Gamma ray pulsar analysis from photon probability maps

A new method is presented of analyzing skymap-type gamma ray data. Each photon event is replaced by a probability distribution on the sky corresponding to the observing instrument's point spread function. The skymap produced by this process may be used for source detection or identification. Most important, the use of these photon weights for pulsar analysis promises significant improvement over traditional techniques

Gamma ray pulsar analysis from photon pobability maps

We present a new method of analyzing skymap-type gamma ray data. Each photon event is replaced by a probability distribution on the sky corresponding to the observing instrument's point spread function. The skymap produced by this process may be used for source detection or identification. Most important, the use of these photon weights for pulsar analysis promises significant improvement over traditional techniques

On Al-26 and Other Short-Lived Interstellar Radioactivity

Several authors have shown that massive stars exploding at a rate of about three per century can account for a large portion, if not all, of the observed interstellar Al-26. In a separate argument using models of Galactic chemical evolution, Clayton (1984) showed that the Al-26/Al-27 production ratio was not large enough to maintain enough Al-26 in the Galactic disk gas of about 10 exp 10 solar masses having solar composition. We present a resolution of those conflicting arguments. A past history of Galactic infall growing the Galactic disk so dilutes the stable Al-27 concentration that the two approaches can be brought into near agreement. If massive stars dominate the production of Al-26, we suggest that the apparent shortfall of their Al-26/Al-27 yield ratio is to be interpreted as evidence for significant growth of the Galactic disk. We also discuss the implications of these arguments for other extinct radioactivities in meteorites, using I-129 and Sm-146 as examples

On 26Al and other Short-lived Interstellar Radioactivity

Several authors have shown that massive stars exploding at a rate of about three per century can account for a large portion, if not all, of the observed interstellar 26Al. In a separate argument using models of Galatic chemical evolution, Clayton (1984) showed that the 26Al/27Al production ratio was not large enough to maintain enought 26Al in the Galactic disk gas of ~ 10^10 M⊙ having solar composition. We present a resolution of those conflicting arguments. A past history of Galactic infall growing the Galatic disk so dilutes the stable 27Al concentration that the two approaches can be brought into near agreement. If massive stars dominate the production of 26Al, we suggest that the apparent shortfall of their 26Al/27Al yield ratio is to be interpreted as evidence for signigicant growth of the Galactic disk. We also discuss the implications of these arguments for other extinct radioactivites in meteories, using 129I and 146Sm as examples

A Statistical Treatment of the Gamma-Ray Burst "No Host Galaxy" Problem: II. Energies of Standard Candle Bursts

With the discovery that the afterglows after some bursts are coincident with faint galaxies, the search for host galaxies is no longer a test of whether bursts are cosmological, but rather a test of particular cosmological models. The methodology we developed to investigate the original "no host galaxy" problem is equally valid for testing different cosmological models, and is applicable to the galaxies coincident with optical transients. We apply this methodology to a family of models where we vary the total energy of standard candle bursts. We find that total isotropic energies of E<2e52~erg are ruled out while log(E)~53 erg is favored.Comment: To appear in Ap.J., 514, 15 pages + 7 figures, AASTeX 4.0. Revisions are: additional author, updated data, and minor textual change

The Production of 44Ti and 60Co in Supernovae

The production of the radioactive isotopes 44Ti and 60Co in all types of supernovae is examined and compared to observational constraints inculding Galactic gamma-ray surveys, measurements of the diffuse 511 keV radiation, gamma-ray observations of Cas A, the late-time light curve of SN 1987A, and isotopic anomalies found in silicon carbide grains in meteorities. The (revished) line flux from 44Ti decay in the Cas A supernova remnant reported by COMPTEL on the Compton Gamma Ray Observatory is near the upper bound expected from our models. The necessary concurrent ejection of 56Ni would also imply that Cas A was a brighter supernova than previously thought unless extinction in the intervening matter was very large. Thus, if confirmed, the reported amount of 44Ti in Cas A provides very interesting constraints on both the supernova environment and its mechanism. The abundances of 44Ti and 60Co ejected by Type II supernovae arch such that gmma-radiation from 44Ti decay SN 1987A could be dectected by a furture generation of gamma-ray telescopes, and that the decay of 60Co might provide an interesting contribution to the late-time light curve of SN 1987A and other core collapse supernovae. To produced the solar 44Ca abundance and satisfy all the obersvational constraints, nature may prfer at least the occasional explosion of sub-Chandrasekhar mass white dwarfs as Type Ia supernovae. Depending on the escape fraction of positrons due to 56Co made in all kinds of Type Ia supernovae, a significant fraction of the steady state diffuse 511 keV emission may arise from the annihilation of positrons produced during the decay of 44Ti to 44Ca. The Ca and Ti isotpic anomalies in presolar grains confirm the production of 44Ti in supernovae and that extensive mixing between zones has occurred, but a quantitative model for this mixing is presently lacking

