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XTE Target of Opportunity News

Maintained by R.H.D.Corbet, XTE SOF
Last Revised: Thursday, 03-Jun-2004 11:02:44 EDT


This page contains information on XTE TOO observations. Both results on observations that have already been performed and plans for upcoming TOO observations. The amount of information that can be provided on future observations will depend on how rapidly the TOO observation must be performed.

Remote Observation Service for Public TOOs
Anyone who is interested in monitoring public TOO observations in real time can use our Remote Observation Service. Detailed information is given in RXTE Remote Observing Interface page. Information of up coming PUBLIC TOO observations is available in All TOO List page.

Request of TOO
In order to request a TOO observation an RFO (Request for Observation) must be submitted. Messages regarding scheduling of regular XTE observations should be sent to xteplan@athena.gsfc.nasa.gov and general questions regarding XTE should go to xtehelp@athena.gsfc.nasa.gov

Please note that there are two categories of TOO observations: (i) Observations for which an accepted proposal exists. In this case data rights are the same as for any accepted proposal. (ii) Observations for which there is no accepted proposal. For the second category the data are public immediately. After an observation of this type has undergone standard processing (which includes conversion to FITS format) and archiving, the data will be available by standard means. Information on how to obtain public TOO data is available from the XTE GOF.

Already performed TOO Observations

  • List of TOO observations after IOC period is available on Web. Realtime FITS data for PUBLIC TOO observations can be downloaded. Also the Information of Public TOO Observations in near future is available.

  • Afterglow of GRB_970616
    RXTE made second trial of the chase of Gamma-Ray Burst (GRB_970616) that is detected by BATSE at 18:09:50.28 of June 16, 1997 (UT).
    BATSE light curve of GRB_970616 has multiple peaks and the maximum flux was 23.8 +/- 0.5 photons/cm2/sec above 20 keV. 3 hrs and 13 mins after the burst RXTE start observing the sky region of this GRB. Between 21:30:58 and 22:19:04, eleven scans were done covering 6 deg. by 4 deg. sky region. During three scans out of eleven, a very faint source (about a half mCrab) was detected and these three detections are consistent with one source at:
    (R.A., Dec.) = ( 01h18m55s +/- 41s, -5d30m +/- 18m) (equinox 2000).
    Figure shows error regions from RXTE, BATSE quick response, BACODINE, and IPN(BATSE/Ulysses). Another follow-up observation was made to confirm the transient nature of this source. Nine scans were done over the 6 deg by 3 deg. region around the source position and no source brighter than a quarter mCrab was detected at the position. This suggests what RXTE had detected during the observation on July 16 was the afterglow of GRB_970616.
    More details are reported in IAU Circ. #6683.

  • Gamma-Ray Burst Quick Response Observation (GRB970603)
    BATSE detected relatively bright gamma-ray burst at 23:35 of June 3, 1997 (UT). TOO replan for quick response observation with RXTE was done and RXTE started the observation 3 hours 15 minutes after the burst. The GRB error region (6x6 degrees) was scanned over, while no evident source brighter than 3 mCrab (2-10keV) was detected. This observation was performed under the collaboration of RXTE and BATSE teams.

  • GRS 1915+105, Galactic Super Luminal Motion Source
    Monitoring campaign for GRS 1915+105 is being performed with RXTE. Results from quick analysis are available on Web pages for the observations on April 29, May 5, 14, 21, 26, 29, 31, June 5, 7, 12, 16, 19, 22, 25, 29, July 3, 6, 7, 11, 14, 16, 19, 26, August 3, 10, 18, 25, September 16, 22, 28, October 1, 7, 13, 15, 25, 29, November 14, 19, 28, December 11, 19, 23 1996, and January 8 1997.,

  • GRO J1744-28, Pulsating Burster
    XTE has been observing the the pulsating burster GRO J1744-28 continuously since the start of XTE observation. As we continue to observe GRO 1744-28 we will be providing information here about the flux level and also providing light curves with 16-sec (1-sec, or 4-sec) binning (and sometimes with power spectra). Information is now available for following days:
    April 26, 28 & 30
    May 3, 10, 12, 13, 14, 15, 16, 17, 18, 21, 22, 29 & 31
    June 2, 4, 6, 7, 9, 11, 16, 19, 21, 23, 26, 28 & 30
    July 2, 4, 6, 8, 10, 12, 14, 16, 21, 23, 25, 27, 29 & 31
    August 4, 6, 11, 13, 15, 17, 19, 23, 25, & 30
    September 6, 11, 14, 17, 19, 24, & 25
    October 1, 6, 7, 8, 13, 14, 22, 26, & 29.

    Long time scale light curve of GRO J1744-28 observed with XTE/PCA is also available. MIT provides long term ASM light curve on their Web Page.

    Table information of PCA count rate and number of bursts of GRO J1744-28, which will appear in Ap.J, is also available.

  • PSR 1821-286, 2 msec isolated pulsar
    RXTE observed 2 msec pulsar PSR1821-24 on Sep. 16. Data will be used for cross-calibration of absolute clock time with ASCA.

