Chandra X-Ray Observatory
NS RX J 1856

Public Release of Archival RXJ1856.5-3754 Data

Nov 9, 2001

The Chandra Director's Discretionary Time (DDT) observation of the isolated neutron star RXJ185636-375 was successfully completed on 15 Oct 2001, UT. The four datasets are now available in the Chandra public archive. Here we provide links to these datasets and information on their quality. We also provide co-added versions of the final source spectrum for your convenience.

The Observations and Data Access

A total of 450 ksec of data were collected in October 2001, Cycle 2, with the LETG/HRC-S comprising the ObsIDs shown in the table. The 55 ksec Cycle 1 observation (ObsID 113) is provided here as well.

Full distributions of the data are accessible through the Chandra Data Archive. Linked from the table, we provide a convenient subset of the default dataset, excluding the large level 1 and 1.5 event files. Note that ObsID 113 has been reprocessed to correct the status-bit filtering and background region size problems. Users who have previously downloaded ObsID 113 data from the archive (dated Dec 05, 2000-- check your data processing date) should reprocess that data themselves or simply retrieve the more recent archival data.

As a courtesy, the CXC is also providing composite Level 2 PHA files for the 4 most recent, and all 5, ObsIDs combined along with the resulting, exposure weighted ARF files (see Table below). For more details on how to combine the datasets, please see below.
NOTE: for the last 4 files, Hold down the Shift key and click to download.

File Size (MB) Contents SeqNumExposure (ks)
113.tar 149 Data products for ObsId 113500000 55.5
3380.tar 526 Data products for ObsId 3380500285 167.5
3381.tar 561 Data products for ObsId 3381500285 171.1
3382.tar 370 Data products for ObsId 3382500285 102.0
3399.tar 293 Data products for ObsId 3399500285 9.3
ns4pha.fits.gz 0.2 Spectrum for ObsIds 3380, 3381, 3382, 3399  449.9
ns4arf.fits.gz 0.2 ARF for ObsIds 3380, 3381, 3382, 3399  
ns5pha.fits.gz 0.2 Spectrum for ObsIds 113, 3380, 3381, 3382, 3399  505.4
ns5arf.fits.gz 0.2 ARF for ObsIds 113, 3380, 3381, 3382, 3399  

Background and Data Filtering

Background rates were reasonably stable during the various obsids that make up the observation, but were enhanced at radiation zone entry and exit (see Figure). Background for ObsID 113 (not shown) was quite stable apart from a small blip near the beginning. Researchers may wish to exclude high-background times to improve the net S/N ratio.

Lightcurves for the 4 most recent obsids (2001). Total onboard detector rate is shown in black and the valid event rate in red. The glitch around 284:18:00 (Oct 11) corresponds to the arrival of a CME that was ejected on day 282 (Oct 9). Figure provided by M. Juda.

Telemetry saturation occurs at 184 cts/sec (valid rate). Beyond this rate, the detector will have some deadtime, with corrections (the DTF, DeadTime Factor, in the secondary data *dtf files) accurate to 10% or better. Telemetry saturation does not cause any spectral distortions, merely a loss of some events.

The data provided are standard Automated Processing data products. No time filtering (beyond standard Good-Time Interval filtering) has been applied, nor any background reduction methods other than standard status-bit filtering. Researchers will likely wish to apply pulse-height filtering to reduce the background.

LETG/HRC-S Calibration Files

Grating Effective Area (ARF) files
Grating Redistribution Matrix Function(gRMF)

Combining Data

The several datasets can be combined using the CIAO threads add_grating_orders and add_grating_spectra as follows. First run add_grating_orders on the pha2 files of a single ObsID using the canned positive and negative 1st order ARF files. The outputs of this run, for each ObsID, are coadded positive and negative order spectra, and coadded positive and negative 1st order ARFs. These are then input to add_grating_spectra two at a time, with the previous coadded spectrum as one of the inputs each time, to build up a coadded spectrum of all the ObsIDs.

Last modified: 12/02/10

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