The TGCat web tool is designed to be easily navigable and straightforward. Because this catalog is designed to be user friendly, we encourage the user to comment on its content and navigability. This can be done by sending comments/questions/suggestion to the TGCat administrator at tgcat@space.mit.edu. On every page there are links that will bring you to a particular topic on this page for in-depth help, please consult these help pages for questions before contacting the administrator.
This catalog is an interface to an archive of X-ray spectra taken
with the diffraction grating spectrometers on the Chandra X-ray
Observatory. Here you can
search for observations by source,instrument, or other criteria
browse selections
review pre-computed summary products
generate custom plots
download data for detailed analysis
Chandra has two diffraction grating instruments, the High Energy
Transmission Grating (HETG), and the Low Energy Transmission Grating
(LETG). When used with their primary readout arrays, they are known
as the HETG and LETG spectrometers (HETGS and LETGS, respectively).
The readout arrays are a CCD array (ACIS), or a microchannel plate
detector (HRC). The LETG is also often paired with ACIS. The
instruments have different sensitivities, resolving powers, and
wavelength coverages. The HETGS itself has two channels, the Medium
Energy Grating and the High Energy Grating (MEG and HEG).
The Chandra grating spectrometers are fully described in the
Proposers' Observatory Guide (POG;
http://cxc.harvard.edu/proposer/POG/).
which describe the wavelength coverage, efficiency, and resolving
power of these instruments.
Note for non-X-ray spectroscopists:
On the summary pages, you will see spectra in counts units which
includes the strong signature of the instrumental response.
Quantitative analysis of X-ray spectra --- even at high resolution
--- is most often done using the counts in conjunction with the
response files via forward-folding. In addition, some instruments
do not allow direct inversion - the LETG/HRC configuration does not
allow separation of overlapping orders, so we cannot provide an
accurate flux corrected spectrum (it is source-model dependent).
On these pages, you will find flux-corrected spectra, and you can
plot in spectra in flux units (for data taken with ACIS), and
download an ASCII table of the plot. But be aware that these are
still approximations and that robust results are available through
detailed analysis.
Navigating TGCat
The
TGCat
Webpage consists of a number of subpages either accesible from the
main page or another subpage. These pages include:
Main page:
This page appears when a user navigates
to tgcat.mit.edu and contains links
to begin searches, learn about TGCat, download software, go to
similar archive, and more
Search Page:
This page is the place to begin a TGCat archive search
Results Page:
After submitting your query on the search page, this page
will open with TGCat entries matching query input
Summary Page:
each TGCat extraction has related summary products viewable
on this page
Custom Plotting:
the extraction spectra can be customized in an interactive
web GUI
The flow diagram to the right shows the
access to various
TGCat
pages and indicates how they are opened. Notice that the HELP page can
be though of as a central hub. Although the HELP page is designed for
one way traffic it can be accessed through virtually any page. Also
note that the Main page has two way traffic to most other pages.
A general user will navigate the path highlighted red:
First begining with a query of the archive based on one of a number of
differing search criteria.
Then they will be presented with the results in tabulated
format.
One then has a choice of previewing/customizing plots for
various Obsids or selecting which results they would like to work
with.
Once they have selected the Obsids of interest, they will then be
able to package and download the desired data products and/or
preview/customize plots.
Glossary of terms
Most of the terms found in TGCat are defined in the CIAO Dictionary. Any terms that cannot be found there will be defined below
TGCat Processing
TGCat processes all data within an automatic system to allow the best access to newly
public gratings data ready for analysis, and to allow the tgcat team to provide the best
extractions of gratings data with ease and little delay. All TGCat processing is done by
ISIS/S-Lang functions which set up and call CIAO tools.
grating/detector/mode combination supported:
Modes of ACIS:
TE: Timed Exposure
CC: Continuous Clocking
grating detector modes:
Detector
Grating
Mode
HETG
ACIS-S
TE
HETG
ACIS-S
CC
LETG
ACIS-S
TE
LETG
ACIS-S
CC
LETG
HRC-S
-
A quick guide to the extractions
Chandra data are identified by a "sequence number" and by an
"observation identifier", or OBSID. The sequence number generally
defines a single scientific observation, but due to operational
constraints, any given sequence number for a specific target may be
broken into several intervals, and each is assigned a unique OBSID.
