Pith. sign in

REVIEW 3 major objections 4 minor 35 references

Probing the Transient Far-IR Sky with PRIMA

T0 review · 3 major / 4 minor · reviewed 2026-08-05 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

Pith's one-line read This paper argues that PRIMA can follow up roughly ten extragalactic millimetre transients per year detected by CMB-S4, giving the first real look at the time-variable far-infrared sky.

desk verdict Transparent feasibility estimate of PRIMA follow-up of CMB-S4 transients; the headline ~10/year is a reasonable order-of-magnitude guess, though built on an untested independence assumption. read the letter →

arxiv 2509.02135 v1 pith:2HAEVPKP submitted 2025-09-02 astro-ph.IM astro-ph.GA

David L Clements , Michael Peel This is my paper
classification astro-ph.IMastro-ph.GA
keywords far-infraredastronomytime-domainmillimetretransientsCMBsurveysPRIMAmissiontidaldisruptioneventsgamma-rayburstsprotostellarvariability
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The time-variable far-infrared sky has essentially never been observed. The paper argues that when the PRIMA far-infrared mission launches, next-generation ground-based CMB experiments—especially CMB-S4—will be issuing alerts for roughly 100 extragalactic millimetre transients per year. Multiplying PRIMA's 26% instantaneous sky access by CMB-S4's roughly 40% survey footprint gives about a 10% overlap, so PRIMA should be able to follow up of order ten events per year. For those events, far-infrared photometry and some spectroscopy can locate the synchrotron peak, probe dust properties, and measure accretion energetics in TDEs, GRBs, SNe, FBOTs, and protostars with episodic accretion. A small but scientifically useful sample would open the transient far-infrared sky for the first time.

What carries the argument

The central object is the 'figure of regard': the fraction of the sky PRIMA can point at at any instant, currently taken to be 26%. The core estimate is the product of this fraction with CMB-S4's approximately 40% sky coverage, giving an overlap of roughly 10%, multiplied by the expected rate of about 100 extragalactic millimetre transients per year to get about ten follow-ups per year. The physical mechanism that makes those follow-ups scientifically valuable is the synchrotron spectral peak: far-infrared and submillimetre data locate the peak frequency, which measures outflow velocity and ambient density, while thermal dust emission reveals dust temperature and mass.

What would settle it

During CMB-S4's first survey year, count the extragalactic millimetre transient alerts actually issued and, for each alert, check whether PRIMA's instantaneous figure of regard includes its position; if the observed overlap rate is well below 10% of the sky, or the alert rate is far below 100 per year, the ten-per-year estimate fails.

Watch

Extended reading notes

Core claim

The central claim is that PRIMA, although not designed for transient follow-up, will be able to observe about ten extragalactic transients per year that CMB-S4 detects. PRIMA's instantaneous figure of regard is 26% of the sky; CMB-S4's footprint will cover about 40% of the sky; and the paper argues the overlap will be close to the product of these fractions, about 10% of the sky. With the anticipated CMB-S4 rate of roughly 100 extragalactic millimetre transients per year, that yields about ten follow-up targets per year. PRIMA's 12-minute slews are fast, but alert dissemination and telemetry delays mean only longer-lived events—those staying bright for days to months—can be caught; the paper

Load-bearing premise

The headline yield of about ten follow-ups per year assumes that PRIMA's 26% instantaneous sky access and CMB-S4's roughly 40% footprint overlap as independent fractions, and it takes the roughly 100-extragalactic-transients-per-year rate as representative; if any of those numbers is wrong, the yield scales proportionally.

