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GINGABGD: Help

GINGABGD - Ginga Background Lightcurves & Spectra


Overview

The GINGABGD database table contains a summary of the contents of the Ginga pointed observations of (nominally empty) background fields. The database has been produced from the raw Ginga LAC First Reduction Files (FRFs), and contains information of the individual pointings in addition to FITS spectra and light curves, HDS and FITS data cubes and the plots produced during the pipeline processing. These products can be used either with the Ginga data analysis software or the XANADU suite of software (http://heasarc.gsfc.nasa.gov/docs/xanadu/xanadu.html).

References

Angelini, L., Pence, W., Tennant, A.F., 1994, The Proposed Timing FITS File Format for High Energy Astrophysics Data. NASA/GSFC

Arnaud, K.A., George, I.M., Tennant, A.F., 1995, The OGIP Spectral File Format. NASA/GSFC

Clearly, M.N., Heiles, C., Haslam, C.G.T., 1979, Astr. Astrophys. Suppl., 36, 95

Hayashida, K., et al., 1989, PASJ, 41, 373

Heiles, C., Clearly, M.N., 1979, Australian J. Phys. Ap. Suppl., 47, 1

Kondo, H., 1988, MSc thesis, University of Tokyo

Makino, F., et al., 1987, Astrophys. Letters Commun., 25, 223

Marshall, F.J., Clark, G.W., 1984, ApJ, 287, 633

Murakami, T., et al., 1989, PASJ, 41, 405

Nandra, K., 1991, PhD these, University of Leicester

Nandra, K., Pounds, K.A., 1994, MNRAS, 268, 405

Stark, A.A., Heiles, C., Bally, J., Linke, R., 1984, Bell Laboratories privately distributed tape

Stella, L., Angelini, L., 1993, XRONOS: A Timing Analysis Software Package User's Guide. NASA/GSFC

Tennant, A.F., 1991, The QDP/PLT User's Guide. NASA Technical Memorandum 4301

Tsunemi, H., Kitamoto, S., Manabe, M., Miyamoto, S., Yamashita, K., PASJ, 41, 391

Turner, M.J.L., et al., 1989, PASJ, 41, 345

Williams, O.R., et al., 1992, ApJ, 389, 157


Provenance

This archive (database and all the associated products) is a copy of the GINGABGD data products held at the Leicester Data Archive Service (http://ledas-www.star.le.ac.uk/). It was delivered to the HEASARC as part of archive exchange between data centers to facilitate the data transfer across the Atlantic.

Description

Ginga was the third Japanese X-ray astronomy satellite. It was launched into a low Earth orbit on 5th February 1987 and re-entered the atmosphere on 1st November 1991. The scientific payload consisted of the Large Area Counter (LAC; Turner et al. 1989), the All-Sky Monitor (ASM; Tsunemi et al. 1989) and the Gamma-ray Burst Detector (GBD; Murakami et al. 1989). A full description of the satellite is given in Makino et al. (1987). During its lifetime Ginga performed over 1000 observations of approximately 350 different targets, covering all then known classes of cosmic X-ray sources.

The LAC experiment, sensitive to X-rays with energy 1.5-37 keV, consisted of an array of eight proportional counters with a total effective area of approximately 4000 cm^2 and an energy resolution of 18% at 6 keV, scaling as E^-0.5 throughout the full energy range. In each counter the anode structure was of a multi-layer and multi-cell design which provided both gain uniformity and low internal background through the use of anticoincidence. The high voltage supply was normally operated at 1830V, but was reduced occasionally to 1745V to achieve a larger energy range. Steel collimators restricted the field of view to 1.1 x 2.0 degrees (FWHM); the top and bottom 15mm were coated with silver paint to prevent contamination through iron, nickel and chrome fluorescent lines. The fluorescent line of silver at 22.1 keV can be visible at high energy but it is well away from lines of astrophysical importance and can be used for calibration.

