Access to BATSE Solar Flare Data for the Solar Physics Community

B. R. Dennis1, R. A. Schwartz2, A.K. Tolbert2
1Laboratory for Astronomy and Solar Physics, NASA/GSFC
2Raytheon STX @Laboratory for Astronomy and Solar Physics

1. Introduction

Although BATSE is optimized for the detection of gamma-ray bursts, it is also the most sensitive instrument regularly available for the detection of hard X-ray solar flares. As such, it is of great value in providing high time resolution spectral observations over a broad energy range for up to 50% of all flares. Since the launch of the Compton GRO, we have maintained an interactive computer facility with the primary objective of making this unique solar flare data base readily accessible for scientific analysis by the international solar physics community.

Our facility contains a continuously updated archive of all BATSE solar flare data since launch together with an extensive package of user-friendly, well-documented programs for data analysis. Internet access is available to the flare catalog and to the list of BATSE solar viewing time intervals. Plots of quick-look orbital data (Figure 1) and flare time profiles (Figure 2) can be obtained, and ASCII or binary data files can be downloaded for further analysis. Thus far, we have cataloged and archived nearly 5000 solar events, 4200 through the end of 1993. During the seven years of its existence, the facility has been used extensively for the following three primary purposes:

For the three years after the launch of CGRO when solar activity was high, the facility was used on a regular basis by more than 80 solar physicists, averaging about 70 queries per month. As the number of flares decreased towards solar minimum (Figure 3), so too the usage dropped off. However, we expect even higher useage during the lead up to the next solar maximum, especially with all of the other solar space missions, such as Yohkoh, SOHO, TRACE, and HESSI (in 2000), making complementary observations. Thus, we believe that this facility will continue to be the method of choice for accessing BATSE solar flare data and will be even more valuable in promoting the joint analysis of the many new flare observations that are expected in the immediate future.

2. Routine Data Processing and Flare Determination

On a daily basis, the complete LAD, CONT, and DISCSP data sets are downloaded from the BATSE computer at MSFC to our computer at GSFC over the Internet. Orbital plots of the DISCLA rates, similar to the plot shown in Figure 1, are made and scanned for solar events. Once an event is identified and verified to be of solar origin, its characteristics are cataloged and all of the data during the flare interval are archived. The database is usually current to within two days of the observations.

Observations made with the BATSE instrument are recorded at the Operations Control Center at GSFC. After accumulating 24 hours of data, the data are copied to the BATSE principal investigator group at MSFC. Data technicians process the data files to create a variety of data sets. We use the following five types of data made accessible to us through a proxy account:

Each night, a data technician at GSFC runs a batch job to copy the five data files to the SDAC computer. These five files are automatically merged into one daily BATSE Database (BDB) file, and orbital plots are produced showing a summary of the activity for the day.  A typical orbital plot of DISCLA counting rates is shown in Figure 1. All of the processing of the data files is done using the Interactive Data Language (IDL) Version 5.

The DISCLA orbital plots are used by the GSFC data technician to identify count rate increases due to solar flares. Once the data technician finds possible flares in the orbital plots created during the previous night, she then uses a flexible, interactive graphics program to verify their solar origin. The determination of solar or non-solar origin is based primarily on whether the count rate increases in the separate detectors are consistent with their orientation with respect to the Sun. Ancillary consideration is given to the timescale of variations, its energy spectrum, and correlative increases in the soft X-ray flux seen by the GOES spacecraft. Also, the increase in the counting rate due to the flare in the most sunward pointing detector must be at least 100 counts s-1 for inclusion in the flare database. When an event is determined to be solar in origin, the data technician visually determines the start and end time of the flare and of the intervals to be used for background determination before and after the flare. The software then automatically calculates the background-subtracted peak rates and total fluxes including rough corrections for the zenith angle of the Sun in each detector. The software assigns a flare number, enters information about the flare into the catalog, and creates an archive flare plot file. The archive plot for flare #445 is shown in Figure 2. It is a standard format plot of Channels 1 and 2 for the two most sunward-pointing detectors. Background subtraction, overflow correction, and livetime correction are done for each detector separately, and then the rates are combined by weighting according to each detector's effective area. Background during the flare is determined by a linear fit over background regions selected, when possible, immediately before and after the flare. A Flare Database (FDB) file, DISCSP file, and CONT file are created for the flare as a subset in time of the BDB file. The FDB file contains all of the data in the original BDB file for time intervals containing solar flares and their associated pre- and post-flare backgrounds. An example of a flare listing for June 10, 1991 is shown in Table 1.
 