Editorial extensions

If this is right

  • If the estimate holds, PRIMA can obtain far-infrared photometry for about ten CMB-S4 extragalactic transients per year and meaningful upper limits for the rest.
  • A small sample of TDEs, GRBs, SNe, and FBOTs with far-infrared data will constrain synchrotron peak frequencies, giving outflow velocities and circumburst densities.
  • Dust-enshrouded TDEs, possibly ten times more common than optically discovered ones, become monitorable with PRIMA's hyperspectral imager over month-to-year timescales.
  • Protostars with episodic accretion can be monitored on roughly monthly timescales, testing the role of accretion bursts in stellar mass assembly.
  • The yield scales directly with design choices: raising the figure of regard from 26% toward the 45% of an earlier mission concept would nearly double the follow-up rate.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The paper does not simulate the actual geometric overlap; a direct footprint simulation using PRIMA's final orbit and CMB-S4's survey mask could show that the 10% overlap is an overestimate or underestimate, since the two regions are not necessarily independent.
  • The paper's own delay discussion implies that only transients staying bright for at least several days will yield usable far-infrared detections; the scientifically most valuable peak-constraining observations may therefore come from a smaller subset of the ten yearly targets.
  • If a rapid-response interrupt mode is not implemented, the effective follow-up yield could be close to zero for short-duration classes like GRB reverse shocks and flaring stars, even though the sky-overlap arithmetic gives ten per year.
  • PRIMA's own repeated sky monitoring, mentioned only as a closing possibility, could turn the mission from a follow-up-only observatory into a discoverer of far-infrared transients, which would change the science case substantially.
Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 4 minor

Summary. The paper argues that the proposed far-IR mission PRIMA, though not designed for transient follow-up, will be able to observe a small but scientifically useful sample of extragalactic millimetre transients discovered by next-generation CMB experiments, especially CMB-S4. It reviews known and predicted mm/submm transients (GRBs, TDEs, SNe, FBOTs, protostars), discusses the scientific value of adding far-IR photometry and spectroscopy, and estimates that PRIMA can follow roughly ten CMB-S4 extragalactic transients per year. That estimate is obtained by multiplying a 26% instantaneous figure of regard (private communication), a ~40% CMB-S4 sky footprint, and a ~100/yr event rate from Eftekhari et al. (2022). The paper also discusses operational constraints (slew time, alert latency, telemetry gaps) and suggests design improvements such as a rapid-response interrupt mode and an increased figure of regard.

Significance. This is a timely and clearly written feasibility/science-case paper. Its strengths are the use of published transient light curves and rate forecasts, the transparency about external inputs and mission uncertainties, and the explicit treatment of operational limitations. If the central yield estimate is correct, the paper makes a strong case that PRIMA can contribute uniquely to the study of the transient far-IR sky and that mission design choices (figure of regard, rapid response) directly affect this science. The quantitative claim, however, rests on an areal-overlap product that is not derived or tested, and on input rates that carry large uncertainties.

major comments (3)
  1. [§5, first paragraph] The estimate '0.26 × 0.4 ≈ 10% of the sky' assumes that PRIMA's instantaneous figure of regard and CMB-S4's survey footprint are independent areal fractions. This is not self-evident: PRIMA's figure of regard is a time-dependent mask with limited range along the ecliptic and wide range perpendicular to it, while CMB-S4's footprint is a static, declination-limited mask with wide RA coverage. The conditional probability that a CMB-S4-detected transient lies in the PRIMA-accessible region when the alert arrives is not simply the product of the two sky fractions; it depends on the correlation of the two masks and on the alert/response delay (quoted as ~30–50 hours in the same section). The paper provides no derivation, simulation, or bounding argument. A correlated geometry could change the yield by a large factor. I recommend a sensitivity analysis or a simple geometric model (e.g., represe
  2. [§5, first paragraph; Abstract; §1] The central yield uses ~100 extragalactic transients per year from CMB-S4 as a point estimate, but the paper itself notes that predicted rates range from tens to thousands over project lifetimes (Abstract, §1). Since the headline number is directly proportional to this rate, the lower and upper ends of the range would give of order one or of order a hundred events per year, respectively. The authors should either present the resulting yield as a range (e.g., ~1–100 per year) or justify the adopted ~100/yr value with the specific assumptions and confidence intervals from Eftekhari et al. (2022).
  3. [§5, first paragraph] The 26% figure of regard is attributed to a private communication and enters linearly into the headline yield, but it is not publicly verifiable. At minimum, the authors should provide a citable mission-design document or technical report for this number. If no public source exists, the yield should be explored as a function of figure of regard over a plausible range (the text itself mentions FIRSST's 45% as a comparison point). This would make the sensitivity of the central claim explicit and would allow the reader to gauge the impact of the uncertainty.
minor comments (4)
  1. [§5] Typo: 'the the detailed properties' should read 'the detailed properties'.
  2. [Fig. 2 caption] 'From.26' should be 'From [26].'
  3. [§2 and passim] Spelling is inconsistent: 'targetted' (e.g., §2) versus 'targeted' (e.g., §5). Use one spelling throughout.
  4. [§5] The discussion of alert latency (~30–50 hr) and spacecraft contact intervals would benefit from a small table summarizing event classes, expected durations in the mm, and whether PRIMA can respond in a useful state. This would strengthen the qualitative 'good chance' statement.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the yield estimate is a transparent product of independently sourced inputs with no fitted parameter or self-citation chain doing the work.

