Astrophysics and Astronomy Commons^™

Improved Comptel 10–30 Mev Event Selections For Point Sources From Inflight Data, W Collmar, U Wessolowski, V Schonfelder, G Weidenspointer, S C. Kappadath, Mark L. Mcconnell, K Bennett

Space Science Center

After several years in orbit the COMPTEL experiment aboard the COMPTON Gamma-RayObservatory has collected a substantial amount of data from the MeV sky. We have used the inflight event data collected from the Crab, which is the brightest point source at MeV energies, to optimize our event selections for point sources. For the COMPTEL 10–30 MeV range we have derived a set of improved parameter selections, which leads to a reduction of background events and—at the same time—increases the number of source events, resulting in an obvious improvement in the signal-to-background ratio for point sources. Due to a revised cut …

Gamma-Ray Observations Of Gro J1655-40, R Kroeger, Mark Strickman, J E. Grove, Philip Kaaret, E. Ford, B A. Harmon, Mark L. Mcconnell

Physics & Astronomy

The bright transient X-ray source GRO J1655-40 = XN Sco 1994 was observed by the OSSE instrument on the Compton Gamma Ray Observatory (GRO). Preliminary results are reported here. The initial outburst from GRO J1655-40 was detected by BATSE on 27 Jul 1994. OSSE observations were made in five separate viewing periods starting between 4 Aug 1994 and 4 Apr 1995. The first, third, and fifth observations are near the peak luminosity. In the second observation, the source flux had dropped by several orders of magnitude and we can only set an upper limit. The fourth observation is a weak …

Performance Of Cdznte Strip Detectors As Sub-Millimeter Resolution Imaging Gamma Radiation Spectrometers, M Mayer, V Boykin, M L. Cherry, J F. Courville, F P. Doty, A Drake, T G. Guzik, L A. Hamel, K Larson, John R. Macri, Mark L. Mcconnell, James M. Ryan, O Tousignant

Space Science Center

We report & gamma;-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for & gamma;-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64×64 orthogonal stripeCdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8×8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (~0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative …

Balloon-Borne Coded Aperture Telescope For Arc-Minute Angular Resolution At Hard X-Ray Energies, Mark L. Mcconnell, V Boykin, R M. Kippen, K Larson, John R. Macri, M Mayer, James M. Ryan, P P. Altice, M L. Cherry, S B. Ellison, B Price, T G. Guzik, R Lockwood, M B. Barakat, K Johnston, N Zotov, M Elaasar

Space Science Center

We are working on the development of a new balloon-borne telescope, MARGIE (minute-of-arc resolution gamma ray imaging experiment). It will be a coded aperture telescope designed to image hard x-rays (in various configurations) over the 20 - 600 keV range with an angular resolution approaching one arc minute. MARGIE will use one (or both) of two different detection plane technologies, each of which is capable of providing event locations with sub-mm accuracies. One such technology involves the use of cadmium zinc telluride (CZT) strip detectors. We have successfully completed a series of laboratory measurements using a prototype CZT detector with …

Charge-Coupled Devices With Fast Timing For Astrophysics And Space Physics Research, M L. Cherry, P P. Altice, S B. Ellison, T G. Guzik, John R. Macri, Mark L. Mcconnell, G Y. Mclean, James M. Ryan, Paul P. Suni

Space Science Center

A charge coupled device is under development with fast timing capability (15 millisecond full frame readout, 30 microsecond resolution for measuring the time of individual pixel hits). The fast timing CCD will be used in conjunction with a CsI microfiber array or segmented scintillator matrix detector to detect x rays and gamma rays with submillimeter position resolution. The initial application will be in conjunction with a coded aperture hard x ray/gamma ray astronomy instrument. We describe the concept and the readout architecture of the device.