The origin and behaviour of the LAC background is described in Hayashida et al. (1989). The main sources of background include the internal component generated after passage through the Earth's radiation belts, in particular the South Atlantic Anomaly (SAA), the high- and low-energy particles in the Earth's magnetosphere, and the diffuse Cosmic X-ray Background (CXB). The first two sources generate a background which is a strong function of time and energy. Summed over the top- and mid-layer electrodes as well as over the full energy range (1.5-37 keV), this varies between 50 and 100 counts/second. The CXB contributes approximately 18 counts/second to the background, which varies as a function of position in the sky but is constant in time.


Accessing HEASARC Data

The data products belonging to an observation may be extracted using the Browse interface. Data can also be retrieved using the legacy.gsfc.nasa.gov anonymous FTP server. A description of the data products is available from the legacy.gsfc.nasa.gov anonymous FTP in the ginga/doc directory.

Spectral FITS

Spectra have been extracted from the cleaned, background subtracted data cubes, and are integrated over the entire observational interval. The top- and mid-layers are treated separately within the database. Where the background subtracted top-layer 2-10 keV count rate exceeds 2 counts/second, both layers are simultaneously fit to simple absorbed power-law and thermal bremsstrahlung models. Plots of the best-fit models are available within both databases as are the results of the fits with their errors. In addition, the top-layer spectra are fitted to power-law and thermal bremsstrahlung models with and without a narrow (intrinsic width much less than the energy resolution of 1 keV) Gaussian emission line at 6-7 keV. As for the joint fits, plots of the best-fit models and results of the fits are available in the database. If the presence of an emission line is significant at the 95% level (determined by an F-test), then the best-fit emission line parameters are also written to the database.

The spectral files within the database can be used in two ways. First, the spectra can be used as a measure of Galactic emission at low latitudes (|b| less than 25 degrees) where this is not already taken into account (e.g. when background data is taken from observations at high Galactic latitudes as is always the case with the "universal" background subtraction technique). Second, to provide spectra of serendipitous sources in the Ginga background fields of view. The format of the spectral files follows the OGIP FITS conventions (Arnaud, George & Tennant 1995) and these files can be used within the XSPEC spectral fitting package, which is part of the XANADU suite of software.

All errors are 90% confidence for one interesting parameter.


Data Selection Post Sortac

The data were "cleaned" as described in Nandra & Pounds (1994) to remove periods of poor quality data. The process consists of the following stages. First, SUD and V1 electrode (LAC anode wires not illuminated via the collimator; PI_MONI) rate were compared, and data from times when they were greater than 3 standard deviations from the best-fit linear relationship were removed from further analysis. Second, the LAC count rates in adjacent spectral channels were compared, and points lying greater than 5 standard deviations from the best-fit linear relationship were also removed (the relatively poor spectral resolution of the LAC ensures that this does not remove valid data). Finally, for background observations, the LAC count rate is expected to vary with the SUD rate (and hence PI_MONI rate). Therefore, points lying greater than 4 standard deviations from the best-fit linear relationship were removed from the background data. Plots are available in the database showing the SUD rate versus PI_MONI rate. A further plot is available showing SUD rate versus LAC top-layer count rate in the energy range 2-10 keV. These plots are produced after data rejection so that the user can verify that the cleaning algorithm has successfully removed poor quality data.

A number of additional plots were produced during the pipeline data selection and cleaning process. First, a plot of SUD rate versus time allows the user to evaluate the background level during an observation (the total background scales with the SUD rate). The user may wish to extract data from periods of low background (i.e. low SUD rate). Second, a plot of YELEV versus the LAC top-layer count rate from the pulse height channel 4 is available. There will be no correlation between these two parameters if the data are unaffected by solar X-rays scattered into the Ginga field of view by the Earth's atmosphere (Data Selection within Sortac). Third, the database contains a plot of DELTXZ versus the LAC top-layer count rate in the energy range 2-10 keV; this can be used to determine whether a source lies within the Ginga field of view. One might expect some correlation between DELTXZ and the LAC count rate if such a source exists. Whilst these data have not been removed (to allow for maximum use of the database), the user is able to exclude such data.


