arXiv subjects

W. Becker

Publications and source records attributed to W. Becker.

At least 55 records · Page 3Linked to original sources

arXiv2007

Radio and X-ray nebulae associated with PSR J1509-5850

We have discovered a long radio trail at 843 MHz which is apparently associated with middle age pulsar PSR J1509-5850. The radio trail has a length of ~7 arcmin. In X-rays, Chandra observations of PSR J1509-5850 reveal an associated X-ray trail which extends in the same orientation as the radio trail. Moreover, two clumpy structures are observed along the radio trail. The larger one is proposed to be the supernova remnant (SNR) candidate MSC 319.9-0.7. Faint X-ray enhancement at the position of the SNR candidate is found in the Chandra data.

astro-ph↗

arXiv2007

A search for X-ray counterparts of the millisecond pulsars in the globular cluster M28 (NGC 6626)

A recent radio survey of globular clusters has increased the number of millisecond pulsars drastically. M28 is now the globular cluster with the third largest population of known pulsars, after Terzan 5 and 47 Tuc. This prompted us to revisit the archival Chandra data on M28 to evaluate whether the newly discovered millisecond pulsars find a counterpart among the various X-ray sources detected in M28 previously. The radio position of PSR J1824-2452H is found to be in agreement with the position of CXC 182431-245217 while some faint unresolved X-ray emission near to the center of M28 is found to be coincident with the millisecond pulsars PSR J1824-2452G, J1824-2452J, J1824-2452I and J1824-2452E.

astro-ph↗

arXiv2007

Nonsequential double ionization: a comparison of classical simulations and $S$-matrix results

In a fully classical simulation, we investigate the recollision mechanism of non-sequential double ionization (NSDI) and its manifestation in the end-of-pulse electron momentum distributions. We compare two different electron-electron potentials: a soft-core Coulombic potential and a Yukawa potential. We also implement the strong-field approximation (SFA), which is commonly made in quantum-mechanical $S$-matrix calculations, in our classical simulations and study its consequences. We find that, regardless of the form of the e-e potential, the SFA modifies the momentum distributions and recollision dynamics significantly, but more so for the long-range than for the short-range e-e interaction. Surprisingly, our classical results, especially those obtained with the Yukawa potential under the SFA, agree well with the results from the $S$-matrix calculations with a contact e-e interaction. This implies that the recollision dynamics initiated by a quantum tunneling process and a purely classical process do not deviate much from each other. Furthermore, our classical predictions of travel times are consistent with the results from the simple-man model, and the most probable thermalization time is found to be within 0.15 and 0.25 laser periods.

physics.atom-ph↗

arXiv2007

X-ray emission properties of the old pulsar PSR B2224+65

Using archival Chandra data we studied the X-ray emission properties of PSR B2224+65 and its environment. Albeit limited by photon statistics the spectral analysis suggests that the bulk of the emission from PSR B2224+65 is non-thermal. Fitting a power-law to the observed energy spectrum yields a photon index of $Γ=1.58^{+0.43}_{-0.33}$. The possible origin of the non-thermal pulsar emission is discussed in the context of the outer-gap model. We did not find any evidence for a compact nebula around PSR B2224+65 though the Chandra data reveal the existence of an extended feature which appears to be associated with PSR B2224+65. It extends from the pulsar position about 2 arcmin to the north-west. Its orientation deviates by $\sim118^{\circ}$ from the pulsar's proper motion direction. Investigating its energy spectrum shows that the emission of this extended feature is much harder than that of the pulsar itself and is non-thermal in nature.

astro-ph↗

arXiv2007

On the Present and Future of Pulsar Astronomy

To face recent observational results obtained in multi-wavelength studies from neutron stars and pulsars with the various theoretical models and to discuss on future perspectives on neutron star astronomy we organized a Joined Discussion (JD02) during the XXVI IAU General Assembly which took place in 2006 August in Prague. More than 150 scientists took actively part in this Joint Discussion. Fourteen invited review talks were presented to view the present and future of pulsar astronomy. Fifty three poster contributions displayed new and exciting results. In this summary we give an overview of the invited review talks and contributed posters. The review talks are subject of review articles which will be published elsewhere. More information on this will be available at http://www.mpe.mpg.de/IAU_JD02 in the near future.

