The X-ray flux from the 3.6 hr binary system H2252-035 is shown to be modulated at a period of 805s. The spectrum is consistent with either a 1.4 photon index power law or  20 keV thermal model. A 560t0r-350 eV equivalent width iron line is seen at approximately 6.7 keV. The possibility that this system contains a slowly rotating neutron star is discussed

Marshall, F. E.

White, N. E.

English

NASA Technical Reports Server

  
 
 
N O T I C E 
 
THIS DOCUMENT HAS BEEN REPRODUCED FROM 
MICROFICHE. ALTHOUGH IT IS RECOGNIZED THAT 
CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED 
IN THE INTEREST OF MAKING AVAILABLE AS MUCH 
INFORMATION AS POSSIBLE 
https://ntrs.nasa.gov/search.jsp?R=19810020522 2020-03-21T13:03:47+00:00Z
NASA
Technical Memorandum 82149
The 805s X-Ray Pulsar H2252-035
N. E. White and F. E. Marshall
(NASA-TH-82149) ZHE 8055 Y-RAY PULSAR	 N81-29060
H2252-035 (NASA) 16 p k1C A02/MF AJ1
CSCL 036
UACla£
63/93 31115
JUNE 1981
National Aeronautics and
Space Administration
Goddard Speoe Flight Center
Greenbelt, Maryland 20771
ITHE BOSs X-RAY PULSAR H2252-035
N.E. NHITB1 and F.E. NARSHALL
dent width iron line is seen at t- 6.7 keV. We discuss the possibility
his system contains a slowly rotating neutron star.
Dept of Physics and Astronomy, Univ. of Maryland
Laboratory for High Energy Astrophysics
NASA/Goddard Space Flight Center
Greenbelt, Maryland 20771
ABSTRACT
We demonstrate that the X-ray flux from the 3.6 hr binary system
H2252-035 is modulated at a period of 8059. The spectrum is consistent with
either a 1.4 photon index power law or > 20 keV thermal model. A 560 3 350 eV
2F-I"I	 I. INTRODUCTION
The 13th magnitude optical counterpart to the X-ray source 82252-035
(Griffiths at al. 1980, Marshall at al. 1979) was discovered to be modulated
with two periods, 858s (Warner 1980, Patterson and Price 1980) and 3.6 hrs
(Patterson and Price 1980) with semi-amplitudes of 5 and 10% respectively.
Subsequent analysis of MW A2 data revealed that the X-ray flux was also
!--	 modulated, but not at ei ther of the optical periods, rather at a third period
of 8059 (White and Marshall 1980). This somewhat surprising result was simply
resolved by the observation that the X-ray period is a beat between the two
optical periods. The optical pulsations most likely come from X-ray
pulsations reprocessed in material that is orbiting about the X-ray pulsar
with a period of 3.6 hrs. The optical pulse period is down shifted because
the orbiting material sees one less pulse per orbital period than a stationary
observer (fur prograde rotation of the pulsar). Further analysis has now
revealed that the X-ray period of 8059 is also present in the optical data at
the 28 level (Warner and Donoghue 1980; Patterson and Jablonski 1981). The
optical emission lines show sinusoidal variations of amplitude 145 km 's~1
commensurate with the orbital period, with maximum velocity away from the
observer occurring one quarter of an orbital period after maximum light
(Patterson and Price 1981). The optical continuum from 1200-22000 A is best
represented by a 12,500 K blackbody, but with IR and W excesses (Hassall et
al. 1981).
Models for H2252-035 have been based on the concept that this system is
fundamentally similar to cataclysimic variables i.e. it is a 3.6 hr binary
system containing a compact object accreting material, via a disk, from a
Roche limited low mass star. Two different reprocessing sites have been
suggested to account for the 858 s optical pulsations. Patterson and Price
3
A. 
kr;'. I
i
i
(1981) discuss, perhaps the most obvious location, the face of the companion
star, while Hassall at al. favor a more exotic model wherein the reprocessing
takes place at a bulge in the accretion disk, corresponcdng to the point where
inflowing material feeds into it. Because the optical to X-ray luminosity of
H2252-035 is eo similar to other CVs, Patterson and Price (1981) assert that
the compact object must be a magnetic white dwarf and that this is an
"unphase-locked" AM Her type system.
We present here the results of the HEAO A2 observation that first
demonstrated the X-ray flux of U2252-035 to be pulsed and consider the
possibility that the compact object in this system is a neutron star.
Ii. RESULTS
The RW A2+
 detectors (Rothschild at al. 1979) made a 6 hr pointed
+The A2 experiment on HEAD-1 is a collaborative effort led by E. Boldt of GSFC
and G. Garmire of CIT, with collaborators at GSFC, CIT, JPL and UCS.
observation of H2252-035 on 1978 Dec 5, starting at 1600 hrs UT. Data from
t:e Medium Energy Detector (MED, 2-15 keV) and High Energy Detector (HED, 2-60
