arXiv subjects

R. E. Lingenfelter

Publications and source records attributed to R. E. Lingenfelter.

At least 19 recordsLinked to original sources

arXiv2013

The Galactic Spatial Distribution of OB Associations and Their Surrounding Supernova-Generated Superbubble

Core collapse supernovae of massive (> 8 Mo) stars are formed primarily in OB associations and help blow giant superbubbles, where their collective shocks accelerate most of the Galactic cosmic rays. The spatial distribution of these stars is thus important to our understanding of the propagation of the observed cosmic rays. In order to better model the Galactic cosmic-ray distribution and propagation, we construct s three-dimensional spatial model of the massive star distribution based primarily on the emission of the H II envelopes surrounding the giant superbubbles which are maintaned by the ionizing radiation of the embedded O stars. The Galactic longitudinal distribution of the 205 micron N II rsdistion emitted by these H II envelopes is used to infer the spatial distribution of the superbubbles. We find that the Galactic superbubble distribution is dominated by the contribution of massive star clusters residing in the spiral arms.

astro-ph.HE↗

arXiv2009

Is There a Dark Matter Signal in the Galactic Positron Annihilation Radiation?

Assuming Galactic positrons do not go far before annhilating, a difference between the observed 511 keV annihilation flux distribution and that of positron production, expected from beta-plus decay in Galactic iron nucleosynthesis, was evoked as evidence of a new source and a signal of dark matter. We show, however, that the dark mater sources can not account for the observed positronium fraction without extensive propagation. Yet with such propagation, standard nucleosynthetic sources can fully account for the spatial differences and the positronium fraction, leaving no signal for dark mater to explain.

astro-ph.HE↗

arXiv2009

The Galactic Positron Annihilation Radiation & The Propagation of Positrons in the Interstellar Medium

We consider positron propagation in the interstellar medium and show that the positrons from the beta-plus decay chains of the radioactive nuclei Ni-56, Ti-44, and Al-26, produced in Galactic supernovae, can fully account for all the features of the diffuse Galactic 511 keV annihilation radiation observed by INTEGRAL/SPI. We also predict additional measurable features that can further test the origin of positrons and provide new information on the nature of the interstellar medium.

astro-ph↗

arXiv2004

The Galactic 26Al Problem and The Close Binary SNIb/c Solution?

The origin of the long-lived radioactive 26Al, which has been observed in the Galactic interstellar medium from its 1.809 MeV decay gamma-ray line emission, has been a persistent problem for over twenty years. Wolf-Rayet (WR) winds were thought to be the most promising source, but their calculated 26Al yields are not consistent with recent analyses of the 1.809 MeV emission from the nearest WR star and nearby OB associations. The expected 26Al yield from the WR star exceeds by as much as a factor of 3, that set by the 2-sigma upper limit on the 1.809 MeV emission, while the WR yields in the OB associations are only about 1/3 of that required by the 1.809 MeV emission. We suggest that a solution to these problems may lie in 26Al from a previously ignored source: explosive nucleosynthesis in the core collapse SNIb/c supernovae of WR stars that have lost most of their mass to close binary companions. Recent nucleosynthetic calculations of SNIb/c suggest that their 26Al yields depend very strongly on the final, pre-supernova mass of the WR star, and that those with final masses around 6 to 8 solar masses are expected to produce as much as 0.01 solar masses of 26Al per supernova. Such binary SNIb/c make up only a small fraction of the current SNIb/c and only about 1% of all Galactic core collapse supernovae. They appear to be such prolific sources that the bulk of the present 26Al in the Galaxy may come from just a few hundred close binary SNIb/c and the intense 1.809 MeV emission from nearby OB associations may come from just one or two such supernova.

astro-ph↗

arXiv2002

Limits to the Cas A $^{44}$Ti Line Flux and Constraints on the Ejecta Energy and the Compact Source