astro-ph↗

arXiv2007

INTEGRAL observations of PSR B0540-69

PSR B0540-69 is often called an extragalactic 'twin' of the Crab pulsar in the Large Magellanic Cloud. The pulsar is embedded in a synchrotron nebula in the center of SNR 0540-69.3. It was discovered with the Einstein satellite with P~50 ms, spin-down age of ~1500 years and a spin-down luminosity of ~10^38 erg/s. It has since been detected with all major X-ray telescopes. At X-ray energies up to ~40 keV the latest observations were reported from RXTE and from INTEGRAL (only spectrum) in the context of a survey of the LMC. Optical pulsed emission and faint radio emission have also been found from PSR B0540-69. The INTEGRAL analysis presented here is based on observations of the LMC obtained in Jan. 2003 and Jan. 2004 with a total exposure of ~1.5 Ms. In the mosaic maps from the total exposure (JEM-X and IBIS/ISGRI) a source at the location of PSR B0540-69 is clearly visible up to energies of ~200 keV. After barycentric correction and determination of the pulsar phases, based on theephemeris available from contemporaneous RXTE data, the lightcurves show the characteristic shape of a broad pulse up into the 40-100 keV band. At higher energies no significant pulsation is detectable. We derive the spectrum of the total source from the ISGRI data. The photon spectrum can be fitted with a power law of index 2.22, which is compatible with the result found by Goetz et al., 2006.

astro-ph↗

arXiv2006

A Fast-Moving Central Compact Object in Puppis-A

Utilizing two Chandra High Resolution Camera (HRC-I) observations with an epoch separation of somewhat more than five years, we have measured the proper motion of the central compact object, RX J0822-4300, in the supernova remnant Puppis-A for the first time. The position of RX J0822-4300 is found to be different by 0.574 +/- 0.184 arcsec, implying a proper motion of 107.49 +/- 34.46 mas/yr with a position angle of 241 degree +/- 24 degree. For a distance of 2.2 kpc, this proper motion is equivalent to a recoil velocity of 1121.79 +/- 359.60 km/s. Both the magnitude and the direction of the proper motion are in agreement with the birth place of RX J0822-4300 being near to the optical expansion center of the supernova remnant. Although the positional shift inferred from the current data is significant at a ~ 3 sigma level only, one or more future HRC-I observations can obtain a much larger positional separation and further constrain the measurement.

astro-ph↗

arXiv2006

Discovery of an X-ray Nebula associated with PSR J2124-3358

We report the discovery of an X-ray nebula associated with the nearby millisecond pulsar PSR J2124-3358. This is the first time that extended emission from a solitary millisecond pulsar is detected. The emission extends from the pulsar to the northwest by ~ 0.5 arcmin. The spectrum of the nebular emission can be modeled by a power law spectrum with photon index of 2.2 +/-0.4. This is inline with the emission being originated from accelerated particles in the post shock flow.

astro-ph↗

arXiv2006

XMM-Newton Observations of PSR B1957+20

We report on XMM-Newton observations of the Black Widow pulsar, PSR B1957+20. The pulsar's X-ray emission is non-thermal and best modeled with a single powerlaw spectrum of photon index 2.03^{+0.51}_{-0.36}. No coherent X-ray pulsations at the pulsar's spin-period could be detected, though a strong binary-phase dependence of the X-ray flux is observed for the first time. The data suggest that the majority of the pulsar's X-radiation is emitted from a small part of the binary orbit only. We identified this part as being near to where the radio eclipse takes place. This could mean that the X-rays from PSR B1957+20 are mostly due to intra-shock emission which is strongest when the pulsar wind interacts with the ablated material from the companion star.

astro-ph↗

arXiv2006

Probing the Proper Motion of the Central Compact Object in Puppis-A with the Chandra High Resolution Camera

