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CGRO Status Report for February, 1996
Compton Gamma Ray Observatory Status Report #189
Friday February 2, 1996
Questions or comments can be sent to
Chris Shrader at the CGRO-SSC.
Guest Investigator News
The Cycle-6 NRA has bee issued. Proposals are due on April 19, 1996, which
is about one month later than originally planned as a result of the two
government furloughs. The NRA and appendicies can be retreived via ftp
from grossc.gsfc.nasa.gov (in PostScript format). Just login in as
anonymous, cd nra, cd cycle6, get nra.ps, etc. Alternatively, visit our
WWW site: http://cossc.gsfc.nasa.gov/cossc/cossc.html. You will, or may
already have, receive the NRA in the mail. Hard copy of the appendicies
will be mailed upon requests to Sandy Barnes (barnes @grossc.gsfc.nasa.gov,
In any case, PLEASE READ THE BULLETED LIST OF CHANGES at the begining
of the NRA (and repeated at the beginning of Appendix A).
Also delayed as a result of government furloughs is the opening of the CGRO
exhibit at the Smithsonian National Air and Space Museum. The exhibit is
completed and delivered to NASM however, and the opening is now imminent - stay
Despite inactivity Washington, the high-energy sky has remained very active!
There have been recent target-of-opportunity declarations for gamma-ray
activity in 3C 279 and the new galactic-center transient GRO J1744-28 - see
all the discussion in hte instrument reports below.
The combination of the U. S. government shut-down and the blizzard
obviously had a significant impact on the work over the last two months.
In spite of this, thanks to the hard work of the EGRET team, the basic
services are almost back to normal, although the scientific analysis and
interpretation work is still well behind the schedule that we had planned.
Delivery of the final phase 4 data to the GRO SSC is back on schedule, and
delivery of the phase 5 preliminary data to the GRO SSC is also back on
schedule. Interaction with guest investigators is nearly back to normal.
The EGRET instrument operations were normal throughout the last two month
During viewing period 511, 3C 279 was found to be at a high level of
intensity, as announced in an IAU telegram. There was a scheduled campaign
of observations so there was good coverage at many wavelengths. The level
of intensity was well above the target of opportunity threshold; so the
observation was continued. This total observation should be extremmely
benefical in helping to understand the basic physical processes involved in
the tremendous release of energy by 3C 279 especially during these high
As you probably noted from recent publications, EGRET has now seen seven
pulsars with high energy gamma ray emission. In spite of the wide variety
of characteristics, some features seem to be emerging. There is an
increased fraction of the emission in gamma rays as a function of age of
the pulsar. The spectral index also increases with age, suggesting that as
pulsars grow older, not only does a larger fraction of the emitted energy
go into gamma rays, but especially into higher energy gamma rays. With one
exception, the polar cap model seems to predict the luminosity well. That
one exception may be due to an exceptionally high magnetic field. The
outer gap model still does well in explaining the relative phases of the
gamma ray pulses to the radio ones.
The COMPTEL instrument is performing well and continues normal
At IAU Colloquium 160, "Pulsars: Problems and Progress," recently held
in Sydney, Australia, W. Hermsen presented an overview of recent
COMPTEL results on pulsars, on behalf of the collaboration. COMPTEL
has either detected or now has indications of emission from six of the
eight pulsars detected to date at gamma-ray energies above 0.5 MeV.
Newly reported is the detection of PSR B1951+32 at MeV energies, as
well as a likely detection of the soft EGRET pulsar PSR B0656+14
between 10 and 30 MeV.
A number of additional gamma-ray bursts have occurred within the field
of view of COMPTEL since the last report (GRBs 951202, 951208, 960102,
960124, 960129, and 960202). Once again, none of these was detected
at MeV energies by COMPTEL, further extending the longest period
(since May 1995) without a field-of-view burst detection by COMPTEL.
