AXP 1E 1547.0-5408 - a magnetar observed through the shields
January 8, 2013
1E 1547.0-5408 is one of only nine confirmed Anomalous X-ray Pulsars (AXP) - isolated, young neutron stars with unusually strong magnetic fields (1014G - 1015G). Together with Soft Gamma Repeaters they make up a class of celestial object known as magnetars. AXP 1E1547.0-5408 has exhibited a small number of outbursts over the past few years but at relatively weak levels. On 22 January 2009, extremely strong flaring activity of this source was detected by different satellites. The Anti-Coincidence Shield (ACS) of the INTEGRAL spectrometer SPI alone detected more than 200 bursts within a few hours. The upper panel of the image shows SPI ACS lightcurve (50 ms time bins during the most active period (Fig. 1 of Mereghetti et al., 2009, ApJL accepted, arXiv:0903.1974). The flux of the soft gamma ray photons produced by the source was so strong that it penetrated through the walls of the IBIS telescope and produced a strong signal in the ISGRI detector, sufficient to even saturate the telemetry flow for short intervals. The lower panel shows a comparison of the lightcurves of the strongest bursts from the source as seen by the SPI/ACS and ISGRI detectors (Savchenko et al., 2009, A&A submitted). Red solid and black dotted lines show the ISGRI lightcurves in, respectively, 20-60 keV and 60-200 keV energy bands. The blue dotted line shows the lightcurves of the same bursts detected by the SPI/ACS detector. The bright short hard spikes of the gamma-ray emission, which are, most probably, produced by the fractures of the crust of the neutron star with extremely strong magnetic field (2×1014 G) or by the reconnection of magnetic field lines, are followed by the softer "afterglows", which occasionally exhibit pulsations with the neutron star's spin period. This is a rare example of the situation when having the source outside the field of view of the IBIS telescope is an advantage, from the viewpoint of the data analysis. If the source would be inside the FoV, the absence of suppression of the signal by the walls of the telescope would lead to immediate telemetry saturation, so that even the "piece-wise" information about the evolution of the source spectrum would not be available. Besides these serendipitous bursts, INTEGRAL also obtained a lot of information about the source and bursts through a series of dedicated pointed observations from 25 January onwards. The analysis of these observations is ongoing. Date: 02 Apr 2009 Satellite: INTEGRAL Depicts: Lightcurves of extremely strong flaring activity Copyright: ESA/INTEGRAL, upper panel: Mereghetti et al.; lower panel: Savchenko et al.
Topics: Space, Star types, Astronomy, INTEGRAL, Neutron, Anomalous X-ray pulsar, Magnetar, Gamma-ray burst, Neutron star, Matter