Michael Burgess

Publications (4)12.05 Total impact

• Source

  Available from: Arne Rau

  Article: Temporal Deconvolution Study of Long and Short Gamma-Ray Burst Light Curves

  P. N. Bhat, Michael S. Briggs, Valerie Connaughton, Chryssa Kouveliotou, Alexander J. van der Horst, William Paciesas, Charles A. Meegan, Elisabetta Bissaldi, Michael Burgess, Vandiver Chaplin, [......], Jochen Greiner, David Gruber, Sylvain Guiriec, Andreas von Kienlin, Marc Kippen, Sheila McBreen, Robert Preece, Arne Rau, Dave Tierney, and Colleen Wilson-Hodge
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  ABSTRACT: The light curves of gamma-ray bursts (GRBs) are believed to result from internal shocks reflecting the activity of the GRB central engine. Their temporal deconvolution can reveal potential differences in the properties of the central engines in the two populations of GRBs which are believed to originate from the deaths of massive stars (long) and from mergers of compact objects (short). We present here the results of the temporal analysis of 42 GRBs detected with the Gamma-ray Burst Monitor onboard the Fermi Gamma-ray Space Telescope. We deconvolved the profiles into pulses, which we fit with lognormal functions. The distributions of the pulse shape parameters and intervals between neighboring pulses are distinct for both burst types and also fit with lognormal functions. We have studied the evolution of these parameters in different energy bands and found that they differ between long and short bursts. We discuss the implications of the differences in the temporal properties of long and short bursts within the framework of the internal shock model for GRB prompt emission.
  The Astrophysical Journal 12/2011; 744(2):141. · 6.02 Impact Factor
• Article: Time-resolved Spectroscopy of the Three Brightest and Hardest Short Gamma-ray Bursts Observed with the Fermi Gamma-ray Burst Monitor

  Sylvain Guiriec, Michael S. Briggs, Valerie Connaugthon, Erin Kara, Frédéric Daigne, Chryssa Kouveliotou, Alexander J. van der Horst, William Paciesas, Charles A. Meegan, P. N. Bhat, [......], Adam Goldstein, Jochen Greiner, David Gruber, Andreas von Kienlin, Marc Kippen, Sheila McBreen, Robert Preece, Arne Rau, Dave Tierney, and Colleen Wilson-Hodge
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  ABSTRACT: From 2008 July to 2009 October, the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope has detected 320 gamma-ray bursts (GRBs). About 20% of these events are classified as short based on their T 90 duration below 2 s. We present here for the first time time-resolved spectroscopy at timescales as short as 2 ms for the three brightest short GRBs observed with GBM. The time-integrated spectra of the events deviate from the Band function, indicating the existence of an additional spectral component, which can be fit by a power law with index ~–1.5. The time-integrated E peak values exceed 2 MeV for two of the bursts and are well above the values observed in the brightest long GRBs. Their E peak values and their low-energy power-law indices (α) confirm that short GRBs are harder than long ones. We find that short GRBs are very similar to long ones, but with light curves contracted in time and with harder spectra stretched toward higher energies. In our time-resolved spectroscopy analysis, we find that the E peak values range from a few tens of keV up to more than 6 MeV. In general, the hardness evolutions during the bursts follow their flux/intensity variations, similar to long bursts. However, we do not always see the E peak leading the light-curve rises and confirm the zero/short average light-curve spectral lag below 1 MeV, already established for short GRBs. We also find that the time-resolved low-energy power-law indices of the Band function mostly violate the limits imposed by the synchrotron models for both slow and fast electron cooling and may require additional emission processes to explain the data. Finally, we interpreted these observations in the context of the current existing models and emission mechanisms for the prompt emission of GRBs.
  The Astrophysical Journal 11/2010; 725(1):225. · 6.02 Impact Factor
• Source

  Available from: Arne Rau

  Article: Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B

  Sylvain Guiriec, Valerie Connaughton, Michael S. Briggs, Michael Burgess, Felix Ryde, Frédéric Daigne, Peter Mészáros, Adam Goldstein, Julie Mcenery, Nicola Omodei, [......], Marc Kippen, Chryssa Kouveliotou, Sheila McBreen, Charles A. Meegan, William Paciesas, Robert Preece, Arne Rau, Dave Tierney, Alexander J. van der Horst, Colleen Wilson-Hodge
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  ABSTRACT: Observations of GRB 100724B with the Fermi Gamma-Ray Burst Monitor (GBM) find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non-thermal emission component, but also includes a statistically highly significant thermal spectral contribution. The simultaneous observation of the thermal and non-thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non-thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non-thermal process, or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux.
  10/2010;
• Source

  Available from: Arne Rau

  Article: Time-Resolved Spectroscopy of the 3 Brightest and Hardest Short Gamma-Ray Bursts Observed with the FGST Gamma-Ray Burst Monitor

  Sylvain Guiriec, Michael S. Briggs, Valerie Connaugthon, Erin Kara, Frederic Daigne, Chryssa Kouveliotou, Alexander J. van der Horst, William Paciesas, Charles A. Meegan, P. N. Bhat, [......], Adam Goldstein, Jochen Greiner, David Gruber, Andreas von Kienlin, Marc Kippen, Sheila McBreen, Robert Preece, Arne Rau, Dave Tierney, Colleen Wilson-Hodge
  [show abstract] [hide abstract]
  ABSTRACT: From July 2008 to October 2009, the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope (FGST) has detected 320 Gamma-Ray Bursts (GRBs). About 20% of these events are classified as short based on their T90 duration below 2 s. We present here for the first time time-resolved spectroscopy at timescales as short as 2 ms for the three brightest short GRBs observed with GBM. The time-integrated spectra of the events deviate from the Band function, indicating the existence of an additional spectral component, which can be fit by a power-law with index ~-1.5. The time-integrated Epeak values exceed 2 MeV for two of the bursts, and are well above the values observed in the brightest long GRBs. Their Epeak values and their low-energy power-law indices ({\alpha}) confirm that short GRBs are harder than long ones. We find that short GRBs are very similar to long ones, but with light curves contracted in time and with harder spectra stretched towards higher energies. In our time-resolved spectroscopy analysis, we find that the Epeak values range from a few tens of keV up to more than 6 MeV. In general, the hardness evolutions during the bursts follows their flux/intensity variations, similar to long bursts. However, we do not always see the Epeak leading the light-curve rises, and we confirm the zero/short average light-curve spectral lag below 1 MeV, already established for short GRBs. We also find that the time-resolved low-energy power-law indices of the Band function mostly violate the limits imposed by the synchrotron models for both slow and fast electron cooling and may require additional emission processes to explain the data. Finally, we interpreted these observations in the context of the current existing models and emission mechanisms for the prompt emission of GRBs. Comment: 14 pages, 10 figures, 9 tables, Accepted for publication in the Astrophysical Journal September, 23 2010 (Submitted May, 16 2010) Corrections: 1 reference updated, figure 10 caption
  09/2010;