Background Estimation

Background subtraction is performed whenever there are blank-sky data available and the background subtracted data cube is made available within the database. Occasionally, we rejected data acquired during periods when the angle between the satellite pointing direction and the Sun was less than 90 degrees or the high voltage supply was reduced to 1745V.

The background is estimated by modelling the known contributions to the count rates and periodicities observed in them. The "universal" method described in Hayashida et al. (1989) and Williams et al. (1992) is used (the background subtraction method is written to each record in the database table). The background count rate, C(E,t), dependent on both energy, E, and time, t, is given as

		C(E,t) =C_1(E) + sum C_n(E,t),
where
        	C_n(E,t) = P_n(t) x F_n(E).

The first term C_1(E) represents the CXB contribution, which is constant in time, but varies across the sky due to fluctuations in the CXB. The remaining, time-variable instrumental components are characterised by their spectra F_n(E) and associated HK parameter P_n (e.g. COR, SUD). The spectral form, F_n(E), was determined by fitting data from background observations as described below.

In modelling the component of the background due to the radioactive decays, we calculate a time counter, accumulated with an exponential decay factor, after each passage through the SAA. In practice, we used up to four time counters with exponential decay timescales corresponding to half-lives of 8 hours, 41 minutes and 20 minutes (see Hayashida et al 1989 and Nandra 1991). The number of decays required in the model was reduced during the latter half of the mission to only one component, because the decay of the Ginga orbit caused the LAC to be further shielded from the Earth's radiation belts. The "universal" method uses all background observations within a contemporary three to four month period to model systematic trends in the particle levels, and hence to estimate the background level at the time of the source observation. A specific time counter is required to account for the 37-day precessional period of Ginga. Unfortunately, during the first six months and last three months of operation of Ginga, the gradual rise and fall of the background made the "universal" method unreliable.

The uncertainty in the background subtraction is limited by source confusion and systematic errors rather than statistical uncertainties in the data. The limiting sensitivity for source detection was chosen to be 2.1 counts/second, equivalent to a 3 sigma detection (Hayashida et al. 1989). All observations whose background subtracted 2-10 kev top-layer count rate exceeded 2.1 counts/second were removed from the background modelling pipeline. This can be achieved only after background subtraction, and so the whole process is an iterative procedure. The LAC mid-layer is insensitive to X-ray photons below 6 keV (Turner et al 1989). Therefore, all observations were rejected from the background modelling pipeline if the background subtracted mid-layer count rate below 6 keV was significantly above or below zero. In addition, observations were rejected from the background modelling pipeline if the background subtracted spectra and light curves (3-10 keV band) showed trends with energy and/or time.


Accessing LEDAS Data

The products belonging to an observation may be extracted using the xp command from browse or form the ARNIE interface to the database (http://ledas-www.star.le.ac.uk/arnie/).

Light Curves

Light curves have been extracted, from the same data cubes as have the spectral data (see Spectral Fits); in the energy bands 2-6, 6-7, 7-17 and 2-17 keV. These bands cover the soft X-ray emission, the iron K line emission, the hard X-ray continuum and the full energy band. There are light curves for both top- and mid-layers. In addition, the intrinsic variability (total variance minus statistical noise) is given in the databases as

	N / (N-1) ((sum x_i^2 / N) - mu^2) - sum sigma_i^2,

where x_i is the count rate for bin i, mu is the mean count rate during the observation and sigma_i^2 is the variance for bin i. There are light curves for both the top- and mid-layers.

The format of the files follows OGIP FITS conventions (Angelini, Pence & Tennant 1994) and they can be used within the XRONOS timing analysis package (Stella & Angelini 1993), which is part of the XANADU suite of software.


