Einstein observations of extended galactic X-ray sources

Features of the X-ray pictures taken aboard the space observatory are presented. Imaging proportional counter pictures in three broad X-ray energy ranges were obtained. The X-ray spectrum of supernova remnants is described

ROSAT HRI Detection of the 16 ms Pulsar PSR J0537-6910 Inside SNR N157B

Based on a deep ROSAT HRI observation, we have detected a pulsed signal in the 0.1-2 keV band from PSR J0537-6910 --- the recently discovered pulsar associated with the supernova remnant N157B in the Large Magellanic Cloud. The measured pulse period 0.01611548182 ms (+- 0.02 ns), Epoch MJD 50540.5, gives a revised linear spin-down rate of $5.1271 \times 10^{-14} s s^{-1}$, slightly greater than the previously derived value. The narrow pulse shape (FWHM = 10% duty cycle) in the ROSAT band resembles those seen in both XTE and ASCA data (> 2 keV), but there is also marginal evidence for an interpulse. This ROSAT detection enables us to locate the pulsar at R.A., Dec (J2000) = $5^h37^m47^s.2, -69^\circ 10' 23''$. With its uncertainty $\sim 3''$, this position coincides with the centroid of a compact X-ray source. But the pulsed emission accounts for only about 10% of the source luminosity $\sim 2 \times 10^{36} ergs^{-1}$ in the 0.1-2 keV band. These results support our previous suggestions: (1) The pulsar is moving at a high velocity ($\sim 10^3 km/s$); (2) A bow shock, formed around the pulsar, is responsible for most of the X-ray emission from the source; (3) A collimated outflow from the bow shock region powers a pulsar wind nebula that accounts for an elongated non-thermal radio and X-ray feature to the northwest of the pulsar.Comment: 6 pages including 3 figures. To be published in ApJ

X-ray Survey of the Small Magellanic Cloud

A region of over 40 square degrees centered on the Small Magellanic Cloud (SMC) has been surveyed with the imaging instruments of the Einstein Observatory. The survey is approximately complete to Lx = 1036 ergs s-1, and the faintest source detected in the SMC, has Lx ≈ 3 x 1035 ergs s-1. Twenty-six sources were clearly seen. Five are identified with objects not associated with the SMC. The only previously known source detected was SMC X-1 which, when in a high state, is the brightest source in the SMC. The second brightest source observed, a previously unknown supernova remnant (SNR), is located in the central part of the SMC. Four other weaker sources are probably also SNRs in the SMC. The remaining 15 sources are not yet identified and, since some are far from the center of the cloud, are probably not all members of the SMC

X-ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth

The 105-ms X-ray pulsar J1852+0040 is the central compact object (CCO) in SNR Kes 79. We report a sensitive upper limit on its radio flux density of 12 uJy at 2 GHz using the NRAO GBT. Timing using XMM and Chandra over a 2.4 yr span reveals no significant change in its spin period. The 2 sigma upper limit on the period derivative leads, in the dipole spin-down formalism, to an energy loss rate E-dot < 7e33 ergs/s, surface magnetic field strength B_p < 1.5e11 G, and characteristic age tau_c = P/2P-dot > 8 Myr. This tau_c exceeds the age of the SNR by 3 orders of magnitude, implying that the pulsar was born spinning at its current period. However, the X-ray luminosity of PSR J1852+0040, L(bol) ~ 3e33(d/7.1 kpc)^2 ergs/s is a large fraction of E-dot, which challenges the rotation-powered assumption. Instead, its high blackbody temperature, 0.46+/-0.04 keV, small blackbody radius ~ 0.8 km, and large pulsed fraction, ~ 80%, may be evidence of accretion onto a polar cap, possibly from a fallback disk made of supernova debris. If B_p < 1e10 G, an accretion disk can penetrate the light cylinder and interact with the magnetosphere while resulting torques on the neutron star remain within the observed limits. A weak B-field is also inferred in another CCO, the 424-ms pulsar 1E 1207.4-5209, from its steady spin and soft X-ray absorption lines. We propose this origin of radio-quiet CCOs: the B-field, derived from a turbulent dynamo, is weaker if the NS is formed spinning slowly, which enables it to accrete SN debris. Accretion excludes neutron stars born with both B_p 0.1 s from radio pulsar surveys, where B_p 40 Myr) or recycled pulsars. Finally, such a CCO, if born in SN 1987A, could explain the non-detection of a pulsar there.Comment: 8 pages, 3 figures, to appear in The Astrophysical Journa

