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The GRASP mission Gamma-Ray Astronomy with Spectroscopy and Positioning addresses the scientific goals of fine spectroscopy with imaging and accurate positioning of gamma-ray sources, an unexplored area within gamma-ray astronomy. The assessment of GRASP as a future space astronomy mission in the mid-1990s has led to the design of the instrument outlined in this article. Thus GRASP is a third generation gamma-ray telescope and is designed to operate as a high quality spectral imager in the mid-1990s, when, following the GRO, SIGMA, and GAMMA-1 missions, there will be requirement for a more sophisticated instrument to maintain the momentum of advance in gamma-ray astronomy. The telescope will be capable of locating point sources with a precision of typically 1 arc min, whilst making a fine spectral analysis (E/ΔE ∼ 1000) of any gamma-ray line features. The high sensitivity of this instrument and the long (> 2 year) lifetime of the mission will enable a large number (∼ 1000) of astronomical objects to be studied. The GRASP mission has the potential to move gamma-ray astronomy from an era of basic exploration to one in which detailed and novel measurements can be used to gain a better understanding of many astrophysical problems.

The GRASP mission (Gamma-ray Astronomy with Spectroscopy and Positioning) is currently under study as an ESA space astronomy mission to be launched in the mid 90’s. GRASP is designed as a high quality spectral imager (E/DE ≈ 500 at 1 Mev) with positioning to the arc minute level within a large field of view (“7”) which operates over a wide spectral range (30 Kev-100 Mev) with a 3a sensitivity of typically 10 mcrab or better over the entire operational range within an observational period of ≈105 seconds. In this paper, we will mainly discuss the capability of the instrument with respect to the study of both point source and diffuse source measurements of the galactic center region.

The GRASP mission (Gamma‐ray Astronomy with Spectroscopy and Positioning) is currently under study as an ESA space astronomy mission to be launched in the mid 90’s GRASP is designed as a high quality spectral imager (E/ΔE≊1000 at 1 MeV) with positioning to the arc minute level within a large field of view (≊7°) which operates over a wide spectral range (30 keV–100 Mev) with a 3σ sensitivity of typically 10 mcrab or better over the entire operational range within an observational period of ≊105 seconds. In this paper, we will mainly discuss the capability of the instrument with respect to the study of both point source and diffuse source measurements.

The second COS-B catalogue of high-energy ( > 100 MeV) ..gamma..-ray sources lists 25 objects which appear as both significant and unresolved excesses in the ..gamma..-ray sky. The majority of them are galactic in nature, as shown by their celestial distribution, and are yet unidentified. Geminga is the brightest unidentified source in the COS-B catalogue, second only to the Vela pulsar PSRO833-45, with a flux limit of 5x10/sup -6/ photons (> 100 MeV)/cm/sup 2/ -s, approx. 2.4. x 10/sup -9/ ergs/cm/sup 2/-s in the interval 50 MeV-3GeV/sup 13/. The source, discovered during the SAS-2 mission, was repeatedly observed by COS-B. No long term variability was found. Short term variability was also actively sought, with no convincing success. The long observation times devoted by COS-B to Geminga, coupled with the relatively hard spectrum of the source allow for a positional accuracy unusually high for current ..gamma..-ray astronomy: the error box, centered at 1 = 195/sup 0/.1 and b = 4/sup 0/.2, has a radius of approx. 24 arcmins. The complete ..gamma..-ray error box could thus be contained in a single Einstein IPC field, providing a unique opportunity for in-depth search in the keV region. The several sources found were investigated atmore » radio and optical wavelengths, leading to some identifications. 18 references, 1 figure.« less

Mission aspects of the project GRASP (Gamma-Ray Astronomy with Spectroscopy and Positioning) are described as documented in the ESA assessment study at the end of 1986. The goals of this study addressed scientific objectives, technical solutions and feasibility of the mission. Two accommodation studies accompanied the assessment study. Their results show that GRASP can be accommodated on two existing space platforms, EURECA-B and ROBUS, respectively.

We report the results of recent HST observations of three Middle Aged Isolated Neutron Stars i.e. PSR1055-52, Geminga and PSR0656+14. For PSR1055-52, a probable optical counterpart has been identified with the FOC. For PSR0656+14, WFPC2 imaging provided a clear detection of the proposed optical counterpart and was used to obtain a tentative measure of its proper motion. For Geminga, new FOC colors lead to a better characterization of the source spectral shape. The results are also discussed in the general framework of the optical emission of Middle Aged Isolated Neutron Stars (MINS).