Data Selection Within Sortac

The program SORTAC allows the selection of data in the FRFs, producing data cubes (time, spectral and detector resolution) as output. Initially the data were selected from the FRFs, with full spectral resolution and a time resolution of 64 seconds (for higher time resolution studies, and different modes, it will be necessary to return to the FRFs held within the GINGAFRF database). Limits were placed on certain HK parameters during the extraction of data, with the LAC count rate above 24 keV (known as Surplus above Upper Discriminator or SUD), the energy that a cosmic-ray requires to penetrate the magnetosphere (Cut-Off Rigidity or COR) and the solid state electron monitor count rate (SOL2) all restricted to avoid periods of high particle background (these limits are listed below). Contamination from the bright Earth was prevented by restricting the angle between the satellite pointing direction and the Earth's horizon (YELEV) to greater than 6 degrees. Occasionally it was necessary to restrict the data to tighter constraints. The constraints actually used are stored for each observation in the database. In addition, DELTXZ (the angle between the satellite pointing direction and the nominal Ginga field of view) has been restricted to 0.5 degrees. This removes periods when the collimator transmission was less than 60 and 70% for the X- and Z-directions respectively. For solar angles (angle between the satellite pointing direction and the Sun) less than 90 degrees, solar X-rays can penetrate the LAC via the collimator when the satellite is in sunlight. These data were excluded from the database by restricting the observational intervals to those in the Earth's shadow. Whilst this may lead to a large reduction in the useful length of an observation, it does ensure that the data products are free of solar contamination. The minimum acceptable exposure time for any observation was 1000 seconds.
              ---------------------------------
              HK Parameter       Data selection
              ----------------------------------
                  SUD           < 14 counts/sec
                  COR             7-20 GeV/c
                  SOL2          < 15
                  PI/SUD        < 3 sigma
                  LAC/LAC       < 5 sigma
                  LAC/SUD       < 4 sigma
              ----------------------------------

Quality Flag

The quality of the data products is primarily determined by the quality of the background subtraction. This is indicated by the QFLAG field which has been filled after visual examination of all the products. QFLAG has a range of 0 to 5 (no background subtraction to excellent; see table below). Observations with a QFLAG less than 3 are usually not of sufficient quality for spectral and/or timing analysis and the experienced user is recommended to re-background subtract the cleaned data cubes for spectral and/or timing analysis.
          ------------------------------------------
           Qflag                 Description
          ------------------------------------------
             0            No background subtraction
             1                 Unusable
             2                   Poor
             3                 Acceptable
             4                   Good
             5                 Excellent
          ------------------------------------------

Completeness

The GINGABGD database contains all the LAC background pointings except those taken in modes other than MPC1 or where the pointing direction is particularly unstable.

Gain

To provide an indication of the gain, for each observation, the 10-35 keV pulse height spectra, which include the collimator silver line, from the top- and mid-layers (all detectors combined to provide good signal-to-noise) were fitted with a model consisting of a second order polynomial plus Gaussian emission line. The best-fit energy of the Gaussian is given in the database table and is accurate to approximately 0.5 keV. In addition, four plots were produced during the extraction of data. These show the pulse height spectra from 20 to 35 keV for the top- and mid-layers and for each detector in use (two detectors per plot). The plots can be used within QDP (Tennant 1991), which is part of the XANADU suite of software, to verify that the silver line is at the expected energy of 22.1 keV for individual layers. Individual plots may be missing if the detectors were excluded during the pipeline processing (e.g. because of electronic noise on detectors 5 & 6).

Attitude Correction

No attempt has been made to correct to the response of the collimator. The background subtracted data cubes contain information regarding the satellite pointing direction and roll angle as a function of time, thus allowing the user to calculate the appropriate correction for extended and confused sources.

In addition, two plots are available which show the LAC top- and mid-layer count rates versus a number of HK parameters. In particular, the plots show the LAC count rate versus SUD, SOL2 and DELTXZ. LAC count rate versus SUD and SOL2 can be used to verify that there are no count rate enhancements on the Ginga orbital period (SUD) or due to hard (SUD) and soft (SOL2) particles. The LAC count rate versus DELTXZ can be used to identify periods of count rate enhancements due to sources in the Ginga field of view. The user may wish to remove these periods when using the data to model the background either in its own right or for another observation.