By making use of the sub-arcsecond angular resolution of the High Resolution Camera (HRC-I) aboard the Chandra X-ray satellite we have examined the central compact object RX J0822-4300, in the supernova remnant Puppis-A for a possible proper motion. Using data which span an epoch of 1952 days we found the position of RX J0822-4300, different by $0.574\pm0.184$ arcsec, implying a proper motion of $μ=107.49\pm34.46$ mas/yr. For a distance of 2.2 kpc, this proper motion is equivalent to a recoil velocity of $1121.79\pm 359.60$ km/s. The position angle is found to be $241^\circ \pm 24^\circ$. Since both the magnitude and direction of the proper motion are in agreement with the birth place of RX J0822-4300, being near to the optical expansion center of the supernova remnant, the result presented in this letter is a promising indication of a fast moving compact object in a supernova remnant. Although the positional shift inferred from the current data is significant at a $\sim3σ$ level only, one or more future HRC-I observations can obtain a much larger positional separation and further constrain the measurement.

astro-ph↗

arXiv2006

Exploring the Central Compact Object in the RX J0852.0-4622 Supernova Remnant with XMM-Newton

The properties of the presumably young galactic supernova remnant (SNR) RX J0852.0-4622, discovered by ROSAT, are still uncertain. The data concerning the distance to the SNR, its age, and the presence of a compact remnant remain controversial. We report the results of several XMM-Newton observations of CXOU J085201.4-461753, the central compact source in RX J0852.0-4622. The currently prefered interpretation of CXOU J085201.4-461753 being a neutron star is in line with our analysis. The Chandra candidate pulsation periods are not confirmed; actually no period was found down to a 3-sigma upper limit for any pulsed fraction. The spectrum of CXOU J085201.4-461753 is best described by either a two blackbody spectrum or a single blackbody spectrum with a high energy power law tail. The two blackbody temperatures of 4 MK and 6.6 MK along with the small size of the emitting regions with radii of 0.36 and 0.06 km invalidate the interpretation that the thermal radiation is cooling emission from the entire neutron star surface. The double blackbody model suggests emission from the neutron star's hot polar regions. No X-ray lines, including the emission feature previously claimed to be present in Chandra data, were found.

astro-ph↗

arXiv2006

X-ray observations of RX J0822-4300 and Puppis-A

Based on observations with the X-ray observatories Chandra and XMM-Newton we present results from a detailed spectro-imaging and timing analysis of the central compact X-ray source RX J0822-4300 in the supernova remnant Puppis-A. The superior angular resolution of Chandra allows for the first time to pinpoint the point source nature of this object down to $0.59\pm0.01$ arcsec (FWHM) and to determine its position:{RA=$08^{\rm h}21^{\rm m}57.40^{\rm s}$, Dec=$-43^{\circ}00^{'}16.69^{''}$ (J2000)} with sub-arcsecond accuracy. Spectral fits based on Chandra and XMM-Newton data provide a tight constraint on the emission properties of RX J0822-4300. Most of its X-ray emission seems to be of thermal origin. A model spectrum consisting of two blackbody components with $T_{1}\simeq 2.6\times10^{6}$ K, $T_{2}\simeq 5.0\times10^{6}$ K and $R_{1}\simeq 3.3$ km, $R_2 \simeq 0.75$ km for the blackbody temperatures and the size of the projected emitting regions, respectively, provides the best model description of its spectrum. A search for X-ray pulsations from RX J0822-4300, revealed an interesting periodicity candidate which, if confirmed, does not support a scenario of steady spin-down.

astro-ph↗

arXiv2006

Searches for diffuse X-ray emission around millisecond pulsars: An X-ray nebula associated with PSR J2124-3358

We report on diffuse X-ray emission associated with the nearby solitary millisecond pulsar PSR J2124-3358 detected with XMM-Newton and Chandra. The emission extends from the pulsar to the northwest by ~0.5 arcmin. The spectrum of the nebular emission can be modeled with a power-law of photon index $2.2\pm0.4$, in line with the emission originating from accelerated particles in the post shock flow. For PSR J0437-4715, PSR J0030+0451 and PSR J1024-0719, which all have spin parameters comparable to that of PSR J2124-3358, no diffuse emission is detected down to a 3-sigma limiting flux of $4-7\times10^{-15}$ ergs s$^{-1}$ cm$^{-2}$.