We extract spectra by OBSID. During analysis, these may be
combined. In the summary plots, we show combined data in order to
provide the best overview of the quality of the observation. The
data products themselves maintain the individual components of the
spectra (different orders, gratings).
- In a later release, we intend to also provide data combined over
the obsids of each sequence number
Very briefly, the extraction process consists of the following
steps:
perform event processing (geometric and pulse-height
corrections; filtering on good events, good times);
determine the zeroth order's centroid (this is the
origin of the wavelength scale);
define a spatial mask which encloses spectral regions;
filter on the spatial mask and transform spatial to spectral
coordinates (wavelength, and cross-dispersion angle); if the
detctor is ACIS, use the CCD energy to resolve orders.
bin the spectra, sorted by order and grating, filtering on the
cross-dispersion region; from the region adjacent to the
source spectrum, bin a background spectrum (most important for
LETG/HRC, rarely important for HETG/ACIS).
Generate response files (effective area, or "ARF", and
line-spread-function, or "RMF");
compute a light curve from the diffracted photons;
compute some summary spectral quantities (counts and fluxes in
bands);
generate summary plots.
- For an in-depth look at the pipelines for each Grating/Detector/Mode combination see
Processing Definitions
Finding the Zeroth Order
TGCat uses one of two automatic methods for determining the zero order position:
the standard CIAO tool, tgdetect
and for cases in which the zeroth order is blocked or heavily distorted by pileup, we use findzo, an ISIS program
which intersects the MEG trace with the ACIS readout streak.
The methods used are checked during the Validation and Verification ( V&V ). If the
method used failed to center on the zero order accurately, the alternate automatic method will be
used or the V&V scientist will provide either exact coordinates of the zero order centroid or a region
to act as an initial guess ( for cases where the target source is displaced from the proposers TARGET
coordinates )
V&V process
All the extractions were inspected by a person familiar with the
instruments and spectra. We check that the zeroth order position is
accurate, that the spectral extraction region is appropriate, check
for avoidable source confusion, and that all the products exist.
The V&V procedure is guided by the same plots as presented in the
preview pages.
Comments and warnings are available in the results table ("v" link),
and as download products. Comments provide information about the
source which may be relevant for analysis. Warnings indicate
problems or features which may complicate analysis.
Some common comments and warnings are:
COMMENTS:
Comment: Bright, hard spectrum; extracted with narrow sky masks to
improve HEG flux at very short wavelengths (1.2-1.7A) (but at the
expense of background regions).
Comment: Mildly extended source <~size arcsec>
Comment: Complex source:
Comment: Multiple sources; extraction is of
WARNINGS:
Warning: Extended source, large extraction region used to include
extended emission.
Warning: Very extended source; special analysis required.
Warning: Background important
Warning: Spectra only valid in wavelength range [lo-hi] (energy
range [lo-hi]) due to detector masking.
Warning: Multiple sources in the field may cause contamination of
the primary extraction at some wavelengths.
Warning: CC-mode order-sorting with "osip=none" (a "flat" order
sorting PHA region) accepts some zeroth order scattering at short
wavelengths (<2A).
Warning: ACIS T = -110C, no CTI correction available.
Warning: Very bright: spectra may be piled.
Warning: heavy "streaking" on S4 not rejected; (custom application
of "destreak" might mitigate).
VV process - Obsids Not in Catalog
There were some processing errors which caused us to reject
extraction until custom processing is done (
these are not included in the catalog):
Error: Multiple sources - background contaminated. Need to
extract only backgrounds from one side. [Mainly relevant for
LETG/HRC-S; default backgrounds are very wide.]
