CASTING LIGHT ON THE “ANOMALOUS” STATISTICS OF Mg II ABSORBERS TOWARD GAMMA-RAY BURST AFTERGLOWS: THE INCIDENCE OF WEAK SYSTEMS

Tejos, Nicolás; López, Sebastián; Prochaska, J. Xavier; Bloom, J.; Chen, Hsiao‐Wen; Dessauges‐Zavadsky, M.; Maureira, María José

doi:10.1088/0004-637x/706/2/1309

Cited by 27 publications

(38 citation statements)

References 39 publications

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“…Since both GRBs and quasars probe intervening material randomly, it was a puzzling discovery a decade ago that GRBs apparently had four times as many strong intervening Mg ii absorbers with rest-frame equivalent widths W λ2796 r > 1 Å as did quasars (Prochter et al 2006b). The same conclusion about Mg ii absorber statistics was reached by Sudilovsky et al (2007), with the addition that the incidence rate of C iv absorbers and weak Mg ii absorbers with W r < 1 Å did agree between the two background source types (Tejos et al 2007(Tejos et al , 2009Vergani et al 2009). Also blazars were found to have twice as many strong Mg ii absorbers as did quasars (Bergeron et al 2011).…”

Section: Introductionsupporting

confidence: 61%

Solving the conundrum of intervening strong Mg II absorbers towards gamma-ray bursts and quasars

Christensen

Vergani

Schulze

et al. 2017

A&A

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Previous studies have shown that the incidence rate of intervening strong Mg ii absorbers towards GRBs were a factor of 2 − 4 higher than towards quasars. Exploring the similar sized and uniformly selected legacy data sets XQ-100 and XSGRB, each consisting of 100 quasar and 81 GRB afterglow spectra obtained with a single instrument (VLT/X-shooter), we demonstrate that there is no disagreement in the number density of strong Mg ii absorbers with rest-frame equivalent widths W λ2796 r > 1 Å towards GRBs and quasars in the redshift range 0.1 z 5. With large and similar sample sizes, and path length coverages of ∆z = 57.8 and 254.4 for GRBs and quasars, respectively, the incidences of intervening absorbers are consistent within 1σ uncertainty levels at all redshifts. For absorbers at z < 2.3 the incidence towards GRBs is a factor of 1.5 ± 0.4 higher than the expected number of strong Mg ii absorbers in SDSS quasar spectra, while for quasar absorbers observed with X-shooter we find an excess factor of 1.4 ± 0.2 relative to SDSS quasars. Conversely, the incidence rates agree at all redshifts with reported high spectral resolution quasar data, and no excess is found. The only remaining discrepancy in incidences is between SDSS Mg ii catalogues and high spectral resolution studies. The rest-frame equivalent width distribution also agrees to within 1σ uncertainty levels between the GRB and quasar samples. Intervening strong Mg ii absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong.

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Section: Introductionsupporting

confidence: 61%

Solving the conundrum of intervening strong Mg II absorbers towards gamma-ray bursts and quasars

Christensen

Vergani

Schulze

et al. 2017

A&A

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“…These authors found that nearly every GRB sightline exhibits at least one absorber ( z = 1.1) whereas the incidence of strong Mg ii QSO absorbers is about four times smaller. This excess is confirmed by Sudilovsky et al (2007) for a small, homogeneous sample of GRB VLT-UVES high-resolution spectra, and more recently by Tejos et al (2009) and Vergani et al (2009). Based on their improved statistics, these latter authors find the excess to be smaller than initially reported, by a factor of 2.1 ± 0.6 instead of ∼4.…”

Section: Introductionmentioning

confidence: 53%

“…One of the strong system given in Table 2 is excluded (northern blazar) since the low S /N prevents detection of weak systems. We thus get: The errors are based on Poisson statistics for small numbers with limits corresponding to 1σ confidence level of a Gaussian distribution as tabulated by Gehrels (1986) and also adopted by Tejos et al (2009). To compare this value to the incidence of Mg ii absorbers measured along QSO sight lines, we use the incidence of these systems per unit redshift derived from SDSS data.…”

