Frequently Asked Questions

Note: FAQ are added to regularly between CfP release and proposal deadline. Check back for new information.

All proposal rules and information about proposal submission can be found in the Call for Proposals.

Before you get too far into the process, check to see if your target has already been observed. If it has, you may want to consider an archive proposal. Or, if you don't know the target you want to observe, check if a similar proposal has already been approved. ChaSeR allows you to search the database of all observations. Lists of approved programs, which include archive and theory proposals, are also available.

Once you have selected a target, check to be sure that the object is visible to Chandra during the proposal cycle and that there are no bright sources in the field-of-view that you will need to avoid. You can check target visibility over time using the tool ProVis. The ObsVis software will allow you to inspect sky images with overlaid instrument fields-of-view and facilitates detailed manipulation of Chandra pointing and instrument parameters.

Once you know the target is visible to Chandra and has not previously been observed, decide which instrument configuration would work best for your science goals. Detailed information about Chandra instruments is given in the Proposers' Observatory Guide.

From there you should simulate the observation to determine the ideal instrument settings, observing time, constraints (etc.). A variety of tools are available to help with simulating Chandra data. These include such software as Sherpa, WebSpec, PIMMS and the rest of the Proposal Toolkit.

You will need to prepare Proposal Forms in the RPS proposal submission software that specify the target configuration(s) necessary to meet your science requirements.

A detailed science justification narrative is also required. This document should describe the science objectives of your investigation, explain your data analysis plans and demonstrate technical feasibility.

For more information, please refer to our New Proposer GuideJan 11, 2018


Yes, please refer to our example document that plans a proposal to observe an on-axis point source. Jan 12, 2018


The CXC has a Helpdesk that operates during normal business hours (EST/EDT), with extended evening and weekend coverage the two weeks prior to the proposal deadline. If you would prefer to send email instead of using the web interface, you can send a message to cxchelp@cfa.harvard.edu.Dec 13, 2017

Chandra policies and proposal rules can be found in the CfP.Dec 13, 2017


Yes. Multi-Cycle Observing Proposals (MCOPs) allow you to request time up to two cycles in the future. In addition to future time, time must be requested for the current cycle and there must be a scientific justification for requesting future time.Dec 13, 2017


Yes. You can submit a Target of Opportunity (TOO) proposal that will trigger its observation when the object has been identified. One common use of the TOO type is to observe recently discovered transient events.Dec 13, 2017


A "slew tax" of 1.5 ks is added to each observation at the Chandra peer review. This represents the average slew, settle and set-up time required for an observation. Generally, most proposals only have a few observations, so slew tax is minimal. But grid or raster observations typically have many observations.Dec 13, 2017


Not necessarily. Because some or all of the pointings in a grid can often be done consecutively, the average slew time is less than the nominal 1.5 ks and is calculated differently. To qualify for the reduced slew tax, the observations in a grid must satisfy the following conditions: 1) Maneuvers from one observation to the next must be less than or equal to one degree. 2) There can be no change in instrument configuration. 3) Individual exposure times must be 44 ks or less (which corresponds to a minimum to 2 grid observations per 90 ksec group - including slew time).

To calculate slew tax, pointings will be assembled into one or more groups with a maximum of 90 ks per group, including slew tax and the slew tax for the first observation in a group will be 1.5 ks. Subsequent observations in the same group are charged at a rate of 0.5 ks.Dec 13, 2017


A proposal is classified as "joint" if time is requested on one or more joint partner observatories (JPOs) in addition to Chandra. Please see Chapter 5 in the CfP for more details. An observation is "coordinated" if the Chandra observations are to be scheduled in conjunction with another space observatory or NRAO. For example, if the observations are required to be simultaneous with, or offset from, those of another observatory. Joint proposals are not always coordinated. The awarding of joint Chandra time with another observatory does not mean that the observations will be coordinated. Proposers must specifically request a coordination.Dec 13, 2017


Yes. If the "coordinated" flag is not set, the observation is unconstrained. Observations that are unconstrained are often designated as "pool" targets. Pool targets may be scheduled at any time during the cycle to fill gaps between constrained observations and are often scheduled with only a few days notice. This makes it almost impossible to give the other observatory time to change their schedule.Dec 13, 2017


Yes. A percentage of joint time is reserved for future cycles, contingent on science justification and continued availability. The exact details are available in the CfP.Dec 13, 2017