CHANDRA Observations of the X-ray Halo around the Crab Nebula

Two Chandra observations have been used to search for thermal X-ray emission from within and around the Crab Nebula. Dead-time was minimized by excluding the brightest part of the Nebula from the field of view. A dust-scattered halo comprising 5% of the strength of the Crab is clearly detected with surface brightness measured out to a radial distance of 18 arcminutes. Coverage is 100% at 4 arcminutes, 50% at 12 arcminutes, and 25% at 18 arcminutes. The observed halo is compared with predictions based on 3 different interstellar grain models and one can be adjusted to fit the observation. This dust halo and mirror scattering form a high background region which has been searched for emission from shock-heated material in an outer shell. We find no evidence for such emission. We can set upper limits a factor of 10-1000 less than the surface brightness observed from outer shells around similar remnants. The upper limit for X-ray luminosity of an outer shell is about 10e34 erg/s. Although it is possible to reconcile our observation with an 8-13 solar mass progenitor, we argue that this is unlikely.Comment: 26 pages, 12 figures, accepted by Ap

Interim readiness plan

This report provides rough designs and costs for 3 payloads which can be built on a relatively fast time scale. With these, Lawrence Radiation Laboratory (LRL) could measure neutrons and X-rays from high altitude shots. No measurements of soft X-rays (less than or approximately equal to 5 kev), hard X- rays (greater than or approximately equal to 60 kev), or gamma rays would be made. Plans could be made to fly the Simplex payload as part of the spring Lapwing exercise. Some interim capability exists from other sources which might compliment the above measurements. Sandia has developed a mylar sail sampler which could be used for debris experiments. There is a LASL/Sandia scan converter which could be fielded to make fast time-history measurements of the X-ray or gamma ray pulse. Interval time could be measured with a ground based EMP detector. The LRL cost of this interim rocket program is approximately 5 man years of effort and about $140,000 of major procurement. Sandia would need approximately$450,000 to stockpile payloads. I believe the necessary rockets are already stockpiled but some work on the ranges might be required. For example, more launchers are needed on Johnston Atoll. All this money and effort would be expended in FY- 1970 and these rocket experiments would be ready (`on the shelf` or close) by June 1970

ROSAT Observations of the Vela Pulsar

The ROSAT HRI was used to monitor X-ray emission from the Vela Pulsar. Six observations span 2-1/2 years and 3 glitches. The summed data yield a determination of the pulse shape, and X-ray emission from the pulsar is found to be 12 % pulsed with one broad and two narrow peaks. One observation occurred 15 days after a large glitch. No change in pulse structure was observed and any change in X-ray luminosity, if present, was less than 3 %. Implications for neutron star structure are discussed.Comment: To be publisned in the Astrophysical Journa

Chandra Observation of the Magellanic Cloud Supernova Remnant 0454-672 in N9

A Chandra observation has defined the extent of the SNR B 0454-692 in the LMC H II region N9. The remnant has dimension 2.3" x 3.6" and is elongated in the NS direction. The brightest emission comes from a NS central ridge which includes three bright patches. There is good agreement between X-ray and [O III] and [S II] morphology. The remnant is old enough so that optical data give more information about dynamics than do the X-ray data. The SN energy release was >= 4 x 10^50 ergs and the age is ~3 x 10^4 years. There are several unresolved sources nearby but none are clearly associated with the remnant. The X-ray spectrum is soft and indicates enhanced Fe abundance in the central region, consistent with a Type Ia SN origin, but a Type II origin cannot be ruled out.Comment: AASTeX, 20 pages including 5 figures. Accepted for publication in The Astrophysical Journal. Figures have been reduced in resolution for space requirements; full-resolution figures may be requested by email to [email protected]

An ASCA Study of the W51 Complex

We present the analysis of ASCA archival data from the Galactic source W51. The ASCA spectra show that the soft (kT<= 2.5 keV) X-rays are of thermal origin and are compatible with W51C being a single, isothermal (kT~0.3 keV) supernova remnant at the far-side of the Sagittarius arm. The ASCA images reveal hard (kT>=2.5 keV) X-ray sources which were not seen in previous X-ray observations. Some of these sources are coincident with massive star-forming regions and the spectra are used to derive X-ray parameters. By comparing the X-ray absorbing column density with atomic hydrogen column density, we infer the location of star-forming regions relative to molecular clouds. There are unidentified hard X-ray sources superposed on the supernova remnant and we discuss the possibility of their association.Comment: 13 pages, 11 figures, to be published in Astronomical Journa