Search

The first year of full SXC operations has resulted in the detection of over a dozen GRBs and XRFs, and the SXC GRB catalog continues to grow at a rate of approximately 1/month. The small error circles, rapid position dissemination, and most importantly, aggressive follow up observations have led to a remarkable trend: nearly all SXC detections have an associated optical/IR/radio/X-ray counterpart. The systematic errors dominating the SXC astrometry are being reduced, and recent recalibration efforts will result in smaller error radii sent out to the GCN. Flight localizations calculated tens of seconds after the burst onset will also enable large telescopes with small fields of view to engage in rapid, deep searches. These two factors will aid in building a unique database of GRBs with associated transients. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The X-ray-flash XRF 030723 was detected by the HETE satellite and rapidly disseminated, allowing for an optical transient to be detected ∼ 1 day after the burst. We discuss observations in the optical with Magellan, which confirmed the fade of the optical transient. In a 2-epoch ToO observation with Chandra, we discovered a fading X-ray source spatially coincident with the optical transient. We present spectral fits to the X-ray data. We also discuss the possibility that the source underwent a rebrightening in the X-rays, as was observed in the optical. We find that the significance of a possible rebrightening is very low (∼ 1σ). © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We review the significance determination for emission lines in the Chandra HETGS spectrum for GRB 020813, and we report on a search for additional lines in high resolution Chandra spectra. No previously unclaimed features are found. We also discuss the significance of lines sets reportedly discovered using XMM data for GRB 011211 and GRB 030227. We find that these features are likely of modest, though not negligible, significance. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The X-ray-rich GRB 030528 was detected by the HETE satellite and its localization was rapidly disseminated. However, early optical observations failed to detect a counterpart source. In a 2-epoch ToO observation with Chandra, we discovered a fading X-ray source the likely counterpart to GRB 030528. The source brightness was typical of X-ray afterglows observed at similar epochs. Other observers detected an IR source at a location consistent with the X-ray source. The X-ray spectrum is not consistent with a large absorbing column. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The High Energy Transient Explorer (HETE) mission is devoted to the study of gamma-ray bursts (GRBs) using soft X-ray, medium X-ray, and gamma-ray instruments mounted on a compact spacecraft. The METE satellite was launched into equatorial orbit on 9 October 2000. A science team from France, Japan, Brazil, India, Italy, and the US is responsible for the METE mission, which was completed for ∼ 1/3 the cost of a NASA Small Explorer (SMEX). The METE mission is unique in that it is entirely "self-contained," insofar as it relies upon dedicated tracking, data acquisition, mission operations, and data analysis facilities run by members of its international Science Team. A powerful feature of METE is its potential for localizing GRBs within seconds of the trigger with good precision (∼ 10') using medium energy X-rays and, for a subset of bright GRBs, improving the localization to ∼ 30' accuracy using low energy X-rays. Real-time GRB localizations are transmitted to ground observers within seconds via a dedicated network of 14 automated "Burst Alert Stations," thereby allowing prompt optical, IR, and radio follow-up, leading to the identification of counterparts for a large fraction of METE -localized GRBs. METE is the only satellite that can provide near-real time localizations of GRBs, and that can localize GRBs that do not have X-ray, optical, and radio afterglows, during the next two years. These capabilities are the key to allowing METE to probe further the unique physics that produces the brightest known photon sources in the universe. To date (December 2002), HETE has produced 31 GRB localizations. Localization accuracies are routinely in the 4'-20' range; for the five GRBs with SXC localization, accuracies are ∼1-2'. In addition, METE has detected ∼ 25 bursts from soft gamma repeaters (SGRs), and >600 X-ray bursts (XRBs). [ABSTRACT FROM AUTHOR]

The HETE Soft X-ray Camera (SXC) uses X-ray CCDs and a micro-fabricated coded aperture mask to image X-ray sources with sub-arcminute accuracy over a steradian field of view. Calibration of imaging with observations of the Crab and Sco X-1 is described. The accuracy of SXC localizations is determined trough observations of known steady and transient galactic X-ray sources and sensitivity to GRBs is estimated through detections of steady and transient Galactic X-ray sources. [NB: As of October 2002, the SXC had localized 4 GRBs to arcminute accuracy]. [ABSTRACT FROM AUTHOR]

We report the discovery of kHz fluctuations, including quasi-periodic oscillations (QPO) at ∼ 330 Hz and ∼ 760 Hz and a broadband kHz continuum in the power density spectrum of the high mass X-ray binary pulsar Centaurus X-3 (Jernigan, Klein and Arons 2000). These observations of Cen X-3 were carried out with the Rossi X-ray Timing Explorer (RXTE). The fluctuation spectrum is fiat from mHz to a few Hz, then steepens to f[sup -2] behavior between it few Hz and ∼ 100 Hz. Above a hundred Hz, the spectrum shows the QPO features, plus a fiat continuum extending to ∼ 1200 Hz and then falling out to ∼ 1800 Hz. Multi-dimensional radiation hydrodynamics simulations of optically thick plasma flow onto a magnetized neutron star show that the fluctuations at frequencies above 100 Hz are the likely consequence of the photon bubble turbulence and oscillations (PBO) previously predicted (Klein et al. 1996) to be observable in this source. We show that previous observations of Cen X-3 constrain the models to depend on only one parameter, the size of the polar cap. For a polar cap opening angle of 0.25 radians (polar cap radius ∼ 2.5 km and area ∼ 20 km², for a neutron star radius of 10 km), we show that the spectral form above 100 Hz is reproduced by the simulations, including the frequencies of the QPO and the relative power in the QPO and the kHz continuum. This has resulted in the first measurement of the polar cap size of an X-ray pulsar. [ABSTRACT FROM AUTHOR]

We describe the scientific goals, the spacecraft and instrumentation, and the operation of the High-Energy Transient Explorer-2 (HETE-2), which is currently scheduled to be launched in early 2000. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The theory of torque free precession (TFP) of the outer crust of a neutron star (NS) as the signature of the approach to NS breakup is a viable explanation of the uniform properties of kHz Quasi-periodic Oscillations (QPO) observed in X-rays emitted by Low Mass X-ray Binary (LMXB) sources. The TFP model is in strong contrast to existing models which primarily relate the kHz QPO phenomenon to the physics of gas dynamics near the inner edge of the accretion disk and the transition flow onto the surface of the NS. We suggest the possibility of the direct detection of very low frequency (~ 1 kHz) radio waves from magnetic dipole radiation and also predict kHz gravitational wave emission from the LMXB Sco X-1 that may be detectable by LIGO. The high accretion rates consistent with the predicted GW emission indicate the likely conversion of some LMXBs to maximally rotating Kerr black holes (BH) and further suggest that these systems are progenitors of some gamma-ray bursts (GRB). [ABSTRACT FROM AUTHOR]