A new release of COMPTEL data to the CGRO public archive has recently
taken place, including the first delivery of standard-processing
maximum-likelihood skymaps by viewing period for Phases 1 and 2. A
further delivery of low-level and first high-level data products
covering the later viewing periods of Phase 3 is anticipated in the
OSSE operations are normal. The instrument is working as designed, with all
subsystems in complete and full operation. The slewing response to BATSE burst
triggers has been disabled since 11 December, because of the bursting pulsar,
GRO J1744-28, discovered by BATSE.
OSSE monitored this new object from 14 Dec. to 20 Dec. 1995 and from 5 Jan. to
30 Jan. 1996. Data from early in the observation helped position the source,
and were summarized in IAUC 6276 (see below). We have observed about 400
bursts, from which we detect emission above 100 keV. We also detect the 2.1 Hz
pulsar to similar energies. Analysis is currently concentrating on
spectroscopy of the bursts and pulsations. Results to date are reasonably
consistent with a featureless blackbody or simple exponential.
J. D. Kurfess and J. E. Grove, Naval Research Laboratory; D.
Messina, SFA, Inc.; and J. Tueller, Goddard Space Flight Center,
report: "We have acquired further Compton Observatory observations
that further constrain the position of the source first reported on
IAUC 6272. Data obtained during Dec. 15-17 with the four OSSE
detectors scanning along the galactic plane provide a galactic-
longitude position between -0.27 and +0.17 deg (95-percent
confidence). The OSSE field-of-view normal to the scan direction
is 11.4 deg FWHM. When coupled with the position reported on IAUC
6275, the location of the transient repeater is constrained to a
region with the following vertices (equinox 2000.0): R.A. =
17h44m34s, Decl. = -28o34'.6; 17h45m58s, -28o46'.4; 17h43m11s,
-29o01'.6; 17h41m43s, -28o49'.0."
Data through viewing period 402.5 have been delivered to the Compton GRO
Science Support Center archive.
Since the last report the BATSE team has been kept very busy by a newly
discover transient source. BATSE team contributions to the IAU Circulars
are as follows:
IAU Circular 6272:
G. J. Fishman, Marshall Space Flight Center (MSFC), NASA; C.
Kouveliotou, Universities Space Research Association and MSFC; J.
van Paradijs, University of Alabama at Huntsville (UAH) and
University of Amsterdam; B. A. Harmon, MSFC; W. S. Paciesas and M.
S. Briggs, UAH; and J. Kommers and W. H. G. Lewin, Massachusetts
Institute of Technology, report observations from the Compton
Observatory's BATSE experiment: "A transient x-ray source is being
observed that emits bursts at energies between 10 and 50 keV from
the general direction of the Galactic Center. Over 200 bursts with
typical widths between 8 and > 30 s have been seen from the source
since Dec. 2. The rate of the x-ray bursts has declined from a
maximum of about 18 events per hour on Dec. 2.7 UT to a current
average rate of about 1.2 events per hour (corrected for live-time
and earth occultation). The average burst peak flux is about 5 x
10E-8 erg cmE-2 sE-1 and the typical fluence is about 5 x 10E-7
erg/cm2 per burst in the energy band 20-40 keV. No steady emission
is seen from the source. The spectra of the events are similar to
bursts from soft gamma-ray repeaters, but much harder than those of
type-II bursts from the rapid burster 1730-335. The most probable
location of the source is centered at R.A. = 17h52m, Decl. = -23o,
with an error radius of about 6 deg (1 sigma). The behavior
reported here is unlike that previously seen from any x-ray or
gamma-ray transient source."
IAU Circular 6275:
NEW X-RAY TRANSIENT REPEATER
K. Hurley, on behalf of the Ulysses Gamma-Ray Burst Team; C.
Kouveliotou, A. Harmon, G. Fishman, and M. Briggs, on behalf of the
BATSE/GRO team; J. van Paradijs, University of Amsterdam; and J.
Kommers and W. Lewin, Massachusetts Institute of Technology, report:
"A preliminary network synthesis position (cf. Hurley 1994, Ap.J.
