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Doty, J.

Publications and source records attributed to Doty, J..

18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Broadband X-ray burst spectroscopy of the fast-radio-burst-emitting Galactic magnetar

Magnetars are young, magnetically powered neutron stars that possess the strongest magnetic fields in the Universe. Fast radio bursts (FRBs) are extremely intense millisecond-long radio pulses of primarily extragalactic origin, and a leading attribution for their genesis focuses on magnetars. A hallmark signature of magnetars is their emission of bright, hard X-ray bursts of sub-second duration. On 27 April 2020, the Galactic magnetar SGR J1935+2154 emitted hundreds of X-ray bursts within a few hours. One of these temporally coincided with an FRB, the first known detection of an FRB from the Milky Way. Here, we present spectral and temporal analyses of 24 X-ray bursts emitted 13 hours prior to the FRB and seen simultaneously with the Neutron Star Interior Composition Explorer (NICER) mission of the National Aeronautics and Space Administration and with the Fermi Gamma-ray Burst Monitor (GBM) mission in their combined energy range of 0.2 keV to 30 MeV. These broadband spectra permit direct comparison with the spectrum of the FRB-associated X-ray burst (FRB-X). We demonstrate that all 24 NICER and GBM bursts are very similar temporally to the FRB-X, but strikingly different spectrally. The singularity of the FRB-X burst is perhaps indicative of an uncommon locale for its origin. We suggest that this event originated in quasi-polar open or closed magnetic field lines that extend to high altitudes.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2004

Observations of Gamma-Ray Bursts by HETE-2

The High Energy Transient Explorer 2 (HETE-2), launched in October 2000, is currently localizing gamma-ray bursts (GRBs) at a rate of approximately 20/yr, many in real time. As of August 2003, HETE-2 had localized 43 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.

Kawai, N.↗
NASA NTRS1993

A radiation belt monitor for the High Energy Transient Experiment Satellite

A Radiation Belt Monitor (RBM) sensitive to protons and electrons with energy approximately greater than 0.5 MeV has been designed for the High Energy Transient Experiment (HETE) satellite in order to: first, control the on-off configuration of the experiments (i.e. those susceptible to proton damage); and second, to indicate the presence of proton and/or electron events that could masquerade as legitimate high energy photon events. One of the two RBM channels has an enhanced sensitivity to electrons. Each channel of the RBM, based on a PIN silicon diode, requires a typical power of 6 milliwatts. Tests have been performed with protons with energies from approximately 0.1 to 2.5 MeV (generated by a Cockcroft-Walton linear accelerator via the d(d,p)t reaction), and with electrons with energies up to 1 MeV (from a 1.0 microcurie Bi-207 source).

Lo, D. H.↗
NASA NTRS1979

Simultaneous radio and X-ray observations of the X-ray burst source MXB 1636-53

On June 17, 1977, the X-ray burst source MXB 1636-53 was simultaneously monitored for about 4 hr with the Parkes 64-m radio telescope at a frequency of 14.7 GHz and the SAS 3 X-ray satellite (1.3-12 keV). One X-ray burst was observed; an upper limit (2 sigmas) of 200 mJy is reported for any radio burst coincident with the X-ray event. During the X-ray burst the radio/X-ray time-integrated flux ratio was no more than 375 with a 90 percent confidence. An upper limit (2 sigmas) of 22 mJy was determined for any steady 14.7-GHz source coincident with the X-ray position.

Thomas, R. M.↗
NASA NTRS1979

Further analysis of SAS 3 observations of the rapid burster /MXB 1730-335/

SAS 3 observations of the rapid burster MXB 1730-335 are analyzed with specific reference to the rapidly repetitive type II bursts and also the type I bursts. It is found that: (1) there are two stable patterns in the recurrence of the rapidly repetitive type II bursts, designated modes I and II; (2) the range of type II burst energies is a factor of about 100 for mode I and a factor of about 10 for mode II; (3) type II burst spectra are best fitted by a blackbody of constant temperature (of the order of 18 million K), constant column density, and decreasing intensity; and (4) type I bursts are best fitted by a blackbody spectrum with decreasing temperature (approximately 24 million K during the first few seconds and 16 million K about 10 sec later). The spectral fits for both types of burst are shown to yield sizes for the emission region comparable to the radius of a neutron star. A model for the rapid burster is suggested.

