National Aeronautics and Space Administration

Contents:

RXTE Cycle 8 Deadline has Passed! (November 26, 2002)
RXTE Detects Strongest Known Magnetic Field (November 4, 2002 )
The Nature of Anomalous X-ray Pulsars (September 12, 2002)
New FTOOLS for Our Trade (June 25, 2002)
RXTE Breaks Six Figures, Shares with Public (June 12, 2002)
Discovery of Fastest Known Accreting Millisecond Pulsar (April 12, 2002)
Black Holes play the Same Tune (April 09, 2002)
New and Improved Background Models Released on New and Improved PCA Digest Page! (February 27, 2002)

November 26, 2002

The deadline for receipt of observing proposals for RXTE's Cycle 8 was November 21, 2002. Despite sharing the X-ray astronomy stage with newer, higher profile missions such as Chandra and XMM-Newton, RXTE has proven more popular than ever, receiving a total number of proposals more than 10% above Cycle 7's submissions. RXTE is also proving popular with a new crowd---about 10% of submitted proposals came from first-time RXTE PIs. Could it be those reinstated GO funds?

In total, nearly 76 Megaseconds of observing time have been requested by Cycle 8 proposers, slightly less than half of which is for Target of Opportunity investigations. Targets span the gamut from single stars to clusters of galaxies.

With a review planned for early 2003, and resulting new observations set to enter the schedule in March 2003, RXTE's Cycle 8 promises to be an exciting year for further exploration of the limits of gravity, space and time.

RXTE observers have identified the most magnetic object known in the Universe, the result of the first direct measurement of a magnetic field around the peculiar neutron star SGR 1806-20. The immense magnetic field strength of this magnetar is approximately a million billion (10^15) gauss (100 billion tesla), according to a team led by Alaa Ibrahim, a doctoral candidate at George Washington University conducting research at NASA's Goddard Space Flight Center in Greenbelt, Md. His team's results were published in the Astrophysical Journal Letters in July 2002.

Check out the NASA press release for more information.

September 12, 2002

A team of RXTE researchers (Fotis Gavriil & Vicki Kaspi, McGill University, Montreal, Canada; Peter Woods, NASA's Marshall Space Flight Center) announced their discovery of Magnetar-like X-ray Bursts from an Anomalous X-ray Pulsar in the 12 September issue of the journal Nature. The two bursts from AXP 1E 1048-5937 observed with RXTE are similar to bursts in Soft Gamma Repeaters (SGRs), implying that AXPs and SGRs are closely related, and both are magnetars---young neutron stars powered by a decaying ultra-high-strength magnetic field. For more information, check out the NASA Press Release.

June 25, 2002

A new version of the HEAsoft FTOOLS package, version 5.2, is now available. The package includes several improvements for RXTE data analysis, including new and greatly improved PCA response matrices, a new energy-to-channel file, and an updated PCABACKEST which operates on the latest combined background model files. The barycenter correction script FAXBARY has been released with a bug correction.

The new PCA background models and tools work much better for PCU0, however they still produce slightly discontinuous results during the time period near the loss of the propane layer. PCABACKEST now supports the new Combined Models (CM), and its output files contain documentation in the header stating which background models were used. XTEFILT has been updated to produce a new derived quantity necessary for the Combined Models. This requires the addition of some new AppIDs to the XTEFILT AppID list; the new list appears in the fhelp for XTEFILT. Consult the PCA Digest page for instructions on using the new tools, as well as the latest information on the new models and additional details about PCA background issues.

For more details about all the RXTE changes please see the full release notes.

June 12, 2002

On January 12, 2002 the Rossi X-ray Timing Explorer reached an impressive milestone---its 100,000th obsID since the beginning of the guest observer program. Fittingly, observation 100,000 belongs to no single PI, but is part of an ongoing series of background pointings, the data from which are immediately public. The obsID in question is 60801-01-23-23Z, from mission day 2933. Since all RXTE users benefit from a well understood and well modeled background, we can all participate in a toast to the satellite next time the champagne comes around. The GOF will be toasting "to 100,000 more!"