Too triggers can not be proposed for a future cycle, however follow up observations may extend into future cycles..Jan 18, 2018


No, a large or difficult to schedule proposal might be extended over several cycles for technical reasons, but that is at the discretion of the Mission Planning group and does not qualify as a MCOP.Dec 13, 2017

An observation is time constrained if the proposer restricts the time during which that observation can be performed. Constrained observations are reviewed by the CXC for feasibility before proposals go to the Peer Review. Many targets can only be observed at certain times of the year because of pitch angle or sun block restrictions. These observatory-imposed restrictions do not count as "constraints". However, proposers should check that any user-imposed constraints do not push the target into the "cannot do" pitch range (see Chapter 3 of the POG). Proposers can also check the visibility of a target object using PRoVis.Dec 13, 2017


The following will result in a constrained observation:

Time Windows: specific time intervals in which observation must be scheduled. Such constraints are primarily for use in coordinated observing campaigns or for arranging an observation to coincide with some time-critical aspect of the target.

Monitoring Intervals: for observing a target at semi-regular intervals for a specified duration.

TOO Followups: for repeated observations of a TOO target at specified intervals.

Group Observation: a target which needs to be observed within a particular time range with other targets in the program.

Phase Interval: specific phase intervals for observing sources with long, regular periods.

Coordinated Observations: targets specified to be observed by Chandra and another observatory in a given time period.

Continuity of observation: specifying that an observation may not be interrupted (up to 180 ks).

Roll Constraints: specifying a particular roll angle and tolerance.

Any other constraints not listed above that are specified in the "Remarks" box in the "Constraints" section of RPS.Dec 13, 2017


A "preference" is met on a best-effort basis, unlike "constraints", which have to be fixed into the appropriate slot in the Long Term Schedule to meet the constraints. A proposer can designate a constraint as a "preference". In this scenario, the major goals of the project can be achieved without the requested constraint, but superior results might be expected if it is met.Dec 13, 2017


Trigger targets may or may not be constrained by the proposer, but follow-up observations will always be considered to be constrained.Dec 13, 2017


Yes! If you have any scientific requirements for the spacing of observations that are not compelled by target visibility alone, you must mark the observation as constrained. The most efficient way to schedule multiple observations of the same target may be to do them back-to-back. Any requirement that they NOT be scheduled this way would indeed qualify as a constraint. The best way to specify such a constraint on the RPS form is a monitor with large tolerances.Dec 13, 2017


RPS provides an ESTIMATE of the constraint grade. Final constraint difficulty classifications for each proposal will be determined by the CXC after the proposal deadline, taking into account all declared constraints, including those that are specified in the remarks.Dec 13, 2017


Refer to Section 4.4 of the CfP. Specifically, Table 5 gives classification definitions for each type of constraint.Dec 13, 2017


Calculate the classification value for each type of constraint that applies to your target. The final total will be that associated with the most restrictive classification. For example, if you had a target that requested one 'easy' phase constraints and two 'average' uninterrupted constraints, then the final value would be equal to two 'average' constraints.Dec 13, 2017

Advanced CCD Imaging Spectrometer (ACIS) and High Resolution Camera (HRC). These can be combined with the Low Energy Transmission Grating (LETG) or the High Energy Transmission Grating (HETG) to create a high resolution spectrometer. For more detailed information please see the POG.Dec 13, 2017


There are a number of things to consider when developing a proposal for ACIS time. For example, you will need to consider background rates, potential for pile-up, and thermal constraints, among others. For comprehensive information about ACIS, please refer to Chapter 6 of the POG.Jan 11, 2018


Timed Exposure (TE) mode: Here the array integrates photons for a fixed period of time (Frame Time) before being read out. In TE mode, the available Telemetry Formats are Very Faint, Faint, and Graded.

Continuous Clocking (CC) mode: In CC mode, rows from the imaging array are continuously clocked into the framestore array, giving a 1x1024 pixel image. In CC mode, the available Telemetry Formats are Faint and Graded.Dec 13, 2017


The Telemetry Format determines what information about each detected event is telemetered to the ground. ACIS Telemetry Formats are described in the POG Section 6.15.2. In general, the optimal format is that which telemeters the maximum information without saturation.

For ACIS, the choices are:

Faint (F) Format: Gives position, time, and total pulse height for each detected event, plus pixel values in a 3x3 region surrounding the event that characterizes the event grade.

Very Faint (VF) Format: Same as for Faint, but pixel values in a 5x5 region surrounding the event are telemetered.

