Interplanetary Network Research Articles

A new type of transient high-energy source in the direction of the Galactic Centre

* Universities Space Research Association, 4950 Corporate Drive, Suite100, Huntsville, Alabama 35806, USA¢NASA Marshall Space Flight Center, ES-84, Huntsville, Alabama 35812,USA$Astronomical Institute Anton Pannekoek and Center for High-EnergyAstrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands§Physics Department, University of Alabama in Huntsville, Huntsville,Alabama 35899, USAIIDepartment of Physics, Center for Space Research, MIT 37-627,Cambridge, Massachusetts 02139, USASotJaCES of high-energy (>20keV) bursts fall into two distincttypes: the non-repeating /-ray bursters I, several thousand ofwhich have been detected but whose origin remains unknown,and the soft y-ray repeaters (SGRs), of which there are onlythree 2. The SGRs are known to be associated with supernovaremnants, suggesting that the burst events most probably origi-nate from young neutron stars 3. Here we report the detection of athird type of transient high-energy source. On 2 December 1995,we observed the onset of a sequence of hard X-ray bursts from adirection close to that of the Galactic Centre 4. The intervalbetween bursts was initially several minutes, but after two days,the burst rate had dropped to about one per hour and has beenlargely unchanged since then. More than 1,000 bursts have nowbeen detected, with remarkably similar light curves and inten-sities; this behaviour is unprecendented among transient X-rayand ,/-ray sources. We suggest that the origin of these burstsmight be related to the spasmodic accretion of material onto aneutron star.Visual inspection of the X-ray intensity records of the eightLarge Area Detectors (LADs) of BATSE 5 showed that bursts ofhard X-rays were emitted in rapid succession from a source in thegeneral direction of the Galactic Centre beginning 1995 Decem-ber 2 12:17 UT (Fig. 1). The bursts came at intervals of about 5minutes; they lasted for typically 30 seconds and reached a peakintensity of _300countss _ in the 25-611keV energy band.Spectral analysis of the events showed significant emission to60 kcV in virtually all bursts; in _ 17% of them, emission wasdetected to about 75 keV. The outbursts were also registered bythe Spectroscopy Detectors _ which look into the same sky direc-tions as the LADs and are sensitive down to _ 10 keV. The burstsusually show a clear single peak; in many cases a tail of extendedemission can be seen. The burst which we could unambiguouslyidentify as the first in this sequence of rapid hard X-ray burstsoccurred on December 2 08:22 UT. Between December 2 17:1111and 20:00 UT, the burst intervals clustered around (172 + 15)s.After 20:00 UT the intervals became more erratic and longer.Figure 2 shows the behaviour of the burst interval evolution duringthe first 4 days of emission. Between 4 and 16 December the burstdetection rate remained remarkably constant at an average of 18events per day (about one-third of the bursts were missed becauseof data gaps).We determined the location of the individual events from therelative strengths of the signals detected in different BATSEdetectors, using an algorithm that includes a detailed descriptionof the energy/angular detector response and the contribution fromX-rays scattered off the Earth atmosphere% Initially, the burstswere seen in two detectors only; to improve the constraints on thelocation, the Compton Gamma Ray Observatory (CGRO) wasreoriented on December 8 (10:57 trr, after which the events wereregistered by four detectors. The BATSE locations combined with(1) Earth occultation constraints of the source, (2) a galacticlongitude constraint from observations with the Oriented Scintil-lation Spectroscopy Experiment (OSSE) on CGRO v, and (3)Interplanetary Network (IPN) triangulation results _', producedan _ 2# × 6' error box centred on right ascension 17 h 44 min 28 s,declination -28' 45.0' (equinox 20110.0). A 3-arcmin error boxrecently m obtained with the X-Ray Timing Explorer (XTE) liesentirely within the IPN location. This error box does not containknown bright X-ray sources_LAs part of a current project .2we made a comprehensive searchfor events in the 20-60 keV energy, range in archival BATSE data,covering the period 13 January 1993 to 24 December 1993 (345FIG. 1 The BATSE(25-60 keY) intensity recordsobtained during three consecutive orbits of CGROon 2 December 1995 between 13:50 and 17:30UT;the data are displayed with a time resolution of4s. (The time scale starts at 00:00 UTon 2December 1995).

HOW FAR AWAY ARE GAMMA-RAY BURSTERS?