keV) were searched using Fourier techniques for evidence: of a periodicity.
The power spectrum is shown in Figure 1 and a period at 805s (13.4 minutes) is
clearly detected. The arrow indicates the optical pulse period of 8589. The
two symmetric side lobes about the main peak represent the sampling pattern
convolved with the power at the detected frequency and results from regular
gaps in the data. The period we obtain is 805.14 t 0.90s with (fitting a sine
wave to the data) heliocentric maximum light occurring at JD2443848.32695 t
0.00012. In Figure 1 the data folded modulo this period are shown in two
different energy bands, 2-5 keV and 5-15 keV. There is a decrease in pulse
4semi-amplitude from * S0% to * 259 with increasing ensrW and the
semi-amplitude of ! 909 seen between 0.1 and 4 keV by Patterson and Jablonski
supports this trend.
The X-ray data were folded into 16 phase bins (1 bin • one pulse period)
about the orbital period using the ephemeris for maximum light from Patterson
and Jablonski of JD2443808.682+0.149553E. 509 intensity variations from pulse
to pulse were evident, but there was no evidence for any systematic trend
associated with the orbital peri-,u. In particular there was no sign of any
eclipse. Patterson and Jablonski have also reported a non-coherent
periodicity in the optical flux at * 81s. we have searched for a
corresponding modulation of the X-ray data and find none greater than * S9.
Scanning data were obtained for 3 five day observation intervals in December
1977, June 1978 and December 1978. The average intensity of the source for
each observation was the same to within T 308.
Spectral data from the MW and H$D detectors were each summed over the
entire pointed observation and tested against standard spectral models. A
power law model of photon index a 1.4 or a thermal model with temperature > 20
keV were found to be equally acceptable. In both cases a 550 eV equivalent
width iron line was required at s
 6.7 keV. The best fitting spectra are given
in Table 1 and the incident spectra, deconvolved using the best thermal fit,
are shown in rigure 2. The distance to this source is estimated to be %. 220
pc. by Patterson and Jablonski or between 100 and 750 pc by Hassall et al.,
giving an Lx of 4 x 1032 x (d/220 pc) 2 ergs s-1.
III. DISCUSSION
Patterson and Price argue that the similarity of the L x/Lopt of this
system to that of other Cvs indicates the compact object must be a magnetic
white dwarf. Their line of reasoning is as follows. The optical light of CVs
."I
5
M
is dominated by emission from the accretion disk, with the bolometrie disk
r
i	
luminosity proportional to the mass accretion rate 1%
A
 (e.g. Bath, Pringle and
Whelan 1980= Cordova, Mason and Nelson 1981). To obtain an X-ray luminosity
of 1032 ergs 97 1 from an accreting white dwarf requires an MA of a 10 15 gm
8-1,  which is at the lower limit of that generally seen from CVs (Warner
1976). The deeper potential well of a neutron star requires an MA three
orders of magnitude lower and makes the intrinsic light output from the disk
trivial when compared to the X-ray luminosity i.e. a much larger Le/Lopt would
be expected.
If the variations in the optical light are attributed to reprocessed
X-ray flux, then at least an average 58 and most probably 10% of the optical
flux cannot come directly from the accretion disk. As already noted by
Patterson and Jablonski and Hassall et al. the optical luminosity between 1200
and 7500 A of 2.5 x 10-10 ergs s 1 is four times greater than the X-ray
luminosity of 7 x 10-11 ergs a- '.  This means to meet the energy budget, the
reprocessing material must intercept at least 25% of the X-ray flux, which is
physically unreasonable. In view of the relative stability of the X-ray
intensity over 1.5 yr this difficulty can only be avoided if there exists
either a large unseen soft X-ray/far W flux or the peak X-ray flux in the
orbital plane is at least four times larger than we observe. In either event,
the need for this additional flux is independent of the nature of the compact
object and, apart from illuminating the secondary, All also light up the
accretion disk. The argument for the compact object being a white dwarf, that
is based on the similarity of the ",pt of 82252-035 to other CVs (Patterson
and Price 1981), mist be viewed with caution since the light from the disk may
be totally due to reprocessed X-ray emission.
The X-ray properties (spectrum, pulse profile and luminosity) exhibit
little to distinguish it from the other X-ray pulsars that are believed to be
rotating neutron stars.
	
