MS-072: Adin B. Thayer, Co. B, 16th Maine Volunteer Infantry

This collection contains twenty-one Civil War era letters, ranging from 1862-1865, written by Adin Thayer of the 16th Maine. Most of his letters are written to family members prior to his capture and imprisonment in the Confederate prison camp in Salisbury, North Carolina. The final letter in the collection is dated April 26th, 1865 and is addressed to Thayer’s father from Sgt. William Fennelly, of the 16th Maine informing him of his son’s death. Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1066/thumbnail.jp

MS-076: George C. Wynkoop, 2nd Brigade, 2nd Division, Dept. of Pennsylvania

This collection consists of records from George Wynkoop’s service as a Brigadier General in the three month Pennsylvania Volunteers. Over three hundred pieces of correspondence, orders, forms, and daily reports make up the collection. The correspondence and reports come from a variety of locals at which the Department of Pennsylvania set up camp. Locations include Camp Scott and Camp Chambers, Pennsylvania, Hagerstown, Maryland and Harper’s Ferry, Virginia (Today West Virginia). Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1070/thumbnail.jp

MS-075: Henry W. Siebert, Company E, 16th Pennsylvania Volunteer Cavalry

The Henry W. Siebert journals, of which there are two, cover the years 1863 and 1865 respectively. The journals themselves are leather bound notebooks closed with straps, the whole measuring 3 inches by 6 inches. The 1863 volume numbers 90 pages, with entries for every day. The 1865 diary numbers 150 pages and has entries for January 1, 1865 through May 24, 1865. The entries are generally short in nature, not exceeding a paragraph in length. The text is normally limited to a discussion of the morning weather, general activity of the day and the geographic location reached by nightfall. A number of battles are mentioned, including Chancellorsville, Aldie, Upperville, Gettysburg, Petersburg and Appomattox. Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1069/thumbnail.jp

MS-074: Thomas B. McGaffick, Co. F, 101st Pennsylvania Volunteer Infantry

The letters of Thomas B. McGaffick, a corporal in Company F of the 101st Pennsylvania Volunteer Infantry range in date from January 19th, 1861 to February 11, 1863. The collection contains twenty two pieces of correspondence, including two fragments of letters along with a number of official documents relating to McGaffick’s discharge from the army. The letters are all addressed to members of Thomas’s family, including his sisters Belle and Mary, his brother Benjamin and his parents. The letters address a variety of subjects ranging from the rigors of army life to McGaffick’s constant battle with his own health. Thomas rarely received enough correspondence to keep him satisfied and was constantly after family members to write more. He described his thoughts on General McClellan, his desire to return home and the various women to whom he wrote during the conflict. Also of interest is McGaffick’s view towards the African Americans he encountered while in the south. “If I thought I was fighting to free the niggers I would go home and let and let Lincoln fight it out himself.” Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1068/thumbnail.jp

Ultra-High Resolution Intensity Statistics of a Scintillating Source

We derive the distribution of flux density of a compact source exhibiting strong diffractive scintillation. Our treatment accounts for arbitrary spectral averaging, spatially-extended source emission, and the possibility of intrinsic variability within the averaging time, as is typical for pulsars. We also derive the modulation index and present a technique for estimating the self-noise of the distribution, which can be used to identify amplitude variations on timescales shorter than the spectral accumulation time. Our results enable a for direct comparison with ultra-high resolution observations of pulsars, particularly single-pulse studies with Nyquist-limited resolution, and can be used to identify the spatial emission structure of individual pulses at a small fraction of the diffractive scale.Comment: 14 Pages, 4 Figures, accepted for publication in Ap

