ASKAP Detection of the Ultra-Long Spin Period Pulsar PSR J0901-4046

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents new observations of a radio pulsar that has the longest period of any pulsar in the ATNF pulsar catalog. The authors present a comprehensive analysis of all of the individual 10-s correlator dumps from the ASKAP telescope make in observations from 2019 to 2025. This allows them to extend the timing baseline and show that the pulsar emission seems to be persistent. Even though the dump time is much longer than the pulse width, they are able to see many individual pulses and construct a timing model that spans the full dataset. A timing analysis of the low frequency MWA observation yielded a non-detection, consistent with a spectral turnover at low frequencies. This work adds substantially to the understanding of this unique pulsar and will certainly be of interest to the community.  It is well written and the analysis is clearly described.  I don't have any substantial comments and believe that the paper is acceptable for publication as is. 

I just have a couple minor comments to consider:

• The red cross in Fig 5, is hard to see, especially in a printed version. I recommend replacing it with a white reticle that indicates the point source, without obscuring it and would be more visible.
• The statements in lines 156-160 and 162-166 about the distribution of  the off-peak SNRs are not easy to verify in the current figures.  Is there a way to show this more clearly, either as a histrogram of SNRs, or as a time series with the pulses removed? That might be helpful but isn't absolutely necessary.

Author Response

Comment 1: The red cross in Fig 5, is hard to see, especially in a printed version. I recommend replacing it with a white reticle that indicates the point source, without obscuring it and would be more visible.

Response 1: We have revised Fig 5, changing from white-on-black to black-on-white, adding RA and Dec axes, and marking the point source much more clearly, especially when printing. The reviewer is thanks for this suggestion.

Comment 2: The statements in lines 156-160 and 162-166 about the distribution of  the off-peak SNRs are not easy to verify in the current figures.  Is there a way to show this more clearly, either as a histrogram of SNRs, or as a time series with the pulses removed? That might be helpful but isn't absolutely necessary.

Response 1: We have addressed this by making the description in the text clearer. We don't think that a histogram of SNRs or time series without pulses is required to see the point we were trying to make, and believe that the revised text is sufficient.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I have carefully read your manuscript and I think it's interesting and well written.
I've only a few suggestions to improve its readability, which should be easy to implement, before I can recommend it for publication.

In order of appearance in the text:

Abstract:

* I appreciate the abbreviations list, but it's at the end of the manuscript and some are missing (e.g. CRACO, MeerKAT ...). There are many initialisations and acronyms in the Abstract, some are well known, others less so (e.g. MWA), and a frequency is given only for the ASKAP image. Can you try to make the abstract a bit more readable and informative?

Introduction 

* ... revealed a source with a period of 75.88 seconds
Maybe you can give the number of detected pulses.

* ... a distance of ∼0.4 kpc.
For what free e- distribution model?

** l.17-23: very difficult to read and follow

* In part this is due to the unusually long period.
I'd say it's only due to that. Please, clarify.

Sect. 2

** Table 1, l.101-107
- Please, add also the stop time and the duration of the observation
- I think that the description of the columns in l.101-107 should go in the caption of the table

** l.70-73
I thing that I understood what you mentioned, but also that the sentence is difficult to read and follow. Please rephrase.

* l.162: a typo: a a

Author Response

Comment 1: Abstract: I appreciate the abbreviations list, but it's at the end of the manuscript and some are missing (e.g. CRACO, MeerKAT ...). There are many initialisations and acronyms in the Abstract, some are well known, others less so (e.g. MWA), and a frequency is given only for the ASKAP image. Can you try to make the abstract a bit more readable and informative?

Response 1: We have made the abstract more readable and informative, and expanded the abbreviations list. These changes appear in boldface in the revised manuscript.

Comment 2: Introduction:  ... revealed a source with a period of 75.88 seconds. Maybe you can give the number of detected pulses.

Response 2: This is not as simple as it might seem, with a detailed description given in the cited Caleb et al. paper and so we do not attempt to summarise it here and trust readers interested in that detail will refer to that paper.

Comment 3:  ... a distance of ∼0.4 kpc. For what free e- distribution model?

Response 3: As described in Caleb et al., the two main free electron distribution models give distances of 0.3 kpc and 0.5 kpc, which we have averaged to the "~0.4 kpc" in the text. As the distance is not overly critical to the work described here, we trust this is sufficient.

Comment 4:  l.17-23: very difficult to read and follow

Response 4: Yes, the wording was poor! We have revised and simplified to make it clearer.

