arXiv subjects

V. M. Kaspi

Publications and source records attributed to V. M. Kaspi.

At least 199 records · Page 11Linked to original sources

arXiv2002

Optical Identification of Multiple Faint X-ray Sources in the Globular Cluster NGC 6752: Evidence for Numerous Cataclysmic Variables

We report on the Chandra ACIS-S3 imaging observation of the globular cluster NGC 6752. We detect 6 X-ray sources within the 10.5" core radius and 13 more within the 115" half-mass radius down to a limiting luminosity of Lx approx 10^{30} erg/s for cluster sources. We reanalyze archival data from the Hubble Space Telescope and the Australia Telescope Compact Array and make 12 optical identifications and one radio identification. Based on X-ray and optical properties of the identifications, we find 10 likely cataclysmic variables (CVs), 1-3 likely RS CVn or BY Dra systems, and 1 or 2 possible background objects. Of the 7 sources for which no optical identifications were made, we expect that ~2-4 are background objects and that the rest are either CVs or some or all of the five millisecond pulsars whose radio positions are not yet accurately known. These and other Chandra results on globular clusters indicate that the dozens of CVs per cluster expected by theoretical arguments are being found. The findings to date also suggest that the ratio of CVs to other types of X-ray sources is remarkably similar in clusters of very different structural parameters.

astro-ph↗

arXiv2002

Constraining the Birth Events of Neutron Stars

The prescient remark by Baade and Zwicky that supernovae beget neutron stars did little to prepare us for the remarkable variety of observational manifestations such objects display. Indeed, during the first thirty years of the empirical study of neutron stars, only a handful were found to be associated with the remnants of exploded stars. But recent X-ray and radio observations have gone a long way toward justifying the theoretical link between supernovae and neutron stars, and have revealed the wide range of properties with which newborn compact remnants are endowed. We review here our current state of knowledge regarding neutron star-supernova remnant associations, pointing out the pitfalls and the promise which such links hold. We discuss work on the ranges of neutron star velocities, initial spin periods, and magnetic field strengths, as well as on the prevalence of pulsar wind nebulae. The slots in neutron star demography held by AXPs, SGRs, radio-quiet neutron stars, and other denizens of the zoo are considered. We also present an attempt at a comprehensive census of neutron star-remnant associations and discuss the selection effects militating against finding more such relationships. We conclude that there is no pressing need to invoke large black hole or silent neutron star populations, and that the years ahead hold great promise for producing a more complete understanding of neutron star birth parameters and their subsequent evolution.

astro-ph↗

arXiv2001

Chandra imaging of the X-ray nebula powered by pulsar B1509-58

We present observations with the Chandra X-ray Observatory of the pulsar wind nebula (PWN) powered by the energetic young pulsar B1509-58. These data confirm the complicated morphology of the system indicated by previous observations, and in addition reveal several new components to the nebula. The overall PWN shows a clear symmetry axis oriented at a position angle 150 degrees (N through E), which we argue corresponds to the pulsar spin axis. We show that a previously identified radio feature matches well with the overall extent of the X-ray PWN, and propose the former as the long-sought radio nebula powered by the pulsar. We further identify a bright collimated feature, at least 4' long, lying along the nebula's main symmetry axis; we interpret this feature as a physical outflow from the pulsar, and infer a velocity for this jet >0.2c. The lack of any observed counter-jet implies that the pulsar spin axis is inclined at approx 30 deg to the line-of-sight, contrary to previous estimates made from lower-resolution data. We also identify a variety of compact features close to the pulsar. A pair of semi-circular X-ray arcs lie 17 and 30 arcsec to the north of the pulsar; the latter arc shows a highly-polarized radio counterpart. We show that these features can be interpreted as ion-compression wisps in a particle-dominated equatorial flow, and use their properties to infer a ratio of electromagnetic to particle energy in pairs at the wind shock sigma approx 0.005, similar to that seen in the Crab Nebula. We further identify several compact knots seen very close to the pulsar; we use these to infer sigma < 0.003 at a separation from the pulsar of 0.1 pc.

astro-ph↗

arXiv2001

Young Pulsars from the Parkes Multibeam Pulsar Survey and their Associations

The Parkes multibeam pulsar survey is covering a 10deg-wide strip of the southern Galactic plane from l=260deg to l=50deg. It utilizes a 13-beam receiver operating in the 20-cm band on the Parkes 64-m radio telescope and is much more sensitive than any previous large-scale survey. Most of the 608 pulsars discovered so far are relatively distant and many are young, with 37 having a characteristic age of less than 10^5 years. At least one of these is associated with a supernova remnant and four other probable associations are suggested. Several multibeam pulsars have high values of the parameter Edot/d^2 and are within the position error contours of unidentified EGRET gamma-ray sources. These possible associations will be tested with the advent of new gamma-ray telescopes.

