Formation, Possible Detection and Consequences of Highly Magnetized Compact Stars
Round 1
Reviewer 1 Report
Comments for author File: 
Comments.pdf
Author Response
First, we thank the referee for their time to review the manuscript with
suggestions. Below we respond to their comments point-by-point with changes in
the manuscript as appropriate. All changes in the revised manuscript are
kept in bold-face.
First and foremost, the manuscript is based on a talk given in a conference.
Hence, it has to be written based on the existing papers, and mostly by our
group. It is also a review about a particular model-idea and its success, as
the talk was. For example, it is written in Introduction that "In this review
paper, we discuss the broad implications of these compact stars as well as the
current status of observations." Clearly by "these compact stars" we explicitly
meant the cases mentioned in the previous paragraphs. This is not a general
review about massive white dwarfs and neutron stars.
1. We have included references. Also the sentence has been modified to remove
ambiguity.
2. We have included a reference.
3. It is an important point. We already stated this gap in Abstract
as a "so called" mass gap. In the revised version we have included a cautionary
statement.
4. The reference included.
5. Not sure, what the referee intends to mean. Of course coalescence can do the
job in principle. But what is the context in the present line? Coalescence's
doing the job does not rule out our statement. This is just a statement.
Moreover, we will be happy if the referee suggests a paper which shows that
the coalescence could create a 2.8 solar mass object.
6. Again, we will be happy if the referee suggests a paper which shows that
the rotation could create a 2.8 solar mass object. Do not misunderstand our
response, we are really interested to know them, if the referee directs us
to appropriate references. Being an observer Howell et al. may suggest it,
but to write it here I need a reference being a theorist.
7. We are sorry, but we have to differ with the referee. Any one may have
their liking/disliking of the personal level, which is fine. However, the
referee cannot rule out, particularly the cases of SGRs/AXPs having no
supernova association found, the B-WD based ideas. Requested to look at the
referred papers therein (e.g. refs. 30-35), even if the referee thinks the
ideas proposed by Usov and Paczynski are outdated.
8. By "Many of these" we basically meant all such objects brought up above,
not only SGRs/AXPs. Also by "turn out to be" we meant even some of them
eventually may convert to WDs with super-Chandrasekhar mass, e.g. by accretion,
not necessarily SGRs/AXPs.
9. They are general thoughts, there are several examples. Is fossil field
(flux-freezing) based idea of strong field not very common in astrophysics,
what we have been hearing since the beginning of MHD study? That had been
used by, e.g., Das, Mukhopadhyay, Rao (ApJL, 2013) as well, apart from other
authors who explore relatively lowly magnetized WDs (see the added references
of Wickramasinghe, Ferrario, Chanmugam etc. in the revised version).
In the revised version, we mention that the field can be generated due to
WD mergers. We have included the example references.
10. As mentioned, this is a simple estimation based on flux-freezing. We are
sorry that we have to differ with the referee again, because additional
mechanisms can add more fields as well. Hence, it need not be the maximum
field.
11. There we have explicitly mentioned "neglecting the effect of magnetic
tension", while there is a dedicated section discussing anisotropic effects
(Section 8). Hence, we do not find the comment falling in place.
12. Done.
13. This is a representative plot, as mentioned in the original work.
Choice of initial field of 10^8 G is just to include stronger field
without affecting the stellar structure. Actually, a lower initial
field does not affect the result qualitatively. Anyway, thanks for
the point, we have revised the relevant sentence to avoid confusion.
14. The spin-down stuff is precisely discussed below that line, even though
for a generalized case.
15. The expression is coming from standard electromagnetic theory,
by equating dipole energy loss rate and the change of rotational energy
(though often authors assume \alpha (now \chi)=90, what we do not)
with replacement of \dot{\Omega}=\Omega^3 by \dot{\Omega}=\Omega^{n-m}.
Of course 'I' is assumed to be of the order of MR^2, but in the expression
we keep it as it is. Naturally smaller \chi gives stronger fields.
However, for consistency, in the revised version we have replaced \alpha
by \chi and have defined it.
16. Appropriate amendment is done.
17. In few lines below, the statement clarifies this.
18. We have clarified that neutrino cooling is neglected in two paragraph
below while discussing Figure 7 in the revised version.
19. This is a very good point. This mentioned time is after their birth.
The growth shown in the said figure is due to accretion, an example of
possibility. But there may have other causes including fossil effect and
dynamo. Nevertheless, the revised version is amended appropriately mentioning
possible restructuring the geometry above a critical accretion rate.
After decay of the field, either the star may collapse and hence triggers
a SNIa or mass may shed off, which is yet to check, will be taken
rigorously in future, as mentioned in the revised version.
20. Done.
21. This is in the spirit of nonmagnetic original 1.4 solar mass limit
of WDs. We mention about a plausibility. We have revised the portion.
22. The main hindrance of detectability is their plausible short life,
due to field decay. Some sources like AR Sco may eventually become a B-WD,
may be at this moment in its preliminary stage as argued by Mukhopadhyay
et al. (MNRAS, 2017), but not yet super-Chandrasekhar. We have added
a sentence related to this above Section 8 in the revised version.
