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Context.The origin of X-ray Flashes (XRFs) is still a mystery and several models have been proposed. To disentangle among these models, an important observational tool is the measure of the XRF distance scale, so far available only for a few of them.

We present detailed spatially-resolved spectroscopy results of the observation of Abell 1835 using the European Photon Imaging Cameras (EPIC) and the Reflection Grating Spectrometers (RGS) on the XMM-Newtonobservatory. Abell 1835 is a luminous (1046ergs $\rm{s}^{-1}$), medium redshift ($z=0.2523$), X-ray emitting cluster of galaxies. The observations support the interpretation that large amounts of cool gas are present in a multi-phase medium surrounded by a hot ($kT_{\rm{e}}=8.2$keV) outer envelope. We detect O VIII Lyαand two Fe XXIV complexes in the RGS spectrum. The emission measure of the cool gas below $kT_{\rm{e}}=2.7$keV is much lower than expected from standard cooling-flow models, suggesting either a more complicated cooling process than simple isobaric radiative cooling or differential cold absorption of the cooler gas.

Using a pulse-fit method, we investigated the spectral lags between the traditional gamma-ray band (50–400 keV) and the X-ray band (6–25 keV) for 8 GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB 030528, GRB 040924, GRB 041006, and GRB 050408), detected with the WXM and FREGATE instruments aboard the HETE-2 satellite. We found several relations for individual GRB pulses between the spectral lag and other observables, such as the luminosity, pulse duration, and peak energy, $E_{\rm peak}$. The obtained results are consistent with those for BATSE, indicating that the BATSE correlations are still valid at lower energies (6–25 keV). Furthermore, we found that the photon energy dependence for the spectral lags can be reconciled with the simple curvature effect model. We discuss the implications of these results from various points of view.

Context. As a result of the numerous missions dedicated to the detection of Gamma-ray bursts (GRBs), the observed properties of these events are now well known. However, studying their parameters in the source frame is not simple since it requires having measurements of both the bursts' parameters and of their distances.Aims. Taking advantage of the forthcoming Catalog of the High Energy Transient Explorer?2 (HETE-2) mission, the aim of this paper is to evaluate the main properties of HETE-2 GRBs?? the peak energy (Epeak), the duration?(T90) and the isotropic energy (Eiso) ? in their source frames and to derive their unbiased distribution.Methods. We first construct a complete sample containing all the bursts localized by the Wide-Field X-ray Monitor (WXM) on-board HETE-2, which are selected with a uniform criterion and whose observed parameters can be constrained. We then derive the intrinsic?Epeak, T90and Eiso? distributions using their redshift when it is available, or their pseudo-redshift otherwise. We finally compute the ?volume of detectability??Vmaxof each GRB, i.e. the volume of the universe in which the burst is bright enough to be part of our sample, and the corresponding number of GRB within their visibility volume?NVmax, in order to derive a weight for each detected burst accounting both for the detection significance and the star formation history of the universe.Results. We obtain unbiased distributions of three intrinsic properties of HETE-2 GRBs: Epeakintr, T90intrand the isotropic energy of the burst. These distributions clearly show the predominence of X-ray flashes (XRFs) in the global GRB?population. We also derive the rate of local GRBs: R0H2?? 11?Gpc-3?yr-1, which is intermediate between the local rate obtained by considering only the ?high-luminosity? bursts (~1?Gpc-3?yr-1) and that obtained by including the ?low-luminosity? bursts (?200?Gpc-3?yr-1).Conclusions. This study shows that the XRFs are predominent in the GRB population and are closely linked to the ?classical? GRBs. We show that HETE-2 detected no low-luminosity GRB like GRB?980425 or XRF?060218, due to the small size of its detectors, excluding this type of burst from our statistical analysis. The comparison of the GRB?rate derived in this study with the known rate of type?Ib/c supernovae clearly shows that the progenitors of SNe?Ib/c must have some special characteristics in order to produce a gamma-ray burst or an X-ray flash.

