure of gamma ray burst
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: A Pescalli, G Ghirlanda, O S Salafia, G Ghisellini, F Nappo, R SalvaterraAbstract:The structure of Gamma Ray Burst (GRB) jets impacts on their prompt and afterglow emission properties. The jet of GRBs could be uniform, with constant energy per unit solid angle within the jet aperture, or it could instead be structured, namely with energy and velocity that depend on the angular distance from the axis of the jet. We try to get some insight about the still unknown structure of GRBs by studying their Luminosity function. We show that low (1e46-1e48 erg/s) and high (i.e. with L > 1e50 erg/s) Luminosity GRBs can be described by a unique Luminosity function, which is also consistent with current lower limits in the intermediate Luminosity range (1e48-1e50} erg/s). We derive analytical expressions for the Luminosity function of GRBs in uniform and structured jet models and compare them with the data. Uniform jets can reproduce the entire Luminosity function with reasonable values of the free parameters. A structured jet can also fit adequately the current data, provided that the energy within the jet is relatively strongly structured, i.e. E propto theta^{-k} with k > 4. The classical E propto theta^{-2} structured jet model is excluded by the current data.
