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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

26362 results found.

  1. GRB 250821A: Swift/UVOT Upper Limits
  2. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  3. EP250821a: Swift XRT and UVOT counterpart detection
  4. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  5. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  6. GRB 250821A: LCOGT Optical Upper Limits
  7. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  8. GRB 250821A: Swift detection of a burst
  9. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  10. EP250821a: Einstein Probe detection of an X-ray transient
  11. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  12. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  13. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  14. GRB 250814A: Swift/UVOT Upper Limits
  15. GRB 250813B: Swift/UVOT Upper Limit
  16. IPN triangulation of GRB 250816A (short)
  17. IPN triangulation of GRB 250814C (short)
  18. IPN triangulation of GRB 250804B (short)
  19. GRB 250818B: Kilonova-Catcher optical afterglow detection
  20. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  21. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  22. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  23. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  24. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  25. GRB 250818B: Swift/UVOT Detection
  26. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  27. GRB 250818B: SAO RAS optical observations
  28. GRB 250818A: Swift-XRT refined Analysis
  29. GRB 250818B: EP-FXT counterpart detection
  30. GRB 250818A: Swift-BAT refined analysis
  31. GRB 250818B: KAIT optical observations
  32. GRB 250818A: Swift/UVOT Upper Limits
  33. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  34. GRB 250818A: Enhanced Swift-XRT position
  35. GRB 250813B: SVOM/ECLAIRs refined analysis
  36. GRB 250818A: Fermi GBM Observation
  37. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  38. GRB 250814A: Further GRAWITA TNG NIR observations
  39. GRB 250818B: Swift-XRT afterglow detection
  40. GRB 250818B: SVOM detection of a short burst
  41. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  42. GRB 250818A: Swift detection of a burst
  43. sb25081602: Swift-XRT observations
  44. GRB 250816A: SVOM/GRM observation of a short burst
  45. GRB 250814A: Swift-BAT refined analysis
  46. GRB 250813B: Liverpool Telescope optical upper limits
  47. GRB 250814A: Further COLIBRÍ optical upper limit
  48. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  49. GRB 250814A: GRAWITA TNG NIR observations
  50. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  51. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  52. GRB250814A: TRT optical upper limits
  53. GRB 250814B: SVOM/GRM observation
  54. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  55. GRB 250813B: SVOM/GRM observation
  56. GRB 250814A: P200/WIRC observations of the afterglow candidate
  57. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  58. GRB 250814A: KAIT optical upper limit
  59. GRB 250814A: Swift-XRT refined Analysis
  60. GRB 240814A: Fermi GBM Observation
  61. GRB 250814A: Possible afterglow candidate from P200/WIRC
  62. GRB 250813B: Fermi GBM Observation
  63. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  64. GRB 250814A: J-band upper limit from WINTER
  65. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  66. GRB 250813B: NOT observations of the optical afterglow
  67. GRB 250814A: COLIBRÍ optical upper limit
  68. GRB 250813A: AstroSat CZTI detection
  69. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  70. GRB 250814A: DDOTI Optical Upper Limit
  71. GRB 250813B: EP-FXT counterpart detection
  72. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  73. GRB 250813B: Swift-XRT afterglow detection
  74. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  75. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  76. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  77. GRB 250813B: SVOM detection of a bright long burst
  78. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  79. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  80. EP250812a: Nickel optical upper limit
  81. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  82. EP250812a: NOT, NTT, and GS observations
  83. GRB 250812A: Swift/UVOT Detection
  84. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  85. EP250812a: Liverpool Telescope upper limits
  86. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  87. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  88. GRB 250812A: EP-FXT counterpart detection
  89. GRB 250807B: Swift-BAT refined analysis
  90. EP 250812a: GOTO optical upper limit
  91. GRB 250812A: Kilonova-Catcher optical afterglow detection
  92. EP250812a: Swift-XRT counterpart detection
  93. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  94. EP250812a: Einstein Probe detection of an X-ray transient
  95. GRB 250812A: Swift-XRT afterglow detection
  96. GRB 250812A: TRT likely optical counterpart detection
  97. IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
  98. GRB 250809A: Swift-BAT refined analysis
  99. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  100. GRB 250807A: Swift-BAT refined analysis

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