Error: Blocking of some orders/regions due to HRC-S shutters
(requires re-extraction of <+/-> side). (some Crab observations)
Error: far off-axis source - requires wider cross-dispersion
extraction region.
Finally, there were obsids which could not be processed due to inherent
limitations (e.g., HETG used with just the ACIS-S3 (acis-7) readout, or
LETG used with HRC-I); the list of these obsids can be viewed
here .
The Search Page
The search page is the beginning of the path for finding, reviewing, and downloading Chandra gratings data. The page is separated into several mutually exclusive search types, each of which can be accessed by clicking on the appropriate button on the left side of the page.
Note that in all searches ( with the exception of "Derived Spectral Properties" )
the character "%" will match Zero or more characters ( numbers,
symbols, letters ). In other words
722% will match 722,7220,7221,...,7228,7229
HD9312% will match HD93129 and HD93218 and HD93129A and HD93218B
In addition most searches allow the user to narrow down the results by
limiting the detector and gratings to only certain combinations. This is typically
useful when searching over a large coordinate area, or selecting on all
obsids ( i.e. to find all ACIS/HETG observations ). These options can
generally be ignored for other searches due to the limited number of
gratings observations, see the trends page for more.
Target Name Search
Search by extraction target name(s), to search on more than a single name at a time enter each name
separated by a new line.
During the V&V process the scientist verifies that automatic processing has
identified the appropriate target for the extraction and ensures that the name matches the names stored in the
TGCat database, which include:
TGCat name. Chosen by the TGCat team
SIMBAD Primary Identifier. This is the ID that
shows at the top of any simbad query result
This search will return any TGCat source that has the given string within it, meaning that wildcards
are implied at the begining and ending of the entry value. Additionaly any whitespace is both searched
for and compressed, i.e. when in doubt include spaces
tau - will match "V* CM Tau" ( SIMBAD primary ID ) as well as "Proxima Centauri" and or course "tau CMa"
HD93129 - does not return any matches, while
HD 93129 - returns HD 93129AB
The TGCat name search provides the option to match the input to a SIMBAD
identifier for the target. If the input is one of the SIMBAD Identifiers
for a target, the coordinates of that target, as recorded in the SIMBAD
catalog, will be passed back to TGCat to be matched within the "search radius" chosen. The following URL search is performed
for each query:
if using a 2 arcmin search radius ( default ), the TGCat database is
then queried on
ra < 83.666543333333 and ra > 83.599876666667 and decl < 22.047803333333 and decl > 21.981136666667
Object Type Search
TGCat stores type information for each source it extracts. At present the only types
stored are SIMBAD types, but there are
plans for expanding this.
the "primary type" will always be the SIMBAD primary type.
to select more than one type in a single category press the Control button and select. The numbers that
appear beside each type are the number of sources to which that type is assigned but does not reflect the
number of objects with a particular type as their primary type. There are three types of type searches
that can be done:
Inclusive: will return all sources that have at least one of the selected types assigned to it
Exclusive: will return all sources that have all of the selected types assigned to it
Primary Type: will return all sources that have any of the selected types as their primary id
Coordinate Search
Coordinates can be entered in sexigessimal format or decimal format as per the following:
sexagessimal - 123:45:67.890 or 123 45 67.890 for RA and should be between 000:00:00.00 and 360:00:00.00
for DEC a "+" or "-" can be appended and values should be between -90:00:00.00 and +90:00:00.00 Decimal - 123.4567890 for RA and should be between 0.000 and 360.000
and (+/-)123.4567899 for DEC and should be between -90.000 and +90.000
All coordinates are Galactic J2000 epoch and in the IRCS frame
Spectral Properties Search
Obsid Search
All Chandra Observations are marked with a unique ObsId which can be used to query
for particular observations. This search has two options for specifying obsids:
entering a comma, space, or new line separated list in the text box marked "Obsid(s):" and/or,
uploading a file with one obsid per line. Both options are allowed at the same time. If the file being parsed
has characters other than numbers or "%" it will be ignored, however the obsids specified in the text box will still
be searched. One can display allTGCat obsids by entering "%" in the obsid search box.
