Engineering topics

Fruchter, A. S.

Publications and source records attributed to Fruchter, A. S..

12 records

NASA NTRS2016

Late Time Multi-Wavelength Observations of Swift J1644+5734: A Luminous Optical/IR Bump and Quiescent X-Ray Emission

We present late time multi-wavelength observations of Swift J1644+57, suggested to be a relativistic tidal disruption flare (TDF). Our observations extend to greater than 4 years from discovery and show that 1.4 years after outburst the relativistic jet switched off on a timescale less than tens of days, corresponding to a power-law decay faster than t (sup -70). Beyond this point weak X-rays continue to be detected at an approximately constant luminosity of L (sub X) approximately equal to 5 times 10 (sup 42) ergs per second and are marginally inconsistent with a continuing decay of t (sup minus 5 divided by 3), similar to that seen prior to the switch-off. Host photometry enables us to infer a black hole mass of M (mass) (sub BH (black hole) equal to 3 times 10 (sup 6) the mass of the sun, consistent with the late time X-ray luminosity arising from sub-Eddington accretion onto the black hole in the form of either an unusually optically faint active galactic nucleus or a slowly varying phase of the transient. Optical/IR observations show a clear bump in the light curve at timescales of 30 to 50 days, with a peak magnitude (corrected for host galaxy extinction) of M (sub R) approximately equal to minus 22 to minus 23. The luminosity of the bump is significantly higher than seen in other, nonrelativisticTDFs and does not match any re-brightening seen at X-ray or radio wavelengths. Its luminosity, light curve shape, and spectrum are broadly similar to those seen in superluminous supervnovae, although subject to large uncertainties in the correction of the significant host extinction. We discuss these observations in the context of both TDF and massive star origins for Swift J1644+5734 and other candidate relativistic tidal flares.

galaxies: active â€“ galaxies: jets â€“ supernovae↗

NASA NTRS2014

Hubble Space Telescope Observations of the Afterglow, Supernova and Host Galaxy Associated with the Extremely Bright GRB 130427A

We present Hubble Space Telescope (HST) observations of the exceptionally bright and luminous Swift gamma-ray burst, GRB 130427A. At z=0.34 this burst affords an excellent opportunity to study the supernova and host galaxy associated with an intrinsically extremely luminous burst (E(sub iso) greater than 10(exp 54) erg): more luminous than any previous GRB with a spectroscopically associated supernova. We use the combination of the image quality, UV capability and and invariant PSF of HST to provide the best possible separation of the afterglow, host and supernova contributions to the observed light approximately 17 rest-frame days after the burst utilising a host subtraction spectrum obtained 1 year later. Advanced Camera for Surveys (ACS) grism observations show that the associated supernova, SN 2013cq, has an overall spectral shape and luminosity similar to SN 1998bw (with a photospheric velocity, vph approximately 15,000 kilometers per second). The positions of the bluer features are better matched by the higher velocity SN 2010bh (vph approximately 30,000 kilometers per second), but SN 2010bh (vph approximately 30,000 kilometers per second but this SN is significantly fainter, and fails to reproduce the overall spectral shape, perhaps indicative of velocity structure in the ejecta. We find that the burst originated approximately 4 kpc from the nucleus of a moderately star forming (1 Solar Mass yr(exp-1)), possibly interacting disc galaxy. The absolute magnitude, physical size and morphology of this galaxy, as well as the location of the GRB within it are also strikingly similar to those of GRB980425SN 1998bw. The similarity of supernovae and environment from both the most luminous and least luminous GRBs suggests broadly similar progenitor stars can create GRBs across six orders of magnitude in isotropic energy.

host↗

NASA NTRS2005

Low-resolution VLT Spectroscopy of GRBs 991216, 011211, 021211 and 030328

We present low-resolution VLT spectroscopy of the aftergiow position of the gamma ray bursts 991216, 011211, 021211 and 030328. The spectmm of GRB 991216 shows two probable absorption systems at z = 0.80 and z = 1.02, where the highest redshift most likely reflects the distance to the host galaxy. A third, more uncertain, system may be detected at z = 0.77. HST imaging of the field obtained 4 months later, show two amorphous regions of emission, one at the projected OT position, the presumed host galaxy at z = 1.02, and the other 0"6 away. All significant lines in the spectrum of GRB 011211 are identified with lines originating in a single absorption system at z = 2.142 plus or minus 0.002, the redshift of the GRB 011211 host galaxy. We also detect Lya in the host, for which we fit a neutral hydrogen column density of log N(HI)=20.4 plus or minus 0.2, which indicates that it is a damped Lya system. For GRB021211, we detect a single emission line in a spectrum tens of days after the burst, which we identify as [OII] at z = 1.006. The galaxy l"5 away from the afterglow location has z = 0.800, and is therefore unrelated to the GRB. Finally, for GRB030328 at least two absorption systems are required to explain all significant lines: one at z = 1.522, the likely redshift of the GRB, and the other at z = 1.295. For the latter system we only detect two lines, and we consider the reality of this system to be uncertain.

