1 / 12

Dave Tierney S. McBreen, R. Preece, G. Fitzpatrick and the GBM Team

Low-Energy Spectral Deviations in a Sample of GBM GRBs. Dave Tierney S. McBreen, R. Preece, G. Fitzpatrick and the GBM Team. DT acknowledges support from SFI under grant No. 09-RFP-AST-2400. Introduction. Band Model Spectral model for fitting prompt GRB emission Consistent across GRBs

dominique-anderson
Download Presentation

Dave Tierney S. McBreen, R. Preece, G. Fitzpatrick and the GBM Team

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Low-Energy Spectral Deviations in a Sample of GBM GRBs Dave Tierney S. McBreen, R. Preece, G. Fitzpatrick and the GBM Team DT acknowledges support from SFI under grant No. 09-RFP-AST-2400

  2. Introduction Band Model Spectral model for fitting prompt GRB emission Consistent across GRBs Parameterised by a, b, Epeak Empirical Model Additional components using Fermi Band+PL Abdo et al. 2009, Ackermann et al. 2010 Band+BB Guiriec et al. 2011, McGlynn et al. in prep Band+PL+BB Guiriec et al. in prep, Previous Work An X-ray excess of greater than 5 sigma above the Band model (~ 5 – 20 keV) was reported for ~14% of an 86 burst sample observed by BATSE (Preece et al 1996).

  3. Fermi – GBM Key Advantages of GBM over BATSE Much higher data resolution Single detector from 8 – 1000 keV

  4. Sample Selection Fluence > 2x10-5 erg / cm2 10 -1000 keV (Paciesas et al. 2012) Detector Angle < 60o Blockages Good In Sample Bad Not In Sample

  5. Analysing the Sample (Initial) 45 GRBs from the first 2 years Single Fit Select all good NaIs Select at least 1 BGO Perform a Band fit from 8 keV - 40 MeV Sum Low-Energy Residuals below 15, 20, 25, 30, 50, 100 keV Performed for time-integrated fitting only.

  6. Analysing the Sample (Extended) 45 GRBs from the first 2 years Extrapolated Fit Select all good NaIs Select at least 1 BGO Perform a Band fit from LET* keV - 40 MeV Extrapolate function downwards to 8 keV Compare data to extrapolated function Sum Low-Energy Residuals between 8 keV and the LET Blind search using time-integrated, time-resolved spectral analysis. *LET = Low-Energy Threshold. Selected to be 15, 20, 25, 30, 50 & 100 keV

  7. Distributions of Low-Energy Residuals Time-Integrated Time-Resolved (SN 50s) Some cuts are applied to the results… Epeak > 100 keV for LET = 15, 20, 25, 30 Epeak > 300 keV for LET = 50, 100 Alpha_Err < 0.2 Epeak_Err/Epeak < 0.45 GRB090902B

  8. How to quantify the uncertainty... Simulations… Simulations (Perfect Band) Sample Data Left: Combined distribution of 5 GRBs simulated with perfect Band model Right: Time-Integrated Data Distribution

  9. How to quantify the uncertainty... Simulations…Simulations… Distributions (Blue) showing when no deviations are present and a line (Red) showing the deviations in the data. GRB080817.161 – No Deviations in the Time-Integrated GRB090902.462 – Strong Deviations in the Time-Integrated

  10. How to quantify the uncertainty... Simulations…Simulations…Simulations… Distributions (Blue) showing when no deviations are present and a line (Red) showing the deviations in the data. GRB090926.181 – Strong Excess in the Time-Resolved (9 – 10 s) GRB090424.592 – Strong Deficit in the Time-Resolved (2 – 3 s)

  11. Closer Analysis Low-Energy Excesses GRB090902B - PL (TI) GRB090926A – PL (TR) GRB090323 – BB (TR) Low-Energy Deficits GRB090424 – BB (TR) GRB090820 – BB (TR) This method demonstrates the requirement for an extra component without any prior knowledge of the nature of the extra component.

  12. Conclusions Excesses and Deficits can mean additional components… Excess tend to be an additional component dominant at low energies. Deficits tend to be an additional component dominant between the LET and Epeak, forcing alpha higher. Systematic blind search shows that low-energy deviations are rarer than previously thought. 2% of my sample compared to 14% from BATSE (Time-Integrated). Additional components can become washed out with time-integrated spectral fitting. Time-resolved analysis is a must. There is more spectral curvature in some bursts than expected. This gives hints of extra-components BB, PL, other / new models.

More Related