Two long observations of Cas A supernova remnant were made by the \emph{Rossi X-ray Timing Explorer} in 1996 and 1997 to search for hard X-ray line emission at 67.9 and 78.4 keV from decay of $^{44}$Ti formed during the supernova event. Continuum flux was detected up to 100 keV, but the $^{44}$Ti lines were not detected. The 90% confidence upper limit to the line flux is 3.6$\times10^{-5}$ photons cm$^{-2}$s$^{-1}$. This is consistent with the recent \emph{BeppoSAX} detection and with the \emph{CGRO}/COMPTEL detection of the companion transition line flux for $^{44}$Sc decay. The mean \emph{BeppoSAX}--COMPTEL flux indicates that 1.5$\pm$0.3 $\times10^{-4}$M$_\odot$ of $^{44}$Ti was produced in the supernova explosion. Based upon recent theoretical calculations, and optical observations suggesting a WN Wolf-Rayet progenitor with an initial mass of $\geq$25 M$_\odot$, the observed $^{44}$Ti yield implies that the Cas A supernova ejecta energy was $\sim2\times10^{51}$ ergs, and as a result a neutron star was formed, rather than a black hole. We suggest Cas A is possibly in the early stages of the AXP/SGR scenario in which the push-back disk has yet to form, and when the disk does form, the accretion will increase the luminosity to that of present-day AXP/SGRs and pulsed emission will commence.

astro-ph↗

arXiv2001

Resolution of the Age Discrepancies in Pulsar/SNR Associations

Pulsars associated with supernova remnants (SNRs) are valuable because they provide constraints on the mechanism(s) of pulsar spin-down. Here we discuss two SNR/pulsar associations in which the SNR age is much greater than the age of the pulsar obtained by assuming pure magnetic dipole radiation (MDR) spin-down. The PSR B1757-24/SNR G5.4-1.2 association has a minimum age of ~40 kyr from proper motion upper limits, yet the MDR timing age of the pulsar is only 16 kyr, and the newly discovered pulsar PSR J1846-0258 in the >2 kyr old SNR Kes 75 has an MDR timing age of just 0.7 kyr. These and other pulsar/SNR age discrepancies imply that the pulsar spin-down torque is not due to pure MDR, and we discuss a model for the spin-down of the pulsars similar to the ones recently proposed to explain the spin-down of soft gamma-ray repeaters and anomalous x-ray pulsars.

astro-ph↗

arXiv2001

Issues of LiBeB, Oxygen and Iron Evolution

We discuss the highlights of our recent research, specifically the refractory vs. volatile interpretation of the rise of [O/Fe] with decreasing [Fe/H], and the issue of primary vs. secondary evolution of Be.

astro-ph↗

arXiv2000

Nature vs. Nurture: The Origin of Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars

Soft gamma-ray repeaters (SGRs) and anomalous x-ray pulsars (AXPs) are young and radio-quiet x-ray pulsars which have been rapidly spun-down to slow spin periods clustered in the range 5-12 s. Most of these unusual pulsars also appear to be associated with supernova shell remnants (SNRs) with typical ages <30 kyr. By examining the sizes of these remnants versus their ages, we demonstrate that the interstellar media which surrounded the SGR and AXP progenitors and their SNRs were unusually dense compared to the environments around most young radio pulsars and SNRs. We explore the implications of this evidence on magnetar and propeller-based models for the rapid spin-down of SGRs and AXPs. We find that evidence of dense environments is not consistent with the magnetar model unless a causal link can be shown between the development of magnetars and the external ISM. Propeller-driven spin-down by fossil accretion disks for SGRs and AXPs appears to be consistent with dense environments since the environment can facilitate the formation of such a disk. This may occur in two ways: 1) formation of a ``pushback'' disks from the innermost ejecta pushed back by prompt reverse shocks from supernova remnant interactions with massive progenitor wind material stalled in dense surrounding gas, or 2) acquisition of disks by a high velocity neutron stars, which may be able to capture a sufficient amounts of co-moving outflowing ejecta slowed by the prompt reverse shocks in dense environments.

astro-ph↗

arXiv2000

Does Pulsar B1757--24 Have a Fallback Disk?

Radio pulsars are thought to spin-down primarily due to torque from magnetic dipole radiation (MDR) emitted by the time-varying stellar magnetic field as the star rotates. This assumption yields a `characteristic age' for a pulsar which has generally been assumed to be comparable to the actual age. Recent observational limits on the proper motion of pulsar B1757-24, however, revealed that the actual age (>39 kyr) of this pulsar is much greater than its MDR characteristic age (16 kyr) - calling into question the assumption of pure MDR spin-down for this and other pulsars. To explore the possible cause of this discrepancy, we consider a scenario in which the pulsar acquired an accretion disk from supernova ejecta, and the subsequent spin-down occurred under the combined action of MDR and accretion torques. A simplified model of the accretion torque involving a constant mass inflow rate at the pulsar magnetosphere can explain the age and period derivative of the pulsar for reasonable values of the pulsar magnetic field and inflow rate. We discuss testable predictions of this model.