The hard X-ray spectrum with an iron line is typical
{ of both neutron stars and magnetic white dwarfs. The fact that the pulse
asplitude ins  with decreasing energy is contrary to that seen in most
neutron star pulsars although one, OX 301-4 does show such a trend (McClintock
at al. 1977).	 While the intrinsic luminosity of this source of 1032 ergs 871 
is several orders of magnitude below the more typical values of 10 35-1038 ergs
8-1,  there is one pulsar, X Per (3UO352+30), that has a similar luminosity
and, coincidentally, a similar period (834s).
	
Measurements of the period of
this pulsar have demonstrated that it is decreasing with time and that the
rate of decrease indicates the moment of inertia of the underlying body to be
that of a neutron star (White, Mason and Sanford 1977). 	 The current limit on
t
p for H2252-035 of < 9 x 10-11 s . 9' 1 (Patterson and Price 1981) is not yet
good enough to utilize this as a test for this source.
We can express the expected Alfven radius for a compact magnetic star
(neutron star or white dwarf) as
-2/7	 2/7
ra = 4 x 109 
u304^	 (HM0 )1^ 	L33R6	 cm
where U30 is the magnetic moment and R6 the stellar radius (from Blsner and
Lamb 1976).
	 Typical neutron star values set the above parameters to unity and
` give ra r 4 x 105 cm.	 Approximately the same value for ra is obtained for a
magnetic white dwarf with a surface field of order 10 4
 gauss.
	 In either case
this radius is similar to the inner disk radius obtained from the width of
the HO emission by Patterson and Jablonski.
	 Further, a Keplerian period of
81s about a 1.2 No
 star gives an orbital radius of 3 x 109 cm and it some
likely that the 81s non-coherent periodic oscillations reported by Patterson
7	 'I
and Jablonski result from inhomogeneities in the inner region of the disk,.
I".
(Bath 1973). These twoints have thepo important implication that the A1lven
radius is well within the co-rotation radius ( rc - 1.5 x 10 10 cm) and gives a
fastness parameter ws, as defined by Ghosh and Lamb ( 1980), of 0.1 i .e. it is
a slow rotator. This allows no to estimate $, which from Ghosh and Lamb
(1980) is
^]
-^ - 6.0 x 10 16 Y
30 6^	
3/7
(M )	 n(ws: I45-1 (P L33 ) 2 s s 1	
j,
o
where I45 is the moment of interia of the compact object in 10 45 gm cm2
(which - 2 for a neutron star or - 105 for a white dwarf) and n (ws ) - 1 for ws
- 0.1. This gives - -7 x 10 -11 x a s s-1 for 145 - 2, Mx - 1.3 and L - 4 x
32 7/1.
10 x a ergs a-1 , where a - (L/Lx ) 6/7 accounts for the unseen flux. This
value of ¢ is near the current upper limit to $ for a - 4. However, the
uncertainties in the distance to the source and the physical parameters of the
neutron star could change the predicted P by up to a factor 5 and a definitive
test of the neutron star model requires a reduction in the observational
