Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOptical observations of the bright long duration peculiar GRB 021004 afterglow
67
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The CCD magnitudes in Johnson $B,V$ and Cousins $R$ and $I$ photometric passbands are determined for the bright long duration GRB 021004 afterglow from 2002 October 4 to 16 starting $sim$ 3 hours after the $gamma-$ray burst. Light curves of the afterglow emission in $B$,$V$,$R$ and $I$ passbands are obtained by combining these measurements with other published data. The earliest optical emission appears to originate in a revese shock. Flux decay of the afterglow shows a very uncommon variation relative to other well-observed GRBs. Rapid light variations, especially during early times ($Delta t < 2$ days) is superposed on an underlying broken power law decay typical of a jetted afterglow. The flux decay constants at early and late times derived from least square fits to the light curve are $0.99pm0.05$ and $2.0pm0.2$ respectively, with a jet break at around 7 day. Comparison with a standard fireball model indicates a total extinction of $E(B-V)=0.20$ mag in the direction of the burst. Our low-resolution spectra corrected for this extinction provide a spectral slope $beta = 0.6pm0.02$. This value and the flux decay constants agree well with the electron energy index $psim 2.27$ used in the model. The derived jet opening angle of about $7^{circ}$ implies a total emitted gamma-ray energy $E_{gamma} = 3.5times10^{50}$ erg at a cosmological distance of about 20 Gpc. Multiwavelength observations indicate association of this GRB with a star forming region, supporting the case for collapsar origin of long duration GRBs.
rate research
Read More
We present optical follow up observations of the long GRB 001007 between 6.14 hours and ~468 days after the event. An unusually bright optical afterglow (OA) was seen to decline following a steep power law decay with index alpha = -2.03 +/- 0.11, possibly indicating a break in the light curve at t - to < 3.5 days, as found in other bursts. Upper limits imposed by the LOTIS alerting system 6.14 hours after the gamma ray event provide tentative (1.2 sigma) evidence for a break in the optical light curve. The spectral index beta of the OA yields -1.24 +/- 0.57. These values may be explained both by several fireball jet models and by the cannonball model. Fireball spherical expansion models are not favoured. Late epoch deep imaging revealed the presence of a complex host galaxy system, composed of at least two objects located 1.2 (1.7 sigma) and 1.9 (2.7 sigma) from the afterglow position.
We present polarimetric observations of the afterglow of gamma-ray burst (GRB) 021004, obtained with the Nordic Optical Telescope (NOT) and the Very Large Telescope (VLT) between 8 and 17 hours after the burst. Comparison among the observations shows a 45 degree change in the position angle from 9 hours after the burst to 16 hours after the burst, and comparison with published data from later epochs even shows a 90 degree change between 9 and 89 hours after the burst. The degree of linear polarization shows a marginal change, but is also consistent with being constant in time. In the context of currently available models for changes in the polarization of GRBs, a homogeneous jet with an early break time of t_b ~ 1 day provides a good explanation of our data. The break time is a factor 2 to 6 earlier than has been found from the analysis of the optical light curve. The change in the position angle of the polarization rules out a structured jet model for the GRB.
We present multiwavelength (optical/near infrared/millimetre) observations of a short duration gamma-ray burst detected by Swift (GRB 050509b) collected between 0 seconds and ~18.8 days after the event. No optical, near infrared or millimetre emission has been detected in spite of the well localised X-ray afterglow, confirming the elusiveness of the short duration events. We also discuss the possibility of the burst being located in a cluster of galaxies at z= 0.225 or beyond. In the former case, the spectral energy distribution of the neighbouring, potential host galaxy, favours a system harbouring an evolved dominant stellar population (age ~360 Myr), unlike most long duration GRB host galaxies observed so far, i.e. thus giving support to a compact binary merger origin. Any underlying supernova that could be associated with this particular event should have been at least 3 magnitudes fainter than the type Ib/c SN 1998bw and 2.3 magnitudes fainter than a typical type Ia SN.
We present U,B,V,R_C,and I_C photometry of the optical afterglow of the gamma-ray burst GRB 021004 taken at the Nordic Optical Telescope between approximately eight hours and 30 days after the burst. This data is combined with an analysis of the 87 ksec Chandra X-ray observations of GRB 021004 taken at a mean epoch of 33 hours after the burst to investigate the nature of this GRB. We find an intrinsic spectral slope at optical wavelengths of beta_UH = 0.39 +/- 0.12 and an X-ray slope of beta_X = 0.94 +/- 0.03. There is no evidence for colour evolution between 8.5 hours and 5.5 days after the burst. The optical decay becomes steeper approximately five days after the burst. This appears to be a gradual break due to the onset of sideways expansion in a collimated outflow. Our data suggest that the extra-galactic extinction along the line of sight to the burst is between A_V = 0.3 and A_V = 0.5 and has an extinction law similar to that of the Small Magellanic Cloud. The optical and X-ray data are consistent with a relativistic fireball with the shocked electrons being in the slow cooling regime and having an electron index of p = 1.9 +/- 0.1. The burst occurred in an ambient medium that is homogeneous on scales larger than approximately 10e18 cm but inhomogeneous on smaller scales. The mean particle density is similar to what is seen for other bursts (0.1 < n < 100 cm^{-3}). Our results support the idea that the brightening seen approximately 0.1 days was due to interaction with a clumpy ambient medium within 10^{17} and 10^{18} cm of the progenitor. The agreement between the predicted optical decay and that observed approximately ten minutes after the burst suggests that the physical mechanism controlling the observed flux approximately ten minutes is the same as the one operating at t > 0.5 days.
The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos National Laboratory observed GRB 050319 starting 25.4 seconds after gamma-ray emission triggered the Burst Alert Telescope (BAT) on-board the Swift satellite. Our well sampled light curve of the early optical afterglow is composed of 32 points (derived from 70 exposures) that measure the flux decay during the first hour after the GRB. The GRB 050319 light curve measured by RAPTOR can be described as a relatively gradual flux decline (power-law index alpha = -0.37) with a transition, at about 400 s after the GRB, to a faster flux decay (alpha = -0.91). The addition of other available measurements to the RAPTOR light curve suggests that another emission component emerged after 10^4 s. We hypothesize that the early afterglow emission is powered by extended energy injection or delayed reverse shock emission followed by the emergence of forward shock emission.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
