Bright Afterglow Research Articles

The first hours of the optical afterglow from the cosmic gamma-ray burst 030329

We describe the first results of our observations of the exceptionally bright optical afterglow from the cosmic gamma-ray burst (GRB) of March 29, 2003 (030329), with the 1.5-m Russian-Turkish telescope (RTT150) installed at the TUBITAK National Observatory (Turkey) at Mount Bakyrlytepe. RTT150 was one of the first medium-class telescopes pointed at the afterglow. The observations began as early as about six hours after the GRB. During the first five hours of our observations, the BV RI flux fell off exactly as a power law with the same slope −1.19±0.01. Subsequently, in all of the BV RI bands, we observed the same increase in the power-law slope of the light curve to a value that was later recorded during the observations at observatories in the western hemisphere. The break in the power-law light curve occurs at t − t 0 ≈ 0.57 days (13.5 h) and lasts for about 0.2 days. Apart from this smooth decrease in the flux, the afterglow exhibited no flux variability. The upper limits on the variability are 10–1% on time scales of 0.1–1000 s, respectively. The BV RI spectral flux distribution during the first night of our observations closely corresponds to a power-law spectrum with a spectral index α=0.66±0.01. The change in the power-law slope of the light curve at the end of our observations is probably attributable to the deceleration of the ultrarelativistic jet to a gamma factor when its structural features begin to show up in the light curve. The radio, optical, and X-ray broadband spectrum is consistent with the assumption about the synchrotron radiation of the ultrarelativistic jet. This unique object continues to be observed with RTT150.

The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003.

Past studies of cosmological gamma-ray bursts (GRBs) have been hampered by their extreme distances, resulting in faint afterglows. A nearby GRB could potentially shed much light on the origin of these events, but GRBs with a redshift z <or= 0.2 have been estimated to occur only rarely, about once per decade. Here we report the discovery of the bright optical afterglow emission from the burst of 29 March 2003 (GRB030329; ref. 2). The brightness of the afterglow and the prompt report of its position resulted in extensive follow-up observations at many wavelengths, along with the measurement of the redshift, z = 0.169 (ref. 4). The gamma-ray and afterglow properties of GRB030329 are similar to those of GRBs at cosmological redshifts. Observations have already identified the progenitor as a massive star that exploded as a supernova.

Structure in the early afterglow light curve of the gamma-ray burst of 29 March 2003.

Gamma-ray bursts (GRBs) are energetic explosions that for 0.01-100 s are the brightest gamma-ray sources in the sky. Observations of the early evolution of afterglows are expected to provide clues about the nature of the bursts, but their rapid fading has hampered such studies; some recent rapid localizations of bursts have improved the situation. Here we report an early detection of the very bright afterglow of the burst of 29 March 2003 (GRB030329). Our data show that, even early in the afterglow phase, the light curve shows unexpectedly complicated structures superimposed on the fading background.

Optical and NIR observations of the afterglow of GRB 020813

We present optical and near-infrared (NIR) photometry of the bright afterglow of GRB 020813. Our data span from 3 hours to 4 days after the GRB event. A rather sharp achromatic break is present in the light curve, 14 hours after the trigger. In the framework of jetted fireballs, this break corresponds to a jet half-opening angle of $1.9\degr\pm0.2\degr$, the smallest value ever inferred for a GRB. We discuss our results in the framework of currently available models, and find that they have problems in explaining the joint temporal and spectral properties, and in particular the slow decay before the break.