astro-ph↗

arXiv2000

LiBeB, O and Fe Evolution: Refractory Element and Cosmic Ray Transport Delays

Employing a Monte-Carlo based evolutionary code, we show that the delay of Fe deposition relative to O, due to the incorporation of supernova ejecta refractories in high velocity grains, can account for the rise of [O/Fe] with decreasing [Fe/H]. The predicted behavior of refractory Mg, Si, Ca and Ti, and volatile S, namely that the refractories should not show the rise, but that the behavior of S should be similar to that of O, appears to be confirmed (Takeda et al. 2000, astro-ph/0007007). The delayed deposition of Be, due to cosmic ray transport in a relatively low density medium, leads to consistency of primary Be evolution as a function of both [Fe/H] and [O/H].

astro-ph↗

arXiv2000

Cosmic Ray Acceleration in Superbubbles and the Composition of Cosmic Rays

We review the evidence for cosmic ray acceleration in the superbubble/hot phase of the interstellar medium, and discuss the implications for the composition of cosmic rays and the structure and evolution of the interstellar medium. We show that the bulk of the galactic supernovae, their expanding remnants, together with their metal-rich grain and gas ejecta, and their cosmic ray accelerating shocks, are all confined within the interiors of superbubbles, generated by the multiple supernova explosions of massive stars formed in giant OB associations. This superbubble/hot phase of the ISM provides throughout the age of the Galaxy a cosmic ray source of essentially constant metallicity for acceleration by the shocks of many supernovae over time scales of a few Myr, consistent with both the Be/Fe evolution and ACE observations of Ni-59/Co-59. We also show that if the refractory cosmic ray metals come from the sputtering of fast refractory grains then the accompanying scattering of ambient gas by these fast grains can also account for the relative abundance of cosmic ray volatiles.

astro-ph↗

arXiv2000

LiBeB Evolution: Three Models

We consider the three principal LiBeB evolutionary models, CRI in which the cosmic-ray source at all epochs of Galactic evolution is the average ISM, CRI+LECR in which metal enriched low energy cosmic rays (LECRs) are superimposed onto the CRI cosmic rays, and CRS in which the cosmic-ray source, accelerated in superbubbles, is constant, independent of the ISM metallicity. By considering the evolutionary trend of log(Be/H) vs. both [Fe/H] and [O/H], we demonstrate that the CRI model is energetically untenable. We present evolutionary trends for B-11/B-10 and B/Be which, combined with future precision measurements, could distinguish between the CRS and CRI+LECR models. We show that delayed LiBeB synthesis in the CRS model, due to the transport of the cosmic rays, could explain why log(Be/H) is steeper vs. [O/H] than vs. [Fe/H]. We also show that delayed deposition of Fe into star forming regions, due to its incorporation into high velocity dust, could provide an explanation for the possible rise of [O/Fe] with decreasing [Fe/H]. Observations of refractory and volatile alpha-elements could test this scenario. There seems to be a need for pregalactic or extragalactic Li-6 sources.

astro-ph↗

arXiv1999

Magnetic Field Limits on SGRs

We measure the period and spin-down rate for SGR 1900+14 during the quiescient period two years before the recent interval of renewed burst activity. We find that the spin-down rate doubled during the burst activity which is inconsistent with both mangetic dipole driven spin down and a magnetic field energy source for the bursts. We also show that SGRs 1900+14 and 1806-20 have braking indices of $\sim$1 which indicate that the spin-down is due to wind torques and not magnetic dipole radiation. We further show that a combination of dipole radiation, and wind luminosity, coupled with estimated ages and present spin parameters, imply that the magnetic fields of SGRs 1900+14 and 1806-20 are less than the critical field of 4$\times10^{13}$ G and that the efficiency for conversion of wind luminosity to x-ray luminosity is <2%.

astro-ph↗

arXiv1999

Magnetic Field Limit on SGR 1900+14

We measured the period and spin-down rate for SGR 1900+14 during the quiescient period two years before the recent interval of renewed burst activity. We have shown that the spin-down age of SGR 1900+14 is consistent with a braking index of ~1 which is appropriate for wind torques and not magnetic dipole radiation. We have shown that a combination of dipole radiation, and wind luminosity, coupled with estimated ages and present spin parameters, imply that the magnetic field for SGR 1900+14 is less than 6 x 10^13 G and that the efficiency for conversion of wind luminosity to x-ray luminosity is <2%.