Ground-Based Gamma-Ray Burst Follow-Up Efforts: Results Of The First Two Years Of The Batse/Comptel/Nmsu Rapid Response Network, B Mcnamara, T Harrison, James M. Ryan, R M. Kippen, Mark L. Mcconnell, John R. Macri, C Kouveliotou, Gerald J. Fishman, C Meegan, L O. Hanlon, K Bennett, T. A. Spoelstra, V. G. Metlov, N. V. Metlova, E. Feigelson, A. J. Beasley, D. M. Palmer, Scott Barthelmy, Dale E. Gary, E. T. Olsen, S. Levin, P. G. Wannier, M. A. Janssen, The Macho Collaboration, J. Borovicka, P. Pravec, R. Hudec, M. J. Coe

Physics & Astronomy

No abstract provided.

Search For Gamma-Ray Emission From The Lagrangian Points Of Psr 1957+20, R Buccheri, V. Salamone, K Bennett, M Busetta, L Kuiper, W Hermsen, Mark L. Mcconnell, R Much, James M. Ryan, H Steinle, V. Schonfelder

Physics & Astronomy

Compton Gamma Ray Observatory data of the COMPTEL and EGRET telescopes from 3 viewing periods have been used to search for gamma-ray emission from the Lagrangian points L_4_ and L_5_ of the binary system including the eclipsing pulsar PSR1957+20. The result was negative and the upper limits derived remain significantly below detections reported earlier.

Extended Γ‐Ray Emission In Solar Flares, G Rank, K Bennett, H Bloemen, H Debrunner, J Lockwood, Mark L. Mcconnell, James M. Ryan, V Schonfelder, R Suleiman

Space Science Center

During the solar flare events on 11 and 15 June 1991, COMPTEL measured extended emission in the neutron capture line for about 5 hours after the impulsive phase. The time profiles can be described by a double exponential decay with decay constants on the order of 10 min for the fast and 200 min for the slow component. Within the statistical uncertainty both flares show the same long‐term behaviour. The spectrum during the extended phase is significantly harder than during the impulsive phase and pions are not produced in significant numbers before the beginning of the extended emission. Our results …

Comptel Measurements Of Mev Gamma-Ray Burst Spectra, R M. Kippen, James M. Ryan, A Connors, Mark L. Mcconnell, C Winkler, L O. Hanlon, V Schonfelder, J Greiner, M Varendorff, W Collmar, W Hermsen, L Kuiper

Space Science Center

We present results from the on-going spectral analysis of gamma-ray bursts measured by the COMPTEL instrument in its main Compton “Telescope” observing mode (0.75–30 MeV). Thus far, 18 bursts have been analyzed from three years (April 1991–April 1994) of observations. The time-averaged spectra of these events above 1 MeV are all consistent with a simple power law model with spectral index in the range 1.5–3.5. Exponential, thermal bremsstrahlung and thermal synchrotron models are statistically inconsistent with the burst sample, although they can adequately describe some of the individual burst spectra. We find good agreement between burst spectra measured simultaneously by …

Using Batse To Measure Gamma-Ray Burst Polarization, Mark L. Mcconnell, D J. Forrest, W T. Vestrand, M H. Finger

Space Science Center

We describe a technique for measuring the polarization of hard x-rays from γ-ray bursts based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Although the BATSE design (with its large field-of-view for each …

Looking For The Source Of ∼Hour-Long Soft X-Ray Emission Following Grb 780506, A Connors, Mark L. Mcconnell

Space Science Center

GRB 780506, a gamma-ray burst discovered in HEAO 1 A-4 data, was unusual in three respects. First, it was well-measured (by HEAO 1 A-2) in 2–60 keV X-rays. Second, two minutes after it ended, HEAO 1 A-2 detected a faint resurgence of 2–10 keV flux, lasting roughly an hour. From recently calculated position constraints, it appears the source of the extended flux is consistent with the source of the burst, and probably not from a serendipitous transient along the Galactic plane. Third, it now appears GRB 780506 belongs to a newly discovered softer subclass of gamma-rays bursts. This subclass is …

The Angular Distribution Of Comptel Gamma-Ray Bursts, R M. Kippen, James M. Ryan, A Connors, Mark L. Mcconnell, H Hartmann, C Winkler, L O. Hanlon, V Schonfelder, J Greiner, M Varendorff, W Collmar, W Hermsen, L Kuiper