Comment 5: "In part this is due to the unusually long period." I'd say it's only due to that. Please, clarify.

Response 5: Agreed. The wording has been amended.

Comment 6: ** Table 1, l.101-107

- Please, add also the stop time and the duration of the observation
- I think that the description of the columns in l.101-107 should go in the caption of the table

Response 6: The table already spans the full page width, so adding additional detail is problematic. We have added information about the length of the observations to the table caption. The description of the columns is sufficiently lengthy that we have kept it in the text rather than have an overly long caption. 

Comment 7:  l.70-73 "I thing that I understood what you mentioned, but also that the sentence is difficult to read and follow. Please rephrase."

Response 7: Again, the wording was poor and has been revised to make clearer.

Comment 8:  l.162: a typo: a a

Response 8: Fixed!

The reviewer is thanks for their careful reading and helpful comments and suggestions. 

 

Reviewer 3 Report

Comments and Suggestions for Authors

This paper reports on observations of PSR J0901−4046 with the ASKAP radio telescope and the Murchison Widefield Array (MWA), which precede the original MeerKAT discovery and extend beyond some later monitorings. It demonstrates that the radio emission from PSR J0901 is quite persistent. The presented ASKAP image is also helpful in invoking future observations. Although the impact of this paper is modest, it is worth publishing. Some remarks are listed below for the authors’ consideration:

 

Is it possible to derive the flux density for each detected peaks? If yes, that would be important to see whether there is a trend of flux declining. If not, the author should note the reason why one cannot do it with these data.

 

Line 19: item (iii) is not considered to be a common property of ‘normal’ pulsars.  It is better to start a new sentence to say that although there is no detectable X-ray emissions, some other properties more closely resemble those of magnetars ……

 

Line 142-143: The author may also add that only three peaks are observed in two mid-band observations.

 

Line 174-176: 10-sec integration time in one hour (3600 sec) yields about 360 bins. At 3.4 sigma, one may expect to see about 0.36 random peaks. Now there are three. The false positive rate does not seem really low.  Of course these are all small number statistics, but maybe the authors should comment on this point.

 

Line 183: The reported period derivative in the literature is 2.25 x 10^{-13}, which is not consistent with the value reported here in this manuscript (2.2(1) x 10^{-14}). Hopefully it is just a typo.

Author Response

Comment 1: Is it possible to derive the flux density for each detected peaks? If yes, that would be important to see whether there is a trend of flux declining. If not, the author should note the reason why one cannot do it with these data.

Response 1: Attempting to derive flux densities for the peaks is not straightforward as we are in a relatively low signal-to-noise regime. Caleb et al. showed that there is considerable variation between pulses, and the limited number of pulses in the RACS observations would not, we feel, result in meaningful values. We have added an explanation to the text for why flux densities are not given. 

Comment 2: Line 19: item (iii) is not considered to be a common property of ‘normal’ pulsars.  It is better to start a new sentence to say that although there is no detectable X-ray emissions, some other properties more closely resemble those of magnetars ……

Response 2: The text has been reworded following these suggestions.

Comment 3: Line 142-143: The author may also add that only three peaks are observed in two mid-band observations.

Response 3: This has been done

Comment 4: Line 174-176: 10-sec integration time in one hour (3600 sec) yields about 360 bins. At 3.4 sigma, one may expect to see about 0.36 random peaks. Now there are three. The false positive rate does not seem really low.  Of course these are all small number statistics, but maybe the authors should comment on this point.

Response 4: A comment on this point has been added tot he discussion.

Comment 5: Line 183: The reported period derivative in the literature is 2.25 x 10^{-13}, which is not consistent with the value reported here in this manuscript (2.2(1) x 10^{-14}). Hopefully it is just a typo.

Response 5: Yes, this was indeed a typo! The reviewer is thanked for picking this up!

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript improves our knowledge of the ultra long period pulsar J0901-4046 by extending the timescale over which this pulsar has been observed. The manuscript shows that the emission is highly regular over all the years of observations. The paper also shows more evidence of the suspected turn-over in the spectrum at low frequencies. 

The manuscript shows that ASKAP is capable of observing the single pulses of the pulsar even in integrations lasting more than 30 times the width of the pulse. 

I suggest that the manuscript is accepted for publication in its present form.

Author Response

Comment 1: I suggest that the manuscript is accepted for publication in its present form.

Response 1: The reviewer is thanked for their positive review!