A long X-ray flash was detected and localized by instruments aboard the High Energy Transient Explorer II (HETE-2) at 00:03:30 UT on 2004 September 16. The position was reported to the GRB Coordinates Network (GCN) approximately 2 hours after the burst. This burst consisted of two peaks separated by $\sim 200$s, with durations of about 110 s and 60 s. We analyzed the energy spectra of the 1st and 2nd peaks observed with the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE). We discuss the origin of the 2nd peak in terms of the flux variabilities and timescales. We find that it is most likely to be part of prompt emission, and is explained by a long-acting engine model. This feature is similar to some bright X-ray flares detected in the early afterglow phase of bursts observed by the Swift satellite.

GRB 051022 was detected at 13:07:58 on 2005 October 22 UT by HETE-2. The location of GRB 051022 was determined immediately by the flight localization system. This burst contained multiple pulses, and had a rather long duration of about 190 s. The detections of candidate X-ray and radio afterglows were reported, whereas no optical afterglow was found. Optical spectroscopic observations of the host galaxy revealed a redshift of $z = 0.8$. Using data derived by a HETE-2 observation of the prompt emission, we found absorption of $N_{\mathrm{H}} = (8.8_{-2.9}^{+3.1}) \times 10^{22} \,\mathrm{cm}^{-2}$and visual extinction of $A_{V} = 49_{-16}^{+17}$mag in the host galaxy. If this is the case, no detection of any optical transient would be quite reasonable. The absorption derived by Swift XRT observations of the afterglow is fully consistent with those obtained from an early HETE-2 observation of the prompt emission. Our analysis implies an interpretation that the absorbing medium may be outside the external shock at $R \sim 10^{16} \,\mathrm{cm}$, which could be a dusty molecular cloud.

A bright, long gamma-ray burst (GRB) was detected and localized by the instruments on board the High Energy Transient Explorer 2 satellite (HETE-2) at 02:44:19.17 UTC (9859.17 s UT) on 2002 August 13. The location was reported to the GRB Coordinates Network (GCN) about 4 min after the burst. In the prompt emission, the burst had a duration of approximately 125 s, and more than four peaks. We analyzed the time-resolved 2–400 keV energy spectra of the prompt emission of GRB 020813 using the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE) in detail. We found that the early part of the burst (17–52 s after the burst trigger) shows a depletion of low-energy photons below about 50 keV. It is difficult to explain the depletion by either synchrotron self-absorption or Comptonization. One possibility is that the low-energy depletion may be understood as a mixture of “jitter” radiation with the usual synchrotron radiation component.

PRECISE (20–40″) celestial positions of 10 galactic X-ray sources in the region 55° < lII< 320° are reported here. These positions were measured with the rotating modulation collimator detectors on the SAS-3 X-ray observatory. The data were taken as part of a systematic survey of the galactic plane1–7. Five positions reaffirm the identification of optical counterparts for 4U0614+09 (refs 8, 9), 2S0053+604 (refs 1, 10), 4U1145−61 (refs 1, 11–13), GX301−2 (refs 1, 12, 14), and GX304−1 (refs 1 15). Positions for the latter four sources and for 4U0142+61 are refinements of previously reported SAS-3 positions1,16. The position for 2S0114+650 has led to the discovery of an optical counterpart17,18. Positions for 4U0142+61, 4U0919−54, A1239−59, and 4U1254−69 are also presented, The optical counterparts of these sources are still to be discovered. The source 2S0114+650 was discovered as part of this work.

We present 9.7 and 11.8 µm narrow band (??/?=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 µm feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M? hydrogen burning core star.

PRECISE (20–40″) positions of seven X-ray sources in the celestial region 320° < lII< 340° are reported here. These include a recurrent transient X-ray source (MX1608–52; refs 1–4) and a source 2S1553–542 (ref. 5) coincident with a γ-ray source6within the given errors of position. The positions reported here reduce the previously reported areas of the error region for six of the sources by factors ranging between 10 and 100. In the case of MX1608–52, a preliminary report of this work2led to the identification of an optical candidate7,8. The present results add confidence to the proposed radio candidates for 4U1624–49 (ref. 9) and 4U1642–45 (refs 9, 10). But they eliminate proposed possible optical candidates5,11–14for the sources 4U1543–62, 2S1553–542, 4U1624–49 and 4U1642–45.

An IR camera has been built at the University of California at Berkeley for astronomical observations. The camera has been used primarily for high angular resolution imaging at mid-IR wavelengths. It has been tested at the University of Arizona 61- and 90-in. telescopes near Tucson and the NASA Infrared Telescope Facility on Mauna Kea, HI. In the observations the system has been used as an imager with interference coated and Fabry-Perot filters. These measurements have demonstrated a sensitivity consistent with photon shot noise, showing that the system is limited by the radiation from the telescope and atmosphere. Measurements of read noise, crosstalk, and hysteresis have been made in our laboratory.

