We present the 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 approx20 super('') x 10 super('') 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 sub(infinity) = 0.15 plus or minus 0.02 keV). We have named the nebula G75.2+0.1. Its spectrum is well fitted by an absorbed power-law model with a photon index of gamma = 1.7image, a hydrogen column density of N sub(H) = (7.8image) x 10 super(21) cm super(-2), and an unabsorbed 0.5-10.0 keV flux of (1.7 plus or minus 0.1) x 10 super(-12) ergs cm super(-2) s super(-1). We have spatially fitted G75.2+0.1 with a model that assumes a toroidal morphology, and from this we infer that the axis of the torus is highly inclined 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 approx65% and an H-test probability of occurring by chance of 8.9 x 10 super(-5). Timing observations with the Arecibo radio telescope spanning 2 yr show that PSR J2021+3651 glitched sometime between MJD 52,616 and 52,645 with parameters delta nu / nu = (2.587 plus or minus 0.002) x 10 super(-6) and deltaimage/image = (6.2 plus or minus 0.3) x 10 super(-3), similar to those of the largest glitches observed in the Vela pulsar. PSR J2021+3651 is heavily scattered ( tau sub(sc) = 17.7 plus or minus 0.9 ms at 1 GHz) and exhibits a significant amount of timing noise.
Using the Giant Metrewave Radio Telescope, we performed deep observations to search for radio pulsations in the directions of unidentified Fermi-Large Area Telescope gamma -ray sources. We report the ...discovery of an eclipsing blackwidow millisecond pulsar, PSR J1544+4937, identified with the uncataloged gamma -ray source Fermi J1544.2+4941. This 2.16 ms pulsar is in a 2.9 hr compact circular orbit with a very low mass companion (M sub(c) > 0.017M sub(middot in circle)). At 322 MHz this pulsar is found to be eclipsing for 13% of its orbit, whereas at 607 MHz the pulsar is detected throughout the low-frequency eclipse phase. Variations in the eclipse ingress phase are observed, indicating a clumpy and variable eclipsing medium. Moreover, additional short-duration absorption events are observed around the eclipse boundaries. Using the radio timing ephemeris we were able to detect gamma -ray pulsations from this pulsar, confirming it as the source powering the gamma -ray emission.
We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and ...Delta *g-ray millisecond pulsars (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind Delta *g-ray pulsation searches. They seem to be relatively normal, nearby (<=2 kpc) MSPs. These observations, in combination with the Fermi detection of Delta *g-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient Delta *g-ray producers. The Delta *g-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few GeV, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of ~1030-1031 erg s--1 are typical of the rare radio MSPs seen in X-rays.
In preparation for the Gamma-Ray Large Area Space Telescope (GLAST), we have compiled a sample of blazar candidates to increase the pool of well-studied active galactic nuclei from which GLAST ...counterparts will be drawn. Sources were selected with our figure-of-merit (FoM) ranking; thus, they have radio and X-ray properties very similar to the EGRET blazars. Spectroscopic confirmation of these candidates is in progress, and more than 70% of these objects have been identified as flat spectrum radio quasars and BL Lac objects. We present similar to 250 new optical blazar identifications based on McDonald Observatory spectroscopy, 224 with redshifts. Of these, 167 are in our FoM-selected set. To motivate the gamma -ray nature of these objects, we analyzed the current release of the EGRET data for possible point sources at their radio positions. We develop two distinct methods to combine multiple EGRET observations of a sky position into a single detection significance. We report a detection of the signal of the set of blazar candidates in the EGRET data at the >3 sigma level by both techniques. We predict that the majority of these blazar candidates will be found by GLAST because of its increased sensitivity, duty cycle, and resolving power.
