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Register a new userHard X-ray observations of PSR J1833-1034 and its associated pulsar wind nebula
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Authors
A. De Rosa
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PSR J1833-1034 and its associated Pulsar Wind Nebula (PWN) has been investigated in depth through X-ray observations ranging from 0.1 to 200 keV. The low energy X-ray data from Chandra reveal a complex morphology that is characterised by a bright central plerion, no thermal shell and an extended diffuse halo. The spectral emission from the central plerion softens with radial distance from the pulsar, with the spectral index ranging from $Gamma $ = 1.61 in the central region to $Gamma $ =2.36 at the edge of the PWN. At higher energy INTEGRAL detected the source in the 17--200 keV range. The data analysis clearly shows that the main contribution to the spectral emission in the hard X-ray energy range is originated from the PWN, while the pulsar is dominant above 200 keV. Recent HESS observations in the high energy gamma-ray domain show that PSR J1833-1034 is a bright TeV emitter, with a flux corresponding to $sim$2 per cent of the Crab in 1--10 TeV range. In addition the spectral shape in the TeV energy region matches well with that in the hard X-rays observed by INTEGRAL. Based on these findings, we conclude that the emission from the pulsar and its associated PWN can be described in a scenario where hard X-rays are produced through synchrotron light of electrons with Lorentz factor $gammasim10^{9}$ in a magnetic field of $sim$10 micro Gauss. In this hypothesis the TeV emission is due to Inverse Compton interaction of the cooled electrons off the Cosmic Microwave Background photons. Search for PSR J1833-1034 X-ray pulsed emission, via RXTE and Swift X-ray observations, resulted in an upper limit that is about 50 per cent.
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We present results from X-ray and radio observations of the recently discovered young Vela-like pulsar PSR J2021+3651, which is coincident with the EGRET gamma-ray source GeV 2020+3658. A 19.0-ks Chandra ACIS-S observation has revealed a ~20 x 10 pulsar wind nebula that is reminiscent of the equatorial tori seen around some young pulsars, along with thermal emission from an embedded point source (kT = 0.15 +/- 0.02 keV). We name the nebula G75.2+0.1. Its spectrum is well fit by an absorbed power-law model with photon index 1.7 +/- 0.3, hydrogen column density nH = 7.8 +/- 1.7 x 10^21 cm^-2, and an unabsorbed 0.3-10.0 keV flux of 1.9 +/- 0.3 x 10^-12 erg cm^-2 s^-1. We have spatially fit G75.2+0.1 with a model that assumes a toroidal morphology, and from this we infer that the torus is highly inclined 83 deg +/- 1 deg to the line of sight. A 20.8-ks Chandra observation in continuous-clocking mode reveals a possible pulse detection, with a pulsed fraction of ~37% and an H-test probability of occuring by chance of 1.2 x 10^-4. Timing observations with the Arecibo radio telescope spanning two years show that PSR J2021+3651 glitched sometime between MJDs 52616 and 52645 with parameters delta(v)/v = (2.587 +/- 0.002) x 10^-6 and delta(dot(v))/v = (6.2 +/- 0.3) x 10^-3, similar to those of the largest glitches observed in the Vela pulsar. PSR J2021+3651 is heavily scattered (T_sc = 17.7 ms +/- 0.9 ms at 1 GHz) and exhibits a significant amount of timing noise.