Arbitrary Search
The Results Page
TGCat stores information on each extraction and the resulting data products
in a set of flexible MySQL tables. The results
page presents the user with column information from these tables based on the search criteria.
The user may choose to add relavent display columns, sort data by any available column, link to
publications, obsid information and _SIMBAD target information. Data download requests, custom
spectral plotting, further row filtering and other functions may also be performed from this page
The Results page is opened after pressing the submit button on the search page and presents the results
of a TGCat database query using the entered search parameters. There are two types of Tables that can be
accessed from a TGCat search:
The first table to appear depends on the type of search performed. In general the Source Table will be given
for any query whose parameters are not specific to an extraction, and the Extractions table will be given for
any query whose parameters cannot be generalized for all extractions of it's target.
The title box at the top of the page reports how many records ( if any ) were matched and returned. One row is
listed in the data table for each row matched in the TGCat database, and either the default or user selected
set of columns are displayed giving information on the Source or Extraction. The rows can be sorted by any
displayed column by simply clicking the title of the column wherever it appears ( every ten rows a column header
is displayed. Any one of these can be clicked to sort ). To sort the opposite direction simply click the desired
column header twice.
Each row contains a set of links on the left hand side of the table and each link is coded by a single character
and provides a tool tip eplaining where it goes. Several of the display columns also are links with tooltips describing
their target ( please see the Table descriptions below for details on Links in each type of table )
Each row also has a checkbox on the far left hand column, when selected pressing the "Go" button will perfom the
action selected in the radio buttons just above the "Go" button ( i.e. Clicking the "plot combined" radio button and
pressing "Go" will open a plotting GUI combining spectra from all of the extractions whose checkbox are checked ).
All of the checkboxes for the current data can be toggled using the "+/-" button in the header rows
( also requires javascript ).
The Extractions Data Table
The Extractions Data Table is a list of unique TGCat extractions. An extraction is a single unit of TGCat
processing, and contains it's own uniqe data products and measures. There may be multiple extractions for
any given source. To view the unique source information ( source table ) for a given set of extractions select
the desired extraction(s) ( or none for all ) and select the "view sources" radio at the bottom of the page
and hit "Go"
Each row on the data table contains a wealth of information and resources relating to the extraction it
represents. Each row also provides the user with a very quick way to preview the spectral data by way of
a tool tip that displays a flux spectra plot of the extraction. Here is a quick reference to the links
and actions available in the Extractions Table:
Obsid Column -- Provides a link to the TGCat summary page and gives the user a quick view of the flux spectrum
Object Column -- Also Provides a link to the TGCat summary page and gives the user a quick view of the flux spectrum
limit -- Pressing "Go" eliminates all rows from the table who have not been selected
Download -- Pressing "Go" brings up a dialog allowing the user to schedule a download request
Plot Combined -- Pressing "Go" opens the plotting GUI combining spectra from all selected extractions
A set of Links in each row provide the user with as much information as possible in a
straightforward and non-imposing manner, limiting the amount of clutter presented with
each query yet maximizing the usefulness of the results
o -- Provides a link to the Obscat Data Page displaying observational
parameters for the obsid this extraction is in
p -- Is a link to an ADS ( NASA Astrophysical Data System ) publication
search on the _Chandra obsid this extraction is in
v -- Mouse over to see the VV status and comments, Click to go to the
review page with VV report
s -- Is a link to a _SIMBAD indentifier query using the "object" field
in the TGCat database
Mousing over one of the Obsid or Object Column links displays a tooltop
with a counts specta plot for quick preview. Clicking the link will open the summary/custom plotting page
Each column header is also a link that when clicked will sort the table by that column in ascending
or descending order. Clicking it more than once will reverse the behaviour. A tip will let the user know