Graded Format: Gives position, time, total pulse height, and grade of the event. Pixel values are not telemetered.Dec 13, 2017


Please refer to the Sherpa Simulations threads Jan 18, 2018

The complete Chandra Data Archive is searchable via the WebChaSeR interface. For more information about the archive, visit the Data Archive web pages.Dec 13, 2017


The Chandra Source Catalog (CSC) the definitive catalog of X-ray sources detected by the Chandra X-ray Observatory. The first official release of the CSC includes information about sources detected in public ACIS and HRC imaging observations from roughly the first eight years of the Chandra mission, with exceptions as explained on the CSC home page.Dec 13, 2017


CSCview is a Java stand-alone application which provides access to the source properties and data products of the Chandra Source Catalog. To download, visit CSCview. For complete CSCview documentation, please visit the CSC threads page. There is an alternative command-line interface that you might also want to read about.Jan 12, 2018

The MARX software can be used to help in proposal planning by allowing users to simulate observations.

For more information refer to the following threads:
Using MARX to Simulate an Existing Observation
Using MARX to Simulate a Planned Observation Jan 11, 2018


You can use WebSpec, or the Sherpa fake_pha command to simulate an ACIS-S spectra.Dec 13, 2017


You can use Sherpa to simulate spectra. There is a Sherpa thread that addresses this question.


The degree to which the source is piled up can be estimated from PIMMS. The effect of pileup on a spectrum can also be evaluated using WebSpec. It is possible to download the simulated spectra and responses from the WebSpec results page and read them into command line versions of Sherpa or Xspec. The effect of pile-up on a spectrum can then be compared to the spectrum without the effects of pile-up.Dec 13, 2017


You may need to impose a roll constraint to avoid unwanted bright sources in the field-of-view. You can use ObsVis to simulate the field-of-view and determine what constraints may be necessary. Once you determine your roll angles, you will need to use PRoVis to investigate when those roll angles are observable at a good pitch angle. Jan 18, 2018

After determining the minimum counts you need in order to do your analysis, you should figure out the total count rate of the field and the background count rate. The tool PIMMS can help you calculate these values, as well as help you determine if you need to consider the effects of pile-up.Dec 13, 2017


If it is essential to have uniform coverage, the proposer must restrict the roll angles of the observations. This can be done: 1) Impose a roll constraint (with associated tolerances) if the roll angle of the survey must be fixed. 2) A group constraint should be used if the absolute value of the group constraint forces all the observations to be done within a certain time interval, but does not specify the exact window. Refer to About Grid Proposals for more information.Jan 18, 2018


Information about slew tax of grid proposals can be found in About Grid Proposals. Jan 18, 2018


The maximum uninterrupted exposure time is different for each target and depends on several factors such as pitch angle, spacecraft thermal history and instrument constraints. All these factors are described in detail in the POG.Dec 13, 2017


The tool Colden can be used to determine this amount.Dec 13, 2017


The total count rate includes the target source, any other sources in the field, and the background. The tool PIMMS can help you calculate these values. Information about the background rates for each instrument are given in the POG.Dec 13, 2017


ObsVis is a tool that allows the inspection of sky images with overlaid instrument fields-of-view (FoV). ObsVis interfaces with the SAOimage DS9 image display tool, and facilitates detailed manipulation of Chandra pointing and instrument parameters. For more detailed information please visit the ObsVis page.Dec 13, 2017


If an observation has a roll constraint, the observer should use PRoVis to check that this roll constraint does not force the target to be at bad pitch. A window-constrained observation must take place within a specific time window, due to some time-critical aspect of the target. Any proposer placing a window constraint on his or her observation must use PRoVis to check that this constraint does not force the target to be at bad pitch.Dec 13, 2017


PIMMS is a tool than can calculate ACIS pileup. Pileup results when the count rate is so high that two or more photons are detected as a single event. Pileup and pileup mitigation are further discussed in the ACIS chapter of the POG.Dec 13, 2017


The proposer should use PRoVis to determine how feasible it is to obtain the uninterrupted observation. A PRoVis plot will show if a target resides at good pitch for sufficient time.Dec 13, 2017

Proposals must be submitted electronically using the Remote Proposal Submission (RPS) software. RPS is stateless, so nothing is done with the entered information until you use one of the action buttons at the top of the RPS page. We strongly advise using the Save button frequently to avoid losing your work.Dec 13, 2017


