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We present observations of the Type Ic supernova (SN Ic) 2011bm spanning a period of about one year. The data establish that SN 2011bm is a spectroscopically normal SN Ic with moderately low ejecta velocities and with a very slow…

We present the photometric and spectroscopic evolution of the type IIn SN 1995G in NGC 1643, on the basis of 4 years of optical and infrared observations. This supernova shows very flat optical light curves similar to SN 1988Z, with a slow…

XMM-Newton EPIC observations have revealed a bright point-like X-ray source in the nearby Magellanic-type galaxy NGC 55. At the distance of NGC 55, the maximum observed X-ray luminosity of the source, designated as XMMU J001528.9-391319, is…

We have examined X-ray and optical observations of two ultra-luminous X-ray sources, X7 and X10 in NGC4559, using XMM-Newton, Chandra and HST. The UV/X-ray luminosity of X7 exceeds 2.1e40 erg/s in the XMM-Newton observation, and that of X10…

The nature of the synchrotron superbubble in the IC 10 galaxy is discussed using the results of our investigation of its ionized gas structure, kinematics, and emission spectrum from observations made with the 6-m telescope of the Special…

We present an optical spectrum of the energetic Type Ib supernova (SN) 2012au obtained at an unprecedented epoch of 6.2 years after explosion. Forbidden transition emission lines of oxygen and sulfur are detected with expansion velocities…

Optical spectra of the bright Type II-L supernova SN 1979C obtained in April 2008 with the 6.5 m MMT telescope are compared with archival late-time spectra to follow the evolution of its optical emission over the age range of 11 to 29…

Optical and near-infrared light curves of the Type IIn supernova 1999el in NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is covered from the first observation obtained a few days before maximum light.…

We present results from a fully relativistic investigation of matter fallback in a supernova, assuming that the central compact star is a black hole (BH). Our goal is to answer the following questions: can we infer from the light curve…

We have analyzed an XMM-Newton observation of the nearby spiral galaxy NGC 1313, which contains two "ultra-luminous" X-ray (ULX) sources. We measure isotropic luminosities of L_X = 2.0 * 10^(40) erg/s and L_X = 6.6 * 10^(39) erg/s for NGC…

The possibility of making stellar mass black holes in supernovae that otherwise produce viable Type II and Ib supernova explosions is discussed and estimates given of their number in the Milky Way Galaxy. Observational diagnostics of…

Near-Infrared (NIR) observations are presented for five Type IIn supernovae (SN 1995N, SN 1997ab, SN 1998S, SN 1999Z, and SN 1999el) that exhibit strong infrared excesses at late times (t >= 100 d). H- and K-band emission from these objects…

While performing a survey to detect recoiling supermassive black holes, we have identified an unusual source having a projected offset of 800 pc from a nearby dwarf galaxy. The object, SDSS J113323.97+550415.8, exhibits broad emission lines…

We have analysed the light curve of the two brightest X-ray flares from the Galactic Center black hole, one flare observed by XMM-Newton on October 3, 2002 (Porquet et al. 2003), and the other flare observed by Chandra on October 26, 2000…

The M81 group member dwarf galaxy IC 2574 hosts a supergiant shell of current and recent star-formation activity surrounding a 1000 x 500 pc hole in the ambient Hi gas distribution. Chandra X-ray Observatory imaging observations reveal a…

Spectral studies of a luminous X-ray source, NGC 253 X21, are presented based on archival Chandra and XMM-Newton data. The Chandra observation on 1999 December 16 detected the source at a bolometric luminosity of 0.3 x 10^39 erg/s (assuming…

Broad-lined type Ic supernovae (SNe Ic-BL) are peculiar stellar explosions that distinguish themselves from ordinary SNe. Some SNe Ic-BL are associated with long-duration (\gtrsim 2 s) gamma-ray bursts (GRBs). Black holes and magnetars are…

M82 X-1, the brightest X-ray source in the galaxy M82, has been thought to be an intermediate-mass black hole (100 to 10,000 solar masses) because of its extremely high luminosity and variability characteristics, although some models…

We present VLA observations of 16 Type IIn and Type II-L supernovae (SNe IIn and SNe II-L) at ~1000--7000 days after explosion, probing circumstellar matter (CSM) at distances >10^16 cm from the progenitor corresponding to mass-loss over…

The recurrent nova IM Nor was observed twice in X-rays with Chandra ACIS-S, 1 and 6 months after the optical outburst. It was not detected in the first observation, with an upper limit on the X-ray luminosity in the 0.2-10 keV range L(x) <…