full rationale

The central quantitative claim in Section 5 is that there will be of order ten CMB-S4 extragalactic transients per year observable by PRIMA. This is obtained as 100/yr (CMB-S4 transient rate, attributed to Eftekhari et al. 2022) × 0.26 (PRIMA figure of regard, attributed to a private communication from Pontoppidan) × 0.4 (CMB-S4 sky coverage, stated as similar to the SO-LAT survey). Each input is externally sourced and is not fitted or derived from the target number. The arithmetic is simple multiplication, not an inverse calculation, and no parameter is tuned to make the result come out. The paper itself flags the uncertainty in the rate and notes the figure of regard is current and could change. The independence assumption in multiplying two sky fractions is a modeling assumption that could be challenged empirically, but it is not a circular reduction: the output is not equivalent to any single input by construction. The authors' self-citations (e.g., Herschel survey papers for background context) are not load-bearing for the transient-followup yield estimate. No evidence of self-definition, fitted-input-renamed-as-prediction, or uniqueness imported from self-citations was found. The paper is best read as a scoped forecast built on external forecasts and mission parameters, not as a circular derivation.

Assumptions & free parameters 0 free parameters · 5 assumptions · 0 invented entities

No parameters are fitted to data; the inputs are externally determined forecasts and mission specifications. The central claim also depends on a mission parameter obtained by private communication. No new particles, forces, dimensions, or other entities are introduced.

assumptions (5)
  • domain assumption PRIMA's instantaneous figure of regard is 26% of the sky
    Section 5 states this is from Pontoppidan (private communication). The central ten per year yield scales linearly with this number.
  • domain assumption CMB-S4 will survey about 40% of the sky and detect about 100 extragalactic millimetre transients per year
    Section 5 and the introduction cite Eftekhari et al. (2022) and CMB-S4 documentation. The yield 0.26 x 0.4 x 100 = 10 per year is built on these external forecasts.
  • ad hoc to paper The geometric overlap of PRIMA sky access and CMB-S4 survey area factorizes as 0.26 x 0.4
    Section 5 says the available sky area will be close to 0.26 x 0.4, about 10%, assuming independent sky coverage with no time or declination correlation. This is not derived from actual pointing schedules.
  • domain assumption Extragalactic millimetre transient light curves stay bright for tens of days, so PRIMA's alert and slew latency of roughly 30 to 50 hours plus 12 minutes permits useful follow-up
    Section 5 and Figure 1 from Eftekhari et al. (2022) are used to conclude that most TDEs, GRBs, SNe, and FBOTs remain detectable long enough for PRIMA to respond.
  • domain assumption Far-IR SEDs of these transients are bright enough for PRIMA's instruments
    Section 2 uses the PRImager exposure time calculator and external models, for example the TDE Swift J164449+573451 with a predicted 235 micron flux of 10 to 20 mJy, to argue that pointed observations are feasible. No actual far-IR observations of these transients exist.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Probing the Transient Far-IR Sky with PRIMA." pith.science (2026). https://pith.science/paper/2HAEVPKP