Since the start of the mission, we have continuously enhanced the package to make more data and better analysis software readily available over the Internet. Now the graphics and data storage formats are all device independent, all data and analysis products are available over the World Wide Web and by anonymous FTP, and archives of high spectral and temporal resolution solar flare products are also available. The flare high resolution data products are collected from the archives of the COSSC and BATSE teams.  We have also developed the software to display all of these data sets in the form of light curves. Software hooks are provided for each data set in the spectroscopy analysis routines. We plan to continue enhancing the facility at a low level-of-effort to increase the flexibility of the WWW interfaces.
 
 


Figure 1. Number of solar flares detected with the BATSE LADs per day corrected for observing time for the period April, 1991 through February, 1998. Each bin covers 2 days.
 

 


Figure 2. An example of an archive flare plot. The archive flare plot is a standard format plot of Channels 1 and 2 for the two most sunward-pointing detectors. Background subtraction, overflow correction, and livetime correction are done for each detector separately, and then the rates are combined by scaling by each detector's effective area. The horizontal bar near the top of the plot indicates the duration of the flare. The vertical bar shows the time of the corresponding burst-trigger and the upper x-axis is labeled with seconds relative to the burst-trigger. Note that not all flares that we record generate a burst-trigger.

 3. On-line Data Access

All of the data products mentioned above (except the BDB files containing the complete DISCLA data) are available to the solar physics community. (Through agreement with the BATSE Principal Investigator, J. Fishman, this facility is not to be used for anything other than solar research.) The FDB flare files, quicklook plot files, and archive flare plot files for the almost 5000 flares detected so far, as well as the BATSE flare catalog and the daily event files are on-line and available at all times. Remote users have access to the data products described above by either logging onto a captive or guest account,  displaying files through the WWW interface, or by copying files using FTP to their system for local display and analysis. When logging onto an account, the user is notified of the ten flares most recently cataloged and presented with a menu of options. >From this menu, the user may display parts of the BATSE flare catalog, display archive flare plots or quick-look plots, plot selected intervals/detectors/channels from the FDB, CONT, or DISCSP files, dump raw or livetime- and overflow-corrected rate data for selected times, or display help files. After generating any kind of display - flare list, plot file, data dump, or help file - the user has the option to have the list-file or plot-file electronically mailed to himself in order to read the dump data and manipulate it locally, or to make hard copies on local printers.
 
Below we present several tables showing the scope of the archive:
 
Data
Files Online
Yearly Max.
Detector
Channels
 Time Resolution
Access
Lightcurve
Spectrum
FDB (DISCLA)
4940
2900
LAD
6
1.024 s
MENU, FTP,WWW
X
X
CONT
4940
2900
LAD
16
2.048 s
MENU, FTP,WWW
X
X
DISCSP
4940
2900
SPEC
2
2.048 s
MENU, FTP,WWW
X
X
MER
653
450
LAD
16
0.016 s
FTP,WWW
X
-
TTS
613
450
LAD
4
0.001 s
FTP,WWW
X
-
DISCSC
840
450
LAD
4
0.064 s
FTP,WWW
X
-
SHERB
654
450
SPEC
256
0.128 s
FTP,WWW
X
X
HERB
734
450
LAD
128
0.128 s
FTP,WWW
X
X
 The table lists the basic raw packetized data files obtained from the BATSE PI team and the COSSC. The Yearly Max. is the number of files expected during a year of Solar Maximum for Cycle 23, around the years 2000-2001. The 3 values in Access refer to means of remote access, MENU means available through the original remote login interface, FTP means access through ftp interface, and WWW means the FTP directories can be found easily through our URL of http://umbra.nascom.nasa.gov at the SDAC.