astro-ph↗

arXiv1999

Light Element Evolution and Cosmic Ray Energetics

Using cosmic-ray energetics as a discriminator, we investigate evolutionary models of LiBeB. We employ a Monte Carlo code which incorporates the delayed mixing into the ISM both of the synthesized Fe, due to its incorporation into high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the transport of the cosmic rays. We normalize the LiBeB production to the integral energy imparted to cosmic rays per supernova. Models in which the cosmic rays are accelerated mainly out of the average ISM significantly under predict the measured Be abundance of the early Galaxy, the increase in [O/Fe] with decreasing [Fe/H] notwithstanding. We suggest that this increase could be due to the delayed mixing of the Fe. But, if the cosmic-ray metals are accelerated out of supernova ejecta enriched superbubbles, the measured Be abundances are consistent with a cosmic-ray acceleration efficiency that is in very good agreement with the current epoch data. We also find that neither the above cosmic-ray origin models nor a model employing low energy cosmic rays originating from the supernovae of only very massive progenitors can account for the $^6$Li data at values of [Fe/H] below $-$2.

astro-ph↗

arXiv1999

Is SGR 1900+14 a Magnetar?

We present RXTE observations of the soft gamma--ray repeater SGR 1900+14 taken September 4-18, 1996, nearly 2 years before the 1998 active period of the source. The pulsar period (P) of 5.1558199 +/- 0.0000029 s and period derivative (Pdot) of (6.0 +/- 1.0) X 10^-11 s/s measured during the 2-week observation are consistent with the mean Pdot of (6.126 +/- 0.006) X 10^-11 s/s over the time up to the commencement of the active period. This Pdot is less than half that of (12.77 +/- 0.01) X 10^-11 s/s observed during and after the active period. If magnetic dipole radiation were the primary cause of the pulsar spindown, the implied pulsar magnetic field would exceed the critical field of 4.4 X 10^13 G by more than an order of magnitude, and such field estimates for this and other SGRs have been offered as evidence that the SGRs are magnetars, in which the neutron star magnetic energy exceeds the rotational energy. The observed doubling of Pdot, however, would suggest that the pulsar magnetic field energy increased by more than 100% as the source entered an active phase, which seems very hard to reconcile with models in which the SGR bursts are powered by the release of magnetic energy. Because of this, we suggest that the spindown of SGR pulsars is not driven by magnetic dipole radiation, but by some other process, most likely a relativistic wind. The Pdot, therefore, does not provide a measure of the pulsar magnetic field strength, nor evidence for a magnetar.

astro-ph↗

arXiv1999

Spallogenic Light Elements and Cosmic-Ray Origin

Using a Monte Carlo code which incorporates the delayed mixing into the ISM of supernovae nucleosynthetic yields and ejecta kinetic energies (including events with very large energies, e.g. collapsars/hypernovae), we tested three evolutionary models of spallogenic light element origin, specifically Be. The CRI, in which the cosmic rays are accelerated out of an ISM which is increasingly metal poor at early times, under-predicts the measured Be abundance at the lowest [Fe/H], the increase in [O/Fe] with decreasing [Fe/H] indicated by recent data notwithstanding. The CRS, in which cosmic rays with composition similar to that of the current epoch cosmic rays are accelerated out of fresh supernova ejecta and maintain a constant metallicity at all epochs, can account for the measured Be abundances with an acceleration efficiency that is in good agreement with the current epoch cosmic-ray data. The LECR, in which a postulated low energy component also accelerated out of fresh ejecta coexists with the CRI cosmic rays, can account for the observations as well, except that the required acceleration efficiency becomes prohibitively large for some of the parameters that have been previously assumed for this as-yet undetected cosmic-ray component.

astro-ph↗

arXiv1997

Evidence of X-ray Synchrotron Emission from Electrons Accelerated to 40 TeV in the Supernova Remnant Cassiopeia A

We present the 2-60 keV spectrum of the supernova remnant Cassiopeia A measured using the Proportional Counter Array and the High Energy X-ray Timing Experiment on the Rossi X-ray Timing Explorer satellite. In addition to the previously reported strong emission-line features produced by thermal plasmas, the broad-band spectrum has a high-energy "tail" that extends to energies at least as high as 120 keV. This tail may be described by a broken power law that has photon indices of 1.8 +0.5/-0.6 and 3.04 +0.15/-0.13 and a break energy of 15.9 +0.3/-0.4 keV. We argue that the high-energy component, which dominates the spectrum above about 10 keV, is produced by synchrotron radiation from electrons that have energies up to at least 40 TeV. This conclusion supports the hypothesis that Galactic cosmic rays are accelerated predominantly in supernova remnants.

astro-ph↗