Discovery of a 115 Day Orbital Period in the Ultraluminous X-ray Source NGC 5408 X-1 (2009)
We report the detection of a 115 day periodicity in SWIFT/XRT monitoring data from the ultraluminous X-ray source (ULX) NGC 5408 X-1. Our ongoing campaign samples its X-ray flux approximately twice...
Evidence for an Intermediate Mass Black Hole in NGC 5408 X-1 (2009)
Strohmayer, Tod E., Mushotzky, Richard F.
We report the discovery with XMM-Newton of correlated spectral and timing behavior in the ultraluminous X-ray source (ULX) NGC 5408 X-1. An ~100 ksec pointing with XMM/Newton obtained in January,...
Gavriil, Fotis P., Strohmayer, Tod E., Bhattacharyya, Sudip
We report on Chandra X-ray Observatory (CXO) High-Energy Transmission Grating (HETG) spectra of the dipping Low Mass X-ray Binary (LMXB) 1A 1744-361 during its July 2008 outburst. We find that its...
The Advanced X-ray Timing Array (AXTAR) (2008)
Chakrabarty, Deepto, Ray, Paul S., Strohmayer, Tod E., Collaboration, For The AXTAR
AXTAR is an X-ray observatory mission concept, currently under study in the U.S., that combines very large collecting area, broadband spectral coverage, high time resolution, highly flexible...
Fast X-ray Oscillations During Magnetar Flares (2007)
The giant flares produced by highly magnetized neutron stars, "magnetars," are the brightest sources of high energy radiation outside our solar system. Serendipitous observations with NASA's Rossi...
Cackett, Edward M., Miller, Jon M., Bhattacharyya, Sudip, Grindlay, Jonathan E., Homan, Jeroen, Van Der Klis, Michiel, ...
Using Suzaku observations of three neutron star low-mass X-ray binaries (Ser X-1, 4U 1820-30 and GX 349+2) we have found broad, asymmetric, relativistic Fe K emission lines in all three objects....
Bhattacharyya, Sudip, Strohmayer, Tod E.
We report on an analysis of XMM-Newton data from the neutron star low mass X-ray binary (LMXB) Serpens X-1 (Ser X-1). Spectral analysis of EPIC PN data indicates that the previously known broad iron...
Bhattacharyya, Sudip, Strohmayer, Tod E.
Millisecond period brightness oscillations during the intensity rise of thermonuclear X-ray bursts are likely caused by an azimuthally asymmetric, expanding burning region on the stellar surface. The...
Discovery of 442-Hz Pulsations from an X-ray Source in the Globular Cluster NGC 6440 (2007)
Gavriil, Fotis P., Strohmayer, Tod E., Swank, Jean H., Markwardt, Craig B.
We report on the serendipitous discovery of a 442-Hz pulsar during a Rossi X-ray Timing Explorer (RXTE) observation of the globular cluster NGC 6440. The oscillation is detected following a...
Quasi-Periodic Variability in NGC 5408 X-1 (2007)
Strohmayer, Tod E., Mushotzky, Richard F., Winter, Lisa, Soria, Roberto, Uttley, Phil, Cropper, Mark
We report the discovery with XMM-Newton of quasiperiodic variability in the 0.2 - 10 keV X-ray flux from the ultraluminous X-ray source NGC 5408 X-1. The average power spectrum of all EPIC-pn data...
Neutron star oscillations and QPOs during magnetar flares (2006)
Watts, Anna L., Strohmayer, Tod E.
The high frequency oscillations discovered in the tails of giant flares from two magnetars are thought to be the first direct detections of seismic vibrations from neutron stars. The possibility of...
High frequency oscillations during magnetar flares (2006)
Watts, Anna L., Strohmayer, Tod E.
The recent discovery of high frequency oscillations during giant flares from the Soft Gamma Repeaters SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star...
The 2004 Hyperflare from SGR 1806-20: Further Evidence for Global Torsional Vibrations (2006)
Strohmayer, Tod E., Watts, Anna L.