Space Science Center

The superior burst location capability of the COMPTEL instrument aboard the Compton Gamma-Ray Observatory allows us to study the small-scale angular distribution of burst sources with good sensitivity even though the number of burst detections is small. We accumulate four years (April 1991–April 1995) of observations to form a catalog of 27 burst locations whose mean 1σ uncertainty is ∼1°. We find that the COMPTEL bursts are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts within COMPTEL’s angular resolution indicates the possibility of repetition. This possibility is studied using the two-point angular …

Comptel Solar Flare Measurements, James M. Ryan, Mark L. Mcconnell

Space Science Center

We review some of the highlights of the COMPTEL measurements of solar flares. These include images of the Sun in γ rays and neutrons. One of the important features of the COMPTEL instrument is its capability to measure weak fluxes of γ rays and neutrons in the extended phase of flares. These data complement the spectra taken with the COMPTEL burst spectrometer and the telescope during the impulsive phase of flares. We focus our attention on some of these general capabilities of the instrument and the latest results of two long‐duration γ‐ray flares, i.e., 11 and 15 June 1991

Hard X‐Ray Polarimetry Of Solar Flares With Batse, Mark L. Mcconnell, D J. Forrest, W T. Vestrand, M Finger

Space Science Center

We describe a technique for measuring the polarization of hard X‐rays from solar flares based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Since the albedo component can represent a relatively large fraction …

Development Of An Orthogonal-Stripe Cdznte Gamma Radiation Imaging Spectrometer, John R. Macri, Boris A. Apotovsky, J F. Butler, M L. Cherry, Brian K. Dann, A Drake, F P. Doty, T G. Guzik, K Larson, M Mayer, Mark L. Mcconnell, James M. Ryan

Space Science Center

We report performance measurements of a sub-millimeter resolution CdZnTe strip detector developed as a prototype for astronomical instruments operating with good efficiency in the 30-300 keV photon energy range. The prototype is a 1.4 mm thick, 64×64 contact stripe CdZnTe array of 0.375 mm pitch in both dimensions. Pulse height spectra were recorded in orthogonal-stripe coincidence mode which demonstrate room-temperature energy resolution <10 keV (FWHM) for 122 keV photons with a peak-to-valley ratio >5:1. Good response is also demonstrated at higher energies using a coplanar grid readout configuration. Spatial resolution capabilities finer than the stripe pitch are demonstrated. We present the image of a ¹³³Ba source viewed through a collimator …

Large-Area Submillimeter Resolution Cdznte Strip Detector For Astronomy, James M. Ryan, John R. Macri, Mark L. Mcconnell, Brian K. Dann, M L. Cherry, T G. Guzik, F P. Doty, Boris A. Apotovsky, J F. Butler

Space Science Center

We report the first performance measurements of a sub-millimeter CdZnTe strip detector developed as a prototype for space-borne astronomical instruments. Strip detector arrays can be used to provide two-dimensional position resolution with fewer electronic channels than pixellated arrays. Arrays of this type and other candidate technologies are under investigation for the position-sensitive backplane detector for a coded-aperture telescope operating in the range of 30 - 300 keV. The prototype is a 1.4 mm thick, 64 multiplied by 64 stripe CdZnTe array of 0.375 mm pitch in both dimensions, approximately one square inch of sensitive area. Pulse height spectra in both …

The Black-Hole Candidate Gro J0422+32: Mev Emission Measured With Comptel., R Van Dijk, K Bennett, W Collmar, R Diehl, W Hermsen, G G. Lichti, Mark L. Mcconnell, James M. Ryan, V. Schonfelder, A W. Strong, J Van Paradijs, C Winkler