We present the results from timing observations with the GMRT of the young pulsar J1833-1034, in the galactic supernova remnant G21.5-0.9. We detect the presence of 4 glitches in this pulsar over a period of 5.5 years, making it one of a set of pulsars that show fairly frequent glitches. The glitch amplitudes, characterized by the fractional change of the rotational frequency, range from 1 times 10^-9 to 7 times 10^-9, with no evidence for any appreciable relaxation of the rotational frequency after the glitches. The fractional changes observed in the frequency derivative are of the order of 10-5 . We show conclusively that, in spite of having significant timing noise, the sudden irregularities like glitches detected in this pulsar can not be modeled as smooth timing noise. Our timing solution also provides a stable estimate of the second derivative of the pulsar spin-down model, and a plausible value for the braking index of 1.857, which, like the value for other such young pulsars, is much less than the canonical value of 3.0. PSR J1833-1034 appears to belong to a class of pulsars exhibiting fairly frequent occurrence of low amplitude glitches. This is further supported by an estimate of the glitch activity parameter, Ag = 1.53 times 10^-15 s^-2, which is found to be significantly lower than the trend of glitch activity versus characteristic age (or spin frequency derivative) that a majority of the glitching pulsars follow. We present evidence for a class of such young pulsars, including the Crab, where higher internal temperature of the neutron star could be responsible for the nature of the observed glitch activity.
We report on Australia Telescope Compact Array observations of the ~10^5 yr old pulsar PSR B0906-49. In an image containing only off-pulse emission, we find a weak, slightly extended source coincident with the pulsars position, which we argue is best interpreted as a pulsar wind nebula (PWN). A trail of emission extending behind the pulsar aligns with the major axis of the PWN, and implies that the pulsar is moving north-west with projected velocity ~60 km/s, consistent with its scintillation speed. The consequent density we infer for the pulsars environment is >2 cm^(-3), so that the PWN around PSR B0906-49 is confined mainly by the high density of its surroundings rather than by the pulsars velocity. Other properties of the system such as the PWNs low luminosity and apparent steep spectrum, and the pulsars large characteristic age, lead us to suggest that this nebula is substantially different from other radio PWNe, and may represent a transition between young pulsars with prominent radio PWNe and older pulsars for which no radio PWN has been detected. We recommend that further searches for radio PWNe should be made as here: at low frequencies and with the pulsed emission subtracted.
Previous observations of the middle-aged pulsar Geminga with XMM-Newton and Chandra have shown an unusual pulsar wind nebula (PWN), with a 20 long central (axial) tail directed opposite to the pulsars proper motion and two 2 long, bent lateral (outer) tails. Here we report on a deeper (78 ks) Chandra observation and a few additional XMM-Newton observations of the Geminga PWN. The new Chandra observation has shown that the axial tail, which includes up to three brighter blobs, extends at least 50 (i.e., 0.06 d_{250} pc) from the pulsar. It also allowed us to image the patchy outer tails and the emission in the immediate vicinity of the pulsar with high resolution. The PWN luminosity, L_{0.3-8 keV} ~ 3times 10^{29} d_{250}^2 erg/s, is lower than the pulsars magnetospheric luminosity by a factor of 10. The spectra of the PWN elements are rather hard (photon index ~ 1). Comparing the two Chandra images, we found evidence of PWN variability, including possible motion of the blobs along the axial tail. The X-ray PWN is the synchrotron radiation from relativistic particles of the pulsar wind; its morphology is connected with the supersonic motion of Geminga. We speculate that the outer tails are either (1) a sky projection of the limb-brightened boundary of a shell formed in the region of contact discontinuity, where the wind bulk flow is decelerated by shear instability, or (2) polar outflows from the pulsar bent by the ram pressure from the ISM. In the former case, the axial tail may be a jet emanating along the pulsars spin axis, perhaps aligned with the direction of motion. In the latter case, the axial tail may be the shocked pulsar wind collimated by the ram pressure.
In this work, we study the X-ray bow-shock nebula powered by the mature pulsar PSR B1929+10 using data from XMM-Newton, with an effective exposure of $sim$ 300 ks, offering the deepest investigation of this system thus far. We found the X-ray axial outflow extends as long as $sim$ 8 arc minute behind the proper motion direction, which is a factor of two longer than the result reported in the previous study. Furthermore, we found evidence of two faint lateral outflows extending laterally with respect to the proper motion. We also found indications of spectral hardening along the axial outflow, suggesting that certain acceleration processes might occur along this feature.
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