ABSTRACT The positions of over 1000 gamma-ray bursts detected with the BATSE experiment on board of the Compton Gamma Ray Observatory are uniformly and randomly distributed in the sky, with no significant concentration to the galactic plane or to the galactic center. The strong gamma-ray bursts have an intensity distribution consistent with a number density independent of distance in Euclidean space. Weak gamma-ray bursts are relatively rare, indicating that either their number density is reduced at large distances or that the space in which they are distributed is non-Euclidean. In other words, we appear to be at the center of a spherical and bounded distribution of bursters. This is consistent with the distribution of all objects that are known to be at cosmological distances (like galaxies and quasars), but inconsistent with the distribution of any objects which are known to be in our galaxy (like stars and globular clusters). If the bursters are at cosmological distances then the weakest bursts should be redshifted, i.e., on average their durations should be longer and their spectra should be softer than the corresponding quantities for the strong bursts. There is some evidence for both effects in the BATSE data. At this time, the cosmological distance scale is strongly favored over the galactic one, but is not proven. A definite proof (or dis-proof) could be provided with the results of a search for very weak bursts in the Andromeda galaxy (M31) with an instrument ~10 times more sensitive than BATSE. If the bursters are indeed at cosmological distances then they are the most luminous sources of electromagnetic radiation known in the universe. At this time we have no clue as to their nature, even though well over a hundred suggestions were published in the scientific journals. An experiment providing ~1 arc second positions would greatly improve the likelihood that counterparts of gamma-ray bursters are finally found. A new interplanetary network would offer the best opportunity.

Gamma-burst positions - are they reliable?

Ever since the discovery of the Cosmic Gamma-Ray Bursts we have searched for the quiescent counterparts of these mysterious flashes. Without definite counterparts our pictures of the sources must remain vague. The review discusses a number of techniques which have been applied to the gamma burst localization problem and their limitations. The most accurate technique to-date is the Interplanetary Network (IPN) timing technique. Considering the lack of success in the searches for counterparts in even the smallest gamma burst error boxes, it seems, that the next generation of satellite gamma burst detectors must be designed to allow immediate follow-up with sensitive telescopes. Concepts to achieve this goal are discussed.

Preliminary results of optical searches of IPN3 localizations

We present preliminary results from deep optical searches of small (≤∼5 arcmin2) GRB error boxes determined using the Third Interplanetary Network (IPN3). Two of these fields also have been found to have historical OT events located within the IPN3 error boxes. We compare the preliminary results of these searches to those reported for the larger IPN1 error boxes. The small size of the IPN3 error boxes should allow a test of the hypothesis suggested by the IPN1 study that there are excess QSOs associated with the GRB fields.

Ulysses observations of cosmic gamma-ray bursts

We review the current status of the Ulysses mission and summarize the results to date of the GRB experiment. This instrument detects bursts at the rate of about one every 3.5 days, and the localization data are being disseminated rapidly via the BACO-DINE and NMSU networks. The mission should operate through 2001, and future missions to Mars starting in 1996 will complete the 3rd Interplanetary Network.

The first search for a gamma-ray burst quiescent counterpart in the extreme ultraviolet with EUVE

The opening of the extreme ultraviolet window by the Extreme Ultraviolet Explorer (EUVE) satellite has provided the unique opportunity to perform the first search for a quiescent gamma-ray burst counterpart at these wavelengths. Such emission might be expected if some bursts are related to nearby hot neutron stars or neutron stars with accretion disks, among other objects. We report here on a 40 ks observation on the 1992 March 25 gamma-ray burst error box, determined by triangulation with the Third Interplanetary Network. No quiescent 40-190 A Extreme Ultraviolet (EUV) source was identified using the Deep Survey instrument, and a 3 sigma upper limit of 2.9 x 10(exp -14) erg/sq cm/s was obtained. Similarly, upper limits to the 140-380 and 280-760 A fluxes were obtained with the medium- and long-wavelength spectrometers; they are 1.1 x 10(exp -12) and 5.0 x 10(exp -13) erg/sq cm/s, respectively. We discuss the constraints which these limits impose on thermally radiating quiescent counterparts.

The optical and X-ray content of the 1992 May 1 gamma-ray burst error box

A gamma-ray burst which occurred on 1992 May 1 was observed by three spacecraft in the third interplanetary network, and rapidly localized to a small error box. The coordinates were promptly circulated to a wide astronomical community, and radio, optical, and X-ray counterpart searches were carried out. A weak X-ray source was found in the error box, and two radio sources are discovered outside the error box, but in alignment with the X-ray source. The X-ray source position contains approximately 25 optical objects down to 23d magnitude. We discuss the prospects for identifying the burster counterpart.

Observational evidence linking a quasar with an optical transient

We present evidence for the association of a quasi stellar object (QSO) with a bright optical transient (OT). A V = 20.6 mag QSO with redshift z = 1.78 has been found within the 38 seconds x 62 seconds error ellipse of a bright OT discovered on a Harvard Patrol Camera plate taken in 1905. The chance of finding a random QSO at V less than or equal to 20.6 mag within this area is estimated as approximately 0.5%. Although the OT is within the error circle of the gamma-ray burst (GRB) GB 910219 position determined from the WATCH experiment, the localization for this same event determined from the Third Interplanetary Network does not include the OT or the QSO. Whether the GRB is related to the OT/QSO or not, the probable association of a bright OT with a QSO is a discovery that warrants further investigation.