@misc{pith2026250902135,
  author       = {Pith},
  title        = {Pith review of: Probing the Transient Far-IR Sky with PRIMA},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/2HAEVPKP}},
  note         = {Machine review of arXiv:2509.02135}
}
abstract

The time variable far-IR/mm sky is largely unexplored. However, when PRIMA launches, next generation ground-based CMB experiments, including Simons Observatory and CMB-S4, will be operating. These will survey large areas of the sky for transient mm sources as a byproduct of their observations, producing regular mm-transient alerts. The results from current experiments show they can detect a wide variety of mm transients ranging from Galactic stars to extragalactic sources associated with AGNs and other energetic phenomena, and moving Solar System objects such as asteroids. These results, and theoretical predictions, indicate that future mm/submm facilities will detect many kinds of transient, including flaring stars, protostars, GRBs, TDEs, neutron star mergers, FBOTs, and SNe. New classes of mm-variable may be uncovered by CMB experiments, and transient searches at other wavelengths, such as the optical LSST survey, will produce additional targets to followup with PRIMA. Predicted rates for extragalactic mm transients to be detected by CMB experiments range from 10s to 1000s of events over the lifetime of these projects. CMB-S4 is most relevant for PRIMA, producing $\sim$100 extragalactic transients per year. Galactic transients and variable sources will also be detected, but the most common Galactic transients, flaring stars, operate on such short timescales that direct follow-up with PRIMA will not be feasible. Variable accretion rates in forming protostars, conversely, produce long term brightness variations that will be ideal monitoring targets. The addition of mid- and far-IR data points for all these sources can determine much about their radiation mechanisms and underlying physics. PRIMA followup of representative examples of various mm-transient and variable sources will thus have a powerful impact on our understanding of a wide range of astrophysical phenomena.

Discussion (0). Sign in to comment.

Reference graph

Works this paper leans on

35 extracted references · 31 canonical work pages

  1. [1]

    S. J. Oliver , J. Bock , B. Altieri , et al. , `` The Herschel Multi-tiered Extragalactic Survey: HerMES ,'' MNRAS, 424 , 1614--1635 (2012)

    work page 2012

  2. [2]

    Eales , L

    S. Eales , L. Dunne , D. Clements , et al. , `` The Herschel ATLAS ,'' PASP, 122 , 499 (2010)

    work page 2010

  3. [3]

    Pearson , T

    C. Pearson , T. W. O. Varnish , X. Wu , et al. , `` The Herschel-SPIRE Dark Field I: The deepest Herschel image of the submillimetre Universe ,'' MNRAS, (in press) (2025)

    work page 2025

  4. [4]

    D. S. Swetz , P. A. R. Ade , M. Amiri , et al. , `` Overview of the Atacama Cosmology Telescope: Receiver, Instrumentation, and Telescope Systems ,'' ApJSupp, 194 , 41 (2011)

    work page 2011

  5. [5]

    J. E. Carlstrom , P. A. R. Ade , K. A. Aird , et al. , `` The 10 Meter South Pole Telescope ,'' PASP, 123 , 568 (2011)

    work page 2011

  6. [6]

    E. K. Biermann , Y. Li , S. Naess , et al. , `` The Atacama Cosmology Telescope: Systematic Transient Search of Single Observation Maps ,'' arXiv e-prints , arXiv:2409.08429 (2024)

    arXiv 2024

  7. [7]

    Guns , A

    S. Guns , A. Foster , C. Daley , et al. , `` Detection of Galactic and Extragalactic Millimeter-wavelength Transient Sources with SPT-3G ,'' ApJ, 916 , 98 (2021)

    work page 2021

  8. [8]

