5 research outputs found
Viscous timescale in high mass X-ray binaries
Context: Low mass X-ray binaries were found to have very low frequency breaks
in their power density spectra below which the power density spectra are nearly
in white noise structure and at higher frequencies they approximately follow
the law.
Aims: In 2005, Gilfanov and Arefiev studied X-ray variability of persistent
LMXBs in the Hz frequency range and
To determine whether high mass X-ray binary power density spectra have
similar properties and the findings for low mass X-ray binaries are also valid
for high mass binaries, we analyzed the time series of high mass X-ray binary
sources produced by All Sky Monitor of Rossi X-ray Timing Explorer.
Method: We obtained the power density spectra of the high mass X-ray binaries
using the cosine transform of autocorrelation function.
Results: We identified break frequencies for seven sources, namely OAO
1657-415, SS 433, Vela X-1, SMC X-1, 4U 1700-377, GX 301-2, and LMC X-1. The
normalized break frequencies with respect to the orbital frequency
() for sources OAO 1657-415, SS 433, SMC X-1 and LMC X-1
are consistent with those of Roche lobe overflow systems. The other high mass
X-ray binary systems, Vela X-1, GX 301-2, and 4U 1700-377, however, have larger
break frequency ratios, , which are indicative of short
viscous times. These are all wind-accreting sources and the stellar winds in
the systems allow the formation of only short radius discs.
Consequently, we qualitatively distinguished the Roche lobe overflow binaries
from the wind accreting system by comparing their normalized break frequencies.Comment: 9 pages, 5 figures, accepted by A&
An Anti-Glitch in a Magnetar
Magnetars are neutron stars showing dramatic X-ray and soft -ray
outbursting behaviour that is thought to be powered by intense internal
magnetic fields. Like conventional young neutron stars in the form of radio
pulsars, magnetars exhibit "glitches" during which angular momentum is believed
to be transferred between the solid outer crust and the superfluid component of
the inner crust. Hitherto, the several hundred observed glitches in radio
pulsars and magnetars have involved a sudden spin-up of the star, due
presumably to the interior superfluid rotating faster than the crust. Here we
report on X-ray timing observations of the magnetar 1E 2259+586 which we show
exhibited a clear "anti-glitch" -- a sudden spin down. We show that this event,
like some previous magnetar spin-up glitches, was accompanied by multiple X-ray
radiative changes and a significant spin-down rate change. This event, if of
origin internal to the star, is unpredicted in models of neutron star spin-down
and is suggestive of differential rotation in the neutron star, further
supporting the need for a rethinking of glitch theory for all neutron stars
Observations of the magnetars 4U 0142+61 and 1E 2259+586 with the MAGIC telescopes (Research Note)
Context. Magnetars are an extreme, highly magnetized class of isolated neutron stars whose large X-ray luminosity is believed to be driven by their high magnetic field. Aims. We study for the first time the possible very high energy gamma-ray emission above 100 GeV from magnetars, observing the sources 4U 0142+ 61 and 1E 2259+586. Methods. We observed the two sources with atmospheric Cherenkov telescopes in the very high energy range (E > 100 GeV). 4U0142+61 was observed with the MAGIC I telescope in 2008 for about 25 h and 1E 2259+586 was observed with the MAGIC stereoscopic system in 2010 for about 14 h. The data were analyzed with the standard MAGIC analysis software. Results. Neither magnetar was detected. Upper limits to the differential and integral flux above 200 GeV were computed using the Rolke algorithm. We obtain integral upper limits to the flux of 1.52 x 10(-12) cm(-2) s(-1) and 2.7 x 10(-12) cm(-2) s(-1) with a confidence level of 95% for 4U 0142+ 61 and 1E 2259+586, respectively. The resulting differential upper limits are presented together with X-ray data and upper limits in the GeV energy range