Pipeline Processing

The pipeline has been run on all MPC1 mode pointed observations; in this mode data have full spectral resolution (48 channels), at the expense of a lower time resolution (16 seconds at low bit rate). Over 80% of all Ginga observations were made in MPC1 mode. The pipeline is described below. All observations have been subject to expert quality assessment, and a simple quality flag is added to each observation record (see Quality).

Parameters

RA
Nominal Right Ascension of the Ginga field of view (1950.0 equinox).

Dec
Nominal Declination of the Ginga field of view (1950.0 equinox).

LII
Nominal Galactic Longitude of the Ginga field of view (1950.0 equinox).

BII
Nominal Galactic Latitude of the Ginga field of view (1950.0 equinox).

Beta
Angle between the satellite pointing direction and the Sun at the time of observation (degrees).

NH
Galactic hydrogen column density in the direction of the Ginga field of view. These values were calculated using an interpolation from data taken from Marshall and Clark (1984). This covers the entire sky and uses various 21-cm surveys for its source (Stark et al. 1984; Clearly, Heiles & Haslam 1979; Heiles & Clearly 1979).

Start_Time
Start time of observation. Times are stored in the shf key format, which is seconds since January 1st, 1980 at 00:00 hours UT.

End_Time
End time of observation. Times are stored in the shf key format, which is seconds since January 1st, 1980 at 00:00 hours UT.

Duration
Duration of the observation (i.e. End_Time minus Start_Time; in days).

Exposure
Total live time on source (seconds).

Count_Rate
Mean 2-10 keV count rate after background subtraction (counts/second). Counts are taken from the top-layer only.

Count_Rate_Error
2-10 keV Count Rate Error

HR
Hardness ratio [(H-M)/(H+M), where H and M are the 10-17 keV and 6-10 keV count rates respectively]. The HR_Error is the one sigma uncertainty in the hardness ratio.

HR_Error
Hardness Ratio Error

SR
Softness ratio [(S-M)/(S+M), where S and M are the 2-6 keV and 6-10 keV count rates respectively]. The SR_Error is the one sigma uncertainty in the softness ratio.

SR_Error
Softness Ratio Error

Filespec
String identifying the set of data products associated with an observation.

Root
String identifying the set of data products associated with an observation.

Respfile
String identifying the response matrices associated with an observation.

Qflag
Quality flag.

Mode
Mode of observation (i.e. MPC1).

Time_Res
Increment for temporal data (seconds).

MJDs
Start time of observation (MJD).

MJDe
End time of observation (MJD).

Sol_Max
Maximum accepted rate of the solid state electron monitor (counts/second).

Cor_Min
Minimum accepted value for the cut-off rigidity (GeV/c).

Cor_Max
Maximum accepted value for the cut-off rigidity (GeV/c).

Hv_Min001
Minimum accepted high voltage level for detector 1.

Hv_Min002
Minimum accepted high voltage level for detector 2.

Hv_Min003
Minimum accepted high voltage level for detector 3.

Hv_Min004
Minimum accepted high voltage level for detector 4.

Hv_Min005
Minimum accepted high voltage level for detector 5.

Hv_Min006
Minimum accepted high voltage level for detector 6.

Hv_Min007
Minimum accepted high voltage level for detector 7.

Hv_Min008
Minimum accepted high voltage level for detector 8.

Hv_Max001
Maximum accepted high voltage level for detector 1.

Hv_Max002
Maximum accepted high voltage level for detector 2.

Hv_Max003
Maximum accepted high voltage level for detector 3.

Hv_Max004
Maximum accepted high voltage level for detector 4.

Hv_Max005
Maximum accepted high voltage level for detector 5.

Hv_Max006
Maximum accepted high voltage level for detector 6.

Hv_Max007
Maximum accepted high voltage level for detector 7.

Hv_Max008
Maximum accepted high voltage level for detector 8.

Yelev_Min
Minimum accepted angle between the satellite pointing direction and the Earth's horizon (degrees).

