THE HESSI CATALOG

J.McTiernan and A.Csillaghy

Space Sciences Lab

University of California, Berkeley

The HESSI mission is scheduled to be launched in late 2000-early 2001. HESSI will provide images and spectra of solar flares in the energy range from 3 keV to 10 MeV.

HESSI data are stored as telemetry packets, as received from the spacecraft, in FITS binary tables. The HESSI data catalog for each file is appended to that data file as FITS binary tables. The catalog includes: the Observing Summary, which contains count rates in 9 energy bands, and other information, the Flare list, a summary of the solar flares observed for the time range covered by the file, the Instrument Log, which summarizes the instrument state-of-health data for the given time range, quick-look images for different energy bands for each flare, and quicklook spectra for each flare

Here we present a sample of HESSI catalog data derived from simulations for a week of data. We will also demonstrate how to access the HESSI catalog from the data files.

Simulated HESSI data files are available at http://hessi.ssl.berkeley.edu/data/test_data .

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HESSI SCIENCE OPERATIONS

Telemetry to CD production:

Start with telemetry files:

An IDL routine, HSI_CONTACT2FITS, writes the original telemetry files into FITS files 1 per each orbit, named hsi_yyyymmdd_hhmm_nnn.fits. The date and time, yyyymmdd_hhmm, corresponds to the middle of spacecraft night between two orbits.

The "nnn" is a version number, for instances in which a file is generated that has the same yyyymmdd_hhmm as a previous file.

The catalog data will be generated as part of HSI_CONTACT2FITS, and appended to the hsi_yyyymmdd_hhmm_nnn.fits files.

These files are then written to CD.

Contents of the various files:

Inputs to hsi_contact2fits:

Outputs from hsi_contact2fits:

Other database files needed by hsi_contact2fits:

Other data to be generated after contact:

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HESSI Observing Summary:

The observing Summary is obtained directly from the telemetry packets. The photons are time-binned and the count rate is compressed to bytes (0.03 accuracy up to 1.0e6 counts/sec). Modulation variance is calculated for the 2 coarsest collimators by calculating the standard deviation of counts for the given 4 sec interval and dividing by the square root of the total counts in that interval. The spacecraft position and data from the particle detector are also included.

Accessing the Observing Summary

The observing summary is an object that contains pointers to objects that contain the data. When the software package is complete, there will be GUI and traditional IDL command-line access to the data. Here we use the object syntax. Given a filename or a time range, you get the observing summary as follows:

IDL> obs_summ_obj = obj_new('hsi_obs_summary')

IDL> data = obs_summ_obj -> getdata(filename = filename)

Or

IDL> data = obs_summ_obj -> getdata(ut_time_range = ut_time_range)

The getdata method returns an array of structures containing time and count rates in 9 energy channels. If the data is not found, the object is returned with all of the pointers set to -1.

The data is assumed to be in a directory that is pointed to by the environmental variable $HSI_DATA_ARCHIVE. This can be changed by setting the data_dir keyword to the appropriate directory.

Contents of the Observing Summary:

Each type of data in the summary is contained in a separate object.

In order to access the objects or structures in a given obs_summary, use the Get method:

IDL> info = obs_summ_obj -> get(/info)

IDL> rate_obj = obs_summ_obj -> get(/obs_summ_rate)

Info Structure:

Time Arrays

Data times are not saved with the observing summary structure, but they can be obtained using Get, e.g., data_times = obs_summ_obj -> get(/data_times) Returns the time array for the given observing summary. Also the Getdata method will return a structure including times.

So if, for example, you want to plot the countrate in the 25 to 50 keV channel, you could do this:

IDL> countrate = obs_summ_obj -> get(/countrate)

IDL> data_times = obs_summ_obj -> get(/data_times)

IDL> utplot, anytim(data_times, /yohkoh), countrate[3, *]

A typical plot of simulated data is shown below.

Details for the individual Objects:

Each object in the observing summary contains its own info structure, and data structure. The get method can be used on the individual objects as follows, to obtain the info structure and the data structure. Each object can be read individually from the data file also.

IDL> rate_info = rate_obj -> get(/info)

IDL> rate_data = rate_obj -> get(/data)

Or

IDL> rate_obj = obj_new('hsi_obs_summ_rate')

IDL> data = rate_obj -> getdata(filename = filename)

Obs_summ_rate Info:

Obs_summ_rate Data Structure, one for each 4 sec interval:

Mod_variance Info:

Mod_variance Data Structure, one for each 4 sec interval:

Ephemeris Info Structure:

Ephemeris Data Structure, one every 20 sec.