astro-ph↗

arXiv2001

X-ray Detection of PSR 1757-24 and its Nebular Tail

We report the first X-ray detection of the radio pulsar PSR B1757-24 using the Chandra X-ray Observatory. The image reveals point-source emission at the pulsar position, consistent with being magnetospheric emission from the pulsar. In addition, we detect a faint tail extending nearly 20" east of the pulsar, in the same direction and with comparable morphology to the pulsar's well-studied radio tail. The X-ray tail is unlikely to be emission left behind following the passage of the pulsar, but rather is probably from synchrotron-emitting pulsar wind particles having flow velocity ~7000 km/s. Assuming the point-source X-ray emission is magnetospheric, the observed X-ray tail represents only ~0.01% of the pulsar's spin-down luminosity, significantly lower than the analogous efficiencies of most known X-ray nebulae surrounding rotation-powered pulsars.

astro-ph↗

arXiv2001

The Pulsar Wind Nebula of G11.2-0.3

We present high-resolution radio and X-ray studies of the composite supernova remnant G11.2-0.3. Using archival VLA data, we perform radio spectral tomography to measure for the first time the spectrum of the shell and plerion separately. We compare the radio morphology of each component to that observed in the hard and soft Chandra X-ray images. We measure the X-ray spectra of the shell and the emission in the interior and discuss the hypothesis that soft X-ray emission interior to the shell is the result of the expanding pulsar wind shocking with the supernova ejecta. We also see evidence for spatial variability in the hard X-ray emission near the pulsar, which we discuss in terms of ion mediated relativistic shocks.

astro-ph↗

arXiv2001

15 Years Going Steady - Timing the Magnetar 1E 1841-045

We report on a long-term monitoring campaign of 1E 1841-045, the 12-s anomalous X-ray pulsar and magnetar candidate at the center of the supernova remnant Kes 73. We have obtained approximately monthly observations of the pulsar with the Rossi X-ray Timing Explorer spanning over two years, during which time 1E 1841-045 is found to be rotating with sufficient stability to derive a phase-connected timing solution. A linear ephemeris is consistent with observations of the pulse period made over the last 15 yrs with the Ginga, ASCA, XTE, & SAX observatories. Phase residuals suggest the presence of "timing noise", as is typically observed from young radio pulsars. These results confirm a rapid, constant spin-down for the pulsar, which continues to maintain a steady flux; this is inconsistent with most accretion scenarios.

astro-ph↗

arXiv2001

Chandra observations of PSR B1509-58 and Supernova Remnant G320.4-1.2

The young and energetic pulsar B1509-58 powers a bright X-ray synchrotron nebula, embedded in the unusual supernova remnant G320.4-1.2. We present observations of this system with the Chandra X-ray Observatory, which show a spectacularly complicated source. The nebula is dominated by a bright collimated feature which we interpret as a relativistic jet directed along the pulsar spin axis. Several compact knots can be seen in the immediate vicinity of the pulsar. While many of these features are similar to those seen around the Crab pulsar, the nebula surrounding PSR B1509-58 shows important differences which are possibly a result of the the latter's low nebular magnetic field and low density environment.

astro-ph↗

arXiv2001

X-ray Detection of Pulsar PSR B1757-24 and its Nebular Tail

We report the first X-ray detection of the radio pulsar PSR B1757-24 using the Chandra X-ray Observatory. We detect point-source emission at the pulsar position plus a faint tail extending nearly 20" east of the pulsar, in the same direction and with comparable morphology to the radio tail. Assuming the point-source X-ray emission is magnetospheric, the observed X-ray tail represents only ~0.01% of the pulsar's spin-down luminosity. This is significantly lower than the analogous efficiencies of most known X-ray nebulae surrounding rotation-powered pulsars. Assuming a non-thermal spectrum for the tail photons, we show that the tail is unlikely to be emission left behind following the passage of the pulsar, but rather is probably from synchrotron-emitting pulsar wind particles having flow velocity ~7000 km/s. We also show that there must be a significant break in the tail synchrotron spectrum between the radio and X-ray bands that is intrinsic to the particle spectrum. No emission is detected from the shell supernova remnant G5.4-1.2. The upper limits on remnant emission are unconstraining.