The Pliofilm cohort is the most intensely studied group of workers chronically exposed to benzene. Information on this cohort has been the basis for regulations and/or guidelines for occupational and environmental exposure to benzene. Rinsky et al. (1986, 1987) and Crump and Allen (1984) developed different approaches for reconstructing the exposure history of each member of the group. The predicted levels of exposure, combined with the data on the incidence of disease, have been used to estimate benzene's carcinogenic potency. In this paper, recent information from worker interviews and historical records from the National Archives and elsewhere were used to evaluate the accuracy of prior exposure estimates and to develop better ones for the cohort. The following factors were accounted for: (1) uptake of benzene due to short-term, high-level exposure to vapors, (2) uptake due to background concentrations in the manufacturing building, (3) uptake due to contact with the skin, (4) morbidity and mortality data on workers in the Pliofilm process, (5) the installation of industrial hygiene engineering controls, (6) extraordinarily long work weeks during the 1940s, (7) data indicating that airborne concentrations of benzene were underestimated due to inaccurate monitoring devices and the lack of adequate field calibration mated due to inaccurate monitoring devices and the lack of adequate field calibration of these devices, and (8) likely effectiveness of respirators and gloves. Our estimates suggest that Crump and Allen (1984) overestimated the exposure of workers in some job classifications and underestimated others, and that Rinsky et al. (1981, 1986) almost certainly underestimated the exposure of nearly all workers. Airborne concentrations of benzene at the St. Marys facility during the years of its operation were found (on average) to be about half those of the two Akron facilities. Our analysis indicates that short-term, high-level exposure to benzene vapors and dermal exposure significantly increased (by about 25-50%) the total absorbed dose of benzene for some workers. One of the key findings was that, unlike prior analyses, the three facilities probably had significantly different airborne concentrations of benzene, especially during the 1940s and 1950s.

Precise positions, determined with data from the SAS-3 X-ray observatory, are presented for eight galactic plane X-ray sources (Aq1 X-1, Ser X-1, 3U1956 + 11, 3U1822−00, 3U1915−05, A1845−02, A1850−08, A1905+00). Error radii for the positions range from 20 to 50 arc s. Previously proposed optical identifications of three of the sources (Ser X-1, 3U1956 + 11, A1850−08) are supported by these results. Three (Ser X-1, A1905+00, 3U1915−05) have been identified as X-ray burst sources.

The data from a recently completed survey of the galactic plane with the SAS-3 modulation collimators provide precise (20″–60″) celestial positions of galactic X-ray sources. Preliminary positions of 60″ precision are reported for five sources. One of these led to the identification of the star, γ Cas, as an X-ray source, and the others lend substantial confidence to previously proposed optical identifications: 3U0352 + 30 = X Per, 3U1145 −61 =HEN 715, GX301 −2 = WRA977, and GX304 −1 = MMVstar. These identifications seem to establish the existence of a previously suggested class of De-star X-ray emitters.

We have obtained resolved IR images, at wavelengths from 1.2µm to 12.5µm, of a small sample of protoplanetary nebulae. The results suggest that all PPNe are axially, not spherically, symmetric, that spherical symmetry ends at the tip of the AGB, and that AGB evolution terminates with a burst of remarkably rapid, equatorially concentrated mass-loss.

THE precise (20–60″) positions of nine X-ray sources, in the vicinity of the galactic centre are reported here. The data were obtained as part of the comprehensive survey of the galactic plane performed with the rotating modulation collimator (RMC) detectors on the SAS-3 X-ray observatory1–6. One of the nine is the binary X-ray source 4U1700–37 which has a well established optical counterpart that lies 7″ from the position reported here. This supports the validity of our calibration procedures2. The other eight sources GX349+2, 4U1702–42, 4U1705–44, MX1716–31, A1742–294, 4U1755–33, GX5–1, and 2S1803–245 lack established counterparts at other wavelengths. Our position for GX5–1 adds confidence to the previously proposed radio counterpart7and our position for 4U1755–33 excludes its proposed optical counterpart8. Three of the unidentified sources have distinguishing X-ray properties : MX1716–31 is a flaring source9,10and possibly an X-ray burst source11; A1742–294 is a transient12and possibly also the X-ray burst source MXB1742–29 (ref. 13); and 2S1803–245 (MX 1803–24) is a very bright transient discovered14in the course of this work.