Section: Global Excessmentioning

confidence: 99%

Incidence of Mg ii absorbers towards blazars and the GRB/QSO puzzle

Bergeron

Boissé

Ménard

2010

A&A

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In order to investigate the origin of the excess of strong Mg ii systems towards GRB afterglows as compared to QSO sightlines, we have measured the incidence of Mg ii absorbers towards a third class of objects: the blazars. This class includes the BL Lac object population for which a tentative excess of Mg ii systems had already been reported. We observed with FORS1 at the ESO-VLT 42 blazars with an emission redshift 0.8 < z em < 1.9, to which we added the three high z northern objects belonging to the 1 Jy BL Lac sample. We detect 32 Mg ii absorbers in the redshift range 0.35-1.45, leading to an excess in the incidence of Mg ii absorbers compared to that measured towards QSOs by a factor ∼2, detected at 3σ. The amplitude of the effect is similar to that found along GRB sightlines. Our analysis provides a new piece of evidence that the observed incidence of Mg ii absorbers might depend on the type of background source. In front of blazars, the excess is apparent for both "strong" (w r (2796) > 1.0 Å) and weaker (0.3 < w r (2796) < 1.0 Å) Mg ii systems. The dependence on velocity separation with respect to the background blazars indicates, at the ∼1.5σ level, a potential excess for β ≡ v/c ∼ 0.1. We show that biases involving dust extinction or gravitational amplification are not likely to notably affect the incidence of Mg ii systems towards blazars. Finally we discuss the physical conditions required for these absorbers to be gas entrained by the powerful blazar jets. More realistic numerical modelling of jet-ambient gas interaction is required to reach any firm conclusions as well as repeat observations at high spectral resolution of strong Mg ii absorbers towards blazars in both high and low states.

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“…Cucchiara et al (2009) compare properties of foreground Mg ii systems along quasar and GRB sightlines and find no significant differences, concluding that the GRB systems are probably not associated with material ejected near the GRB at relativistic velocities (intrinsic origin). Tejos et al (2009) and Vergani et al (2009) also study the incidence of weak Mg ii systems, and both come to the conclusion that the incidence of weak systems is similar along quasar and GRB afterglow sightlines, implying that the best explanation is that the GRB afterglows of the echelle sample have been amplified by gravitational lensing (see also Wyithe et al 2010, but see Cucchiara et al 2009). Both studies also find that the excess is smaller than originally deduced from the original small sample by Prochter et al (2006), but the significance that the excess is real has increased with increasing sample size and redshift path.…”

Section: Does the High Number Of Mg II Foreground Absorbersmentioning

confidence: 96%

“…All GRBs in the UVES sample of Vergani et al (2009) are included in our Golden Sample (with GRB 021004 being part of the pre-Swift Golden Sample, and GRB 060607A not having any data at 0.5 rest-frame days, so we will not include it in this discussion), and two further GRBs with echelle spectra (Keck HIRES) from the sample of Tejos et al (2009) are also part of our Silver Sample. Furthermore, a GRB with published UVES spectroscopy not included in the sample of Vergani et al (2009) is XRF 080330, which also shows a very strong Mg ii foreground absorber (D'Elia et al 2009b), and another strong foreground system is seen in the afterglow of GRB 090313, as measured by X-Shooter (de Ugarte Postigo et al 2010).…”

Section: Does the High Number Of Mg II Foreground Absorbersmentioning

confidence: 99%

THE AFTERGLOWS OFSWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFTANDSWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS

Канн

Klose

Zhang

et al. 2010

ApJ

286

356

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15131514 KANN ET AL.Vol. 720 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 highluminosity, 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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CASTING LIGHT ON THE “ANOMALOUS” STATISTICS OF Mg II ABSORBERS TOWARD GAMMA-RAY BURST AFTERGLOWS: THE INCIDENCE OF WEAK SYSTEMS

Cited by 27 publications

References 39 publications

Solving the conundrum of intervening strong Mg II absorbers towards gamma-ray bursts and quasars

Solving the conundrum of intervening strong Mg II absorbers towards gamma-ray bursts and quasars

Incidence of Mg ii absorbers towards blazars and the GRB/QSO puzzle

THE AFTERGLOWS OFSWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFTANDSWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS

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