uncertainty of # by at least an order of magnitude.
We thank Joe Patterson for providing his and other results in advance of
publication.
f.
4 1
i	 8
REP6RIMCiS
Bath, O.T. t973, Nature Phys- Sci. 246. 84.
Bath, Q.T., Pringle, J.E., and Whelan, J.A.J. 1980, MI MB 190, 185.
Cordova, F., Mason, K.O., and Belson, J. 1981, Ape J. 2451 609.
Elsner, R.F., and Lamb, F.K. 1976, Nature 2620 356.
Elsner, R.F., Qlosh, P., and Lamb, F.K. 1980, preprint.
Ghosh, P., and Lamb, F.K. 1979, Apo J. Z34, 2%.
Griffiths. R.E., Lamb, D.Q., Ward, M.J., Wilson, A.S., Charles, P•A.,
Thorstensen, J., Mcnardy, I.M., and Lawrence, A. 1980, MNRAS 193, 25p.
Bassall, B.J.M., Pringle, J.E., Ward, M.J., Whelan, J.A.J., May*, S.K.,
Schevarria, J., Jones, D.H.P., and Wallis, R.E. 1981, preprint.
Marshall, F.B., Boldt, E.A., AGlt, S.8., Mushotaky, R.F., Pravdo, S.H.,
Rothschild, R.B., and Serlemitsos, P.J. 1979, Ap. J. Sup. 40, 657.
McClintock, J.B. et al. 1977, Apo J. 216, L15.
Patterson, J., and Jablonski, F.J. 1981, preprint.
Patterson, J., and Price, C. 1980, IAUC 3511.
Patterson, J., and Price, C. 1981, Apo J. 243, L83.
Rothschild, R. et al. 1979, Space Sci. Inst. 4, 269.
Warner, 8. 1976, in I= Symp. No. 73, p. 85.
Warner, B. 1980, IAUC 3911.
Warner, B., and Donaghu*, O. 1980, IAUC 3525.
White, N.E., and Marshall, F.B. 1980, IAUC 3514.
White, N.E., Mason, R.O., and Sanford, P.W. 1977, Nature 267, 229.
;a
r
.y
i
9TABLE 1s 82252-035 ' SPECTRAL PARA	 (90% uncertainties)
Normalization PL
a+1
NH
 (H atoms clo 2 )
2
Xr
i
Normalization Th
kT(keV)
NH
 (H atom cm 2)
2
Xr
NED HID
0.0044 0.010
1.4t0.2' 1.9t0.3
< 2 x 1022 (513) x 1022
1.0 0.9
0.0014 0.0015
244 24 9
< 2 x 1022 (3 t 2) X'1022
1.1 0.9
LINE PARAMETERS
NED	 HED
Line Strength (phs pa 2 S71)
	
(1.6 1 0.8) x 10 -4 (1.6 t 1.0) x 10-4
LpWM (keV)	 < 3
	
< 4
Energy (kev)
	
6.8 1 0.2	 6.5 t 0.3
..	 EW (eV)
	
560 t 350	 550 t 450
Lx - 6.7 x 10-" ergs cai 2 
8-1  (0.5 - 50 keV)
qr
t-
N
11.1
V
0
le
t
a3MOd
10
FZQM CAPTIOUS
Figure 1 - The power spectrum of the am of the IND and MD rates data * The
arrow indicates the expected position of the 858s optical pulsation.
Figure 2 - The background subtracted pulse profile in two different energy
bands normalized to the nom count rate. The plot has been repeated once for
clarity. An arbitrary epoch of JD2443847.5 vas used.
Figure 3 - The incident spectrum obtained when the best fitting thermal
Model is assumed.
k.a
2 N225^ -03T	 HEAD A2
5-15 keV
W
..J
LL
0a
W
J
CL
2-5 keV
ARBITARY PULSE PHASE
J^^  1
y' l
	 0
R
t
w..
I
8mv0 }
IxWZW
ADDRESS OF AUTHORS
I
F.S. MARSHALL and N.S. WHITS, Code 661, Laboratory For Nigh Energy
Astrophysics, NASA/Goddard Space Flight Center, Greenbelt, ND 20771
s


The 805s X-ray pulsar H2252-035

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server