Showing papers by "S. D. Hunsberger published in 2006"

Swift panchromatic observations of the bright gamma-ray burst GRB 050525a

Abstract: The bright gamma- ray burst GRB 050525a has been detected with the Swift observatory, providing unique multiwavelength coverage from the very earliest phases of the burst. The X- ray and optical / UV afterglow decay light curves both exhibit a steeper slope similar to 0.15 days after the burst, indicative of a jet break. This jet break time combined with the total gamma- ray energy of the burst constrains the opening angle of the jet to be 3 degrees.2. We derive an empirical `` timelag'' redshift from the BAT data of (z) over bar z 0: 69 +/- 0: 02, in good agreement with the spectroscopic redshift of 0.61. Prior to the jet break, the X- ray data can be modeled by a simple power law with index alpha = - 1: 2. However, after 300 s the X- ray flux brightens by about 30% compared to the power- law fit. The optical / UV data have a more complex decay, with evidence of a rapidly falling reverse shock component that dominates in the first minute or so, giving way to a flatter forward shock component at later times. The multiwavelength X- ray/ UV/ optical spectrum of the afterglow shows evidence for migration of the electron cooling frequency through the optical range within 25,000 s. The measured temporal decay and spectral indexes in the X- ray and optical/ UV regimes compare favorably with the standard fireball model for gamma- ray bursts assuming expansion into a constant- density interstellar medium.

Optical, Infrared, and Ultraviolet Observations of the X-Ray Flash GRB 050416A

Abstract: We present ultraviolet, optical, and infrared photometry of the afterglow of the X-ray flash XRF 050416A taken between approximately 100 seconds and 36 days after the burst. We find an intrinsic spectral slope between 1930 and 22,200 Angstrom of beta = -1.14 +/- 0.20 and a decay rate of alpha = -0.86 +/- 0.15. There is no evidence for a change in the decay rate between approximately 0.7 and 4.7 days after the burst. Our data implies that there is no spectral break between the optical and X-ray bands between 0.7 and 4.7 days after the burst, and is consistent with the cooling break being redward of the K_s band (22,200 Angstrom) at 0.7 days. The combined ultraviolet/optical/infrared spectral energy distribution shows no evidence for a significant amount of extinction in the host galaxy along the line of sight to XRF 050416A. Our data suggest that the extragalactic extinction along the line of sight to the burst is only approximately A_V = 0.2 mag, which is significantly less than the extinction expected from the hydrogen column density inferred from $X$-ray observations of XRF 050416A assuming a dust-to-gas ratio similar to what is found for the Milky Way. The observed extinction, however, is consistent with the dust-to-gas ratio seen in the Small Magellanic Cloud. We suggest that XRF 050416A may have a two-component jet similar to what has been proposed for GRB 030329. If this is the case the lack of an observed jet break between 0.7 and 42 days is an illusion due to emission from the wide jet dominating the afterglow after approximately 1.5 days.

Prompt Optical Observations of GRB 050319 with the Swift UVOT

Abstract: The UVOT telescope on the Swift observatory has detected optical afterglow emission from GRB 050319. The flux declined with a power-law slope of alpha = -0.57 between the start of observations some 230 s after the burst onset (90 s after the burst trigger) until it faded below the sensitivity threshold of the instrument after similar to 5 x 10(4) s. There is no evidence for the rapidly declining component in the early light curve that is seen at the same time in the X-ray band. The afterglow is not detected in UVOT shortward of the B band, suggesting a redshift of about 3.5. The optical V-band emission lies on the extension of the X-ray spectrum, with an optical-to-X-ray slope of beta = 0.8. The relatively flat decay rate of the burst suggests that the central engine continues to inject energy into the fireball for as long as a few x 10(4) s after the burst.

