The very soft X-ray transient H1853 + 60

Abstract

The increased sensitivity, sky coverage and spectral range of X-ray observatories have revealed a wide range of transient phenomena. The ‘classical’ X-ray transients flare rapidly, sometimes increasing by more than an order of magnitude in X-ray flux in a matter of days, and decay on time scales of months. Such transients are mainly located in the galactic plane, often associated with ‘steady’ X-ray sources¹. Some high galactic latitude transients, most of which are optically unidentified, have been observed to vary on time scales of tens of seconds to days^2,3. Most transient sources have been detected at energies greater than 1 keV; more recently, however, softer X-ray transients have been detected with observations on HEAO 1 and other satellites^4–9. We now report detection of a new soft X-ray transient, H1853 + 60, using datafrom the low energy detectors (LEDs) on the HEAO 1 A-2 experiment.