Search results for "Pulsar"
showing 10 items of 209 documents
“Study of Pulsar Light Curves by Cluster Analysis”
1986
The distribution of the phase numbers, corresponding to the arrival times of the gamma-ray photons detected by the COS-B satellite from the directions of the Crab and Vela pulsars, is analyzed by a clustering technique with the aim to detect possible microstructures in the pulsed emission. The method is found to be promising especially in view of the future gamma-ray experiments where better photon counting statistics is expected.
The New X-Ray Pulsar J1802.7-2017 Observed by BeppoSAX
2004
We report on the serendipitous discovery of a new X-ray source, SAX J1802.7-2017, ~ 22' away from the bright X-ray source GX 9+l, during a BeppoSAX observation of the latter source on 2001 September 16-20.The source was outside the FOV of the BeppoSAX/ LECS. We have verified its presence in both the MECS2 and MECS3 images, which probably excludes that this was a ghost image of a source outside the MECS FOV. Moreover, we can be sure that the source was within the PDS FOV. because the source X-ray pulsations were detected also in the PDS data (see below). We searched for known X-ray sources in a circular region of 30' centered at GX 9+1 in the SIMBAD data base. We found no known sources with …
A newly discovered accreting pulsar in Terzan 5
2011
The 11 Hz accreting pulsar, IGR J17480-2446, was recently discovered in the globular cluster Terzan 5. The analisys of the Doppler shifts induced by the orbital motion reveals how the neutron star belongs to a ∼ 21.3 hr binary system with a companion star of 0.4-1.5 M. The X-ray pulsar spins up while accreting at an average rate of 1.48(2)×10−12 Hz s−1, in agreement with the accretion of disc matter angular momentum given the observed luminosity. From the presence of pulsations at different accretion rates we constrain the magnetic field to lie within ∼2×108 and ∼2×1010 G. From this estimate, the value of the spin period and of the observed spin-up rate, we associate this source with the st…
The FIGARO II experiment: a general outline of the mission and the principal scientific results
1992
The FIGARO II (French Italian Gamma-Ray Observatory) experiment has been launched successfully three times: in July 1986 from Milo (Trapani), in November 1988 from Charleville (Australia) and in July 1990 again from Milo. In the first flight the observational program was limited to the Crab pulsar PSR0531+21 only because of a telemetry failure: the high sensitivity of FIGARO II allowed an accurate study of the pulse shape as well as a phase-resolved spectroscopy. It was also possible to evaluate the dispersion measure of the Crab pulsar at the flight date from the time delay between gamma-ray and radio pulses. The major results of the second flight were a stringent upper limit to the low-en…
Harmonic Coupling of the Red Noise in X‐Ray Pulsars
1997
The power spectra of X-ray pulsars often show the presence of a red-noise component. This noise is produced by aperiodic variability believed to be associated with instabilities that seem to occur in accretion flows onto compact objects. In this paper we discuss how, independently of the details of the physical processes that generate these instabilities, a careful analysis of the power spectra can furnish some constraints on the distance from the stellar surface at which the sudden energy release associated with the instabilities occurs. In particular, any aperiodic variability coming from the accretion flow funneled toward the magnetic poles should be modulated at the pulsar spin period (…
A search for short-period pulsars
1985
On utilise le radiotelescopede Parkes pour rechercher des pulsars de courte periode a 1,4 GHz de frequence. On trouve quatre nouveaux pulsar radio
Binary evolution of PSR J1713+0747
2007
PSR J1713+0747 is a binary millisecond radio pulsar with a long orbital period (Porb ∼ 68 d) and a very low neutron star mass (M NS = 1.3 ± 0.2 M⊙). We simulate the evolution of this binary system with an accurate numerical code, which keeps into account both the evolution of the primary and of the whole binary system. We show that strong ejection of matter from the system is fundamental to obtain a mass at the end of the evolution that is within 1 - σ from the observed one, but propeller effects are almost negligible in such a system, where the accretion rate is always near to the Eddington limit. We show that there are indeed two mechanisms can account for the amount of mass loss from the…
JEM-X observations of the Be/X-ray binary EXO 2030+375
2003
We have used data from the Joint European Monitor (JEM-X) to perform an X-ray spectral and timing analysis of the 42-s transient pulsar EXO 2030+375 during an X-ray outburst. X-ray pulsations are clearly detected with an average pulse period of 41:66 +- 0:05 s and an average pulse fraction of 60%. The profile of the energy spectrum did not change appreciably throughout the X-ray outburst, although the source shows a slightly softer spectrum during periastron passage in the energy range 9–25 keV. The 5–25 keV X-ray luminosity changed by a factor of 2 throughout the observations, reaching a maximum value of 3x10^36 erg s^−1. These observations allowed us to verify the in-flight instrumental p…
Timing and spectral changes of the Be X-ray transient EXO 0531-6609.2 through high and low state
2004
We report on spectral and timing analysis of BeppoSAX data of the 13.6 s period transient X-ray pulsar EXO 0531-6609.2. Observations were carried out in March 1997 and October 1998, catching the source during a high and a low emission state, respectively. Correspondingly, the X-ray luminosity is found at a level of 4.2x10^37 erg/s and 1.5x10^36 erg/s in the two states. In the high state the X-ray emission in the energy range 1-100 keV is well fitted by an absorbed power-law with photon index Gamma ~1.7 plus a blackbody component with a characteristic temperature of ~3.5 keV. Moreover, we find an evidence of an iron emission at ~6.8 keV, typical feature in this class of sources but never rev…
Further evidence for the presence of a neutron star in 4U 2206+54. INTEGRAL and VLA observations
2005
The majority of High Mass X-ray Binaries (HMXBs) behave as X-ray pulsars, revealing that they contain a magnetised neutron star. Among the four HMXBs not showing pulsations, and that do not show the characteristics of accreting black holes, there is the unusual HMXB 4U 2206+54. Here we present contemporaneous high-energy and radio observations of this system conducted with INTEGRAL and the VLA in order to unveil its nature. The high-energy spectra show clear indications of the presence of an absorption feature at ~32 keV. This is the third high-energy observatory which reveals marginal evidence of this feature, giving strong support to the existence of a cyclotron resonance scattering featu…