Hard X-ray Emission from Cassiopeia A SNR

We report the results of extracting the hard X-ray continuum spectrum of Cas A SNR from RXTE/PCA Target of Opportunity observations (TOO) and CGRO/OSSE observations. The data can rule out the single thermal bremsstrahlung model for Cas A continuum between 2 and 150 keV. The single power law model gives a mediocre fit (∼5%) to the data with a power-law index, Γ = 2.94±0.02. A model with two component (bremsstrahlung + bremsstrahlung or bremsstrahlung + power law) gives a good fit. The power law index is quite constrained suggesting that this continuum might not be the X-ray thermal bremmstrahlung from accelerated MeV electrons at shock fronts [1] which would have Γ ≃2.26. With several SNRs detected by ASCA showing a hard power-law nonthermal X-ray continuum, we expect a similar situation for Cas A SNR which has Γ=2.98±0.09. We discuss the implication of the hardest nonthermal X-rays detected from Cas A to the synchrotron radiation model

Three X-ray Transients in M31 Oberserved with Swift

Aims.The purpose of this study is to find transient X-ray sources in M 31, and to investigate and classify their nature.Methods.Three X-ray transients were observed with Swift. For each of the three X-ray transients we use the Swift X-ray and opticaldata together with observations from XMM-Newton and Chandra to investigate the lightcurves and the spectra of the outburst, andthereby to identify the source types. Results.The outburst of XMMU J004215.8+ 411924 lasted for about one month. The source had a hard power-law spectrum with aphoton index of 1.6. It was previously identified as a Be/X-ray binary based on the optical identification with a star. However, we showthat with improved source coordinates it is clear that the optical source is not the counterpart to the X-ray source. The source SWIFTJ004217.3+ 411532 had a bright outburst, after which it slowly decayed over half a year. The spectrum was soft, corresponding to athermal accretion disk with innermost temperature of ∼ 250 − 600 eV. The source was not seen in the optical, and the soft spectrumindicates that the source is most likely a black hole low mass X-ray binary. M31N 2006-11a is a nova that was previously observed inthe optical. We detected it both in X-rays and UV with Swift ∼ half a year after the optical maximum, after which it decayed below theSwift detection threshold within a month. The spectrum of the X-ray transient can be modelled by a black-body with a temperature of50 eV. We use catalogues of X-ray transients in M 31 to estimate their rate, and we find a lower limit of 9 yr−

Modeling the Extragalactic Background Light and the Cosmic Star Formation History

We present an updated model for the extragalactic background light (EBL) from stars and dust, over wavelengths approximately 0.1 to 1000 $\mu$m. This model uses accurate theoretical stellar spectra, and tracks the evolution of star formation, stellar mass density, metallicity, and interstellar dust extinction and emission in the universe with redshift. Dust emission components are treated self-consistently, with stellar light absorbed by dust reradiated in the infrared as three blackbody components. We fit our model, with free parameters associated with star formation rate and dust extinction and emission, to a wide variety of data: luminosity density, stellar mass density, and dust extinction data from galaxy surveys; and $\gamma$-ray absorption optical depth data from $\gamma$-ray telescopes. Our results strongly constraint the star formation rate density and dust photon escape fraction of the universe out to redshift $z=10$, about 90% of the history of the universe. We find our model result is, in some cases, below lower limits on the $z=0$ EBL intensity, and below some low-$z$ $\gamma$-ray absorption measurements.Comment: 23 pages, 12 figures, 3 tables. Accepted for publication in AAS journal

X-Ray Source Variability Study of the M31 Central Field Using Chandra HRC-1

Context. The central field of the Andromeda galaxy (M 31) has been monitored, using the Chandra HRC-I detector (about 0.1-10 keV energy range) from 2006 to 2012 with the main aim to detect X-rays from optical novae. We present a systematic analysis of all X-ray sources found in the 41 nova monitoring observations, along with 23 M 31 central field HRC-I observations available from the Chandra data archive starting in December 1999. Aims. Based on these observations, we studied the X-ray long-term variability of the source population and especially of X-ray binaries in M 31. Methods. We created a catalogue of sources, detected in the 64 available observations, which add up to a total exposure of about 1 Ms. To study the variability, we developed a processing pipeline to derive long-term Chandra HRC-I light curves for each source over the 13 years of observations. In the merged images we also searched for extended X-ray sources. Results. We present a point-source catalogue, containing 318 X-ray sources with detailed long-term variability information. 28 of which are published for the first time. The spatial and temporal resolution of the catalogue allows us to classify 115 X-ray binary candidates showing high X-ray variability or even outbursts in addition to 14 globular cluster X-ray binary candidates showing no significant variability. The analysis may suggest, that outburst sources are less frequent in globular clusters than in the field of M 31. We detected 7 supernova remnants, one of which is a new candidate and in addition resolved the first X-rays from a known radio supernova remnant. Besides 33 known optical nova/X-ray source correlations, we also discovered one previously unknown super-soft X-ray outburst and several new nova candidates. Conclusions. The catalogue contains a large sample of detailed long-term X-ray light curves in the M 31 central field, which helps to understand the X-ray population of our neighbouring spiral galaxy M 31