Calculations are made of the electrochemical pumping rates needed to reach known optical lasing thresholds in a dye laser. Rates and yields have been measured or checked as needed. An optimum cavity is used for the calculations, but the best pumping rate is still more than 2 orders of magnitude below threshold. These calculations help explain the many failures to make an EGCL laser.

Abstract: Trimethylamine and triethylamine are shown to luminesce at their wavelengths of fluorescence when excited by electrical discharge. When excited at low pressures or at high frequencies, a longer wavelength emission is observed at 380 nm. This emission, rather than being due to excimers which are known to exist for some tertiary aliphatic amines, is shown to be due to emission from a decomposition product. Lasing using electrical discharge pumping was attempted, but yielded negative results due to the rapid decomposition. Optical pumping might be successful however, and produce a tunable gas-phase ultraviolet laser

WE report here the discovery of an X-ray emitting QSO, the first to be initially identified from X-ray observations. Previously, the only QSO known to be an X-ray source was 3C273 (refs 1 and 2). The new QSO has been found within a 40′′ error circle established by the SAS-3 X-ray Observatory. The SAS-3 error circle lies within the Ariel V error box (∼0.2 square degrees) for the source 2A 2251-179 (ref. 3). Following the convention for optical QSOs, we have designated the optical object MR2251 — 178. The X-ray luminosity (2–11 keV) of this object, presently ∼5×1044erg s−1, has been as large as ∼1.6×l045erg s−1(in 1975) and exceeds the optical luminosity by a factor of ∼ 10. Among known compact X-ray sources, only 3C273 has a greater luminosity. Also, in radio observations at 4,885 MHz with the NRAO Very Large Array (VLA), we have discovered a point-like radio source coincident with MR2251—178.

PRECISE (20–30″) positions of three steady X-ray sources which have been identified recently as X-ray burst sources 4U1636–53 = MXB1636–53 (refs 1, 2), 4U1728–33 = MXB1728–34 (refs 3, 4), and 4U1735–44 = MXB1735–44 (refs 5, 6, 7) are reported here. These positions, hereafter designated with a 2S prefix, have been derived from data obtained with the SAS-3 rotalting modulation collimators during a survey of the galactic plane8–10. The small solid angles of the error regions make possible a thorough survey of all potential optical, infrared, and radio counterparts of these burst sources. Two of these positions, 2S1636–536 and 2S1735–444, have led to the probable identifications of optical counterparts11.

PRECISE (20–25″) positions of six X-ray sources located in the galactic bulge, GX1+4, GX9+9, GX3+1, GX+1, G%13+1 and GX17+2 are reported here. The data were taken as part of the survey of the galactic plane performed with the SAS-3 rotating modulation collimators1–4. Previously proposed optical counterparts for three of these sources (GX1+4, GX9+9, and GX17+2) lie within our error circles. The positions, error radii, and intensities (2–11 keV) determined for the sources are given in Table 1. We compare our results with those determined with previous sounding rocket and satellite experiments in Fig. 1. Proposed optical and radio candidates are also included. Finding charts for the six sources are given in Fig. 2.

SAS 3 ROTATING modulation collimator (RMC) measurements are reported here which yield a new, more precise, position for the Ariel 5 X-ray source A1710–34 (ref. 1). We also report optical observations of stars in the X-ray error box and discuss evidence obtained with the Parkes 64m radio telescope for 2-cm radio emission from the vicinity of the X-ray source.

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The High Energy Transient Explorer, scheduled to be launched in late 1999 or early 2000, will carry a pair of Soft X-ray Cameras (SXC), capable of localizing the X-ray counterparts of GRBs with unprecedented precision. Each SXC consists of a pair of large-format CCDs behind a 1-D coded aperture: the two SXCs are oriented orthogonal to each other to permit two-dimensional image reconstruction. The SXCs on HETE will be able to localize bright X-ray afterglows to $<20''$precision within seconds of burst onset. The coordinates of detected bursts will be distributed immediately to ground-based observers and to the GCN via the HETE Burst Alert System.

