Frequently Asked Questions

Note: FAQ are added regularly between Call for Proposals 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 should also use Starchecker to ensure there are roll angles and dates with suitable fields for guide star acquisition given your target and offset configuration.

You may also want to know the Resource Cost (RC) of your target by using the RC calculator. More information is available in the constrained observation FAQs.

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 required. This document should be appropriately anonymized and should describe the science objectives of your investigation, explain your data analysis plans and demonstrate technical feasibility.

A one-page Team Experience document is also required. This document should not be anonymized.

A sample walkthrough of this process can be found in this document about proposing to observe an on-axis point source

For more information about proposing, please refer to our New Proposer GuideDec 9, 2022

Yes, please refer to this walkthrough that prepares the technical elements of a proposal to observe an on-axis point source. Dec 9, 2022

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 13, 2017

Chandra policies and proposal rules can be found in the Call for Proposals.Dec 13, 2017

Yes, all citations in the Scientific Justification text must use the numerical citation format and not the parenthetical citation format ([2] versus (LastName YYYY)). Proposals that do not use numerical citation format will be deemed non-compliant with the Dual Anonymous Peer Review (DAPR) requirements. For more information and examples of common violations of DAPR requirements, please refer to Section 7.2 of the Call for Proposals and this online guide.

References should be listed on a separate page after the Scientific Justification and the reference-only page does not count against your page limit. Dec 12, 2022

The text of the Scientific Justification must be anonymized. Proposers must not reveal any members of the proposing team nor their institutions in the Scientific Justification. Additionally, proposers must not directly associate references with the proposing team (e.g., “In [2] we determined…” directly associates reference [2] with the proposing team and is in violation of the anonymizing requirement).

Proposals that reveal members of the proposing team directly or through directly associated references will be deemed non-compliant with the Dual Anonymous Peer Review (DAPR) requirements. For more information and examples of common violations of Dual Anonymous Peer Review (DAPR), please refer to Section 7.2 of the Call for Proposals and this online guide.

Proposers may provide essential non-anonymized information in the Team Expertise document. Dec 12, 2022

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. Refer to the Call for Proposals for more information.Dec 9, 2022

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

Maybe. A "slew tax" of 1.5 ks is added to each 30ks of observing time at the Chandra peer review and represents the average slew, settle and set-up time required for a non-grid observation. Slew tax is part of the total time that is available for the Cycle. Generally, most proposals only have a few observations, so slew tax impact is minimal. However, proposals with grids, longer exposure times or many different observations may require significant slew tax.

The slew tax for a proposal can be calculated in CPS in the "target checks" section. Dec 9, 2022

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 30 ks or less.

To calculate slew tax, pointings will be assembled into one or more groups with a maximum of 30 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 9, 2022

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 Call for Proposals 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 Call for Proposals.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

Degradation of the thermal insulation of the Chandra spacecraft has resulted in significant restrictions in the durations of observations at various solar pitch angles. To produce a list of targets for which scheduling can be managed in the face of both thermal and user-imposed science constraints, a system for assessing the effective "Resource Cost" (RC) of each non-TOO observation has been devised. This RC is derived from both the position and any science constraint. For more information, see the most recent Call for Proposals.

The nominal resource cost is 1.6 RC per 1 ks of observing time, but the range is quite broad. To see a distribution plot, please refer to the figure labeled "Resource Cost vs. Ecliptic Latitude" in the Call for proposals. Dec 14, 2020

An observation is time constrained if the proposer restricts the time during which that observation can be performed. 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 and the suitability of the guide star field using Star Checker.Dec 9, 2022

The Call for Proposals (specifically, Chapter 4) details the types of constraints that may be imposed by proposers.Dec 17, 2019

Not by default, however TOO targets may be constrained by the proposer. All TOO triggers and followups will be counted against the TOO allotment, which is separate from any constraint considerations. Dec 17, 2019

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

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 ChaSeR interface. For more information about the archive, visit the Data Archive web pages.Dec 9, 2022

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

The Source Catalog has a streamlined quick search interface. The full search capabilities are available in CSCview, which 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.Dec 12, 2022

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.Dec 13, 2017

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. Longer uninterrupted observations are likely to have a higher resource cost than the nominal resource cost of 1.6 RC per 1 ks of observing time. You can check the RC of any observation using the RC Calculator. Dec 12, 2022

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

Star Checker is a web-based tool which allows a user to determine roll angles and dates that have suitable fields for guide star acquisition given a target and offset configuration.

Proposers need to determine if their target field contains suitable fields for guide star acquisition with Star Checker due to increasing operating temperatures of the Aspect Camera Assembly (ACA), which results in higher background and increased difficulty at identifying suitable fields for guide star acquisition. Small pointing and/or offset adjustments can improve the quality of the star field for the ACA. Dec 12, 2022

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

Resource Cost (RC) is reported to the proposer in CPS for a given target’s configuration (including exposure time, coordinates, and any potential constraints input by the proposer). Additionally, a proposer may use the standalone web-based Resource Cost Calculator (RCC) to adjust a target’s configuration to estimate the RC.

The nominal value is 1.6 RC per ks, but can vary widely. If a proposer receives any numerical value from the RCC for a given target, then the target and its configuration are feasible. However, there is a cycle-wide limit on RC (see Section 4.3 of the CfP) that is tracked by review panels at the Peer Review. Hence, proposers are advised to address the importance of high RC targets in their program to improve their competitiveness.

Note for Multi-Cycle Proposals: The total resource cost for a multi-cycle program is estimated from the exposure-weighted values in current and future cycles. When using the RCC, you would enter the total exposure time and determine exposure-weighted values to estimate the resource cost per cycle requested. For more detailed consideration, you may contact the Chandra Helpdesk. Dec 12, 2022

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

If there is time before the proposal deadline, contact the person and ask them to update their CPS profile. Confirm that they have done so before you add them to the proposal.

If there is no time, you can add their information to the form as though they were a new person. If you do this, the person will not have access to the proposal and their profile will still be out of date. Dec 9, 2022

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

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