High‐Resolution Grating Spectroscopy of GRB 020405 with theChandraLow Energy Transmission Grating Spectrometer

We present high-resolution X-ray spectroscopy of GRB 020405 obtained with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-Ray Observatory starting 1.68 days after the burst. The spectrum appears featureless, with no evidence for emission lines, absorption edges, or narrow radiative recombination continua. The continuum can be fitted by a power law of photon index Γ = 1.72 ± 0.21 and temporal decay index α = 1.87 ± 1.10, with a marginally significant excess column density of cold gas NH = (4.7 ± 3.7) × 1021 cm-2 at the redshift of the host galaxy. The absence of iron lines indicates that the density of surrounding material was unlikely to be very dense (n 5 × 1012 cm-3) at the time of the Chandra observation. In the case of recombination following photoionization in an optically thin medium, most ionic species would be completely stripped at lower gas densities than this. In the case of a power-law spectrum reflecting off a cold, opaque medium of low density, negligible emission features would be produced. Alternatively to these possible explanations for the lack of emission features, any X-ray line emission taking place in a dense medium in a nearby reprocessor scenario might have been overwhelmed by the bright afterglow continuum. Although the absence of discrete features does not unambiguously test for a connection between GRB 020405 and nucleosynthesis, it emphasizes the need for high-resolution X-ray spectroscopy to determine the exact emission mechanism responsible for the reported discrete lines in other gamma-ray burst afterglows.

The bright optical afterglow of the long GRB 001007

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 α = -2.03 ± 0.11, possibly indicating a break in the light curve at 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 (1.2σ) evidence for a break in the optical light curve. The spectral index β 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´´ (1.7σ) and 1.9´´ (2.7σ) from the afterglow position.

The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy

Observations of the extraordinarily bright optical afterglow (OA) of GRB 991208 started 2.1 d after the event. The flux decay constant of the OA in the R-band is -2.30 +/- 0.07 up to 5 d, which is very likely due to the jet effect, and after that it is followed by a much steeper decay with constant -3.2 +/- 0.2, the fastest one ever seen in a GRB OA. A negative detection in several all-sky films taken simultaneously to the event implies either a previous additional break prior to 2 d after the occurrence of the GRB (as expected from the jet effect). The existence of a second break might indicate a steepening in the electron spectrum or the superposition of two events. Once the afterglow emission vanished, contribution of a bright underlying SN is found, but the light curve is not sufficiently well sampled to rule out a dust echo explanation. Our determination of z = 0.706 indicates that GRB 991208 is at 3.7 Gpc, implying an isotropic energy release of 1.15 x 10E53 erg which may be relaxed by beaming by a factor > 100. Precise astrometry indicates that the GRB coincides within 0.2" with the host galaxy, thus given support to a massive star origin. The absolute magnitude is M_B = -18.2, well below the knee of the galaxy luminosity function and we derive a star-forming rate of 11.5 +/- 7.1 Mo/yr. The quasi-simultaneous broad-band photometric spectral energy distribution of the afterglow is determined 3.5 day after the burst (Dec 12.0) implying a cooling frequency below the optical band, i.e. supporting a jet model with p = -2.30 as the index of the power-law electron distribution.

Expected Number and Flux Distribution of Gamma‐Ray Burst Afterglows with High Redshifts

If gamma-ray bursts (GRBs) occur at high redshifts, then their bright afterglow emission can be used to probe the ionization and metal enrichment histories of the intervening intergalactic medium during the epoch of reionization. In contrast to other sources, such as galaxies or quasars, which fade rapidly with increasing redshift, the observed infrared flux from a GRB afterglow at a fixed observed age is only a weak function of its redshift. This results from a combination of the spectral slope of GRB afterglows and the time stretching of their evolution in the observer's frame. Assuming that the GRB rate is proportional to the star formation rate and that the characteristic energy output of GRBs is ~1052 ergs, we predict that there are always ~15 GRBs from redshifts z ≳ 5 across the sky that are brighter than ~100 nJy at an observed wavelength of ~2 μm. The infrared spectrum of these sources could be taken with the future Next Generation Space Telescope as a follow-up to early X-ray localization with the Swift satellite.

Bright afterglow illuminator made of phosphorescent material and fluorescent fibers

Phosphorescent oxides and fluorescent dyes were used together to create a fiber-type illuminator that glows in the dark without the need for electric power. Dye-doped polymer fibers, which were bundled at one end, were linearly arrayed in a polysiloxane resin that contained phosphorescent oxide particles. The phosphorescent resin continued to glow for a long time even after the excitation light was removed. Organic dyes in a polymer fiber were excited by the phosphorescence and emitted fluorescence toward the fiber end. Fluorescence from a number of dyes was combined in the long fiber, and, consequently a bright light beam emerged from the fiber end. Useful performance, i.e., high power density, narrow beam divergence, and long afterglow, is demonstrated by the prototype fiber illuminator.