When you are in RPS, you can obtain an explanation of a field by clicking field name link. There is also an RPS help page.Dec 13, 2017


Once you are finished filling out the RPS form, click "Verify" at the top of the page. This checks to make sure that all of the required fields have been filled out. If you receive an error, you must fix it before you can submit. If no errors are found, first click "Save" to save a version of the html form to your local disk. Click the "Submit" button to submit your proposal and record the proposal number for when you submit the science justification, Previous Chandra Programs file, and CV.Dec 13, 2017


After submitting the RPS form, record your proposal number and click "Upload Science Justification" at the top of the RPS page. You will be asked to upload the Science Justification, the optional Previous Chandra Programs file, and your CV. Enter the P.I.'s last name and first initial and the previously recorded proposal number.Dec 13, 2017


If the mistake is discovered before the deadline, please go through the submission process again and answer "yes" to the question at the top of the cover page: "Does this replace a previously submitted proposal for the current cycle?" And give the number of the proposal to be discarded. It is possible to correct minor errors in forms after the proposal deadline, especially if it is critical to the success of the potential observation. Please inform CDO as soon as possible via HelpDesk. Late changes in the Science Justification are not allowed. However, some typographical or numerical errors can be misleading, and corrections of such nature can be sent to the CDO in a letter of explanation. If appropriate, this letter will be included in material sent to the Peer Review. Note that a long list of corrections to a careless submission cannot be accepted since this would be de facto a late-proposal submission.Dec 13, 2017


You will receive a confirmation web page after a successful submit. In addition, an email confirmation will be sent to the email address of the PI. Jan 12, 2018


RPS does not have a method for users to view files that were submitted. If you saved your proposal form before submitting, you can load it in a browser to review. Additionally, you also have the option to save as LaTeX or PDF files before submission.

Similarly, after uploading a pdf (science justification, previous chandra programs file, CV), you will be returned a confirmation page telling you what was uploaded.

If you do need to review the files that were submitted, you can send a request to helpdesk, and we will accommodate as resources permit. Jan 12, 2018

In the RPS Cover Page the question "Is this a multi-cycle observing proposal?" should be answered "Y". In the RPS Target Page the total observing time for all cycles combined should be entered, in addition to the projected time for future cycles.Dec 13, 2017


Please refer to the section about RPS grid parameters in About Grid Proposals. Jan 18, 2018


The email server is particularly useful when you have a large number of targets in a proposal. Otherwise, the web interface is generally the simpler choice.Dec 13, 2017


If you wish to continue working on your proposal using the RPS Email option, you can take existing work done in the web version and have RPS convert it to the necessary format for email submission. Use the "RPS Email" button and, when prompted, specify where you want to save the resulting file. To obtain a blank form to fill out, send a plain text email to rps@head.cfa.harvard.edu.Dec 13, 2017


If there is more than one target in your proposal, click "Add Target" at the top or bottom of the page. You will be given the option of cloning an existing target form or adding a blank target form to your proposal. Individual targets' forms appear in RPS as new items in the expanded Target Form.Dec 13, 2017


Expand the target you wish to delete, and for the question "Do you want to delete this target?" at the top of the form, mark "Y". Then click the "Delete Target" button at the top or bottom of the page to remove any targets marked "Y".Dec 13, 2017


If all the follow-up observations had the same instrument configuration as the trigger target, no additional target forms would be needed. However, if the follow-ups have different configurations, additional information is required. One target form is required for each unique instrument configuration.Dec 13, 2017


In the Target Form on the RPS, there is a TOO section that includes the TOO Followup Summary Form. First enter the exposure time for the initial TOO observation, then enter the the exposure time (in ks), minimum and maximum time interval between the preceding TOO observation (in days), and target number for each followup.Dec 13, 2017


In the TOO section of the Target Form in the RPS, there is a field that lets you specify the Alternate Target Group Name. Add targets to the RPS form using the "Add Target" button and enter the same Alternate Target Group Name as the other targets in the same group. Fill out the "Number of targets requested for this alternate group" to indicate the total number of targets you want to observe from within the group.Dec 13, 2017


If you have already completed the proposal forms, the number of constrained observations can be estimated simply by using the "Constraints/Slewtax" button in RPS. However, additional constraints specified in the "Remarks" section cannot be evaluated by that tool, so any classifications should be taken as estimates. Final constraint difficulty classifications for each proposal will be determined by the CXC after the proposal deadline.Dec 13, 2017