  • GX 339-4, a Blackhole Candidate
    RXTE observed GX339-4 as a public TOO on July 26, 1996, soon after the CGRO monitoring campaign of the source. RXTE detected QPO at ~0.35 Hz from the source and the source count rate was ~1050 c/s/PCU including background of 20-30 c/s/PCU. Click here to see the results of quick analysis.

  • PKS 0405-385, Extra-Galactic Radio Source
    Following the detection of rapid time variability less than one hour in radio band, RXTE observed the source as TOO on July 24, 1996. Here is a light curve from quick analysis, but we do not seem to have detected the source.

  • 4U 1907+097 Raster Scan
    ASM has been detecting significant flux from the vicinity of 4U 1907+097 for these months. There are couple of sources including GRS 1915+105 and X1915-053. To clarify which source is responsible for the flux ASM has been detecting, XTE performed raster scans around this region and revealed that 4U1907_097 is only ~8 mCrab during this observation. X1915-053 is the most plausible source responsible for the flux in ASM. Count history of PCA during the observation is available on Web.

  • Cyg X-1, a Black Hole Candidate, in High-State
    ASM observation (ASM Light Curve: GIF Image) revealed that Cyg X-1 became very bright up to ~ 2 Crab in ASM energy band(2-10 KeV), which strongly suggested Cyg X-1 came into high-sate (or soft-state). As Cyg X-1 in high-state is not reported since 1980, XTE TOO observation was triggered immediately. TOO observations have done on May 22, 23, and 30 1996. Light curves of the observation on May 23, 30, June 4, 17, August 11, and 12 are now on Web pages.

  • Outburst of VW HYI, Cataclysmic Variable
    Since AAVSO reported that VW Hyi came into super-outburst, the accepted TOO proposal #10041 (PI: Dr. Eric M. Schlegel) was triggered. XTE started the monitoring campaign since May 2, 1996 and performed 34 observations until the end of May 13.

  • GRS 1739-278, Black Hole Candidate
    XTE had performed TOO observation of GRS 1739-278 once on Mar 31, 1996 and the quick results are reported at IAU Circ. No. 6390. An request for TOO observation (RFO) of GRS 1739-278 was submitted by Dr. Robert M. Hjellming on May 7 to investigate the similarity of this source with the galactic super luminal motion sources. We started a series of XTE TOO observations on May 10 (day 131) and quick look light curves are available on Web.

  • 4U 1630-47, Transient Black Hole Candidate
    A series of TOO observations of 4U1630-47 with XTE are now in progress since the day 124 (May 3) of 1996 following the detection of the source with PCA at ~230m Crab level during a slew and also with ASM for these 40 days. Some results from quick look analysis during real time monitoring of these TOO observations by duty scientists and experiment monitors are shown on Web page.

    On April 26th the non-burst count rate was about 1500 counts/s in the PCA (approximately 115 mCrab). One burst was observed preceded by the usual "choppy" variability.

  • 4U 0614+091, X-ray Burster
    From BATSE observation Prof. Kaaret reported X-ray burster 4U 0614+091 became up to about 40 mCrab level in 20-160 keV and triggered TOO observation (Proposal #10095), which was partly accepted by Project Scientist. 10 ksec observation was done from Apr. 22 19:04 to Apr. 23 00:14, 1996.

  • Hyakutake Comet
    RXTE observed Hyakutake Comet as TOO on Apr. 12, 1996 for about 2.5 hours. Unfortunately, no clear evidence of the detection of X-rays from the comet was seen in the real time monitoring of the observation. Data of this observation will be open to public when it is ready.

  • GRS 1915+105
    Dr. Ed Morgan (MIT) et. al reported from the analysis of All Sky Monitor (ASM) aboard RXTE that GRS 1915+105, the galactic super luminal motion source, is now in highly active state with flux of about 1 Crab (2-10 keV) accompanied by almost 100 % variability on time scale from seconds to days. RXTE team decided to observe GRS 1915+105 as TOO observation from Apr. 6 05:26 to 07:51, 1996. During the TOO observation, X-ray flux from GRS 1915+105 was about 11500 cps in 3 PCUs (including background).

  • GRS 1739-278
    TOO observation of GRS 1739-278 (GRANAT source), which is believed to be a black hole candidate, was performed on Mar 31, 1996. The net exposure time was about 6.8 ksec. The source count rate of about 5000 cps (without background) in PCA was reported. By correcting the source transmission due to offset observation to avoid contamination, the source flux was ~490 mCrab in 2-60 keV. The energy spectrum was relatively soft, and peaks at around 3 keV in the PCA. No clear pulsation or quasi-periodic oscillations (QPO) was detected for time scales between 0.002 and 256 second. A plot of the observed light curve in 32 seconds bin is also available. The time 0 in the light curve corresponds to March 31 18:25:39, 1996 (UT).

  • 4U 1608-522
    XTE made TOO observations of 4U 1608-522 (X-ray burster) on March 3, 6, 9 and 12, 1996. The source was about 3000-3500 counts/sec in PCA (with background) on March 3 It decayed gradually to 650-750 counts/sec on March 12 observation.

