CRITERIOS PARA LA SELECCIÓN DE BROCAS DE

As briey disussed in hapter 2, setion 2.5, the physial mehanism of harge

exhange between ions from the solar wind and neutral material has been pointed

out as the mehanism responsible for the soft x-ray emission, normally explained

withintheLBparadigm,seeLallement[144, 145℄. Therefore,thepossibilityofsolar

windharge exhange (SWCE), being the mehanism responsible forsome fration

Figure 4.6: Ophiuhus Spetra

analysisonSWCE.Theplotshowsthe

two spetraobtainedsixmonthsapart

from the same regions of the dark

lament in the Ophiuhus moleular

loud. Given the statistis, no signi-

ant variationof intensityisobserved.

The spetrum of the seond observa-

tion, named Ophiuhus II, is plotted

in blak while the spetrum obtained

during the third observation, named

Ophiuhus III, is plotted in red. The

bakground spetrumusuedfor dete-

tor subtration in Ophiuhus III ob-

servation was also orreted using the

PMHratio.

an not be ignored, even if the exat quiesent level of this ontribution is not

known. Another important fat about the soft x-ray emission, due to SWCE, is,

that this ontribution is a physial phenomenon variable in time. An eet that

may have been seen already duringthe ROSAT era by Freyberg [148℄, and dubbed

aslong-termenhanements(LTE)[113℄. We haveinvestigated apossible variability

onthe three dark lamentOphiuhusXMM-Newton observations. They were then

ompared with another XMM-Newton observation, where SWCE was deteted by

Snowden et al.[149℄.

This was done in two ways. First by studying the spetra of the same sky

region, whih were observed about six months apart, and seond, by analysing for

eah observation the ount rate intwo energybands.

Sine the third observation named Oph III was performed about six months

apart and sine it partly overs the same sky region as Oph II, we have seleted

the same region of the loud, with the highest possibleolumn density, in order to

investigate the possibility of seasonal SWCE emissionvariability in a time sale of

sixmonths.

The region of the loud orresponds to a irle, entered at the position

α

=

16h₄₀m₂₀s

and

δ=−24

d₃₂m₀₀s

,witharadiusof3armin. Thesamedataredution

proedure, as desribed in setion3, was appliedto these spetra. In gure 4.6the

spetraare shown. As itan be seen, nosigniantvariation inthe intensity of the

spetra isobserved.

Reently, thesameastrophysialphenomenon wasdetetedinoneof theXMM-

Newton observations in the Hubble Deep Field North (HDFN) by Snowden et al.

[149℄. ThesameSWCEeethasbeendetetedinotherXMM-Newtonobservations,

e.g. in the observation with ID 0109060101, performed during revolution 0139.

Anotherwaytoinvestigateapossibleontamination,duetoSWCE, is,tostudy the

in this range due to O vii, O viii and Fe xvii ions. We then ompare these rate

with the rate in agiven energy interval, wherethe SWCE doesnot ontribute, e.g.

inthe 2.0- 8.0 keV interval, where the x-ray photons are due to the Cosmi X-ray

Bakground.

Count rates of the three Ophiuhus observations and of the HDFN observation

(revolution0271,ID0111550401)were reated, using onlythedata fromthe EPIC-

pn detetor. The proedure for reating this ount rates onsists on the following:

First, light urves are produed for eah observation after leaning the event les

from bad pixels, bad olumns (FLAG==0) and after removing all deteted point

soures. The point soures have to be removed, beause their emission an be

variableand produe asimilar eet mimikinga SWCE situation. Therefore, itis

importantto be sure, that there isno x-ray emission ontribution fromthe soures

in the eld of view. Snowden et al. [149℄ have not removed the point soures in

their analysis. The rate light urves were produed, having 200 s for the three

Ophiuhus observations, and 1150 s for the HDFN one. The high time bin for

the HDFN observation was hosen, in order to better distinguish the two emission

regimes. Otherwise, a ontinuous ount rate from

∼

0.2

to

∼

0.7

ounts/s in the 0.5 - 0.75 keV band would be the relevant result.

The seond step onsists on the reation of appropriate good time intervals

(GTI's) foreah observation.

The third step, the prodution of ount rates is done by seleting the events

obeyingthelteringriterionof(PATTERN==0),usingtheorrespondingGTIle,

seletingthe x-ray photons inthe energy bands of 0.5-0.75 keV and 2.0- 8.0keV,

and using the same time bins as before. In gure 4.7 we show the sattergrams

of the eight ount rates. The sattergrams a), b), ) show the ount rates for the

rst, seond, and third observation, dediated to the Ophiuhus moleular loud,

d) shows the ount rate from the HDFN observation. The sattergrams a) and b)

orrespond to the XMM-Newton on-loud pointings, where the highest hydrogen

olumndensitiesareobserved. Thesattergram)orresponds totheo-loudand,

therefore,is highlyontaminated by the Loop i superbubble and halo emission.

Given the GTIs for these three observations, one annot infer what is, if there

is any, a quiesent x-ray emission level, due to SWCE. However, one may on-

dently assume,thatduringthese threeobservations nosigniantvariationof x-ray

emission due to SWCE oured. Any strong x-ray emission variation in the 0.5 -

0.75 keV band should then be followed by a distribution of this ount rate over a

onstant ount rate in the 2.0 - 8.0 keV band. An eet that is not onviningly

seen inany of the sattergrams a),b) and ). The sattergram d) isthe equivalent

fortheHDFN observation. Asitan beseeninthis sattergramandasreportedby

Snowdenetal.[149℄,twodierentx-rayemissionregimesourduringthisobserva-

tion. The dashedlines inthe sattergrams represent the rate averages for the total

GTI. It is interresting to note, that the level, orresponding to the x-ray emission

in the 0.5 - 0.75 keV band of the low ount rate regime in the HDFN observation,

is not signiantly higher than the ones from the rst and seond observations to

the Ophiuhus moleular loud, respetively a) and b) plots. This points to the

Figure 4.7: SWCEanalysissattergrams. Thefour sattergrams showtheount rates

in the 0.5 - 0.75 keV and 2.0 - 8.0 keV bands for four dierent observations. The rst

threesattergramsorrespondtothedediatedOphiuhus shadowexperiment(Ophiuhus

I, II, III, respetively sattergram a), b) and )). The fourth sattergram d) orresponds

to one of the dediated XMM-Newton Hubble Deep Field North (HDFN) observations.

These sattergrams were produed to investigate possible Solar Wind Charge Exhange

(SWCE) ontamination of theOphiuhus shadow experiment data, and to ompare with

an observation, known to be ontaminated by SWCE [149 ℄. The dashed lines in eah

sattergram show the average ount rate values for the total GTI. The sattergram d)

showsonviningly two distintsoft x-rayemissionregimes.

may bethe best methodto study a quiesent x-ray emission leveldue toSWCE.

In document Optimización de la hidráulica para brocas de perforación en los campos Drago y Auca de EP Petroecuador (página 60-63)