Comments to the review "Nonthermal phenomena in clusters of galaxies" by Y.Rephaeli et al. that will appear on the book: Clusters of galaxies: beyond the thermal view
aa r X i v : . [ a s t r o - ph ] F e b Comments to the review ” Nonthermal phenomena in clusters ofgalaxies” by Y.Rephaeli et al. that will appear on the book:Clusters of galaxies: beyond the thermal view.
Roberto Fusco-Femiano a , Mauro Orlandini b When the review on nonthermal phenomena in clusters of galaxies by Rephaeli, Nevalainen,Ohashi & Bykov 2008 (astro-ph/08010982; hereafter, RNOB08) appeared on the WEB wesent our comments to Prof. Y.Rephaeli. But the answer of the Editor, Dr J.Kaastra, ofthe book: ”Clusters of galaxies: beyond the thermal view”, was that he has checked withSpringer, but unfortunately their process is already too far to make any changes to the paper.For this reason we have decided to put on the WEB these comments.The comments regard: a) the boring controversial between the analysis of the PDS/ BeppoSAX data of the Coma cluster with the software package XAS by Fusco-Femiano et al. b) the a hard excess in A2199, A2163 and the Bullet cluster. Coma cluster:
In 2007 Fusco-Femiano, Landi & Orlandini (hereafter, FF07) have re-analyzed the PDS data using the same software of RM04 showing that it is possible toobtain the same results of FF04 explaining of course the reasons of the discrepancy betweenFF04 and RM04. Rossetti & Molendi replied to our paper (FF07) with an electronic preprintonly (RM07) and we were obliged to a new reply (FF07R).Unfortunately, the authors of the review have not read with the due attention the papersFF04, FF07 and FF07R (the last is not reported in the review) and this is a serious mistakefor people that intend to write a review. So, we are obliged to repeat here briefly some ofthe things that are contained in the above papers.In FF07 and in the reply FF07R we have reported that to explain the discrepancy betweenFF04 and RM04 a rigorous selection of the events is necessary in order to eliminate thepresence of any spikes able to introduce noise that hides the presence of a nonthermal excesswith respect to the thermal radiation. We have a significant increase of the c.l. of the excess a Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF/Roma), INAF, via del Fosso del Cavaliere, I–00133 Roma, Italy - [email protected]; b IASF/Bologna, INAF, via Gobetti 101, I–40129Bologna, Italy - [email protected] ∼ . σ to ∼ . σ ) when we consider in the SAXDAS analysis (FF07) the same timewindows used in the XAS analysis (FF04). The authors of the review report instead that thediscrepancy is only due to the different determination of the background between FF04 andRM04. In FF04 we consider only the -OFF direction for the presence of a contaminating BLLac object in the +OFF direction. Besides, the authors of the review omit to report that inFF04 and FF07R we have shown that also considering the standard technique that impliesan average of the two backgrounds determinations, the c.l. of the excess is still at 3 . σ .The authors of the review report that a point raised by RM07 to defend their re-analysisand the lower detection significance of the hard excess was also the choice in FF04 of thevalue of the temperature (8 . ± .
07 keV measured by
Ginga , David et al. . ± .
16 keV. RBNO08 omit to report intheir review that in FF07R we have computed, to satisfy Rossetti & Molendi, the excessassuming a gas temperature of 8.4 keV, the upper limit of the reported interval in RM04and RM07. We obtain a c.l. for the excess of 4 . σ . Moreover, the Ginga value has beenconfirmed by
RXTE that reports 7 . ± .
03 keV (Rephaeli & Gruber 2002) and in the fitof Fig. 1 of the review the
RXTE data give 7.67 keV (!!).The authors of the review report that we have never clarified the point regarding the possiblepresence of systematic errors raised by RM04 and RM07. In FF07 and in FF07R we havestressed that the systematic errors are discussed in detail by Fusco-Femiano, Landi & Or-landini 2005 (FF05) for the analysis of the excess in A2256. Our surprise for this statementpresent in the review is that the referee of FF05 was Dr J.Nevalainen, one of the authors ofthe review. In particular, the referee was in agreement with our analysis on the whole sampleof PDS pointings (869, while RM04 consider only 69 observations) regarding the possiblesystematic difference between the OFF fields reported in RM04 and RM07. Our analysisgives a value of (5 . ± . × − , consistent with no contamination at all. Besides, the samesample was used to measure the X-ray background (Frontera et al. ∼
10% of theIntegral flux. This a further confirmation of the correctness of the PDS results.
A2199: for this cluster the authors of the review probably ignore that Fusco-Femiano et al. (2003)have re-analyzed the MECS data showing that the nonthermal excess reported by Kaastra et al. (1999) is not present. The discrepancy is probably due to the use of a more evolvedsoftware package by Sabrina De Grandi.
A2163: the authors of the review do not report in Sect. 3.4 ”Search for NT emission with
BeppoSAX ” that the PDS observation gives only an upper limit to the nonthermal flux asreported by Feretti et al. (2001). 3 –
A2163 & Bullet cluster:
Finally, we have expressed to the authors of the review our inviteto avoid to present the excess in these two clusters reported by
RXTE observations as firmdetections considering the large error bars in the spectra.Even if the book editor, Dr. J.Kaastra, affirms that the publishing process is already toofar, we would have same doubt to publish a review that contains uncorrect statements.We think that, for the sake of intellectual honesty, at least an addendum page should beincluded in the book taking into account our comments, in order to allow the reader to havea more complete grasp on one of the book main topics: non-thermal phenomena in clustersof galaxies.
REFERENCES
David, L.P.etal 1993, ApJ, 412, 479Feretti, L., Fusco-Femiano, R., Giovannini, G., & Govoni, F. 2001, A&A, 373, 106Frontera, F., Orlandini, M., Landi, R. et al. et al.