Frequently Asked Questions

Note: FAQ are added 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 CPS 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 CPS.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 CPS form is a monitor with large tolerances.Dec 13, 2017


CPS 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.Nov 14, 2018


Refer to Section 4.4 of the CfP. Specifically, Table 6 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. Information about the latest release can be found on the CSC home page.Dec 13, 2018


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 Chandra Proposal Software (CPS). We strongly advise using the Save button frequently to avoid losing your work.Dec 13, 2018


Please refer to the Guide to Proposing with CPS.Dec 13, 2018


When you are in CPS, you can obtain an explanation of a field by clicking field name link. This takes you to the right place in the CPS help page.Dec 13, 2018


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, 2018


Only one person is required to have an account. This person could be the proposal PI or a CoI, or they could be another person submitting on behalf of either the PI or a CoI. They are the only person with edit permission on the proposal and they are responsible for final submission. Responsibility for the proposal may be transferred to anyone else with an account, but there is only one person with write permission at any given time.Dec 13, 2018


You must have a name, institution, phone number and a valid email address.Dec 13, 2018


If you have access to the email account you used when you signed up, then you can use the “Forgot your username” and “Forgot your password” links on the login page. If you do not have access to that email account, please contact the CXC Helpdesk. Dec 13, 2018


If you remember your original username and password, or if you still have access to the email account you used to sign up, then you can log into your CXC account and update your profile.

If you have forgotten your username or password, or if you no longer have access to that email account, please contact the CXC Helpdesk. Dec 13, 2018


The “searchable list” is a drop-down list of names of people with accounts who have opted-in to the list. Selecting a name automatically fills in the form with that person’s basic contact information and links them to the proposal with read-access.

If you opt-in, other CPS users can view your name, institution and country. Only authorized CXC staff will have access to all users’ full contact information.

People opt-in to this list by checking a box in their account profile, or submitting a helpdesk ticket requesting inclusion. Not all people with accounts will be included in the list. You must opt-in to be included in the list.

People do not need an account to be included in the proposal. If someone does have an account and you select them from the list, they will automatically be granted read-access to your proposal. Dec 13, 2018


1: The person responsible for proposal submission.
2: PI and CoIs who have an account, provided the person submitting the proposal selected their names from the drop-down list and did not enter information manually. They will have read-only access.
3: Authorized CXC staff. They will see your full information. Dec 13, 2018


One of a couple things might have happened here. Either the CoI didn’t have an account at the time that you added them to the proposal, or you manually updated their information after you selected them from the drop-down list.

In either case, you can open the proposal, go to the CoI list, remove their entry from the list and then add them again using the correct entry in the drop-down list. If that doesn’t fix the issue, please contact the CXC Helpdesk. Dec 13, 2018


Yes, but only one person can edit a proposal at any given time. If you are the person currently responsible for submission (the ‘owner’), but you need a CoI to make edits, you will have to transfer ownership of the proposal to your CoI’s account. They then become responsible for submission, or they can transfer ownership back to you once they are done with their edits. Note that this only works if your CoI opted-in to the searchable list. Dec 13, 2018


Yes, you can see old proposals that were created in CPS. Additionally, the CXC will be attempting to backfill with proposals from the past three cycles. If you want to request that specific proposals from past cycles are linked to your account, please contact the CXC helpdesk. Requests will be filled depending on available CXC resources.Dec 13, 2018


Yes, any proposal that you ‘own’ in the CPS can be “cloned” for use in the current cycle. If you want to allow a collaborator to make use of one of your old proposals, you can clone it and then transfer ownership. Dec 13, 2018

No, there is no email option. If you are having difficulty using CPS, please contact the CXC Helpdesk.Dec 13, 2018


There is no autosave feature, you must save your work as you progress. There is a “Save” button at the bottom of every section of the proposal. Dec 13, 2018


Yes, there is a timeout after 30 minutes of inactivity. A five-minute warning will appear on the page. You will lose any unsaved work.Dec 13, 2018


Grey proposals are read-only. This could be because you have already submitted the proposal, you have ‘withdrawn’ the proposal, the proposal is from a previous cycle, or that you are not the ‘owner’ of the proposal.Dec 13, 2018


Proposals that appear in the sidebar when you log in are those that you can edit. If you open a different proposal for reading, it will also appear in the sidebar navigation for the duration of your session. Dec 13, 2018


You can add people manually if they are not in the searchable list. Note that people added this way will not have access to the proposal. If someone creates an account after you entered them manually, they won’t automatically have access to the proposal. You will need to remove the manually added entry and put them back into the proposal using the searchable list.Dec 13, 2018


You can add them manually. If you do this, that person will not have access to the proposal and thir profile will still be out of date. Or, if you have time before the deadline, you can ask them to update their profile, then add them to your proposal. Dec 13, 2018


If it is before the proposal deadline you can log into CPS, select the row of the proposal you need to fix on the homepage, and click on “Modify”. You will then need to respond to the prompt “Do you want to modify this previously submitted proposal and change the status to In progress?” Don’t forget to submit your proposal again once you have fixed the error.

If it is after the proposal deadline, please contact the CXC Helpdesk. Dec 13, 2018


Yes, we took this opportunity to redesign the proposal layout. The new design includes more space around elements, only presents relevant information (e.g. doesn’t include TOO information for proposals that aren’t TOOs), uses easier-to-read font sizes and presents information about each target separately. Dec 13, 2018


In the CPS Cover Page section the question "Is this a multi-cycle observing proposal?" should be answered "Y". In the CPS Target section the total observing time for all cycles combined should be entered, in addition to the projected time for future cycles.Nov 13, 2018


Please refer to the section about CPS grid parameters in About Grid Proposals. Nov 14, 2018


If all the follow-up observations had the same instrument configuration as the trigger target, no additional targets would be needed. However, if the follow-ups have different configurations, additional information is required. One target is required for each unique instrument configuration.Nov 14, 2018


If you have already completed the proposal forms, the number of constrained observations can be estimated simply by using the "Constraints/Slewtax" option in the Submit&Verify section of CPS. 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.Nov 14, 2018