Dear referee
we would like to thank you for very useful comments/remark.
A detailed response is reported below.
Best regards,
Mariateresa Fiocchi


(abstract)
The writing of the abstract is not clear in places. Rather than provide a long list of changes, below is a proposed modified version, changes marked in boldfont and struck through text.
The principal motivations for studying the X-ray binaries is that the accretion onto neutron stars and black holes provides a unique window on the physics of the strong gravity and dense matter. For this reason, a renewed interest has developed in ultracompact X-ray binaries and their identification is very important, albeit complex because of the difficulty in measuring orbital periods in low mass X-ray binaries. The ultracompact low-mass X-ray binary 4U 0513â^À^Ó40 in the globular cluster NGC1851 reveals a clear sinusoidal periodic signal with a period of ~17 minutes when the source is in a typical high/soft
state with a dominant soft thermal component (using BeppoSAX and Chandra data).
The periodicity disappears when the source is in a low/hard state and the thermal soft component is no longer required any more to model the data (using XMM-Newton and INTEGRAL observations). These properties indicate the orbital
nature of the detected signal and imply an high inclination angle of the binary system (> 80â^צ).
**********OK, done


(section 1)
'to measure' -> 'in measuring'
the reference to in 't Zand should not be split across two lines. Use a non-breaking space (~) in the latex.
'The IBIS results of the long' -> 'IBIS results from long-term'
**********OK, done


section 2)
'from EPIC-pn' -> 'in the EPIC-pn'
Although there are reference for the INTEGRAL telescopes and interments (Winkler, Lund, Ubertini), there are none for the other telescopes (SAX, Chandra etc), only the analysis software, despite the fact that these other
instruments play a strong role in the analysis. Perhaps these should be added to be more balanced?
When the phrase 'high-energy detectors' is first used in the 4th paragraph, it is ambiguous, and only explained in the following sentences. Please re-phrase to be less ambiguous.
In Table 1, should PN be EPIC-pn (all other observations refer to the instrument)
**********OK, done


(section 3)
The phrase 'we folded the light curves' is confusing, as previously only one light curve was mentioned. Is this simply a typo, or were more light curves analysed?
**********OK, this is a typo.


While the errors on the period are quoted, no significance for the detection is given. Can the confidence level be specified?
************Ok, we added this c.l. 


in the final sentence on p3, 'timing modulations have been' -> 'periodic signals were'
In the last paragraph on p4...
'second not' -> 'second, not' ; 'extract' -> 'extracted' ; 'bursts starting' ->'burst starting'
********OK, done


(section 4)
what is the meaning of 'average phase spectrum' in the caption of Table 2? Is it just an average spectrum?
The description of the analysis is a bit confusing, you state that spectra are summed when data from BOTH instruments are available, and yet there are different exposures quoted for the two instruments (IBIS and JEM-X). I don't think that's possible!
OK, we re-phrase this sentence, adding that we sum data from scw when source is detected at >5sigma c.l.   
I also have doubts about the F-test results - the delta chi2 and degrees of freedom do not look so different, but the probabilities are 9 orders of magnitude different? I cannot check this easily, but it seems unlikely.
**************We check these values and these are OK.


(references)
There are a few small formatting issues (like missing punctuation) in refs:
refs [2] and [6] seem incomplete, can more reference data be provided? Is [6] published?
[4] missing , after date
[12] missing space before & and an extra 'astro'
**********Ok, done