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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.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
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"
body:"GRB"
submitter:"Judith Racusin"

27398 results found.

  1. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  2. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  3. GRB 250823A: Swift-BAT refined analysis
  4. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  5. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  6. GRB 250823A: Swift-XRT refined Analysis
  7. EP250821a: MeerKAT radio counterpart
  8. GRB 250823A: COLIBRÍ optical observations
  9. GRB 250823A: SVOM/VT optical observation
  10. GRB 250823A: Swift/UVOT Detection
  11. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  12. GRB 250823A: Fermi GBM Observation
  13. GRB 250823A: Enhanced Swift-XRT position
  14. GRB 250823A: LCOGT Optical Detection
  15. GRB 250823A: Swift detection of a burst
  16. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  17. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  18. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  19. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  20. GRB 250806A: Gemini observations of host galaxy candidate
  21. GRB 250821A: Kilonova-Catcher optical upper limits
  22. EP250821a: Swift/XRT counterpart fading
  23. GRB 250821A: Swift-BAT refined analysis
  24. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  25. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  26. GRB 250821A: VLT/FORS2 Optical Observation
  27. GRB 250821B: SVOM/GRM observation
  28. EP250821a: SVOM/VT optical observation
  29. GRB 250821A: NOT z-band upper limit
  30. GRB 250821A: KAIT optical upper limit
  31. GRB 250821A: Swift-XRT refined Analysis
  32. GRB 250821B: Fermi GBM Detection
  33. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  34. GRB 250821A: Enhanced Swift-XRT position
  35. GRB 250821A: Swift/UVOT Upper Limits
  36. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  37. EP250821a: Swift XRT and UVOT counterpart detection
  38. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  39. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  40. GRB 250821A: LCOGT Optical Upper Limits
  41. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  42. GRB 250821A: Swift detection of a burst
  43. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  44. EP250821a: Einstein Probe detection of an X-ray transient
  45. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  46. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  47. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  48. GRB 250814A: Swift/UVOT Upper Limits
  49. GRB 250813B: Swift/UVOT Upper Limit
  50. IPN triangulation of GRB 250816A (short)
  51. IPN triangulation of GRB 250814C (short)
  52. IPN triangulation of GRB 250804B (short)
  53. GRB 250818B: Kilonova-Catcher optical afterglow detection
  54. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  55. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  56. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  57. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  58. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  59. GRB 250818B: Swift/UVOT Detection
  60. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  61. GRB 250818B: SAO RAS optical observations
  62. GRB 250818A: Swift-XRT refined Analysis
  63. GRB 250818B: EP-FXT counterpart detection
  64. GRB 250818A: Swift-BAT refined analysis
  65. GRB 250818B: KAIT optical observations
  66. GRB 250818A: Swift/UVOT Upper Limits
  67. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  68. GRB 250818A: Enhanced Swift-XRT position
  69. GRB 250813B: SVOM/ECLAIRs refined analysis
  70. GRB 250818A: Fermi GBM Observation
  71. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  72. GRB 250814A: Further GRAWITA TNG NIR observations
  73. GRB 250818B: Swift-XRT afterglow detection
  74. GRB 250818B: SVOM detection of a short burst
  75. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  76. GRB 250818A: Swift detection of a burst
  77. sb25081602: Swift-XRT observations
  78. GRB 250816A: SVOM/GRM observation of a short burst
  79. GRB 250814A: Swift-BAT refined analysis
  80. GRB 250813B: Liverpool Telescope optical upper limits
  81. GRB 250814A: Further COLIBRÍ optical upper limit
  82. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  83. GRB 250814A: GRAWITA TNG NIR observations
  84. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  85. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  86. GRB250814A: TRT optical upper limits
  87. GRB 250814B: SVOM/GRM observation
  88. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  89. GRB 250813B: SVOM/GRM observation
  90. GRB 250814A: P200/WIRC observations of the afterglow candidate
  91. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  92. GRB 250814A: KAIT optical upper limit
  93. GRB 250814A: Swift-XRT refined Analysis
  94. GRB 240814A: Fermi GBM Observation
  95. GRB 250814A: Possible afterglow candidate from P200/WIRC
  96. GRB 250813B: Fermi GBM Observation
  97. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  98. GRB 250814A: J-band upper limit from WINTER
  99. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  100. GRB 250813B: NOT observations of the optical afterglow

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