    Y. Li , E. Biermann , S. Naess , et al. , `` The Atacama Cosmology Telescope: Systematic Transient Search of 3 Day Maps ,'' ApJ, 956 , 36 (2023)

    work page 2023

Show all 35 references
  1. [9]

    Tandoi , S

    C. Tandoi , S. Guns , A. Foster , et al. , `` Flaring Stars in a Nontargeted Millimeter-wave Survey with SPT-3G ,'' ApJ, 972 , 6 (2024)

    2024

  2. [10]

    Herv \' as-Caimapo , S

    C. Herv \' as-Caimapo , S. Naess , A. D. Hincks , et al. , `` The Atacama cosmology telescope: flux upper limits from a targeted search for extragalactic transients ,'' MNRAS, 529 , 3020--3034 (2024)

    2024

  3. [11]

    P. M. Chichura , A. Foster , C. Patel , et al. , `` Asteroid Measurements at Millimeter Wavelengths with the South Pole Telescope ,'' ApJ, 936 , 173 (2022)

    2022

  4. [12]

    Orlowski-Scherer , R

    J. Orlowski-Scherer , R. C. Venterea , N. Battaglia , et al. , `` The Atacama Cosmology Telescope: Millimeter Observations of a Population of Asteroids or: ACTeroids ,'' ApJ, 964 , 138 (2024)

    2024

  5. [13]

    G. J. Herczeg , D. Johnstone , S. Mairs , et al. , `` How Do Stars Gain Their Mass? A JCMT/SCUBA-2 Transient Survey of Protostars in Nearby Star-forming Regions ,'' ApJ, 849 , 43 (2017)

    2017

  6. [14]

    Y.-H. Lee , D. Johnstone , J.-E. Lee , et al. , `` The JCMT Transient Survey: Four-year Summary of Monitoring the Submillimeter Variability of Protostars ,'' ApJ, 920 , 119 (2021)

    2021

  7. [15]

    Mairs , B

    S. Mairs , B. Lalchand , G. C. Bower , et al. , `` The JCMT Transient Survey: An Extraordinary Submillimeter Flare in the T Tauri Binary System JW 566 ,'' ApJ, 871 , 72 (2019)

    2019

  8. [16]

    W. J. Fischer , C. Battersby , D. Johnstone , et al. , `` Far-infrared Luminosity Bursts Trace Mass Accretion onto Protostars ,'' AJ, 167 , 82 (2024)

    2024

  9. [17]

    P. Ade , J. Aguirre , Z. Ahmed , et al. , `` The Simons Observatory: science goals and forecasts ,'' JCAP, 2019 , 056 (2019)

    2019

  10. [18]

    C. L. Chang , K. M. Huffenberger , B. A. Benson , et al. , `` Snowmass2021 Cosmic Frontier: Cosmic Microwave Background Measurements White Paper ,'' arXiv e-prints , arXiv:2203.07638 (2022)

    2022

  11. [19]

    D. I. Novikov and K. O. Parfenov , `` Extraction of the angular power spectrum produced by inflation from observations of experiments such as Simons Observatory ,'' arXiv e-prints , arXiv:2411.15959 (2024)

    2024 arXiv

  12. [20]

    Abazajian , G

    K. Abazajian , G. Addison , P. Adshead , et al. , `` CMB-S4 Science Case, Reference Design, and Project Plan ,'' arXiv e-prints , arXiv:1907.04473 (2019)

    1907 arXiv

  13. [21]

    Aravena , J

    CCAT-Prime Collaboration , M. Aravena , J. E. Austermann , et al. , `` CCAT-prime Collaboration: Science Goals and Forecasts with Prime-Cam on the Fred Young Submillimeter Telescope ,'' ApJSupp, 264 , 7 (2023)

    2023

  14. [22]