Swift X-ray telescope observations of the deep impact collision

Abstract: Comet9P/Tempel1wasobservedbytheSwiftX-RayTelescope(XRT)foratotalof 250,024s.SoftX-rayemission, 0.2Y1.0keV,wasseenasadiffuseextendedhalowithanFWHMof1:03 ;10 5 kmcenteredonthecomet’snucleus.The X-raylightcurveindicatesthatthecometexhibitedaprolongedsoftX-rayoutburstjustafterimpactoftheNASADeep Impact (DI) spacecraft and enhanced X-ray activity lasted for 12 days. The radial brightness distribution and X-ray spectrumareinexcellentagreementwithamodelof X-rayproductioninwhichhighlychargedminorheavyionspecies inthesolar windundergochargeexchangereactions withwatergrouporcarbondioxidegroup moleculesintheneutral comaof thecomet.Usingthismodel,wederiveasimpleexpressionfortheX-rayemissionandshowthattheX-rayflare is, in part, due to an increase in solar wind flux at the comet but is largely due to an enhanced molecule production rate. Assuming that the main outgassing constituent was water, the comet produced (2:9 � 0:4) ;10 8 kg over the 12 day period postimpact. The quiescent water production was expected to inject � 1:0 ;10 8 kg into the coma over the same period so the observed X-ray flux indicates that an additional (1:9 � 0:4) ;10 8 kg of water or, alternatively, (3:9 � 0:5) ; 10 8 kg of carbon dioxide were liberated by the DI impact. Subject headingg comets: general — comets: individual (9P/Tempel 1) Online material: color figures

Optical, Infrared, and Ultraviolet Observations of the X-Ray Flash GRB 050416A

Abstract: We present ultraviolet, optical, and infrared photometry of the afterglow of the X-ray flash XRF 050416A taken between approximately 100 seconds and 36 days after the burst. We find an intrinsic spectral slope between 1930 and 22,200 Angstrom of beta = -1.14 +/- 0.20 and a decay rate of alpha = -0.86 +/- 0.15. There is no evidence for a change in the decay rate between approximately 0.7 and 4.7 days after the burst. Our data implies that there is no spectral break between the optical and X-ray bands between 0.7 and 4.7 days after the burst, and is consistent with the cooling break being redward of the K_s band (22,200 Angstrom) at 0.7 days. The combined ultraviolet/optical/infrared spectral energy distribution shows no evidence for a significant amount of extinction in the host galaxy along the line of sight to XRF 050416A. Our data suggest that the extragalactic extinction along the line of sight to the burst is only approximately A_V = 0.2 mag, which is significantly less than the extinction expected from the hydrogen column density inferred from $X$-ray observations of XRF 050416A assuming a dust-to-gas ratio similar to what is found for the Milky Way. The observed extinction, however, is consistent with the dust-to-gas ratio seen in the Small Magellanic Cloud. We suggest that XRF 050416A may have a two-component jet similar to what has been proposed for GRB 030329. If this is the case the lack of an observed jet break between 0.7 and 42 days is an illusion due to emission from the wide jet dominating the afterglow after approximately 1.5 days.

Extreme Properties Of GRB061007: A Highly Energetic Or A Highly Collimated Burst?

Abstract: GRB061007 is the brightest gamma-ray burst (GRB) to be detected by Swift and is accompanied by an exceptionally luminous afterglow that had a V-band magnitude <11.1 at 80s after the prompt emission. From the start of the Swift observations the afterglow decayed as a power law with a slope of \alpha_X=1.66+/-0.01 in the X-ray and \alpha_{opt}=1.64+/-0.01 in the UV/optical, up to the point that it was no longer detected above background in the optical or X-ray bands. The brightness of this GRB and the similarity in the decay rate of the X-ray, optical and gamma-ray emission from 100s after the trigger distinguish this burst from others and present a challenge to the fireball model. The lack of a cooling or jet break in the afterglow up to \~10^5s constrains any model that can produce the large luminosity observed in GRB061007, which we found to require either an excessively large kinetic energy or highly collimated outflow. Analysis of the multi-wavelength spectral and high-resolution temporal data taken with Swift suggest an early time jet-break to be a more plausible scenario. This must have occurred within 80s of the prompt emission, which places an upper limit on the jet opening angle of \theta_j=0.8deg. Such a highly collimated outflow resolves the energy budget problem presented in a spherical emission model, reducing the isotropic equivalent energy of this burst to E_{\gamma}^{corr}=10^{50} ergs; consistent with other GRBs.