DURING a continuing program of radio observations of X-ray sources carried out with the NRAO very large array (VLA), we have made high sensitivity searches for radio emission from MXB1837 + 05 = Ser X − 1 (ref. 1), particularly during the SAS 3 MIT world-wide X-ray burster watch in June 19772. Observations of MXB1837 + 05 were carried out on 26 April, 12 and 13 June 1977, with six 25-m antennas of the VLA operated at 4,884 MHz with system temperatures of ∼60 K and bandwidths of 50 MHz. Upper limits of 1 mJy were obtained for the time-averaged radio emission from Ser X − 1 during the three periods of observation, and no short time scale radio emission was detected during or after the times X-ray bursts were observed on 12 and 13 June 1977.

WE suggest faint (B ∼ 18), blue stars as the optical counterparts of two X-ray bursters, 4U1636–53 (MXB1636–53)1–4and 4U1735–44 (MXB1735–44; KGX345–6?)1,4–6, and for the 7-s X-ray pulsar, 4U1626–671,7,8. The candidate stars have large ultraviolet excesses and were discovered well within the 20″ and 30″ X-ray error radii determined using the rotating modulation collimator experiment aboard the SAS-3 X-ray Observatory9,10. Photographic observations of several X-ray error boxes were performed (by C.R.C. and W.A.H.) in April 1976 (before final SAS-3 X-ray positions were known) with the 4-m telescope at the Cerro Tololo Interamerican Observatory (CTIO). R, B and U plates were obtained for the regions including 4U1636–53 and 4U1735–44. The R plates (RG610 filter with 127-04 emulsion) are shown as finding charts in ref. 9. Preliminary iris photometry of some of the plates was performed to identify the bluest stars in each error box for further study.

THE positions of three celestial X-ray sources were measured with the rotating modulation collimators (RMC) on SAS-3 during a survey of the galactic plane1and are precise to ≤ 25″ (ref. 2). One of these sources, Cir X-1 (ref. 3), is a highly variable X-ray source often compared with the black-hole candidate, Cyg X-1. Another, TrA X-1 = A1524–61, is a 1974 X-ray nova4, and the third, 3U1626–67 (ref. 5), is a 7.68-s X-ray pulsar6. The results reported here support recently proposed optical and radio identifications7–9of these three sources. In two cases (TrA X-1 and 3U1626–67), they have been instrumental in bringing about the proposed identifications. Cir X-1 exhibits a binary periodicity10of 16.6 d, extreme aperiodic variability on timescales of > 0.1s (refs 11, 12) and 1–3 s (ref. 13), and flaring14,15with time constants of a few ms. This variability and the absence of a shorter (spin) period13,15have led to suggestions11,13–15that this object may be similar to Cyg X-1. The absence of a compelling optical or radio counterpart, however, has prevented the further exploration of this hypothesis.

The High Energy Transient Explorer 2 (HETE-2), launched in October 2000, is currently localizing gamma-ray bursts (GRBs) at a rate of ∼20 yr-1, many in real time. As of September 2003, HETE-2 had localized 47 GRBs; 16 localizations had led to the detection of an X-ray, optical, or radio afterglows. The prompt position notification of HETE-2 enabled probing the nature of so-called “dark bursts” for which no optical afterglows were found despite of accurate localizations. In some cases, the optical afterglow was found to be intrinsically faint, and its flux declined rapidly. In another case, the optical emission was likely to be extinguished by the dust in the vicinity of the GRB source. The bright afterglows of GRB021004 and GRB030329 were observed in unprecedented details by telescopes around the world. Strong evidence for the association of long GRBs with the core-collapse supernovae was found. HETE-2 has localized almost as many X-ray rich GRBs as classical GRBs. The nature of the X-ray rich GRBs and X-ray flashes have been studied systematically with HETE-2, and they are found to have many properties in common with the classical GRBs, suggesting that they are a single phenomenon.

THE discovery of a faint X-ray source with the X-ray detectors on SAS 3 at a location with galactic coordinates lII∼282°, bII∼−9° is reported here. A subsequent optical search has revealed a likely optical counterpart in the form of a 17th magnitude star with He II 4686 and Hβin emission. It is, therefore, likely to be a low-luminosity galactic X-ray source.

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