Gamma-ray bursts (GRBs) come in two classes: long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at ...high redshift (z 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars. In contrast, no short GRB had been accurately (< 10″) and rapidly (minutes) located. Here we report the detection of the X-ray afterglow from-and the localization of-the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect if the origin of this GRB is through the merger of neutron-star or black-hole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs.
Long gamma-ray bursts (GRBs) are bright flashes of high-energy photons that can last for tens of minutes; they are generally associated with galaxies that have a high rate of star formation and ...probably arise from the collapsing cores of massive stars, which produce highly relativistic jets (collapsar model). Here we describe γ- and X-ray observations of the most distant GRB ever observed (GRB 050904): its redshift (z) of 6.29 means that this explosion happened 12.8 billion years ago, corresponding to a time when the Universe was just 890 million years old, close to the reionization era. This means that not only did stars form in this short period of time after the Big Bang, but also that enough time had elapsed for them to evolve and collapse into black holes.
The Swift Gamma-Ray Burst Mission Gehrels, N; Chincarini, G; Giommi, P ...
The Astrophysical journal,
08/2004, Letnik:
611, Številka:
2
Journal Article
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The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is a first-of-its-kind autonomous rapid-slewing satellite for transient ...astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts yr super(-1) and performing detailed X-ray and UV/optical afterglow observations spanning timescales from 1 minute to several days after the burst. The objectives are to (1) determine the origin of GRBs, (2) classify GRBs and search for new types, (3) study the interaction of the ultrarelativistic outflows of GRBs with their surrounding medium, and (4) use GRBs to study the early universe out to z > 10. The mission is being developed by a NASA-led international collaboration. It will carry three instruments: a new-generation wide-field gamma-ray (15-150 keV) detector that will detect bursts, calculate 1arcmin-4arcmin positions, and trigger autonomous spacecraft slews; a narrow-field X-ray telescope that will give 5arc sec positions and perform spectroscopy in the 0.2-10 keV band; and a narrow-field UV/optical telescope that will operate in the 170-600 nm band and provide 0!!3 positions and optical finding charts. Redshift determinations will be made for most bursts. In addition to the primary GRB science, the mission will perform a hard X-ray survey to a sensitivity of approx1 mcrab (approx2 x 10 super(-11) ergs cm super(-2) s super(-1) in the 15-150 keV band), more than an order of magnitude better than HEAO 1 A-4. A flexible data and operations system will allow rapid follow-up observations of all types of high-energy transients, with rapid data downlink and uplink available through the NASA TDRSS system. Swift transient data will be rapidly distributed to the astronomical community, and all interested observers are encouraged to participate in follow- up measurements. A Guest Investigator program for the mission will provide funding for community involvement. Innovations from the Swift program applicable to the future include (1) a large-area gamma-ray detector using the new CdZnTe detectors, (2) an autonomous rapid-slewing spacecraft, (3) a multiwavelength payload combining optical, X-ray, and gamma-ray instruments, (4) an observing program coordinated with other ground-based and space-based observatories, and (5) immediate multiwavelength data flow to the community. The mission is currently funded for 2 yr of operations, and the spacecraft will have a lifetime to orbital decay of approx8 yr.
Fermi Gamma-Ray Imaging of a Radio Galaxy Abdo, A A; Ajello, M; Ballet, J ...
Science (American Association for the Advancement of Science),
05/2010, Letnik:
328, Številka:
5979
Journal Article
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The Fermi Gamma-ray Space Telescope has detected the γ-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved γ-ray image shows the lobes clearly separated from ...the central active source. In contrast to all other active galaxies detected so far in high-energy γ-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The γ-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light.These measurements provide ã-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.