April 12, 2002

RXTE PCA Team members have discovered a new millisecond accreting pulsar near the Galactic center. The source was discovered by Craig Markwardt in his twice-weekly monitoring scans of the Galactic bulge using the RXTE PCA, scans specifically designed to catch fast-evolving and low luminosity transient outbursts of X-ray sources. This new source, XTE J1751-305, has a frequency of 435.3 Hz (equivalent to a pulsar period of 2.3 msec). Prior to this discovery, the only millisecond pulsar known was SAX J1808.4-3658, with a spin frequency of 401.5 Hz.

Accreting Millisecond pulsars are thought to be a link between low mass X-ray binaries, which are systems where a neutron star accretes matter and is presumably spun up by accretion torques, and isolated millisecond pulsars, which are rapidly spinning but have no companion. SAX J1808.4-3658 was the first source where a rapidly spinning neutron star was definitively discovered in an accreting system.

The outburst of SAX J1808.4-3658 was both low luminosity and rapidly decaying, making it difficult to detect and make follow-up observations. The RXTE PCA bulge monitoring program was an effort to detect sources like SAX J1808.4-3658 quickly before they had a chance to fade. The effort has paid off with the discovery of this new millisecond pulsar system, designated XTE J1751-305. The new source has a faster pulsar spin frequency than SAX J1808.4-3658, but they are notably close in frequency and clearly the same sort of beasts.

In further analysis of RXTE data from XTE J1751-305, Markwardt and collaborator Jean Swank have determined that the spin frequency is modulated with a period of 42 minutes, probably Doppler modulation due to motion in a binary orbit. This orbital period of 42 minutes is much shorter than the 2 hour period of SAX J1808.4-3658, and one of the shortest known for neutron star systems.

The modulations also constrain the nature of the companion star. The projected radius of the neutron star's circular motion is only 10 light-milliseconds -- about 3000 km. It is likely that the system is viewed at an intermediate angle and that the companion is of very low mass, about 0.014 solar masses, or approximately 15 Jupiter masses. Such a star is likely to be a helium-rich star. The discovery of a second accreting millisecond pulsar indicates that SAX J1808.4-3658 was not a special case, but one of a population of sources.

April 09, 2002

A press release today by Phil Uttley and Ian McHardy (U. Southampton) has attracted considerable media interest. Uttley and McHardy have concluded that timescales of X-ray variability apparently scale with black hole mass which would suggest that AGN X-ray variations are just a super-slowed down version of XRB variations. See more about The Music of the Singularities at:

http://www.cnn.com/2002/TECH/space/04/09/black.holes/index.html http://space.com/scienceastronomy/astronomy/blackhole_music_020409-1.html

February 27, 2002

New Bright and Faint Background Models for Epoch 3 and beyond, featuring measurable improvement over previous models as well as a reorganization of the files for ease of use, are here! Visit the PCA Digest your source for the latest PCA news, for details on the new models, and a user-friendly table where you can download all you need for better background subtraction today. The PCA Digest has been reorganized for clarity. A pointer from the PCA Digest to model-builder Craig Markwardt's documentation guides users through many things, including the steps of using the new models with the current tools for PCU0 background subtraction. Coming soon: a patch to the RXTE FTOOLs which will make background subtraction much more straightforward for all Epochs.

Briefly, the new models feature:

• sensitivity to X-ray variations improved by factor of ~2 over previous models;
• applicability to PCU0 (needs new FTOOLS to fully exploit);
• new model packaging means fewer files to deal with;
• gain Epoch 3 is now divided into Epochs 3a and 3b for faint sources;

This page is maintained by the RXTE GOF and was last modified on Wednesday, 24-Aug-2022 11:10:31 EDT.