Change search
ReferencesLink to record
Permanent link

Direct link
Fermi/GBM observations of the ultra-long GRB 091024. A burst with an optical flash
Show others and affiliations
2011 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 528, no A15Article in journal (Refereed) PublishedText
Abstract [en]

Aims: In this paper we examine gamma-ray and optical data of GRB 091024, a gamma-ray burst (GRB) with an extremely long duration of T90 $\approx$ 1020 s, as observed with the Fermi Gamma-ray Burst Monitor (GBM). Methods: We present spectral analysis of all three distinct emission episodes using data from Fermi/GBM. Because of the long nature of this event, many ground-based optical telescopes slewed to its location within a few minutes and thus were able to observe the GRB during its active period. We compare the optical and gamma-ray light curves. Furthermore, we estimate a lower limit on the bulk Lorentz factor from the variability and spectrum of the GBM light curve and compare it with that obtained from the peak time of the forward shock of the optical afterglow. Results: From the spectral analysis we note that, despite its unusually long duration, this burst is similar to other long GRBs, i.e. there is spectral evolution (both the peak energy and the spectral index vary with time) and spectral lags are measured. We find that the optical light curve is highly anti-correlated to the prompt gamma-ray emission, with the optical emission reaching the maximum during an epoch of quiescence in the prompt emission. We interpret this behavior as the reverse shock (optical flash), expected in the internal-external shock model of GRB emission but observed only in a handful of GRBs so far. The lower limit on the initial Lorentz factor deduced from the variability time scale (Γmin = 195_-110+90) is consistent within the error to the one obtained using the peak time of the forward shock (Γ0 = 120) and is also consistent with Lorentz factors of other long GRBs.

Place, publisher, year, edition, pages
EDP Sciences, 2011. Vol. 528, no A15
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-184469DOI: 10.1051/0004-6361/201015891ISI: 000288541600041OAI: oai:DiVA.org:kth-184469DiVA: diva2:916021
Note

QC 20160404

Available from: 2016-03-31 Created: 2016-03-31 Last updated: 2016-04-04Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full texthttp://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011A%26A...528A..15G&link_type=EJOURNAL

Search in DiVA

By author/editor
Burgess, J Michael
In the same journal
Astronomy and Astrophysics
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 9 hits
ReferencesLink to record
Permanent link

Direct link