Yelev_Max
Maximum accepted angle between the satellite pointing direction and the Earth's horizon (degrees).

Sud_Min
Minimum accepted SUD count rate (counts/second).

Sud_Max
Maximum accepted SUD count rate (counts/second).

Htvolts001
Observed high voltage level for detector 1.

Htvolts002
Observed high voltage level for detector 2.

Htvolts003
Observed high voltage level for detector 3.

Htvolts004
Observed high voltage level for detector 4.

Htvolts005
Observed high voltage level for detector 5.

Htvolts006
Observed high voltage level for detector 6.

Htvolts007
Observed high voltage level for detector 7.

Htvolts008
Observed high voltage level for detector 8.

Srce_Mask
The detectors in which data has been accumulated (0 = off; 1 = on; i.e. 11110011 indicates that the data has been accumulated from detectors 1-4 and 7-8).

Cln_Sigma001
Data lying this number of standard deviations from the observed SUD/PI_MONI correlation were rejected (a value of 0.0 indicates that no attempt was made to exclude data using this correlation).

Cln_Sigma002
Data lying this number of standard deviations from the observed SUD/LAC correlation were rejected (a value of 0.0 indicates that no attempt was made to exclude data using this correlation).

Cln_Sigma003
Data lying this number of standard deviations from the observed LAC/LAC correlation were rejected (a value of 0.0 indicates that no attempt was made to exclude data using this correlation).

Bgd_Ndecay
Number of decays used in modelling the LAC background.

Bgd_Decay001
The e-folding timescale of the 1th decay.

Bgd_Decay002
The e-folding timescale of the 2th decay.

Bgd_Decay003
The e-folding timescale of the 3th decay.

Bgd_Decay004
The e-folding timescale of the 4th decay.

Bgd_Version
Method of background subtraction used (i.e. local or universal method).

PI_Moni_Min
Minimum accepted PI_MONI rate (counts/second).

PI_Moni_Max
Maximum accepted PI_MONI rate (counts/second).

Sunshine_Min
Minimum accepted value of the sunshine flag (0: shadow, 1: sunshine).

Sunshine_Max
Maximum accepted value of the sunshine flag (0: shadow, 1: sunshine).

Sud_Error
SUD rate error

PI_Moni_Error
PI_MONI error

Sud
Mean SUD count rate (counts/second). SUD_Error is the one sigma uncertainty in the mean SUD count rate (counts/second).

PI_Moni
Mean PI_MONI count rate (counts/second). PI_MONI_Error is the one sigma uncertainty in the PI_MONI count rate (counts/second).

Cor
Mean cut-off rigidity (GeV/c).

Yelevation
Mean angle between the satellite pointing direction and the Earth's horizon (degrees).

Sol2
Mean rate of the solid state electron monitor.

Sunshine
Mean value of the sunshine flag (0: shadow, 1: sunshine).

Point_RA
Mean observed Right Ascension (1950.0 equinox).

Point_Dec
Mean observed Declination (1950.0 equinox).

Roll
Mean roll angle during the observation (degrees).

Anti
Mean anti-coincidence rate (counts/second).

Yaxis
Mean pointing flag (0: Sky, 1: Dark Earth, 2: Bright Earth).

Alt
Mean satellite altitude (kilometers).

Deltx
Mean angle between the observed pointing direction and the nominal pointing direction (DELTXZ) projected onto the X (short) axis of the collimator (degrees).

Deltz
Mean angle between the observed pointing direction and the nominal pointing direction (DELTXZ) projected onto the Z (long) axis of the collimator (degrees).

Deltxz
Mean angle between the observed pointing position and nominal pointing direction field of view (degrees).

Gbd_Sc
Mean Gamma-ray burst detector scintillation counter rate (counts/second).

Gbd_Pc
Mean Gamma-ray burst detector proportional counter rate (counts/second).

Ag_Energy001
Best-fit energy of the silver emission line in the nth raw spectrum (n = 1 for the top-layer; n = 2 for the mid-layer).

