Redshift filtering by Swift apparent X-ray column density

Dirk Grupe, John A. Nousek, Daniel E. Vanden Berk, Peter W.A. Roming, David N. Burrows, Olivier Godet, Julian Osborne, Neil Gehrels

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

We remark on the 8tility of an observational relation between the absorption column density in excess of the Galactic absorption column density, ΔNH = NH,fit - NH,gal, and redshift, z, determined from all 55 Swift-observed long bursts with spectroscopic redshifts as of 2006 December. The absorption column densities, NH,fit, are determined from power-law fits to the X-ray spectra with the absorption column density left as a free parameter. We find that higher excess absorption column densities with ΔNH > 2 × 1021 cm -2 are only present in bursts with redshifts z < 2. Low absorption column densities with ΔNH < 1 × 1021 cm-2 appear preferentially in high-redshift bursts. Our interpretation is that this relation between redshift and excess column density is an observational effect resulting from the shift of the source rest-frame energy range below 1 keV out of the X-Ray Telescope observable energy range for high-redshift bursts. We find a clear anticorrelation between ΔN H and z that can be used to estimate the range of the maximum redshift of an afterglow. A critical application of our finding is that rapid X-ray observations can be used to optimize the instrumentation used for ground-based optical/near-IR follow-up observations. Ground-based spectroscopic redshift measurements of as many bursts as possible are crucial for gamma-ray burst science.

Original languageEnglish (US)
Pages (from-to)2216-2221
Number of pages6
JournalAstronomical Journal
Volume133
Issue number5
DOIs
StatePublished - May 1 2007

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bursts
x rays
afterglows
gamma ray bursts
instrumentation
energy
power law
telescopes
shift
estimates

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Grupe, D., Nousek, J. A., Vanden Berk, D. E., Roming, P. W. A., Burrows, D. N., Godet, O., ... Gehrels, N. (2007). Redshift filtering by Swift apparent X-ray column density. Astronomical Journal, 133(5), 2216-2221. https://doi.org/10.1086/513014
Grupe, Dirk ; Nousek, John A. ; Vanden Berk, Daniel E. ; Roming, Peter W.A. ; Burrows, David N. ; Godet, Olivier ; Osborne, Julian ; Gehrels, Neil. / Redshift filtering by Swift apparent X-ray column density. In: Astronomical Journal. 2007 ; Vol. 133, No. 5. pp. 2216-2221.
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Grupe, D, Nousek, JA, Vanden Berk, DE, Roming, PWA, Burrows, DN, Godet, O, Osborne, J & Gehrels, N 2007, 'Redshift filtering by Swift apparent X-ray column density', Astronomical Journal, vol. 133, no. 5, pp. 2216-2221. https://doi.org/10.1086/513014

Redshift filtering by Swift apparent X-ray column density. / Grupe, Dirk; Nousek, John A.; Vanden Berk, Daniel E.; Roming, Peter W.A.; Burrows, David N.; Godet, Olivier; Osborne, Julian; Gehrels, Neil.

In: Astronomical Journal, Vol. 133, No. 5, 01.05.2007, p. 2216-2221.

Research output: Contribution to journalArticle

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AU - Grupe, Dirk

AU - Nousek, John A.

AU - Vanden Berk, Daniel E.

AU - Roming, Peter W.A.

AU - Burrows, David N.

AU - Godet, Olivier

AU - Osborne, Julian

AU - Gehrels, Neil

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AB - We remark on the 8tility of an observational relation between the absorption column density in excess of the Galactic absorption column density, ΔNH = NH,fit - NH,gal, and redshift, z, determined from all 55 Swift-observed long bursts with spectroscopic redshifts as of 2006 December. The absorption column densities, NH,fit, are determined from power-law fits to the X-ray spectra with the absorption column density left as a free parameter. We find that higher excess absorption column densities with ΔNH > 2 × 1021 cm -2 are only present in bursts with redshifts z < 2. Low absorption column densities with ΔNH < 1 × 1021 cm-2 appear preferentially in high-redshift bursts. Our interpretation is that this relation between redshift and excess column density is an observational effect resulting from the shift of the source rest-frame energy range below 1 keV out of the X-Ray Telescope observable energy range for high-redshift bursts. We find a clear anticorrelation between ΔN H and z that can be used to estimate the range of the maximum redshift of an afterglow. A critical application of our finding is that rapid X-ray observations can be used to optimize the instrumentation used for ground-based optical/near-IR follow-up observations. Ground-based spectroscopic redshift measurements of as many bursts as possible are crucial for gamma-ray burst science.

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