astro-ph↗

arXiv2005

Strong-field approximation for intense-laser atom processes: the choice of gauge

The strong-field approximation can be and has been applied in both length gauge and velocity gauge with quantitatively conflicting answers. For ionization of negative ions with a ground state of odd parity, the predictions of the two gauges differ qualitatively: in the envelope of the angular-resolved energy spectrum, dips in one gauge correspond to humps in the other. We show that the length-gauge SFA matches the exact numerical solution of the time-dependent Schrödinger equation.

quant-ph↗

arXiv2005

Attosecond double-slit experiment

A new scheme for a double-slit experiment in the time domain is presented. Phase-stabilized few-cycle laser pulses open one to two windows (``slits'') of attosecond duration for photoionization. Fringes in the angle-resolved energy spectrum of varying visibility depending on the degree of which-way information are observed. A situation in which one and the same electron encounters a single and a double slit at the same time is discussed. The investigation of the fringes makes possible interferometry on the attosecond time scale. The number of visible fringes, for example, indicates that the slits are extended over about 500as.

quant-ph↗

arXiv2004

XMM-Newton observations of the supernova remnant RX J0852.0-4622/GRO J0852-4642

RX J0852.0-4622 is a shell type supernova remnant with a power law spectrum in the south-eastern corner of the Vela supernova remnant. We report XMM-Newton observations of three fields centered on the rim of the remnant and confirm the power law shape of the spectra with no prominent emission lines as previously obtained with ASCA. The emission line feature at ~4.1 keV indicated in the ASCA/SIS spectrum of the northern field is detected and found in the southern and western fields, as well, with a total significance of slightly more than 4 sigmas. The line position is improved and the feature is centered on 4.45 +/- 0.05 keV. We suggest this line feature to be emission from Ti and Sc. The measured X-ray flux is consistent with the Ti gamma-ray flux previously measured with COMPTEL. We discuss various physical processes which may lead to the creation of these lines, and we discuss the implications for the progenitor and the supernova type.

astro-ph↗

arXiv2004

Landau damping in thin films irradiated by a strong laser field

The rate of linear collisionless damping (Landau damping) in a classical electron gas confined to a heated ionized thin film is calculated. The general expression for the imaginary part of the dielectric tensor in terms of the parameters of the single-particle self-consistent electron potential is obtained. For the case of a deep rectangular well, it is explicitly calculated as a function of the electron temperature in the two limiting cases of specular and diffuse reflection of the electrons from the boundary of the self-consistent potential. For realistic experimental parameters, the contribution of Landau damping to the heating of the electron subsystem is estimated. It is shown that for films with a thickness below about 100 nm and for moderate laser intensities it may be comparable with or even dominate over electron-ion collisions and inner ionization.

physics.optics↗

arXiv2004

Precise Localization of the Soft Gamma Repeater SGR 1627-41 and the Anomalous X-ray Pulsar AXP 1E1841-045 with Chandra

We present precise localizations of AXP 1E1841-045 and SGR 1627-41 with Chandra. We obtained new infrared observations of SGR 1627-41 and reanalyzed archival observations of AXP 1E1841-045 in order to refine their positions and search for infrared counterparts. A faint source is detected inside the error circle of AXP 1E1841-045. In the case of SGR 1627-41, several sources are located within the error radius of the X-ray position and we discuss the likelihood of one of them being the counterpart. We compare the properties of our candidates to those of other known AXP and SGR counterparts. We find that the counterpart candidates for SGR 1627-41 and SGR 1806-20 would have to be intrinsically much brighter than AXPs to have detectable counterparts with the observational limits currently available for these sources. To confirm the reported counterpart of SGR 1806-20, we obtained new IR observations during the July 2003 burst activation of the source. No brightening of the suggested counterpart is detected, implying that the counterpart of SGR 1806-20 remains yet to be identified.

astro-ph↗