Physics & Astronomy

On Aug. 5, 1992, BATSE detected the bright soft X-ray transient GRO J0422+32,also known as Nova Per 1992. The COMPTEL instrument (0.75-30MeV) aboard the Compton Gamma-Ray Observatory (CGRO) observed this black-hole candidate twice. During the first observation, which started when the X-ray flux was at its maximum, GRO J0422+32 was detected between 1 and 2MeV. The flux in this energy range was higher than expected from an extrapolation of the standard Sunyaev-Titarchuk Comptonisation model fits to the contemporaneous OSSE and SIGMA data. We discuss several models that may explain the total hard-X/γ-ray spectrum, including the generalised Comptonisation model from Titarchuk. …

Comptel Imaging Of The Galactic Disk And The Separation Of Diffuse Emission And Point Sources, H Bloemen, W Hermsen, B Swanenburg, C De Vries, R Diehl, V. Schonfelder, H Steinle, A W. Strong, A Connors, Mark L. Mcconnell, D Morris, G Stacy, K Bennett, C Winkler

Physics & Astronomy

The first MeV image of the inner Galaxy obtained with the COMPTEL telescope aboard the Compton Gamma-Ray Observatory shows a structured ridge of emisssion along the Galactic equator which probably consists of diffuse radiation and unresolved discrete sources. The intensity distribution of this ridge distinctly differs from the expected distribution for a simple model of the diffuse radiation. Most remarkable are the observed excursions out of the disk, which may hint at the presence of gamma-ray point sources located several degrees away from the mid-plane, but a diffuse origin cannot be excluded. If these are indeed discrete sources, a substantial …

Observations Of Gamma-Ray Bursts By Comptel, L O. Hanlon, K Bennett, W Collmar, A Connors, R Diehl, R Van Dijk, J Greiner, J W. Den Herder, W Hermsen, R M. Kippen, L Kuiper, Mark L. Mcconnell, James M. Ryan, V. Schonfelder, H Steinle, A W. Strong, M Varendorff, C Winkler

Physics & Astronomy

During the first year of operation, 22 cosmic gamma-ray bursts were detected within the field of view of the COMPTEL instrument on board the Compton Gamma Ray Observatory. Spectra and time histories for the strongest of these bursts have been obtained from both the main instrument (0.75-30 MeV) and the burst modules (0.3-10 MeV). The deconvolved photon spectra for the majority of bursts are fit by a single power law model with spectral index between -1.6 and -2.8. One strong burst, GRB 910814, exhibited significant curvature and could not be fit by a single power law model. A broken power …

Observations Of Cygnus X-1 Comptel During 1991, Mark L. Mcconnell, D J. Forrest, James M. Ryan, W Collmar, V. Schonfelder, H Steinle, A W. Strong, R Van Dijk, W Hermsen, K Bennett

Physics & Astronomy

The Compton Telescope (COMPTEL) experiment on the Compton Gamma-Ray Observatory (CGRO) has observed the Cygnus region on two occasions during the first (sky survey) phase of its mission. These data represent the most sensitive observations to date of Cygnus X-1 in the 0.75-30 MeV range. The observations in 1991 June and August both showed evidence for emission in the 0.75-2 MeV energy range. The flux level was larger by about a factor of 2 during the August observation. The spectral data were analyzed in the context of a Wien spectral model (the high-energy limit of the Sunyaev-Titarchuk Comptonization spectrum). Fits …

Comptel Measurements Of The Gamma-Ray Burst Grb 930131, James M. Ryan, K Bennett, W Collmar, A Connors, Gerald J. Fishman, J Greiner, L O. Hanlon, W Hermsen, R M. Kippen, C Kouveliotou, L Kuiper, G G. Lichti, John R. Macri, J. Mattox, Mark L. Mcconnell, B Mcnamara, C Meegan, V. Schonfelder, R Vandijk, M Varendorff, W Webber, C Winkler

Physics & Astronomy

On 1993 January 31 at 1857:12 Universal Time (UT), the Imaging Compton Telescope COMPTEL onboard the Compton Gamma Ray Observatory (CGRO) detected the cosmic gamma-ray burst GRB 930131. COMPTEL's MeV imaging capability was employed to locate the source to better than 2 deg (1 sigma error radius) within 7 hr of the event, initiating a world-wide search for an optical and radio counterpart. The maximum likelihood position of the burst from the COMPTEL data is alpha₂₀₀₀ = 12h 18m, delta₂₀₀₀ = -9 deg 42 min, consistent with independent CGRO-Burst and Transient Source Experiment (CGRO-BATSE) and Energetic Gamma Ray …