Vreeswijk, P. M.↗

NASA NTRS2005

The locations of cosmic explosions

When massive stars exhaust their fuel they collapse and often produce the extraordinarily bright explosions known as core-collapse supernovae. Recently, it has become apparent that stellar collapse can power the even more brilliant relativistic explosions known as long-duration gamma-ray bursts. In some cases, a gamma-ray burst and a supernova have been observed from the same event. One would thus expect that gamma-ray bursts and supernovae should be found in similar environments. Here we show that this expectation is wrong. Using Hubble Space Telescope imaging of the host galaxies of long-duration gamma-ray bursts and core-collapse supernovae, we demonstrate that while the distribution of the supernovae in their hosts traces the blue light of young stars, the gamma-ray bursts are much more concentrated on the very brightest regions of their hosts. Furthermore, the host galaxies of the gamma-ray bursts are significantly fainter and more irregular than the hosts of the supernovae. Together these results suggest that long-duration gamma-ray bursts are associated with the very most massive stars and may be restricted to galaxies of limited chemical evolution. Our results directly imply that long-duration gamma-ray bursts are relatively rare in galaxies such as our own Milky Way.

Fruchter, A. S.↗

NASA NTRS2001

First Detection of a Foreground Damped Ly-Alpha Absorber Along a GRB Line of Sight?

We present a VLT spectrum of the optical afterglow of GRB 991216, taken 1.5 days after the burst, and HST (Hubble Space Telescope) imaging of the host galaxy, obtained four months later. The spectrum contains three metal absorption-line systems with redshifts z = 1.024, z = 0.803, and z = 0.771, where the highest redshift most likely reflects the distance to the host galaxy. For the z = 1.024 and z = 0.803 systems we tentatively detect MgI which suggests a dense environment at these redshifts. This and the strength of the z = 0.803 Fe lines indicate that this system very likely is a damped Ly-alpha absorber (DLA), which would be the first foreground DLA to be detected along a GRB afterglow sight line. The HST images are consistent with these findings: they show two blobs of light, one underneath the projected OT position, the presumed host galaxy, and the other 0.6" away, which is probably responsible for the absorption lines at z = 0.803. The lowest redshift system can be explained by either one of the two galaxies that are located roughly 2" away from the transient. Including these newly found systems, the total number of DLAS and Lyman limit systems along GRB afterglow sight lines is consistent with the number expected from QSO (quasi-stellar object) absorption line studies. We expect early spectroscopy of GRB afterglows to significantly increase the number of detected foreground absorption systems, and we discuss some advantages over QSO lines of sight.

Vreeswijk, P. M.↗

NASA NTRS2000

GRB970228: A Supernova Gamma-Ray Burst

We present B-, V-, R(sub c)-, I(sub c)-, J-, H-, and K-band observations of the optical transient (OT) associated with GRB970228 based on a reevaluation of published data. and present yet unpublished data. In order to minimize small calibration differences we collected and analyzed most of the photometry and determined the magnitude of the OT relative to a set of secondary field stars. We confirm that the early decay of the light curves (before March 6. 1997) was faster than that at later times (between March 6 and April 7. 1997). The early-time observations of GRB 970228 are consistent with relativistic blast wave models but the late-time observations are hard to understand in this framework. The observations are well explained by an initial power law decay with alpha = -1.46 +/- 0.33 modified at later times by a type-I(sub c) supernova light curve. together with the evidence for GRB980326 and GRB 980425 this is further evidence that at least some GRBs are associated with an unusual class of core-collapse supernovae.

Galama, T. J.↗

NASA NTRS1994

Orbital variability in the eclipsing pulsar binary PSR B1957+20

We have conducted timing observations of the eclipsing millisecond binary pulsar PSR B1957+20, extending the span of data on this pulsar to more than five years. During this time the orbital period of the system has varied by roughly Delta P(sub b)/P(sub b) = 1.6 x 10(exp -7), changing quardratically with time and displaying with time and displaying an orbital period second derivative of P(sub b) = (1.43 +/- 0.08) x 10(exp -18)/sec. The previous measurement of a large negative orbital period derivative reflected only the short-term behavior of the system during the early observations; the orbital period derivative is now positive. If, as we suspect, the PSR B1957+20 system is undergoing quasi-cyclic orbital period variations similar to those found in other close binaries such as Algol and RS CVn, then the 0.025 solar mass companion to PSR B1957+20 is most likely non-degenerate, convective, and magnetically active.