We report an analysis of the archival Rossi X-ray Timing Explorer (RXTE) data from the December 2004 hyperflare from SGR 1806-20. In addition to the 90 Hz QPO first discovered by Israel et al., we...
An unusual precursor burst with oscillations from SAX J1808.4-3658 (2006)
Bhattacharyya, Sudip, Strohmayer, Tod E.
We report the finding of an unusual, weak precursor to a thermonuclear X-ray burst from the accreting millisecond pulsar SAX J1808.4-3658. The burst in question was observed on Oct. 19, 2002 with the...
RXTE Observations of 1A 1744-361: Correlated Spectral and Timing Behavior (2006)
Bhattacharyya, Sudip, Strohmayer, Tod E., Swank, Jean H., Markwardt, Craig B.
We analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of the transient low mass X-ray binary (LMXB) system 1A 1744-361. We explore the X-ray intensity and spectral...
The Discovery of a Neutron Star with a Spin Frequency of 530 Hz in A1744-361 (2006)
Bhattacharyya, Sudip, Strohmayer, Tod E., Markwardt, Craig B., Swank, Jean H.
We report the detection with the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) of 530 Hz burst oscillations in a thermonuclear (type I) burst from the transient X-ray source...
Watts, Anna L., Strohmayer, Tod E.
The nature of the asymmetry that gives rise to Type I X-ray burst oscillations on accreting neutron stars remains a matter of debate. Of particular interest is whether the burst oscillation mechanism...
Bhattacharyya, Sudip, Strohmayer, Tod E.
We analyse archival Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) data of thermonuclear X-ray bursts from the 2002 outburst of the accreting millisecond pulsar SAX J1808.4-3658....
Bhattacharyya, Sudip, Strohmayer, Tod E.
Non-photospheric-radius-expansion (non-PRE) double-peaked bursts may be explained in terms of spreading (and temporary stalling) of thermonuclear flames on the neutron star surface, as we argued in a...
Watts, Anna L, Strohmayer, Tod E
The recent discovery of high frequency oscillations in giant flares from SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is...
Bhattacharyya, Sudip, Miller, M. Coleman, Strohmayer, Tod E., Lamb, Frederick K., Markwardt, Craig B.
We discuss millisecond period brightness oscillations and surface atomic spectral lines observed during type I X-ray bursts from a neutron star in a low mass X-ray binary system. We show that...
A non-PRE double-peaked burst from 4U 1636-536: evidence for burning front propagation (2005)
Bhattacharyya, Sudip, Strohmayer, Tod E.
We analyse Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of a double-peaked burst from the low mass X-ray binary (LMXB) 4U 1636--536 that shows no evidence for photospheric...
Bhattacharyya, Sudip, Strohmayer, Tod E.
We report on a study of the evolution of burst oscillation properties during the rising phase of X-ray bursts from 4U 1636--536 observed with the proportional counter array (PCA) onboard the Rossi...
Discovery of Fast X-ray Oscillations During the 1998 Giant Flare from SGR 1900+14 (2005)
Strohmayer, Tod E., Watts, Anna L.
We report the discovery of complex high frequency variability during the August 27, 1998 giant flare from SGR 1900+14 using the Rossi X-ray Timing Explorer (RXTE). We detect an 84 Hz oscillation...
Watts, Anna L., Strohmayer, Tod E., Markwardt, Craig B.
The accreting millisecond pulsar XTE J1814-338 exhibits oscillations at the known spin frequency during Type I X-ray bursts. The properties of the burst oscillations reflect the nature of the thermal...
RX J0806.3+1527 is a candidate double degenerate binary with possibly the shortest known orbital period. The source shows an 100% X-ray intensity modulation at the putative orbital frequency of 3.11...
Light curves of oscillating neutron stars (2005)
We calculate light curves produced by $r$-modes with small azimuthal wavenumbers, $m$, propagating in the surface fluid ocean of rotating neutron stars. We include relativistic effects due to rapid...
CHANDRA Detection of the AM CVn binary ES Cet (KUV 01584-0939) (2004)
We report on CHANDRA ACIS observations of the ultracompact AM CVn binary ES Cet. This object has a 10.3 minute binary period and is the most compact of the confirmed AM CVn systems. We have, for the...
