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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

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To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
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submitter:"Judith Racusin"

4055 results found.

  1. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  2. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  3. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  4. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  5. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  6. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  7. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  8. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  9. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  10. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  11. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  12. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  13. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  14. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  15. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  16. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  17. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  18. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  19. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  20. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  21. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  22. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  23. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  24. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  25. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  26. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  27. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  28. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  29. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  30. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  31. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  32. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  33. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  34. GRB 250813B: SVOM/ECLAIRs refined analysis
  35. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  36. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  37. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  38. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  39. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  40. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  41. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  42. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  43. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  44. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  45. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  46. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  47. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  48. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  49. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  50. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  51. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  52. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  53. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  54. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT follow up of AT 2025smm
  55. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  56. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  57. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  58. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  59. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  60. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  61. GRB: Clarification on Gamma-Ray Burst Naming Convention
  62. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  63. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT detection of a new source, AT 2025smm
  64. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  65. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  66. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  67. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  68. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  69. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  70. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  71. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  72. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  73. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  74. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  75. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  76. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  77. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  78. LIGO/Virgo/KAGRA S250720j: Retraction of GW compact binary merger candidate
  79. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  80. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  81. LIGO/Virgo/KAGRA S250712cd: Updated Sky localization
  82. LIGO/Virgo/KAGRA S250712cd: Identification of a GW compact binary merger candidate
  83. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  84. GRB 250702B,D,E/EP250702A: JCMT sub-mm observations at 350 GHz
  85. LIGO/Virgo/KAGRA S250629bs: Upper limits from Swift/BAT-GUANO
  86. LIGO/Virgo/KAGRA S250629ae: Upper limits from Swift/BAT-GUANO
  87. IceCube-250708A: Upper limits from a search for additional neutrino events in IceCube
  88. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 4-Update Localization Volume
  89. IceCube-250706A: Upper limits from a search for additional neutrino events in IceCube
  90. LIGO/Virgo/KAGRA S250705cb: Updated Sky localization
  91. LIGO/Virgo/KAGRA S250704ab: Updated Sky localization and EM Bright Classification
  92. LIGO/Virgo/KAGRA S250702n: Updated Sky localization
  93. LIGO/Virgo/KAGRA S250701bq: Updated Sky localization
  94. LIGO/Virgo/KAGRA S250701bp: Updated Sky localization
  95. LIGO/Virgo/KAGRA S250705cb: Identification of a GW compact binary merger candidate
  96. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 3-Initial Localization Volume
  97. LIGO/Virgo/KAGRA S250704ab: Upper limits from Fermi-GBM Observations
  98. LIGO/Virgo/KAGRA S250704ab: Coverage and upper limits from MAXI/GSC observations
  99. LIGO/Virgo/KAGRA S250704ab: Identification of a GW compact binary merger candidate
  100. LIGO/Virgo/KAGRA S250702n: Identification of a GW compact binary merger candidate

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