which order will result from a click. Please see Sorting Data for more
information
The Source Data Table
The source data table is contains a list of TGCat sources. Any one TGCat source has at least one
extraction in the TGCat archive and may have mutiple. To view the extractions for one or more of the sources
select the desired source(s) ( or none for all ) and choose the "view extractions" radio button at the botton
of the page and hit "Go"
Note At present there are no data products directly tied to a TGCat source, however future
plans include the archiving of combined products
The source table has the following features ( similar to extractions table ):
The source table, like the extractions table, provides links for the user
s -- Is a link to a _SIMBAD indentifier query using the "object" field
in the TGCat database
Each column header is also a link that when clicked will sort the table by that column in ascending
or descending order. Clicking it more than once will reverse the behaviour. A tip will let the user know
which order will result from a click. Please see Sorting Data for more
information
Changing Display Columns
The TGCat database tables store a wide variety of information about each extraction in the
form of column data. A user can select to customize the information that gets displayed for each
query result. To do this from the results page click the button on the bottom of the page
titled "Change Columns". This will popup a dialog box that looks something like:
The available columns are organized by topic and can be selected/unselected for display by
marking the appropriate checkbox and clicking "Apply". Assuming you have cookies enabled,
checking the Save box will keep your preferred column settings for future sessions and queries.
Clicking "Close" returns you to the page as it appeared before getting the dialog ( i.e. no
changes made ) and clicking "Defaults" show only the default TGCat columns ( these setting
may also be saved ) as shown in the DEFAULTS column section
Sorting Data
In order to efficiently browse queried data, TGCat provides the user with several ways to sort
retrieved table data. Initially, when the table is displayed it is sorted by the "object" column
in ascending alphabetical order ( even if the user chooses not to display the "object" column ).
In each of the header columns there are three links that can be used to alter the sort:
Colum Name: The column name in the header will clear any existing sorting,
sort by that column either ascending or descending order, and will
toggle it's function for the next click
Up arrow ( ): This will add it's respective column to the sorting in descending order
Down arrow ( ): This will add it's respective column to the sorting in ascending order
For example:
you searched the entire catalog ( obsid="%" ) and would like sort by several of the returned columns:
first by detector, then by grating, then by object, and finally by exposure, so that for a group of the
same detector,grating,and object the top most entry has the largest exposure.
First, reset the order as detector in ascending alphabetical order by clicking the "detector" column
header twice ( it will start out with desc, twice to toggle ). Now the data list should show ACIS
extractions first and HRC last. Then to add the grating order again alphabetically ascending we will
click the link to the right of the column header "grating". Now we see that all ACIS HETG extractions
appear first, then ACIS LETG and finally HRC LETG. Lets add the object sort by clicking the for
the "object" header effectivly grouping similar objects under detector/grating combinations. Finally,
lets see, for each object, which has the larget and smallest exposures by clicking the to the
left of the "exposure" header, which will sub-sort exposure in descending time.
Download Data
One of the key features of TGCat is the ability to download analysis ready event and spectral data
products. Pre-computed summary products are also available for download.
To download, follow these quick steps:
Search the Catalog
Select one or more extractions from the extractions
table for your search
Select the radio button "download" at the bottom of the page
Hit the "Go" button
A small dialog will appear prompting you for the desired product types for
your selections ( described below )
Once satisfied, optionally enter you email address for notification when your order
is complete
Hit the "Apply" button
This will initiate a download request and will be added to the list
of requested downloads to be handled in the order recieved. There are no gaurentees to how long this
request will take so it is suggested that you enter your email address and wait till a notification
comes. Otherwise you can use check using the "Check Status" button on the download
page which will appear after clicking the "Apply Button".