Detection of Nitrogen and Neon in the X-ray Spectrum of GP Com with XMM/Newton (2004)
We report on X-ray spectroscopic observations with XMM/Newton of the ultracompact, double white dwarf binary, GP Com. With the Reflection Grating Spectrometers (RGS) we detect the Lyman alpha and...
CHANDRA Observations of V407 Vul: Confirmation of the Spin-up (2004)
V407 Vul is a candidate double-degenerate binary with a putative 1.756 mHz (9.5 min) orbital frequency. In a previous timing study using archival ROSAT and ASCA data we reported evidence for an...
Bhattacharyya, Sudip, Strohmayer, Tod E., Miller, M. Coleman, Markwardt, Craig B.
Detailed modeling of the millisecond brightness oscillations during thermonuclear bursts from low mass X-ray binaries can provide important information about neutron star structure. Until now the...
Future Probes of the Neutron Star Equation of State Using X-ray Bursts (2004)
Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have resulted in the discovery of fast (200 - 600 Hz), coherent X-ray intensity oscillations (hereafter, "burst oscillations") during...
X-ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338 (2003)
Strohmayer, Tod E., Markwardt, Craig B., Swank, Jean H., Zand, Jean In 't
Since the discovery of the accreting millisecond pulsar XTE J1814-338 a total of 27 thermonuclear bursts have been observed from the source with the Proportional Counter Array (PCA) onboard the Rossi...
Phase Coherent Timing of RX J0806.3+1527 with ROSAT and CHANDRA (2003)
RX J0806.3+1527 is an ultra-compact, double degenerate binary with the shortest known orbital period (321.5 s). Hakala et al. (2003) have recently reported new optical measurements of the orbital...
Discovery of X-ray QPOs from an Ultra-luminous X-ray Source in M82: Evidence Against Beaming (2003)
Strohmayer, Tod E., Mushotzky, Richard F.
We report the discovery with the EPIC CCD cameras onboard XMM-Newton of a 54 mHz quasiperiodic oscillation (QPO) in the > 2 keV X-ray flux from an ultraluminous X-ray source (ULX) in the starburst...
Evidence for a Millisecond Pulsar in 4U 1636-53 During a Superburst (2002)
Strohmayer, Tod E., Markwardt, Craig. B.
We report the discovery with the Proportional Counter Array on board the Rossi X-ray Timing Explorer of highly coherent 582 Hz pulsations during the February 22, 2001 (UT) ``superburst'' from 4U...
RX J1914.4+2456 is a candidate double-degenerate binary (AM CVn) with a putative 569 s orbital period. If this identification is correct, then it has one of the shortest binary orbital periods known,...
Gravity Waves from Rotating Neutron Stars and Evaluation of Fast Chirp Transform Techniques (2001)
X-ray observations suggest that neutron stars in low mass X-ray binaries (LMXB) are rotating with frequencies from 300 - 600 Hz. These spin rates are significantly less than the break-up rates for...
A Remarkable Three Hour Thermonuclear Burst From 4U 1820-30 (2001)
Strohmayer, Tod E., Brown, Edward F.
We present a detailed observational and theoretical study of a ~3 hr long X-ray burst (the ``super burst'') observed by the Rossi X-ray Timing Explorer (RXTE) from the low mass X-ray binary (LMXB) 4U...
Discovery of a Second High Frequency QPO from the Microquasar GRS 1915+105 (2001)
We report the discovery in archival Rossi X-ray Timing Explorer (RXTE) data of a 40 Hz quasiperiodic oscillation (QPO) in the hard X-ray flux from the galactic microquasar GRS 1915+105. The QPO is...
Discovery of a 450 Hz QPO from the Microquasar GRO J1655-40 with RXTE (2001)
We report the discovery with the proportional counter array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) of a 450 Hz quasiperiodic oscillation (QPO) in the hard X-ray flux from the galactic...
Bounds on Compactness for LMXB Neutron Stars from X-ray Burst Oscillations (2001)
Nath, Nitya, Strohmayer, Tod E., Swank, Jean H.