astro-ph↗

arXiv2001

A Sensitive Targeted Search Campaign at Parkes to Find Young Radio Pulsars at 20 cm

We describe a sensitive targeted search campaign at Parkes to find faint young radio pulsars using the center beam of the 20-cm multibeam receiver. The high frequency of the receiver mitigates scattering effects which can dominate profiles of distant pulsars at low frequencies and prevent detection. The targets included several composite supernova remnants (SNRs), two fast X-ray pulsars, long-period anomalous X-ray pulsars, and a soft gamma repeater. The sensitivity limits in this search are significantly better than those previously reported for these objects. We have discovered three new radio pulsars, two of which are not associated with the target objects. The third pulsar, PSR J1713-3949, is possibly associated with SNR G347.3-0.5; the estimated ages and distances of the two objects are consistent, but a more significant positional coincidence must be established with the central X-ray source in the SNR through pulsar timing to confirm or refute the association.

astro-ph↗

arXiv2001

SNR G292.2-0.5: A Radio Supernova Remnant Associated with the Young Pulsar J1119-6127

We report on Australia Telescope Compact Array observations in the direction of the young high-magnetic-field radio pulsar PSR J1119-6127. In the resulting images we identify a non-thermal radio shell of diameter 15 arcminutes, which we classify as a previously uncataloged young supernova remnant (SNR), G292.2-0.5. This SNR is positionally coincident with PSR J1119-6127, and we conclude that the two objects are physically associated. No radio emission is detected from any pulsar wind nebula (PWN) associated with the pulsar; our observed upper limits are consistent with the expectation that high-magnetic-field pulsars produce radio nebulae which fade rapidly. This system suggests a possible explanation for the lack of associated radio pulsars and/or PWNe in many SNRs.

astro-ph↗

arXiv2001

RXTE Monitoring of the Anomalous X-ray Pulsar 1E 1048.1-5937

We report on long-term monitoring of the anomalous X-ray pulsar 1E 1048.1-5937 using the Rossi X-ray Timing Explorer. This pulsar's timing behavior is different from that of other AXPs. In particular, the pulsar shows significant deviations from simple spin-down such that phase-coherent timing has not been possible over time spans longer than a few months. We show that in spite of the rotational irregularities, the pulsar exhibits neither pulse profile changes nor large pulsed flux variations. We discuss the implications of our results for AXP models. We suggest that 1E 1048.1-5937 may be a transition object between the soft gamma-ray repeater and AXP populations, and the AXP most likely to one day undergo an outburst.

astro-ph↗

arXiv2001

Chandra Observations of G11.2-0.3: Implications for Pulsar Ages

We present Chandra X-ray Observatory imaging observations of the young Galactic supernova remnant G11.2-0.3. The image shows that the previously known young 65-ms X-ray pulsar is at position (J2000) RA 18h 11m 29.22s, DEC -19o 25' 27.''6, with 1 sigma error radius 0.''6. This is within 8'' of the geometric center of the shell. This provides strong confirming evidence that the system is younger, by a factor of ~12, than the characteristic age of the pulsar. The age discrepancy suggests that pulsar characteristic ages can be poor age estimators for young pulsars. Assuming conventional spin down with constant magnetic field and braking index, the most likely explanation for the age discrepancy in G11.2-0.3 is that the pulsar was born with a spin period of ~62 ms. The Chandra image also reveals, for the first time, the morphology of the pulsar wind nebula. The elongated hard-X-ray structure can be interpreted as either a jet or a Crab-like torus seen edge on. This adds to the growing list of highly aspherical pulsar wind nebulae and argues that such structures are common around young pulsars.

astro-ph↗

arXiv2001

PSR J1016-5857: a young radio pulsar with possible supernova remnant, X-ray, and gamma-ray associations

We report the discovery of a young and energetic pulsar in the Parkes multibeam survey of the Galactic plane. PSR J1016-5857 has a rotation period of 107 ms and period derivative of 8e-14, implying a characteristic age of 21 kyr and spin-down luminosity of 2.6e36 erg/s. The pulsar is located just outside, and possibly interacting with, the shell supernova remnant G284.3-1.8. Archival X-ray data show a source near the pulsar position which is consistent with emission from a pulsar wind nebula. The pulsar is also located inside the error box of the unidentified EGRET source 3EG J1013-5915, for which it represents a plausible counterpart.

astro-ph↗

arXiv2001

The Parkes Multibeam Pulsar Survey: I. Observing and Data Analysis Systems, Discovery and Timing of 100 Pulsars