The available products are split into several categories, each one or more files for any given
Grating type ( An "(H)" or "(L)" after the filename indicates that the product is only for HETG
or LETG, respectively. )
OBSPAR
evt0.par
A "parameter file" - an ASCII file listing header
keywords and values from the event file
EVT2
evt2
The event file (level 2); this file is a FITS binary
table, containing the grating coordinates, time, and
other information for each good event.
ARF
leg_.arf (L)
The "Ancillary Response Files" (effective area) (ARF)
for the LETG grating. "" is a diffraction order,
-8 to 8 (excluding 0).
heg_.arf (H)
The "Ancillary Response Files" (effective area) (ARF)
for the HEG grating. "" is a diffraction order,
either -1 or 1.
meg_.arf (H)
The "Ancillary Response Files" (effective area) (ARF)
for the MEG grating. "" is a diffraction order,
either -1 or 1.
RMF
heg_.rmf (H)
The "Response Matrix Files" (line response function,
and enclosed energy fraction) for HEG grating. ""
is a diffraction order, either -1 or 1.
meg_.rmf (H)
The "Response Matrix Files" (line response function,
and enclosed energy fraction) for MEG grating. ""
is a diffraction order, either -1 or 1.
leg_.rmf (L)
The "Response Matrix Files" (line response function,
and enclosed energy fraction) for LETG
grating. "" is a diffraction order,
-8 to 8 (excluding 0).
LTC
lc
The light curve (FITS binary table).
lc_bg
The background light curve (FITS binary table).
PHA
pha2
The binned spectrum (FITS binary table, "Type II PHA"
file).
pha2_bg(L)
Binned background (FITS binary table, "Type I PHA"
file); summed positive an negative orders.
Selected summary information, ASCII file. Contains
some fields from the event file header (e.g., object,
date), and some source properties (count rates)
summary_flux_overview.ps
Overview flux spectrum plot (see the Guide
to the Plots)
summary_fprops.fits
Flux properties (FITS binary table). Contains
counts and rates summed in bands. For coarse
characterization.
summary_[hm]eg_123.fits (H)
Order sorting image (FITS image), for all
photons. See the "Guide to the Plots" for
a description.
summary_[hm]eg_all.fits (H)
Order sorting image (FITS image), for
filtered, binned photons. See the "Guide
to the Plots" for a description.
summary_im-a.ps
Summary image; source region detail (See the "Guide
to the Plots" for a description.)
summary_im-b.ps
Summary image; sky field image (See the "Guide
to the Plots" for a description.)
summary_im_osum.ps (H)
Summary image; order-sorting image (See the "Guide
to the Plots" for a description.)
summary_imsp.ps
Summary image; spectral-spatial image (See the "Guide
to the Plots" for a description.)
summary_lc.ps
Summary plot; light curve (See the "Guide
to the Plots" for a description.)
summary_spc.ps
Summary plot; counts (See the "Guide
to the Plots" for a description.)
summary_spf.ps (H)
Summary plot; flux (See the "Guide
to the Plots" for a description.)
Summary Page
During TGCat processing there are several summary products created for browsing
purposes. These images are displayed for each extraction on it's own summary page
( navigated to by clicking the "v" link or one of several columns in the
extractions data table.
All of the summary products can be downloaded at once by selecting the "SUM" option
when downloading data.
Flux spectrum ([photons/cm2/s]). The first panel shows a broad
spectral range, while subsequent panels show detail in smaller
wavelength ranges. Positive and negative orders have been
summed. For HETGS, HEG and MEG have been combined by regridding the
higher resolving power HEG data and responses to the MEG grid. Flux
correction is done by dividing the counts by the model rate for a
flat spectrum. Errorbars are plotted in light gray.
(There is no flux plot for LETG/HRC-S, since flux determination
requires order-sorting.)
Flux overview
A flux spectrum, adaptively binned to provide a minimum
signal-to-noise ratio and a minimum number of bins, plotted on a
logarithmic energy and flux density scale. This is used for a
uniform overview of the extractions (and is the pop-up plot as you
move the mouse pointer over the results table's obsid or object
links). For LETG/HRC, the flux is approximate, since order-sorting
cannot be done, and this fluxed spectrum often shows artifacts.