We have modelled X-ray burst oscillations observed with the Rossi X-ray Timing Explorer (RXTE) from two low mass X-ray binaries (LMXB): 4U 1636-53 with a frequency of 580 Hz, and 4U 1728-34 at a...
X-ray Observations of Neutron Star Binaries: Evidence for Millisecond Spins (2001)
High amplitude X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly...
Oscillations During Thermonuclear X-ray Bursts (2000)
High amplitude, nearly coherent X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence...
Ibrahim, Alaa I., Strohmayer, Tod E., Woods, Peter M., Kouveliotou, Chryssa, Thompson, Christopher, Duncan, Robert C., ...
The Soft Gamma Repeater SGR 1900+14 entered a remarkable phase of activity during the summer of 1998. This activity peaked on August 27, 1998 when a giant periodic gamma-ray flare resembling the...
Discovery of a 6.4 keV Emission Line in a Burst from SGR 1900+14 (2000)
Strohmayer, Tod E., Ibrahim, Alaa I.
We present evidence of a 6.4 keV emission line during a burst from the soft gamma-ray repeater SGR 1900+14. The Rossi X-ray Timing Explorer (RXTE) monitored this source extensively during its...
Phase Resolved Spectroscopy of Burst Oscillations: Searching for Rotational Doppler Shifts (1999)
X-ray brightness oscillations with frequencies from 300 - 600 Hz have been observed in six low mass X-ray binary (LMXB) bursters with the Rossi X-ray Timing Explorer (RXTE). These oscillations likely...
Oscillations During Thermonuclear X-ray Bursts: A New Probe of Neutron Stars (1999)
Observations of thermonuclear (Type I) X-ray bursts from neutron stars in low mass X-ray binaries (LMXB) with the Rossi X-ray Timing Explorer (RXTE) have revealed large amplitude, high coherence...
Spin Down of Pulsations in the Cooling Tail of an X-ray Burst from 4U 1636-53 (1999)
We report the discovery with the proportional counter array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) of a decrease in the frequency of X-ray brightness oscillations in the cooling tail of...
Strohmayer, Tod E., Markwardt, Craig B.
We investigate the time dependence of the frequency of X-ray brightness oscillations during thermonuclear bursts from several neutron star low mass X-ray binaries. We find that the oscillation...
Observation of Kilohertz Quasiperiodic Oscillations from the Atoll Source 4U 1702-429 (1998)
Markwardt, Craig B., Strohmayer, Tod E., Swank, Jean H.
We present results of Rossi X-Ray Timing Explorer (XTE) observations of the atoll source 4U 1702-429 in the middle of its luminosity range. Kilohertz-range quasiperiodic oscillations (QPOs) were...
Strohmayer, Tod E., Zhang, William, Swank, Jean H., Lapidus, Iosif
We report on the long term stability of the millisecond oscillations observed with the Rossi X-ray Timing Explorer (RXTE) during thermonuclear X-ray bursts from the low mass X-ray binaries (LMXB) 4U...
On the Amplitude of Burst Oscillations in 4U 1636-54: Evidence for Nuclear Powered Pulsars (1998)
Strohmayer, Tod E., Zhang, William, Swank, Jean H., White, Nicholas E., Lapidus, Iosif
We present a study of 581 Hz oscillations observed during a thermonuclear X-ray burst from the low mass X-ray binary (LMXB) 4U 1636-54 with the Rossi X-ray Timing Explorer (RXTE). We argue that the...
RXTE Observations of GX 3+1 (1998)
We summarize new RXTE observations to search for millisecond X-ray variability from the bright Galactic bulge source GX 3+1. During a short 2 ksec observation we did not detect kilohertz (kHz)...
X-ray Spectroscopy of Bursts from SGR 1806-20 with RXTE (1998)
Strohmayer, Tod E., Ibrahim, Alaa
We report on new RXTE X-ray spectral analysis of bursts from SGR 1806-20, the most prolific SGR source known. Previous studies of bursts from this source revealed a remarkable lack of spectral...