Size of the Vela Pulsar's Emission Region at 18 cm Wavelength

We present measurements of the linear diameter of the emission region of the Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a function of pulse phase from the distribution of visibility on the Mopra-Tidbinbilla baseline. As we demonstrate, in the presence of strong scintillation, finite size of the emission region produces a characteristic W-shaped signature in the projection of the visibility distribution onto the real axis. This modification involves heightened probability density near the mean amplitude, decreased probability to either side, and a return to the zero-size distribution beyond. We observe this signature with high statistical significance, as compared with the best-fitting zero-size model, in many regions of pulse phase. We find that the equivalent full width at half maximum of the pulsar's emission region decreases from more than 400 km early in the pulse to near zero at the peak of the pulse, and then increases again to approximately 800 km near the trailing edge. We discuss possible systematic effects, and compare our work with previous results

MS-073: Alexander C. Barr, Battery F, 3rd Independent PA Light Artillery

The Alexander Barr collection consists of 17 letters written in between March 14, 1864 and June 3, 1865. The majority of the letters are addressed to his brother Charles in Taylorstown, PA, with the exception of at least one letter composed for his brother Jeff in April, 1864. Most of the letters in the collection date from the time Barr served on Maryland Heights and Harper’s Ferry. Included in the letters are Barr’s experiences as a new recruit in the artillery with topics ranging from the “very poor grub” at the artillery cookhouse, the oppressiveness of the summer weather and the surrender of Robert E. Lee and the evacuation of Richmond. Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1067/thumbnail.jp

Effects of Intermittent Emission: Noise Inventory for Scintillating Pulsar B0834+06

We compare signal and noise for observations of the scintillating pulsar B0834+06, using very-long baseline interferometry and a single-dish spectrometer. Comparisons between instruments and with models suggest that amplitude variations of the pulsar strongly affect the amount and distribution of self-noise. We show that noise follows a quadratic polynomial with flux density, in spectral observations. Constant coefficients, indicative of background noise, agree well with expectation; whereas second-order coefficients, indicative of self-noise, are about 3 times values expected for a pulsar with constant on-pulse flux density. We show that variations in flux density during the 10-sec integration account for the discrepancy. In the secondary spectrum, about 97% of spectral power lies within the pulsar's typical scintillation bandwidth and timescale; an extended scintillation arc contains about 3%. For a pulsar with constant on-pulse flux density, noise in the dynamic spectrum will appear as a uniformly-distributed background in the secondary spectrum. We find that this uniform noise background contains 95% of noise in the dynamic spectrum for interferometric observations; but only 35% of noise in the dynamic spectrum for single-dish observations. Receiver and sky dominate noise for our interferometric observations, whereas self-noise dominates for single-dish. We suggest that intermittent emission by the pulsar, on timescales < 300 microseconds, concentrates self-noise near the origin in the secondary spectrum, by correlating noise over the dynamic spectrum. We suggest that intermittency sets fundamental limits on pulsar astrometry or timing. Accounting of noise may provide means for detection of intermittent sources, when effects of propagation are unknown or impractical to invert.Comment: 38 pages, 10 figure

Discovery of Substructure in the Scatter-Broadened Image of Sgr A*

We have detected substructure within the smooth scattering disk of the celebrated Galactic Center radio source Sagittarius A* (SgrA*). We observed this structure at 1.3 cm wavelength with the Very Long Baseline Array together with the Green Bank Telescope, on baselines of up to 3000 km, long enough to completely resolve the average scattering disk. Such structure is predicted theoretically, as a consequence of refraction by large-scale plasma fluctuations in the interstellar medium. Along with the much-studied $\theta_\mathrm{d}\propto \lambda^2$ scaling of angular broadening $\theta_\mathrm{d}$ with observing wavelength $\lambda$, our observations indicate that the spectrum of interstellar turbulence is shallow, with an inner scale larger than 300 km. The substructure is consistent with an intrinsic size of about 1 mas at 1.3 cm wavelength, as inferred from deconvolution of the average scattering. Further observations of the substructure can set stronger constraints on the properties of scattering material and on the intrinsic size of SgrA*. These constraints will guide understanding of effects of scatter-broadening and emission physics of the black hole, in images with the Event Horizon Telescope at millimeter wavelengths.Comment: 5 pages, 5 figures, accepted by Astrophysical Journal Letters; minor corrections to the text and figures are introduce