Ag_Energy002
Best-fit energy of the silver emission line in the nth raw spectrum (n = 1 for the top-layer; n = 2 for the mid-layer).

Pl_Alpha
Energy index of the best-fit power-law.

Pl_Alpha_Lo
Lower uncertainty on the energy index.

Pl_Alpha_Hi
Upper uncertainty on the energy index.

Pl_Norm
Power-law normalisation (photons/second/cm/cm/keV at 1 keV).

Pl_Norm_Lo
Lower uncertainty on the power-law normalisation.

Pl_Norm_Hi
Upper uncertainty on the power-law normalisation.

Pl_NH
Column density (10^21 H atoms/cm^2).

Pl_NH_Lo
Lower uncertainty on the column density.

Pl_NH_Hi
Upper uncertainty on the column density.

Pl_Line_Present
Presence of iron emission line (boolean). True/False if the reduction in chi-square is significant/insignificant at the 95% level (determined by an F-test).

Pl_Len
Best-fit energy if line present (keV).

Pl_Len_Lo
Lower uncertainty on line energy.

Pl_Len_Hi
Upper uncertainty on line energy.

Pl_Ew
Equivalent width of emission line (eV).

Pl_Ew_Lo
Lower uncertainty on line equivalent width.

Pl_Ew_Hi
Upper uncertainty on line equivalent width.

Pl_Redchi
Reduced chi-square of best-fit model (chi-square/degrees of freedom).

Pl_Nfree
Number of degrees of freedom.

Pl_Flux
Absorbed 2-10 keV flux (10^-12 erg/second/cm^2).

Br_Kt
Temperature of best-fit thermal bremsstrahlung model (keV).

Br_Kt_Lo
Lower uncertainty on temperature.

Br_Kt_Hi
Upper uncertainty on temperature.

Br_Norm
Bremsstrahlung normalisation (equal to 3.01*10^-15*S*T^(-1/2) / (4*PI*D^2), where S = int Ne^2 dV is emission measure in cm^-3 and D is the distance to the source in cm).

Br_Norm_Lo
Lower uncertainty on the bremsstrahlung normalisation.

Br_Norm_Hi
Upper uncertainty on the bremsstrahlung normalisation.

Br_NH
Column density (10^21 H atoms/cm^2).

Br_NH_Lo
Lower uncertainty on the column density.

Br_NH_Hi
Upper uncertainty on the column density.

Br_Line_Present
Presence of iron emission line (boolean). True/False if the reduction in chi-square is significant/insignificant at the 95% level (determined by an F-test).

Br_Len
Best-fit energy if line present (keV).

Br_Len_Lo
Lower uncertainty on line energy.

Br_Len_Hi
Upper uncertainty on line energy.

Br_Ew
Equivalent width of emission line (eV).

Br_Ew_Lo
Lower uncertainty on line equivalent width.

Br_Ew_Hi
Upper uncertainty on line equivalent width.

Br_Redchi
Reduced chi-square for best-fit model (chi-square/degrees of freedom).

Br_Nfree
Number of degrees of freedom.

Br_Flux
Absorbed 2-10 keV flux (10^-12 erg/second/cm^2).

Int_Var_0206_001
Intrinsic 2-6 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).

Int_Var_0206_002
Intrinsic 2-6 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).

Int_Var_0607_001
Intrinsic 6-7 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).

Int_Var_0607_002
Intrinsic 6-7 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).

Int_Var_0717_001
Intrinsic 7-17 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).

Int_Var_0717_002
Intrinsic 7-17 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).

Int_Var_0217_001
Intrinsic 2-17 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).

Int_Var_0217_002
Intrinsic 2-17 keV variance for the nth light curve (n = 1 for the top-layer; n = 2 for the mid-layer).


Contact Person

Questions regarding the GINGABGD database table can be addressed to the HEASARC User Hotline.

Questions specifically about the content of the GINGABGD database table may also be addressed to ledas-help@star.le.ac.uk.


If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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