    Eftekhari , E

    T. Eftekhari , E. Berger , B. D. Metzger , et al. , `` Extragalactic Millimeter Transients in the Era of Next-generation CMB Surveys ,'' ApJ, 935 , 16 (2022)

    2022

  15. [23]

    Berger , A

    E. Berger , A. Zauderer , G. G. Pooley , et al. , `` Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. I. Jet Energetics and the Pristine Parsec-scale Environment of a Supermassive Black Hole ,'' ApJ, 748 , 36 (2012)

    2012

  16. [24]

    T. M. Reynolds , S. Mattila , A. Efstathiou , et al. , `` Energetic nuclear transients in luminous and ultraluminous infrared galaxies ,'' AAP, 664 , A158 (2022)

    2022

  17. [25]

    Mattila , M

    S. Mattila , M. P \'e rez-Torres , A. Efstathiou , et al. , `` A dust-enshrouded tidal disruption event with a resolved radio jet in a galaxy merger ,'' Science 361 , 482--485 (2018)

    2018

  18. [26]

    Mairs , S

    S. Mairs , S. Lee , D. Johnstone , et al. , `` The JCMT Transient Survey: Six Year Summary of 450/850 m Protostellar Variability and Calibration Pipeline Version 2.0 ,'' ApJ, 966 , 215 (2024)

    2024

  19. [27]

    M. M. Dunham and E. I. Vorobyov , `` Resolving the Luminosity Problem in Low-mass Star Formation ,'' ApJ, 747 , 52 (2012)

    2012

  20. [28]

    Hartmann , G

    L. Hartmann , G. Herczeg , and N. Calvet , `` Accretion onto Pre-Main-Sequence Stars ,'' ARAA, 54 , 135--180 (2016)

    2016

  21. [29]

    W. J. Fischer , L. A. Hillenbrand , G. J. Herczeg , et al. , `` Accretion Variability as a Guide to Stellar Mass Assembly ,'' in Protostars and Planets VII , S. Inutsuka , Y. Aikawa , T. Muto , et al. , Eds., Astronomical Society of the Pacific Conference Series 534 , 355 (2023)

    2023

  22. [30]

    Johnstone , B

    D. Johnstone , B. Hendricks , G. J. Herczeg , et al. , `` Continuum Variability of Deeply Embedded Protostars as a Probe of Envelope Structure ,'' ApJ, 765 , 133 (2013)

    2013

  23. [31]

    Johnstone , B

    D. Johnstone , B. Lalchand , S. Mairs , et al. , `` The JCMT Transient Survey: Single-epoch Transients and Variability of Faint Sources ,'' ApJ, 937 , 6 (2022)

    2022

  24. [32]

    Tomsick and COSI Team , `` The COSI Mission Overview ,'' in AAS/High Energy Astrophysics Division , AAS/High Energy Astrophysics Division 21 , 406.03 (2024)

    J. Tomsick and COSI Team , `` The COSI Mission Overview ,'' in AAS/High Energy Astrophysics Division , AAS/High Energy Astrophysics Division 21 , 406.03 (2024)

    2024

  25. [33]

    Orlowski-Scherer , T

    J. Orlowski-Scherer , T. J. Maccarone , J. Bright , et al. , `` Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Probing the Transient and Time-variable Sky ,'' arXiv e-prints , arXiv:2404.13133 (2024)

    2024 arXiv

  26. [34]

    Andreoni , R

    I. Andreoni , R. Margutti , O. S. Salafia , et al. , `` Target-of-opportunity Observations of Gravitational-wave Events with Vera C. Rubin Observatory ,'' ApJSupp, 260 , 18 (2022)

    2022

  27. [35]

    write newline

    " write newline "" before.all 'output.state := FUNCTION blank.sep after.quote 'output.state := FUNCTION fin.entry output.state after.quoted.block = 'skip 'add.period if write newline FUNCTION new.block output.state before.all = 'skip output.state after.quote = after.quoted.blo...

Pith tools

Reviewed August 5, 2026 · model on record in the stance chip above.