We report on the Fermi Large Area Telescope's detection of γ-ray (> 100 mega-electron volts) pulsations from pulsar J1823-3021A in the globular cluster NGC 6624 with high significance (-~7σ). Its ...γ-ray luminosity, Lγ = (8.4 ± 1.6) ÷ 10³₄ ergs per second, is the highest observed for any millisecond pulsar (MSP) to date, and it accounts for most of the cluster emission. The nondetection of the cluster in the off-pulse phase implies that it contains < 32 γ-ray MSPs, not -100 as previously estimated. The γ-ray luminosity indicates that the unusually large rate of change of its period is caused by its intrinsic spin-down. This implies that J1823-3021A has the largest magnetic field and is the youngest MSP ever detected and that such anomalous objects might be forming at rates comparable to those of the more normal MSPs.
We report the detection of Delta *g-ray pulsations from the high-magnetic-field rotation-powered pulsar PSR J1119--6127 using data from the Fermi Large Area Telescope. The Delta *g-ray light curve of ...PSR J1119--6127 shows a single, wide peak offset from the radio peak by 0.43 ? 0.02 in phase. Spectral analysis suggests a power law of index 1.0 ? 0.3+0.4 -- 0.2 with an energy cutoff at 0.8 ? 0.2+2.0 -- 0.5 GeV. The first uncertainty is statistical and the second is systematic. We discuss the emission models of PSR J1119--6127 and demonstrate that despite the object's high surface magnetic field--near that of magnetars--the field strength and structure in the Delta *g-ray emitting zone are apparently similar to those of typical young pulsars. Additionally, we present upper limits on the Delta *g-ray pulsed emission for the magnetically active PSR J1846--0258 in the supernova remnant Kesteven 75 and two other energetic high-B pulsars, PSRs J1718--3718 and J1734--3333. We explore possible explanations for the non-detection of these three objects, including peculiarities in their emission geometry.
We report on Chandra ACIS imaging of the pulsar wind nebula (PWN) of the young Vela-like PSR B1706-44, which shows the now common pattern of an equatorial wind and polar jets. The structure is ...particularly rich, showing a relativistically boosted termination shock, jets with strong confinement, a surrounding radio/X-ray PWN, and evidence for a quasistatic "bubble nebula." The structures trace the pulsar spin geometry and illuminate its possible relation to SNR G343.1-2.3. We also obtain improved estimates of the pulsar flux and nebular spectrum, constraining the system age and energetics.
We announce the discovery of 1-100 GeV gamma-ray emission from the archetypal TeV pulsar wind nebula (PWN) HESS J1825--137 using 20 months of survey data from the Fermi-Large Area Telescope (LAT). ...The gamma-ray emission detected by the LAT is significantly spatially extended, with a best-fit rms extension of Delta *s = 056 ? 007 for an assumed Gaussian model. The 1-100 GeV LAT spectrum of this source is well described by a power law with a spectral index of 1.38 ? 0.12 ? 0.16 and an integral flux above 1 GeV of (6.50 ? 0.21 ? 3.90) X 10--9 cm--2 s--1. The first errors represent the statistical errors on the fit parameters, while the second ones are the systematic uncertainties. Detailed morphological and spectral analyses bring new constraints on the energetics and magnetic field of the PWN system. The spatial extent and hard spectrum of the GeV emission are consistent with the picture of an inverse Compton origin of the GeV-TeV emission in a cooling-limited nebula powered by the pulsar PSR J1826--1334.
SUB-LUMINOUS γ-RAY PULSARS Romani, R. W.; Kerr, M.; Craig, H. A. ...
The Astrophysical journal,
09/2011, Letnik:
738, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Most pulsars observed by the Fermi Large Area Telescope have gamma -ray luminosities scaling with spin-down power as . However, there exist one detection and several upper limits an order of ...magnitude or more fainter than this trend. We describe these 'sub-luminous' gamma -ray pulsars and discuss the case for this being an orientation effect. Of the 12 known young radio pulsars with E > 10 super(34) erg s super(-1) and d less than or equal to 2 kpc several are substantially sub-luminous. The limited available geometrical constraints favor aligned geometries for these pulsars, although no one case for alignment is compelling. In this scenario GeV emission detected from such sub-luminous pulsars can be due to a lower altitude, lower-power accelerator gap.
PDF
