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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"
  1. GRB 250127B: DDOTI Upper Limit on the Afterglow
  2. Fermi-LAT Gamma-ray Observations of IceCube-250102A
  3. GRB 250127A: EP-FXT afterglow detection
  4. Fermi GRB 250128A: Global MASTER-Net observations report
  5. GRB 250128A: Fermi GBM Final Real-time Localization
  6. GRB 250117A: Fermi GBM Observation
  7. Fermi GRB 250127B: Global MASTER-Net observations report
  8. Fermi-LAT Gamma-ray Observations of IceCube-250101A
  9. GRB 250127A: SVOM/VT upper limit
  10. GRB 250127B: Fermi GBM Final Real-time Localization
  11. IPN triangulation of GRB 250119C
  12. GRB 250127A: Swift ToO observations
  13. GRB 250127A: LCO optical upper limit
  14. GRB 241223A: cubesat Avion detection
  15. GRB 250127A: SVOM detection of a long burst
  16. GRB 250126A: CALET Gamma-Ray Burst Monitor detection
  17. EP250125A: Non-detection from Fermi-GBM Observations
  18. GRB 250126A: MAXI/GSC detection
  19. EP250108a / SN 2025kg: Refined Analysis of EP-WXT Detection
  20. GRB 250126A: BALROG localization (Fermi Trigger 759560335 / GRB 250126208)
  21. GRB 250126A: Fermi GBM Final Real-time Localization
  22. GECAM-A detection of a bright burst from SGR 1E1841-045
  23. GRB 250118A: Fermi GBM Observation
  24. EP250125a: Optical upper limit with Kinder observations
  25. EP250125a: REM optical counterpart detection
  26. GRB 250119C: Fermi GBM Observation
  27. EP250125a: Swift/XRT detection of a fading counterpart
  28. EP250125a: a new X-ray transient detected by Einstein Probe
  29. EP250125a: Gemini-South optical afterglow discovery and redshift z = 2.89
  30. The EP-WXT trigger 01709130758 is a false trigger
  31. The EP-WXT trigger 01709130758 is a false trigger
  32. Konus-Wind detection of a bright burst from SGR 1E1841-045 on 2025 January 23
  33. GRB 250121A: Swift/BAT-GUANO localization skymap of a burst
  34. IPN triangulation of a bright burst from SGR 1E1841-045
  35. GRB 250121A: CALET Gamma-Ray Burst Monitor detection
  36. EP250108a: AbAO, CMO and Terskol optical upper limits
  37. Konus-Wind detection of GRB 250118B
  38. GRB 250121A: Fermi GBM Observation
  39. IPN triangulation of GRB 250118B
  40. Konus-Wind detection of GRB 250119B
  41. IPN triangulation of GRB 250119B
  42. GRB 250122A: Fermi GBM Final Real-time Localization
  43. Improved IPN triangulation of GRB 250107C
  44. GRB 250114A: Swift-BAT refined analysis
  45. GRB 250121A: INTEGRAL/SPI-ACS detection
  46. GRB 250121A: Fermi-LAT detection
  47. LIGO/Virgo S250119cv: Swift XRT observations, 5 X-ray sources
  48. GRB 250119C: Swift/BAT-GUANO localization skymap of a short burst
  49. GRB 250119B: Swift/BAT-GUANO localization skymap of a long burst
  50. GRB 250121A: Fermi GBM Final Real-time Localization
  51. Fermi-LAT Gamma-ray Observations of IceCube-241224A
  52. GRB 250118A: Swift/BAT-GUANO localization skymap of a short burst
  53. GRB 250119B: Fermi GBM Observation
  54. EP250108a/AT2025kg: 1.3m DFOT Optical observations
  55. Konus-Wind detection of GRB 250117A
  56. IPN triangulation of GRB 250117A (short)
  57. ATCA detection of possible radio counterpart to GRB 250114A
  58. EP250108a / SN2025kg: Non-detection from ATCA radio follow-up observations
  59. GRB 250119B: INTEGRAL/SPI-ACS detection
  60. LIGO/Virgo/KAGRA S250119cv: GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  61. EP 250108A: Late-time optical observation by LCO
  62. GRB 250117A: SVOM/GRM observation of a short burst
  63. LIGO/Virgo/KAGRA S250105bn: 1 counterpart neutrino candidate event from an IceCube neutrino search
  64. LIGO/Virgo/KAGRA S250119cv: Updated NED Galaxies in the Localization Volume
  65. LIGO/Virgo/KAGRA S250119cv: Updated Sky localization and EM Bright Classification
  66. GRB 250119C: Fermi GBM Final Real-time Localization
  67. LIGO/Virgo/KAGRA S250119cv: NED Galaxies in the Localization Volume
  68. GRB 250117A: Swift/BAT-GUANO localization skymap of a short burst
  69. EP250108a / SN2025kg: Gemini GMOS-S confirmation of an associated broad-lined SN Ic
  70. LIGO/Virgo/KAGRA S250119cv: Identification of a GW compact binary merger candidate
  71. LIGO/Virgo/KAGRA S250119ag: Updated Sky localization
  72. EP250108a/AT 2025kg: NOT spectroscopy in agreement with SN Ic-BL
  73. EP250108a / AT 2025kg: the kangaroo is hopping, evidence for optical rebrightening
  74. GRB 250117A: GECAM observation of a short burst
  75. LIGO/Virgo/KAGRA S250118dp: Updated Sky localization
  76. GRB 250119B: BALROG localization (Fermi Trigger 758968026 / GRB 250119352)
  77. GRB 250119B: Fermi GBM Final Real-time Localization
  78. LIGO/Virgo/KAGRA S250119ag: Identification of a GW compact binary merger candidate
  79. GRB 250119A: Fermi GBM Final Real-time Localization
  80. GRB 250118A: Fermi GBM Final Real-time Localization
  81. LIGO/Virgo/KAGRA S250118dp: Identification of a GW compact binary merger candidate
  82. LIGO/Virgo/KAGRA S250118t: Updated Sky localization
  83. LIGO/Virgo/KAGRA S250118az: Identification of a GW compact binary merger candidate
  84. EP250108a / AT2025kg: GMG Optical Observations
  85. LIGO/Virgo/KAGRA S250118t: Identification of a GW compact binary merger candidate
  86. EP250108a / AT2025kg: VLA radio upper limit
  87. Fermi Gamma-ray Burst Monitor trigger 758829338/250117747 is not a GRB
  88. Konus-Wind detection of GRB 250116A
  89. GRB 250116A: GECAM-B detection of a long burst
  90. GRB 241217A / EP241217B: radio detection with the VLA
  91. GRB 250116A: INTEGRAL/SPI-ACS and PICsIT detection
  92. Swift Trigger 1282245 is not a GRB
  93. GRB 250116A: Fermi-LAT detection
  94. GRB 250116A: Fermi GBM Observation of an Extremely Interesting Burst
  95. GRB 250114B: Swift-XRT afterglow detection
  96. GRB 250114B: SVOM/VT upper limit
  97. Fermi Gamma-ray Burst Monitor trigger 758659047/250115776 is not a GRB
  98. EP250108a: MeerKAT radio upper limit
  99. LIGO/Virgo/KAGRA S250114ax: Updated NED Galaxies in the Localization Volume
  100. GRB 250101A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations and rebrightening.

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