English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

(Abridged). We present a sample of 77 optical afterglows (OAs) of Swiftdetected GRBs for which spectroscopic follow-up observations have been secured.We provide linelists and equivalent widths for all detected lines redward ofLy-alpha. We discuss to what extent the current sample of Swift bursts with OAspectroscopy is a biased subsample of all Swift detected GRBs. For that purposewe define an X-ray selected sample of Swift bursts with optimal conditions forground-based follow up from the period March 2005 to September 2008; 146 burstsfulfill our sample criteria. We derive the redshift distribution for thissample and conclude that less than 19% of Swift bursts are at z>7. We comparethe high energy properties for three sub-samples of bursts in the sample: i)bursts with redshifts measured from OA spectroscopy, ii) bursts with detectedOA, but no OA-based redshift, and iii) bursts with no detection of the OA. Thebursts in group i) have significantly less excess X-ray absorption than burstsin the other two groups. In addition, the fraction of dark bursts is 14% ingroup i), 38% in group ii) and > 39% in group iii). From this we conclude thatthe sample of GRBs with OA spectroscopy is not representative for all Swiftbursts, most likely due to a bias against the most dusty sight-lines. Finally,we characterize GRB absorption systems as a class and compare them to QSOabsorption systems, in particular DLAs. On average GRB absorbers arecharacterized by significantly stronger EWs for HI as well as for both low andhigh ionization metal lines than what is seen in intervening QSO absorbers.Based on the z>2 bursts in the sample we place a 95% confidence upper limit of7.5% on the mean escape fraction of ionizing photons from star-forminggalaxies.

Low-Resolution Spectroscopy of Gamma-ray Burst Optical Afterglows: Biases in the Swift Sample and Characterization of the Absorbers