  • GK Per
    GK Per, CV with ~5 min rotation period, was observed on Feb. 27th, 1996. Since an optical burst was reported for the source, PI (Dr. Julian Osborne) triggered the approved TOO proposal (#10023). This was the first real-time TOO trigger. XTE SOF prepeared the new command plan and it became effective 7 hours and 10 minutes after PI had sent the trigger e-mail.

  • GX 1+4
    GX 1+4 was observed on Feb. 12th, 1996. This observation was triggered by a BATSE flux level and the corresponding proposal is 10133 (Klein).

  • 4U 1630-47
    4U1630-47, a candidate black hole transient X-ray source will be observed from 08:07 (UT)on February 1. This source is believed to have outbursts every 600 days and the XTE observations will test whether an outburst is presently occurring as is predicted. At the position of the 4U1630-47 we detected an excess, compared to the high Galactic latitude background, of approximately 3.5 mCrab.

  • GRO J1744-28
    GRO J1744-28 was observed again on January 27th. The source continues to be bright and exhibit frequent bursts.

  • MGC 4945
    NGC 4959 - Observed because of source brightness and coordinated ASCA and GRO observations. Data will become public domain.

  • GRO J1744-28
    GRO J1744-28 - Observed because of unusual source properties and brightness. This source was observed as soon as solar constraints made this possible. Observed for 11 hours on Jan. 18-19. Data will become public domain. Additional information on results from this observation will be placed here in the future.
    NASA press release (Feb.28,1996) is here.

  • GRO J1744-28
    GRO 1744-28 was observed with the PCA and HEXTE using the following modes:
    • EDS:
      • D_1US_0_249_1024_16S_F
      • B_4MS_16B_0_249_H
      • F_62US_0_24_249_16S
      • Standard1
      • Standard2_4s
      • B_500US_1M_0_249_H
      • SB_62US_0_249_500MS
      • F_125US_0_24_249_16S
    • HEXTE:
      • B_31MS_8Z_15_250_H_15191D21293D68 (LLDA=15, DWELLA=0, ROCKA=0.0)
      • B_31MS_8Z_15_250_H_15191D21293D68 (LLDB=15, DWELLB=0, ROCKB=0.0)
      • B_62ms_8Z_15_250_DH_15191D21293D68 (LLDA=15, DWELLA=16, ROCKA=3.0)
      • B_62ms_8Z_15_250_DH_15191D21293D68 (LLDB=15, DWELLB=16, ROCKB=3.0)
    PLEASE NOTE
    - the observations of this source were obtained during the checkout phase of satellite operations. While most characteristics of the instruments are now believed to be understood at some level, any interpretation of the data that depends on subtle features should be made with caution.
    Note that several non-standard modes were running during this observation, during bursts some counters over-flowed, dead time corrections have not been applied, definitive response matrices are not yet available for the XTE instruments, a and a variety of pointing positions were used including scans across the source which modulate the count rate.
    The PCA light curve includes scans at the start and end of this observation. There are gaps in the light curve caused by expected Earth occultations and passages through the South Atlantic Anomaly. A large number of bursts can be seen and the flux is depressed after each burst. (The "echo" on the second burst is an artifact caused by conversion from PostScript to GIF format). This is not seen in the PostScript file. An enlargement of one burst shows structure and another burst shows some differences from the first. The PCA light curve is also available as a large QDP format ASCII data file.
    A HEXTE light curve of a shorter section of data shows very different continuum behavior - whether the HEXTE continuum variability is intrinsic to the source or an artifact is under investigation. An ASCII data file is available. A full investigation of the HEXTE background variability as a function of magnetic rigidity is still being undertaken.

    The PCA spectrum is consistent with a power law with number index about 1.2 and a rollover above 13 keV with an e-folding energy of 14 keV. The absorbing column density is less than 10**22 cm**-2. This fit is based on a preliminary PCA response matrix.

    When folded on the best period (no barycentric or other corrections have yet been applied) both the PCA and HEXTE show a pulse shape which is highly sinusoidal which is confirmed by the power spectrum.

Currently Planned TOO Observations

  • GRO J1744-28 - The PCA modes we presently plan to use for this monitoring campaign are:
    • D_1us_0_249_1024_16s_f
    • SB_125us_0_49_1s
    • SB_125us_50_249_1s
    • Standard1
    • Standard2_2s
    • B_16ms_64m_0_249_h
  • We are currently planning a monitoring campaign for GRO 1744-28. If you wish to suggest observing strategies or modes please submit an RFO (Request for Observations). Please note that all data collected will become public domain even if we follow your recommendations for observations strategies or modes!
Please send questions/problem reports to: xtehelp@athena.gsfc.nasa.gov
HEASARC/Office of Guest Investigator Programs


For questions about scheduling of RXTE observations please send email to xteplan@athena.gsfc.nasa.gov If you have other questions about RXTE, please send email to one of our help desks.

This page is maintained by the RXTE SOF and was last modified on Thursday, 03-Jun-2004 11:02:44 EDT.

Responsible NASA Official: Phil Newman
Web Curator: Robin Corbet

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