Counts spectrum
Counts spectrum (counts per bin) for summed positive and negative
orders (first orders only, if ACIS). For LETGS, the background has
been subtracted (ACIS background is usually negligible). For
LETG/HRC-S, the first panel shows a broad spectral range, and
subsequent panels show expanded region. For HETG we show the HEG
and MEG separately.
Light curve
Light curve of the source from the diffracted events, in 1 ks bins
(except for some short CC-mode observations which have smaller
bins). The count rate was determined for orders -1 and +1 from the
spectral binning region. For HETG, HEG and MEG counts were
combined.
Background light curve in the middle panel (if any) from the
background region adjacent to the dispersed spectra. The count
rates have been scaled to the source region size.
Net rate (bottom panel, if any background light curve exists).
Source region detail images
Images of the zeroth order region. The first image has cross-hairs
showing zeroth order position. Other images step out for 5 factors
of 2, and have circles showing zeroth order region. Images are in
rotated sky pixels, such that the long axis of the detector is
horizontal, and positive orders are to the right.
Sky field image
Image of the field in sky pixels, but rotated to make the long axis
of the detector horizontal. Positive orders are on to the right.
The green arrow points to north, and the green bar points east. The
outline shows the grating part regions (if HETG, red outlines HEG
and blue MEG). The aspect ratio is not square.
Dispersion coordinates field image
Image of the field, in grating dispersion coordinates,
order*wavelength ("m*lambda") on the x-axis, cross-dispersion angle
on the y-axis. The outline shows the grating part region(s). The
aspect ratio is not square.
Order-sorting image
The image in order*wavelength (x-axis) vs diffraction order (y-axis)
defined by grating wavelength (m*lambda) divided by CCD "wavelength"
(hc/ENERGY). Order-sorting by selects the order limits as shown on
the left ("123" plot). On the right ("all") is the unfiltered
order. These are useful for assessing calibration issues (CCD
gain), zeroth order position error, or source confusion. The orders
in this diagram should be horizontal, and the bright horizontal
order should not be clipped, compared to the "all" panel. For HETG,
the HEG is on the top, MEG on the bottom.
(These can only be made if the detector was ACIS.)
Other summary products
Flux properties (file *_fprops.fits)
Rates and fluxes in bands. For LETGS: counts are background
subtracted, and there are no flux values, since they depend on
models and higher orders.
These are simple sums of counts or average of flux over a wavelength
region. There is no continuum subtraction or profile fitting.
Band were chosen to give broad-band ratenuum bands.
Plot Customization
TGCat provides a GUI-like interface for the customization of spectral plots of both individual pha sepctra and combined phs spectra. Spectral orders can be combined or plotted separately as well as binned. A user can select from a range of different plot units and optional log scales, choose plotting limits, whether or not to display error bars, and can optionally request an ASCII dump out of the plot data to easily load into their desired plotting program without having to obtain larger file sets
The plot customization page can be accessed in one of two ways:
From the data results page click on either the Obsid or the Object identifiers for your desired extraction. This will take you to the summary preview page showing premade spectral and imaging plots. Click the button at the bottom of this page titled "Customize Plots"
From the data results page you can plot single or combined spectra using the GUI by selecting one or more extractions with the checkboxes on the left hand side of the table, then select the "plot combined" radio button toward the bottom of the page and click "Go". This will take you directly to the plotting page. To get back to your results simply click the "Back" button
Lets Plot Something!
...A walkthrough of TGCat plotting...