LEVEL 1 ONLINE COMMENTS
CATALOG Menu Driven, Select on Peak Rates, Times, or Burst Number
QUICK-LOOK ORBITS Menu Driven,  Multi-Trace, orbit and 24 hour format
FLARE PLOTS Menu , FTP, or WWW select, GIF and PS formats.
 
 

IDL Solar Software Tools Online Category Availability
GEN All Purpose WWW, FTP, SSW-MIRROR
CGRO/BATSE Light Curves, Catalog WWW, FTP, SSW-MIRROR
SPEX Light Curves, Spectroscopy WWW, FTP, SSW-MIRROR
This table illustrates the availability of all the IDL BATSE software developed at the SDAC. All of the procedures can be found within SolarSoftWare (SSW) which is used by all of the principal operating and future solar missions including Yohkoh, SOHO, TRACE, and HESSI. The software can be installed by simple forms and maintained through FTP, WWW, or Mirror. The details of SSW may be found at ftp://sohoftp.nascom.nasa.gov/solarsoft/.

 Database Update Frequency  Purpose
GRO Pointing 1 Month Detector Aspect
Ephemeris 1 Month Dat/Night Crossings
High Voltage Off 1 Month On Fraction 
Telemetry Gaps  1 Month On Fraction
SLLD & SLLD2 1 Month DISCSP Channels
SPEC Gain 3 Months SPEC PHA
CALIB Lines 3 Months SPEC PHA
SPEC Response  Yearly Photon Response
LAD Response  Yearly Photon Response
LAD Gain 6 Months LAD PHA
 


Many solar scientists from around the world have been routinely accessing this solar flare database. They include representatives from every major active program of solar flare observations including, BIMA, OVRO, Yohkoh, the VLA, OSSE, Phoenix, Sac Peak, COMPTEL, Hawaii Spectroheliograph, Marshall Vector Magnetograph, Nancay Radioheliograph, GRANAT, ULYSSES, and the Nobeyama Radioheliograph.
 
This on-line archive of BATSE hard X-ray flare data is both unique and unprecedented in the field of solar flare research. The information on intensity and time variations of the hard X-rays over a broad energy range is compiled into a usable archival flare database, and extensive software packages are available for scientific analysis either alone or in conjunction with the analysis of data at other wavelengths. The flare archive is a crucial tool for research and makes GRO an integral part of the solar physics research program.
 5. Continuous Improvements

Over the course of the seven years that we have operated this archive, we have continuously improved the software,  increased the number of available data products, increased their ease of access, enhanced the quality of the data set, and developed an increasingly sophisticated array of scientific tools, all designed to enhance the scientific utility of the dataset.  One of the more critical issues has been the increase in the variety of the database with the inclusion of DISCSP, CONT, MER, DISCSC, TTS, and (S)HER(B) data together with the creation of the software tools needed to fully utilize them.   One of the latest improvements has been the inclusion of DISCLA channel 0 in the display and analysis software.  The DISCLA0 is a residual rate formed by subtracting all of the other counters from the 5th of the 6 DISCLA counters.  That this meaningful residual existed was unknown until approximately 3 years ago.  At the SDAC we have calibrated DISCLA0 using the corresponding full PHA data, and now have all DISCLA channels edges, which are discrete discriminator leveles, expressed in PHA units making it fully integrated into the analysis procedures.  We also pioneered the utilization of the sixth DISCLA channel, the rate from the Charged-Particle-Detector, as a high-energy photon rate monitor during the intense solar flares of June 1991.  To increase access we have developed WWW interfaces into our most popular data products at http://umbra.nascom.nasa.gov/batse/batse_years.html and will continue to develop this interface.  Another important step was the integration of the primary BATSE data into a complete spectroscopy analysis package, SPEX, written entirely in IDL.  Several remote users have taken advantage of these facilities, several were helped in the analysis for their PhD's including Kristen Blais of U. Hawaii, Paul Feffer of UC Berkeley, and Brian Parks of Stanford. We have also fully developed, tested, and operated our software under both OpenVMS and DigitalUnix operating systems
 6.Summary

We are proposing for one year's funding to continue supporting on-line access to the BATSE/GRO solar flare database for the international solar physics community. We are requesting a smaller dollar amount than last year's proposal because the declining solar activity reduces the time required for data archiving and flare determination. The data obtained with BATSE plays an active role in the analysis of solar flare data observed from a number of instruments because of both its quality and ready availability from this database. The funds will support data acquisition, flare determination, archival storage of flare data, and on-line access to the flare data in a convenient and usable form as an integral part of the activities at the Solar Data Analysis Center at GSFC.