An Overview Of Solar Flare Results From Comptel, Mark L. Mcconnell

Space Science Center

The COMPTEL experiment on the Compton Gamma Ray Observatory (CGRO) has been operating in orbit since April of 1991. During that time, COMPTEL has observed several large flares, the most notable of which were several X‐class flares which took place in June of 1991. As a solar instrument, COMPTEL has the capability to measure solar flare radiation in two parallel observing modes. In its telescope mode, COMPTEL is capable of measuring both solar flare photons (in the 0.75–30 MeV range) and solar flare neutrons (in the 20–150 MeV range) using the double scatter technique with a field‐of‐view of ∼1 steradian. …

First Results Of The Batse/Comptel/Nmsu Rapid Burst Response Campaign, R M. Kippen, A Connors, John R. Macri, Mark L. Mcconnell, James M. Ryan, W Collmar, J Greiner, V Schonfelder, M Varendorff, Gerald J. Fishman, C Meegan, C Kouveliotou, B Mcnamara, T Harrison, W Hermsen, L Kuiper, K Bennett, L O. Hanlon, C Winkler

Space Science Center

The Imaging Compton Telescope (COMPTEL) on board the Compton Gamma Ray Observatory regularly observes gamma‐ray bursts which occur inside the instrument’s ∼1 sr field‐of‐view. COMPTEL images bursts in the 0.75–30 MeV energy range with a typical location accuracy of 1–3 degrees, depending on burst strength, position, duration, and spectrum. COMPTEL’s imaging capability has been exploited in order to search for fading gamma‐ray burst counterparts at other wavelengths through the establishment of a BATSE/COMPTEL/NMSU rapid burst response campaign. This campaign utilizes near real‐time identification and preliminary burst location by BATSE, accelerated COMPTEL imaging, and a world‐wide network of observers to search …

Comptel Gamma‐Ray Observations Of The Quasars Cta 102 And 3c 454.3, J J. Blom, H Bloemen, W Hermsen, W Collmar, V Schonfelder, H Steinle, A W. Strong, Mark L. Mcconnell, G Stacy, K Bennett, C Winkler

Space Science Center

The blazer‐type active galactic nuclei (AGNs) CTA 102 (QSO 2230+114) and 3C 454.3 (QSO 2251+158), located about 7° apart on the sky, were observed by the Compton Gamma Ray Observatory at four epochs in 1992. Both were detected by EGRET and here we present theCOMPTEL observations of the two quasars. These observations clearly indicate that the power‐law spectra measured by EGRET above ∼50 MeV show a flattening at lower MeV energies. A comparison with observations at other wavelengths shows that the power spectra of CTA 102 and 3C 454.3 peak at MeV energies. This behavior appears to be a …

Comptel Detection Of The Variable Radio Source Gt 0236+610, R Vandijk, H Bloemen, W Hermsen, W Collmar, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, K Bennett, M Much, Mark L. Mcconnell, A Connors

Space Science Center

The highly variable and non‐thermal radio source GT 0236+610 exhibits outbursts with a period of 26.496 days, modulated by a four‐year period. Recent EGRET observations confirmed that this source is the counterpart of the COS‐B source 2CG 135+01.

COMPTEL observed this source during three observations in Phase I. We report here on the detections in each of the observations, the time‐averaged spectrum, and address the question of time variability with respect to the radio phase.

Observations Of The 1991 June 11 Solar Flare With Comptel, G Rank, R Diehl, G G. Lichti, V Schonfelder, M Varendorff, B Swanenburg, R Vandijk, D J. Forrest, John R. Macri, Mark L. Mcconnell, M Loomis, James M. Ryan, K Bennett, C Winkler

Space Science Center

The COMPTEL instrument onboard of the Compton Gamma‐Ray Observatory (CGRO) is sensitive to γ‐rays in the energy range from 0.75 to 30 MeV and to neutrons in the energy range from 10 to 100 MeV.

