X-ray transient

NRL astronomer Dr. Joseph Lazio stated:[1] " ... the sky is known to be full of transient objects emitting at X- and gamma-ray wavelengths, ...".

As seen from Earth, the Sun moves from west to east along the ecliptic, passing over the course of one year through the twelve constellations of the Zodiac, and Ophiuchus.

[5] Most astronomical X-ray transient sources have simple and consistent time structures; typically a rapid brightening followed by gradual fading, as in a nova or supernova.

GRO J0422+32[6] is an X-ray nova and black hole candidate that was discovered by the BATSE instrument on the Compton Gamma Ray Observatory satellite on Aug 5 1992.

In effect the compact object "gobbles up" the normal star, and the X-ray emission can provide the best view of how this process occurs.

[12] A gamma-ray burst (GRB) is a highly luminous flash of gamma rays — the most energetic form of electromagnetic radiation.

For several years physicists had expected these bursts to be followed by a longer-lived afterglow at longer wavelengths, such as radio waves, x-rays, and even visible light.

Discovered in 1997, remaining active only one day, with an X-ray spectrum well fitted with a thermal bremsstrahlung (temperature of ~20 keV), resembling the spectral properties of accreting pulsars, it was at first classified as a peculiar Be/X-ray transient with an unusually short outburst.

Small-scale energetic signatures such as plasma heating (observed as compact soft X-ray brightening) may be indicative of impending CMEs.

[18] The first detection of a Coronal mass ejection (CME) as such was made on Dec 1 1971 by R. Tousey of the US Naval Research Laboratory using the 7th Orbiting Solar Observatory (OSO 7).

The burst mode was triggered when the count rate in the 0.1 to 1.5 MeV energy range exceeded the background level by 8 σ (standard deviations) in either 0.25 or 1.0 seconds.

[22] Also on board the Granat International Astrophysical Observatory were four WATCH instruments that could localize bright sources in the 6 to 180 keV range to within 0.5° using a Rotation Modulation Collimator.

During quiet periods, count rates in two energy bands (6 to 15 and 15 to 180 keV) were accumulated for 4, 8, or 16 seconds, depending on onboard computer memory availability.

With the assistance of the Moon's gravitational field Wind's apogee was kept over the day hemisphere of the Earth and magnetospheric observations were made.

The third US Small Astronomy Satellite (SAS-3) was launched on May 7, 1975, with 3 major scientific objectives: 1) determine bright X-ray source locations to an accuracy of 15 arcseconds; 2) study selected sources over the energy range 0.1-55 keV; and 3) continuously search the sky for X-ray novae, flares, and other transient phenomena.

Tenma carried GSFC detectors which had an improved energy resolution (by a factor of 2) compared to proportional counters and performed the first sensitive measurements of the iron spectral region for many astronomical objects.

India's first dedicated astronomy satellite, scheduled for launch on board the PSLV in mid 2010,[23] Astrosat will monitor the X-ray sky for new transients, among other scientific focuses.