Figure A-1. Quick-Look Plot Example This figure shows a quick-look plot of BATSE DISCLA count rates vs time for a typical orbit on 10 June 1991. The traces are, from top to bottom: (A,B,C,D)Count rates in Channel 1 (25-50 keV) for the four most sunward pointing detectors multiplied by scaling factors of 104,103,102, and 101, respectively. (E)Sum of the rates in Channel 1 for the four sunward looking detectors minus 4000. (F)Sum of the rates in Channel 2 (50-100 keV) for the four sunward looking detectors multiplied by 10-1. (G)Sum of the charged particle detector (CPD) rates for the four sunward looking detectors multiplied by 10-2. (H)Sum of the rates in Channel 1 for the four anti-sunward detectors multiplied by 10-3. The geometric areas of the solar flux subtended by each of the four sunward detectors and their associated ID numbers are indicated in the lower left hand corner. Vertical lines marked by `D' and `N' indicate crossings into spacecraft day and night, respectively. This is the type of plot that is scanned by the GSFC data technician for count rate increases due to solar flares. Each plot covers an orbit of data, or about 95 minutes, starting and ending at spacecraft midnight. Activity is most clearly seen in Trace E, the sum of the rates in Channel 1 for the four sunward detectors. Two solar flares and two non-solar events can be seen during this orbit. Flare #444 starts at 04:03 UT and flare #445 starts at 04:42 UT. Flare #445 can clearly be seen, the decreasing amplitude with increasing angle from the Sun (Traces A through D) showing the general sunward direction of the event. In addition, its time profile is unlike the majority of non-solar gamma-ray bursts. Flare #444 is not quite as clear-cut and requires closer examination. The non-solar events occur at 04:23 and 05:10 UT and are almost certainly of magnetospheric origin.

 
 
 

BATSE Event Start Date yy/mm/dd  Start Time hhmm:ss Peak Time hhmm:ss Duration (sec) Peak rate (counts / s/2000cm^2) Total Counts (counts)  Burst Trigger #   Triggertime  (seconds of day)
440 91/06/10 0227:16 0228:51 287 276710 11739691 307 8865
442 91/06/10 0240:19 0141:32 280 2920 252014 0 0
443 91/06/10 0300:006 0300:16 42 1369 11917 0 0
444 91/06/10 0402:51 0404:46 144 473 18994 0 0
445 91/06/10 0441:39 0442:45 521 28381 1437140 308 16949
 


 

 

Table A-1. BATSE Flare List Example This table shows a listing of archived flares observed with BATSE from 02:00 through 05:00 UT on 10 June 1991. The first column lists our archive event number, the second column is the date of the flare, the third lists the start time in UT, the fourth is the time of the peak in the flare time profile, the duration is in seconds determined by operator inspection, the fifth column is the peak count rate which is background-subtracted for the flux below 100 keV and has been normalized to the value expected for a single BATSE detector directly facing the Sun, the sixth column gives the total number of counts integrated over the duration of the flare determined in the same manner as for the peak rate, and the last column shows the time in seconds into the day of the corresponding burst trigger.

Personnel

The quick-look and archival system for solar flare hard X-ray data from the Burst And Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) is an integral part of the Solar Data Analysis Center (SDAC) at Goddard Space Flight Center. The effort is directed by GSFC scientist Dr. Brian Dennis in the Laboratory for Astronomy and Solar Physics. Dr. Dennis has over 18 years experience in the detection of solar flare hard X-rays and in the analysis and archiving of  the data. He was PI for the Hard X-ray Burst Spectrometer (HXRBS) that recorded over 12,000 flares during the 9.75-year lifetime of the Solar Maximum Mission (SMM). Dr. Richard A. Schwartz provides the scientific oversight and A. Kimberley Tolbert manages the software development effort.   Dr. Schwartz and Ms. Tolbert were also members of the HXRBS team.