Context. Swift discovered the high redshift ( z =6.29) GRB 050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This ...gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a very early source-frame time (22 s). The X-ray emission was monitored by the XRT up to 10 days after the burst. Aims. We present the analysis of BAT and XRT observations of GRB 050904 and a complete description of its high energy phenomenology. Methods. We performed time resolved spectral analysis and light curve modeling. Results. GRB 050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution. The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 h after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behavior resembles that of a very long GRB prompt. The spectral energy distribution softens with time, with the photon index decreasing from-1.2 during the BAT observation to-1.9 at the end of the XRT observation. The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al. (2005b, A&A, 443, L1). Conclusions. We interpret the BAT and XRT data as a single continuous observation of the prompt emission from a very long GRB. The peculiarities observed in GRB 050904 could be due to its origin within one of the first star-forming regions in the Universe; very low metallicities of the progenitor at these epochs may provide an explanation.
We present the analysis of the interstellar gamma-ray emission measured by the Fermi Large Area Telescope toward a region in the second Galactic quadrant at 100 degrees <= l <= 145 degrees and ...-15 degrees <= b <= +30 degrees. This region encompasses the prominent Gould Belt clouds of Cassiopeia, Cepheus, and the Polaris flare, as well as atomic and molecular complexes at larger distances, like that associated with NGC 7538 in the Perseus arm. The good kinematic separation in velocity between the local, Perseus, and outer arms, and the presence of massive complexes in each of them, make this region well suited to probe cosmic rays (CRs) and the interstellar medium beyond the solar circle. The gamma-ray emissivity spectrum of the gas in the Gould Belt is consistent with expectations based on the locally measured CR spectra. The gamma-ray emissivity decreases from the Gould Belt to the Perseus arm, but the measured gradient is flatter than expectations for CR sources peaking in the inner Galaxy as suggested by pulsars. The X-CO = N(H-2)/W-CO conversion factor is found to increase from (0.87 +/- 0.05) x 10(20) cm(-2) (K km s(-1))(-1) in the Gould Belt to (1.9 +/- 0.2) x 10(20) cm(-2) (K km s(-1))(-1) in the Perseus arm. We derive masses for the molecular clouds under study. Dark gas, not properly traced by radio and microwave surveys, is detected in the Gould Belt through a correlated excess of dust and gamma-ray emission: its mass amounts to similar to 50% of the CO-traced mass.
Gamma-ray binaries are stellar systems containing a neutron star or black hole, with gamma-ray emission produced by an interaction between the components. These systems are rare, even though binary ...evolution models predict dozens in our Galaxy. A search for gamma-ray binaries with the Fermi Large Area Telescope (LAT) shows that 1FGL J1018.6-5856 exhibits intensity and spectral modulation with a 16.6-day period. We identified a variable x-ray counterpart, which shows a sharp maximum coinciding with maximum gamma-ray emission, as well as an 06V((f)) star optical counterpart and a radio counterpart that is also apparently modulated on the orbital period. 1FGL 1018.6-5856 is thus a gamma-ray binary, and its detection suggests the presence of other fainter binaries in the Galaxy.
The detection of diffuse radio emission associated with clusters of galaxies indicates populations of relativistic leptons infusing the intracluster medium (ICM). Those electrons and positrons are ...either injected into and accelerated directly in the ICM, or produced as secondary pairs by cosmic-ray ions scattering on ambient protons. Radiation mechanisms involving the energetic leptons together with the decay of neutral pions produced by hadronic interactions have the potential to produce abundant GeV photons. Here, we report on the search for GeV emission from clusters of galaxies using data collected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope from 2008 August to 2010 February. Thirty-three galaxy clusters have been selected according to their proximity and high mass, X-ray flux and temperature, and indications of non-thermal activity for this study. We report upper limits on the photon flux in the range 0.2-100 GeV toward a sample of observed clusters (typical values (1-5) x 10(-9) photon cm(-2) s(-1)) considering both point-like and spatially resolved models for the high-energy emission and discuss how these results constrain the characteristics of energetic leptons and hadrons, and magnetic fields in the ICM. The volume-averaged relativistic-hadron-to-thermal energy density ratio is found to be <5%-10% in several clusters.
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