2009ApJ...706.1309T

Query : 2009ApJ...706.1309T

2009ApJ...706.1309T - Astrophys. J., 706, 1309-1315 (2009/December-1)

Casting light on the "Anomalous" statistics of mg II absorbers toward gamma-ray burst afterglows: the incidence of weak systems.

TEJOS N., LOPEZ S., PROCHASKA J.X., BLOOM J.S., CHEN H.-W., DESSAUGES-ZAVADSKY M. and MAUREIRA M.J.

Abstract (from CDS):

We revisit echelle spectra (spectral resolution R ~ 40,000) of eight gamma-ray burst (GRB) afterglows to obtain the incidence (dN/dz) of weak intervening Mg II systems at a mean redshift of = 1.5. We show that dN/dz of systems having rest-frame equivalent widths 0.07 Å≤ WrMgII < 1 Å toward GRBs is statistically consistent with the incidence toward quasi-stellar objects (QSOs). Our result is in contrast to the results for Mg II systems having Wr≥ 1 Å, where dN/dz toward GRBs has been found to be larger than toward QSOs by a factor of ~4. We confirm the overdensity albeit at a factor of ~3 only. This suggests that any explanation for the GRB/QSO discrepancy, be it intrinsic to the absorbers or a selection effect, should be inherent only to the galaxies that host strong absorbers in the line of sight to GRBs. We argue that, of all scenarios that have been proposed, lensing amplification is the one that could explain the strong Mg II enhancement while allowing for no significant enhancement in the weak absorbers.

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Journal keyword(s): gamma rays: bursts - gamma rays: observations - gravitational lensing - intergalactic medium - quasars: absorption lines - techniques: spectroscopic

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 GRB 021004 gB 00 26 54.68 +18 55 41.6           ~ 560 0
2 GRB 060206 gB 13 31 43.420 +35 03 03.60   19.99 17.09     ~ 330 0
3 GRB 050730 gB 14 08 17.090 -03 46 18.90   20.32 17.68     ~ 327 0
4 GRB 060418 gB 15 45 42.600 -03 38 20.00 15.73 16.19 14.98     ~ 389 0
5 GRB 050922C gB 21 09 33.000 -08 45 30.10 15.15 15.86 14.69     ~ 301 0
6 GRB 060607 gB 21 58 50.400 -22 29 46.70 18.49 16.67 15.09     ~ 318 0
7 GRB 050820A gB 22 29 38.110 +19 33 37.10 18.33 19.00 18.47     ~ 409 0
8 GRB 051111A gB 23 12 33.170 +18 22 28.80 19.77 20.08 19.50     ~ 223 0
9 Fermi bn080810549 gB 23 47 08.00 +00 18 35.1           ~ 240 0

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