The aim of this programme is to use the ESO 3.5m class telescopes to search for the optical counterparts of hard X-ray/soft γ-ray sources (including γ-ray bursts and transient events) discovered by the SIGMA telescope on board the GRANAT satellite (successfully launched on Dec. 1st, 1989), also exploiting the soft X-ray data of the all sky survey to be performed by the ROSAT satellite (successfully launched on June 2nd, 1990). It will be the first time that coordination between on going high-energy space missions, such as SIGMA and ROSAT, and ground based telescopes is implemented on a programmed long-term basis.

With 27 detections of Isolated Neutron Stars (INSs) by ROSAT, the soft X-ray band appears by now the most promising energy channel to search for those INSs which are undetectable in radio. Here, we outline a possible identification method and report the preliminary results of a systematic search for INSs candidates performed in the ROSAT/HRI database.

In the News Focus story “GLAST mission prepares to explore the extremes of cosmic violence” (23 May, p. [1008][1]), Y. Bhattacharjee committed two grave oversights. First, no mention is made of any contribution to GLAST from outside of the United States. In fact, Italy, France, Sweden, and

The discovery of deep spectral features in the X-ray spectrum of 1E1207.4-5209 has pushed this Isolated Neutron Star (INS) out of the chorus line, since no other INS has shown significant features in its X-ray continuum. On August 2002, XMM-Newton devoted a two-orbit TOO observation to this target with the aim to better understand the nature of such spectral features, using much improved statistics. Indeed, the 260 ksec observation yielded 360,000 photons from 1E1207.4-5209, allowing for a very sensitive study of the temporal and spectral behaviour of this object., Comment: 4 pages, 3 figures. To appear in "Young Neutron Stars and their Environments" (IAU Symposium 218, ASP Conference Proceedings), eds. F. Camilo and B.M. Gaensler

A deep XMM-Newton/EPIC observation of the field of the Geminga pulsar unveiled the presence of two elongated parallel X-ray tails trailing the neutron star. They are aligned with the object's supersonic motion, extend for ∼ 2′, and have a nonthermal spectrum produced by electron-synchrotron emission in the bow shock between the pulsar wind and the surrounding medium. Such a first ever X-ray detection of a pulsar bow shock allows us to gauge the pulsar electron injection energy and the shock magnetic field while constraining the angle of Geminga's motion and the local matter density.

On presente les resultats de la recherche CCD de l'associe de la source RX 1E 0630+178, elle-meme probablement associee a la source Rγ de haute energie (≥100 MeV) 2CG 195+04, «Geminga». On a trouve un objet de magnitude m v ≃21,3±0,2 dans le rectangle d'erreur de 30 sec arc 2

1E0630+178 was the target of a 64,000 sec EXOSAT observation on March 17–18, 1985. The 1200 photons recorded were folded around the value predicted by previous Einstein '79, '81 and EXOSAT '83 data. The region between 60.20 and 60.35 sec. was searched with independent steps of 0.005 sec, computed according to the relation: step = (period)2/observations length/number of bins in the light curve. A reduced χ2 of 3.85 (9 d.o.f.) was found for 60.285 sec. The data were then divided into five segments and the same search was performed yielding for the third segment a red. χ2 of 4.33. Moreover, the a posteriori periodogram shows also the presence of harmonics at 30.14 and 15.07 (see figure) wich appear to be even more significant (red. χ2 of 5.06 and 4.37, respectively) than the effect at 60.28.

A further optical/IR investigation of the HRI error-box of the X-ray source 1E 0630 + 178, proposed as the counterpart of Geminga (2CG 195 + 04), is presented. After recognizing that the previously suggested m of about 21 object (also called a G candidate) is probably excluded by the recent data, deep CCD data of the region are presented and the two very faint objects which appear compatible with the X-ray position are discussed. No evidence of proper motion is seen, contrary to previous reports. Possible interpretations of this peculiar L(x)/L(v) greater than 1000 X-ray source are then discussed, in the light of the gamma-ray emission. 22 references.

