Engineering topics

Lubin, Lori M.

Publications and source records attributed to Lubin, Lori M..

8 records

NASA NTRS2002

A Detailed Study of Two Optically-Selected, High-Redshift Clusters of Galaxies

We are obtaining detailed X-ray spectral and structural data for two distant, optically-selected clusters of galaxies which are known X-ray emitters, CL1324+3011 at z=0.76 and CL1604+4304 at z=0.90. These observations will allow us to place accurate constraints on the temperature, surface-brightness profile, and mass fraction of the intracluster medium in rich, optically-selected clusters at very high redshift. The two target clusters are the most well-studied systems at z greater than 0.7 in the optical and infrared regimes; therefore, with the addition of the XMM data, we plan to study the specifics of the relationship between the X-ray and optical properties and their implications for galaxy and cluster evolution.

Lubin, Lori M.↗

NASA NTRS2000

A Detailed Study of Two Optically Selected, High-Redshift Clusters of Galaxies

We are obtaining detailed X-ray spectral and structural data for two distant, optically-selected clusters of galaxies which are known X-ray emitters, CL1324+3011 at z = 0.76 and CL,1604+4304 at z = 0.90. These observations will allow us to place accurate constraints on the temperature, surface-brightness profile, and mass fraction of the intracluster medium in rich, optically-selected clusters at very high redshift. The two target clusters are the most well-studied systems at z greater than 0.7 in the optical and infrared regimes; therefore, with the addition of the XMM data, we plan to study the specifies of the relationship between the X-ray and optical properties and their implications for galaxy and cluster evolution.

Lubin, Lori M.↗

NASA NTRS1995

Using X-rays to determine which compact groups are illusory

If the large-scale galaxy distribution is filamentary, as suggested by some observations and recent hydrodynamical simulations, then lengthwise views of filaments will apparently produce compact groups (CGs) that are in reality stretched out along the line of sight. This possibility has been advocated recently by Hernquist, Katz, & Weinberg (1995). Here we propose a test for this hypothesis using X-ray emission from CGs. The observable quantity Q identical with L(sub x)a(sup 3)(sup p)/(L(sup 2)(sup g))T(sup 1/2)(sub x) should be proportional to the axis ratio of the group, a/c, where a and c are the short and long axes of a prolate distribution, a(sub p) is the radius of the group projected onto the sky, L(sub x) is the bolometric X-ray luminosity, L(sub g) is the group blue luminosity, and T(sub x) is the gas temperature. We find that the distribution of Q is consistent with the notion that many CGs with unusually small values of a/c are frauds, i.e., that the values of Q are anomalously small. Absent other information, it is equally possible that CGs are very gas-poor relative to rich clusters; however, this can be tested using the Sunyaev-Zeldovich effect. If the groups have a close to normal ratio of gas to total mass, but are simply stretched out along the line of sight, a Sunyaev-Zeldovich signal should be detectable.

Ostriker, Jeremiah P.↗

NASA NTRS1994

Is a data set distributed as a power law? A test, with application to gamma-ray burst brightnesses

We present a method to determine whether an observed sample of data is drawn from a parent distribution that is pure power law. The method starts from a class of statistics which have zero expectation value under the null hypothesis, H(sub 0), that the distribution is a pure power law: F(x) varies as x(exp -alpha). We study one simple member of the class, named the `bending statistic' B, in detail. It is most effective for detection a type of deviation from a power law where the power-law slope varies slowly and monotonically as a function of x. Our estimator of B has a distribution under H(sub 0) that depends only on the size of the sample, not on the parameters of the parent population, and is approximated well by a normal distribution even for modest sample sizes. The bending statistic can therefore be used to test a set of numbers is drawn from any power-law parent population. Since many measurable quantities in astrophysics have distriibutions that are approximately power laws, and since deviations from the ideal power law often provide interesting information about the object of study (e.g., a `bend' or `break' in a luminosity function, a line in an X- or gamma-ray spectrum), we believe that a test of this type will be useful in many different contexts. In the present paper, we apply our test to various subsamples of gamma-ray burst brightness from the first-year Burst and Transient Source Experiment (BATSE) catalog and show that we can only marginally detect the expected steepening of the log (N (greater than C(sub max))) - log (C(sub max)) distribution.

Wijers, Ralph A. M. J.↗

NASA NTRS1993

Unusual features in the persistent emission of the Rapid Burster

Several distinct features in the persistent X-ray emission after long (greater than 30 s) type II bursts from the Rapid Burster were discovered in August 1985. A specific pattern characterized by a 'hump' was observed in the early portion of the persistent emission after type II bursts with integrated fluxes less than about 4.8 x 10 exp -6 erg/sq cm. This hump which typically lasts about 200 s is almost never observed after bursts with fluences greater than this value. The emission during the hump is found to be always harder than the average persistent emission. Quasi-periodic oscillations with frequencies of about 40 mHz observed in 10 cases occur exclusively during a hump. The persistent emission also exhibited sharp 'glitches' and small 'bumps' lasting about 20-100 s. The glitches always occurred at the same phase in the intervals between bursts. In seven cases the glitches were followed by a bump.

Lubin, Lori M.↗

NASA NTRS1992

A new kind of oscillation in the persistent emission of the Rapid Burster

We present a study of a new kind of oscillation found in the persistent emission after some type II bursts from the Rapid Burster observed during 1985 August with EXOSAT. All 95 bursts observed were longer than 30 s. Ten of them were followed by these oscillations. The frequency of the oscillations ranged from 39 to 56 mHz. A period decrease (by 30-50 percent) over a time-scale of about 100 s was observed in seven cases. The fractional rms variation of the oscillations ranged from 5 to 15 percent. In eight cases, about 4-Hz quasi-periodic oscillations with fractional rms values from 6 to 19 percent were observed simultaneously with the new oscillations. There is a high probability that the two forms of oscillation are related to one another.

Lubin, Lori M.↗

NASA NTRS1992

Quasi-periodic oscillations in the Z source GX 5-1

A detailed study has been conducted of the time variability in the Z source GX 5-1 using Ginga, which observed the source in the horizontal and normal branches (HB, NB). Intensity-dependent HF, quasi-periodic oscillations (QPO) were observed in the HB, in which the source flux varied by a factor of 1.9. The QPO frequency in this portion of the HB ranges from about 13 to 17 Hz; this is lower than previously observed in any Z source. The HF and LF QPO were simultaneously observed in the NB. The strength of both forms of QPO and the strength of the LF noise increase rapidly with increasing photon energy.

Lewin, Walter H. G.↗

NASA NTRS1992

The relation between the bolometric flux and the blackbody temperature at the peak of type II bursts from the Rapid Burster

During about 6 hr of Ginga observations of the Rapid Burster in August 1988, the source emitted type II bursts with durations between about 3 and about 35 s and with peak fluxes which varied by factors of about 5. The Rapid Burster was active in two bursting modes as defined by Marshall et al. (1979): mode I characterize by a burst energy distribution which is 'double-peaked' and mode II by a distribution which is 'single-peaked'. A study of the relationship between the maximum bolometric burst flux, F(max), and the associated blackbody temperature, Tc, shows that mode I bursts consistently show higher Tc values than bursts of mode II. These results, together with previous work, suggest that the relation between F(max) and Tc is dependent on mode. In mode I the color temperature is approximately independent of the burst peak flux, whereas in mode II the two properties are correlated.

Lubin, Lori M.↗