GRB observations with the HETE soft X-ray cameras

The High Energy Transient Explorer, scheduled to be launched in late 1999 or early 2000, will carry a pair of Soft X-ray Cameras (SXC), capable of localizing the X-ray counterparts of GRBs with unprecedented precision. Each SXC consists of a pair of large-format CCDs behind a 1-D coded aperture: the two SXCs are oriented orthogonal to each other to permit two-dimensional image reconstruction. The SXCs on HETE will be able to localize bright X-ray afterglows to precision within seconds of burst onset. The coordinates of detected bursts will be distributed immediately to ground-based observers and to the GCN via the HETE Burst Alert System.

RXTE observations of GRB afterglows

Variable X-ray sources that appear to be the afterglows of the strong gamma-ray bursts GRB 970616 and GRB 970828 have been discovered with the RXTE PCA. First seen less than 4 hours after the burst, the flux from the sources decreased with time. Although near the sensitivity limit of the PCA, the sources are the brightest afterglows yet seen in X-rays. Similar observations of two other bursts did not detect any afterglows. These results are part of a continuing collaboration between RXTE, BATSE, and IPN scientists to rapidly detect X-ray afterglows of bright gamma-ray bursts.

The Expected Rate of Gamma‐Ray Burst Afterglows in Supernova Searches

We predict the rate at which gamma-ray burst (GRB) afterglows should be detected in supernova (SN) searches as a function of limiting flux. Although GRB afterglows are rarer than supernovae (SNs), they are detectable at greater distances because of their higher intrinsic luminosity. Assuming that GRBs trace the cosmic star formation history and that every GRB gives rise to a bright afterglow, we find that the average detection rate of SNs and afterglows should be comparable at limiting magnitudes brighter than K = 18. The actual rate of afterglows is expected to be somewhat lower since only a fraction of all gamma-ray-selected GRBs were observed to have associated afterglows. Hence, current and future SN searches can place strong constraints on the afterglow appearance fraction of GRB sources.

Variations in the After-Glow Brightness of Active Nitrogen Under Varied Experimental Conditions

LORD RAYLEIGH, in a remarkable series of experiments, has studied photometrically the variations in the after-glow brightness of active nitrogen under varied experimental conditions. The results are of extreme importance in testing the various theories of active nitrogen. In the present note, some of these results will be considered in the light of the hypothesis recently proposed by me1,2, namely, that active nitrogen is simply the ionized nitrogen molecule in the N2+(X') state produced by the discharge. If the walls of the vessel are suitably 'conditioned' to prevent the surface from acting as catalyst, the recombination of the positive ions with electrons proceeds mainly in the volume of the gas by a three body collision process in which neutral nitrogen molecules act as the third body.

New chemical fiber surpasses silk

Rare earth strontium aluminate luminous fiber is a novel functional fiber. In order to investigate the influence of Al/Sr ratio on luminescence properties of xSrO·yAl2O3:Eu2+,Dy3+ luminous fibers, several kinds of rare earth strontium aluminate luminous fibers were prepared by using rare-earth strontium aluminate as the rare-earth luminescent material and fiber-forming polymers such as polymer polyethylene terephthalate (PET) as a matrix and combining them with functional additives. X-ray diffraction (XRD), fluorescence spectrophotometer, and afterglow brightness tester as well as microcomputer thermo-luminescence dosimeters were used to characterize the resulting samples. Results from XRD demonstrated that the phase of xSrO·yAl2O3:Eu2+,Dy3+ luminous fibers were different from one another as the Al/Sr ratio changed. Emission spectra of the samples with different Al/Sr ratios showed that emission intensity increased with the decrease of A1/Sr ratio at first then increased when it was over 2/1. From afterglow decay results, it could be found that Sr-rich sample showed lower luminance and shorter persistent time.