431, L31) for the new repeating x-ray transient source (IAUC 6272)
has been obtained using Ulysses and BATSE (specifically, 59 BATSE
events from Dec. 2). The position is an annulus whose half-width
is 0.21 deg centered at R.A. = 2h44m37s, Decl. = -55o31'.0 (equinox
2000.0), with central radius 87.500 deg. Using the BATSE
occultation technique, we excluded a large area of the sky for the
source origin. The intersection of the network synthesis annulus
with the remaining (allowed) area of detection may be approximated
by a box with the following coordinates: R.A. = 17h50m, Decl. =
-28o.1; 17h49m, -28o.5; 17h23m, -30o.3; 17h19m, -31o.0."
IAU Circular 6284:
W. S. Paciesas, University of Alabama, Huntsville; B. A.
Harmon and G. J. Fishman, Marshall Space Flight Center (MSFC),
NASA; and S. N. Zhang and C. R. Robinson, Universities Space
Research Association and MSFC, report: "BATSE occultation
monitoring indicates the emergence of a new hard x-ray source,
designated GRO J1744-28, in the region of the Galactic Center. The
location (equinox 2000.0) is within a region whose vertices are R.A.
= 17h42m, Decl. = -27o15'; 17h45m, -28o25'; 17h43m, -28o43', 17h47m,
-29o46' (90-percent confidence). Archival data show indications of
the source at gradually increasing intensity for approximately the
past month. However, systematic confusion with other sources in
the region limits our ability to quantify the time of earliest
detection. The average intensity between Jan. 1 and 7 was about
0.58 photons cmE-2 sE-1 in the band 20-100 keV, with small (10
percent) daily variations. The spectrum can be approximately
represented by a steep power law with photon number index -4.2.
Contributions to the flux from nearby sources cannot be excluded.
The new source may be the persistent counterpart to the bursting
source previously reported (IAUC 6272, 6275, 6276). If so, the
combination of the occultation source position with that reported
in IAUC 6276 provides a more precise location for this unusual
IAU Circular 6285:
M. H. Finger, Compton Observatory Science Support Center; R.
B. Wilson and B. A. Harmon, Marshall Space Flight Center, NASA; K.
Hagedon, University Space Research Association; and T. A. Prince,
California Institute of Technology, report for the Compton
Observatory BATSE team: "Pulsations with a period of 467 ms are
being detected in the energy band 25-45 keV from a source in the
galactic-center region. The pulsed flux is about 40 percent of the
total flux observed from the hard x-ray transient GRO J1744-28
(IAUC 6284). Absence of any other persistent source consistent
with the direction and flux of the observed pulsed emission implies
that the pulsations are from GRO J1744-28. The 31-ms-resolution
data in which the pulsations were observed excluded time intervals
containing outbursts from the possibly separate burst source in the
same region (IAUC 6272, 6275, 6276). On Jan. 6.0 UT, the measured
barycentric pulse frequency was 2.1409720(5) Hz."
IAU Circular 6286:
TRANSIENT X-RAY BURSTER GRO J1744-28
C. Kouveliotou, Universities Space Research Association; J.
Kommers and W. H. G. Lewin, Massachusetts Institute of Technology;
J. van Paradijs, University of Alabama, Huntsville (UAH) and
University of Amsterdam; G. J. Fishman, Marshall Space Flight
Center (MSFC), NASA; and M. S. Briggs, UAH; report: "Strong
pulsations (about 50 percent modulation) near 2.1 Hz have been
observed in the bursts from the burst source near the galactic
center (IAUC 6275, 6276). Thus this unusual burst source and the
transient pulsar GRO J1744-28 (IAUC 6284, 6285) are the same
source. The hard x-ray bursts are therefore very likely the result
of accretion instabilities on a strongly magnetized neutron star in
a binary system."
K. Hurley, Space Sciences Laboratory, University of California,
Berkeley, on behalf of the Ulysses Gamma-Ray Burst Team;
Kouveliotou, A. Harmon, Fishman, and Briggs, on behalf of the Gamma
Ray Observatory BATSE team; van Paradijs, Kommers, and Lewin, write:
"A refined position for the new repeating x-ray transient source
(IAUC 6272) has been obtained using Ulysses and BATSE (specifically,
one Ulysses/BATSE triggered event on Jan. 8). The position is an
annulus whose halfwidth is 0.047 deg centered at R.A. = 3h02m57s,
Decl. = -61o34'07" (equinox 2000.0), with central radius 83.974 deg.
