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  • Other Sources  (5)
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  • 1
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    Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: We report the discovery by the Swift hard X-ray monitor of the transient source Swift J2058.4+0516 (Sw J2058+05). Our multi-wavelength follow-up campaign uncovered a long-lived (duration approximately greater than months), luminous X-ray (L(sub x.iso) approximates 3 X 10(exp47) erg/s) and radio (vL(sub v.iso) approximates 10(exp 42) erg/s) counterpart. The associated optical emission, however, from which we measure a redshift of 1.1853, is relatively faint, and this is not due to a large amount of dust extinction in the host galaxy. Based on numerous similarities with the recently discovered GRB 110328A / Swift 1164449.3+573451 (Sw 11644+57), we suggest that Sw J2058+05 may be the second member of a new class of relativistic outbursts resulting from the tidal disruption of a star by a supermassive black hole. If so, the relative rarity of these sources implies that either these outflows are extremely narrowly collimated (theta 〈 1 deg), or only a small fraction of tidal disruptions generate relativistic ejecta. Analogous to the case of long duration gamma-ray bursts and core-collapse supernovae, we speculate that the spin of the black hole may be a necessary condition to generate the relativistic component. Alternatively, if powered by gas accretion (i.e., an active galactic nucleus), this would imply that some galaxies can transition from apparent quiescence to a radiatively efficient state of accretion on quite short time scales.
    Keywords: Astronomy
    Type: GSFC.ABS.5632.2011
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  • 2
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    ASASSN-15LH: A Superluminous Ultraviolet Rebrightening Observed by Swift and Hubble (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We present and discuss ultraviolet and optical photometry from the Ultraviolet/Optical Telescope, X-ray limits from the X-Ray Telescope on Swift, and imaging polarimetry and ultraviolet/optical spectroscopy with the Hubble Space Telescope, all from observations of ASASSN-15lh. It has been classified as a hydrogen-poor superluminous supernova (SLSN I), making it more luminous than any other supernova observed. ASASSN-15lh is not detected in the X-rays in individual or co-added observations. From the polarimetry we determine that the explosion was only mildly asymmetric. We find the flux of ASASSN-15lh to increase strongly into the ultraviolet, with an ultraviolet luminosity 100 times greater than the hydrogen-rich, ultraviolet-bright SLSN II SN2008es. We find that objects as bright as ASASSN-15lh are easily detectable beyond redshifts of 4 with the single-visit depths planned for the Large Synoptic Survey Telescope. Deep near-infrared surveys could detect such objects past a redshift of 20, enabling a probe of the earliest star formation. A late rebrightening-most prominent at shorter wavelengths -is seen about two months after the peak brightness, which is itself as bright as an SLSN. The ultraviolet spectra during the rebrightening are dominated by the continuum without the broad absorption or emission lines seen in SLSNe or tidal disruption events (TDEs) and the early optical spectra of ASASSN-15lh. Our spectra show no strong hydrogen emission, showing only Ly absorption near the redshift previously found by optical absorption lines of the presumed host. The properties of ASASSN-15lh are extreme when compared to either SLSNe or TDEs.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN41819 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 828; 1; 3
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  • 3
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    On the Early-Time Excess Emission in Hydrogen-Poor Superluminous Supernovae (2017)
    In:  Other Sources
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    Publication Date: 2019-08-24
    Description: We present the light curves of the hydrogen-poor super-luminous supernovae (SLSNe I) PTF 12dam and iPTF 13dcc, discovered by the (intermediate) Palomar Transient Factory. Both show excess emission at early times and a slowly declining light curve at late times. The early bump in PTF 12dam is very similar in duration (approximately 10 days) and brightness relative to the main peak (23 mag fainter) compared to that observed in other SLSNe I. In contrast, the long-duration (greater than 30 days) early excess emission in iPTF 13dcc, whose brightness competes with that of the main peak, appears to be of a different nature. We construct bolometric light curves for both targets, and fit a variety of light-curve models to both the early bump and main peak in an attempt to understand the nature of these explosions. Even though the slope of the late-time decline in the light curves of both SLSNe is suggestively close to that expected from the radioactive decay of 56Ni and 56Co, the amount of nickel required to power the full light curves is too large considering the estimated ejecta mass. The magnetar model including an increasing escape fraction provides a reasonable description of the PTF 12dam observations. However, neither the basic nor the double-peaked magnetar model is capable of reproducing the light curve of iPTF 13dcc. A model combining a shock breakout in an extended envelope with late-time magnetar energy injection provides a reasonable fit to the iPTF 13dcc observations. Finally, we find that the light curves of both PTF 12dam and iPTF 13dcc can be adequately fit with the model involving interaction with the circumstellar medium.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN44013 , The Astrophysical Journal (ISSN 2041-8205) (e-ISSN 2041-8213); 835; 1; 58
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  • 4
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    Early Radio and X-Ray Observations of the Youngest Nearby Type Ia Supernova PTF 11kly (SN 2011fe) (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: On August 24 (UT) the Palomar Transient Factory (PTF) discovered PTF11kly (SN 2011fe), the youngest and most nearby type Ia supernova (SN Ia) in decades. We followed this event up in the radio (centimeter and millimeter bands) and X-ray bands, starting about a day after the estimated explosion time. We present our analysis of the radio and X-ray observations, yielding the tightest constraints yet placed on the pre-explosion mass-loss rate from the progenitor system of this supernova. We find a robust limit of M(raised dot) less than or equal to 10(exp -8) (w /100 kilometers per second ) solar mass yr(exp -1) from sensitive X-ray non-detections, as well as a similar limit from radio data, which depends, however, on assumptions about microphysical parameters. We discuss our results in the context of single-degenerate models for SNe Ia and find that our observations modestly disfavor symbiotic progenitor models involving a red giant donor, but cannot constrain systems accreting from main sequence or sub-giant stars, including the popular supersoft channel. In view of the proximity of PTF11kly and the sensitivity of our prompt observations we would have to wait for a long time (decade or longer) in order to more meaningfully probe the circumstellar matter of Ia supernovae.
    Keywords: Astrophysics
    Type: GSFC.JA.6043.2012
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  • 5
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    An Early and Comprehensive Millimetre and Centimetre Wave and X-Ray Study of SN 2011dh: a Non-Equipartition Blast Wave Expanding into a Massive Stellar Wind (2013)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3-12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (epsilon(sub e)/epsilon(sub B) approx. 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R(exp 2). Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 +/- 1800 km/s, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (approx.1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio epsilon(sub e)/epsilon(sub B).
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN12189 , Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711) (e-ISSN 1365-2966); 436; 2; 1258-1267
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