Tracking and imaging gamma ray experiment (TIGRE) for 1 to 100 MEV gamma ray astronomy

A large international collaboration from the high energy astrophysics community has proposed the Tracking and Imaging Gamma Ray Experiment (TIGRE) for future space observations. TIGRE will image and perform energy spectroscopy measurements on celestial sources of gamma rays in the energy range from 1 to 100 MeV. This has been a difficult energy range experimentally for gamma ray astronomy but is vital for the future considering the recent exciting measurements below 1 and above 100 MeV. TIGRE is both a double scatter Compton and gamma ray pair telescope with direct imaging of individual gamma ray events. Multi‐layers of Si strip detectors are used as Compton and pair converters CsI(Tl) scintillation detectors are used as a position sensitive calorimeter. Alternatively, thick GE strip detectors may be used for the calorimeter. The Si detectors are able to track electrons and positrons through successive Si layers and measure their directions and energy losses. Compton and pair events are completely reconstructed allowing each event to be imaged on the sky. TIGRE will provide an order‐of‐magnitude improvement in discrete source sensitivity in the 1 to 100 MeV energy range and determine spectra with excellent energy and excellent angular resolutions. It’s wide field‐of‐view of π sr permits observations of the entire sky for extended periods of time over the life of the mission

The Dark Side of ROTSE-III Prompt GRB Observations

We present several cases of optical observations during gamma-ray bursts (GRBs) which resulted in prompt limits but no detection of optical emission. These limits constrain the prompt optical flux densities and the optical brightness relative to the gamma-ray emission. The derived constraints fall within the range of properties observed in GRBs with prompt optical detections, though at the faint end of optical/gamma flux ratios. The presently accessible prompt optical limits do not require a different set of intrinsic or environmental GRB properties, relative to the events with prompt optical detections.Comment: ApJ accepted. 20 pages in draft manuscript form, which includes 6 pages of tables and 2 figure

Prompt Optical Detection of GRB 050401 with ROTSE-IIIa

The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected prompt optical emission from Swift GRB 050401. In this letter, we present observations of the early optical afterglow, first detected by the ROTSE-IIIa telescope 33 s after the start of gamma-ray emission, contemporaneous with the brightest peak of this emission. This GRB was neither exceptionally long nor bright. This is the first prompt optical detection of a GRB of typical duration and luminosity. We find that the early afterglow decay does not deviate significantly from the power-law decay observable at later times, and is uncorrelated with the prompt gamma-ray emission. We compare this detection with the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All three bursts exhibit quite different behavior at early times.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letter

Status of the ROTSE-III telescope network

ROTSE-III is a homogeneous worldwide array of 4 robotic telescopes. They were designed to provide optical observations of γ-ray burst (GRB) afterglows as close as possible to the start of γ-ray emission. ROTSE-III is fulfilling its potential for GRB science, and provides optical observations for a variety of astrophysical sources in the interim between GRB events

The Anomalous Early Afterglow of GRB 050801

The ROTSE-IIIc telescope at the H.E.S.S. site, Namibia, obtained the earliest detection of optical emission from a Gamma-Ray Burst (GRB), beginning only 21.8 s from the onset of Swift GRB 050801. The optical lightcurve does not fade or brighten significantly over the first ~250 s, after which there is an achromatic break and the lightcurve declines in typical power-law fashion. The Swift/XRT also obtained early observations starting at 69 s after the burst onset. The X-ray lightcurve shows the same features as the optical lightcurve. These correlated variations in the early optical and X-ray emission imply a common origin in space and time. This behavior is difficult to reconcile with the standard models of early afterglow emission.Comment: 5 pages, 1 figure. Accepted for publication in ApJ Letter

Optical Lightcurve & Cooling Break of GRB 050502A

We present lightcurves of the afterglow of GRB050502A, including very early data at t-t_{GRB} < 60s. The lightcurve is composed of unfiltered ROTSE-IIIb optical observations from 44s to 6h post-burst, R-band MDM observations from 1.6 to 8.4h post-burst, and PAIRITEL J H K_s observations from 0.6 to 2.6h post-burst. The optical lightcurve is fit by a broken power law, where t^{alpha} steepens from alpha = -1.13 +- 0.02 to alpha = -1.44 +- 0.02 at \~5700s. This steepening is consistent with the evolution expected for the passage of the cooling frequency nu_c through the optical band. Even in our earliest observation at 44s post-burst, there is no evidence that the optical flux is brighter than a backward extrapolation of the later power law would suggest. The observed decay indices and spectral index are consistent with either an ISM or a Wind fireball model, but slightly favor the ISM interpretation. The expected spectral index in the ISM interpretation is consistent within 1 sigma with the observed spectral index beta = -0.8 +- 0.1; the Wind interpretation would imply a slightly (~2 sigma) shallower spectral index than observed. A small amount of dust extinction at the source redshift could steepen an intrinsic spectrum sufficiently to account for the observed value of beta. In this picture, the early optical decay, with the peak at or below 4.7e14 Hz at 44s, requires very small electron and magnetic energy partitions from the fireball.Comment: 22 pages, including 3 tables and 1 figure, Accepted by Ap

The Optical Luminosity Function of Gamma-ray Bursts deduced from ROTSE-III Observations

We present the optical luminosity function (LF) of gamma-ray bursts (GRBs) estimated from a uniform sample of 58 GRBs from observations with the Robotic Optical Transient Search Experiment III (ROTSE-III). Our GRB sample is divided into two sub-samples: detected afterglows (18 GRBs), and those with upper limits (40 GRBs). The $R$ band fluxes 100s after the onset of the burst for these two sub-samples are derived. The optical LFs at 100s are fitted by assuming that the co-moving GRB rate traces the star-formation rate. The detection function of ROTSE-III is taken into account during the fitting of the optical LFs by using Monte Carlo simulations. We find that the cumulative distribution of optical emission at 100s is well-described with an exponential rise and power-law decay (ERPLD), broken power-law (BPL), and Schechter LFs. A single power-law (SPL) LF, on the other hand, is ruled out with high confidence.Comment: 26 pages, 3 figures, ApJ accepte

Optical photometry of the PSR B0656+14 and its neighborhood

We present the results of the broad-band photometry of the nearby middle-aged radio pulsar PSR B0656+14 and its neighborhood obtained with the 6-meter telescope of the SAO RAS and with the Hubble Space Telescope. The broad-band spectral flux $F_\nu$ of the pulsar decreases with increasing frequency in the near-IR range and increases with frequency in the near-UV range. The increase towards UV can be naturally interpreted as the Rayleigh-Jeans tail of the soft thermal component of the X-ray spectrum emitted from the surface of the cooling neutron star. Continuation of the power-law component, which dominates in the high-energy tail of the X-ray spectrum, to the IR-optical-UV frequencies is consistent with the observed fluxes. This suggests that the non-thermal pulsar radiation may be of the same origin in a broad frequency range from IR to hard X-rays. We also studied 4 objects detected in the pulsar's 5" neighborhood.Comment: 12 pages, 20 figures, submitted to A&A. Images are available in FITS format at http://www.ioffe.rssi.ru/astro/NSG/obs/0656-phot.htm