23. Yes, taken care of in the revised version. Many thanks.
24. Actually, for electromagnetic emission indeed it is dipole, but it
could be the surface field only. It may have a stronger central toroidal
field leading effectively to prolate shape. Actually in the Right Panel,
we consider toroidal and poloidal both the cases, as shown in the figure.
Nevertheless, the main notion of this figure is to show the nonspherical
(triaxial) shape.
Reviewer 2 Report
Referee report for the paper titled
"Formation, possible detection and consequences of highly magnetized compact stars", by Banibrata Mukhopadhyay and Mukul Bhattacharya
The paper presents a review about the massive compact objects (white dwarfs and neutron stars, hereafter WDs and NSs), which are involved in their formation properties and broad relations to various observations, e.g., superluminous Type Ia supernovae and their descendents as the highly magnetised white dwarfs with super-Chandrasekhar masses, soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs), and gravitational wave sources by LIGO. The paper includes lots of novel issues of the recent developments of WDs and NSs, and is well organized, so it is worthy of publication. Before it is recommended for publication, the following comments should be considered.
(1) The magnetic fields of WDs have been discussed by Chanmugam (1992 ARAA), as well as by Lilia Ferrarioa, Dayal Wickramasinghe and Adel Kawkab (https://doi.org/10.1016/j.asr.2019.11.012), in theory and observation, so their work should be mentioned or discussed. Moreover, based on the classical magnetic WD paper, e.g., 2005MNRAS.356..615F2005/01 (Magnetic fields and rotation in white dwarfs and neutron stars) by Ferrario and Wickramasinghe; 2000PASP..112..873W2000/07, Magnetism in Isolated and Binary White Dwarfs by Wickramasinghe and Ferrario, it is better to mention how many WDs are measured with magnetic fields.
On the accreting WD magnetic fields, the following two works may be discussed, e.g., Monthly Notices of the Royal Astronomical Society, Volume 333, 589-602, 2002. DOI: 10.1046/j.1365-8711.2002.05434 with arXiv: arXiv:astro-ph/0202079; Is there evidence for field restructuring or decay in accreting magnetic white warfs? https://ui.adsabs.harvard.edu/abs/2009MNRAS.397.2208Z/abstract, 10.1111/j.1365-2966.2009.15154.x, arXiv: arXiv:0905.4829.
(2) On the massive neutron stars and/or white dwarfs, masses as high as 2.5-2.67 Ms (solar mass) by LIGO should be discussed, which are preferred for WDs or NSs. For the NS masses by pulsar observations, over 2 Ms should be not the uausal cases. The observational statistics showed the fact that the averaged mass of NS is about 1.4 Ms, and the accreted millisecond pulsars have the bigger masses, averagely 1.6 Ms, in general (see, Study of measured pulsar masses and their possible conclusions, arXiv:1010.5429, 2011 Astronomy and Astrophysics 527, 83; DOI:10.1051/0004-6361/201015532). See also, 2021, ASSL,461,1, Astrophysical Constraints on Dense Matter in Neutron Stars by Miller, M. C. (https://ui.adsabs.harvard.edu/abs/2021ASSL..461....1M/abstract).
(3) On the mass-radius (M-R) relations of magnetised WDs, 2000 km < R < 10000 km, would you like to explain why all cases give the minimum radius od 2000 km ? Does a WD collapse below this radius ?
(4) On the comapct mass and EOS, the book of Glendenning Norman should be mentioned, see 1996csnp.book.....G1996, Compact Stars. Nuclear Physics, Particle Physics and General Relativity, Springer-Verlag New York.
The authors provided fruitfull resources on the massive WDs and NSs, so it is interesting, with the scope and novelty of researches being clearly demonstrated.
Author Response
First, we thank the referee for their time to review the manuscript with
suggestions. Below we respond to their comments point-by-point with changes in
the manuscript. All changes in the revised manuscript are kept in bold-face.
(1) Done in Introduction and above Section 6.
(2) LIGO detection of 2.5-2.67 solar mass compact object was already discussed
in the previous version in Introduction, now modified too. The references and
discussion related to pulsars are also included in the revised version.
(3) Actually the presented minimum radius of 2000 km is not very special.
It is true that the radius of the order of 1000 km may be the minimum
possible radius for a stable white dwarf, but it need not necessarily be
2000 km exactly. Here we just wanted to present a representative small radius
white dwarf.
(4) Included.
Round 2
Reviewer 1 Report
In no way the referee was informed that the paper is a part of a conference proceedings. That is why I applied requirements which fit a usual review of a broad subject. (by the way, I had a similar negative experience myself few years ago in an MDPI journal).
Despite I still think that some statements made by the authors are scientifically wrong (like the statement that SOME of SGRs/AXPs can be WDs) and some approaches are oversimplified, I think that the paper which reviews mainly scientific results by a particular group (it would be nice to underline it in the abstract, by the way) can be published in the present form.