During the period of unexpectedly high solar activity in June 1991, several flares from active region 6659 were observed by COMPTEL. For the flare on June 11, we have analyzed the COMPTEL telescope data, finding strong 2.223 MeV line emission, that declines with a time constant of 11.8 minutes during the satellite orbit in which the flare occurs. It remains visible for at least 4 …

Tracking And Imaging Gamma Ray Experiment (Tigre) For 1 To 100 Mev Gamma Ray Astronomy, A Alpar, D Bhattacharya, R Buccheri, K Dotson, D J. Forrest, W N. Johnson, G Kanbach, U Kiziloglu, R Kroeger, J Kurfess, M L. Mcconnell, H Ogelman, B O'Neill, Terence J. O'Neill, A Owens, B Pi, B Pierce, James M. Ryan, B Sacco, G Simnett, O T. Tumer, W Wheaton, R S. White, Allen Zych

Space Science Center

A large international collaboration from the high energy astrophysics community has proposed the Tracking and Imaging Gamma Ray Experiment (TIGRE) for future space observations. TIGRE will image and perform energy spectroscopy measurements on celestial sources of gamma rays in the energy range from 1 to 100 MeV. This has been a difficult energy range experimentally for gamma ray astronomy but is vital for the future considering the recent exciting measurements below 1 and above 100 MeV. TIGRE is both a double scatter Compton and gamma ray pair telescope with direct imaging of individual gamma ray events.

Multi‐layers of Si strip …

Comptel’S Solar Flare Catalog, R Suleiman, D J. Forrest, Mark L. Mcconnell, James M. Ryan, R Diehl, G G. Lichti, G Rank, V Schonfelder, A W. Strong, M Varendorff, K Bennett, L O. Hanlon, C Winkler, H Bloemen, W Hermsen, B Swanenburg

Space Science Center

COMPTEL, the imaging gamma‐ray telescope, capable of detecting gamma rays in the range of 0.1–30 MeV, is one of four instruments aboard NASA’s Compton Gamma‐Ray Observatory. The Comptel burst detectors (single Defector Mode) have a field of view of ∼2.5 π sr. These detectors of COMPTEL permit measurements of energy spectra and time histories of solar flare gamma‐ray emission. A search through the Single Detector Mode’s data is being conducted. We summarize the preliminary results of this search.

Comptel Observations Of Gamma‐Ray Flares In October 1991, M Varendorff, D J. Forrest, Mark L. Mcconnell, James M. Ryan, R Suleiman, R Diehl, G G. Lichti, G Rank, V Schonfelder, K Bennett, L O. Hanlon, C Winkler, B Swanenburg

Space Science Center

The COMPTEL experiment on GRO images 0.75–30 MeV celestial gamma‐radiation that falls within its 1 steradian field of view. During observation 12 (primary target Cen A) in October 1991 the sun had been in the fov and several solar flares associated with the active region 6891 had been observed. Time profile and energy spectra had been produced, using COMPTEL’s primary mode of operation (the telescope mode). Additionally the number of counts received in the D2‐single burst detector (the secondary mode of operation) are given. We summarize the preliminary results on all of these flares.

Comptel Upper Limits For Seyfert Galaxies, M Maisack, W Collmar, G G. Lichti, V Schonfelder, H Steinle, H Bloemen, W Hermsen, Mark L. Mcconnell, G Stacy, P Barr, O R. Williams

Space Science Center

The gamma‐ray emission of Seyfert galaxies has fallen far short of pre‐GRO expectations. No single object of this class has been detected by either COMPTEL or EGRET, and OSSE has detected only a fraction of the Seyferts expected. To derive a more stringent upper limit to the emission from these objects in the energy ranges 0.75 to 1 and 1 to 3 MeV, we have summed a large number of COMPTEL observations acquired during Phase 1 of the GRO mission. From a total of 47 observations of 23 individual X‐ray selected Seyfert galaxies, we derive preliminary upper limits of 8×10 …