Available data constrain possible models of the gamma-ray point (or pointlike) sources found by COS B. Apart from the pulsars (Crab, Vela) and possibly the quasar 3C 273, which are ''compact'' objects, and which have been identified at other photon energies, there are some 20-odd other sources with no accepted or acceptable counterpart, as yet. This class of ''gamma-ray objects'' may be due to cosmic ray interaction with aggregates of diffuse interstellar matter--i.e., clouds. The constraints on this hypothesis, both observationally and theoretically, are discussed for various scenarios.

The nature of the high-energy spectra of several types of active galaxies and their contribution to the measured diffuse gamma-ray emission between 1 and 150 MeV are considered, using X-ray spectra of active galaxies and SAS 2 data regarding the intensity upper limits to the gamma-ray emission above 35 MeV. It is found that a substantial increase in slope of the photon energy spectrum must occur in the low energy gamma-ray region for Seyfert galaxies, BL Lac objects, and emission line galaxies; the power-law spectra observed in the X-ray range must steepen substantially between 50 keV and 50 MeV. In addition, a cosmological integration shows that Seyfert galaxies, BL Lac objects, and quasars may account for most of the 1-150 MeV diffuse background, even without significant evolution.

The use of the azimuthal distribution of planes containing e(+)/e(-) pairs from high-energy photon materialization to investigate the nature of gamma-ray sources is discussed. Analytical work done on COS B data for bright COS B sources (Vela, Crab, and Geminga) and for a reference background region is presented along with results which are indicative of a low-chance-probability anisotropy effect for Vela. The case for the Vela pulsar is studied in more detail, starting from its pulsation properties and from a polarization interpretation of the observed anisotropy. A possible physical interpretation of the results is given in the context of pulsar gamma-ray emission, and requirements for future gamma-ray telescopes derived from COS B experience are examined. 29 references.

Results are presented of several Einstein and Exosat X-ray observations of 4U 1145 - 619, an X-ray pulsar orbiting the Be star HD 102567/Hen 715 with marked transient behavior. Pulse-timing analysis of data from imaging instruments on both missions was performed using a period-folding technique, which showed an interesting variation of the light curve shape. During observations at periastron, where the source was predictably brighter, a strong variability was observed on the time scale of several thousand seconds. The global X-ray picture presented can be interpreted in the context of an eccentric binary system with variable accretion, but especially the low-energy Exosat channel multiplier array pulsed light curve raises new questions on the detailed accretion geometry. 24 references.

Optical data taken in January 1987 from La Silla, compared to the discovery plate of 1975.2, show no proper motion for PSR 0833-45, while a very significant one was expected if the pulsar originated in the center of the Vela SNR, believed associated with it. The data yield a good estimate of the position of the parent SN event, highly asymmetric with respect to the present SNR and incompatible with all the Vela centers considered so far at various wavelengths. If the PSR/SNR association is to be kept, either an extreme asymmetry of the SNR is required, or both objects have to be much older than thought so far. Both alternatives are unattractive, thus casting doubts on the reality of this classic SNR/pulsar association. 25 references.

Observations from the Einstein observatory reveal a previously unreported source, 1e1145.1-6141, within 15 arcmin of 2s1145-619 and of comparable intensity during July 1979. Periodicity analysis of the data shows a 290 + or - 2s period for the 2s source and a 298 + or - 4s period for the lE source, confirming the previous Ariel V report of two periods in this range from this region of the sky.

An X-ray exploration of a region of the Galactic plane in Carina near l = 284 deg with the Einstein Observatory is presented, consisting of two IPC and one HRI fields. Three new X-ray sources are seen, of which one is clearly extended and can be associated with RCW 49, an H II region/emission nebula, containing a cluster of young stars. The X-ray data could be consistent with a central source of diffuse emission; however, the X-ray flux appears significantly greater than that expected for an object like RCW 49. 33 references.

Einstein Observatory IPC and HRI observations of a serendipitous, variable, X-ray source in the galactic plane in Carina are presented. Timing analysis shows the source to have a periodicity P ~ 60 msec. The optical identification with the 12.7 mag Wack 2134 star, suggested by the positional coincidence, is confirmed by spectroscopic observations done at ESO La Silla. The star appears to be probably of 05 type. The X-ray and optical data suggest the discovery of a new binary system where a hot massive star loses mass to a spinning neutron star, which would then be the fastest X-ray binary pulsar to date.