First find your favorite Chandra gratings observation in TGCat. Click on the Object or Obsid link for that extraction and then click on the "Customize Plots" button. We chose XTE J1118+48 ( A Low Absorbtion X-Ray Nova ) for this run through
Now you will be presented with a blank plotting GUI
Lets get something on the Canvas to begin with. Find the "replot" button in the far right bottom corner and click it
You will then be presented with a plot of your spectra using the default plotting parameters
This may not be the most interesting plot to look at so lets customize a little. We can bin the plot to obtain better signal to noise. Here chosing 8 seems okay. To do this you must check the "bin" box and enter you desired values in the entry fields. "min S/N" chooses bins that satisfy a signal to noise greater than "?" and min Ch groups the channel by a factor of "?" both can be applied in unison
Lets take a look at an interesting range in the spectrum. There is a nice bump between 2 and 5 angstroms so we can enter those limits in the "X min" and "X max" fields
Just for kicks lets also get the ASCII dump data when we plot. To do this simply check beside "Ascii"
Then press replot and view your customized spectral plot! You can grab that ASCII dump file by clicking on the link at the top of the GUI viewport
The
TGCat
Webpage consists of a number of subpages either accesible from the
main page or another subpage. These pages include:
): This will add it's respective column to the sorting in descending order
): This will add it's respective column to the sorting in ascending order
Flux spectrum ([photons/cm2/s]). The first panel shows a broad
spectral range, while subsequent panels show detail in smaller
wavelength ranges. Positive and negative orders have been
summed. For HETGS, HEG and MEG have been combined by regridding the
higher resolving power HEG data and responses to the MEG grid. Flux
correction is done by dividing the counts by the model rate for a
flat spectrum. Errorbars are plotted in light gray.
(There is no flux plot for LETG/HRC-S, since flux determination
requires order-sorting.)
A flux spectrum, adaptively binned to provide a minimum
signal-to-noise ratio and a minimum number of bins, plotted on a
logarithmic energy and flux density scale. This is used for a
uniform overview of the extractions (and is the pop-up plot as you
move the mouse pointer over the results table's obsid or object
links). For LETG/HRC, the flux is approximate, since order-sorting
cannot be done, and this fluxed spectrum often shows artifacts.
Counts spectrum (counts per bin) for summed positive and negative
orders (first orders only, if ACIS). For LETGS, the background has
been subtracted (ACIS background is usually negligible). For
LETG/HRC-S, the first panel shows a broad spectral range, and
subsequent panels show expanded region. For HETG we show the HEG
and MEG separately.
Light curve of the source from the diffracted events, in 1 ks bins
(except for some short CC-mode observations which have smaller
bins). The count rate was determined for orders -1 and +1 from the
spectral binning region. For HETG, HEG and MEG counts were
combined.
Background light curve in the middle panel (if any) from the
background region adjacent to the dispersed spectra. The count
rates have been scaled to the source region size.
Net rate (bottom panel, if any background light curve exists).
Images of the zeroth order region. The first image has cross-hairs
showing zeroth order position. Other images step out for 5 factors
of 2, and have circles showing zeroth order region. Images are in
rotated sky pixels, such that the long axis of the detector is
horizontal, and positive orders are to the right.
Image of the field in sky pixels, but rotated to make the long axis
of the detector horizontal. Positive orders are on to the right.
The green arrow points to north, and the green bar points east. The
outline shows the grating part regions (if HETG, red outlines HEG
and blue MEG). The aspect ratio is not square.
Image of the field, in grating dispersion coordinates,
order*wavelength ("m*lambda") on the x-axis, cross-dispersion angle
on the y-axis. The outline shows the grating part region(s). The
aspect ratio is not square.
The image in order*wavelength (x-axis) vs diffraction order (y-axis)
defined by grating wavelength (m*lambda) divided by CCD "wavelength"
(hc/ENERGY). Order-sorting by selects the order limits as shown on
the left ("123" plot). On the right ("all") is the unfiltered
order. These are useful for assessing calibration issues (CCD
gain), zeroth order position error, or source confusion. The orders
in this diagram should be horizontal, and the bright horizontal
order should not be clipped, compared to the "all" panel. For HETG,
the HEG is on the top, MEG on the bottom.
(These can only be made if the detector was ACIS.)