Obs_summ_flag Info:

Obs_summ_flag Data Structure, one for each 4 sec interval:

Particle_rate Info:

Particle_rate Data Structure, one for each 4 sec interval:

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HESSI Countrate Plot

The countrate in the energy band of 6 to 100 keV is plotted for the first flare on the list (#124). Spacecraft night is indicated at the start of the plot. The simulated flare is small in order to save time during simulations. (HESSI observes every photon, so every photon must be simulated; this takes a long time!). The background interval used to find the flare times is indicated by the red lines.

Hessi Countrate plot"> <hr> </big> <big> <H1>HESSI Flare List </H1> <P>The flare list is obtained by comparing the observing summary count rate and modulation variance to thresholds. The count rate threshold can be set, or determined from the background level. Defaults can be changed for threshold levels, energy range, minimum flare duration, minimum time between flares. A check using position information may be added. The flare position is found using a 35 arcsec resolution 64X64 image, and collimators 6, 7, and 8. (Tests work well down to 500 photons per detector. A sample position image is shown below) </P> <h2> Accessing the Flare List </h2> <p> The flare list is an object that contains pointers to structures that contain the data. When the software package is complete, there will be GUI and traditional IDL command-line access to the data. Here we use the object syntax. Given a filename or a time range, you get the flare list as follows: <hr> <p> IDL> flare_list_obj = obj_new( IDL> data = flare_list_obj -> getdata(filename = filename)

Or

IDL> data = flare_list_obj -> getdata(ut_time_range = ut_time_range)

The Getdata method returns an array of data structures, one for each flare in the list. If the data is not found, the object is returned with all of the pointers set to -1.

The data is assumed to be in a directory that is pointed to by the environmental variable $HSI_DATA_ARCHIVE. This can be changed by setting the data_dir keyword to the appropriate directory.

Contents of the Flare List:

In order to access the structures in a given flare list, use the Get method:

IDL> info = flare_list_obj -> get(/info)

IDL> data = flare_list_obj -> get(/data)

The Flare List Structures

Flare List Info Structure:

Flare List Data Structure

Writing the Flare List

To Write the flare list to a FITS file, use the write method, and for an ASCII file, use the write_acsii method:

IDL> flare_list_obj -> write, filename = filename

IDL> flare_list_obj -> write_ascii, ascii_filename = ascii_filename

A sample of an Ascii flare list is shown below:

HESSI FLARE LIST FILE

Created: 2000-06-17T16:24:37.000Z

ID: flare list: 2000-08-31T00:16:20.000Z to 2000-08-31T00:42:08.000Z

Number of Flares: 2

Time Range: 2000-08-31T00:16:20.000Z

To: 2000-08-31T00:42:08.000Z

Energy Range Found (keV): 6.00000 25.0000

Simulated Data

DATA:

id_number Start_date Start_time End_time Peak_time hi_eband0 hi_eband1 peak_rate total_cnt xcen ycen Flags
124 2000-08-31 00:16:20 00:16:40 00:16:28 100.00 300.00 624.00 8048.00 402.50 228.50 -1
125 2000-08-31 00:41:48 00:42:08 00:41:56 50.00 100.00 272.00 3696.00 -612.50 -191.50 -1

FLAGS

-1 : NONE

0 : SAA At Start

1 : SAA at End

2 : SAA

3 : Eclipse at Start

4 : Eclipse At End

5 : Flare at SOF

6 : Flare at EOF

7 : Fast Rate Mode

8 : Decimation

9 : Att State at peak

HESSI Flare Position

Flare position is found using a 35 arcsec resolution back-projection image of the sun, using collimators 6, 7, and 8, which have spatial resolutions of 36, 63, and 109 arcsec. This image is a sample from the first flare on the list (#124), synthesized using only the emission at the peak 4 second interval; a total of 860 photons. The brightest point is the white pixel at position (400, 200) and this is indeed the location of the simulated flare. The red pixel at position (-600, -200) is a reflection of the true image and is an artifact due to the form of the simulated aspect solution. The reflection problem is reduced when using larger numbers of photons, but it may be an issue for very small flares (e.g., #125).

Position Image