Marshall, H. L.↗
NASA NTRS1979

Optical observations of X-ray bursts from MXB 1837 + 05

Optical observations of the X-ray burst source MXB 1837 + 05 (Ser X-1) made at different observatories are discussed. Six X-ray bursts were detected with SAS-3 X-ray Observatory during these observations, but no simultaneous optical signals were seen during or after any of these bursts. For an assumed burst duration of 10 sec, the 3-sigma upper limits of the ratio of the detected energy in an optical burst to that in an X-ray burst range from 3 x 10 to the minus fifth to 6 x 10 to the minus fifth.

Bernacca, P. L.↗
NASA NTRS1978

SAS 3 observations of two X-ray transient events with precursors

SAS 3 has observed two unusual fast transient X-ray events from different sources, one lasting about 150 s and one, approximately 1500 s. Both events were preceded by precursor pulses which lasted a few seconds and which rose and fell in less than 0.4 s. The precursors were separated from the 'main' events by several seconds, during which no X-rays were detected. There are similarities between the two main events and X-ray bursts in both their temporal and spectral evolution. The spectra of the main events started out much softer than the spectra of the precursors, became harder as they approached maximum intensity, and softened as they decayed. In the 1500-s event, X-rays with energies greater than 10 keV were delayed by about 80 s compared with 1.5-6-keV X-rays. A blackbody fit to the spectral data of the main event of approximately 1500-s duration gives a maximum temperature of 29 million K and a radius for the emitting region of at least about 9 km (at a distance of 10 kpc); this is similar to the temperature and sizes found for several X-ray burst sources.

Hoffman, J. A.↗
NASA NTRS1977

Observations of the X-ray burst source MXB 1636-53

X-ray bursts have been observed from MXB 1636-53, almost certainly associated with the strong steady X-ray source 2S 1636-536 (Norma X-1, 3U 1636-53). The steady source was observed in January 1977 at roughly half the intensity reported in the 3U catalog and showed about 15% variability on a time scale of hours. The spectra of the X-ray bursts are well fitted by blackbody radiation whose temperature rises rapidly to a maximum of approximately 28 million K and then cools slowly. If the source is at a distance of 10 kpc, the radius of the projected burst emission region is about 10 km, similar to the size of a neutron star.

Hoffman, J. A.↗
NASA NTRS1977

Some further information on the rapid burster MXB 1730-335

Further analysis of SAS-3 data on the rapid burster MXB 1730-335 show the existence of anomalous bursts. They have approximately 3-s rise times and low peak intensities; they also violate the energy vs. interburst-interval relationship for normal bursts. The short normal bursts of about 4-s duration do not show a long tail such as observed in the long normal bursts. Evidence for time structure in normal bursts down to a time scale of 50 ms is presented. No periodic variations in the total X-ray flux were found in the 1-500-Hz range.

Ulmer, M. P.↗
NASA NTRS1977

Galactic distribution of X-ray burst sources

Data on X-ray bursts recorded by the OSO-8 and SAS-3 satellites and criteria (rise time, duration, recurrence) for X-ray bursts are examined in a study of possible correlation between the galactic longitude distribution of X-ray burst sources and globular clusters. Correlations are weak, with only two X-ray bursts sources (NGC6624 and the rapid burster) coinciding with globular clusters, another seven possibly coinciding, most not correlated. Ad hoc explanations (globular clusters obscured by dust clouds, bursts associated with remnants of disrupted globular clusters evolved into supermassive black holes) are considered briefly.