High-energy gamma rays from the intense 1993 January 31 gamma-ray burst

The intense gamma-ray burst of 1993 January 31 was detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. Sixteen gamma rays above 30 MeV were imaged in the telescope when only 0.04 gamma rays were expected by chance. Two of these gamma rays have energies of approximately 1 GeV, and the five bin spectrum of the 16 events is fitted by a power law of photon spectral index -2.0 +/- 0.4. The high-energy emission extends for at least 25 s. The most probable direction for this burst is determined from the directions of the 16 gamma rays observed by Egret and also by requiring the position to lie on annulus derived by the Interplanetary Network.

Optical studies of gamma-ray burst fields, 1: GRB 790329

An optical photometric and proper motion survey of a approximately = 160 sq arcmin region centered on an interplanetary network 41 sq arcmin GRB 790329 error box is presented. No obvious counterparts to the gamma-ray burst were identified. The distribution of stellar colors in the survey region was that expected for the galactic latitude of the burst field. Six stars with significant proper motions were identified. One of these, Gl 397, was found to be a double star. The companion has the color and luminosity of an M4/5 dwarf. We note that associating the gamma-ray burst with the Gl 397 system seems to require energies beyond that seen in the flares of other late-type dwarfs. A small number of galaxies were identified, one of which (object #4), was the bluest object found in the survey (V - I = 0.49).

A second catalog of gamma-ray bursts - 1978-1980 localizations from the interplanetary network

A catalog of 84 gamma-ray bursts which occurred between September 14, 1978 and February 13, 1980 is presented. The data presented consist of earth crossing times, given to about the nearest second, and time histories, in the tens of keV to MeV range, for all 84 events, as well as localizations for 80 of the events. The localizations, derived from arrival-time analysis, are given as single error boxes, double error boxes, or annuli of location, and, where possible, have been compared to the Konus localizations. They range in size from less than a square arcminute to over 1000 square degrees. The fluences of the bursts cataloged are in the range 3 x 10 to the -7th ergs/sq cm and above.

1979 January 13 - an intense gamma-ray burst with a possible associated optical transient

view Abstract Citations (27) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 1979 January 13 - an intense gamma-ray burst with a possible associated optical transient Barat, C. ; Hurley, K. ; Niel, M. ; Vedrenne, G. ; Cline, T. ; Desai, U. ; Schaefer, B. ; Teegarden, B. ; Evans, W. D. ; Fenimore, E. E. Abstract The time history, energy spectra, and precise localization of the intense January 13, 1979 gamma-ray burst, observed by five spacecraft in the interplanetary network, are presented. The time history displays a pulse-afterpulse structure suggestive of periodicity. Fine time resolution spectral analysis shows that a wide variety of models can be used to fit individual spectra, while spectra integrated over longer periods are well fitted by a thermal synchrotron law, making it difficult to identify any specific emission mechanism. The precise localization may be consistent with an archival optical transient having no quiescent counterpart down to 22d mag on recent plates. Publication: The Astrophysical Journal Pub Date: November 1984 DOI: 10.1086/184373 Bibcode: 1984ApJ...286L...5B Keywords: Energy Spectra; Gamma Ray Bursts; Interplanetary Space; Synchrotron Radiation; Bremsstrahlung; Surges; Time Dependence; Space Radiation full text sources ADS |

Time history, energy spectrum, and localization of an unusual gamma-ray burst

A gamma-ray burst lasting about 48 ms was observed on June 13, 1979 by four instruments in the interplanetary network. The event is unusual not only by virture of its extremely short duration, but also by the presence of rise and fall times at the 2 ms level in the time history, and because the energy spectrum is hard, extending to 2 MeV. The 0.7 sq arcmin error box contains no optical counterpart on the POSS plate (limiting magnitude, about 21). The spectral characteristics measured by experiments in the interplanetary network are substantially different from those previously reported for this burst.

γ-Ray burst observations from the UCB/LASL experiment on ISEE-3

Since the discovery of the intense bursts of γ rays by Klebesadel et al.1 in 1973, little progress has been made in the identification of the sources of the bursts. The initial observations provided directions to several sources with sufficient accuracy to establish the approximate isotropic distribution of the sources2, but not to provide a basis for association with any known objects, γ-ray burst astronomy entered a new phase in 1976 with the launch of Helios 2 and Solrad 11 containing the first experiments designed expressly for that purpose3,4. It then became possible to derive several error boxes that were very narrow in one dimension3,5. Using these data it was determined that the bursts are not associated with any type of object that has previously been recognized as a high energy astrophysical source—for example, X-ray sources. In 1978 a true interplanetary network of burst detectors was established with the launch of instruments on Pioneer Venus Orbiter6, ISEE 37–9 and Venera 11 and 1210,11. With baseline separations that can exceed 1 AU, this network provides a basis for the location of the γ burst sources with an accuracy sufficient for optical identifications. We briefly describe here one of these instruments, a joint Berkeley/Los Alamos experiment on the ISEE 3 spacecraft, and present some initial results from that experiment. These results are currently being combined with those from the other experiments to obtain accurate burst locations to be reported elsewhere.