Arzoumanian, Z.↗

NASA NTRS1993

Two newly discovered millisecond pulsars

Two millisecond pulsars have been discovered in the course of systematic surveys being made with the Arecibo radio telescope. PSR J2019 + 2425 has a 3.935 ms period and moves in a nearly circular, 76.5 day orbit around a about 0.3 solar mass companion. PSR J2322 + 2057, with a period of 4.808 ms, is an isolated object. The two pulsars have unusually small period derivatives, corresponding to spin-down time scales of 7.5 +/- 0.5 and 11 +/- 5 Gyr, respectively. Both objects show pulse time-of-arrival residuals no larger than a few microseconds over many months, lending further support to the observation that 'recycled' pulsars have extremely stable rotational behavior. The timing results also confirm that physics related to the rotational dynamics of these strongly self-gravitating stars - in particular, the value of the gravitational coupling constant G - remains essentially constant over time scales comparable to the Hubble time. Dispersion measures of the two pulsars indicate distances of 0.8-0.9 kpc.

Nice, D. J.↗

NASA NTRS1993

A disk about PSR 1957+20?

Although the PSR 1957+20 binary system displays a large orbital period derivative, radio observations of the ablated wind from the companion reveal a low free electron density. If the orbital period derivative provides a true indication of the mass loss rate, then the ablated material must be overwhelmingly neutral or largely confined to a narrow region about the orbital plane. However, the companion's high orbital velocity, the observed turbulence in the eclipsing wind, and the energy density of the pulsar's spin-down radiation conspire to make a neutral evaporate unlikely. Radio, optical and infrared observations are shown to suggest that the companion to PSR 1957+20 is bloated, perhaps approaching the size of its Roche lobe. The wind off the companion is most probably a low velocity flow which does not travel far from the orbital plane.

Fruchter, A. S.↗

NASA NTRS1992

X-rays from the eclipsing pulsar 1957+20

The detection of soft X-rays of about 1 keV energy from the eclipsing pulsar PSR1957+20 is reported. This high-energy radiation should be a valuable diagnostic of the wind in this recycled pulsar system. Possible sources of the X-ray emission are the interstellar nebula driven by the pulsar wind, the interaction between the pulsar and its evaporating companion, and the pulsar itself. The small apparent size of the X-ray object argues against the first of these possibilities and suggests that the X-rays are produced within the binary.

Fruchter, A. S.↗

NASA NTRS1992

The continuum eclipse of PSR 1957 + 20

Observations of the eclipsing of the millisecond pulsar PSR 1957 + 20 as a continuum source at wavelengths of 20 and 90 cm are reported. The average 90-cm continuum flux density of the pulsar is found to drop dramatically during pulsed eclipse. In contrast, the neutron star remains visible as a 20-cm continuum source throughout most of the pulsed eclipse, although there is no evidence for a brief loss of signal immediately preceeding conjunction. The 20-cm pulsed eclipse of PSR 1957 + 20 is therefore predominantly caused by the loss of coherent pulsations rather than the diminution of the average radio flux density. It is inferred from these observations that the density of the ionized component of the eclipsing wind does not substantially exceed 10 exp 9 cu cm, except perhaps in a limited region directly preceeding the companion. Radio, optical, and IR observations indicate that the size of the companion to PSR 1957 + 20 may approach that of its Roche lobe, which could explain the apparent ease with which the pulsar ablates its companion as well as the low plasma density of the observed evaporate.

Fruchter, A. S.↗

NASA NTRS1989

A 110-ms pulsar, with negative period derivative, in the globular cluster M15

The discovery of a 110-ms pulsar, PSR2127+11, in the globular cluster M15, is reported. The results of nine months of timing measurements place the new pulsar about 2 arcsec from the center of the cluster, and indicate that it is not a member of a close binary system. The measured negative value of the period derivative is probably the result of the pulsar being bodily accelerated in our direction by the gravitational field of the collapsed core of M15. This apparently overwhelms a positive contribution to the period derivative due to magnetic braking. Although the pulsar has an unexpectedly long period, it is argued that it belongs to the class of 'recycled' pulsars, which have been spun up by accretion in a binary system. The subsequent loss of the pulsar's companion is probably due to disruption of the system by close encounters with other stars.

Wolszczan, A.↗