The Parkes multibeam pulsar survey is a sensitive survey of a strip along the Galactic plane with |b|<5 deg and l=260 deg to l=50 deg. It uses a 13-beam receiver on the 64-m Parkes radio telescope, receiving two polarisations per beam over a 288 MHz bandwidth centred on 1374 MHz. Receiver and data acquisition systems are described in some detail. For pulsar periods in the range 0.1 - 2 s and dispersion measures of less than 300 cm^{-3} pc, the nominal limiting flux density of the survey is about 0.2 mJy. At shorter or longer periods or higher dispersions, the sensitivity is reduced. Timing observations are carried out for pulsars discovered in the survey for 12 - 18 months after confirmation to obtain accurate positions, spin parameters, dispersion measures, pulse shapes and mean flux densities. The survey is proving to be extremely successful, with more than 600 pulsars discovered so far. We expect that, when complete, this one survey will come close to finding as many pulsars as all previous pulsar surveys put together. The newly discovered pulsars tend to be young, distant and of high radio luminosity. They will form a valuable sample for studies of pulsar emission properties, the Galactic distribution and evolution of pulsars, and as probes of interstellar medium properties. This paper reports the timing and pulse shape parameters for the first 100 pulsars timed at Parkes, including three pulsars with periods of less than 100 ms which are members of binary systems. These results are briefly compared with the parameters of the previously known population.

astro-ph↗

arXiv2001

Polarization Properties of Nine Southern Radio Pulsars

We report on radio polarimetry observations for nine southern pulsars. Six of the nine in the sample are young, with characteristic ages under 100 kyr and high spin-down luminosities. All six show a significant degree of linear polarization. We also confirm a previously noticed trend in which the degree of linear polarization increases with spin-down luminosity. Where possible we have used the rotating-vector model of the pulsar emission geometry to fit the observed position angle data. Our fit for PSR J1513-5908 (B1509-58) in particular is useful for directly testing the magnetospheric model of Melatos (1997) in combination with further timing observations. For this pulsar we find that a magnetic inclination angle greater than or equal to 60 degrees is excluded at the 3-sigma level, and that the geometry suggested by the morphology of an apparent bipolar X-ray outflow is marginally inconsistent with the Melatos model. We also report on polarimetry of three older pulsars: PSR J0045-7319, PSR J1627-4845, and PSR J1316-6232 (whose discovery we also report). Of these, only PSR J0045-7319 shows significant polarization.

astro-ph↗

arXiv2001

PSR J1740-3052 - a pulsar with a massive companion

We report on the discovery of a binary pulsar, PSR J1740-3052, during the Parkes multibeam survey. Timing observations of the 570-ms pulsar at Jodrell Bank and Parkes show that it is young, with a characteristic age of 350 kyr, and is in a 231-day, highly eccentric orbit with a companion whose mass exceeds 11 M_sun. An accurate position for the pulsar was obtained using the Australia Telescope Compact Array. Near-infrared 2.2-um observations make with the telescopes at the Siding Spring observatory reveal a late-type star coincident with the pulsar position. However, we do not believe that this star is the pulsar's companion, because a typical star of this spectral type and required mass would extend beyond the pulsar's orbit. Furthermore, the measured advance of periastron of the pulsar suggests a more compact companion, for example, a main-sequence star with radius only a few times that of the sun. Such a companion is also more consistent with the small dispersion measure variations seen near periastron. Although we cannot conclusively rule out a black-hole companion, we believe the companion is probably an early B star, making the system similar to the binary PSR J0045-7319.

astro-ph↗

arXiv2001

X-ray Observations of the New Pulsar--Supernova Remnant System PSR J1119-6127 and SNR G292.2-0.5

PSR J1119-6127 is a recently discovered 1700-year-old radio pulsar that has a very high inferred surface dipolar magnetic field. We present a detailed analysis of a pointed ASCA observation and archival ROSAT data of J1119-6127 and its surroundings. Both data sets reveal extended emission coincident with the newly-discovered radio supernova remnant G292.2-0.5, reported in a companion paper by Crawford et al. (astro-ph/0012287).. A hard point source, offset ~1.5' from the position of the radio pulsar, is seen with the ASCA GIS. No pulsations are detected at the radio period with a pulsed fraction upper limit of 61% (95% confidence). The limited statistics prevent a detailed spectral analysis, although a power-law model with photon index (Gamma=~1-2) describes the data well. Both the spectral model and derived X-ray luminosity are consistent with those measured for other young radio pulsars, although the spatial offset renders an identification of the source as the X-ray counterpart of the pulsar uncertain.

astro-ph↗