axtaršenâsi-ye partowhâ-ye gâmmâ (#)
Fr.: astronomie en rayons gamma
gamma-ray burst (GRB)
belk-e partowhâ-ye gâmmâ
Fr.: sursaut de rayons gamma
An intense discharge of → gamma rays, which range in duration from tenth of a second to tens of seconds and occur from sources widely distributed over the sky. The radio wave → afterglow from the → burst can last more than a year, making long-term observations of the sources possible. The favored hypothesis is that they are produced by a relativistic jet created by the merger of two → compact objects (specifically two → neutron stars or a neutron star and a → black hole). Mergers of this kind are also expected to create significant quantities of neutron-rich radioactive species, whose decay should result in a faint → transient, known as a → kilonova, in the days following the burst. Indeed, it is speculated that this mechanism may be the predominant source of stable → r-process elements in the Universe. Recent calculations suggest that much of the kilonova energy should appear in the → near-infrared spectral range, because of the high optical opacity created by these heavy r-process elements (Tanvir et al., 2017, Nature 500, 547).
belkvar-e partow-e gâmmâ
Fr.: source à sursaut gamma
xan-e partowhâ-ye gâmma
Fr.: source de rayons gamma
1) An astronomical object that emits → gamma rays.
GCN: The Gamma-ray Coordinates Network
turbast-e hamârâhâ-ye partowhâ-ye gâmâ
Fr.: Le réseau des coordonnées des rayons gamma
A follow-up community network concerned with → gamma-ray burst (GRB)s. It deals with: 1) locations of GRBs and other → transients detected by spacecraft (most in real-time while the GRB is still bursting), and 2) reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other observers. The GCN Circulars allow the GRB follow-up community to make optimum use of its limited resources (labor and telescope time) by communicating what has already been done or will soon be done.
(n.) A color between white and black. (adj.) Having a neutral hue.
M.E., O.E. græg, from P.Gmc. *græwyaz; cf. O.N. grar, O.Fris. gre, Du. graw, Ger. grau; Frank. *gris, Fr. gris.
Xâkestari, "ash-colored," from xâkestar "ashes," from Mid.Pers. *xâkâtur, from xâk "earth, dust" + âtur "fire," varaint âtaxš (Mod.Pers. âtaš, âzar, taš), from Av. ātar-, āθr- "fire," singular nominative ātarš-; O.Pers. ātar- "fire;" Av. āθaurvan- "fire priest;" Skt. átharvan- "fire priest;" cf. L. ater "black" ("blackened by fire"); Arm. airem "burns;" Serb. vatra "fire;" PIE base *āter- "fire."
An SI unit of absorbed radiation dose. One gray is equivalent to an energy absorption of 1 → joule/kg. It has replaced the → rad (rd), an older standard. One gray is equivalent to 100 rad. See also → sievert (Sv).
Named for Louis Harold Gray (1905-1965), British radiologist and the pioneer of use of radiation in cancer treatment.
javv-e xâkestari, havâsepher-e ~
Fr.: atmosphère grise
A simplifying assumption in the models of stellar atmosphere, according to which the absorption coefficient has the same value at all wavelengths.
jesm-e xâkestari (#)
Fr.: corps gris
A hypothetical body which emits radiation at each wavelength in a constant ratio, less than unity, to that emitted by a black body at the same temperature.
partowhâ-ye X-e saxt (#)
Fr.: rayons X durs
The short wavelength, high energy end of the → electromagnetic spectrum. Hard X-rays are typically those with energies greater than around 10 keV. The dividing line between hard and → soft X-rays is not well defined and can depend on the context.
high-energy cosmic rays
partowhâ-ye keyhâni-ye meh-kâruž, ~ ~ por-kâruž
Fr.: rayons cosmiques de hautes énergies
Cosmic rays which typically have energies in the range 1015 to 1020 electron volts. For the most part, they are protons and other atomic nuclei, and come from distant cosmos, perhaps even from outside our own Galaxy.
high-mass X-ray binary (HMXB)
dorin-e partow-e iks-e por-jerm
Fr.: binaire X de forte masse
A member of one of the two main classes of → X-ray binary systems where one of the components is a neutron star or a black hole and the other one a → massive star. HMXBs emit relatively → hard X-rays and usually show regular pulsations, no X-ray bursts, and often X-ray eclipses. Their X-ray luminosity is much larger than their optical luminosity. In our Galaxy HMXBs are found predominantly in the → spiral arms and within the → Galactic disk in young → stellar populations less than 107 years old. One of the most famous HMXB is Cygnus X-1 which was the first stellar-mass black hole discovered. See also: → low-mass X-ray binary.
Fr.: rayon incident
Fr.: détecteur mosaïque infrarouge
A two-dimensional infrared imaging device, consisting of an array of small, individual electronic detectors, each of which records a pixel in the image.
ârast-e andarzanešsanji, ~ andarzanešsanjik
Fr.: réseau interférométrique
A system of several telescopes coupled together in a particular configuration to carry out → interferometry.
partowhâ-ye yoni (#)
Fr.: rayons ioniques
The thin glowing streamers in a comet's ion tail.
Fr.: rayon de lumière
An imaginary line directed along the path that the light follows. In other words, light pictured simply in terms of straight lines.
low-mass X-ray binary (LMXB)
dorin-e partow-e iks-e kam-jerm
Fr.: binaire X de faible masse
A member of one of the two main classes of
→ X-ray binary systems where one of the components is a
→ neutron star or → black hole
and the other component a → low-mass star with a spectral type A
or later. LMXBs mainly emit → soft X-rays.
The ratio of their optical to X-ray luminosities is less than 0.1. They belong
to → old stellar populations
with ages 5-15 × 109 years and are found in
→ globular clusters
and in the → bulge
of our → Milky Way
galaxy; some are also found in the disk.
Hercules X-1 is an example of LMXBs.
Fr.: rayon ordinaire
Fr.: rayon paraxial
A ray that lies close to and almost parallel to the optical axis and behaves according to paraxial equations.