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- Kann, D. A., et al.
(författare)
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THE AFTERGLOWS OF SWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFT AND SWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 720:2, s. 1513-1558
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Tidskriftsartikel (refereegranskat)abstract
- We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
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- Dey, Lankeswar, et al.
(författare)
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Authenticating the Presence of a Relativistic Massive Black Hole Binary in OJ 287 Using Its General Relativity Centenary Flare : Improved Orbital Parameters
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 866:1
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Tidskriftsartikel (refereegranskat)abstract
- Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the BBH model for OJ 287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole no-hair theorem at the 10% level.
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- Vergani, S. D., et al.
(författare)
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GRB 091127/SN 2009nz and the VLT/X-shooter spectroscopy of its host galaxy : probing the faint end of the mass-metallicity relation
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 535, s. A127-
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Tidskriftsartikel (refereegranskat)abstract
- We perform a detailed study of the gamma-ray burst GRB 091127/SN 2009nz host galaxy at z = 0.490 using the VLT/X-shooter spectrograph in slit and integral-field unit (IFU) mode. From the analysis of the optical and X-ray afterglow data obtained from ground-based telescopes and Swift-XRT, we confirm the presence of a bump associated with SN 2009nz and find evidence of a possible jet break in the afterglow lightcurve. The X-shooter afterglow spectra reveal several emission lines from the underlying host, from which we derive its integrated properties. These properties agree with those of previously studied GRB-SN hosts and, more generally, with those of the long GRB host population. We use the Hubble Space Telescope and ground-based images of the host to determine its stellar mass (M⋆). Our results extend to lower M⋆ values the M-Z plot derived for the sample of long GRB hosts at 0.3 < z < 1.0 adding new information to probe the faint end of the M-Z relation and the shift of the LGRB host M-Z relation from that found from emission-line galaxy surveys. Thanks to the IFU spectroscopy, we can build the two-dimensional (2D) velocity, velocity dispersion, and star formation rate (SFR) maps. They show that the host galaxy has perturbed rotation kinematics with evidence of a SFR enhancement consistent with the afterglow position. Based on observations made with ESO Telescopes at Paranal Observatory under programmes ID 084.A-0260 and 086.A-0874.
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