The intersection of this annulus with the positions reported on
IAUC 6276 and 6284 defines a location that may be approximated by a
box with the following coordinates: R.A. = 17h43m22s, Decl. =
-28o46'.7; 17h45m07s, -28o39'.2; 17h45m35s, -28o43'.1; 17h43m49s,
-28o51'.0. This error box is smaller than, but nested within, the
previous network synthesis localizations."
M. H. Finger, Compton Observatory Science Support Center; R. B.
Wilson, MSFC; and van Paradijs, communicate for the Compton
Observatory BATSE team: "The pulse timing of the 467-ms-period x-
ray pulsar GRO J1744-28 shows a binary orbital motion Doppler
signature. A fit of frequencies observed between 1995 Dec. 21 and
1996 Jan. 10 yields the following parameters: orbital period
11.76(3) days; epoch of superior conjunction JD 2450079.71(2);
a sin i = 2.59(3) light seconds; spin frequency 2.1410016(3) Hz (at
1995 Dec. 31.0 UT); and frequency derivative 8.6(5) x 10E-12 Hz/s.
We find a 90-percent confidence upper limit of 0.026 to the
eccentricity. The x-ray mass function is f(M) = 1.31(4) x 10E-4
solar mass. For a 1.4-solar mass neutron star and an inclination >
30 deg, the companion mass is 0.065-0.14 solar mass, with a Roche
lobe radius of 4.1-5.2 solar radii."
IAU Circular 6290:
M. S. Briggs, University of Alabama, Huntsville (UAH); B. A. Harmon,
NASA Marshall Space Flight Center (MSFC); J. van Paradijs, UAH and
University of Amsterdam; C. Kouveliotou, Universities Space Research
Association; G. J. Fishman, MSFC; and J. Kommers and W. H. G. Lewin,
Massachusetts Institute of Technology, report for the Compton
Observatory BATSE team: "The increased intensity of GRO J1744-28
enables improved spectral analysis. Using burst observations with the
BATSE Large Area Detectors (> 30 keV) and a Spectroscopy Detector
(> 8 keV), unabsorbed power law and OTTB models may be excluded.
Acceptable fits are obtained with a blackbody model with no absorption
and kT = 6 keV and with an OTTB model with kT = 10 keV and absorption
of N(H) = 1.6 times 10**24 cm**-2. Very similar spectral results are
obtained for the persistent spectrum from occultation observations.
This similarity argues for a common emission process for the burst and
Fishman, Harmon, Kouveliotou, van Paradijs, Briggs, Kommers and
Lewin, with also K. Deal and P. Woods, UAH, report: "The unusual
burster in the galactic center region, identified with the x-ray pulsar
GRO J1744-28 (IAUC 6286), continues to increase in burst intensity and
steady emission. Over the past four weeks, both the peak flux and the
fluence of the individual bursts have increased by about a factor of six.
On Jan. 15 their average values (20-50 keV) were about 2 and about 7
times 10**-7 erg cm**-2 s**-1, respectively. Over the past ten days,
the burstrate has increased to about 25 observed bursts per day (some 40
per day, corrected for earth occultation and livetime) from a previous
average of about 18 observed bursts per day during the preceding month.
The burst durations have remained the same, 4-6 s FWHM, over the entire
period of observation. The associated steady source, as observed by earth
occultation, has increased in intensity to about 2.5 Crab (20-100 keV)
on Jan. 16."
The burst trigger is currently using count rates from 20-300 keV energy range.
As of February 1 BATSE has detected 1456 gamma-ray bursts out of a total of
on-board triggers in 1745 days of operation. There have been 766 triggers due
to solar flares, 10 due to SGR events, and 52 due to terrestrial gamma-ray