Lewin, W. H. G.↗
NASA NTRS1977

Further observations of the burst source MXB 1728-34

MXB 1728-34 has been observed by the SAS 3 observatory on eight occasions. It was bursting 95-100 per cent of the time, with burst intervals from 4 to 8 hr. The burst intervals were not correlated with the burst intensities. Seven relatively hard bursts occurring in July 1976 were all observed at energies up to about 30 keV. Following each of these bursts, enhanced X-ray emission was observed for several minutes, with a much softer spectrum than that of the bursts themselves. No periodic pulsations were observed from the associated steady source.

Hoffman, J. A.↗
NASA NTRS1977

X-ray bursts from MXB 1837+05

Results are reported for SAS 3 observations of 22 bursts from the X-ray source designated MXB 1837+05. Assuming that all the bursts come from one source, the source position is determined to be right ascension (1950) 18 hr 37.9 min, declination (1950) 5 deg 4.2 min. Integrated burst intensities are listed along with ratios of counts in different energy channels, and it is found that there are significant variations in these ratios from burst to burst. The bursts are also shown to exhibit a variety of temporal structures (including double peaks) and changes in spectral hardness. No regularity was detected in the burst occurrence times during one observing period, but four bursts during another period seemed to recur at regular intervals of about 6.3 hr. It is concluded that an intensity-interval correlation similar to that for a rapid burster does not exist for MXB 1837+05 and that this source is probably identical with the relatively strong and steady source Ser X.1.

Li, F. K.↗
NASA NTRS1976

Discovery of X-ray bursts from several sources near the galactic centre

Three X-ray burst sources have been discovered within approximately 0.5 deg of the Galactic center. All bursts from this region show a low-energy cutoff near 3 keV. The bursts from MXB 1743-29 show distinct double and triple peaks; the time interval between bursts from this source was about 1.46 day. The intervals between bursts from MXB 1742-29 and MXB 1743-28 were approximately 0.55 day and 10 min respectively. Steady emission from this collection of burst sources could account for most of the flux from the apparently extended X-ray source GCX (3U 1743-29).

Lewin, W. H. G.↗
NASA NTRS1976

Discovery of X-ray bursts from two sources in Aquila

Two X-ray burst sources have been discovered in Aquila with the aid of the SAS 3 X-ray Observatory; MXB 1906 + 00 and Aql MXB. The present paper reports on source positions, spectra, time structure, and burst energy. Five bursts were detected from MXB 1906 + 00, and the data are shown to be consistent with the assumption that there was a burst about every 8.9 hr. A comparison of raw counting data for three bursts indicates that the bursts were detected in the energy range from 1.3 to 19 keV and that the spectrum softened during burst decay. The spectrum of the one burst observed from Aql MXB is found not to soften during burst decay. It is suggested that MXB 1906 + 00 and the previously known 'steady' source A 1905 + 00 are very likely to be the same source and that the ratio of time-averaged 'steady' luminosity to time-averaged burst luminosity would be approximately 80.

Lewin, W. H. G.↗
NASA NTRS1976

The discovery of rapidly repetitive X-ray bursts from a new source in Scorpius

Rapidly repetitive X-ray bursts have been observed from a new X-ray source in Scorpius. More than 2000 bursts were observed during the 4-day continual SAS-3 observations of this source designated MXB 1730-335. The time interval between bursts varied from a minimum of about 6 s to a maximum of about 5 minutes. The energy in a given burst is approximately linearly proportional to the time interval to the next burst. The largest bursts observed last for about 60 s and represent an energy release of approximately 10 to the 40th ergs for an assumed distance to the source of 10 kpc. The smallest bursts observed last only for a few seconds. We suggest that the bursts are caused by sporadic precipitations of plasma from a reservoir in the magnetosphere of a neutron star. The reservoir is replenished at a nearly constant rate by mass transferred from a binary companion.

Lewin, W. H. G.↗